Note: Descriptions are shown in the official language in which they were submitted.
CA 02787976 2012-08-23
METHOD AND DEVICES FOR TEMPERATURE-BASED DETERMINATION OF GYROSCOPE BIAS
FIELD
[0001] The present disclosure relates generally to gyroscopes, and
more particularly, to
methods and devices for determining a bias for a gyroscope based on a
temperature.
BACKGROUND
[0002] A gyroscope is a device for measuring rotation. Gyroscopes are
sometimes
included in electronic devices, such as handheld electronic devices, in order
to provide
information about the orientation of such electronic devices. Such orientation
information
allows the electronic device to know information about its own physical
position. The
gyroscope may allow for recognition of movement within a three dimensional
space. The
electronic device may use such orientation information as an input signal.
That is, the
electronic device may be operated in a mode in which gyroscope readings affect
the operation
of the electronic device.
[0003] Even when a gyroscope is not rotating, the gyroscope may have
a signal output.
The output, when the gyroscope is not rotating, is referred to as the bias or
the bias error. Each
sensing axis of the gyroscope may have a different bias. The bias may not be a
fixed amount.
That is, the bias may vary over time. Such variations may, for example, be
caused by changes to
the temperature of the electronic device or changes to the operating state of
the electronic
device. For example, the bias may be affected when the electronic device
switches from an off
state to an on state.
[0004] If the amount of the bias is known, the electronic device may
account for the
bias when using the gyroscope.
BRIEF DESCRIPTION OF THE DRAWINGS
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[0005] Reference will now be made, by way of example, to the
accompanying drawings
which show example embodiments of the present application, and in which:
[0006] FIG. 1 is a front view of an electronic device having a three-
axis gyroscope in
accordance with example embodiments of the present disclosure;
[0007] FIG. 2 is a block diagram of example components of an electronic
device having a
gyroscope in accordance with example embodiments of the present disclosure;
[0008] FIG. 3 is a flowchart of an example method for determining a
bias for an axis of a
gyroscope in accordance with example embodiments of the present disclosure;
[0009] FIG. 4 is a flowchart of an example method for determining a
bias for an axis of a
gyroscope in accordance with example embodiments of the present disclosure;
[0010] FIG. 5 is an example histogram which may be used to determine
a bias of a
gyroscope in accordance with example embodiments of the present disclosure;
[0011] FIG. 6 is a flowchart of an example method for adding a
gyroscope reading to a
histogram in accordance with example embodiments of the present disclosure;
and
[0012] FIG. 7 is an example method of performing bin width reduction in
accordance
with example embodiments of the present disclosure.
[0013] Like reference numerals are used in the drawings to denote
like elements and
features.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0014] In one aspect, the present disclosure provides a processor-
implemented method
of determining a bias for an axis of a gyroscope. The method includes:
obtaining a temperature
reading; maintaining a plurality of bias estimators for the axis, each bias
estimator associated
with a temperature and configured to estimate a bias at the associated
temperature, the
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plurality of bias estimators including a number of short term bias estimators
for estimating
biases for recently obtained temperatures and a number of long term bias
estimators for
estimating biases for temperatures obtained over a comparatively longer period
of time; and
determining a bias for the axis of the gyroscope based on the temperature
reading and one or
more of the bias estimators.
[0015] In another aspect, the present disclosure provides an
electronic device. The
electronic device is configured for determining a bias for an axis of a
gyroscope. The electronic
device includes a memory for storing a plurality of bias estimators for the
axis. Each bias
estimator has a temperature associated therewith. Each bias estimator is
configured to
estimate a bias at the associated temperature. The plurality of bias
estimators include a
number of short term bias estimators for estimating biases for recently
obtained temperatures
and a number of long term bias estimators reserved for estimating biases for
temperatures
obtained over a comparatively longer period of time. The electronic device
also includes the
gyroscope and a temperature sensor. The electronic device also includes a
processor coupled
to the memory and the gyroscope and the temperature sensor. The processor is
configured to:
obtain a temperature reading; maintain the plurality of bias estimators for
the axis; and
determine a bias for the axis of the gyroscope based on the temperature
reading and one or
more of the bias estimators.
[0016] In another aspect, the present disclosure describes a computer
readable storage
medium. The computer readable storage medium includes computer-executable
instructions
for determining a bias for an axis of a gyroscope. The computer-executable
instructions include:
instructions for obtaining a temperature reading; instructions for maintaining
a plurality of bias
estimators for the axis, each bias estimator associated with a temperature and
configured to
estimate a bias at the associated temperature, the plurality of bias
estimators including a
number of short term bias estimators for estimating biases for recently
obtained temperatures
and a number of long term bias estimators for estimating biases for
temperatures obtained
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over a comparatively longer period of time; and instructions for determining a
bias for the axis
of the gyroscope based on the temperature reading and one or more of the bias
estimators.
[0017] Other aspects of the present disclosure will be described
below.
Example Electronic Device
[0018] Gyroscope readings may suffer from a bias. Bias (or bias error) is
the difference
between the ideal output (which is zero) when the gyroscope is not rotating
and the actual
output when the gyroscope is not rotating. That is, the bias is the gyroscope
output when the
electronic device is not rotating. lithe bias is unknown to an electronic
device interpreting the
gyroscope output, then the electronic device may erroneously interpret the
gyroscope output.
For example, the electronic device may believe that the gyroscope output
represents a
rotation, when the gyroscope is, in fact, not rotating.
[0019] When the electronic device which is interpreting the gyroscope
output knows
the bias, then the electronic device can account for the bias when
interpreting the gyroscope
output. That is, when the electronic device knows the amount of the bias, the
electronic device
can effectively cancel out the effect of the bias to ensure that the gyroscope
output is correctly
correlated to rotation of the gyroscope.
[0020] The bias for a gyroscope may be different for each sensing
axis of the gyroscope.
Accordingly, the bias may be determined separately for each sensing axis of
the gyroscope and
the electronic device which interprets the gyroscope output may cancel the
effect of bias on a
per-axis basis. Methods and electronic devices for determining the bias of a
gyroscope will be
discussed below.
[0021] The bias for a gyroscope may vary based on temperature
conditions. That is, the
temperature in the operating environment in which the gyroscope operates may
affect the bias
of that gyroscope. Accordingly, in at least some embodiments described below,
the bias for a
gyroscope may be determined in a manner that is temperature dependent.
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[0022] Referring first to FIG. 1, a gyroscope 108 is shown located
within an electronic
device 201. The electronic device 201 may take many forms. By way of example,
the electronic
device may be a global positioning system (GPS) unit, an inertial navigation
system (INS), a
mobile communication device such as a mobile phone or smartphone, a tablet
computer, a
laptop computer, a wearable computer such as a watch, a camera, or an
electronic device of
another type.
[0023] The electronic device 201 may be any electronic device which
makes use of one
or more gyroscopes 108. In some embodiments, the electronic device 201
includes a display
204, such as a liquid crystal display (LCD), and an input interface 206, such
as a keyboard or
keypad or a navigation tool such as a clickable scroll wheel (also referred to
as a track wheel or
thumbwheel) or trackball. In some embodiments, the display 204 may be a
touchscreen display
which permits a user to provide input to the electronic device 201 by touching
the display 204.
That is, the display 204 may act as an input interface 206.
[0024] The gyroscope 108 measures rotational velocity of the
gyroscope 108. In the
embodiment illustrated, since the gyroscope 108 is integrated within the
electronic device 201,
the gyroscope 108 effectively measures rotational velocity of the electronic
device 201.
[0025] The gyroscope 108 includes one or more sensing axis. In the
embodiment
illustrated, the gyroscope 108 includes three orthogonal primary sensing axes
denoted x, y and
z. Each sensing axis is orthogonal to the other sensing axes. For example, the
x sensing axis is
orthogonal to the y and z sensing axes, the y sensing axis is orthogonal to
the x and z sensing
axes and the z sensing axis is orthogonal to the x and y sensing axes.
[0026] The gyroscope 108 may produce a gyroscope reading for each of
the sensing
axes. For example, a gyroscope reading wx may be produced by the gyroscope
based on
gyroscope readings associated with the x sensing axis (such as a rotation
about the x sensing
axis), a gyroscope reading wy may be produced by the gyroscope based on
gyroscope readings
associated with the y sensing axis (such as a rotation about the y sensing
axis), and a gyroscope
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reading w, may be produced by the gyroscope based on gyroscope readings
associated with the
z sensing axis (such as a rotation about the z sensing axis). These gyroscope
readings
collectively form the gyroscope output. That is, the gyroscope output is an
electronic signal
which is representative of the gyroscope readings wx, wy, w, for the sensing
axes x, y, z of the
gyroscope 108. The electronic signal may, for example, provide the gyroscope
readings wx, wy,
w, for the sensing axes x, y, z of the gyroscope 108 as measures of an amount
of rotation per
unit time about each sensing axis. For example, the gyroscope 108 may produce
an output in
terms of radians per second or degrees per second. The gyroscope output may,
in some
embodiments, be an analog output. In other embodiments, the gyroscope output
may be
digital. A gyroscope reading captured at a point in time may be referred to as
a gyroscope
sample or a gyroscope reading. Such samples may be obtained, for example, at
regular
intervals.
[0027] The gyroscope output may separate the gyroscope readings for
each sensing axis
at a signal level or at an output interface level, or both. For example, in
some embodiments,
the gyroscope 108 may have a separate output interface (such as a separate pad
or pin)
associated with each sensing axis. Each output interface associated with a
sensing axis may
provide an output signal representing gyroscope readings for its associated
sensing axis (thus
separating the gyroscope readings for the sensing axes at an output interface
level). In other
example embodiments, a common output interface (such as a common pad or pin)
may be
associated with a plurality of sensing axes. That is, gyroscope readings for a
plurality of sensing
axes may be provided on a common output interface (such as a common pad or
pin).
[0028] In some embodiments, the gyroscope 108 may be a digital
gyroscope provided in
an integrated circuit (IC) having a memory such as Electrically Erasable
Programmable Read-
Only Memory (EEPROM) or flash memory, analog-to-digital (A/D) converter and a
controller
such as a suitably programmed microprocessor or Field Programmable Gate Array
(FPGA). The
IC may provide an industry standard interface such as an SPI (Serial
Peripheral Interface) or 12C
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(Inter-Integrated Circuit) interface for connecting to a printed circuit board
(PCB) of the
electronic device 201.
[0029] As shown in FIG. 1, the sensing axes x, y, z may be aligned
with the form factor
of the electronic device 201. In some embodiments, the x sensing axis is
aligned along an axis
extending along the midpoint of the electronic device 201 between left and
right sides 126, 128
of the electronic device 201, the y sensing axis is aligned along an axis
extending along the
midpoint of the electronic device 201 between top and bottom ends 122, 124,
and the z
sensing axis extends perpendicularly through the x-y plane defined by the x
and y sensing axes
at the intersection (origin) of these axes. In this way, when the electronic
device 201 is
oriented on a flat surface, such as a table, the x and y sensing axes are
parallel to the table and
the z sensing axis is perpendicular to the table. It is contemplated that the
sensing axes x, y, z
may be aligned with different features of the electronic device 201 in other
embodiments.
[0030] Referring now to FIG. 2, a block diagram of an example
electronic device 201 is
illustrated. The electronic device 201 of FIG. 2 may include a housing which
houses
components of the electronic device 201. Internal components of the electronic
device 201
may be constructed on a printed circuit board (PCB). The electronic device 201
includes a
controller including at least one processor 240 (such as a microprocessor)
which controls the
overall operation of the electronic device 201. The processor 240 interacts
with device
subsystems such as a wireless communication subsystem 211 for exchanging radio
frequency
signals with a wireless network 101 to perform communication functions. The
processor 240
interacts with additional device subsystems including one or more input
interfaces 206 (such as
a keyboard, one or more control buttons, one or more microphones 258, one or
more cameras,
a gyroscope 108, and/or a touch-sensitive overlay associated with a
touchscreen display), flash
memory 244, random access memory (RAM) 246, read only memory (ROM) 248,
auxiliary
input/output (I/O) subsystems 250, a data port 252 (which may be a serial data
port, such as a
Universal Serial Bus (USB) data port), one or more output interfaces 205 (such
as a display 204
(which may be a liquid crystal display (LCD)), one or more speakers 256, or
other output
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interfaces), a temperature sensor 261, a short range communication module 262,
and other
device subsystems generally designated as 264. Some of the subsystems shown in
FIG. 2
perform communication-related functions, whereas other subsystems may provide
"resident"
or on-device functions.
[0031] The electronic device 201 may include a touchscreen display in some
example
embodiments. The touchscreen display may be constructed using a touch-
sensitive input
surface connected to an electronic controller. The touch-sensitive input
surface overlays the
display 204 and may be referred to as a touch-sensitive overlay. The touch-
sensitive overlay
and the electronic controller provide a touch-sensitive input interface 206
and the processor
240 interacts with the touch-sensitive overlay via the electronic controller.
That is, the
touchscreen display acts as both an input interface 206 and an output
interface 205.
[0032] The communication subsystem 211 includes a receiver 214, a
transmitter 216,
and associated components, such as one or more antenna elements 218 and 221,
local
oscillators (L0s) 213, and a processing module such as a digital signal
processor (DSP) 215. The
antenna elements 218 and 221 may be embedded or internal to the electronic
device 201 and a
single antenna may be shared by both receiver 214 and transmitter 216, as is
known in the art.
The particular design of the wireless communication subsystem 211 depends on
the wireless
network 101 in which the electronic device 201 is intended to operate.
[0033] The electronic device 201 may communicate with any one of a
plurality of fixed
transceiver base stations of the wireless network 101 within its geographic
coverage area. The
electronic device 201 may send and receive communication signals over the
wireless network
101 after the required network registration or activation procedures have been
completed.
Signals received by the antenna 218 through the wireless network 101 are input
to the receiver
214, which may perform such common receiver functions as signal amplification,
frequency
down conversion, filtering, channel selection, etc., as well as analog-to-
digital (A/D) conversion.
AID conversion of a received signal allows more complex communication
functions such as
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demodulation and decoding to be performed in the DSP 215. In a similar manner,
signals to be
transmitted are processed, including modulation and encoding, for example, by
the DSP 215.
These DSP-processed signals are input to the transmitter 216 for digital-to-
analog (D/A)
conversion, frequency up conversion, filtering, amplification, and
transmission to the wireless
network 101 via the antenna 221. The DSP 215 not only processes communication
signals, but
may also provide for receiver and transmitter control. For example, the gains
applied to
communication signals in the receiver 214 and the transmitter 216 may be
adaptively
controlled through automatic gain control algorithms implemented in the DSP
215.
[0034] In some example embodiments, the auxiliary input/output (I/O)
subsystems 250
may include an external communication link or interface, for example, an
Ethernet connection.
The electronic device 201 may include other wireless communication interfaces
for
communicating with other types of wireless networks; for example, a wireless
network such as
an orthogonal frequency division multiplexed (OFDM) network.
[0035] In some example embodiments, the electronic device 201 also
includes a
removable memory module 230 (typically including flash memory) and a memory
module
interface 232. Network access may be associated with a subscriber or user of
the electronic
device 201 via the memory module 230, which may be a Subscriber Identity
Module (SIM) card
for use in a GSM network or other type of memory module for use in the
relevant wireless
network type. The memory module 230 may be inserted in or connected to the
memory
module interface 232 of the electronic device 201.
[0036] The electronic device 201 may store data 227 in an erasable
persistent memory,
which in one example embodiment is the flash memory 244. In various example
embodiments,
the data 227 may include service data having information required by the
electronic device 201
to establish and maintain communication with the wireless network 101. The
data 227 may
also include user application data such as email messages, address book and
contact
information, calendar and schedule information, notepad documents, images, and
other
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commonly stored user information stored on the electronic device 201 by its
user, and other
data.
[0037] The data 227 may, in at least some embodiments, include one or
more bias
estimators 298a, 298b, 298c, 298d, 298e, 298f, 298g, 298h, 299. The bias
estimators represent
gyroscope readings from which a bias may be determined. More specifically, at
least some of
the bias estimators may be temperature-associated bias estimators. That is, at
least some of
the bias estimators are associated with a temperature. In the embodiment
illustrated, there
are eight temperature-associated bias estimators ¨ a first bias estimator 298a
(which is
associated with a temperature Ti), a second bias estimator 298b (which is
associated with a
temperature 12), a third bias estimator 298c (which is associated with a
temperature T3), a
fourth bias estimator 298d (which is associated with a temperature T4), a
fifth bias estimator
298e (which is associated with a temperature T5), a sixth bias estimator 298f
(which is
associated with a temperature T6), a seventh bias estimator 298g (which is
associated with a
temperature T7), an eighth bias estimator 298h (which is associated with a
temperature 18).
[0038] Each bias estimator represents or may be used to determine a bias
for an axis of
the gyroscope 108. The bias estimators may include or represent gyroscope
readings. Each
temperature-associated bias estimator 298a, 298b, 298c, 298d, 298e, 298f,
298g, 298h
represents or may be used to estimate the gyroscope bias at an associated
temperature (or a
narrow range of temperatures e.g. a one degree range). By way of example, in
at least some
embodiments, each temperature-associated bias estimator may include a
plurality of gyroscope
readings obtained at a temperature associated with that bias estimator (e.g.
obtained when the
temperature sensor indicated that temperature). For example, the first bias
estimator 298a
may include a plurality of gyroscope readings obtained at a first temperature
Ti. Similarly, the
second bias estimator 298b may include a plurality of gyroscope readings
obtained at the
second temperature 12. The third bias estimator 298c may include a plurality
of gyroscope
readings obtained at the third temperature T3. The fourth bias estimator 298d
may include a
plurality of gyroscope readings obtained at the fourth temperature T4. The
fifth bias estimator
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298e may include a plurality of gyroscope readings obtained at the fifth
temperature T5. The
sixth bias estimator 298f may include a plurality of gyroscope readings
obtained at the sixth
temperature T6. The seventh bias estimator 298g may include a plurality of
gyroscope readings
obtained at the seventh temperature T7. The eighth bias estimator 298h may
include a
plurality of gyroscope readings obtained at the eighth temperature 18. That
is, the
temperature-associated bias estimators 298a, 298b, 298c, 298d, 298e, 298f,
298g, 298h contain
temperature tagged gyroscope readings.
[0039] As will be described in greater detail below, the gyroscope
readings included in a
bias estimator allow a bias to be determined by the electronic device 201 for
that bias
estimator. Where the bias estimator is a temperature-associated bias estimator
298a, 298b,
298c, 298d, 298e, 298f, 298g, 298h (i.e. where it is a bias estimator that is
associated with a
specific temperature), the bias estimator allows a bias to be determined for
the specific
temperature.
[0040] The bias estimators 298a, 298b, 298c, 298d, 298e, 298f, 298g,
298h include a
predetermined number of short term bias estimators 279. In the example
illustrated, the first
bias estimator 298a, second bias estimator 298b and third bias estimator 298c
are short term
bias estimators 279. Accordingly, in the example illustrated, the bias
estimators include three
short term bias estimators 279. The short term bias estimators 279 are
reserved for estimating
biases for recent temperatures. That is, the short term bias estimators 279
are reserved for
estimating biases for temperatures that were observed recently at or near the
electronic device
201. A short term bias estimator 279 may be used to determine the bias at an
associated
temperature which was recently observed by the temperature sensor.
(0041] In at least some embodiments, the short term bias estimators
279 are stored in a
least recently used (LRU) cache. A least recently used (LRU) cache is a short-
term storage which
values elements contained in the cache based on the elapsed period of time
since the elements
were accessed. That is, the least recently used (LRU) cache is configured to
remove bias
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estimators from inclusion among the short term bias estimators 279 based on
how recently a
temperature associated with the bias estimator was observed. In order to free
up space to
create a bias estimator for newly observed temperatures (i.e. temperatures
that are observed
using the temperature sensor 261 and that do not have an existing bias
estimator associated
therewith), the LRU cache may remove the least recently used short term bias
estimator 279.
That is, the short term bias estimator 279 whose associated temperature was
observed least
recently may be removed from inclusion as a short term bias estimator 279 to
make room for a
new short term bias estimator 279. As will be described in greater detail
below, when this
short term bias estimator 279 is removed, it may either be deleted from memory
or may be
stored as a long term bias estimator.
[0042] The electronic device 201 also includes a predetermined number
of long term
bias estimators 280. A long term bias estimator 280 is a bias estimator that
is reserved for
estimating biases for temperatures observed over a comparatively longer period
of time. That
is, the long term bias estimator 280 is used for estimating biases for
temperatures that have
been observed in the past, but which may not have been observed recently. A
long term bias
estimator may store data that can be used to calculate a bias for the
gyroscope at an associated
temperature. For example, a long term bias estimator 280 may store gyroscope
readings all
obtained at the same temperature (or within a narrow range of that
temperature). As will be
described in greater detail below, a bias may be determined from such
measurements (e.g.
using an adaptive histogram of the type described below).
[0043] Long term bias estimators 280 may help to protect the range of
temperatures
that an accurate bias may be calculated for. More specifically, the long term
bias estimators
280 help to ensure that data that may be used to determine a gyroscope is
stored for a wide
range of temperatures. For example, when a user is travelling outside in cold
weather, the
short term bias estimators 279 may become populated with data that may be used
to
determine a bias in cold weather. However, when they move inside into warmer
weather, the
short term bias estimators 279 may not, initially, include data from which a
bias may be
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calculated in the warmer temperatures. In this scenario the long term bias
estimators 280 may
include data for warmer temperatures and may be used to calculate a bias.
Thus, the long term
bias estimators 280 help to ensure that the temperature bias model that is
developed by the
electronic device 201 based on the bias estimators is valid over a wide range
of temperatures.
[0044] As will be described in greater detail below, in order to allow the
long term bias
estimators 280 to operate over a wide range of temperatures, the long term
bias estimators
280 may be managed by the electronic device 201 to represent a wide range of
temperatures.
For example, to ensure that the long term bias estimators 280 represent a wide
range of
temperatures and/or a diverse set of temperatures, one or more of the long
term bias
estimators 280 may be protected from deletion or replacement. That is, the
electronic device
201 may prevent one or more of the long term bias estimators 280 from being
replaced.
[0045] Accordingly, the electronic device 201 manages a predetermined
number of long
term bias estimators 280. In the example illustrated, five long term bias
estimators 280 (these
are labelled as 298d, 298e, 298f, 298g, 298h) are included, each associated
with a different
temperature (these temperatures are labelled as 14, T5, 16, T7, 18). The
temperatures T4, 15,
T6, T7, T8 of the long term bias estimators 280 differ from the temperatures
Ti, T2, T3 of the
short term bias estimators 279.
[0046] In at least some embodiments, the data 227 may also include a
temperature
independent bias estimator 299. The temperature independent bias estimator 299
is not
associated with a specific temperature. Rather, the temperature independent
bias estimator
299 may be used for determining a bias over all temperatures. The temperature
independent
bias estimator 299 may also be referred to as an aggregate bias estimator,
since it may be used
to determine an estimate of a bias for a gyroscope 108 irrespective of
temperature. That is, the
temperature independent bias estimator 299 provides a bias estimate for the
gyroscope across
all temperatures.
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[0047] The temperature independent bias estimator 299 stores data
that may be used
to determine a bias for the gyroscope 108. For example, the temperature
independent bias
estimator 299 may store a plurality of gyroscope readings. As will be
described in greater detail
below, a bias may be determined from such measurements (e.g. using an adaptive
histogram of
the type described below).
[0048] In at least some embodiments, the temperature independent bias
estimator 299
may be used by the electronic device 201 for determining a bias when the bias
estimators 298a,
298b, 298c, 298d, 298e, 298f, 298g, 298h associated with temperatures are not
stable. For
example, the temperature independent bias estimator 299 may be used when the
bias
estimators that are associated with temperatures (such as the long term bias
estimators and
the short term bias estimators) do not yet contain enough data to be reliable
(e.g. when they
do not contain enough gyroscope readings to be reliable).
[0049] Each of the bias estimators 298a, 298b, 298c, 298d, 298e,
298f, 298g, 298h, 299
in the example embodiment illustrated, is associated with the same axis of a
gyroscope 108.
That is, a single axis of a gyroscope 108 may have the bias estimators
described above
associated with that axis. Since the bias may vary for each axis of a
gyroscope, in embodiments
in which the gyroscope 108 is a multi-axis gyroscope, each axis may have bias
estimators of the
type described above associated therewith and the methods for determining the
bias for a
gyroscope may be performed independently for each axis using the techniques
described
herein. The determination of a bias for an axis may be performed using the
bias estimators
associated with that axis (and not the bias estimators associated with other
axes).
[0050] In at least some embodiments, the bias estimators may be
configured to rely on
a histogram to determine a bias measurement. In at least some such
embodiments, each bias
estimator may include a histogram. The histogram is a representation of past
gyroscope
readings for a sensing axis. For a bias estimator 298a, 298b, 298c, 298d,
298e, 298f, 298g, 298h
that is associated with a temperature, the histogram for that bias estimator
represents past
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gyroscope readings obtained at that temperature. That is, for a bias estimator
associated with
a temperature, T, the histogram is obtained based on gyroscope readings
obtained when the
temperature sensor 261 indicated the temperature, T.
[0051] As will be described in greater detail below with reference to
FIGs. 4 to 7, the
histograms may be created, maintained, and/or used by a software application
or module, such
as a gyroscope calibration application 297.
[0052] The data 227 stored in the persistent memory (e.g. flash
memory 244) of the
electronic device 201 may be organized, at least partially, into a number of
databases or data
stores each containing data items of the same data type or associated with the
same
application. For example, email messages, contact records, and task items may
be stored in
individual databases within the electronic device 201 memory.
[0053] The data port 252 may be used for synchronization with a
user's host computer
system. The data port 252 enables a user to set preferences through an
external device or
software application and extends the capabilities of the electronic device 201
by providing for
information or software downloads to the electronic device 201 other than
through the
wireless network 101. The alternate download path may for example, be used to
load an
encryption key onto the electronic device 201 through a direct, reliable and
trusted connection
to thereby provide secure device communication.
[0054] In some example embodiments, the electronic device 201 is
provided with a
service routing application programming interface (API) which provides an
application with the
ability to route traffic through a serial data (i.e., USB) or Bluetooth
(Bluetooth is a registered
trademark of Bluetooth SIG, Inc.) connection to the host computer system using
standard
connectivity protocols. When a user connects their electronic device 201 to
the host computer
system via a USB cable or Bluetooth connection, traffic that was destined for
the wireless
network 101 is automatically routed to the electronic device 201 using the USB
cable or
Bluetooth connection. Similarly, any traffic destined for the wireless
network 101 is
CA 02787976 2012-08-23
automatically sent over the USB cable Bluetooth connection to the host
computer for
processing.
[0055] The electronic device 201 also includes or is connectable to a
power source, such
as a battery 238. The battery 238 may be one or more rechargeable batteries
that may be
charged, for example, through charging circuitry coupled to a battery
interface 236 such as the
serial data port 252. The battery 238 provides electrical power to at least
some of the electrical
circuitry in the electronic device 201, and the battery interface 236 provides
a mechanical and
electrical connection for the battery 238. The battery interface 236 is
coupled to a regulator
(not shown) which provides power V+ to the circuitry of the electronic device
201.
[0056] The short range communication module 262 provides for communication
between the electronic device 201 and different systems or devices, which need
not necessarily
be similar devices. For example, the short range communication module 262 may
include an
infrared device and associated circuits and components, or a wireless bus
protocol compliant
communication mechanism such as a Bluetooth communication module to provide
for
communication with similarly-enabled systems and devices.
[0057] The electronic device 201 includes a gyroscope 108 which is
configured to sense
rotation of the electronic device 201. The gyroscope 108 may, in at least some
embodiments,
be a three-axis gyroscope of the type described above with reference to FIG.
1.
[0058] The electronic device 201 includes a temperature sensor 261.
The temperature
sensor 261 is an electronic temperature sensor which is configured to produce
an electronic
signal in dependence on an observed temperature. This electronic signal may be
referred to as
a temperature reading or a temperature measurement. The temperature sensor 261
may be
an analog temperature sensor or a digital temperature sensor. While the
temperature sensor
261 is illustrated as a separate component, in some embodiments, the
temperature sensor 261
may be embedded with another component such as, for example, the gyroscope
108.
16
CA 02787976 2012-08-23
[0059] A predetermined set of applications that control basic device
operations,
including data and possibly voice communication applications may be installed
on the
electronic device 201 during or after manufacture. Additional applications
and/or upgrades to
an operating system 222 or software applications 224 may also be loaded onto
the electronic
device 201 through the wireless network 101, the auxiliary I/O subsystem 250,
the data port
252, the short range communication module 262, or other suitable device
subsystems 264. The
downloaded programs or code modules may be permanently installed; for example,
written
into the program memory (e.g. the flash memory 244), or written into and
executed from the
RAM 246 for execution by the processor 240 at runtime.
[0060] In some example embodiments, the electronic device 201 may provide
two
principal modes of communication: a data communication mode and a voice
communication
mode. In the data communication mode, a received data signal such as a text
message, an
email message, or webpage download will be processed by the communication
subsystem 211
and input to the processor 240 for further processing. For example, a
downloaded webpage
may be further processed by a web browser or an email message may be processed
by the
email messaging application and output to the display 204. A user of the
electronic device 201
may also compose data items, such as email messages; for example, using an
input interface
206 in conjunction with the display 204. These composed items may be
transmitted through
the communication subsystem 211 over the wireless network 101.
[0061] In the voice communication mode, the electronic device 201 provides
telephony
functions and may operate as a typical cellular phone. The overall operation
is similar to the
data communication mode, except that the received signals would be output to
the speaker
256 and signals for transmission would be generated by a transducer such as
the microphone
258. The telephony functions are provided by a combination of
software/firmware (i.e., a voice
communication module) and hardware (i.e., the microphone 258, the speaker 256
and input
devices). Alternative voice or audio I/O subsystems, such as a voice message
recording
subsystem, may also be implemented on the electronic device 201. Although
voice or audio
17
CA 02787976 2012-08-23
signal output may be accomplished primarily through the speaker 256, the
display 204 may also
be used to provide an indication of the identity of a calling party, duration
of a voice call, or
other voice call related information.
[0062] The processor 240 operates under stored program control and
executes
software modules 220 stored in memory such as persistent memory; for example,
in the flash
memory 244. As illustrated in FIG. 2, the software modules 220 may include
operating system
software 222 and one or more additional applications 224 or modules such as,
for example, a
gyroscope calibration application 297.
[0063] In the example embodiment of FIG. 2, the gyroscope calibration
application 297
is illustrated as being implemented as a stand-alone application 224. However,
in other
example embodiments, the gyroscope calibration application 297 could be
provided by another
application or module such as, for example, the operating system software 222.
Furthermore,
while the gyroscope calibration application 297 is illustrated with a single
block, the functions
or features provided by the gyroscope calibration application 297 could, in at
least some
embodiments, be divided up and implemented by a plurality of applications
and/or modules.
[0064] Furthermore, while, in the example embodiment of FIG. 2, the
gyroscope
calibration application 297 is illustrated as being associated with the main
processor 240 of the
electronic device 201, in other embodiments, the gyroscope calibration
application 297 could
be associated with another processor, or group of processors. For example, in
some
embodiments, the gyroscope 108 may include or be connected to a secondary
processor. The
secondary processor may provide a narrow set of functions or features and may
be used to
offload some processing from the main processor 240. For example, in some
embodiments,
the secondary processor is a gyroscope-specific processor which is coupled to
the gyroscope
108 and which is configured to provide gyroscope related functions such as
those provided by
the gyroscope calibration application 297. For example, the secondary
processor may be
configured to determine the bias of the gyroscope in the manner described
herein and may, in
18
CA 02787976 2012-08-23
at least some embodiments, be configured to correct for the bias. For example,
the secondary
processor may separate and remove the effect of the bias from gyroscope
readings and may
provide the resulting corrected gyroscope readings to the main processor 240
for further
analysis and/or interpretation.
[0065] The gyroscope calibration application 297 may be configured to
determine the
bias for a gyroscope 108. Example methods of determining a bias for a
gyroscope will be
described in greater detail below.
[0066] The electronic device 201 may include a range of additional
software
applications 224, including, for example, a notepad application, voice
communication (i.e.
telephony) application, mapping application, a media player application, or
any combination
thereof. Each of the software applications 224 may include layout information
defining the
placement of particular fields and graphic elements (e.g. text fields, input
fields, icons, etc.) in
the user interface (i.e. the display 204) according to the application.
[0067] The software modules 220 or parts thereof may be temporarily
loaded into
volatile memory such as the RAM 246. The RAM 246 is used for storing runtime
data variables
and other types of data or information. Although specific functions are
described for various
types of memory, this is merely one example, and a different assignment of
functions to types
of memory could also be used.
Temperature-Dependent Bias Determination
[0068] As noted previously, gyroscope bias tends to vary based on
temperature.
Accordingly, in at least some embodiments, the determination of a bias for a
gyroscope is
dependent on the current temperature. Referring now to FIG. 3, an example
method 350 for
determining a bias for an axis of a gyroscope 108 is illustrated.
[0069] The method 350 may include features which may be provided by
an electronic
device 201, such as the electronic device 201 of FIGs. 1 and 2. For example,
one or more
19
CA 02787976 2012-08-23
applications or modules associated with an electronic device 201, such as the
gyroscope
calibration application 297 (FIG. 2), may contain processor readable
instructions for causing a
processor associated with the electronic device 201 to perform one or more
operations of the
method 350. That is, in at least some example embodiments, the electronic
device 201 may be
configured to perform the method 350. For example, the method 350 may be
implemented by
a processor 240 (FIG. 2) of an electronic device 201 (FIG. 2).
[0070] In at least some embodiments, one or more of the functions or
features of the
method 350 may be performed, in whole or in part, by another system, software
application,
module, component or device apart from those specifically listed above. For
example, in some
embodiments, the method 350 may be performed by a processor associated with
the
gyroscope 108. That is, in at least some embodiments, the method 350 or a
portion thereof
may be performed by a processor other than the main processor 240 the
electronic device 201.
A processor which is associated with the gyroscope 108 and which may be used
for the specific
purpose of controlling the gyroscope 108 (i.e. a gyroscope-specific processor)
may be
configured to perform the method 350 or a portion thereof.
[0071] At 352, a temperature reading is obtained. More particularly,
a temperature
reading is obtained by the electronic device 201 from the temperature sensor
261 (FIG. 2).
[0072] At 354, a gyroscope reading is obtained from the gyroscope
108. The gyroscope
reading is obtained at or near the time when the temperature reading is
obtained. In some
embodiments, the gyroscope reading and the temperature reading are obtained
simultaneously. Thus, the gyroscope reading is effectively a temperature-
tagged reading. That
is, the gyroscope reading is associated with a temperature.
[0073] At 356, the electronic device 201 maintains a plurality of
bias estimators 298a,
298b, 298c, 298d, 298e, 298f, 298g, 298h (FIG. 2). More particularly, at 356,
the electronic
device may update one or more bias estimators 298a, 298b, 298c, 298d, 298e,
298f, 298g, 298h
stored in memory of the electronic device 201 based on the gyroscope reading
and the
CA 02787976 2012-08-23
temperature reading. The bias estimators 298a, 298b, 298c, 298d, 298e, 298f,
298g, 298h that
are maintained at 356 may each have a temperature associated therewith. Each
bias estimator
298a, 298b, 298c, 298d, 298e, 298f, 298g, 298h that is associated with a
temperature may be
configured to estimate a bias at that temperature.
[0074] The plurality of bias estimators that are maintained at 356 include
a
predetermined number of short term bias estimators 279 (FIG. 2) that are
reserved for
estimating biases for recent temperatures and a predetermined number of long
term bias
estimators 280 (FIG. 2) reserved for estimating biases for temperatures
observed over a
comparatively longer period of time. The short term bias estimators 279 and
long term bias
estimators are described in greater detail in the discussion of FIG. 2 above.
[0075] In at least some embodiments, the temperature-tagged gyroscope
reading
obtained at 354 may be used to update a bias estimator 298a, 298b, 298c, 298d,
298e, 298f,
298g, 298h. That is, a bias estimator may be updated so that the newly
obtained gyroscope
reading may be used when calculating a bias for that bias estimator.
279 may be updated based on the gyroscope reading or a long term bias
estimator 280 may be
updated based on the gyroscope reading.
[0077] In at least some embodiments, at 358, the electronic device
may determine
whether the temperature represented by the temperature reading obtained at 352
is
associated with an existing bias estimator 298a, 298b, 298c, 298d, 298e, 298f,
298g, 298h. That
is, the electronic device 201 may determine whether one of the short term bias
estimators 279
or the long term bias estimators 280 are associated with that temperature.
[0078] If one of the existing bias estimators 298a, 298b, 298c, 298d,
298e, 298f, 298g,
298h is associated with that temperature, then at 360, the electronic device
201 may update
the bias estimator associated with that temperature. More specifically, the
electronic device
21
CA 02787976 2012-08-23
201 may update the bias estimator associated with that temperature to include
or represent
the gyroscope reading obtained at 354.
[0079] If, however, it is determined at 358 that the temperature
represented by the
temperature reading obtained at 352 is not associated with an existing bias
estimator, then the
electronic device 201 may create a new short term bias estimator 279 to be
associated with
that temperature.
[0080] To prevent the bias estimators from consuming too much memory,
the number
of bias estimators 298a, 298b, 298c, 298d, 298e, 298f, 298g, 298h that will be
maintained (e.g.
the number of bias estimators that will be permitted to exist in memory) may
be
predetermined. In at least some embodiments, the number of short term bias
estimators 279
may be predetermined and the number of long term bias estimators 280 may also
be
predetermined. For example, as illustrated in FIG. 2, in some embodiments,
three short term
bias estimators 279 may be maintained and five long term bias estimators 280
may be
maintained.
[0081] Thus, when the number of bias estimators that are being maintained
by the
electronic device 201 has reached the maximum that will be allowed, in order
to create a new
short term bias estimator 279, an existing short term bias estimator 279 is
removed. That is, if it
is determined that the temperature reading obtained at 352 defines a
temperature that does
not have a bias estimator 298a, 298b, 298c, 298d, 298e, 298f, 298g, 298h
associated therewith,
then one of the short term bias estimators 279 may be replaced with a new
short term bias
estimator 279. The new short term bias estimator 279 is associated with the
temperature
defined by the temperature reading obtained at 352.
[0082] The short term bias estimator 279 that will be removed to free
up space for a
new short term bias estimator 279 may be automatically selected by the
electronic device 201.
As noted previously, in at least some embodiments, the electronic device 201
is configured to
value short term bias estimators 279 based on how recently those bias
estimators have been
22
CA 02787976 2012-08-23
accessed. That is, in at least some embodiments, the short term bias
estimators 279 are stored
in a least recently used cache. A least recently used (LRU) cache is a short-
term storage which
values elements contained in the cache based on the elapsed period of time
since the elements
were accessed. The least recently used (LRU) cache is configured to remove
bias estimators
from inclusion among the short term bias estimators 279 based on how recently
a temperature
associated with the bias estimator was observed. In order to free up space to
create a bias
estimator for newly observed temperatures (i.e. temperatures that are observed
using the
temperature sensor and that do not have an existing bias estimator associated
therewith), the
LRU cache may remove the least recently used short term bias estimator 279.
That is, the short
term bias estimator 279 whose associated temperature was observed least
recently may be
removed from inclusion as a short term bias estimator 279.
[0083] In embodiments in which the least recently used short term
bias estimator is
removed, at 361 the electronic device 201 may identify the least recently used
short term bias
estimator. The electronic device 201 may do so by identifying the short term
bias estimator
that is associated with a temperature that has not been observed recently. For
example, the
electronic device 201 may examine all of the temperatures associated with the
short term bias
estimators 279 and may determine which of those temperatures was observed
least recently.
The bias estimator associated with this temperature may be considered by the
electronic
device 201 to be the least recently used (LRU) short term bias estimator 279.
[0084] The identified least recently used short term bias estimator 279 may
be the bias
estimator that will be removed from inclusion among the short term bias
estimators to free up
space for a new short term bias estimator based on the temperature represented
in the
temperature reading obtained at 352.
[0085] However, in at least some embodiments, before removing a short
term bias
estimator 279 from memory, the electronic device 201 may determine, at 362,
whether a long
term bias estimator 280 should be replaced with the short term bias estimator
279 that is to be
23
CA 02787976 2012-08-23
removed. That is, the electronic device 201 determines whether the short term
bias estimator
279 that is to be removed will be re-designated as one of the long term bias
estimators 280.
[0086] In at least some embodiments, at 362, the electronic device
201 may determine
if the least recently used short term bias estimator contains too few samples
to be considered
for inclusion as a long term bias estimator. This determination may be made by
comparing a
number of gyroscope readings represented by the least recently used short term
bias estimator
to a predetermined threshold. The predetermined threshold may represent a
minimum
number of gyroscope readings that must be represented by a short term bias
estimator for the
short term bias estimator to be considered reliable enough for inclusion among
the long term
bias estimators.
[0087] If, based on the comparison, the electronic device 201
determines that the least
recently used short term bias estimator contains too few samples (e.g. enough
gyroscope
readings) to be considered for inclusion as a long term bias estimator 280,
then the electronic
device 201 may determine that a long term bias estimator 280 should not be
replaced with the
short term bias estimator (i.e. it determines that the short term bias
estimator 279 should not
become a long term bias estimator) and the method 350 may proceed to 366 where
the short
term bias estimator 279 is replaced by discarding the least recently used
short term bias
estimator 279 and by also storing a new short term bias estimator 279 based on
the gyroscope
reading obtained at 364. The new short term bias estimator 279 is associated
with the
temperature represented by the temperature reading obtained at 362.
[0088] When the electronic device 201 determines that the least
recently used short
term bias estimator contains enough samples to be considered for inclusion as
a long term
estimator, it may then determine whether it would be better to keep all of the
existing long
term bias estimators rather or whether it would be better to replace one of
the long term bias
estimators with the least recently used short term bias estimator. To do so,
at 362 the
electronic device 201 may select one of the long term bias estimators 280 for
possible
24
CA 02787976 2012-08-23
replacement. As noted in the discussion of FIG. 2 above, the electronic device
201 may be
configured to protect one or more of the long term bias estimators from
replacement to ensure
that the bias estimators maintained by the electronic device 201 represent
bias estimators for a
wide range of temperatures.
[0089] To ensure that the bias estimators represent a wide range of
temperatures, in at
least some embodiments, when selecting a long term bias estimator 280 for
possible
replacement, the electronic device 201 may identify the range of temperatures
represented by
the bias estimators. That is, the electronic device 201 may identify the
minimum and maximum
temperatures that are represented by the bias estimators (and/or may identify
the maximum
and minimum temperatures that have ever been observed at the temperature
sensor 261).
Based on the identified range of temperatures, the electronic device 201 may
selectively
protect one or more of the long term bias estimators 280 from replacement. For
example, in at
least some embodiments, the identified range of temperatures represented by
the bias
estimators 298a, 298b, 298c, 298d, 298e, 298f, 298g, 298h may be separated
into a plurality of
sub-ranges. These sub ranges may all be of the same size. That is, the
difference between the
maximum temperature and minimum temperature may be the same for each sub-
range. By
way of example, in at least some embodiments, the identified range of
temperatures
represented by the bias may be separated into three sub-ranges (e.g. the range
of
temperatures represented by the bias estimators may be separated into thirds).
In at least
some embodiments, the electronic device 201 may attempt to ensure that a long
term bias
estimator may be included in each sub-range.
[0090]
For example, in some embodiments, for each sub-range that does not include
the temperature associated with the short term bias estimator 279 that was
identified as the
least recently used short term bias estimator at 361, the electronic device
201 may protect,
from replacement, one of the long term bias estimators 280 having a
temperature included in
that range. In each of these sub-ranges, the electronic device 201 may
identify the long term
bias estimator 280 representing the greatest number of gyroscope readings in
that sub-range
CA 02787976 2012-08-23
and may protect the identified long term bias estimator 280 from being
replaced. This ensures
that, even after replacement, each sub-range will have at least one bias
estimator.
[0091] After the electronic device 201 selectively protects one or
more of the long term
bias estimators, it may identify the unprotected long term bias estimator
representing the
fewest gyroscope readings. This identified bias estimator is selected for
possible replacement.
[0092] The electronic device 201 may then compare the number of
gyroscope readings
associated with the short term bias estimator 279 identified at 361 as the
least recently used
short term bias estimator with the number of gyroscope readings associated
with the
unprotected long term bias estimator identified as representing the fewest
number of
gyroscope readings. Based on this comparison, the electronic device 201 may
determine
whether the identified long term bias estimator 280 should be replaced. For
example, if the
least recently used short term bias estimator represents fewer gyroscope
readings than the
identified unprotected long term bias estimator, then the electronic device
201 may determine
that no long term bias estimators 280 should be replaced. Conversely, if the
least recently used
short term bias estimator represents more gyroscope readings than the
identified unprotected
long term bias estimator, then the electronic device 201 may determine that
the long term bias
estimator that was identified for possible replacement should be replaced.
[0093] If the electronic device determines, at 362, that a long term
bias estimator
should be replaced, then at 364, the electronic device 201 may replace one of
the long term
bias estimators 280 with the least recently used short term bias estimator.
The long term bias
estimator that was identified for possible replacement may be discarded and,
in its place, the
least recently used short term bias estimator may be re-designated as a long
term bias
estimator.
[0094] Then, at 366, the short term bias estimator 279 may be
replaced. That is, a new
short term bias estimator may be stored based on the gyroscope reading
obtained at 354. The
26
CA 02787976 2012-08-23
new short term bias estimator is associated with the temperature defined by
the temperature
reading obtained at 352.
[0095] If, at 362, the electronic device 201 determines that the long
term bias estimator
should not be replaced, then 364 may not be performed. Instead, the method 350
may
proceed directly to 366 where the least recently used short term bias
estimator 279 is replaced
with a new bias estimator. More particularly, the least recently used short
term bias estimator
may be discarded and a new short term bias estimator may be stored based on
the gyroscope
reading obtained at 354. The new short term bias estimator is associated with
the temperature
defined by the temperature reading obtained at 352.
[0096] In at least some embodiments (not illustrated), when maintaining the
bias
estimators, the electronic device 201 may be configured to periodically reduce
the number of
gyroscope readings represented by the long term bias estimators. For example,
in at least
some embodiments, the electronic device 201 may periodically reduce the number
of
gyroscope readings represented by the long term bias estimators by a
predetermined factor
(e.g. by a factor of two). Such periodic reductions may avoid an old outlier
bias estimator from
permanently affecting bias estimates.
[0097] As will be described in greater detail below, in at least some
embodiments, each
bias estimator may include a histogram which may be used for determining a
bias associated
with that bias estimator. As will be described in greater detail below, the
histogram may
represent the gyroscope readings associated with the bias estimator (i.e. the
histogram
represents the gyroscope readings at the temperature associated with that bias
estimator).
[0098] In some embodiments, the electronic device 201 may be
configured to maintain
a temperature independent bias estimator 299 (at 368). The temperature
independent bias
estimator 299 is a bias estimator that is configured for providing a bias
estimate across all
temperatures. That is, the temperature independent bias estimator 299 is
composed of
gyroscope readings irrespective of the temperature associated with such
readings. Accordingly,
27
CA 02787976 2012-08-23
at 368, the gyroscope reading obtained at 354 may be added to the temperature
independent
bias estimator 299.
[0099] The temperature independent bias estimator 299 may, for
example, be used for
determining the bias of a gyroscope when the bias estimators that are
associated with
temperatures (i.e. the bias estimators maintained at 356) are not yet stable.
[00100] At 370, the electronic device 201 may determine the bias for
the gyroscope
based on the temperature reading obtained at 352 and based on one or more of
the bias
estimators maintained by the electronic device 201.
[00101] As noted previously, in at least some instances, the bias
estimators that are
associated with temperatures (i.e. the bias estimators maintained at 356) may
not yet be
reliable. For example, when the electronic device 201 is first powered on, the
bias estimators
298a, 298b, 298c, 298d, 298e, 298f, 298g, 298h that are associated with
temperatures may not
yet contain enough data to be reliable. Since the temperature independent bias
estimator (i.e.
the bias estimator maintained at 368) is constructed using gyroscope readings
irrespective of
temperature, this bias estimator may be quicker to stabilize. Accordingly, in
at least some
embodiments, the electronic device 201 may determine whether the bias
estimators that are
associated with temperatures are reliable (e.g. whether they contain
sufficient data) and, if
they are not reliable, may use the temperature independent bias estimator 299
to determine
the bias for the gyroscope 108.
[00102] The determination of a bias using the temperature independent bias
estimators
may, for example, be performed according to a method described below with
reference to FIG.
4. For example, a plurality of gyroscope readings may be represented as a
histogram 800 (an
example of which is illustrated in FIG. 5). The histogram 800 for the
temperature independent
bias estimator 299 may represent gyroscope readings irrespective of
temperature. That is, the
histogram may be constructed based on gyroscope readings without regard to the
temperature
28
CA 02787976 2012-08-23
indicated by the temperature sensor 261 at the time such readings were
obtained. Using the
histogram 800, a bias may be determined.
[00103] After the bias estimators 298a, 298b, 298c, 298d, 298e, 298f,
298g, 298h
associated with temperatures become reliable, then these bias estimators may
be used to
determine a bias for the gyroscope 108 based on the temperature reading
obtained at 352.
[00104] If the temperature reading obtained at 352 represents a
temperature that does
not have a bias estimator 298a, 298b, 298c, 298d, 298e, 298f, 298g, 298h
associated therewith
(apart from a possible newly created short term bias estimator which may have
been created at
366 but which would not yet have sufficient data to be useful), a least
squares fit may be
performed to model the relationship between temperature and bias. For example,
a least
squares fit may be performed on the long term bias estimators 280 and, in some
embodiments,
on one or more of the short term bias estimators 279 (e.g. short term bias
estimators 279 may
be used if they contain enough gyroscope readings to be considered reliable).
[00105] To perform a least squares fit, a bias may be determined for
each of these bias
estimators. The bias for each bias estimator may be determined according to a
method
described below with reference to FIG. 4. For example, a plurality of
gyroscope readings may
be represented as a histogram (an example of which is illustrated in FIG. 5).
Since the long term
bias estimators 280 and the short term bias estimators 279 are associated with
temperatures,
each bias estimator provides a bias at a specific temperature. By modeling the
relationship
between the bias and temperature, a bias may be determined based on
temperatures that are
not directly associated with a bias estimator. Accordingly, when the bias
estimators (apart from
a possible newly created short term bias estimator, which will not be
considered) are not
associated with the temperature represented by the temperature reading
obtained at 352,
then the bias may be determined by performing a least squares fit using a
plurality of bias
estimators (i.e. by first determining the bias represented by those bias
estimators) and the
temperatures associated with those bias estimators.
29
CA 02787976 2012-08-23
[00106] In some embodiments, when one of the bias estimators 298a,
298b, 298c, 298d,
298e, 2981, 298g, 298h (other than a possible new short term bias estimator
created at 366) is
associated with the temperature represented by the temperature reading
obtained at 352,
then that bias estimator may be used to determine the bias of the gyroscope
108 at the current
temperature (i.e. the other bias estimators may not be used and the bias may
be determined
directly from the bias estimator associated with the current temperature).
[00107] In at least some embodiments, when one of the bias estimators
298a, 298b,
298c, 298d, 298e, 298f, 298g, 298h is associated with the temperature
represented by the
temperature reading obtained at 352, then the electronic device may evaluate
the stability of
that bias estimator and may use that bias estimator directly for determining
the bias only if that
bias estimator is stable. In at least some embodiments, the stability of that
bias estimator may
be evaluated relative to the stability of other bias estimators and/or to the
stability of the least
squares fit model. The stability may be based on the number of gyroscope
readings
represented by such bias estimators. For example, in some embodiments, the
electronic device
201 may determine whether the bias estimator associated with the temperature
is more stable
than the least squares fit model by comparing the number of gyroscope readings
represented
by the bias estimator associated with the temperature to a fraction of the
number of gyroscope
readings represented by the bias estimators used to generate the least squares
fit model. In at
least some embodiments, if the bias estimator associated with the temperature
represented by
the temperature reading obtained at 352 is determined to be stable and/or if
it is determined
to be more stable than the least squares fit model, then the bias may be
determined directly
from the bias estimator associated with the temperature represented by the
temperature
reading obtained at 352. If, however, the bias estimator associated with the
temperature
represented by the temperature reading obtained at 352 is determined to not be
stable and/or
if it is determined to be less stable than the least squares fit model, then
the bias may be
determined using the least squares fit model.
CA 02787976 2012-08-23
[00108] The method described above generally described the
determination of a bias for
a single axis of a gyroscope. Since the bias may vary for each axis of a
gyroscope, the method
may be performed independently for each axis of the gyroscope to obtain biases
for all axes.
That is, a separate set of bias estimators may be maintained for each axis.
Example Bias Estimator Using Histograms
[00109] As noted previously, in some embodiments, each bias estimator
may use a
histogram to determine a bias associated with that bias estimator. In the
description that
follows, a technique for determining a bias associated with bias estimator
will be described.
This technique may be used for each of the bias estimators described above to
determine a bias
associated with that bias estimator.
[00110] In the description which follows, reference will be made to
methods 300, 500,
600 which are illustrated in FIGs. 4, 6 and 7. Any one or more of these
methods 300, 500, 600
may include features which may be provided by an electronic device 201, such
as the electronic
device 201 of FIGs. 1 and 2. For example, one or more applications or modules
associated with
an electronic device 201, such as the gyroscope calibration application 297
(FIG. 2), may contain
processor readable instructions for causing a processor associated with the
electronic device
201 to perform one or more operations of the methods 300, 500, 600 of FIGs. 4,
6 and 7. That
is, in at least some example embodiments, the electronic device 201 may be
configured to
perform one or more of the methods 300, 500, 600. For example, one or more of
the methods
300, 500, 600 may be implemented by a processor 240 (FIG. 2) of an electronic
device 201 (FIG.
2).
[001 1 1] In at least some embodiments, one or more of the functions or
features of one
or more of the methods 300, 500, 600 may be performed, in whole or in part, by
another
system, software application, module, component or device apart from those
specifically listed
above. For example, in some embodiments, one or more of the methods 300, 500,
600 may be
performed by a processor associated with the gyroscope 108. That is, in at
least some
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CA 02787976 2012-08-23
embodiments, one or more of the methods 300, 500, 600 or a portion thereof may
be
performed by a processor other than the main processor the electronic device
201. A
processor which is associated with the gyroscope 108 and which may be used for
the specific
purpose of controlling the gyroscope 108 (i.e. a gyroscope-specific processor)
may be
configured to perform one or more of the methods 300, 500, 600 or a portion
thereof.
(00112] Referring first to FIG. 4, at 302, the electronic device 201
represents a plurality of
gyroscope readings for an axis of the gyroscope 108 in a histogram 800. These
gyroscope
readings may include the reading obtained at 354 of FIG. 3.
[00113] An example histogram 800 will be described below with
reference to FIG. 5. As
will be described in greater detail below with reference to FIG. 5, the
histogram includes a
plurality of bins that are associated with respective ranges. That is, each
bin has a range which
is associated with that bin. The range of the bin defines gyroscope readings
which are
considered to be included within that bin. That is, the ranges of the bins
define boundaries
which are used to separate gyroscope readings into the bins.
[00114] Accordingly, at 302, the electronic device 201 effectively builds a
histogram 800
which includes past gyroscope readings for the bias estimator. The histogram
800 represents
the number of times a gyroscope reading was within each of the ranges of the
bins of the
histogram 800. That is, the histogram 800 is used to track past gyroscope
readings in to allow
for easy identification of highly concentrated gyroscope reading values.
[001 1 5] The histogram 800 which is generated at 302 may have a small
number of bins.
For example, in some embodiments, the number of bins is less than twenty. In
some
embodiments, the number of bins is less than ten. In some embodiments, the
histogram 800
includes eight bins. A small number of bins may allow gyroscope readings to be
assigned to a
bin rapidly and may allow for easier evaluation of bins when determining the
bias from the
histogram 800.
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[00116] An example method for adding a gyroscope reading for an axis
to a histogram
will be described in greater detail below with reference to FIG. 6. That is, a
method 500 of
generating a histogram based on gyroscope readings will be described in
greater detail below.
(00117] At 304, the bias is determined for the bias estimator
associated with the
histogram 800 obtained at 302. The bias is determined by identifying a
concentration of the
gyroscope readings within the histogram 800. That is, the bias is determined
by looking for an
area of the histogram 800 where there are a large number of gyroscope readings
within a small
range.
[00118] In at least some embodiments, the bias may be determined, at
304, based on bin
populations of the bins. The bin population for a bin identifies a total
number of gyroscope
readings associated with that bin. The bias may, in at least some embodiments,
also be
determined based on bin widths for the bins.
(00119] For example, in some embodiments, the electronic device 201
may, at 304,
identify a most significant bin 410 (FIG. 5) for the histogram 800. The most
significant bin is
identified based on the bin population for the bins and the width for the
bins. For example, in
some embodiments, the gyroscope calibration application 297 may determine the
most
significant bin by calculating a bin significance score for each of the bins.
The bin significance
score for a bin may be calculated by dividing the bin population for the bin
by the width of the
bin. Accordingly, the bin significance score varies directly with the bin
population and inversely
with the width of the bin. The bin having the highest bin significance score
may be selected as
the most significant bin.
[00120] After identifying the most significant bin, the electronic
device 201 may
determine the bias for an axis of the gyroscope 108 based on the identified
most significant bin.
For example, the electronic device 201 may determine the bias for the
gyroscope 108 by
averaging the gyroscope readings in the most significant bin. That is, the
bias may be
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CA 02787976 2012-08-23
determined as the average of the values of the gyroscope readings which were
included in the
most significant bin.
(00121] In at least some embodiments, at 306, after the bias is
determined, the bias may
be stored in memory of the electronic device 201.
[00122] In some embodiments, at 308, the electronic device may perform
histogram
maintenance on the histogram. That is, at 308, one or more maintenance
operations may be
performed on the histogram 800. The maintenance operations may be used to
improve the
efficiency of the histogram 800. That is, the maintenance operations may be
used to improve
the speed at which the histogram 800 may be used to identify a bias, and/or
the accuracy of the
bias which is identified.
[00123] In at least some embodiments, at 308, the electronic device
201 may improve
precision in concentrated areas of the histogram 800 by adapting bin widths.
In at least some
embodiments, at 308, the electronic device 201 may reduce the size of the
histogram 800.
[00124] In at least some embodiments, the method 300 may be repeated.
That is, the
method 300 may be performed multiple times in order to ensure that the
determined bias
remains accurate. Since the bias of a gyroscope 108 tends to vary over time,
the method 300
may be repeated to ensure that such changes are reflected in the determined
bias. That is, the
method 300 may be repeated to ensure that the electronic device 201 continues
to have a
current estimate of the bias. In at least some embodiments, the method 300 may
be
continually repeated. For example, the method 300 may, upon completing, resume
operation
again at 302.
Example Histogram
[00125] Referring now to FIG. 5, at example histogram 800 is
illustrated. The example
histogram 800 includes a plurality of bins 402. For the sake of clarity, only
a single bin has been
labelled.
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CA 02787976 2012-08-23
[00126] The example histogram 800 illustrates the bin population of
each bin (illustrated
on the y-axis). For the sake of clarity, only a single bin population 405 has
been labelled. Each
bin 402, has an associated bin population 405. The bin population 405 is a
measure of the
number of gyroscope readings which were included in the bin 402. That is, the
bin population
405 illustrates the number of samples which were considered to fall within the
bin 402.
[00127] In the example histogram 800, the x-axis has been used to
represent gyroscope
reading values which are considered to be associated with that bin. That is,
the x-axis of the
histogram 800 effectively illustrates the range of each bin 402. It will be
appreciated that, in
other examples, the histogram 800 may be represented so that the x-axis
represents a bin
number instead of the range of gyroscope reading values for the bin.
[00128] Each bin 402 has an associated bin width 404 (only one of
which has been
labelled). The bin width 404 is defined by the range of the bin. That is, the
bin width 404 is the
difference between an upper limit for gyroscope readings which are considered
to be
associated with the bin 402 and a lower limit for gyroscope readings which are
considered to be
associated with the bin 402.
[00129] Two bins may be considered to be extreme bins 406, 408. The
extreme bins 406,
408 are the bins which are at the outside of the histogram 800. The extreme
bins include a
lower extreme bin 406 and an upper extreme bin 408. The extreme bins 406 and
408
effectively define the range of the histogram 800. A lower limit of the range
of the lower
extreme bin 406 defines a lower limit associated with the histogram 800 and an
upper limit of
the range of the upper extreme bin 408 defines an upper limit associated with
the histogram
800.
[00130] One of the bins may be considered to be a most significant bin
410. The most
significant bin 410 identifies a point of concentration in the histogram 800.
That is, the most
significant bin 410 is a bin 402 having the best combination of bin width and
bin population.
CA 02787976 2012-08-23
Methods of identifying which bin 402 is the most significant bin 410 are
described in greater
detail with reference to FIG. 4.
Obtaining Histogram
[00131] Referring now to FIG. 6, a method 500 for obtaining a
histogram 800 is
illustrated in flowchart form. The method 500 may, for example, be performed
at 302 of the
method of FIG. 4.
[00132] At 502, the electronic device 201 may, in some embodiments,
determine
whether the histogram 800 is already initialized. For example, the electronic
device 201 may
determine whether the memory of the electronic device 201 already includes the
histogram
800 or whether a new histogram 800 must be created.
[00133] If the histogram 800 is not already initialized then, at 504,
the histogram 800
may be initialized. In at least some embodiments, the histogram 800 may be
initialized by
storing, in memory, a histogram 800 having one or more default properties. For
example, the
histogram 800 may have a default number of bins, each having default ranges.
In at least some
embodiments, the histogram 800 may be created so that all bins 402 initially
have the same bin
width 404. The bin population 405 for the bins 402 of the newly created
histogram 800 may
initially be nil.
[00134] After a histogram 800 is initialized (i.e. after a new
histogram is initialized at 504
or if it is determined at 502 that a histogram is already initialized), then
at 508, the gyroscope
reading (which may have been obtained at 354 of FIG. 3) may be added to the
histogram 800.
That is, the histogram 800 may be updated to reflect the additional gyroscope
reading. More
particularly, the electronic device 201 may use the ranges associated with the
bins of the
histogram 800 to assign the gyroscope reading to a specific one of the bins
402. That is, an
appropriate bin for the gyroscope reading is identified based on the ranges of
the bins 402. A
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CA 02787976 2012-08-23
bin population 405 for identified bin may be updated to reflect the fact that
the bin 402 has a
new bin member.
[00135] In some embodiments, a sum of gyroscope readings within each
bin 402 may be
maintained by the electronic device 201. For example, rather than track all of
the individual
gyroscope readings associated with a bin 402, the electronic device 201 may
instead maintain a
sum of the gyroscope readings which were associated with that bin 402. The sum
of the
readings, when coupled with the bin population 405 allows an average gyroscope
reading for a
bin to be determined. As noted in the discussion of 304 of the method 300 of
FIG. 4 above, the
average gyroscope reading for the most significant bin 410 may provide the
bias.
[00136] In some embodiments and in some situations, a gyroscope reading may
be
obtained which falls outside of the range of the histogram 800. In some such
embodiments,
the reading may be ignored. In other embodiments, if a gyroscope reading is
outside of a range
of the histogram, the electronic device 201 may automatically increase the
range of one of the
extreme bins 406, 408 of the histogram so that the gyroscope reading may be
included in that
bin.
[00137] The method 500 of FIG. 6 may be repeatedly performed in order
to provide a
well-populated histogram 800 which yields an accurate estimate of bias.
Adapting Bin Widths
[00138] Referring now to FIG. 7, a method 600 of adapting bin widths
404 of a histogram
800 is illustrated in flowchart form. The method 600 may, for example, be
performed at 308 of
the method 300 of FIG. 4. The bin adaptation is performed to maintain the
histogram so that
the histogram may easily identify areas of concentration.
[00139] At 601, the electronic device 201 determines whether width
adaptation is
required. The electronic device 201 may make this determination based on one
or more
predetermined criteria. The predetermined criteria may consider, for example,
the bin
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CA 02787976 2012-08-23
population of the bin having the largest bin population. The predetermined
criteria may also
consider, for example, the sum of the bin populations for a pair of adjacent
bins of the
histogram which collectively contain fewer gyroscope readings than any other
pair of adjacent
bins. For example, in some embodiments, the electronic device 201 may
determine the ratio of
the bin population of the bin having the largest bin population to the sum of
the bin
populations for the pair of adjacent bins which collectively contain fewer
gyroscope readings
than any other pair of adjacent bins. If this ratio exceeds a threshold, then
the electronic device
201 may determine that bin width adaptation is required.
[00140] If bin adaptation is required, then at 602, the electronic
device 201 may identify
the bin 402 of the histogram 800 containing the greatest number of gyroscope
readings and
may, at 604, identify the pair of adjacent bins of the histogram 800 which
collectively contain
fewer gyroscope readings than any other pair of adjacent bins.
[00141] At 606, the electronic device 201 may split the largest bin
into two bins. That is,
the electronic device may form two bins from the single largest bin. The bin
width of each of
the newly formed bins may be half the bin width of the largest bin. In some
embodiments, the
bin population of each of the newly formed bins is half the bin population of
the largest bin.
Similarly, if the electronic device 201 maintains a sum of gyroscope readings
associated with
each bin, then the sums for the new bins may be half of the sum from the
largest bin.
[00142] At 608, the electronic device 201 may merge the pair of
adjacent bins identified
at 604. That is, the electronic device 201 may combine these two bins so that
these two bins
now become one bin. The bin width of the newly formed bin may be the sum of
the bin widths
of both bins in the pair. Similarly, the bin population of the newly formed
bin may be the sum
of the bin populations for both bins in the pair. The sum of gyroscope
readings associated with
the newly formed bin may be the sum of the gyroscope readings for both bins in
the pair.
[00143] In at least some embodiments, the method 600 maintains the number
of bins in
the histogram at a constant number. That is, the number of bins in the
histogram 800 is the
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CA 02787976 2012-08-23
same before the method 600 is performed as it is after the method 600 is
performed. While the
ranges of individual bins may be affected, the number of bins is static.
[00144] The method 600 eventually causes the bin with the most
gyroscope readings to
continually split and increase its resolution. Accordingly, the bin which
contains the bias (and
which contains a high concentration of measurements) will eventually become
very precise.
Furthermore, the splitting allows slow changing bias signals to be tracked
because, after the bin
with the bias is split, one of the two sides of that bin will typically take
the new gyroscope
readings representing the bias.
[00145] While the present disclosure is primarily described in terms
of methods, a person
of ordinary skill in the art will understand that the present disclosure is
also directed to various
apparatus such as a handheld electronic device including components for
performing at least
some of the aspects and features of the described methods, be it by way of
hardware
components, software or any combination of the two, or in any other manner.
Moreover, an
article of manufacture for use with the apparatus, such as a pre-recorded
storage device or
other similar computer readable storage medium including program instructions
recorded
thereon (which may, for example, cause a processor to perform one or more of
the methods
described herein), or a computer data signal carrying computer readable
program instructions
may direct an apparatus to facilitate the practice of the described methods.
It is understood
that such apparatus, articles of manufacture, and computer data signals also
come within the
scope of the present disclosure.
[00146] The term "computer readable storage medium" as used herein
means any
medium which can store instructions for use by or execution by a computer or
other computing
device including, but not limited to, a portable computer diskette, a hard
disk drive (HDD), a
random access memory (RAM), a read-only memory (ROM), an erasable programmable-
read-
only memory (EPROM) or flash memory, an optical disc such as a Compact Disc
(CD), Digital
39
CA 02787976 2012-08-23
Versatile/Video Disc (DVD) or Blu-rayTM Disc, and a solid state storage device
(e.g., NAND flash
or synchronous dynamic RAM (SDRAM)).
[00147] The embodiments of the present disclosure described above are
intended to be
examples only. Those of skill in the art may effect alterations, modifications
and variations to
the particular embodiments without departing from the intended scope of the
present
disclosure. In particular, features from one or more of the above-described
embodiments may
be selected to create alternate embodiments comprised of a sub-combination of
features
which may not be explicitly described above. In addition, features from one or
more of the
above-described embodiments may be selected and combined to create alternate
embodiments comprised of a combination of features which may not be explicitly
described
above. Features suitable for such combinations and sub-combinations would be
readily
apparent to persons skilled in the art upon review of the present disclosure
as a whole. The
subject matter described herein and in the recited claims intends to cover and
embrace all
suitable changes in technology.
40
