Note: Descriptions are shown in the official language in which they were submitted.
CA 02758710 2011-11-07
Cadence Detection
FIELD OF INVENTION
[0001] The present invention relates to portable media devices and, more
particularly, to method
for detecting cadence of body motion.
BACKGROUND OF THE INVENTION
[0002] Characterizing body movements can be useful when applied to portable
electronic
devices such as cellular phones, game controllers, and portable computers.
These devices already
incorporate sensors such as accelerometers and gyroscopes and have ample
processing power.
The applications range from synchronizing media output for pleasure or for
exercising, and to
security or safety alerts.
[0003] Typical human activity involves walking, jogging and running. One
attempt to obtain the
cadence of this motion includes using a sensor embedded in a shoe detecting
the repetitive
motion of the leg. While it works it requires batteries and a special shoe and
would therefore be
an advantage to derive useful information from the sensors which are available
in the portable
media device. Furthermore, an alternative method may provide useful
information for body
motions other than running.
[0004] An example of the method to obtain cadence information from the
accelerometer
embedded in a portable electronic device is described in US Patent 7,457,719.
The method is
based on identification of gravitational influence on rolling averages of
acceleration over a
sample periond and on generating a dominant axis based upon the gravitational
influence.
However, the problem is that the accuracy of the method is compromised by the
failure to detect
rotation of the device and by lack of calibration for the global acceleration.
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SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a method for
detecting cadence of body
motion from the signal of a sensor incorporated in the portable electronic
device independent of
the orientation, rotation or global acceleration of the device.
[0005] The invention relates, in one embodiment, to a method for detecting a
cadence value of a
body motion by measuring a signal from a sensor registering body motion of the
user over a
sample period. Cadence value is defined as a frequency of repeated set of body
movements. The
signal is transformed to obtain amplitude versus frequency information over a
desired first range
of frequencies. A low end cut-off value is then applied to the amplitudes in
this range of
frequencies. If a maximum amplitude frequency is detected in the first range
of frequencies a
second range of frequencies is created starting at the frequency set by s
multiplier of the
maximum amplitude frequency of the first range. A low end cut-off value is
applied to the
amplitudes of the second range of frequencies, the value being different than
the cut-off value
used in the first range. The maximum amplitude frequency from the first range
is used as
cadence value only if not detected in the second range. If maximum amplitude
frequency is
detected in both ranges the maximum from the second range is used as a cadence
value.
[0006] The principle of detecting a cadence value described above can be
extended by creating
three or more ranges within the measured first range of frequencies. Every
additional frequency
range is created using the multiplier of the maximum of the previous range and
applying a new
cut-off value. A maximum amplitude frequency detected in the last range is
applied as a cadence
value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] These and other features of the invention will become more apparent
from the following
description in which reference is made to the appended drawings wherein:
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[0008] Figure 1 illustrates an exemplary motion graph displaying amplitude
versus frequency
transformation of a signal measured by an accelerometer;
[0009] Figure 2 illustrates exemplary motion graphs for a case when the same
type of body
motion intensifies from walking, jogging to running;
[0010] Figure 3 illustrates application of the method of detecting cadence of
the body motion
using two frequency ranges;
[0011] Figure 4 illustrates application of the method of detecting cadence of
the body motion
using three frequency ranges;
DETAILED DESCRIPTION
[0012] The following description is of a preferred embodiment.
[0013] A typical portable media device is measuring acceleration of the device
in three
coordinate directions relative to the orientation of the device. Since the
device is located on the
body of the user either firmly attached or loosely placed it changes its
orientation while the user
is engaged in a physical activity. If a vector of acceleration is calculated
using information
measured from the three coordinate directions it would denote a dominant
acceleration of the
body independent of the orientation of the device. When acceleration vector
measurements are
sampled over time sufficient information is obtained to perform amplitude
versus frequency
transformation allowing assessment of amplitudes at frequencies which are
related to movements
of individual body parts. Figure 1 shows one example of such transformation.
The peaks 2,3,4
and 5 of the curve 1 are caused by parts of the body moving at a particular
frequency. Some of
the peak frequencies can be more indicative of the general rhythm of the body
than others. The
selection could be subjective preference or the criterion can be that the
frequency of the body
part which is closer to the frequency intended application is desired. For
example, in running
frequency of leg movement is generally closer to tempo of music than frequency
of the arm
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movement. However, from the graph shown in Figure 1 it is not obvious which
peak belongs to
the leg frequency.
[0014] When the motion of the body intensify while performing the same type of
activity the
amplitudes and the frequencies generated by the body parts change. For
example, when walking
progresses into jogging and running, the frequency of movements typically
rises but the
associated amplitudes increase or decrease. Figure 2 shows for walking the
maximum peak B
associated with leg movement since it is obviously caused by the highest
acceleration in this
mode of body movement. While running, however, the amplitude peak A of the arm
frequency
may be higher than leg frequency peak B.
[0015] The movement frequency of the desired body part is used for
synchronization of media as
the cadence value. In order to obtain the cadence value reliably at any
intensity of a particular
body activity the set of rules is applied to the motion graph as shown in
Figure 3. First, a cut-off
amplitude value 6 is applied over the whole range 7 of the frequencies. The
purpose is to discard
amplitudes which are arbitrary. For example, just standing still or moving
slowly the
accelerometer may register peaks at frequencies unrelated clearly repetitive
body movements. If
a distinctive maximum amplitude 8 is found in the range 7 then a new
evaluating range of
frequencies 9 is created. This range starts at a distance 10 from the peak 8.
The distance 8 is
determined using a multiplier which is determined by trial and error. Then a
cut-off amplitude
value 11 is applied over the range 9. The purpose of the cut-off value 11 is
the same as the
purpose for value 6. If a maximum amplitude frequency peak 12 is found in the
range 9 it is used
as a cadence value. If no amplitude frequency peak is found in the range 9
then peak frequency 8
is used as the cadence value.
[0016] The principle explained above can be expanded by applying more
evaluating ranges to
the same motion graph. Figure 4 shows using additional range 13 starting at
distance 14 from the
peak 12. A lower cut-off value 15 is shown in this example as compared to the
value 11 of the
previous range 9. If a maximum amplitude peak value 16 is found in the range
13 it is used as a
cadence value.
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[0017] In the foregoing specification, the invention has been described with
reference to specific
exemplary embodiments thereof. It will, however, be evident that various
modifications and
changes may be made thereto without departing from the broader spirit and
scope of the
invention as set forth in the appended claims.
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