Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 2023/055359
PCT/US2021/052652
1
REAR AXLE CENTER LOCATING
BACKGROUND
[0001] Tractors are frequently used to carry, push
and/or pull
attachments and implements when carrying out various tasks. Global
positioning systems, also known as global navigation satellite systems, are
sometimes used to determine a geo-referenced location of the tractor (and
any attachments or implements) when traversing a field, construction site or
other landscape.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] Figure 1 is a block diagram illustrating portions
of an example
rear axle center (RAC) location system.
[0003] Figure 2 is a block diagram illustrating portions
of an example
non-transitory computer-readable medium of an example RAC location
acquisition unit.
[0004] Figure 3 is a flow diagram illustrating portions
of an example
RAC location acquisition method.
[0005] Figure 4 is a flow diagram illustrating portions
of an example
RAC location acquisition method.
[0006] Figure 5 is a graph depicting example roll
measurements over
time from a high cost IMU sensor and a low cost IMU sensor on a tractor.
[0007] Figure 6 is a graph depicting example roll
measurements over
time from the high cost IMU sensor and from combined measurements from
multiple low-cost IMU sensors on the tractor
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[0008] Figure 7 is a top perspective view of an example
RAC location
acquisition system including an example tractor.
[0009] Figure 8 is a bottom view of the example tractor
of the example
RAC location acquisition system of Figure 5.
[00010] Figure 9 is a diagram illustrating transformation
of a GPS point
to a base link location.
[00011] Figure 10 illustrates a 4 x 4 transformation
matrix from the GPS
frame to the map frame.
[00012] Throughout the drawings, identical reference
numbers designate
similar, but not necessarily identical, elements. The figures are not
necessarily to scale, and the size of some parts may be exaggerated to more
clearly illustrate the example shown. Moreover, the drawings provide
examples and/or implementations consistent with the description; however,
the description is not limited to the examples and/or implementations provided
in the drawings.
DETAILED DESCRIPTION OF EXAMPLES
[00013] Disclosed are example tractors, computer-readable
mediums
and methods that may facilitate more accurate and lower cost tractor
positioning estimates. Global positioning system (GPS) signals are often
acquired by the tractor using a GPS antenna. To enhance signal reception,
such GPS antenna may be located or supported by the roof of the tractor.
Although the GPS antenna is located on the roof of the tractor, the
positioning
of the tractor may be in terms of the base link, the center of the rear axle
of
the tractor. To address this offset of the GPS antenna and the base link, any
determined position of the GPS antenna is translated to the position of the
base link. Such a translation may encounter difficulty due to the GPS antenna
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being located on the roof of the tractor, where vibration, roll and pitch may
be
exacerbated.
[00014] The example tractors, computer-readable mediums and
methods determine a current roll and pitch of the tractor and utilize the
determined roll and pitch to translate the determined position of the GPS
antenna to the determined position of the base link. The example tractors,
computer-readable mediums and methods determine the roll and pitch of the
tractor by utilizing multiple inertial measurement units and combining the
data
from the multiple inertial measurement units. As a result, lower fidelity and
lower cost inertial measurement units may be utilized for determining the roll
and the pitch of the tractor. In some implementations, the data is combined
using a Kalman type filter, such as an extended Kalman filter.
[00015] To further reduce cost, the example tractors, computerized
readable mediums and methods utilize existing inertial measurement units of
a camera or cameras. Such cameras may be located in the roof of the tractor
for better image capturing angles or perspectives. To also reduce cost, the
example tractors, computerized readable mediums and methods utilize inertial
measurement units provided as part of GPS units that provide the GPS
antenna or antennas. Such GPS units may also be supported by the roof of
the tractor. Although the individual inertial measurement units provided in
such cameras and GPS units may not provide satisfactory roll and pitch
measurements, especially given the vibration which may occur on the roof of
the tractor, the combination of data from the multiple individual inertial
measurement units offers enhanced roll and pitch accuracy to facilitate better
position estimates for the tractor.
[00016] In some implementations, a trust level for the inertial
measurement units is evaluated. The trust level may depend upon various
factors such as the extent or degree of vibration being experienced by the
roof
of the tractor or by the inertial measurement sensors. A high level of
vibration
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may result in less accurate sensor readings from the inertial measurement
units. In some implementations, the level of vibration is detected using the
inertial measurement sensors themselves. In other implementations, level of
vibration may be determined using additional sensors. In circumstances
where the trust level for the data received from the inertial measurement
units
is less than a predefined threshold, such as when the sensed level of
vibration
exceeds a predetermined threshold, the data from the inertial measurement
units may be provided with a lower weighting (relied upon to a lesser extent)
when determining roll and pitch or may be ignored.
MOM In some implementations, the geographic location of the RAC is
in terms of the longitudinal and latitudinal coordinates of the RAC. In some
implementations, the geographic location of the RAC may additionally include
a heading of the vehicle, heading up the RAC. In some implementations, this
heading may be determined using multiple GPS antennas, fore and aft, to
determine the orientation or heading (yaw) of the RAC.
[00018] Once the position of the tractor has been determined, the
example tractors, computerized readable mediums and methods may utilize
the previously determined tractor position and signals from wheel encoders,
indicating the speed and yaw rate or yaw (steering) of the tractor wheels, to
determine a new position of the tractor. Such position estimates may be
made in the absence of GPS signals, such as where and when GPS signals
are not able to be acquired. Once the position of the tractor has been
determined, its position may be utilized to control steering of the wheels and
of the tractor through a field, between plant rows or over a terrain. Such
steering control may be carried out in an automated fashion using a processor
that follows instructions found on a non-transitory computer-readable medium.
[00019] For purposes of this disclosure, the term "coupled" shall mean
the joining of two members directly or indirectly to one another. Such joining
may be stationary in nature or movable in nature. Such joining may be
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achieved with the two members, or the two members and any additional
intermediate members being integrally formed as a single unitary body with
one another or with the two members or the two members and any additional
intermediate member being attached to one another. Such joining may be
permanent in nature or alternatively may be removable or releasable in
nature. The term "operably coupled" shall mean that two members are
directly or indirectly joined such that motion may be transmitted from one
member to the other member directly or via intermediate members.
[00020] .. For purposes of this disclosure, unless explicitly recited to the
contrary, the determination of something "based on" or "based upon" certain
information or factors means that the determination is made as a result of or
using at least such information or factors; it does not necessarily mean that
the determination is made solely using such information or factors. For
purposes of this disclosure, unless explicitly recited to the contrary, an
action
or response "based on" or "based upon" certain information or factors means
that the action is in response to or as a result of such information or
factors; it
does not necessarily mean that the action results solely in response to such
information or factors.
[00021] .. For purposes of this disclosure, the term "processing unit" shall
mean a presently developed or future developed computing hardware that
executes sequences of instructions contained in a non-transitory memory.
Execution of the sequences of instructions causes the processing unit to
perform steps such as generating control signals. The instructions may be
loaded in a random-access memory (RAM) for execution by the processing
unit from a read only memory (ROM), a mass storage device, or some other
persistent storage. In other embodiments, hard wired circuitry may be used in
place of or in combination with software instructions to implement the
functions described. For example, a controller may be embodied as part of
one or more application-specific integrated circuits (ASICs). Unless otherwise
specifically noted, the controller is not limited to any specific combination
of
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hardware circuitry and software, nor to any particular source for the
instructions executed by the processing unit.
[00022] Figure 1 is a schematic diagram illustrating portions of an
example rear axle center (RAC) locating system 20. RAC locating system 20
determines a geographic location of a center of the rear axle of a tractor
based upon the geographic location of a GPS antenna, an offset of the GPS
antenna relative to the center of the rear axle, and roll and pitch of the
tractor
as determined from a combination of multiple inertial measurement units. By
compensating for roll and pitch of the tractor, a more accurate translation of
the GPS antenna location to the RAC location may be achieved. By
determining roll and pitch using signals from a combination of multiple
inertial
measurement units, accurate roll and pitch values may be achieved at a lower
cost. RAC locating system 20 comprises tractor 24 and RAC location
acquisition unit 28.
[00023] .. Tractor 24 comprises a vehicle configured to carry, push and/or
pull attachments and implements when carrying out various tasks. Tractor 24
may be employed in various settings such as an agricultural setting, a
residential setting, or in a construction setting. Tractor 24 comprises rear
axle
30, GPS antenna 32 and inertial measurement units (IMUs) 40-1 and 40-2,
collectively referred to as IMUs 40.
[00024] .. Rear axle 30 comprises a rod or shaft (or multiple rods or shafts)
that conducts power to propel tractor 24. For some implementations, the rear
axle may be part of an assembly that includes a differential. Rear axle 30
comprises a center, rear axle center (RAC) 42 that serves as a base link or
origin for identifying the geographic positioning or location of tractor 24.
The
positioning of other components of tractor 24 as well as any attachments or
implements being carried, pushed or pulled by tractor 24 may be defined in
terms of this base link, the RAC 42 of tractor 24. Although rear axle 30 is
illustrated as transmitting or conducting power to wheels or tires 44, in some
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implementations, rear axle 30 may transmit or conduct power to wheels of a
belt or track drive of tractor 24.
[00025] GPS antenna 32 comprises a device to receive and expand
radio signals sent by distinct frequencies from a GPS or GNS system. The
signals are converted into electronic signals that are used by a GPS receiver
to determine the geographic location, such as longitudinal and latitudinal
coordinates, of the GPS antenna 32. GPS antenna 32 is physically spaced
from or offset from RAC 42. In some implementations, the positioning of GPS
antenna 32 may be in accordance with structural constraints of tractor 24 and
available space of tractor 24. In some implementations, the positioning of
GPS antenna 32 may be to enhance signal reception quality or to protect the
GPS antenna 32. In some implementations, GPS antenna 32 may be
supported or mounted upon a roof or other top surface of tractor 24 to
enhance signal reception.
[00026] Inertial measurement units 40 comprises electronic devices that
measure and report angular rate of movement, force and orientation of a
body. Such inertial measurement units 40 may utilize a combination of
accelerometers, gyroscopes and/or magnetometers. Inertial measurement
units 40 may be used to calculate altitude, angular rates, linear velocity and
position relative to a global reference frame. In the example illustrated,
tractor
24 comprises two IMUs 40-1 and 40-2 which are physically spaced from one
another. In the example illustrated, IMUs 40 are positioned in close proximity
to GPS antenna 32 to evaluate roll and pitch in regions proximate to GPS
antenna 32. In the example illustrated, IMU 40-1 is positioned close to GPS
antenna 32, forward of RAC 42, while IMU 40-2 is positioned rearward of RAC
42. In the example, both IMUs 40 are positioned within generally the same
horizontal plane above RAC 42 as GPS antenna 32. Although tractor 24 is
illustrated as comprising two IMUs 40, in some implementations, tractor 24
may include greater than two IMUs.
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[00027] RAC location acquisition unit 28 determines the position of RAC
42 of tractor 24, wherein the position may be utilized to drive or steer
tractor
24 and to control the positioning or operation of various attachments, and/or
implements associate with tractor 24. In the example illustrated, unit 28 is
mounted to, carried by are provided as part of tractor 24. In such an
implementation, unit 28 may include a processing unit and a non-transfer
accumulation readable medium that are not only used to determine the RAC
location but also used for other functions of tractor 24. For example, unit 28
may be utilized to additionally control steering of vehicle 20 and/or to
control
the use and operation of various attachments and implements carried or
moved by vehicle 20. In some implementations, unit 28 may be remote from
tractor 24, wherein unit 28 is cloud-based or is in wireless communication
with
tractor 24. Some limitations, RAC location acquisition unit 28 may comprise
processing unit and/or storage mediums 52 across various componentry and
locations and connected to one another in a wireless fashion. RAC location
acquisition unit 28 comprises processing unit 50 and non-transitory computer-
readable medium 52. Processing unit 50 carries out functions or operations in
accordance with instructions provided on computer-readable medium 52.
[00028] Non-transitory computer-readable medium 52 comprise a
persistent storage device storing recorded instructions for processing unit
50.
Examples of medium 52 include, but are not limited to, solid-state memory
(flash memory), disk memory and the like. As shown by Figure 2, medium 52
comprises global positioning system data acquisitions instructions 60,
inertial
measurement unit signal acquisition instructions 62 and RAC location
determining instruction 64. Instructions 60-64 direct processing unit 50 to
carry out method 100 outlined in Figure 3.
[00029] As indicated by block 104 in Figure 3, global positioning system
data acquisition directions direct processing unit 50 to acquire GPS signals
from GPS antenna 32, wherein the GPS signals indicate a geographic
location of the GPS antenna 32 which is offset from RAC 34 of tractor 24.
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[00030] As indicated by block 106 in Figure 3, inertial measurement unit
signal acquisition instructions 62 direct processing unit 50 to acquire
signals
from multiple inertial measurement units, such as inertial measurement units
40-1 and 40-2 of tractor 24.
[00031] As indicated by block 108 in Figure 3, RAC location determining
instruction 64 direct processing unit 50 to determine a geographic location of
the center 34 of the rear axle 30 based upon the determined position of the
GPS antenna 32, as indicated from the GPS signals acquired in block 104,
and from a combination of the signals from the multiple IMUs 40. In some
implementations, the signals from the multiple IMUs 40 are combined to
determine a roll and a pitch of tractor 24 which is used as a basis for
translating the position of GPS antenna 32 to the position or location of RAC
34. In some implementations, the positioning of antenna 32, is offset relative
to RAC 34, wherein the offset and the determined roll and pitch of tractor 24
are used in combination to estimate the location of RAC 34 (its longitudinal
and latitudinal coordinates or other geographic location identification
parameters). In some implementations, the signals from the multiple IMUs are
combined using a Kalman filter. In some implementations, the Kalman filter is
an extended Kalman filter.
[00032] Once the geographic location of the RAC 34 has been
determined, the determine geographic location/position of RAC 34 may be
used as a basis to control steering of the wheels 44 and of the tractor 24
through a field, between plant rows or over a terrain. Such steering control
may be carried out in an automated fashion using a processor that follows
instructions found on a non-transitory computer-readable medium 52. In
some implementations, two different estimates for the geographic
location/position of RAC 34 at two different times may be used to estimate the
speed and/or velocity of tractor 24 and of RAC 34. In some implementations,
the determined geographic location of RAC 34 may also be utilized by an
operator or an automated control system to control the positioning or
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operation of various attachments, and/or implements associate with tractor
24.
[00033] .. In some circumstances, GPS signals indicating the position of
GPS antenna 32 may not be available. In some circumstances, vibration or
other conditions may impair the reliability and accuracy of the signals from
IMUs 40. Figure 4 is a flow diagram of an example method 200 for locating
RAC 34 and the positioning of tractor 24. Although method 200 is described
in the context of being carried out by tractor 24, it should be appreciated
that
method 200 may likewise be carried out by other similar vehicles or other
similar tractors.
[00034] As indicated by block 220, the rear axle center (RAC) location
estimate is initiated. In some implementations, the determination of the RAC
location may be initiated (and repeated in a periodic fashion (i.e., every X
seconds) until termination) in response to input from an operator, either an
operator riding or driving tractor 24 or a remote operator. In some
implementations, the determination of the RAC location may be initiated
according to a predetermined pattern. For example, the RAC location may be
initiated periodically based on time or periodically based upon distance
traversed by the tractor.
[00035] In some implementations, the determination of the RAC location
may be automatically triggered in response to certain conditions or certain
operations being carried out or to be carried out by tractor 24 or by any
attachments/implements moved by tractor 24. In some implementations, the
RAC location estimation process may be triggered automatically in response
to tractor 24 or unit 28 receiving signals from a sensor or commands from an
operator or automated program indicating that a particular implement
operation is about to begin. For example, in circumstances where the precise
positioning of tractor 24 is beneficial, such as the initiation of planting,
spraying a chemical or fertilizer, applying a fertilizer, cultivation,
performing a
pruning operation, harvesting a crop, or the like, the RAC location estimation
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process may be initiated. The process may be repeated or continued until the
circumstances that demand the precise positioning of tractor 24 have expired.
In some implementations, the RAC location estimate may be initiated and
may continue to be carried out in a periodic fashion (i.e., every X seconds)
while tractor 24 is being used or operated.
[00036] As indicated by decision block 222, processing unit 50, following
instructions in non-transitory computer-readable medium 52, may determine
the current GPS trust level for the signals received from GPS antenna 32.
The GPS trust level is a measure of the current accuracy and/or reliability of
the location indication provided by the signals received by GPS antenna 32.
In some circumstances, the signals may be intermittent so as to be less
reliable. In some circumstances, GPS antenna 32 may not be receiving any
location indicating signals or an insufficient number of signals to accurately
determine a location.
[00037] .. As indicated by block 224, in circumstances where the GPS
trust level (GPS TL) fails to satisfy the predetermined threshold TH1, such as
when the reception of a GPS signal is obstructed or is not being received due
to a distance from a GPS signal source, instructions 64 may direct processing
unit 50 to determine or estimate geographic location of RAC 34 using data
other than the GPS signal. In some implementations, processing unit 50 may
determine or estimate the current geographic location of RAC 34 based upon
a prior determined and stored RAC estimate, subsequent wheel rotation data
and subsequent steering data. In such circumstances, the wheel rotation data
may be obtained by processing unit 50 from a wheel encoder or multiple
wheel encoders that sense the speed at which wheels 44 have been driven
since the last determined RAC position, wherein the duration of time at the
various speeds indicates a distance traveled. The steering data may be
obtained by processing unit 50 from a potentiometer, IMU 40-1 and/or IMU
40-2. The steering data may indicate the direction of travel of tractor 24 at
the
various speed or speeds.
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[00038] As indicated by decision block 226, in circumstances where the
GPS signal is being received and is reliable, instructions 62 may direct
processing unit 50 to determine the GPS antenna location from the GPS
signals received by GPS antenna 32.
[00039] As indicated by block 228, instructions 52 may direct processing
unit 50 to determine the current trust level for the signals received from
IMUs
40. The IMU trust level is a measure of the current accuracy and/or
reliability
of the roll and pitch indications provided by the output by IMUs 40. In
circumstances where IMUs are experiencing high levels of vibration, the
ability of the signals output by IMUs 40 to accurately and/or reliably
indicate
roll and/or pitch of the vehicle may be impaired. Such vibration
measurements may be taken by one or more vibration sensors provided on
tractor 24. In some implementations, one of IMUs may be experiencing a
higher degree of vibration or bouncing as compared to the other of IMUs 40.
In such circumstances, a lower weighting may be applied to the signals from
the particular IMU experiencing the larger vibrations when determining roll
and pitch correction values. For example, in some implementations, an IMUs
covariance matrix (trust) may be dynamically updated based upon the
magnitude of acceleration (vibration) as sensed by the particular IMU at any
given time.
[00040] As indicated by block 230, following the instructions contained in
medium 52, processing unit 50 determines roll and pitch corrections using the
data or signals from the multiple IMUs 40. Roll refers to movement of tractor
24 about a longitudinal axis rotational axis of wheels 44. Pitch refers to
movement of tractor 24 about a transverse axis parallel to the rotational axis
of wheels 44. Yaw refers to movement or orientation of tractor 24 about a
vertical axis. Each of such movements may further impact the geographic
location of GPS antenna 32 relative to RAC 34. The determined correction
constitutes a vector (distance and direction) value indicating the additional
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amount of movement of GPS antenna 32 towards or away from RAC 34
caused by such yaw, roll and/or pitch.
[00041] In some implementations, the different signals from the multiple
different IMUs are combined to determine the roll and pitch correction. In
some implementations, the different signals for the multiple different IMUs
are
combined using sensor and data fusion such as with a Kalman filter. In some
implementations, the signal or data from the different IMUs are combined
using an extended Kalman filter. The extended Kalman filter uses a series of
measures observed over time, including statistical noise and other
inaccuracies to produce estimates. The extended Kalman filter includes a
prediction phase wherein the filter produce estimates of current state
variables along with their uncertainties. The extended Kalman filter relies on
the covariance (confidence) from the current measurement and state. In this
way it indirectly uses the measurements from the previous states, but
previous measurements are not directly fed into the filter at the new update
step. The extended Kalman filter operates in real time using present input
measurements and prior measurements.
L00042] Figure 5 is a graph illustrating a comparison of two example
vehicle roll estimations over time from two different single IMUs. The
comparison depicts signals from a low cost Bosch IMU that comes with a
Piksi multi GPS board (shown in red) and a high cost XSENS IMU (shown in
blue). Figure 6 is a graph illustrating a comparison of roll estimations over
time from a combination of multiple low cost Bosch IMUs (using an extended
Kalman filter) and from a high cost XSENS IMU (shown in blue). As shown by
Figure 6, by combining or fusing the signals or data from multiple low-cost
IMUs, roll estimate accuracy similar to those of a single high cost IMU may be
achieved. Similar results are achieved when estimating pitch of a vehicle by
fusing signals from multiple low-IMUs. Because low-cost IMUs maybe
drastically less expensive than high cost IMUs and because low-cost time use
may already exist on other componentry, such as with GPS units camera
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units and the like, roll and pitch estimates may be made with existing
componentry and such are without higher cost IMUs.
[00043] As indicated by block 232, processing unit 50, following the
instructions contained in medium 52, applies a roll and pitch corrections to
the
GPS antenna location.
[00044] .. As indicated by block 234, processor unit 50, following
instructions contained in medium 52, transforms the GPS location (as
corrected based upon roll and pitch) to the RAC location. This transformation
may be based upon the offset (direction and distance) between the GPS
antenna and the RAC 34. The offset maybe in terms of the relative physical
positioning of the RAC 34 and the GPS antenna 32 due to the mounting
locations on tractor 24.
[00045] In some implementations, processing unit 50 may begin with
the GPS signal determined position of the GPS antenna and then adjust this
location based upon both the roll and pitch correction and the offset to
derive
the geographic location of RAC 34. The geographic location of RAC 34 may
then be stored and/or used to control the steering and movement of tractor
24, to control the positioning and/or operation of implement or attachments of
tractor 24 and/or to map the geographic locations of information regarding
plants, moisture level, weeds, conditions or other parameters sensed by
sensors or cameras of tractor 24 as tractor 24 moves in a field, orchard or
the
like.
[00046] Figures 7 and 8 illustrate an example RAC locating system 320.
System 320 is similar to system 20 described above in that system 320
determines a current roll and pitch of a tractor using the combined signals
from multiple IMUs to translate the determined position of the GPS antenna to
the determined position of the base link, the RAC. Figures 7 and 8 illustrate
a specific implementation of system 20, wherein some of the IMUs used to
determine roll and pitch are provided by existing GPS units and existing
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camera units. Figures 7 and 8 illustrate an example RAC locating system that
may be at a lower cost as compared to other systems that utilize higher
fidelity IMUs or IMUs dedicated to determining roll and pitch. System 320
comprises tractor 324 and RAC location acquisition unit 328.
[00047] Tractor 324 comprises a vehicle that may be employed in
various settings such as an agricultural setting, a residential setting or a
construction setting. Tractor 324 may be used for a variety of purposes in
agricultural construction and residential purposes. Tractor 324 may be used
to push or pull an implement. Tractor 324 may include attachments, such as
a bucket, blade, backhoe, or the like for digging, displacing, and/or carrying
various materials such as earthen materials, animal waste and produce.
Tractor 324 may include forks or other coupling mechanisms for engaging
pallets, bins, boxes, or the like, wherein the tractors carry and/or lift the
engaged items.
[00048] Tractor 324 comprises chassis 400, ground propulsion members
402, battery 404, vehicle cab 406, GPS units 408-1 and 408-1 (collectively
referred to as GPS units 408), camera units 410-1, 410-2 (collectively
referred
to as camera units 410), IMUs 440-1, 440-2 (collectively referred to as IMUs
440), front wheel encoders 442, rear wheel encoders 444 and steering
actuator 446.
[00049] Chassis 400 comprises a frame supporting the remaining
components of tractor 324. In the example illustrated, chassis 400 comprises
a front cargo bed 448 for storing and transporting cargo. In the example
illustrated, chassis 400 is further configured for connection to an
attachment/implement with a hitch or other mounting structure. In the
example illustrated, chassis 400 supports a propulsion unit in the form of an
an electric motor driven by electrical power supplied by battery 404.
[00050] Ground propulsion members 402 comprise members that
engage the underlying terrain and which are driven. In the example
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illustrated, ground propulsion members 402 comprise rear wheels 450 and
front wheels 452. In the example illustrated, rear wheels 450 are driven by an
electrical drive while front wheels 452 are manipulated or turned by steering
actuator. In other implementations, ground propulsion members 402 may
comprise tracks or other ground engaging members.
[00051] As shown by Figure 6, rear wheels 450 are supported by an/or
driven by a rear axle 454 having a rear axle center (RAC) 456. RAC 456
serves as a base link or origin for identifying the geographic positioning or
location of tractor 324. The positioning of other components of tractor 324 as
well as any attachments or implements being carried, pushed or pulled by
tractor 324 may be defined in terms of this base link, the RAC 456 of tractor
324.
[00052] .. Battery 404 comprises a battery unit that is removably received
within a corresponding chamber or cavity extending rearwardly from the front
of chassis 400. Battery 404 mates with a corresponding connection interface
for transferring electrical power from battery 404 to the electrically powered
components of tractor 324. In other implementations, battery 404 may be
located at other locations. In other implementations, battery 404 may be fixed
and non-swappable or not removable. In the example illustrated, battery 404
electrically powers an electric motor or motors that drive rear wheels 450. In
some implementations, wheels 450 of tractor 324 may alternatively be driven
by an internal combustion engine and associated transmission or by a hybrid
system using both a battery and an internal combustion engine.
[00053] Cab 406 comprises a compartment in which an operator may be
seated when operating tractor 324. Cab 406 comprises a seat 460, a steering
wheel 462, a control console 464 and a roof 466. Roof 620 extends over
control seat 612 and control console 618. In some implementations, roof 466
may be raised and lowered.
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[00054] GPS units 408 are supported by roof 466. As schematically
illustrated, each of GPS units 408 comprises a GPS antenna 470 and an
inertial measurement unit (IMU) 472 housed in a single enclosure or housing
473. In some implementations, each GPS unit 408 is a commercially
available GPS unit sold as a single component, having a reduced overall cost
as compared to individual GPS antenna and IMUs. Each of antenna 470 is
similar to GPS antenna 32 described above. Each of IMUs 472 may be
similar to IMUs 40 described above. Signals from IMUs 472 are transmitted to
RAC location acquisition unit 328.
[00055] In the example illustrated, GPS unit 408-1 is located at a front
end of roof 466, forward of rear axle 454 while GPS unit 408-2 is located at a
rear end of roof 466, rearward of rear axle 454. Because tractor 324
comprises two offset spaced GPS units 408, GPS signal reception and GPS
position estimates may be enhanced.
[00056] Camera units 410-1 and 410-2 are supported by roof 466 at a
front and a rear of roof 466, facing in forward and rearward directions,
respectively. Camera unit 410-1 is positioned forward of rear axle 454 while
camera unit 410-2 is supported rearward of rear axle 454. As schematically
illustrated, each of camera units 410 comprises a camera 474 and inertial
measurement unit 476. In the example illustrated, each of camera units 410
integrate a camera and inertial measurement as a single integrated
component contained within a single housing 477. In some implementations,
each camera unit 410 is a commercially available camera unit sold as a single
component, having a reduced overall cost as compared to individual cameras
and IMUs.
[00057] Camera 474 of camera unit 410-1 captures video or images in
front of tractor 324. Camera 474 of camera unit 410-2 captures video images
towards a rear of tractor 324. In some implementation, camera 474 may
comprise a stereo camera. In other implementations, camera 474 may
comprise a monocular camera.
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[00058] Inertial measurement units (IMUs) 476 of camera units 410 may
be similar to inertial measurement units 40 described above. IMUs 476 output
signals which may indicate or may be used to determine the roll and pitch of
tractor 324 at the location of the individual IMUs. Signals from IMUs 476 are
transmitted to RAC location acquisition unit 328.
[00059] IMUs 440 (schematically illustrated) are supported by roof 466
and provide inertial measurements at additional locations on roof 466. IMUs
440 may be similar to IMUs 40 described above. In the example illustrated,
IMUs 440 are embedded within roof 466. Signals from IMUs 440 are
transmitted to RAC location acquisition unit 328.
[00060] Front wheel encoders 442 comprise electronic devices that
sense or measure the orientation of front wheels 452. In some
implementations, front wheel encoders 442 may comprise potentiometers.
Signals from front wheel encoders 442 are transmitted to RAC location
acquisition unit 328.
[00061] Rear wheel encoders 444 (schematically shown) comprise
electronic devices that sense or measure the rotational rate or speed of rear
wheels 450. Signals from front wheel encoders 442 are transmitted to RAC
location acquisition unit 328. In other implementations, other speed sensors
may be used to detect the rotation of wheels 450 or the speed of tractor 324.
[00062] Steering actuator 446 comprises mechanical, hydraulic or
electric actuator (pump etc.) configured to rotate front wheels 452 to
effectuate steering of tractor 324. Steering actuator 446 receives steering
commands or control signals from a processing unit of tractor 324. In some
implementations, the processing unit may be part of RAC location acquisition
unit 328. Forces from steering actuator 446 result in wheels 452 turning,
wherein such turning is sensed by wheel encoder 442.
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[00063] RAC location acquisition unit 328 is similar to RAC location
acquisition unit 28 described above except that instruction 64 of medium 52 of
RAC location acquisition unit 328 directs processing unit 50 to determine or
estimates the current roll and pitch of tractor 324 based upon a combination
of
signals received from each of IMUs 472 of GPS units 408-1, 408-2, IMUs 476
of each of camera units 410-1 and 410-2 and both of IMUs 440-1, 440-2. In
some implementations, the IMU signals are combined using a Kalman filter to
determine roll and pitch estimates. In some implementations, the IMU signals
are combined using an extended Kalman filter to determine roll and pitch
estimates. Because a combination of signals from multiple IMUs are used to
estimate roll and pitch, accurate roll and pitch estimates may be made using
individual IMUs that may have a lower fidelity and that may be provided at a
lower cost.
[00064] Further reducing the overall cost of system 320, many of the
IMUs used to determine roll and pitch estimates are already existing as part
of
the GPS units 408 and camera units 410. By taking advantage of the
existing IMUs (albeit possibly lower fidelity IMUs) in the GPS units 408 and
the camera units 410 to estimate roll and pitch, a greater number of IMUs are
available to provide enhanced accuracy while reducing cost. Although system
320 is illustrated as estimating roll and pitch using a combination of signals
from six IMUs supported by roof 466, in other implementations, system 320
may utilize a fewer number of IMUs to estimate roll and pitch, such as where
one or both of IMUs 440 are omitted, such as where one or both of IMUs 472
are omitted such as where one or both of IMUs 476 are omitted. In
implementations, system 320 may include even additional IMUs, wherein
such additional signals will be combined with signals from other IMUs for
estimating roll and pitch.
[00065] As described above with respect to method 100, RAC location
acquisition unit 328 comprises medium 52 having instruction 60, 62 and 64.
Such instructions 60 direct processing unit 50 to acquire GPS signals from
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both of antennas 70 of GPS units 408. Such instructions 62 direct processing
unit 50 to acquire IMU signals from each of the six IMUs. Instructions 64
direct processing unit 50 to determine or estimate the geographic location of
RAC 456 based upon a the geographic antennas 470 (as determined by a
GPS receiver from the received GPS signals), the offsets from each of the
antennas 470 to RAC 456, the current yaw or orientation of tractor 324 (as
determined from wheel encoders 442 or from steering control signals
transmitted to steering actuator 446) and the roll and pitch corrections as
determined from the combination of signals from the six IMUs.
[00066] In some implementations, the RAC location additionally includes
a heading of the vehicle RAC and is determined by unit 328 as follows.
Figure 9 illustrates tractor 324 and its base link, RAC 456 in an example
location in a map frame which may be defined in terms of latitude and
longitude. Figure 9 further illustrates a GPS point, the location of one of
the
GPS antenna of tractor 324. In the example illustrated, the GPS point may
refer to the geographic location of the GPS antenna 470 of GPS unit 408-1.
[00067] The determination of the geographic location or position of the
base link, the RAC 456 may utilize a simple matrix multiplication of the base
link point in the GPS frame and a 4 x 4 transformation matrix from the GPS
frame to the map frame as follows:
Prasa eP unk = TglnpasP ' PbgaPsselink
wherein:
PeaPsselink: The position of the baselink in the gps frame (this is a fixed
position
on the tractor that never moves).
TinaP The gps and imu's provide the 4x4 homogeneous transformation matrix
gps
from the gps frame to the map frame (shown in 10). This transformation
matrix consists of a rotation matrix and the translated position of the gps in
the
map frame.
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The 3x3 rotation matrix R describes the roll, pitch, and yaw of the tractor
R = RzRyRx, wherein
Rz = rotation about the z axis (yaw),
Ry = rotation about the y axis (pitch), and
Rx = rotation about the x axis (roll).
[00068] The yaw (heading) of the tractor is measured by comparing the
position of the front and rear gps antennas (470 of GPS units 408-1 and 408-
2) of the tractor 324. The pitch may be determined by the relative position of
the front and rear gps antennas and is supplemented with data from the
inertial measurement units mounted on the vehicle body. The roll of the
tractor
can only be calculated from the IMU given the mounting of the rear and front
gps on the body.
[00069] If only acceleration from gravity is present, the roll and pitch
angles can be calculated from the measured acceleration values ax, ay, az.
ay
roll = arctan(
Vax2 + az2)
a,
pitch = arctan(
V ay2 + az2
[00070] As described above, the 3 x 3 rotation matrix R may be the
result of the fusion of measurements provided by the multiple IMUs of tractor
324: IMUs 472of GPS units 408, IMUs 476 of camera units 477 and IMUs
440. The measurements provided by the multiple IMUs may be fused using a
Kalman filter, such as an extended Kalman filter. In other implementation, the
measurements provided by the multiple IMUs may be fused using other filters,
such as other forms of Kalman filters or other data fusion algorithms or
techniques.
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[00071] In some implementations, RAC location acquisition unit 328 may
carry out method 200 described above. In response to insufficient or
unreliable GPS signals (as indicated by block 222 in Figure 4), unit 328 may
determine or estimate the RAC location using a prior RAC estimate, wheel
rotation data acquired from wheel encoders 444 and steering data acquired
from wheel encoders 442.
[00072] Once the geographic location of RAC 456 has been, it may be
used to output control signals to steering actuator 446 to control future
movement of tractor 324. The location of RAC 456 may also be utilized by
control circuitry associated with tractor 324 to control the positioning
and/or
operation of various attachments or implements being carried, pushed or
towed by tractor 324. In implementations where cameras or other sensors
are used to detect plants or conditions adjacent to tractor 324 while tractor
324 is traversing a field, orchard of the like, the current positioning of RAC
456 may be associated with the concurrently detected plant conditions, field
conditions or the like to generate maps linking different detected plant,
field
orchard characteristics to different geographic locations.
[000731 Although the claims of the present disclosure are generally
directed to a rear axle center locating system, medium and method, the
present disclosure is additionally directed to the features set forth in the
following definitions.
1. A non-transitory computer-readable medium
containing
instructions to direct a processor, the instructions comprising:
global positioning system data acquisition instructions to direct
the processor to acquire GPS signals indicating a position of a GPS
antenna offset from a center of a rear axle of a tractor;
inertial measurement unit signal acquisition instructions to direct
the processor to acquire signals from multiple inertial measurement
units; and
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geographic location determining instructions to direct the
processor to determine a geographic location of the center of the rear
axle of the tractor based upon the position of the GPS antenna and the
signals from a combination of the multiple inertial measurement units.
2. The medium of definition 1, wherein the instructions comprise
roll and pitch determination instructions to direct the processor
to determine a roll and pitch of the tractor based upon the
signals from a combination of the multiple inertial measurement
units and wherein the geographic location determining
instructions are to direct the processor to determine the
geographic location of the center of the rear axle of the tractor
based upon the position of the GPS antenna and the determined
roll and pitch of the tractor.
3. The medium of definition 1, wherein the instructions are to direct
the processing unit to determine the geographic location of the
center of the rear axle based upon a prior geographic location of
the center the rear axle and the signals indicating rotation and
yaw of wheels of the tractor.
4. The medium of definition 1, wherein the tractor comprises a roof
and wherein the inertial measurement units are supported by the
roof.
5. The medium of definition 4 further comprising a camera
supported by the roof, wherein one of the inertial measurement
units is part of the camera.
6. The medium of definition 5 further comprising a GPS unit
supported by the roof, wherein the GPS unit comprises both the
GPS antenna and another of the inertial measurement units.
7. The medium of definition 4 further comprising a GPS unit
supported by the roof, wherein the GPS unit comprises both the
GPS antenna and one of the inertial measurement units.
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8. The medium of definition 1, wherein the instructions are to direct
the processing unit to combine the data from the inertial
measurement units using a Kalman filter.
9. The medium of definition 8, wherein the Kalman filter is an
extended Kalman filter.
10. The medium of definition 11, wherein the instructions are to
direct the processing unit to output control signals to an actuator
to adjust steering of wheels of the tractor based upon the
determined geographic location of the center of the rear axle.
11. A method comprising:
acquiring GPS signals indicating a position of a GPS antenna
offset from a center of a rear axle of a tractor;
acquiring signals from multiple inertial measurement units; and
determining a geographic location of the center of the rear axle
of the tractor based upon the position of the GPS antenna and the
signals from a combination of the multiple inertial measurement units.
12. The method of definition 11 further comprising determining a roll
and pitch of the tractor based upon the signals from a
combination of the multiple inertial measurement units and
wherein the determination of the geographic location of the
center of the rear axle of the tractor is based upon the position
of the GPS antenna, an offset between the GPS antenna and
the RAC, and the determined roll and pitch of the tractor.
13. The method of definition 11 further comprising determining the
geographic location of the center of the rear axle based upon a
prior geographic location of the center the rear axle and the
signals indicating rotation and yaw of the wheels of the tractor.
14. The method of definition 11, wherein the tractor comprises a
roof and wherein the inertial measurement units are supported
by the roof.
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15. The method of definition 11, wherein one of the inertial
measurement units are part of a camera supported by the roof.
16. The method of definition 15, wherein another of the inertial
measurement units is part of a GPS unit that includes the GPS
antenna and that is supported by the roof.
17. The method of definition 14, wherein the inertial measurement
units are part of a GPS unit that includes the GPS antenna and
that is supported by the roof.
18. The method of definition 11, wherein data from the inertial
measurement units is combined using a Kalman filter.
19. The method of definition 18, wherein the Kalman filter is an
extended Kalman filter.
20. The method of definition 11 further comprising adjusting the
steering of wheels of the tractor is based upon the determined
geographic location of the center of the rear axle.
[00074] Although the present disclosure has been described with
reference to example implementations, workers skilled in the art will
recognize
that changes may be made in form and detail without departing from the
scope of the claimed subject matter. For example, although different example
implementations may have been described as including features providing
benefits, it is contemplated that the described features may be interchanged
with one another or alternatively be combined with one another in the
described example implementations or in other alternative implementations.
Because the technology of the present disclosure is relatively complex, not
all
changes in the technology are foreseeable. The present disclosure described
with reference to the example implementations and set forth in the following
claims is manifestly intended to be as broad as possible. For example, unless
specifically otherwise noted, the claims reciting a single particular element
also encompass a plurality of such particular elements. The terms "first",
"second", "third" and so on in the claims merely distinguish different
elements
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Atty. Dkt. No.: M220-142
and, unless otherwise stated, are not to be specifically associated with a
particular order or particular numbering of elements in the disclosure.
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