U.S. patent application number 10/815858 was filed with the patent office on 2004-10-07 for sensing steering axis inclination and camber with an accelerometer.
Invention is credited to Bryan, Eric F..
Application Number | 20040194327 10/815858 |
Document ID | / |
Family ID | 33159719 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040194327 |
Kind Code |
A1 |
Bryan, Eric F. |
October 7, 2004 |
Sensing steering axis inclination and camber with an
accelerometer
Abstract
Methods and devices for measuring and calculating wheel
alignment angles. Light weight and mechanically robust
accelerometers in measurement heads are attached to a vehicle's
wheels during an alignment procedure. The output of the
accelerometers may be compensated for effects of temperature or
thermal hysteresis by memory lookup or a temperature based feedback
control loop.
Inventors: |
Bryan, Eric F.; (Conway,
AR) |
Correspondence
Address: |
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Family ID: |
33159719 |
Appl. No.: |
10/815858 |
Filed: |
April 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60459998 |
Apr 4, 2003 |
|
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Current U.S.
Class: |
33/203.18 |
Current CPC
Class: |
G01B 7/315 20130101;
G01B 2210/28 20130101 |
Class at
Publication: |
033/203.18 |
International
Class: |
G01B 005/24 |
Claims
What is claimed is:
1. A method for measuring a wheel alignment angle, the method
comprising: attaching to a wheel a measurement head including an
accelerometer; and measuring, with the accelerometer, a wheel angle
with respect to gravity.
2. The method of claim 1, wherein the accelerometer comprises a
micro-electromechanical systems (MEMS) device.
3. The method of claim 1, wherein the accelerometer includes a
solid proof mass.
4. The method of claim 1, wherein the accelerometer measures
internal changes in heat transfer caused by acceleration.
5. The method of claim 1, further comprising: calculating, by a
computing device, at least one wheel alignment parameter based on
the measured angle.
6. The method of claim 5, wherein the wheel alignment parameter
includes at least one of toe, camber, and steering axis
inclination.
7. A method for measuring a wheel alignment angle, the method
comprising: attaching to a wheel a measurement head including an
accelerometer; operatively connecting a thermal sensor to the
accelerometer; measuring, with the accelerometer, an uncompensated
wheel angle; measuring, with the thermal sensor, a temperature to
which the accelerometer is subjected; and calculating a compensated
wheel angle as a function of the uncompensated wheel angle and the
measured temperature.
8. The method of claim 7, wherein the accelerometer comprises a
micro-electromechanical systems (MEMS) device.
9. The method of claim 7, wherein the accelerometer includes a
solid proof mass.
10. The method of claim 7, wherein the accelerometer measures
internal changes in heat transfer caused by acceleration.
11. A measurement head for a wheel alignment system, the
measurement head comprising: an accelerometer configured to measure
an uncompensated wheel angle with respect to gravity; a thermal
sensor configured to measure a temperature to which the
accelerometer is subjected; and a compensator operatively coupled
to the accelerometer and the thermal sensor and configured to
calculate a compensated wheel angle as a function of the
uncompensated wheel angle and the measured temperature.
12. The measurement head of claim 11, further comprising: a memory
component operatively coupled to the compensator and configured to
store at least one of a plurality of angles and corresponding
temperatures and an adjustment function.
13. The measurement head of claim 11, wherein the accelerometer
comprises a thermal accelerometer and the compensator is further
configured to compensate for sensitivity and for zero gravity
offset of the thermal accelerometer.
14. The measurement head of claim 11, wherein the compensator
implements a feedback control loop to compensate for at least one
of thermal sensitivity and zero gravity offset.
15. The measurement head of claim 11, wherein the compensator
implements an approximation using at least two temperature points
for calculating zero gravity offset.
16. A wheel alignment system comprising: a measurement head
including an accelerometer configured to calculate a wheel angle
with respect to gravity; and a computing device operatively coupled
to the measurement head and configured to receive the wheel angle
and to compute a wheel alignment parameter based on the wheel
angle.
17. The wheel alignment system of claim 16, wherein the wheel
alignment parameter includes at least one of toe, camber, and
steering axis inclination.
18. The wheel alignment system of claim 16, wherein the
accelerometer comprises a micro-electromechanical systems (MEMS)
device.
19. The wheel alignment system of claim 16, wherein the
accelerometer includes a solid proof mass.
20. The wheel alignment system of claim 16, wherein the
accelerometer measures internal changes in heat transfer caused by
acceleration.
Description
RELATED APPLICATION
[0001] This application claims the benefit under 35 U.S.C. .sctn.
119(e) of U.S. Provisional Patent Application No. 60/459,998 filed
on Apr. 4, 2003, entitled "Convection Based Accelerometers for
Sensing SAI and Camber," which is incorporated by reference herein
in its entirety.
TECHNICAL FIELD
[0002] The disclosures herein relate to wheel alignment systems,
and to methods and devices for measuring various relevant
parameters. More specifically, the disclosures relate to use of
lightweight, mechanically robust inclination sensors in wheel
alignment systems.
BACKGROUND
[0003] Wheel alignment is a process of adjusting the angles of
wheels on a vehicle so that they are generally perpendicular to the
ground and parallel to one another. The purpose of such adjustments
is to attain maximum tire life, as well as to ensure that the
vehicle tracks straight when driving along a straight and level
road.
[0004] In order to adjust the wheel angles to achieve proper wheel
alignment, the actual wheel angles must first be measured, such
that the requisite adjustments may then be calculated. Two
particular angles that are utilized in wheel alignment methods are
commonly referred to as "camber" and "toe." Camber, which is
typically measured in degrees, is the angle of the wheel's
deviation from a vertical plane. Therefore, camber is angle of the
wheel that is seen when viewed from the front of the vehicle. If
the top of the wheel is leaning out from the center of the car, the
camber is positive; if it is leaning in toward to center of the
car, then the camber is negative. Toe is the difference in distance
between the front of two tires and the back of those tires. It is
normally measured in fractions of an inch, and is usually set close
to zero, meaning that the wheels are substantially parallel to one
another. "Toe-in" means that the fronts of the tires are closer to
each other than the rears; "toe-out" is the opposite situation.
[0005] Some types of wheel alignment procedures involve placing
optical instrumentation on each of a vehicle's four wheels. The
instrumentation may be assembled together in a "head" that is
clamped to each of the wheels. A head may include a transmitting
device such as an LED emitter, and a receiving device such as a
photosensor. During an alignment procedure, the receiving device of
each head "looks" at the transmitted light from two heads of the
two adjacent wheels. The optical "box" that is formed around the
four wheels by the transmitting devices may thus be sensed by the
four receiving devices as the wheels are rotated, and the various
angle wheels may thereby be calculated. However, such procedures
involve certain inherent measurement inaccuracies and can therefore
result in alignment errors. For example, if a head is clamped to a
wheel incorrectly, inaccurate measurements may result.
[0006] Other alignment systems have utilized non-optical sensors
for measuring alignment angles, such as magneto resistive sensors
on pendulums, electrolytic vials and other pendulum type devices.
These types of sensors may not be as susceptible to wobble and
other errors that optical sensors may encounter. However, magneto
resistive and pendulum based elements are susceptible to breakage
and accuracy problems caused by mechanical shock. An additional
drawback is that these types of sensors can often be bulky and
difficult to handle, and are relatively expensive.
[0007] What is needed is a wheel alignment method that utilizes a
lighter, less expensive sensor on the measurement heads. What is
further needed is a wheel alignment system whose measurement heads
have improved robustness capable of withstanding increased
mechanical shock without breaking or deviating in measurement
accuracy.
SUMMARY
[0008] The methods and devices disclosed herein help solve these
and other problems by providing a wheel alignment system and method
that utilize tilt sensors that are mechanically robust and easier
to use. The thermal based sensors utilized by the methods and
devices disclosed herein are less expensive than conventional tilt
sensors, and are lighter, such that they are easier to handle.
[0009] In one aspect, a method for measuring a wheel alignment
angle includes attaching to a wheel a measurement head including an
accelerometer, and measuring, with the accelerometer, a wheel angle
with respect to gravity.
[0010] In another aspect, a method for measuring a wheel alignment
angle includes attaching to a wheel a measurement head including an
accelerometer, operatively connecting a thermal sensor to the
accelerometer, measuring, with the accelerometer, an uncompensated
wheel angle, and measuring, with the thermal sensor, a temperature
to which the accelerometer is subjected. The method also includes
calculating a compensated wheel angle as a function of the
uncompensated wheel angle and the measured temperature.
[0011] In a further aspect, a measurement head for a wheel
alignment system includes an accelerometer configured to measure an
uncompensated wheel angle with respect to gravity, a thermal sensor
configured to measure a temperature to which the accelerometer is
subjected, and a compensator operatively coupled to the
accelerometer and the thermal sensor and configured to calculate a
compensated wheel angle as a function of the uncompensated wheel
angle and the measured temperature.
[0012] In another aspect, a wheel alignment system includes a
measurement head including an accelerometer configured to calculate
a wheel angle with respect to gravity, and a computing device
operatively coupled to the measurement head and configured to
receive the wheel angle and to compute a wheel alignment parameter
based on the wheel angle.
[0013] Additional aspects and advantages of the present disclosure
will become readily apparent to those skilled in this art from the
following detailed description, wherein only exemplary embodiments
are shown and described, simply by way of illustration of the best
mode contemplated for carrying out the present disclosure. As will
be realized, the present disclosure is capable of other and
different embodiments, and its several details are capable of
modifications in various obvious respects, all without departing
from the disclosure. Accordingly, the drawings and description are
to be regarded as illustrative in nature, and not as
restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings illustrate several embodiments
and, together with the description, serve to explain the principles
of the present disclosure.
[0015] FIG. 1 illustrates camber as measured by an exemplary wheel
alignment system.
[0016] FIG. 2 illustrates toe as measured by an exemplary wheel
alignment system.
[0017] FIG. 3 illustrates steering axis inclination as measured by
an exemplary wheel alignment system.
[0018] FIG. 4 illustrates an exemplary wheel alignment setup and
various angles of measurement.
[0019] FIG. 5 illustrates an exemplary thermal based measurement
head for use in a wheel alignment system.
[0020] FIG. 6 is a schematic illustrating a compensator
circuit.
[0021] FIG. 7 illustrates a computing device for use in a wheel
alignment system.
[0022] FIG. 8 illustrates an exemplary wheel alignment process.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0023] The present disclosure is now described more fully with
reference to the accompanying figures, in which several embodiments
are shown. One skilled in the art will recognize that methods,
apparatus, systems, data structures, and computer readable media
implement the features, functionalities, or modes of usage
described herein. For instance, an apparatus embodiment can perform
the corresponding steps or acts of a method embodiment.
[0024] FIG. 1 illustrates camber as measured by an exemplary wheel
alignment system. Camber is the angle of the wheel 100, generally
measured in degrees, when viewed from the front of the vehicle. If
the top of wheel 100 is leaning out from the center of the vehicle,
then the camber is positive as indicated at angle 102. If the top
of wheel 100 is leaning in toward the center of the vehicle, then
the camber is negative as indicated at angle 104.
[0025] FIG. 2 illustrates toe as measured by an exemplary wheel
alignment system. The toe of two adjacent tires 200 and 202 is the
difference in distance 204 between the fronts of tires 200 and 202
and distance 206 between the rears of tires 200 and 202. Toe is
typically measured in fractions of an inch, and a measurement of
zero inches would indicate that tires 200 and 202 are substantially
parallel with one another.
[0026] FIG. 3 illustrates steering axis inclination (SAI) as
measured by an exemplary wheel alignment system. The SAI angle 300
is typically in degrees, and represents the steering pivot line
when viewed from the front of a vehicle. When added to camber, SAI
causes the vehicle to lift slightly when its wheel 302 is turned
away from a straight ahead position.
[0027] FIG. 4 illustrates an exemplary wheel alignment setup and
various angles of measurement. In the exemplary setup, a vehicle
has four wheels 400, 402, 404, 406 arranged for alignment testing.
Measurement heads 408, 410 may be attached to each wheel. For
example, measurement head 408 is attached to wheel 400, and
measurement head 410 is attached to wheel 406. Wheels 402 and 404
may also have measurement heads attached to them (not
illustrated).
[0028] Wheels 400 through 406 may be rotated through a distance 412
while measurement heads 408, 410 make gravity-dependent
measurements, as described in further detail below, of various
alignment angles. For example, angles measured by measurement head
408 may include toe 414, SAI 416 and camber 418. Toe 414 is
measured relative to a measurement head attached to wheel 402,
while SAI 416 and camber 418 are measured relative to gravity.
[0029] In one embodiment, the measurement heads 408, 410 are
convection- or thermal-based accelerometers. One suitable thermal
accelerometer is a micro-electromechanical systems (MEMS)
accelerometer, which is commercially available from MEMSIC, Inc. of
North Andover, Mass.
[0030] As one skilled in the art will appreciate, embodiments of
the present disclosure may include various MEMS accelerometers,
such as conventional solid proof mass accelerometers. Various
conventional micro-machined or MEMS devices can be used to measure
wheel alignment parameters or positions (e.g., toe, camber and
SAI).
[0031] FIG. 5 illustrates an exemplary thermal based measurement
head for use in a wheel alignment system. Measurement head 500
comprises a thermal sensor 502 and a thermal accelerometer 504,
such as a commercially available thermal accelerometer as described
above. Of course, in another embodiment, the measurement head 500
may include another type of MEMS accelerometer (e.g., solid proof
mass) and corresponding logic functions.
[0032] Thermal accelerometer 504 may include dual axis, linear
motion sensors with integrated mixed signal processing. The thermal
accelerometer 504 can measure varying and constant accelerations. A
special case of constant acceleration is the force of gravity. When
the thermal accelerometer 504 is stationary (i.e., no lateral or
vertical accelerations are present) the only force acting on the
accelerometer is gravity. The angle between the (vertical)
gravitational force, and an accelerometer sensing axis is the
inclination angle.
[0033] In one embodiment, to measure inclination from a horizontal
orientation of the thermal accelerometer 504, a calculation is
performed because the thermal accelerometer output (i.e., measured
inclination 510) represents the acceleration of gravity acting on
the sensing axis, as described in MEMSIC Application Note
#AN-00MX-007, entitled "Inclination Sensing with Thermal
Accelerometers," dated Mar. 21, 2002, which is incorporated herein
by reference. The relationship between accelerometer outputs
(x-axis and y-axis) and gravity is expressed by Equations 1 and 2,
where Ax and Ay represent accelerometer outputs, g is the
acceleration due to gravity, and .alpha., .beta. are the
inclination angles.
Ax=g.multidot.sin(.alpha.) (1)
Ay=g.multidot.sin(.beta.) (2)
[0034] The inclination angle may be calculated from the inverse of
the sine function as expressed by Equations 3 and 4.
.alpha.=sin.sup.-1(Ax/g) (3)
.beta.=sin.sup.-1(Ax/g) (4)
[0035] In another embodiment, the thermal accelerometer 504 may be
positioned in a vertical orientation. When inclination measurement
is needed for angles greater than 90.degree. arc, the accelerometer
outputs (x-axis and y-axis) can be combined to obtain good
resolution for angles through a 360.degree. arc range. With this
approach, one dual axis accelerometer is configured to measure a
single axis of inclination.
[0036] The relationship between acceleration and inclination angles
in this configuration is defined by Equations 5 and 6. In this
configuration (.delta.+.gamma.)=90.degree. arc, so it suffices to
know either one of .delta. or .gamma..
Ax=g.multidot.sin(.delta.) (5)
Ay=g.multidot.sin(.gamma.) (6)
[0037] The Ax relationship in Equation 5 can be rewritten as
Equation 7. Dividing Equations 5 and 6 yields Equation 8.
Ax=g.multidot.sin(-y+90.degree.arc)=g.multidot.cos(.gamma.) (7)
[Ay/Ax]=[(g.multidot.sin(.gamma.))/(g.multidot.cos(.gamma.))]=tan(.gamma.)
(8)
[0038] Therefore the inclination angle .gamma. can be calculated by
applying the inverse of the tangent function as shown in Equation
9.
.gamma.=tan.sup.-1[Ay/Ax] (9)
[0039] As one skilled in the art will appreciate, one advantage of
the vertical orientation is that errors that are common to both
outputs are removed in the signal process of dividing Ay by Ax.
Further details of thermal accelerometers may be found in the
MEMSIC Application Note #AN-00MX-007, which is also referenced
above.
[0040] Referring again to FIG. 5, an inclination input 506 is
received by thermal accelerometer 504, and a temperature input 508
is received by thermal sensor 502. The measured inclination 510 is
output from thermal accelerometer, and the measured temperature 512
is output from thermal sensor 512, and both signals are input to
compensator 514. As one skilled in the art will appreciate, the
sensitivity and zero gravity (g) bias change when the thermal
accelerometer 504 is exposed to different ambient temperatures.
Although the thermal accelerometer 504 and the temperature sensor
502 are distinctly illustrated, the thermal accelerometer 504 may
incorporate a temperature sensor or other functionality with the
same physical package. Compensator 514 adjusts the output of
thermal accelerometer 504 to compensate for temperature effect
induced by measured temperature 512.
[0041] The sensitivity typically decreases with increasing
temperature, and the zero g bias may increase or decrease with
increasing temperature. Various techniques may be used to
compensate for temperature changes. For example, MEMSIC Application
Note #AN-00MX-002, entitled "Thermal Accelerometers Temperature
Compensation," dated Apr. 11, 2002, which is incorporated by
reference herein, describes some temperature compensation
techniques.
[0042] The temperature effect on the sensitivity of the thermal
accelerometer 504 can be characterized by Equation 10, where
S.sub.i is the sensitivity at any initial temperature T.sub.i, and
S.sub.f is the sensitivity at any other final temperature T.sub.f,
with the temperatures in degrees Kelvin (K). The exponential of the
temperature term T is typically provided by the manufacturer
because the exponential may vary depending on the structure of the
thermal accelerometer 504.
S.sub.i.multidot.T.sub.i.sup.2.67=S.sub.f.multidot.T.sub.f.sup.2.67
(10)
[0043] In one embodiment, measured temperature 512 may be received
as an input by thermal accelerometer 504 which may use it directly
in a feedback control loop to compensate for temperature effect.
For example, the thermal sensor 502 (e.g., a conventional
thermistor) can be used in the input network of an operational
amplifier circuit. The resulting feedback gain circuit includes a
resistor network to approximate the inverse of the behavior of the
accelerometer sensitivity. Additional details on the feedback gain
circuit are described below and with reference to FIG. 6. The
output 516 of thermal based measurement head 500 is a compensated
inclination, adjusted for effects of temperature measured by
thermal sensor 502.
[0044] For use in thermal based measurement head 500, thermal
accelerometer 504 may be calibrated for zero gravity (g) offset.
The amount that the zero g bias changes with temperature can be
characterized by Equation 11, where Z is the zero g bias at any
temperature T, and a, b, c are constants characteristic to the
thermal accelerometer 504.
Z=a+b.multidot.T+c.multidot.T.sup.2 (11)
[0045] In one embodiment, the zero g bias compensation may be
achieved by measuring a change in calculated angle for various
temperatures while maintaining thermal accelerometer 504 in a level
position. For example, thermal accelerometer 504 may be driven
through three temperatures while held in a level position.
[0046] The zero offsets for each axis are measured for a plurality
of temperatures and stored in a memory component 520 of compensator
514, such as in a data table or as a calculable function. The
compensator 514 may also include signal processing capabilities,
such as an analog-to-digital converter, an digital-to-analog
converter, and a microcontroller (or other processor). Compensator
514 may then access memory component 520 to retrieve these data,
and subsequently use them to compensate for changes in measurement
sensitivity of thermal accelerometer 504 that occur due to changes
in temperature measured by thermal sensor 502. For example,
compensator 514 may compare measured temperature 512 to an
adjustment factor, such as adjustment data or an adjustment
function, stored in memory component 520. The adjustment factor is
retrieved and applied by compensator 514 to measured inclination
510 to generate compensated inclination 516. In one embodiment, a
conventional linear approximation can be used to calculate the
offset correction from the zero offsets. As one skilled in the art
will appreciate, other curve fitting techniques, such as splines
may also be used.
[0047] Similarly, compensator 514 may be configured to enhance the
accuracy of the thermal accelerometer 504. Several accelerometer
measurements may be taken for each of a plurality of angles as
described above with respect to the level position. These data may
be stored in memory component 520 and retrieved by compensator 514
according to measured temperature 512 to compensate for measured
inclination 510.
[0048] Further, in an embodiment, the compensator 514 may use the
calculated offset correction to set a voltage in a
digital-to-analog converter (DAC) that is electrically
added/subtracted from the output of the thermal accelerometer 504.
Although one skilled in the art will appreciate that the setting of
the voltage may be accomplished in software, one advantage of an
analog circuit is that higher gains can be obtained in the analog
chain for more accuracy with a given voltage swing from the thermal
accelerometer 504. That is, the measurement range of the
analog-to-digital converter (ADC) is not compromised in order to
measure the zero offset of the thermal accelerometer 504. The
acceleration signal full scale output (at room temperature) is set
so as not to exceed the ADC full scale range.
[0049] In one embodiment, after calibration in a level position,
the thermal accelerometer 504 is placed so that both the x and the
y axis are at a known angle with respect to gravity. The angle can
be selected to be at the middle of the measurement range, for
example. The output (in each axis) of the thermal accelerometer 504
is compensated for temperature offset and recorded. This value
yields the gain (in volts per G) of the thermal accelerometer 504,
which is used as the basis for a calculation for the gain at
various temperatures as defined in Equation 12. As one skilled in
the art will recognize, Equation 12 is particularly applicable to
the MEMS accelerometer described above (which is commercially
available from MEMSIC, Inc. of North Andover, Mass.), and there may
be different characteristics for other types of devices. Similar to
the offset correction described above, the exponential function in
Equation 12 may be approximated by conventional interpolation
techniques (e.g., linear or quadratic). In another embodiment,
Equation 12 may be implemented or evaluated with a programmable
gain amplifier in a feedback control loop.
A.sub.outcompensate d=A.sub.out*(TOUT.sup.2.67/TOUT.sub.25.degree.
C..sup.2.67) (12)
[0050] FIG. 6 is a schematic illustrating a compensator circuit. In
the illustrated embodiment, the compensator circuit generally
includes an offset correction portion 605. By way of example, the
offset correction portion 605 is illustrated for one axis of the
thermal accelerometer output 510. Of course, in a dual or multiple
axis environment, the same or similar offset correction portion 605
may be implemented for the other axes if desired. The thermal
accelerometer output 510 is provided to a buffer/filter circuit
610. Resistors R25 and R27 then perform an offset correction on the
buffered/filtered signal. A calculated offset correction 612 is
electrically added or subtracted from the buffered/filtered signal.
The calculated offset correction 612 is received from the
microcontroller DAC.
[0051] An operational amplifier 614 is then used to shift the
signal level to about halfway between the supply rails. A reference
voltage 616 is selected to be between the supply rail voltages and
is provided to the operational amplifier 614. A low pass filter 620
then filters the level adjusted signal and outputs an offset
compensated inclination 516 to the microcontroller.
[0052] FIG. 7 illustrates a computing device for use in a wheel
alignment system, such as the exemplary wheel alignment setup
illustrated in FIG. 4. As illustrated in FIG. 7, the computing
device 705 includes a connection network 710, a processor 715, a
memory 720, a flash memory 722, an input/output device controller
725, an input device 727, an output device 729, a storage device
controller 730, and a communications interface 735.
[0053] The connection network 710 operatively couples each of the
processor 715, the memory 720, the flash memory 722, the
input/output device controller 725, the storage device controller
730, and the communications interface 735. The connection network
710 can be an electrical bus, optical network, switch fabric, or
other suitable interconnection system.
[0054] The processor 715 is a conventional microprocessor. In one
embodiment, the computing device 705 is portable and powered by a
battery. In this instance, the processor 715 or other circuitry may
be designed for low power operation in order to provide
satisfactory runtime before requiring recharging or replacement of
the battery.
[0055] The processor 715 executes instructions or program code
modules from the memory 720 or the flash memory 722. The operation
of the computing device 705 is programmable and configured by
program code modules. Such instructions may be read into memory 720
or the flash memory 722 from a computer readable medium, such as a
device coupled to the storage device controller 730.
[0056] Execution of the sequences of instructions contained in the
memory 720 or the flash memory 722 cause the processor 715 to
perform the method or functions described herein. In alternative
embodiments, hardwired circuitry may be used in place of or in
combination with software instructions to implement aspects of the
disclosure. Thus, embodiments of the disclosure are not limited to
any specific combination of hardware circuitry and software. The
memory 720 can be, for example, one or more conventional random
access memory (RAM) devices. The flash memory 722 can be one or
more conventional flash RAM, or electronically erasable
programmable read only memory (EEPROM) devices. The memory 720 may
also be used for storing temporary variables or other intermediate
information during execution of instructions by processor 715. For
example, the memory 720 may be used to store wheel angle
information received from one or more measurement heads 408,
410.
[0057] The input/output device controller 725 provides an interface
to the input device 727 and the output device 729. The output
device 729 can be, for example, a conventional display screen. The
display screen can include associated hardware, software, or other
devices that are needed to generate a screen display. In one
embodiment, the output device 729 is a conventional liquid crystal
display (LCD). The display screen may also include touch screen
capabilities. The illustrated embodiment also includes an input
device 727 operatively coupled to the input/output device
controller 725. The input device 727 can be, for example, an
external or integrated keyboard or cursor control pad. Signals from
the measurement heads 408, 410 may also be received by the
input/output device controller 725. These signals may be converted,
if necessary, and interfaced to the communication network 710. As
one skilled in the art will appreciate, the processor 715 can use
these signals to calculate wheel alignment parameters.
[0058] The storage device controller 730 can be used to interface
the processor 715 to various memory or storage devices, such as
magnetic, optical, or electrical storage. The communications
interface 735 provides bidirectional data communication coupling
for the computing device 705. The communications interface 635 can
be functionally coupled to a network 750. In one embodiment, the
communications interface 735 provides one or more input/output
ports for receiving electrical, radio frequency, or optical signals
and converts signals received on the port(s) to a format suitable
for transmission on the connection network 710. The communications
interface 735 can include a radio frequency modem and other logic
associated with sending and receiving wireless or wireline
communications. For example, the communications interface 735 can
provide an Ethernet interface, Bluetooth, and/or 802.11 wireless
capability for the computing device 705. The communications
interface 735 may also be used to receive signals in various
formats from the measurement heads 408, 410.
[0059] FIG. 8 illustrates an exemplary wheel alignment process. In
the illustrated embodiment, the process begins with attaching 805
one or more measurement heads 408, 410 to corresponding wheels 400,
406. The computing device 705 receives 810 from the measurement
heads 408, 410 one or more signals representing wheel alignment
angles. The computing device 705 calculates 815 wheel alignment
parameters using the received angle information, and the process
ends.
[0060] Having described embodiments of sensing steering axis
inclination and camber with an accelerometer (which are intended to
be illustrative and not limiting), it is noted that modifications
and variations can be made by persons skilled in the art in light
of the above teachings. It is therefore to be understood that
changes may be made in the particular embodiments disclosed that
are within the scope and spirit of the invention as defined by the
appended claims and equivalents.
* * * * *