U.S. patent application number 10/037145 was filed with the patent office on 2002-05-09 for method and apparatus for temperature compensating a piezoelectric device.
Invention is credited to Gallmeyer, Christopher F., Waterfield, Larry G..
Application Number | 20020053952 10/037145 |
Document ID | / |
Family ID | 24121321 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020053952 |
Kind Code |
A1 |
Gallmeyer, Christopher F. ;
et al. |
May 9, 2002 |
Method and apparatus for temperature compensating a piezoelectric
device
Abstract
A control system for temperature compensating a piezoelectric
device. The control system includes a temperature compensating
circuit that is operable to receive a control signal corresponding
to a desired position of the piezoelectric device and compensate
the control signal in response to an estimated temperature
proximate the piezoelectric device. A piezoelectric device control
circuit is operable to receive the temperature compensated control
signal and generate a control signal that is adapted to drive the
piezoelectric device to the desired position. The temperature
proximate the piezoelectric device may be estimated from an
estimated ferroelectric polarization of the piezoelectric device or
from a temperature sensor.
Inventors: |
Gallmeyer, Christopher F.;
(Peoria, IL) ; Waterfield, Larry G.; (Peoria,
IL) |
Correspondence
Address: |
CATERPILLAR INC.
100 N.E. ADAMS STREET
PATENT DEPT.
PEORIA
IL
616296490
|
Family ID: |
24121321 |
Appl. No.: |
10/037145 |
Filed: |
December 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10037145 |
Dec 21, 2001 |
|
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|
09532328 |
Mar 21, 2000 |
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Current U.S.
Class: |
331/176 |
Current CPC
Class: |
H02N 2/062 20130101 |
Class at
Publication: |
331/176 |
International
Class: |
H03L 001/00 |
Claims
1. An apparatus for temperature compensating a piezoelectric
device, comprising: a temperature compensating circuit operable to
receive a first control signal corresponding to a desired position
of the piezoelectric device and generate a second control signal in
response to the first control signal that is compensated in
response to an estimated temperature proximate the piezoelectric
device; and a piezoelectric device control circuit coupled to said
temperature compensating circuit and operable to receive the second
control signal and generate a third control signal in response to
the second control signal that is adapted to drive the
piezoelectric device to the desired position.
2. The apparatus of claim 1 wherein said temperature compensating
circuit includes a first data structure operable to correlate the
first control signal with the estimated temperature proximate the
piezoelectric device to generate the second control signal.
3. The apparatus of claim 2 wherein said temperature compensating
circuit further includes a polarization estimating circuit coupled
to said piezoelectric device control circuit and operable to
estimate ferroelectric polarization of the piezoelectric
device.
4. The apparatus of claim 3 wherein said temperature compensating
circuit further includes a second data structure operable to
estimate the temperature proximate the piezoelectric device from
the estimated ferroelectric polarization of the piezoelectric
device.
5. The apparatus of claim 3 wherein said polarization estimating
circuit includes a comparator circuit operable to measure a change
in voltage applied to the piezoelectric device over a predetermined
duration of time.
6. The apparatus of claim 5 wherein said polarization estimating
circuit further includes an integrator circuit operable to
integrate current flowing in the piezoelectric device over the
predetermined duration of time.
7. The apparatus of claim 1 wherein said temperature estimating
circuit includes a temperature sensor operable to estimate
temperature proximate the piezoelectric device.
8. The apparatus of claim 7 wherein said temperature compensating
circuit includes a first data structure operable to correlate the
first control signal with the estimated temperature proximate the
piezoelectric device to generate the second control signal.
9. An apparatus for temperature compensating a piezoelectric
device, comprising: a first data structure operable to correlate a
first control signal corresponding to a desired position of the
piezoelectric device with an estimated temperature proximate the
piezoelectric device to generate a second control signal in
response to the first control signal that is compensated in
response to the estimated temperature proximate the piezoelectric
device; and a piezoelectric device control circuit operable to
receive the second control signal and generate a third control
signal in response to the second control signal that is adapted to
drive the piezoelectric device to the desired position.
10. The apparatus of claim 9 further including a polarization
estimating circuit coupled to said piezoelectric device control
circuit and operable to estimate ferroelectric polarization of the
piezoelectric device.
11. The apparatus of claim 10 further including a second data
structure operable to estimate the temperature proximate the
piezoelectric device from the estimated ferroelectric polarization
of the piezoelectric device.
12. The apparatus of claim 10 wherein said polarization estimating
circuit includes a comparator circuit operable to measure a change
in voltage applied to the piezoelectric device over a predetermined
duration of time.
13. The apparatus of claim 12 wherein said polarization estimating
circuit further includes an integrator circuit operable to
integrate current flowing in the piezoelectric device over the
predetermined duration of time.
14. The apparatus of claim 9 further including a temperature sensor
operable to estimate temperature proximate the piezoelectric
device.
15. A method of temperature compensating a piezoelectric device,
comprising: receiving a first control signal that corresponds to a
desired position of a piezoelectric device; estimating temperature
proximate the piezoelectric device; and generating a control signal
adapted to drive the piezoelectric device to the desired position,
wherein the control signal is temperature compensated in response
to the estimated temperature proximate the piezoelectric
device.
16. The method of claim 15 wherein the step of generating the
control signal comprises: generating a second control signal in
response to the first control signal that is compensated in
response to the estimated temperature proximate the piezoelectric
device; and generating a third control signal in response to the
second control signal that is adapted to drive the piezoelectric
device to the desired position.
17. The method of claim 15 further comprising: estimating
ferroelectric polarization of the piezoelectric device; and
estimating temperature proximate the piezoelectric device from the
estimated ferroelectric polarization of the piezoelectric
device.
18. The method of claim 15 further comprising estimating
temperature proximate the piezoelectric device from a temperature
sensor.
19. The method of claim 16 further comprising: providing a first
data structure operable to correlate the first control signal with
the estimated temperature proximate the piezoelectric device to
generate the second control signal.
20. The method of claim 17 further comprising: providing a second
data structure operable to estimate temperature proximate the
piezoelectric device from the estimated ferroelectric polarization
of the piezoelectric device.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to piezoelectric
devices and, more particularly, to an apparatus and method for
accurately controlling movement of a piezoelectric device under
varying operating temperatures.
BACKGROUND ART
[0002] Piezoelectric devices alter their shape in response to an
applied electric field. An electric field applied in the direction
of polarization effects an expansion of the piezoelectric material
in the same direction, while a voltage applied in the opposite
direction of polarization will cause a contraction of the material
in that same direction. Piezoelectric bending actuators, such as
thermally pre-stressed bending actuators, use the "bending" action
of the actuator to convert electrical energy into mechanical
energy.
[0003] Due to the nature of their construction, however, the
performance of these devices is temperature dependent and presents
a problem in applications such as an engine system where the
temperature of the actuator may range from 0.degree. C. to
100.degree. C. during operation. In this wide temperature range,
the position of the actuator changes as a function of applied
voltage and temperature so the actuator must be temperature
compensated to provide a consistent, reliable and predictable
movement or displacement of the actuator in response to the input
command signal.
[0004] In the past, piezoelectric actuators applied as fuel system
actuators were temperature compensated by mechanical means, such as
by hydraulic compensation. These mechanical methods require complex
designs that add significant product cost and decrease the
reliability of the valve control system.
[0005] Thus, there is a need for a piezoelectric actuator that
eliminates the need for complex and unreliable mechanical devices
to provide temperature compensation of the actuator. There is also
a need for a piezoelectric actuator that may be accurately and
reliably driven to a desired position in a relatively wide
temperature range of the actuator.
DISCLOSURE OF THE INVENTION
[0006] While the invention will be described in connection with
certain embodiments, it will be understood that the invention is
not limited to these embodiments. On the contrary, the invention
includes all alternatives, modifications and equivalents as may be
included within the spirit and scope of the present invention.
[0007] In accordance with the principles of the present invention,
a control system for temperature compensating a piezoelectric
device includes a temperature compensating circuit that is operable
to receive a control signal from a control signal source that
corresponds to a desired position of the piezoelectric device. The
temperature control circuit is operable to generate a temperature
corrected or compensated control signal in response to an estimated
temperature proximate the piezoelectric device. A piezoelectric
control circuit is coupled to the temperature compensating circuit
and operable to generate a control signal in response to the
control signal generated by the temperature control circuit to
drive the piezoelectric device to the desired position in response
to the estimated temperature of the piezoelectric device.
[0008] The above and other objects and advantages of the present
invention shall be made apparent from the accompanying drawings and
the description thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and, together with a general description of the
invention given above, and the detailed description of the
embodiments given below, serve to explain the principles of the
invention.
[0010] FIG. 1 is a block diagram of a control system for
temperature compensating a piezoelectric device in accordance with
the principles of the present invention; and
[0011] FIG. 2 is an alternative embodiment of the temperature
compensating control system shown in FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0012] With reference to the figures, and to FIG. 1 in particular,
a control system 10 is shown in accordance with the principles of
the present invention for temperature compensating a piezoelectric
device 12, such as a thermally pre-stressed bending actuator, that
is coupled to the control system 10 through a pair of leads 14a,
14b. As will be described in detail below, control system 10 is
operable to receive a control signal on line 16 from a control
signal source (not shown) that corresponds to a desired position of
the actuator 12. In response to the control signal on line 16, the
control system 10 applies a voltage related control signal to the
actuator 12 that has been appropriately compensated in response to
an estimated temperature proximate the operating environment of the
actuator device 12. In this way, the control system 10 accurately
controls displacement of actuator 12 in response to receipt of the
control signal on line 16 from the control signal source (not
shown) over a range of actuator operating temperatures. While not
shown, it will be appreciated that the control signal source may be
any position control system that can control the position of a
piezoelectric device through a control signal.
[0013] Further referring to FIG. 1, control system 10 includes a
one-dimensional empirical map or data structure 18 that is operable
to receive the desired actuator position control signal on line 16
from the control signal source (not shown) as an input to the map
18. In response to receipt of the control signal on line 16, the
data structure 18 generates as an output on line 20 a desired
control signal that is electrically compatible with a conventional
actuator control circuit 22 readily known to those skilled in the
art. Data structure 18 may be a look-up table stored in RAM or ROM,
a software algorithm or a hardwired circuit as will be readily
appreciated by those skilled in the art that is operable to
generate as an output on line 20 the desired control signal having
a value or parameter defined by the empirical map 18 in response to
the desired actuator position control signal on input line 16.
[0014] In accordance with the principles of the present invention,
control system 10 includes a temperature compensating circuit,
indicated generally at 24, that is coupled to the data structure or
map 18 and the actuator control circuit 22. The temperature
compensating circuit 24 is operable to receive the control signal
on line 20 generated as an output of the data structure 18, and to
generate a temperature compensated control signal on line 26 that
is corrected or compensated in response to an estimated temperature
proximate the operating environment of the piezoelectric device
12.
[0015] In particular, there is a hysteresis involved in the
relationship between the magnitude of the control signal applied to
the actuator 12, i.e., the control voltage, and the displacement of
the actuator 12 in response to that control signal. Since
piezoelectric devices are not linear gain devices, the physical
motion profile of the device is not directly proportional to the
profile of the control signal applied to the actuator. Moreover,
the hysteresis curve is temperature dependent so that an input
control signal applied to an actuator to produce a desired
displacement at one temperature of the actuator will not produce
the same displacement of the actuator at a different temperature.
To this end, the temperature compensating circuit 24 is operable to
correct or compensate the control signal on line 20 in response to
the estimated temperature proximate the operating environment of
the actuator 12 to generate a temperature corrected or compensated
control signal on line 26 that will drive the actuator 12 to the
desired position or displacement at the estimated temperature
proximate the actuator.
[0016] In particular, the temperature compensating circuit 24 of
control system 10 includes a two-dimensional empirical map or data
structure 28 that is operable to receive the desired actuator
position control signal on line 20 from the one-dimensional map or
data structure 18 as an input to the map 28. The map 28 is also
operable to receive an estimated temperature proximate the actuator
12 on line 30 as another input to the map 28. In response to
receipt of the desired actuator position control signal on line 20
and the estimated temperature proximate the actuator 12 on line 30,
the data structure 28 generates as an output on line 26 the
temperature corrected or compensated control signal that will drive
the actuator-12 to the desired position or displacement in response
to the estimated temperature proximate the actuator 12. The
temperature corrected or compensated control signal on line 26 is
coupled to the actuator control circuit 22 to drive the actuator 12
to the desired position or displacement at the estimated
temperature proximate the actuator 12. Data structure 28 may also
be a look-up table stored in RAM or ROM, a software algorithm or a
hardwired circuit as will be readily appreciated by those skilled
in the art that is operable to generate as an output on line 26 the
temperature corrected or compensated control signal on line 26
having a value or parameter defined by the empirical map 28 in
response to the desired control signal on input line 20 and the
estimated temperature proximate the actuator 12 on input line
30.
[0017] In accordance with one aspect of the present invention, the
temperature proximate the actuator 12 may be estimated from an
estimated ferroelectric polarization of the actuator 12. More
particularly, the temperature compensating circuit 24 of control
system 10 typically includes a polarization estimating circuit,
indicated generally at 32, that is coupled to the data structure or
map 28 and the actuator control circuit 22. For a given duration of
time, the polarization estimating circuit 32 measures the change in
applied voltage to the actuator 12 (V) through a comparator circuit
34 coupled to the actuator control circuit 22 through line 36.
During that same duration of time, the polarization estimating
circuit 32 measures the change in charge on the actuator 12 (Q)
through a current integrating circuit 38 coupled to actuator
control circuit 22 through line 40. From the measured V and Q
values, an equivalent capacitance of the actuator 12 (C.sub.E) is
determined by the following equation, where the equivalent
capacitance (C.sub.E) is dependent on the physical construction of
the actuator 12 and on the temperature proximate the operating
environment of the actuator 12:
C.sub.E=Q/V
[0018] To ensure an accurate estimation of the equivalent
capacitance (C.sub.E), V must be a significant portion (>50%) of
the full travel range of the actuator 12. The voltage vs. charge
hysteresis curve of the actuator will determine the minimum value
of V that can be used in this calculation without a loss of
accuracy.
[0019] The polarization estimating circuit 32 of control system 10
includes a one-dimensional empirical map or data structure 42 that
is operable to receive the equivalent capacitance (C.sub.E) on line
44 as an input to the map 42. The empirical map or data structure
42 is preferably derived from the ferroelectric polarization
hysteresis curves of the actuator 12 to generate the estimated
temperature on line 30. The equivalent capacitance (C.sub.E)
effectively gives a unique slope value on the ferroelectric
polarization hysteresis curves that can be correlated to the
estimated temperature proximate the actuator 12 as will be
appreciated by those skilled in the art. Data structure 42 may also
be a look-up table stored in RAM or ROM, a software algorithm or a
hardwired circuit as will be readily appreciated by those skilled
in the art that is operable to generate as an output on line 30 the
estimated temperature having a value or parameter defined by the
empirical map 42 in response to the equivalent capacitance
(C.sub.E) on input line 44.
[0020] Alternatively, as shown in FIG. 2 where like numerals
represent like parts, a control system 10' is shown in accordance
with another aspect of the present invention for temperature
compensating the actuator 12. In this embodiment, the polarization
estimating circuit 32 of FIG. 1 is replaced with a temperature
sensor 46 that is adapted to be mounted in the general operating
environment of the actuator 12. For example, in an engine system,
the temperature sensor 46 could be mounted to sense engine oil or
coolant temperature, or the sensor could be mounted directly on the
actuator 12. In this way, the sensor 46 generates an estimated
temperature proximate the operating environment of actuator 12 as
an input on line 30 to the two-dimensional empirical map or data
structure 28. The map 28 is operable to receive the desired
actuator position control signal on line 20 from the
one-dimensional map or data structure 18 as an input to the map 28.
The map 28 is also operable to receive the estimated temperature
proximate the actuator 12 on line 30 as another input to the map
28. In response to receipt of the desired actuator position control
signal on line 20 and the estimated temperature proximate the
actuator 12 on line 30, the data structure 28 generates as an
output on line 26 the temperature corrected or compensated control
signal that will drive the actuator 12 to the desired position or
displacement in response to the estimated temperature proximate the
actuator 12. The temperature corrected or compensated control
signal is coupled on line 26 to the actuator control circuit 22 to
drive the actuator 12 to the desired position or displacement at
the estimated temperature proximate the actuator.
[0021] Industrial Applicability
[0022] In use, it will be appreciated that control system 10 is
operable to provide a temperature corrected or compensated control
signal to the actuator 12 to drive the actuator 12 to the desired
position or displacement in response to the estimated temperature
proximate the actuator. The temperature compensating circuit 24 of
control system 10 eliminates the need for complex and unreliable
mechanical devices to provide temperature compensation of the
actuator 12. Additionally, the polarization estimating circuit 32
of FIG. 1 eliminates the need for a temperature sensor 46 (FIG. 2)
to estimate the temperature proximate the operating environment of
the actuator 12. The control system 12 of the present invention
provides accurate movement control of the actuator 12 under varying
operating temperatures.
[0023] While the present invention has been illustrated by a
description of various embodiments and while these embodiments have
been described in considerable detail, it is not the intention of
the applicants to restrict or in any way limit the scope of the
appended claims to such detail. Additional advantages and
modifications will readily appear to those skilled in the art. The
invention in its broader aspects is therefore not limited to the
specific details, representative apparatus and method, and
illustrative example shown and described. Accordingly, departures
may be made from such details without departing from the spirit or
scope of applicant's general inventive concept.
[0024] Other aspects, objects and advantages of the present
invention can be obtained from a study of the drawings, the
disclosure and the appended claims.
* * * * *