U.S. patent application number 10/734403 was filed with the patent office on 2004-07-01 for method and apparatus for controlling a piezo actuator.
Invention is credited to Cabatic, Sherwin D., Melvin, Dennis E., Pease, John.
Application Number | 20040124743 10/734403 |
Document ID | / |
Family ID | 22589545 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040124743 |
Kind Code |
A1 |
Pease, John ; et
al. |
July 1, 2004 |
Method and apparatus for controlling a piezo actuator
Abstract
A method and apparatus for controlling a piezo-electric actuator
coupled to a driven member is disclosed. The piezo-electric
actuator is responsive to waveforms with asymmetrical
voltage/current profiles on the rising and falling edge to effect
consistent and cumulative movement of the driven member in one of
two directions throughout the reciprocations of the piezo-electric
actuator. The waveforms are digitally generated from a stored set
of numbers or a function for generating the set of numbers. The
numbers correspond with the discrete digital values associated with
the desired waveforms for moving the driven member in either of at
least two directions. The controller may be used to drive more than
one piezo-electric actuator. The controller may include
responsiveness to a feedback of the position of the driven member
to accurately position the driven member. The controller may also
include the ability to update the function or values stored in
memory so as to couple more efficiently with new or existing
actuators. The controller exhibits a relatively smaller form factor
and reduced complexity when compared with prior art analog
drivers.
Inventors: |
Pease, John; (Santa Clara,
CA) ; Cabatic, Sherwin D.; (Mountain View, CA)
; Melvin, Dennis E.; (Santa Clara, CA) |
Correspondence
Address: |
IP CREATORS
P. O. BOX 2789
CUPERTINO
CA
95015
US
|
Family ID: |
22589545 |
Appl. No.: |
10/734403 |
Filed: |
December 12, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10734403 |
Dec 12, 2003 |
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10202945 |
Jul 24, 2002 |
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6707231 |
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10202945 |
Jul 24, 2002 |
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09706369 |
Nov 3, 2000 |
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6476537 |
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60163329 |
Nov 3, 1999 |
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Current U.S.
Class: |
310/317 |
Current CPC
Class: |
H02N 2/0095 20130101;
H02N 2/145 20130101; H02N 2/101 20130101 |
Class at
Publication: |
310/317 |
International
Class: |
H02N 002/00; H01L
041/04; H01L 041/08; H01L 041/18 |
Claims
What is claimed is:
1. A controller for controlling at least one piezo actuator coupled
frictionally with at least one positioning member to move the at
least one positioning member in either of two directions as
determined by relative absolute rates of expansion and contraction
of the at least one piezo actuator, and the controller comprising:
a logic for generating digitized pulses each with a rising edge and
a falling edge and with relative absolute values of corresponding
average slopes of the rising edge and the falling edge of each of
the digitized pulses corresponding with a selected direction of
movement of the at least one positioning member; a
digital-to-analog (A/D) converter with an input coupled to said
logic and an output coupled to said at least one piezo actuator,
and the A/D converter converting said digitized pulses at said
input to an analog waveform at said output to move said at least
one positioning member in the selected direction.
2. The controller of claim 1, further comprising: an amplifier
coupled between said A/D converter and said at least one piezo
actuator for amplifying said analog waveform to a level sufficient
to move said at least one positioning member in the selected
direction.
3. The controller of claim 1, wherein said logic further comprises:
a memory for storing data corresponding to the digitized pulses;
and a processor with an input coupled to said memory and an output
coupled to said AID converter, and said processor responsive to
instructions to move said at least one positioning member in a
selected one of the two directions to read said data and to
iteratively write digitized pulses at the output with relative
absolute values of the corresponding average slopes of the rising
and falling edges of each pulse corresponding with the selected one
of the two directions of movement.
4. The controller of claim 3, wherein the data stored in said
memory includes at least one of an ordered sequence of numbers and
a function for generating the ordered sequence of numbers and with
the ordered sequence of numbers corresponding with at least one of
the digitized pulses.
5. The controller of claim 3, wherein the data stored in said
memory includes an ordered sequence of numbers which when read by
said processor and written to said A/D converter in a selected one
of either of two opposing directions results in movement of the at
least one positioning member in a corresponding one of either of
the two directions.
6. The controller of claim 3, wherein the data stored in said
memory includes a first ordered sequence of numbers for moving said
at least one positioning member in a first of the two directions
and a second ordered sequence for moving said at least one
positioning member in a second of the two directions.
7. The controller of claim 3, with said processor responsive to
instructions to increase a speed of movement of said at least one
positioning member to decrease an interval between the iterative
writing of each of the digitized pulses to said A/D converter while
substantially maintaining the duration of each of the digitized
pulses.
8. The controller of claim 1, wherein said at least one piezo
actuator includes a first piezo actuator and a second piezo
actuator and said controller further comprising: a multiplexer with
a control input, a signal input, and a pair of outputs, and the
signal input coupled to the output of said A/D converter and a pair
of outputs each coupled to a corresponding one of the first piezo
actuator and a second piezo actuator, and the multiplexer
responsive to a control signal at the control input to couple a
selected one of the first piezo actuator and the second piezo
actuator to the A/D converter.
9. The controller of claim 1, further comprising: an electrical
sink switchably coupled to the output of said A/D converter to
remove charge from said at least one piezo actuator after movement
of said at least positioning member in the selected direction.
10. The controller of claim 1, further comprising: a position
detector with an input coupled with said at least positioning
member and an output coupled to said logic and said position
detector generating at the output a position feedback signal
corresponding with the position of said at least one positioning
member; and said logic responsive to a said position feedback
signal to move said at least one positioning member to a desired
position.
11. A method for controlling at least one piezo actuator coupled
frictionally with at least one positioning member to move the at
least one positioning member in either of two directions as
determined by relative absolute rates of expansion and contraction
of the at least one piezo actuator, and the method for controlling
comprising the acts of: generating digitized pulses each with a
rising edge and a falling edge and with relative absolute values of
corresponding average slopes of the rising edge and the falling
edge of each of the digitized pulses corresponding with a selected
direction of movement of the at least one positioning member;
converting said digitized pulses to an analog waveform; and driving
said at least one positioning member with said analog waveform to
move said at least one positioning member in the selected
direction.
12. The method for controlling of claim 11, wherein said driving
act further comprises the act of: amplifying said analog waveform
to a level sufficient to move said at least one positioning member
in the selected direction.
13. The method for controlling of claim 11, wherein said at least
one piezo actuator includes a first piezo actuator and a second
piezo actuator and wherein said driving act further comprises the
act of: selectively driving a selected one of the first piezo
actuator and a second piezo actuator.
14. The method for controlling of claim 11 wherein said driving act
further comprises the act of: switchably coupling an electrical
sink to remove charge from said at least one piezo actuator after
movement of said at least positioning member in the selected
direction.
15. The method for controlling of claim 11, further comprises the
act of: generating a position feedback signal corresponding with
the position of said at least one positioning member; and moving
said at least one positioning member to a desired position
responsive to a the position feedback signal generated in said act
of generating.
16. The method for controlling of claim 11, wherein said generating
act further comprises the acts of: storing data corresponding to
the digitized pulses; and moving said at least one positioning
member in a selected one of the two directions by; a) reading said
data; and b) iteratively writing digitized pulses with relative
absolute values of the corresponding average slopes of the rising
and falling edges of each pulse corresponding with the selected one
of the two directions of movement.
17. The method for controlling of claim 16, wherein said storing
act further comprises the acts of: writing at least one of an
ordered sequence of numbers and a function for generating the
ordered sequence of numbers into said memory with the ordered
sequence of numbers corresponding with at least one of the
digitized pulses.
18. The method for controlling of claim 16, wherein the data
corresponds with an ordered sequence of numbers and wherein further
said act of iteratively writing further comprises the acts of:
reading the ordered sequence of numbers in a selected one of either
of two opposing directions to move the at least one positioning
member in a corresponding one of either of the two directions.
19. The method for controlling of claim 16, wherein the data
includes a first ordered sequence of numbers for moving said at
least one positioning member in a first of the two directions and a
second ordered sequence for moving said at least one positioning
member in a second of the two directions.
20. The method for controlling of claim 16, wherein said act of
iteratively writing further comprises the acts to increase a speed
of movement of said at least one positioning member of: decreasing
an interval between the iterative writing of each of the digitized
pulses to said A/D converter; and substantially maintaining the
duration of each of the digitized pulses.
21. The method for controlling of claim 16, wherein said storing
act further comprises the act of: updating the data stored in said
storing act with updated digitized pulses.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from Provisional
Application No. 60/163,329, entitled "PICO MOTOR DRIVER" filed on
Nov. 3, 1999 (Attorney Docket #NFC1P014P) which is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention generally relates to controllers for
electromechanical actuators and more particularly to controllers
for piezoelectric elements.
[0004] 2. Description of the Related Art
[0005] Piezo-electric actuators are used in for positioning
elements in a wide range of applications. In optical test and
measurement they are used for positioning of lenses, filters,
polarizers, mirrors, radiation sources, detectors or a stage to
which any of the aforementioned may be attached. In cameras
piezo-electric actuators are used for focusing lenses.
[0006] Typically such actuators have opposing ends, one of which is
fixed and the other of which is frictionally coupled with a driven
member, e.g. lens. As voltage is applied to the piezo-electric
actuator an expansion or contraction of the actuator takes place.
Since one end of the piezo-electric actuator is fixed the expansion
or contraction of the actuator causes a corresponding movement of
the driven member to which it is frictionally connected. Above some
threshold rate of expansion or contraction the force of the
frictional coupling between the actuator and the driven member is
insufficient to overcome the inertia of the driven member and there
is slippage or in the extreme no movement of the driven member. By
driving the piezoelectric actuator with waveforms with asymmetrical
voltage/current profiles on the rising and falling edge it is
possible to effect consistent and cumulative movement of the driven
member in one of two directions throughout the reciprocations of
the piezo-electric actuator.
[0007] U.S. Pat. No. 5,394,049 entitled "Piezoelectric Actuator for
Optical Alignment Screws Cross References to Co-Pending
Applications" issued on Feb. 28, 1995 and U.S. Pat. No. 5,410,206
entitled "Piezoelectric Actuator for Optical Alignment Screws"
issued on Apr. 25, 1995, U.S. Pat. No. 6,092,431 and entitled
"Rotary type driving device employing electromechanical transducer
and apparatus provided with the rotary type driving device" issued
on Jul. 25, 2000 and U.S. Pat. No. 6,111,336 entitled "Driving
apparatus using transducer" issued on Aug. 29, 2000 each disclose
piezo-electric actuators which exhibit the above discussed
principals. Each of these references is incorporated by reference
as if fully set forth herein.
[0008] Each of these references discloses various analog drive
mechanisms for delivering the asymmetrical waveforms to the
piezo-electric actuator. These circuits rely on various analog
components, e.g. resistors, capacitors, current sources and sinks
in conjunction with appropriate transistor switches to deliver the
required waveform to the piezo-electric actuator. There are several
problems which such circuits exhibit. First, they are complex and
may require a large form factor. Second, the waveforms they
generate are not consistent over time since they are generated
using the time constants associated with resistor capacitor
combinations or of fixed current sources.
[0009] What is needed is a drive circuit with reduced cost and
complexity which delivers repeatable waveforms with the desired
characteristics to the piezo-electric actuator.
SUMMARY OF THE INVENTION
[0010] The present invention provides a method and apparatus for
controlling a piezo-electric actuator coupled to a driven member.
The piezo-electric actuator is responsive to waveforms with
asymmetrical voltage/current profiles on the rising and falling
edge to effect consistent and cumulative movement of the driven
member in one of two directions throughout the reciprocations of
the piezo-electric actuator. The waveforms are digitally generated
from a stored set of numbers or a function for generating the set
of numbers. The numbers correspond with the discrete digital values
associated with the desired waveforms for moving the driven member
in either of at least two directions. The controller may be used to
drive more than one piezo-electric actuator. The controller may
include responsiveness to a feedback of the position of the driven
member to accurately position the driven member. The controller may
also include the ability to update the function or values stored in
memory so as to couple more efficiently with new or existing
actuators. The controller exhibits a relatively smaller form factor
and reduced complexity when compared with prior art analog
drivers.
[0011] In an embodiment of the invention a controller for
controlling at least one piezo actuator is disclosed. The piezo
actuator is coupled frictionally with at least one positioning
member to move the positioning member in either of two directions
as determined by relative rates of expansion and contraction of the
piezo actuator. The controller includes a logic for generating
digitized pulses and an digital-to-analog (A/D) converter. The
logic includes the capability to generate digitized pulses each
with a rising edge and a falling edge. The relative absolute values
of the corresponding average slopes of the rising edge and the
falling edge of each of the digitized pulses corresponds with a
selected direction of movement of the at least one positioning
member. The A/D converter includes an input coupled to the logic
and an output coupled to the at least one piezo actuator. The A/D
converter converts the digitized pulses at the input to an analog
waveform at the output. This effects the movement of the
positioning member in the selected direction.
[0012] In an alternate embodiment of the invention a method for
controlling at least one piezo actuator is disclosed. The method
for controlling comprises the acts of:
[0013] generating digitized pulses each with a rising edge and a
falling edge and with relative absolute values of corresponding
average slopes of the rising edge and the falling edge of each of
the digitized pulses corresponding with a selected direction of
movement of the at least one positioning member;
[0014] converting said digitized pulses to an analog waveform;
and
[0015] driving said at least one positioning member with said
analog waveform to move sad at least one positioning member in the
selected direction.
[0016] Other aspects and advantages of the invention will become
apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The present invention will be readily understood by the
following detailed description in conjunction with the accompanying
drawings, wherein like reference numerals designate like structural
elements, and in which:
[0018] FIG. 1 is a hardware block diagram of a controller coupled
to a plurality of piezo-electric actuators.
[0019] FIG. 2 shows an embodiment of the data structures from which
the desired waveforms generated by the controller may be
derived.
[0020] FIG. 3 is a signal diagram showing the discrete digital
values corresponding with the desired waveforms, both after an D/A
conversion and a subsequent amplification to the appropriate levels
for driving the piezo-electric actuators.
[0021] FIG. 4 is a process flow diagram showing the processes
associated with the operation of an embodiment of the
controller.
[0022] FIG. 5 is a detailed cross-sectional view of a first of the
piezo-electric actuators shown in FIG. 1.
[0023] FIG. 6 is a detailed cross-sectional view of a second of the
piezo-electric actuators shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention provides a method and apparatus for
controlling a piezo-electric actuator coupled to a driven member.
The piezo-electric actuator is responsive to waveforms with
asymmetrical voltage/current profiles on the rising and falling
edge to effect consistent and cumulative movement of the driven
member in one of two directions throughout the reciprocations of
the piezo-electric actuator. The waveforms are digitally generated
from a stored set of numbers or a function for generating the set
of numbers. The numbers correspond with the discrete digital values
associated with the desired waveforms for moving the driven member
in either of at least two directions. The controller may be used to
drive more than one piezo-electric actuator. The controller may
include responsiveness to a feedback of the position of the driven
member to accurately position the driven member. The controller may
also include the ability to update the function or values stored in
memory so as to couple more efficiently with new or existing
actuators. The controller exhibits a relatively smaller form factor
and reduced complexity when compared with prior art analog
drivers.
[0025] FIG. 1 is a hardware block diagram of a controller coupled
to a plurality of piezo-electric assemblies. The controller 100 is
shown coupled to a linear piezo-electric assembly 102 and a rotary
piezo-electric assembly 104. The controller in this embodiment of
the invention accepts input from a workstation 106. The workstation
may be used to select one or both of the linear and rotary
assemblies for activation. The workstation may also be used to
input directional, or speed parameters for either of the
piezo-electric assemblies. The workstation may also be used as a
display device to display relative or absolute position parameters
for the assemblies, as well as other control information.
[0026] In alternate embodiments of the invention input to the
controller may be in the form of an analog signal the polarity of
which indicates the desired direction of movement of the associated
piezo-electric assembly. Alternately a digital input may be
provided in which a first bit line selects the direction of motion
and a second bit line the frequency at which waveforms are
generated by the controller thereby governing the speed of the
driven member of the piezo-electric assembly. In still another
embodiment of the invention an input may be provided for triggering
a single output waveform of either a forward or reverse type.
[0027] The controller 100 includes a processor 110, memory 112, a
digital-to-analog converter (DAC) 114, an amplifier 116, a power
converter 118, a multiplexer 132, and a switchable connection 128
to a current sink 130. Collectively the processor and memory form a
logic for generating digitized pulses. The pulses may be generated
by a reading by the processor of an ordered set of numerical values
122 stored in memory (See FIG. 2) or from a function stored in
memory the execution of which by the processor results in the
ordered set of numerical values. The operation of the processor may
be controlled by program code 120 also stored in memory. The
numerical values are output by the processor to the input of the
DAC 114 where they are converted to a stepped analog waveform (See
FIG. 3). The stepped analog waveform may be filtered and smoothed
as it is passed to the input of the amplifier. The amplifier
amplifies the analog waveform from the DAC to a range suitable for
the associated piezo-electric assembly to which it is coupled via
the multiplexer 132. Peak voltages of over 100 volts may be
required to scale the waveform from the DAC to levels at which the
desired motion of the driven member of either of the piezo-electric
assemblies is achieved. The power supply to the amplifier 116 may
include the converter 118 to boost a low voltage input to the
required level for powering the amplifier. The output waveforms
which correspond with opposite directions of motion in the driven
members have substantially opposing symmetries in their leading and
trailing edges (See FIG. 3). By driving the piezo-electric actuator
with waveforms with asymmetrical voltage/current profiles on the
rising and falling edge it is possible to effect consistent and
cumulative movement of the driven member in one of two directions
throughout the reciprocations of the piezo-electric actuator. When
the driven member of the associated piezo-electric assembly is
properly positioned switch 128 may be shorted to a current sink 130
to drain current from the piezo-electric actuator. This effect of
this is to arrest further movement of the driven member by keeping
the contraction rate of the piezo-electric actuator in the range at
which slipping between the actuator and the driven member
results.
[0028] Linear Piezo-electric Assembly
[0029] The piezo-electric assembly 102 includes an actuator 148 a
driven member 158, and a frame 146. The actuator has jaw elements
(See FIG. 5) positioned about the driven member, e.g. a cylindrical
shaft, which includes a threaded portion 144 passing through the
jaws. The base of the piezo-electric actuator is affixed to the
frame 146. For the purpose of this explanation, the inertial
characteristics of the driven member are represented by the
flywheel portion 140 at the head of the cylindrical shaft 158.
Where closed loop control of the position of the driven member is
enabled position detector 150 operating with linear encoding 142 on
the shank of the driven member provides position feedback to the
controller 100.
[0030] When the electrical signal across piezo-electric element 160
is such that element extends relative longitudinal movements of jaw
elements occurs. If there is no slippage between the jaws and shaft
158 rotation of the shaft takes place in the direction of arrow
154. As the amplitude of the electrical signal across
piezo-electric element is reduced, contraction occurs, causing
relative longitudinal movement of the jaw elements in the opposite
direction. Again assuming that no slippage occurs between the jaws
and shaft, rotation of shaft takes place in the direction of arrow
156. A spring clip 152 generates clamping force of the opposing
jaws on the threaded portion of the shaft.
[0031] Because of the inertia of the shaft 158, a rapidly rising or
falling electrical signal will induce such rapid movement of the
jaw elements that slippage between the jaws and the shaft will
occur. The duration of slippage depends on the waveform and
amplitude of the electrical signal applied across the
piezo-electric element 160, as well as the mechanical
characteristics of the system, such as the frictional engagement
between the jaws and shaft, and the inertia of the shaft and other
mechanical elements connected to it. Conversely, application of a
slowly rising or falling signal across piezo-electric element will
cause a correspondingly slow longitudinal movement of the jaw
elements, and very little or no slippage between the jaws and shaft
will take place.
[0032] It follows that selective rotation of shaft 158 may be
obtained in either direction 154-156 simply by applying a cyclic
electrical signal having the proper waveform to the piezo-electric
element 160. Thus, a waveform having a slowly rising leading edge
followed by a rapidly falling trailing edge will cause rotation in
a first direction. Conversely, a waveform having a rapidly rising
leading edge followed by a slowly falling trailing edge will be
effective to rotate the shaft in the opposite direction.
[0033] Rotary Piezo-electric Assembly
[0034] The rotary piezo-electric assembly 104 is a rotary optical
stage. It includes a piezo-electric element 176 mounted in a
piezo-electric actuator 174 which is affixed to the base member 170
to which a driven member, e.g. rotary stage 172 is rotatably
coupled. An optical element such as a diffraction grating, mirror,
polarized, or similar device may be affixed to the rotary stage.
Cut out portions in base member allow the rotatable stage member to
be grasped by hand for manual rotation. A knurled portion on the
top of rotary stage may be used in conjunction with scale on the
top of rotatable stage member 194 to achieve a coarse initial
position. Where closed loop control of the position of the driven
member is enabled position detector 178 operating with encoding on
the rotary stage provides position feedback to the controller
100.
[0035] The piezo-electric element 176 has a first end which fits
into a receptor portion of the base member 170 and second end which
is affixed a drive pad which frictionally couples with the rotary
stage. The reciprocating motion of the drive pad developed by the
piezo-electric element is converted to rotary motion of the optical
stage by moving the drive pad relatively slowly in a first
direction such that the coefficient of friction between the drive
pad and the rotatable optical stage overcomes the inertial and
rotational friction of the rotatable optical stage, causing the
moveable optical stage to rotate slightly. A relatively rapid rate
of motion in a direction opposite the first direction results in
slippage between the drive pad and the rotary stage thereby
avoiding motion of the rotary stage with respect to the base 170.
When the relative rates of motion are reversed the direction, i.e.
counter-clockwise or clockwise, of the rotary stage with respect to
the base is reversed as well.
[0036] The linear or rotary assemblies discussed above may utilize
a variety of position sensors, e.g. linear and rotary encoders, to
provide absolute/relative position feedback.
[0037] FIG. 2 shows an embodiment of the data structures from which
the desired waveforms generated by the controller may be derived.
In this embodiment of the invention two files 202 and 212 each
including an ordered set of numbers 204 and 214 respectively are
stored in memory 112. The ordered set 204 corresponds with a first
pulse the leading edge 206 of which has a gradual slope and the
trailing edge 208 of which has a steep slope. The relative absolute
value of the average slope along the trailing edge exceeds that
along the leading edge. A pulse resulting from this ordered
sequence will correspond with a first of the two directions of
motion of the driven member. The ordered set 214 corresponds with a
second pulse the leading edge 216 of which has a steep slope and
the trailing edge 218 of which has a gradual slope. The relative
absolute value of the average slope along the trailing edge is less
than that along the leading edge. A pulse resulting from this
ordered sequence will correspond with a second of the two
directions of motion of the driven member.
[0038] In alternate embodiments of the invention a single ordered
sequence read in either top-down order or a bottom-up order may be
sufficient to effect a selected one of the two possible directions
of motion in the driven member. In still another embodiment of the
invention a plurality of files may be stored in memory each
corresponding to the optimal digital drive signal for an associated
piezo-electric assembly. In still another embodiment of the
invention the files may be updated with new digital values to
activate a new piezo-electric assembly or to improve the efficiency
of an existing assembly. In still another embodiment of the
invention the data 122 stored in memory may be a function the
execution of which by the processor 110 results in one or the other
of the ordered sequences of numbers 204 and 214.
[0039] FIG. 3 is a signal diagram showing the waveforms resulting
from the ordered sequence of numbers after an D/A conversion and a
subsequent amplification to the appropriate amplitudes for driving
the piezo-electric actuators. Three pulse sequences are shown. The
first two of these show a low frequency train of pulses 306. The
second of these show an increase in the frequency of the pulses
306. Pulse 306 corresponds to the output of the D/A converter 114
(See FIG. 1) resulting from an input of the ordered sequence of
numbers 214 shown in the previous FIG. 2. Pulse 330 corresponds to
the amplified output of amplifier 116 (See FIG. 1) resulting from
an input of pulse 306. The amount of amplification corresponds with
the ratio of the peak amplitudes 340 and 320 corresponding to the
outputs of the amplifier and the DAC respectively. The increase in
frequency between pulse train 302 compared with pulse train 300
results from a decrease in the interval 312 between pulses rather
than in a change in the duration of the pulse itself. This
decreases the overall period 310 of the waveform without effecting
the pulse duration In an embodiment of the invention the duration
of the pulse leading edge, peak dwell interval 314, and trailing
edge 316 remains constant as frequency varies. After amplification
the same durations are found for the leading edge, the peak dwell
time 334 and the trailing edge 336 in the amplified waveform 330 as
well.
[0040] The third of the pulse trains 304 shows high frequency train
of pulses 308. Pulse 304 corresponds to the output of the D/A
converter 114 (See FIG. 1) resulting from an input of the ordered
sequence of numbers 204 shown in the previous FIG. 2. Pulse 360
corresponds to the amplified output of amplifier 116 (See FIG. 1)
resulting from an input of pulse 308. The amount of amplification
corresponds with the ratio of the peak amplitudes 370 at the output
of the amplifier and the peak amplitude of pulse 308. The duration
of the leading edge, the peak dwell time, and the trailing edge of
this pulse also, in an embodiment of the invention, remains
substantially constant as the frequency of the pulses is increased
or decreased.
[0041] FIG. 4 is a process flow diagram showing the processes
associated with the operation of an embodiment of the controller in
which multiplexing of various piezo-electric assemblies is
effected. Additionally in this embodiment closed loop feedback of
position is effected along with alterations in the direction of
movement and/or the speed of the corresponding driven member may be
effected. The process flow diagram shows one embodiment of the
ordering of these processes.
[0042] Processing commences at start block 400 in which downloading
of new program code 120 (See FIG. 1) and/or updated or new control
data 122 to the memory 112 (See FIG. 1) may take place. After
initialization of any software or hardware registers etc,
processing passes to decision block 402. In decision block 402 a
determination is made as to whether motion of the driven member
currently selected by the multiplexer 132 (See FIG. 1) is to start
or stop. This determination may be based on the value in a
register, a user input, or a comparison between a closed loop
feedback of actual position with a desired position for the driven
member. If a change in the position of the selected one of the
multiplexed piezo-electric assemblies is called for control passes
to decision process 408. If alternately no further motion for the
selected assembly is required then control passes to stop block
404. In stop block 404 the piezo-electric actuator is temporarily
shorted to a current sink 130 via switch 128. This avoids further
drift of the selected actuator through a rapid discharge thereof
Then control is passed to next channel process 406 for the
selection of the next of the multiplexed actuators after which
control returns to decision block 402.
[0043] The processing of the selected one of the channels continues
in decision block 408, in which a determination is made as to the
required speed for the driven member. The speed of the driven
member correlates with the frequency of pulses output by the
amplifier. If a faster speed is required control passes to process
410 in which a register with a value corresponding to the duration
of the idle interval 312 (See FIG. 3) between pulses is
decremented. Alternately if a slower speed is called for control
passes to process 412 in which the same register is up incremented.
After either operation on the idle interval register control passes
to decision block 414.
[0044] In decision block 414 a determination is made as to whether
a forward/clockwise or reverse counter-clockwise motion of the
selected driven member is called for. Depending on the outcome of
the decision control may be passed to process 416 or process 418.
In process 416 a pointer is set to the appropriate one of the two
ordered sequences of numbers, e.g. sequence 204 for the selected
actuator. Alternately, in process 418 the pointer is set to the
other of the two ordered sequences, e.g. sequence 214. In an
alternate embodiment of the invention an appropriate function for
generating the ordered sequence would be selected in either of
these processes. In still another embodiment of the invention the
pointer by which the processor 110 increments through the file
could be initialized at the top or bottom of a single ordered
sequence for subsequent reading in opposing directions. Subsequent
to either processes 416 or 418 control passes to process 420.
[0045] In processes 420-422 the pointer controlled by the processor
110 (See FIG. 1) is incremented through the ordered sequence row by
row until the end of the ordered sequence is detected in process
422. Control then passes to process 424.
[0046] At this point one pulse has been output by the processor to
the input of the DAC 114 ( SEE FIG. 1). Next in processes 424-426 a
delay 312 (SEE FIG. 3) of an amount corresponding to the idle
interval set in either of processes 410-412 above is injected into
the output waveform This delay is the method by which the frequency
of the composite waveform resulting from the pulses is varied in an
embodiment of the invention. At the termination of the delay
control passes to decision block 428 in which a determination is
made as to whether closed loop position feedback and control is
enabled. If not control returns directly to decision process 402 in
which either the next channel is selected or the next pulse for the
currently selected channel is output.
[0047] Alternately, where closed loop position feedback is enabled
control passes to decision process 430. In decision process 430 a
determination is made as to whether the actual position of the
selected driven member corresponds with the desired position
Depending on the outcome of the comparison control will be passed
to either of process blocks 432-434 for an appropriate setting of a
forward or reverse register. This is the register read in process
414 discussed above. Control then returns to decision process 402
in which either the next channel is selected or the next pulse for
the currently selected channel is output.
[0048] FIG. 5 is a detailed cross-sectional view of a first of the
piezo-electric assemblies 148 shown in FIG. 1. This actuator
includes a piezo-electric element 160 having electrodes 512 and 510
at opposite ends with lead wires electrically connected thereto to
allow the analog waveform output by the amplifier 116 (See FIG. 1)
to be applied across piezo-electric element. A first end of the
piezo-electric element adjacent electrode 510 is affixed to the
base portion of the actuator frame (body), and an opposite end is
affixed to a first movable jaw element 504, which co-acts with
second movable jaw element 502 to engage an adjustment screw 158
(See FIG. 1) held between the inner faces 528 and 506 of the
jaws.
[0049] Resilient flexure connects base portion and the first
movable jaw element to accommodate bi-directional lengthwise
longitudinal motion of piezo-electric element 160. Such lengthwise
motion of element 160 causes a longitudinal reciprocating motion of
jaw elements, which in turn imparts a rotational motion to a
cylindrical element, such as a threaded adjustment screw, held
between inner faces of the jaws. A pair of spring retention grooves
522-524 on the opposing outer surfaces of the jaws serve to
position and retain a flat clamp spring 152, as shown in FIG. 1.
This clamp increases the pressure of the inner faces of the jaws
against the cylindrical element, such as a threaded adjustment
screw, positioned between them The actuator frame may be fabricated
from suitable brass stock by means of conventional wire
elector-discharge machining techniques. Flat clamp sprint 152 may
be fashioned from any material having suitable spring and fatigue
characteristics.
[0050] Holes, extending through the actuator frame, are used during
fabrication of the actuator to stretch the frame during cementing
of the piezo-electric element 160 so that, after assembly, the
piezo-electric element is under compression. This is done to avoid
fracturing the bond between the frame and piezo-electric element
when an electrical signal is applied to piezo-electric element.
[0051] FIG. 6 is a detailed cross-sectional view of the rotary
piezo-electric assembly 174 shown in FIG. 1. The stainless steel
rotatable stage member 172 has a complementary stainless steel
lower member 604 each of which screwingly secure to each other. The
rotatable stage member includes outer surface threads aligned
beneath the outer cylindrical drive surface 602. Internal threads
are located on the walls of an aperture within the rotatable stage
member 172 to accommodate an optic or other device. Upper stage
member and lower member have beveled bearing races which combine
with a complementary race in the base member 170 to provide a high
precision, low friction ball bearing for rotation of stage member
172.
[0052] An actuator cut-out 600 in base member 170 accommodates a
piezo-electric cover and frame element 610. The piezo-electric
element 176 has a spherical cap 620 on a first end portion and a
brass drive pad 616 on a second end portion. Spherical cap and
drive pad may be affixed to piezo-electric element by suitable
adhesive such as epoxy. Bias spring 614 fits between drive pad and
the base is held in position by spring adjustment screw 612. The
spherical cap 620 bears against the first opposing face of the base
and allows motion of piezo-electric element 176 to accommodate
runout of the rotary stage 172. The drive pad 616 has a bias spring
retention means slot which accepts the tapered end of bias spring
614. The bias spring adjustment screw 612 has a tapered point and
engages in the screw mount hole to engage one end of the bias
spring. The bias spring is positioned to force drive portion of the
drive pad into engagement with the cylindrical drive surface
portion 602 of rotatable stage member and to simultaneously force
the spherical cap of the piezo-electric element against frame
element face.
[0053] The piezo-electric element is operative to effect
reciprocating motion in the drive pad. The reciprocating motion of
the drive pad developed by the piezo-electric element is converted
to rotary motion of the optical stage by moving the drive pad
relatively slowly in a first direction such that the coefficient of
friction between the drive pad and the rotatable optical stage
overcomes the inertial and rotational friction of the rotatable
optical stage, causing the moveable optical stage to rotate
slightly. The waveform is configured to maintain engagement between
the drive pad and the rotatable optical stage to incrementally
rotate the optical stage. When the limit of extension of the
piezo-electric element is reached, the electrical drive signal is
shifted to cause rapid movement of the drive pad in a second,
opposite direction such that the inertial characteristics of the
rotatable optical stage prevents the rotatable stage from following
the drive pad motion and the drive pad slips against the rotatable
optical stage.
[0054] The many features and advantages of the present invention
are apparent from the written description, and thus, it is intended
by the appended claims to cover all such features and advantages of
the invention. Further, since numerous modifications and changes
will readily occur to those skilled in the art, it is not desired
to limit the invention to the exact construction and operation as
illustrated and described. Hence, all suitable modifications and
equivalents may be resorted to as falling within the scope of the
invention.
* * * * *