U.S. patent application number 09/924130 was filed with the patent office on 2001-12-06 for reduced-energy-consumption latching actuator.
Invention is credited to Mo, Xiaoxiong, Parsons, Natan E..
Application Number | 20010048086 09/924130 |
Document ID | / |
Family ID | 23675393 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010048086 |
Kind Code |
A1 |
Parsons, Natan E. ; et
al. |
December 6, 2001 |
Reduced-energy-consumption latching actuator
Abstract
A latching-valve system (10) includes a piezoelectric transducer
(44) mounted on its housing (16). To change the valve's state, a
microcontroller (54) causes a valve driver (58) to drive current
through the actuator's coil (12). It continues driving current
through the coil (12) until the transducer's output reaches a
magnitude characteristic of the disturbance that typically results
when the actuator's armature (22) reaches the end of its travel At
that point, the microcontroller (54) stops driving current through
the coil. If the characteristic sound does not occur within a
predetermined duration, the microcontroller (54) causes a
voltage-multiplier circuit (Q1, L1, D1) to increase the voltage
that the valve driver (58) applies to the coil.
Inventors: |
Parsons, Natan E.;
(Brookline, MA) ; Mo, Xiaoxiong; (Nashua,
NH) |
Correspondence
Address: |
CESARI AND MCKENNA, LLP
88 BLACK FALCON AVENUE
BOSTON
MA
02210
US
|
Family ID: |
23675393 |
Appl. No.: |
09/924130 |
Filed: |
August 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09924130 |
Aug 7, 2001 |
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09422553 |
Oct 21, 1999 |
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6293516 |
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Current U.S.
Class: |
251/129.04 ;
251/65; 361/160 |
Current CPC
Class: |
F16K 31/0675 20130101;
F16K 31/082 20130101 |
Class at
Publication: |
251/129.04 ;
251/65; 361/160 |
International
Class: |
F16K 031/08 |
Claims
What is claimed is:
1. An actuator system comprising: A) latching actuator including an
armature and a coil operable by application of a coil drive thereto
in a first drive direction to conduct current in a first current
direction and thereby tend to drive the armature to a first end
position; B) a sound sensor so coupled to the actuator as to sense
sound made by the armature in reaching the first end position, the
sound sensor generating a sensor output indicative of the sound
that it senses; and C) a control circuit operable to begin applying
coil drive to the coil in the first drive direction and responsive
to the sensor output's meeting a predetermined first
current-termination criterion to stop applying coil drive to the
coil in the first drive direction:
2. An actuator system as defined in claim 1 wherein: A) the coil is
operable by application of a coil drive thereto in a second drive
direction to conduct current in a second current direction and
thereby tend to drive the armature to a second end position; B) the
sound sensor is so coupled to the actuator as to sense sound made
by the armature in reaching the second end position; and C) the
control circuit is operable to begin applying coil drive to the
coil in the second drive direction and responsive to the sensor
output's meeting a predetermined second current-termination
criterion to stop applying coil drive to the coil in the second
drive direction.
3. An actuator system as defined in claim 2 wherein the first and
second current-termination criteria differ.
4. An actuator system as defined in claim 1 wherein the sound
sensor includes a piezoelectric transducer.
5. An actuator system as defined in claim 4 wherein, if the sensor
output does not meet the first current-termination criterion within
a predetermined first drive duration after the control circuit
begins application of coil drive to the coil in the first drive
direction, the control circuit applies coil drive to the coil in
the first drive direction at a level higher than that at which it
began application of coil drive to the coil.
6. An actuator system as defined in claim 5 wherein, if the sensor
output does not meet the second current-termination criterion
within a predetermined second drive duration after the control
circuit begins application of coil drive to the coil in the second
drive direction, the control circuit applies coil drive to the coil
in the second drive direction at a level higher than that at which
it began application of coil drive to the coil.
7. An actuator system as defined in claim 4 wherein: A) the
actuator system includes a housing that contains the armature and
coil; and B) the piezoelectric transducer is secured to the
housing.
8. An actuator system as defined in claim 1 wherein, if the sensor
output does not meet the first current-termination criterion within
a predetermined first drive duration after the control circuit
begins application of coil drive to the coil in the first drive
direction, the control circuit applies coil drive to the coil in
the first drive direction at a level higher than that at which it
began application of coil drive to the coil.
9. An actuator system as defined in claim 8 wherein, if the sensor
output does not meet the second current-termination criterion
within a predetermined second drive duration after the control
circuit begins application of coil drive to the coil in the second
drive direction, the control circuit applies coil drive to the coil
in the second drive direction at a level higher than that at which
it began application of coil drive to the coil.
10. An actuator system as defined in claim 9 wherein the first and
second drive durations are the same.
11. An actuator system as defined in claim 1 wherein: A) the system
includes first and second coil terminals by which the control
circuit applies the coil drive to the coil; B) the system includes
first and second sensor terminals by which the control circuit
receives the sensor output from the sound sensor; and C) the second
coil and sensor terminals are the same.
12. An actuator system comprising: A) a latching actuator including
an armature and a coil operable by application of a coil drive
thereto in a first drive direction to conduct current in a first
current direction and thereby tend to drive the armature to a first
end position; B) an endpoint detector that detects the armature's
reaching the first end position and responds thereto by generating
a detector output indicative thereof; and C) a control circuit
operable to begin application of coil drive to the coil in the
first direction at a normal first-direction drive level and, if the
detector output has not indicated within a predetermined first
drive duration thereafter that the armature has reached the first
end position, to apply coil drive to the coil in the first
direction at an elevated first-direction drive level higher than
the normal first-direction drive level.
13. An actuator system as defined in claim 12 wherein: A) the coil
is operable by application of a coil drive thereto in a second
drive direction to conduct current in a second current direction
and thereby tend to drive the armature to a second end position; B)
the endpoint detector responds to the armature's reaching the
second end position by generating a detector output indicative
thereof; and C) the control circuit is operable to begin
application of coil drive to the coil in the second direction at a
normal second-direction drive level and, if the detector output has
not indicated within a predetermined second drive duration
thereafter that the armature has reached the second end position,
to apply coil drive to the coil in the second direction at an
elevated second-direction drive level higher than the normal
second-direction drive level.
14. An actuator system as defined in claim 13 wherein the first and
second drive durations are the same.
15. An actuator system as defined in claim 13 wherein: A) the
endpoint detector includes a sound sensor that is so coupled to the
actuator as to sense sound made by the armature in reaching the
first and second end positions and generates a sensor output
indicative of the sound that it senses; B) the detector output
indicates that the armature has reached the first end position if
the sensor output meets a predetermined first current-termination
criterion; and C) the detector output indicates that the armature
has reached the second end position if the sensor output meets a
predetermined second current-termination criterion.
16. An actuator system as defined in claim 15 wherein the sound
sensor includes a piezoelectric transducer.
17. An actuator system as defined in claim 12 wherein the control
circuit stops applying the coil drive in the first direction after
the predetermined normal first-direction drive duration before
driving the coil at the higher level.
18. An actuator system as defined in claim 17 wherein: A) the coil
is operable by application of a coil drive thereto in a second
drive direction to conduct current in a second current direction
and thereby tend to drive the armature to a second end position; B)
the endpoint detector responds to the armature's reaching the
second end position by generating a detector output indicative
thereof; and C) the control circuit is operable to begin
application of coil drive to the coil in the second direction at a
normal second-direction drive level and, if the detector output has
not indicated within a predetermined second drive duration
thereafter that the armature has reached the second end position,
to apply coil drive to the coil in the second direction at an
elevated second-direction drive level higher than the normal
second-direction drive level.
19. An actuator system as defined in claim 18 wherein the control
circuit stops applying the coil drive in the second direction after
the predetermined normal second-direction drive duration before
driving the coil at the higher level.
20. An actuator system as defined in claim 12 wherein: A) the
endpoint detector includes a sound sensor that is so coupled to the
actuator as to sense sound made by the armature in reaching the
first end position and generates a sensor output indicative of the
sound that it senses; and B) the detector output indicates that the
armature has reached the first end position if the sensor output
meets a predetermined first current-termination criterion.
21. An actuator system as defined in claim 20 wherein the sound
sensor includes a piezoelectric transducer.
22. An actuator system as defined in claim 20 wherein: A) the
system includes first and second coil terminals by which the
control circuit applies the coil drive to the coil; B) the system
includes first and second sensor terminals by which the control
circuit receives the sensor output from the sound sensor; and C)
the second coil and sensor terminals are the same.
23. A flow-control system comprising: A) a valve operable between
open and closed states; B) a latching actuator including an
armature operatively connected to the valve and further including a
coil operable by application of a coil drive thereto in a first
drive direction to conduct current in a first current direction and
thereby tend to drive the armature to a first end position, in
which the armature holds the valve in one of said open and closed
states; C) an endpoint detector that detects the armature's
reaching the first end position and responds thereto by generating
a detector output indicative thereof; and a control circuit
operable to begin application of coil drive to the coil in the
first direction and responsive to the detector output indicative of
the armature's reaching the first end position to stop applying
coil drive to the coil in the first drive direction.
24. A flow-control system as defined in claim 23 wherein: A) the
flow-control system additionally includes an object sensor that
produces an object sensor output; and B) the control circuit's
application of the coil drive to the coil is dependent on the
object-sensor output.
25. A flow-control system as defined in claim 23 wherein: A) the
coil is operable by application of a coil drive thereto in a second
drive direction to conduct current in a second current direction
and thereby tend to drive the armature to a second end position, in
which the armature holds the valve in the other of said open and
closed states; B) the endpoint detector detects the armature's
reaching the second end position and responds thereto by generating
a detector output indicative thereof; and C) the control circuit is
operable to begin application of coil drive to the coil in the
second direction at a normal first-direction drive level and
responsive to the detector output indicative of the armature's
reaching the second end position to stop applying coil drive to the
coil in the second drive direction.
26. A flow-control system as defined in claim 25 wherein: A) the
flow-control system additionally includes an object sensor that
produces an object sensor output; and B) the control circuit's
application of the coil drive to the coil is dependent on the
object-sensor output.
27. A flow-control system as defined in claim 25 wherein: A) the
endpoint detector includes a sound sensor that is so coupled to the
actuator as to sense sound made by the armature in reaching the
first and second end positions and generates a sensor output
indicative of the sound that it senses; B) the detector output
indicates that the armature has reached the first end position if
the sensor output meets a predetermined first current-termination
criterion; and C) the detector output indicates that the armature
has reached the second end position if the sensor output meets a
predetermined second current-termination criterion.
28. An actuator system as defined in claim 27 wherein the sound
sensor includes a piezoelectric transducer.
29. An actuator system as defined in claim 23 wherein: A) the
endpoint detector includes a sound sensor that is so coupled to the
actuator as to sense sound made by the armature in reaching the
first end position and generates a sensor output indicative of the
sound that it senses; and B) the detector output indicates that the
armature has reached the first end position if the sensor output
meets a predetermined first current-termination criterion.
30. A flow-control system as defined in claim 29 wherein: A) the
flow-control system additionally includes an object sensor that
produces an object sensor output; and B) the control circuit's
application of the coil drive to the coil is dependent on the
object-sensor output.
31. An actuator system as defined in claim 29 wherein the sound
sensor includes a piezoelectric transducer.
32. A flow-control system comprising: A) a valve operable between
open and closed states; B) a latching actuator including an
armature operatively connected to the valve and further including a
coil operable by application of a coil drive thereto in a first
drive direction to conduct current in a first current direction and
thereby tend to drive the armature to a first end position, in
which the armature holds the valve in one of said open and closed
states; C) an endpoint detector that detects the armature's
reaching the first end position and responds thereto by generating
a detector output indicative thereof; and D) a control circuit
operable to begin application of coil drive to the coil in the
first direction at a normal first-direction drive level and, if the
detector output has not indicated within a predetermined first
drive duration thereafter that the armature has reached the first
end position, to apply coil drive to the coil in the first
direction at an elevated first-direction drive level higher than
the normal first-direction drive level.
33. A flow-control system as defined in claim 32 wherein: A) the
flow-control system additionally includes an object sensor that
produces an object sensor output; and B) the control circuit's
application of the coil drive to the coil is dependent on the
object-sensor output.
34. A flow-control system as defined in claim 32 wherein: A) the
coil is operable by application of a coil drive thereto in a second
drive direction to conduct current in a second current direction
and thereby tend to drive the armature to a second end position; B)
the endpoint detector responds to the armature's reaching the
second end position by generating a detector output indicative
thereof; and C) the control circuit is operable to begin
application of coil drive to the coil in the second direction at a
normal second-direction drive level and, if the detector output has
not indicated within a predetermined second drive duration
thereafter that the armature has reached the second end position,
to apply coil drive to the coil in the second direction at an
elevated second-direction drive level higher than the normal
second-direction drive level.
35. A flow-control system as defined in claim 34 wherein: A) the
flow-control system additionally includes an object sensor that
produces an object sensor output; and B) the control circuit's
application of the coil drive to the coil is dependent on the
object-sensor output.
36. A flow-control system as defined in claim 32 wherein: A) the
endpoint detector includes a sound sensor that is so coupled to the
actuator as to sense sound made by the armature in reaching the
first end position and generates a sensor output indicative of the
sound that it senses; and B) the detector output indicates that the
armature has reached the first end position if the sensor output
meets a predetermined first current-termination criterion.
37. A flow-control system as defined in claim 36 wherein the sound
sensor includes a piezoelectric transducer.
38. A flow-control system as defined in claim 36 wherein: A) the
flow-control system additionally includes an object sensor that
produces an object sensor output; and B) the control circuit's
application of the coil drive to the coil is dependent on the
object-sensor output.
39. For controlling a latching actuator including an armature and a
coil operable by application of a coil drive thereto in a first
drive direction to conduct current in a first current direction and
thereby tend to drive the armature to a first end position, a
method comprising the steps of: A) applying coil drive to the coil
in the first drive direction; B) determining whether the armature
has reached the first end position; and C) if so, stopping
application of the coil drive to the coil.
40. For controlling a latching actuator including an armature and a
coil operable by application of a coil drive thereto in a first
drive direction to conduct current in a first current direction and
thereby tend to drive the armature to a first end position, a
method comprising the steps of: A) applying coil drive to the coil
in the first drive direction; B) determining whether the armature
has reached the first end position; and C) if the armature has
reached the first end position within a predetermined first drive
duration thereafter, applying coil drive to the coil in the first
direction at an elevated first-direction drive level higher than
the normal first-direction drive level.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed to latching actuators and
in particular to the systems that control them.
[0002] For many automatic flow-control installations, such as
automatic toilet and urinal flushers, one particularly stringent
design requirement is that the system consume as little power as
possible. The reason for this varies from case to case, but it is
typically that the circuitry and other apparatus required to make
the flusher's operation automatic are quite frequently provided on
a retrofit basis. That is, manual flushers are being converted to
automatic operation. Unless the retrofit unit can be
battery-operated or otherwise self-contained, the installation
process is quite expensive, typically requiring that walls be
opened to provide the necessary wiring. That expense can be avoided
if the automatic system is battery-operated, but a battery-operated
system's acceptability depends greatly on battery life.
[0003] A significant determinant of the battery's longevity is the
energy that valve actuation consumes. So retrofit systems tend to
employ valves of the latching variety, i.e., valves whose actuators
require power to open or close the valve but not to keep it open or
closed. The use of valves that employ such actuators has greatly
extended the feasibility of employing battery-operated systems.
Still, such systems would be more attractive if battery longevity
could be extended further.
SUMMARY OF THE INVENTION
[0004] The present invention achieves this result by reducing the
energy waste that usually occurs in driving the actuator's
armature. The approach employed by the invention involves
determining when the armature has reached the end of its travel. In
accordance with one of the invention's aspects, actuator-coil drive
ends when it has. This can reduce energy consumption greatly,
because coil-drive duration thereby does not always need to be long
enough to meet worst-case requirements. This can result in a
significant battery-longevity increase.
[0005] In accordance with another of the invention's aspects, the
drive applied to the actuator coil is increased if the armature has
not reached the end of its travel within a predetermined duration.
This allows less coil drive to be used ordinarily, since the coil
drive does not always need to be great enough to overcome the
resistance that can occasionally result from, for instance,
accretion of foreign matter. This coil-drive reduction, too, can
contribute to longevity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The invention description below refers to the accompanying
drawings, of which:
[0007] FIG. 1 is a cross-sectional view of a latching valve on
which a piezoelectric transducer has been mounted; and
[0008] FIG. 2 is a block diagram of a control system for the
valve's actuator.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
[0009] FIG. 1 shows in cross section a valve system 10 that
includes a latching actuator. The actuator includes a coil 12 wound
on a bobbin 14 mounted in an actuator housing 16. In the
illustrated position, a latching magnet 18 mounted on the bobbin 14
acts through a rear pole piece 20 to hold an armature 22 in an
upper position against the force that a return spring 24 exerts on
a shoulder 26 formed near the armature's lower end. In the FIG. 1
position, a resilient valve member 28 at the bottom of the armature
is spaced from a valve seat 30 formed about a valve inlet 32. Fluid
can therefore flow through inlet 32 and an annular cavity 34 to the
valve's outlet 36.
[0010] To close the valve, a drive voltage applied through
terminals 37 and 38 drives current through the coil 12. Terminal 38
is in ohmic contact with the conductive housing 16, which a contact
spring 39 in turn connects to one end of the coil 12. A lead 40
connects the coil 12's other end to terminal 37, and a
non-conducting bushing 41 insulates terminal 37 from the housing
16.
[0011] The drive voltage's polarity is such that the resultant
magnetic flux, guided largely by the ferromagnetic housing 16, rear
pole piece 20, and front pole piece 42, opposes that of the
permanent magnet 18. This breaks the magnet 18's hold on the
armature 22 and allows the return spring 24 to urge the valve
member 28 onto the valve seat 30. Once the valve has thus closed,
the return spring keeps it closed without any further assistance
from the coil; the armature 22's increased distance from the magnet
makes the magnetic force on the armature 22 less than that of the
return spring 24.
[0012] To open the valve, coil drive is applied to leads 37 and 38
in the opposite direction, so the resultant flux reinforces that of
the permanent magnet 18 and overcomes the force of the return
spring. The armature 22 therefore returns to the FIG. 1 position,
where the permanent magnet 18's force is great enough to hold the
armature 22 against the return spring 24's force without assistance
from the coil.
[0013] Because of the latching valve's bistable nature, control
circuits that operate it typically discontinue current flow after
the valve has reached the desired state. Since the time required
for the valve to reach the desired state can vary widely,
conventional control circuits make the current-flow duration
relatively long so that it will be adequate for worst-case
conditions. Since most actuations are not performed under
worst-case circumstances, though, coil drive typically continues
for some time after the valve reaches its stable position. This is
a waste of battery energy. To reduce this waste, a system that
employs the present invention monitors the armature to determine
whether the armature has reached its endpoint, and it stops
applying coil drive when that occurs. To this end, the illustrated
embodiment takes advantage of the sound that the armature makes
when it reaches either end of its travel.
[0014] We use the term sound here in a broad sense of a pressure or
strain wave. In most embodiments, moreover, the predominant
frequency components of the "sound" are typically above the audible
range. The illustrated embodiment's sensor is a piezoelectric
transducer 44 that responds to vibrations in the housing wall. The
piezoelectric element 44's size and shape have typically been so
chosen as to maximize its response to the predominant frequency
components, and it normally is mounted in a location where the
sounds to be detected are greatest in amplitude or most
distinguishable from noise.
[0015] A terminal 46 provides electrical communication to one of
the transducer 44's electrodes through a contact spring 48 that a
plastic cap 49 secured to the housing holds in place. The
transducer 44's other electrode can share terminal 38 with the coil
because the transducer is secured to the housing 16 by conductive
bonding between the housing and that electrode.
[0016] As FIG. 2 shows, a control circuit for the valve includes a
sensor amplifier and envelope detector 50, which receives the
transducer output. The amplifier and envelope detector 50 includes
an amplifier tuned to the expected sound's predominant (typically
ultrasonic-range) frequency components, rectifies the resultant
filtered signal, and low-pass filters the result to produce an
output representative of the tuned-amplifier output's envelope.
When the armature 22 reaches an endpoint and causes housing
vibration, the resultant envelope value exceeds a threshold that a
comparator 52 applies. Since in the illustrative embodiment the
sonic amplitude is higher when the valve opens than when it closes,
a microcontroller 54 sets a comparator threshold whose value when
the valve is being opened is different from the value it has when
the valve is being closed.
[0017] The microcontroller may operate the valve in response to
triggering by an object sensor 56. For example, it may open the
valve when the sensor detects user's leaving the flusher's
vicinity, and it may then close it once the valve has been open for
a predetermined duration. To open the valve, the microcontroller
sets an OPEN signal applied to a valve-driver circuit 58. This
causes that circuit to drive current through the actuator 60's coil
in the direction that will cause the valve to open.
[0018] When that current starts flowing, comparator 52's output
initially indicates that amplifier 50's output is less than the
threshold, so the amplifier is not receiving sound of a magnitude
consistent with the armature's reaching the end of its travel. The
microcontroller 54 therefore keeps the OPEN signal asserted. But
comparator 52's output changes in response to the sound made by the
armature 22 at the end of its travel. When the armature 22 has
reached that point, the valve will stay open without current flow,
so the microcontroller de-asserts its OPEN output and thereby
causes the valve driver 58 to stop applying drive current to the
actuator 60's coil. The result usually is that the current-flow
duration has been much less than the time required to open the
valve under worst-case conditions, so the system has saved
considerable energy.
[0019] To close the valve, the microcontroller 54 asserts its CLOSE
output and thereby causes the valve driver 58 to drive the actuator
60 in the opposite direction. Again, the microcontroller allows
current flow only until comparator 52 informs it that the armature
has reached the end of its travel.
[0020] The invention can be used to control not only the drive
signal's duration but also its magnitude. A coil-drive level high
enough for ordinary operation may occasionally be inadequate, and
the coil-drive level can be increased if the armature fails to
reach the endpoint. One way to increase the coil-drive level is to
increase the voltage on capacitors discharged through the actuator
coil.
[0021] FIG. 2 depicts the valve driver 58 as being powered by a
battery 62. The valve driver 58 typically includes energy-storage
capacitors, which the battery 62 charges up between actuations
through an inductor L1 and a Shottky diode D1. When the
microcontroller 54 asserts its OPEN or CLOSE signal, the driver
discharges the capacitors through the actuator 60's coil.
Ordinarily, it is the voltage of battery 62 itself that determines
the voltages to which the capacitors will be charged, and this in
turns determines coil current and thus armature force.
[0022] Now, factors such as the accretion of foreign matter may
make it harder than usual to open or close the valve. But energy
use that normally is unnecessarily high would result if the battery
voltage were set high enough to deal with such more-difficult
circumstances. The illustrated embodiment therefore uses a
battery-voltage level that is adequate for normal situations but
not for more-difficult ones.
[0023] Instead, it increases the capacitor voltage if the armature
has not reached the end of its travel within a predetermined
maximum current-flow duration. Specifically, the microcontroller 54
turns the valve driver off temporarily when the predetermined
maximum current-flow duration is reached, and it begins to pulse a
transistor Q1 through a current-limiting resistor R1. During each
pulse, the transistor draws current from the battery through
inductor L1. Because of diode D1, though, it does not discharge the
valve driver's capacitors. At the end of each pulse, transistor Q1
turns off, and the resultant electromotive force in inductor L1
causes current to continue to flow and thereby charge the drive
circuit's capacitors through diode D2 even if those
batteries'voltage exceeds that of the battery 62. So those
capacitors can be charged to voltages that exceed the
battery's.
[0024] To achieve the appropriate capacitor voltage, a comparator
64 compares the capacitor voltage to a level that microcontroller
54 sets. In response to the comparator's resultant output, the
microcontroller increases the pulses' duty cycle if the capacitor
voltage is less than the threshold, and it decreases their duty
cycle if the capacitor voltage exceeds the threshold. The threshold
is set higher than the battery voltage, so the force on the
armature is greater and more likely to open or close the valve when
the microcontroller then turns the valve driver on again.
[0025] The illustrative embodiment is only one of many that can
employ the present invention's teachings. For example, although we
prefer to use a sonic sensor--in particular, an ultrasonic
transducer--other ways of detecting the end of armature travel can
be used instead. Also, although the illustrated embodiment controls
coil-drive duration both when the valve is being opened and when it
is being closed, some embodiments may control that duration only
during opening or only during closing. And latching-actuator
systems that operate mechanisms other than valves can also benefit
from the present invention's teachings.
[0026] Moreover, although we have employed a simple amplitude
criterion to determine whether the armature has reached the end of
its travel, other criteria may be found preferable for some
applications. For instance, the sonic signal could be sampled and
compared by signal processing with a stored waveform known to be
characteristic of the armature's reaching one of its endpoints. The
stored signal may be different for different endpoints, and there
may be circumstances in which it will be considered valuable to use
such a comparison to distinguish between the actuator's two
states.
[0027] The present invention can thus be employed in a wide range
of embodiments and constitutes a significant advance in the
art.
* * * * *