Note: Descriptions are shown in the official language in which they were submitted.
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This is a divisional application of copending
application 534,031, filed April 7,1987.
POWER TRA2~SMISSION
The present invention is directed to electrohydraulic
servo systems, and more particularly to an electrohydraulic
servo valve assembly for use in such systems.
Background and Objects of the Invention
In electrohydraulic systems which include a plurality
of electrohydraulic devices, such as servo actuators, motors
and pumps, it is conventional practice to couple all of such
devices to a remote master controller for coordinating or
orchestrating device operation to perform a desired task. Motors
and actuators may be employed, for example, at several
coordinated stages of a machine tool line for automated transfer
and machining ofparts at a series of workstations. In accordance
with conventional practice, the master controller may comprise
a programmable controller or the like coupled through individual
digital-to-analog converters to the various remotely-positioned
electrohydraulic devices for supplying control signals thereto.
For closed-loop operation, a sensor is positioned at each
electrohydraulic device for sensing operation thereof, and feeds
a corresponding signal to the master controller through an
analog-to-digital converter.
Thus, in a system which embodies a plurality of
electrohydraulic devices, a substantial quantity of electrical
conductors must be provided for feeding individual control
signals to the various devices and returning sensor signals to
the master controller. Such conductors interfere with system
design and operation, and are subject to failure. The bank of
d/a and a/d converters for feeding signals from and to the
master controller add to the expense and complexit~ of the
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overall system. Perhaps most importantly, system performance
is limited by capabilities of the master controller. For
example, a programmable controller may require one hundred
milliseconds to scan a device sensor signal, compute a new
control signal and transmit such control signal to the remote
device. Such overburdened programmable controller operations
are not acceptable in high performance applications which may
require a six millisecond response time, for example, at each of
a plurality of remote devices.
It is therefore a general object of the present
invention to provide an electrohydraulic servo system which
exhibits the fast response time necessary for high performance
applications,while at the same time reducing cost and complexity
which inhere in prior art system of the character described
above. In furtherance of the foregoing, a more specific object
of the invention is to provide a system of thedescribed character
wherein each of the system electrohydraulic devices embodies
microprocessor-based control adapted to communicate with a
central ormastercontroller and for therebydistributing control
of the several electrohydraulic devices while maintaining
overall coordination thereamong.
Electrohydraulic servo valves are conven~ionally
employed for controlling operation of hydraulic devices, such
as rotary actuators, linear actuators and hydraulic motors for
example. Such servo valves are conventionally controlled by
remotelypositionedmaster electronics as describedhereinabove,
whether operating individually or as part of a coordinated
system. A further object of the present invention, therefore,
is to provide an electrohydraulic servo valve assembly which
embodies on-board microprocessor-based control electronics. In
furtherance of the foregoing, as well as the system ob~ectives
previously set forth above, yet another object of the i~vention
is to provide an electrohydraulic servo valve assembly which
includes facility for connection to the sensor on the device
with which the servo valve is associated for facilitating local
closed-loop servo control of the same, while at the same time
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embodying facility for communication with a remote master
controller to obtain coordinated operation with other system
devices.
In systems which embody a servo valve coupled to a
hydraulic actuator, particularly a linear actuator, it is
conventional practice to monitor actuator position using an
electroacoustic linear displacement transducer mar~eted by
Temposonics, Inc. of Plainview, New York and disclosed in United
States Patent No. 3,898,555. This transducer includes a magnet
coupled to the actuator piston for motion conjointly therewith,
and a electroacoustic waveguide adjacent to the path of the
magnet. A current pulse is launched on a wire which extends
through the waveguide and coacts with the magnet to launch an
acoustic signal withinthe waveguide. Acouplerormode converter
receives such acoustic signal, with the time between the
launching of the current pulse and receipt of the acoustic
signal being a function of position of the magnetic relative
to the waveguide. This transducer is durable, is directly
mounted on the actuator cylinder but magnetically rather than
physically coupled to the actuator piston, and is capable of
providing an accurate indication of actuator piston position.
~owever, conventional electronics for obtaining such position
readings are overly complex and inordinately expensive.
Furthermore, such electronics are conventionally supplied in a
separate package which must be appropriately positioned and
protected in the actuator operating environment. Another object
of the present invention, therefore, is to provide inexpensive
electronics for coupling to actuator position transducers of
the described character. In furtherance of the objectives set
forth above relative to provision of a servo valve assembly
with on-board control electronics, another object of the~present
invention is to provide transducer interface electronics of the
described character which are sufficiently compact for inclusion
in such servo valve on-board control electronics package.
Another problem in the art of electrohydraulic servo
valve control lies in overcoming effects of temperature on the
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valve coil. Coil force is proportional to current. Valve coils
are conventionally driven- by -constant current amplifiers so
that change in coil resistance due to temperature has little
affect. However, such constant current amplifiers are bulky
and expensive. Constant voltage amplifiers are preferable in
terms of size and expense, but control of current and force
becomes a problem. Another object of the present invention is
to provide a valve coil arrangement with reduced temperature
sensitivity, and which can thus be used-with constant-voltage
amplifiers of the type described. A further object-of the
invention is to provide improved valve driver electronics
characterized by reduced cost, reduced generation of
electromagnetic interference, and/or increased safety at the
load.
Summary of the Invention
In accordance with a first important aspect of the
present invention, an electrohydraulic servo control system,
which includes a plurality of electrohydraulic devices coupled
to a remote master controller, is characterized in that each
of the electrohydraulic devices includes on-board
microprocessor-based control electronics for receiv~ng and
storing control signals from the master controller, receiving
signals from the device sensor which indicate operation thereof,
comparing the sensor signals to the control signals from the
mastercontroller,andoperating the associated electrohydraulic
device as a function of the resulting error signal. The on-
board control electronics associated with each electrohydraulic
device preferably include facility for bidirectional
communication with the master controller for receiving control
signals therefrom for coordinated system operation and r~porting
device status thereto. The individual control electro~nics in
the preferred embodiments of the invention further include
facility for individually and selectively addressing the device
microprocessors, and for remote selection among a plurality of
control programs prestored in the device control microprocessor
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memory. In preferred embodiments of the invention wherein the
electrohydraulic devices are controlled by pulse width modulated
error signals, the microprocessor-based control electronics
further include a watchdog timer which monitors the pulse width
modulated control signal to the hydraulic device and causes
program restart in the absence of such signal.
In accordance with another aspect of the present
invention, an electrohydraulic servo valve assembly includes a
manifold having openings for connection to a source of hydraulic
fluid and to a hydraulic load, such as an actuator or hydraulic
motor. A valve element is variably positionable in the manifold
for controlling flow of fluid among the manifold openings. A
torque motor is mounted on the manifold for receiving valve
control signals, and is electromagnetically coupled to an
armature which is responsive to signals in the stator for
variably positioning the valve element within the manifold.
Microprocessor-based control electronics are mounted to the
manifold beneath a cover which encloses and protects both the
control electronics and the armature/stator assembly. The
control electronics include facility for receiving and storing
control signals from an external source, and for generating
valve control signals to the valve torquemotor. In the preferred
embodiments of the invention, such microprocessor-based control
electronics include the addressability, bidirectional
communication and watchdog_timer features previously discussed.
A further aspect of the present invention, which finds
particular application in a servo-valve/linear-actuator
combination, features improved circuitry for monitoring
operation of the Temposonics electroacoustic transducer
previously discussed. In accordance with this aspect of the
present invention, electronics for monitoring operation of
such sensor include facility for launching the initial~current
pulse in the waveguide in response to a measurement demand from
the microprocessor-based control electronics, and for
simultaneously resetting a counter. Upon receipt of the acoustic
return pulse from the waveguide, the counter is automatically
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incremented and a current pulse is relaunched in the waveguide.
The output of the counter includes facility for preseiecting a
number of launch/return cycles in the waveguide, and for
generating an interrupt signal to the microprocessor-based
control electronics to indicate that the preselected number of
recirculations has been reached and that an actuator position
reading has been obtained and stored in a clock which measures
the amount of time between the initial measurement demand signal
and the interrupt signal The clock output is stored and
transmitted to the control microprocessor on demand. In the
preferred embodiments of the invention herein disclosed, such
sensor electronics are combined with microprocessor-based
control electronics and valve drive electronics in a compact
package which forms part of an electrohydraulic servo valve
assembly coupled to the monitored actuator.
Brief Description of the Drawings
The invention, together with additional objects,
features and advantages thereof, will be best understood from
the following description, the appended claims and the
accompanying drawings in which:
FIG. 1 is a functional block diagram of an
electrohydraulic system in accordance with one aspect of the
present invention;
FIG. 2 is a sectioned elevational view of an
electrohydraulic servo valve assembly in accordance with another
aspect of the present invention;
FIG. 3 is a top plan view of the servo valve assembly
illustrated in FIG. 2;
FIG. 4 is a functional block diagram of the servo
valve assembly illustrated in FIGS. 2-3 coupled to a source of
hydraulic fluid and to a linear hydraulic actuator;
FIGS. 5A and 5~ together comprise an electrical
schematic diagram of the microprocessor board in the valve
assembly as shown in FIG. 2;
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FIGS. 6A and 6B together comprise an electrical
schematic diagram of the sensor board in the valve assembly as
illustrated in FIG. 2;
FIGS. 7A and 7B together comprise an electrical
schematic diagram of the power/display/driver board in the valve
assembly as illustrated in FIG. 2;
FIG. 8 is a fragmentary electrical schematic diagram
of a modified embodiment of the microprocessor watchdog
electronics illustratea in FIG. SA;
FIG. 9 is a functional block diagram of an alternative
embodiment of the sensor electronics illustrated in FIGS. 6A
and 6B; and
FIG. 10 is an electrical schematic diagram of a
modified valve driver in accordance with the invention.
Detailed Description of Preferred Embodiments
FIG. 1 illustrates an electrohydraulic system 20which
features distributed servo control in accordance with a first
important aspect of the present invention. A plurality of
electrohydraulic devices 22a-22n are illustrated as each
individually comprising a linear actuator 24 coupled to a load.
Each actuator 24 is hydraulically controlled by an associated
servo valve 26, with the several valves 26 being connected in
the usual manner through a pump 28 to a source 30 of hydraulic
fluid. Each servo valve 26 has associated therewith a
microprocessor-based electronic valve controller 32 which, in
accordance with the preferred embodiments of the invention
herein described, is combined with servo valve 26 in a unitary
package or assembly 34. Each valve controller 32 receives a
feedback signal indicative of operation at the associated
actuator 24 and/or the load coupled thereto. A master controller
36 is connected to each valve controller 32 for providing control
signals thereto, and thereby coordinating operation of the
various actuators 24 in a desired manner in accordance with
programming stored in master controller 36. It will be
appreciated, of course, that FIG. 1 illustrates only two
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electrohydraulic devices or implements 22a, 22n of a system
which may includea substantial number of suchdevices. ~ikewise,
it will be appreciated that the system and servo valve aspects
of the present invention are not limited to linear actuators 24
of the type illustrated in FIG. 1, but apply equally as well
to other controllable hydraulic devices such as pumps, hydraulic
motors and rotary actuators, for example.
FIGS. 2 and 3 illustrate a servo valve assembly 34
wherein microprocessor-based valve controller 32 in accordance
with the present invention is mounted by the cover io on an
otherwise generally conventional servo valve 26. Valve 26
includes a manifold 42 baving orifices or passages opening at
the lower face thereof for connection to pump 28 (FIG. 1),
return 30 and actuator 24. A spool 44 is slidable within
manifold 42 for controlling flow of fluid among the various
orifices through the filter 46. An electromagnetic torque motor
assem~ly 48 is carried by manifold 42 remotely of the fluid
orifices and surrounds an armature 50 which is coupled by the
flapper 52 to spool 44. The combination of stator 48 and
armature 50, conventionally termed a torque motor 49 in the
art, thus slidably controls position of spool 44, and thereby
controls fluid transport among the valve orifices, as a function
of signals applied to the stator coils 54. Valve controller
32 includes a stacked assembly of three printed circuit board
subassemblies: a sensor feedback board 56 (FIGS. 2, 6A and 6B~,
a microprocessor board 58 (FIGS. 2, 5A and 5B) and a
power/display/valve-driver board 60 (FIGS. 2, 7A and 7B).
Power/display/driver board 60 is carried by a bracket 62 which
is mounted internally of cover 34 such that board 60 is positioned
adjacent and parallel to the cover top wall. Boards 56, 58 are
mounted as shown in FIG. 2 beneath bracket 62 and adjacent to
torque motor 49. Suitable spacers maintain boards 58-60 and
bracket 62 in parallel spaced relation as shown. A first
connector 64 is affixed to a sidewall of cover 34 for connection
of valve controller 32 to master controller 36 (FIG. 1). A
second connector 66 on cover 40 adjacent to connector 64 provides
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for coupling of controller 32, specifically sensor feedback
board 56, to the actuator position sensor. An aperture or
opening 68 in the top wall of cover 40 is externally covered by
a removable translucent panel 70 to afford viewing ofacontroller
LED display 72 (FIGS. 2-4 and 7B) and access to controller
station access switches 74 for purposes to be described.
In the preferred application where a servo valve power
stage is controlled by an electro-magnetic-mechanical torque
motor driven pilot stage, the temperature coefficients of the
coils are reduced, allowing the use of simpler voltage mode
driver electronics, by winding the coils with a low temperature-
coefficient wire. By using a ~60 Alloy~ wire with a temperature
coefficient of resistance of 550 parts per million per degree C,
a 1.65% coil resistance increase would occur over a thirty
degree C temperature rise, as compared with a 12% resistance
increase in conventional copper coils over the same temperature
range. In applications, such as the preferred servo valve
application, where the servo valve component itself exhibits a
positive gain shift, the coil temperature coefficient of
resistance can be selected to nearly exactly compensate for the
valve positive gain shift. In the case of the servo valves, a
1.5% gain increase is observed over the same thirty degree C
temperature range. The subject servo valve family can therefore
be electrically driven in a voltage mode with no electronic
compensation simply by implementing this temperature
compensating coil. Low temperature coefficient wire materials
also exhibit higher bulk resistivity, usually of the same order
of magnitude as the reduction in temperature coefficient as
compared to copper wire. ~or this reason higher voltages are
required to drive the same coil application for a given coil
space envelope, at the cost of higher coil power dissipation.
In the case of the preferred servo valve application the power
dissipation is very small, providing an excellent opportunity
to exploit this technique. This temperature (/gain) compensated
coil means can also be implemented in a pulse width modulated
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mode where the voltage duty cycle is varied to modulate the
average current in the coil(s), as in the preferred application.
FIG. 4 is a schematic and functional block diagram
of servo valve assembly 34 coupled to an actuator 24 and a
position transducer 80. Control electronics on microprocessor
board 58 receive input commands from master controller 36 (FIG.
1) and provide a pulse width modulated output to coils 54 of
servo valve torque motor 49 through an amplifier 76 (FIGS. 4
and 7B) carried by power/display/driver board 60. Switches 74
preferably comprise a conventional multiple-pole dïpswitch
assembly carried by power/display/driver board 60 and coupled
to microboard 58 for setting a unique address at which master
controller 26 may communicate with valve controller 34. LED
display 72 includes a first LED 78 (FIGS. 2-3 and 7B) which is
continuously alternately energized and de-energized by micro
control 58 at fixed frequency to indicate continuing operation
of servo valve assembly 34. That is, either continuous
illumination or continuous extinction of LED 78 indicates
malfunction at the servo valve assembly and/or its associated
actuator 24. A second LED 79 (FIGS. 3 and 7B) is energized
during communication between associated control electronics 58
and master controller 36 (FIG. 1-). Actuator position tr~ansducer
80 is schematically illustrated in FIG. 4 as comprising an
annular magnet 82 carried by actuator piston 84. An
electroacoustic waveguide 86 is carried by the cylinder 88 of
actuator 24 and is encircled by magnet 82. A conductor 90
projects into waveguide 86 and is connected to position feedback
electronics carried by sensor feedback board 56 for receiving
current pulses therefrom. A mode converter or coupler 92 is
responsive to acoustic or sonic signals within waveguide 86 to
provide a corresponding electronic return signal to feedback
electronics 56. As previously noted hereinabove, the-general
construction and operation of transducer 80 is illustrated in
greater detail in United States Patent No. 3,898,555.
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FIGS. 5A-7B collectively illustrate the electronics of
valve controller 32, FIGS. 5A and 5B illustrating microprocessor
board 58, FIGS. 6A and 68 illustrating sensor feedback board 56, and
FIGS. 7A and 7B illustrating power/display/driver board 60. The
various printed circuit boards 56-60 are interconnected in assembly
32 by plugs P and sockets S carried by the individual circuit boards.
In the schematic drawings of FIGS. 5A-7B, interconnected plugs P and
sockets S are designated by corresponding suffix numerals - i.e.
plug P2 in FIG. SA is connected in assembly to socket S2 in FIGS.
7A, etc. The major integrated circuit components in-FIGS. 5A-7B
bear standard component identifications in parentheses, such
identifications being by way of example only. Individual components,
e.g. resistors, capacitors and transistors, are numbered in sequence
on each board in keeping with conventional practice, so that identical
identification between boards does not necessarily indicate identical
components.
Turning to FIGS. 5A and 5B, microprocessor printed circuit
board 58 includes a microprocessor 100 having address terminals
coupled, either directly or through a latch 102, to a ROM 104. Most
preferably, ROM 104 has stored therein, as firmware, one or more
programs for controlling actuator 24 in various modes of operation.
These control programs are selectable by master controller 36. A
crystal 106 is coupled to the clock inputs of microprocëssor 100 for
establishing microprocessor timing. A differential
receiver/transmittermodule 108 (FIG. 5B)iscoupled between connector
64 (FIGS. 2, 3 and 5B) and microprocessor transmit and receive
terminals TX, RX for receiving and storing control signals from
master controller 36 (FIG. 1 ) or transmitting station status
information to master controller 36. Microprocessorl00 also supplies
a transmit/receive signal T/R to connector 64 to indicate whether
the microprocessor is in the transmit or receive communication mode.
Exemplary control programs are disclosed in the following copending
applications, all of which are assigned to the assignee hereof:
Canadian Serial No. 498,077 filed December 19, 1985, Canadian
1 335605
Serial No. 503,456 filed March 6,1986, Canadian Serial No.
510,287 filed May 29, lg86, Canadian Serial No. 515,489 filed
August 7, 1986.
Torque motor 49 (FIG. 2) is constructed to control
position of spool 44 as a function of the duty cycle of pulse
width modulated signals applied to stator coils 54. Such pulse
width modulated signals are supplied at the P3.6 output of
microprocessor 100 to amplifier 76 (FIGS. 4 and 7B) on
power/display/driver board 60. A watchdog timer 110 includes
an NPN transistor Ql coupled to the pulse width modulated control
output of microprocessor 100 through the isolation capacitor
C6. A capacitor C3 is connected across the collector and emitter
of transistor Ql, with the emitter being connected to ground
and the collector being connected through the resistor R3 to
the positive voltage supply. An oscillator 112 receives an
enable/disenable input from the collector of transistor Ql.
The timing terminals of oscillator 112 are connected in the
usual manner to resistors Rl, R2 and capacitors Cl, C2 to provide
a continuous pulsed output to the reset input of microprocessor
100 in the absence of a disenabling reset input. As long as
the pulse width modulated output of microprocessor 100 remains
above a preselected frequency, determined by the values of
resistor R3 and capacitor C3, transistor Ql will prevent
capacitor C3 from charging to a voltage level which will permit
operation of oscillator 112. However, should the frequency or
amplitude of the microprocessor pulse width modulated output
decrease below the alarm levels determined by resistor R3 and
capacitor C3, capacitor C3 will charge to a higher voltage level
which, when applied to the reset input of oscillator 112, permits
oscillator operation so as to pulse the reset input of
microprocessor 100 and thereby terminate servo -control
operation. Absence of pulse width modulated control signals
to torque motor 49 (FIG. 2) automatically returns spool 44 to
its neutral or centered position illustrated in FIG. 2 and
thereby prevents uncontrolled or runaway operation of actuator
24. Reinitiation of the pulse width modulated output of
microprocessor 100 at the desired frequency and voltage level
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discharges capacitor C3 ( FIG. 5A) through transistor Ql and
thereby disenables or inhibits further operation of oscillator
112 so as to terminate reset inputs to microprocessor 100.
FIGS.6A and6B illustrate the sensor position feedback
electronics on circuit board 56 as comprising a decoder 120
which receives and decodes a measurement command input from
microprocessorl00 (FIG. 5B), and provides corresponding outputs
first to reset a pair of counters 122 (FIG. 6A) and 124 (FIG.
6B) and then to set a flip-flop 126 for enabling operation of
`counter 122. A oneshot 128 (F~G. 6B) is simultaneously triggered
through a diode D3 to provide a first pulsed output for
incrementing counter 124 and a second pulsed output for
triggering a second oneshot 130. Either the high-going or the
low-going output of oneshot 130 is fed by a suitable jumper at
plug P5 through resistor R10 to connector 66 for selecting
either positive or negative polarity for the current pulse
transmitted by oneshot 130 to position transducer 80. Return
or echo signals from mode convertor 92 (FIG. 4) of transducer
80 are fed through connector 66 to an amplifier 132. The output
of amplifier 132 is connected through a diode D2 and ORed with
the output of decoder 120 at the trigger input of oneshot 128.
Thus, a measurement command signal from the-control
microprocessor first resets counters 122, 124 and then triggers
oneshots 128, 130. Oneshot 130 propagates an initial current
pulse along the conductor of sensor 80 at polarity selected by
plug P5, while oneshot 128 increments counter 124. ~pon receipt
of an echo or return signal from the transducer at a level above
that set by resistors R2, R3, amplifier 132 retriggers oneshot
128 so as to increment counter 124 and retrigger oneshot 130
to propagate a second current pulse at the position transducer.
Thus, each return signal sensed at amplifier 132 functions to
propagate a further current pulse and to increment counter 124,
such that the counter continuously indicates the number of
transducer propagation/return cycles. Preferably, the duration
of the pulsed output of oneshot 128 is made relatively long,
such as fifteen microseconds for example, as compared with the
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duration of oneshot 130, such as one microsecond. Oneshot 128
thus functions to mask false echo signals which occasionally
occur when the the transducer current pulsé is initially
propagated.
Counter 124 has a plurality of count-indicating
outputs, a selected one of which is connected through an inverter
134 (FIG. 6A) to reset counter-enable flip-flop 126. The output
of inverter 134 i8 also connected through a diode Dl, plug P4
and socket S4 to an interrupt input of microprocessor 100 tFIG.
SB) so as to indicate completion of a transducer measurement
cycle. The output of flip-flop 126 enables connection of a
high frequency oscillator 136 to the count input of counter
122. Thus, counter 122 and oscillator 136 effectively form a
digital clock which measures the time duration of the transducer
measurement sequence. A latch 138 has data inputs connected
to the outputs of counter 122 and has load inputs connected to
decoder 120. A read command signal from microprocessor 100
(FIG. S~) to decoder 120 loads the output of counter 122 into
latch 138 so as to present such position-indicating count output
to microprocessor 100 through plug P3 tFIG. 6A) and socket S3
(FIG. 5A). Thus, in operation, current pulses are sequentially
propagated and return signals received over a number of cycles
determined by the output connection to counter 124, and counter
122 measures the total time duration of the several cycles. Use
of multiple cycles rather than a single cycle provides enhanced
measurement resolution. The number of measurement cycles is
selected at a function of range of position measurements and
desired resolution, as well ac desired speed of the overall
measurement operation.
FIG. 7A and 7B illustrate circuitry on
power/display/driver board 60. In particular, FIG. 7A
illustrates a power supply 140 for supplying power to the
remainder of the control electronics. It will be noted that
input power is received from master controller 36 through
connector 64. Power is supplied to position transducer 80
through connector 66. Thus, in the event of loss of connection
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1 3356~5
to master controller 36, power is automatically removed from
valve torque motor 49 (FIG. 2) so that spool 44 and actuator
24 automatically return to the null position. Of course, ROM
104 (~IG. 5A) is nonvolatile so that control programming is not
lost in the event of power loss. ~IG. 7B illustrates address
switches 74 connected to the microprocessor control electronics
through soc~et Sl and plug Pl (FIG. SB). By removal of panel
70 (FIGS. 2-3), an operator may select unique addresses for
each of the ~alve controllers 32 (FIG. 1) so that master
controller 36 can communicate therewith. Programming suitable
for controlling microprocessor 100 (FIG. 5A) to perform the
operations hereinabove described will be self-evident to the
artisan in view of such detailed description.
In valve driver 76, an operational amplifier has one
input which receives differentiated pulses from the highpass
filter C6, R5 (FIG. SA) and a second input referenced to ground.
The amplifier output thus alternately switches from positive
to negative under control of the pulse width modulated signal.
It will be noted that, in the absence of such control signals,
the amplifier output is at ground, centering spool 44 in manifold
42 and arresting all motion. The minimum pulse frequency is set
by capacitor C6 (FIG. 5A). The back-to-back zener diodes Z2,
Z3 across the amplifier limit output voltage to ~ 12 volts
without requiring separate supply regulation. Inherent
amplifier slew rate eliminates EMI problems. It will also be
noted that driver 76 i8 a single-input driver, not requiring a
separate direction - control input.
FIG. 8 illustrates a watchdog timer 150 which may be
employed in place of timer 110 (FIG. 5A) in the preferred
embodiment of the invention. Watchdog timer 150 includes an
oscillator 152 which receives the pulse width modulated output
of microprocessorl00 (FIG. 5A) through capacitorC6todisenable
or inhibit oscillator operation as long as the frequency of
such microprocessor output remains above a threshold level set
by resistor Rl and capacitor Cl. When oscillator operation is
enabled,a continuous train of pulsed reset signalsata frequency
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1 335605
determined resistor R2 and capacitor C2 is æupplied to the reset
input of the control microprocessor. The watchdog timer 150
of FIG. 8 further embodies a separate non-pulsed output for
disabling peripheral components, and includes facility for a
manual reset input from and operator switch or the like.
FIG. 9 is a functional block diagram of position
sensor electronics whic~ may be employed in place of the
electronics of FIGS. 6A and 6B in the preferred embodiment of
the invention. In general, electronics 160 of FIG. 9 differ
from that in the preferred embodiment of the invention
hereinabove discussed primarily in that electronics 160 is more
directly controlled by microprocessor 100. The microprocessor
initiates a current pulse in transducer 80, and at the same
time enables operation of time measurement counter 122. Each
return signal reinitializes a current pulse in transducer 80
and simultaneously increments a pulse or a cycle counter 124.
When the count in counter 124 reaches the value preset directly
~y microprocessor 100, operation of counter 122 is terminated
and microprocessor 100 is so advised. Microprocessor 100 may
then inhibit propagation of further current pulses at gate 162
and read the output of counter 122 for obtaining a position
signal.
FIG. 10 illustrates a valve driver 170 which may be
employed in place of driver 76 (FIGS. 4 and 7B). A first power
MOSFET 172 has a gate which receives pulse width modulated valve
control signals from pin 16 of microprocessor 100 (FIG. SA), a
source connected to a negative voltage supply and a drain
connected to torque motor 49. A second power MOSFET 174 has a
gate connected to the gate of MOSFET 172 through an inverter 176,
a drain connected to the positive supply and a source connected
to torque motor 49. Diodes 178, 180 are connected across MOSFETS
172, 174 to limit reverse voltage spikes~ In operation, MOSFETs
172, 174 alternately connect the respective supplies to torque
motor 49 as a function of polarity of the input signal from
microprocessor 100 (FIG. ~A). Driver 170 has the advantage of
lower cost as compared with driver 76 and conventional drivers,
~ ` ~
1 335655
and would be advantageously employed in the environment of all-
digital electronics where EMI is less of a problem.
