Abstract:
An energy efficient multiple actuator control circuit is disclosed comprising a timing-slicing circuit for arranging and processing a pulsed select signal into a plurality of staggered pulse signals and a steering logic circuit for receiving the pulse signals and generating corresponding actuator enable signals. Latching solenoid actuators are arranged into position upon receipt of the pulsed actuator enable signals. The actuators maintain their position without any additional power. The circuitry is hardwired in that for a given select signal each actuator is activated into a predetermined position. The circuitry is scalable to arrange any plurality of actuators in any prearranged configuration, and the circuitry can perform properly over a broad variation of select signals.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to actuator control circuitry and, in particular, to a multiple actuator control circuit capable of arranging a plurality of push-pull latching actuators into a plurality of predetermined positions of a prearranged configuration upon the receipt of a single select signal. The circuitry is scalable in that it can arrange any number of actuators into any number of prearranged configurations upon receipt of a separate select signal corresponding to each prearranged configuration. 
     2. Description of the Prior Art 
     It is well known in many industries to utilize solenoid type actuators as switches for controlling fluid flow, gas flow, and the like. As new actuator designs have been introduced in order to reduce power consumption, so to has new circuitry been designed to control them. One new actuator design of recent years has been the latching solenoid. The latching solenoid has an advantage in utilizing less power than conventional solenoids. 
     One circuit for controlling a bistable actuator is disclosed in U.S. Pat. No. 4,409,638 issued to Sturman et al. The control circuit in Sturman is integrated into the actuator that is intended to replace conventional solenoid actuators controlling water flow in such devices as dishwashers, sprinklers, and the like. Compared to conventional solenoid actuators the integrated latching actuator in Sturman consumes substantially less power in the actuated state however the input signal must remain on at all times in order to keep the actuator in position. Maintaining the coil of the actuator in an energized state in order to maintain the actuator in a predetermined position is highly undesirable in applications where available power is generally scarce. 
     Another circuit for controlling a number of direct current operated solenoid valves is disclosed in U.S. Pat. No. 5,909,353 issued to Alberter et al. Although the circuit in Alberter is primarily designed to reduce power loss by retrieving the magnetic energy stored in the inductive coils of the solenoids when the power is turned off, the solenoids must initially be maintained in an energized state by the power source. Hence, maintaining the solenoids in a given position requires the continuous supply of direct current power to the solenoid. This is undesirable in low power applications. 
     In recent years, considerable research effort has taken place in the field of electromagnetic devices for space applications. This research has led to the development of energy-efficient, small-envelope, low-weight latching actuators. Uniquely, these devices can maintain their selected position when their inductive coils are disconnected from the power source. As used herein, a “latching actuator” refers to a switching device having at least two positions in which either position, once achieved, can be maintained without the application of a power source. The latching force for the positions of the switch are generally produced by permanent magnets, and switching between positions is accomplished by energizing the coils for a brief period of time at a magnitude sufficient to transfer the actuator armature from one latched position to another. The dual position push-pull inductive solenoid, or bistable actuator, is one example of a latching actuator. 
     The thrust of the present invention is to provide a highly reliable, energy efficient, scalable control and drive system for latching actuators adapted for use in reduced power applications such as in space. These and other difficulties of the prior art have been overcome according to the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     A preferred embodiment of the energy efficient multiple actuator control circuit according to the present invention comprises a timing-slicing circuit for arranging and processing a select signal into a plurality of staggered pulse signals and a steering logic circuit for receiving the pulse signals and generating corresponding actuator enable signals. An actuator enable signal is generated for each actuator to be controlled and preferably each enable signal has a duration greater than the actuator switching time rating of its corresponding actuator. The circuitry is hardwired in that for a given select signal each actuator is arranged into its own predetermined position. The predetermined positions of all the actuators makeup a prearranged configuration or actuator output. The circuitry is scalable to achieve any multiple of prearranged configurations of the actuators by providing separate select signal path for each prearranged configuration. 
     In one embodiment the actuators are push-pull latching solenoids having two opposed switch positions. These latching bistable solenoids do not require a constant power source to energize their inductive coils in order to maintain either switch position. Switching from one position to the other only requires the application of a reverse polarity enable signal or pulse. Latching is typically accomplished mechanically or with permanent magnets. These solenoids are well suited for use with the present invention control circuit as they can be activated to either position by the application of a pulse enable signal without the need for a continuous power supply. One such suitable bistable solenoid is disclosed in the U.S. Patent Application filed on even date herewith and identified by Attorney Docket No. 20025. Thus, the present invention control circuit significantly differs from a conventional electronic transistor type switch in that it does not utilize a small input signal to activate a short circuit path for continuous power flow. 
     A significant advantage to the present invention circuitry is that the select signal can substantially vary in voltage, current, and duration, yet still achieve the desired result of arranging the actuators into the prearranged configuration. This makes the circuitry well adapted for applications where high switching reliability is required yet the power available for achieving such switching varies. Thus the present invention circuitry is well suited for spacecraft applications, remote robotics, and the like. 
     The control circuit is able to arrange a plurality of actuators into a plurality of predetermined positions by the receipt of a single select signal. The single select signal is preferably a brief direct current pulse signal. Advantageously the select signal does not have to be continuously applied to maintain the actuators in their predetermined positions. The control circuit is able to achieve the desired actuation even when the select signal varies substantially in voltage, current or duration. The circuit is energy efficient as actuation is achieved by the select signal alone without the assistance of an additional power source. 
     The circuitry of the present invention is capable of accurately arranging the actuators into their predetermined positions in response a single select signal that can vary greatly in voltage, current and duration. The circuitry is scalable in that it can arrange any number of actuators into any number of prearranged configurations upon receipt of a separate select signal corresponding to each prearranged configuration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring particularly to the drawings for the purposes of illustration and not limitation: 
     FIG. 1 is a schematic block diagram of the actuator control circuit of the present invention where the select signal is negative. 
     FIG. 2 is a schematic block diagram of the actuator control circuit of the present invention where the select signal is positive. 
     FIG. 3 is a timing diagram of the relationship of solenoid actuation in response to a given select signal. 
     FIG. 4 is a schematic circuit diagram of the actuator control circuit controlling three actuators and having three select signal path inputs for receiving negative input signals. 
     FIG. 5 is a schematic circuit diagram of the input section of the actuator control circuit of FIG.  4 . 
     FIG. 6 is a schematic circuit diagram of the timing section of the actuator control circuit of FIG.  4 . 
     FIG. 7 is a schematic circuit diagram of the second solenoid driver and steering logic of the actuator control circuit of FIG.  4 . 
     FIG. 8 is a schematic circuit diagram of the third solenoid driver and steering logic of the actuator control circuit of FIG.  4 . 
     FIG. 9 is a schematic circuit diagram of the first solenoid driver and steering logic of the actuator control circuit of FIG.  4 . 
     FIG. 10 is a schematic circuit diagram of the actuator control circuit controlling three actuators and having three select signal path inputs for receiving positive input signals. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring particularly to the drawings there is illustrated generally at  10  an actuator control circuit. The actuator control circuit  10  is shown schematically in FIGS. 1 and 2, and comprises a timing slicing circuit  12 , a steering logic circuit  14  and actuator drivers  16 ,  18 , and  20 . Three separate signal paths are provided at  22 ,  24 , and  26  in which a single select signal pulse can be applied. Any number of separate signal paths can be provided, if desired. Each signal path correspond s to a prearranged configuration of all the actuators. The three actuator drivers  16 ,  18 , and  20  respectively control three separate actuators, however, any number of actuators and drivers can be provided, if desired. Each actuator has two positions, a forward position (Fwd) and reverse position (Rev), and for each signal path provided there is a corresponding predetermined position (either Fwd or Rev) for each actuator. Each actuator has an actuator switching time rating. As used herein, an “actuator switching time rating” is the time required to activate the switch from one position to the other. The actuator switching time rating is typically measured in milliseconds and varies substantially depending on a given actuator design. 
     In the schematics shown in FIGS. 1 and 2, when single select signal  22  is energized by the momentary closure of contact  28 , the actuator associated with driver  16  is moved to its Fwd position, the actuator associated with driver  18  is moved to its Rev position, and the actuator associated with driver  20  is moved to its Rev position. When select signal  24  is energized by the momentary closure of contact  30 , driver  16  moves its actuator to its Rev position, driver  18  moves its actuator to its Fwd position, and driver  20  moves its actuator to its Rev position. When select signal  26  is energized, driver  16  moves its actuator to its Rev position, driver  18  moves its actuator to its Rev position, and driver  20  moves its actuator to its Fwd position. Hence, each select signal path has a predetermined position for each actuator that, in combination establishes a prearranged configuration of the actuators. The prearranged configurations of the select signals shown in the figures are exemplary only and can be modified accordingly depending on the requirements of a given control application. 
     The schematics of the control circuit shown in FIGS. 1 and 2 comprise 3 main logical sections; the timing-slicing circuit  12 , the steering logic circuit  14 , and the solenoid drivers  16 ,  18 , and  20 . The single select signal is provided through either path  22 ,  24 , or  26 , upon the momentary closure of respective contacts  28 ,  30 , and  32 . The only difference between the schematics of FIGS. 1 and 2 is that in FIG. 1 the select signal is negative and in FIG. 2 the select signal is positive. The duration of the select signal is noted as “T” in the schematics, and the timing-slicing circuit divides the select signal pulse into staggered pulse signals. The number of staggered pulse signals equals the number of actuators for a given control circuit. FIG. 3 charts the division of select signal pulse of path  22  into three staggered pulse signals  34 ,  36 , and  38 , by the timing-slicing circuit  12 . The staggered pulse signals are delivered to the steering logic circuit  14 , which in turn processes these signals and generates corresponding actuator enable signals  40 ,  42 , and  44 . The enable signals are then delivered to the actuator drivers. 
     Distributing available current of the single select signal by time-slicing it among the actuators substantially minimizes the power requirements of the multiple actuator control circuit. In addition, by providing a single select signal pulse at or near the full input voltage rating of the actuators allows operation of the circuitry over a wide input voltage range. 
     The steering logic section directs the staggered pulse signals  34 ,  36 , and  38  to the appropriate solenoid drivers as enable signals  40 ,  42 , and  44  such that if select signal path  22  is momentarily energized, driver  18  and  20  will energize their actuators in the reverse direction (Rev) and driver  16  will energize its actuator in the forward direction (Fwd). The steering logic section in effect incorporates the predetermined configuration of each separate select signal. Thus, the steering logic section must be designed to deliver the enable signals to the actuators according to their predetermined position for each predetermined configuration. 
     The diodes  46  in each driver sections have dual functions. They function as part of the solenoid drivers and also as part of the steering logic. Diode D 1  protects the circuit from accidental application of input voltage in reverse and makes the circuitry inoperative until the condition is corrected. Diodes D 2 , D 3  and D 4  make power available to the timing and steering sections when any of the switch position selection pulse is present. 
     The function of the timing-slicing and steering sections may be implemented using a microcontroller or digital logic integrated circuits. However, the high cost and limited availability of such screened components may be a deciding factor in excluding the use of microcontroller or digital integrated circuits in some applications. 
     The following embodiments make use of discrete semiconductors that are readily available in screened versions. These embodiments have a wide input operating voltage range and do not require fixed voltage for operation as microcontrollers or digital integrated circuits do. FIGS. 4 through 9 show embodiments designed to accept negative voltage select signal pulses having duration “T” of 100 milliseconds. 
     In the preferred embodiment referred to for purposes of illustration, in FIG. 4 is the multiple actuator control circuit  10  adapted to receive negative voltage select signal pulses. In this embodiment three actuators are controlled whose actuator solenoids are designated as L 1 , L 2 , and L 3  respectively, however more or less actuators may be controlled, if desired. The following description will be described when select signal position  1  is energized by connecting SEL  1  terminal to the supply ground. It is desirable that the pulse duration of the SEL  1  signal approximately equal to or greater than the sum of all the actuator switching times. In the embodiments shown, each actuator switching time rating is, for example 25 milliseconds, and the pulse duration should at least approximately equal or exceed the sum total of the switching time ratings. Although the sum total for the three switches in the embodiments shown is 75 milliseconds, the pulse duration of the SEL  1  signal is preferably set for 100 milliseconds. The outputs of actuator solenoids L 1 , L 2 , and L 3  in this example correspond to the outputs previously discussed and shown in the chart of FIG.  3 . 
     SELECT SIGNAL INPUT SECTION 
     FIG. 5 shows the select signal input section of the circuit of FIG.  4 . The COM+ terminal is connected to a positive voltage supply. D 1  provides protection for the circuit against reverse polarity. When SEL  1  is at ground, D 2  conducts bringing circuit NET B close to supply ground. Since the values of R 2  and R 18  are equal, the voltage at the emitter of Q 4  is one half that of the input voltage. Current flows through R 1  and R 12  and since the value of R 1  is lower than that of R 12 , the base of Q 4  is more positive than its emitter, causing Q 4  to conduct. Q 4  causes the base of Q 1  to be more negative than its emitter through R 8  causing Q 1  to conduct. The conducting Q 1  provides input power to the timing and steering logic sections. 
     If one or two more other select signal switch positions are inadvertently energized at the same time as SEL  1 , R 12  will effectively be in parallel with R 10  and/or R 11 . The effective resistance of R 12  in parallel with R 10  and/or R 11  is lower than R 1  and will make the base of Q 4  negative compared to its emitter, turning Q 4  off and turning Q 1  off. With Q 1  off, the timing and steering logic sections are disabled and the entire circuit becomes inoperative. R 1 , R 2  R 3 , R 8 , R 10 , R 11 , R 12 , R 18 , Q 4  and Q 1  can be deleted if it can be guaranteed that only one select signal position will be selected at any given time. If deleted, circuit NET A is connected directly to circuit NET C as shown by the top dashed line in FIG.  5 . 
     TIMING-SLICING SECTION 
     FIG. 6 shows the timing-slicing section. This section generates the internal staggered pulse signals designated as REV A, REV B, and FWD. Q 2  and Q 3  turn on after a delay time set by the RC network at their bases. The RC network values are selected for a delay of about 33 milliseconds. The Zener diodes and associated resistors, D 7 -R 13 , D 5 -R 7 , D 8 -R 14 , and D 6 -R 21  stabilize the delay time over the input voltage range. At the beginning of the select pulse, Q 2 , Q 3  and Q 6  are initially off. With Q 6  off, circuit net REV A is positive through R 5 . R 17  applies a positive voltage to the base of Q 5 , which is turned on. With Q 5  on, circuit net REV B is close to supply ground. Circuit net FWD is also close to supply ground because Q 3  is still off. These conditions create the first ⅓ of the internal staggered pulse signal sequence. 
     Initially the anode of D 7  is at −10 volts from NET C charging C 1  through R 6 . After about 33 milliseconds, Q 2  turns on, which then turns on Q 6 . With Q 6  on, circuit REV A goes down close to supply ground. With Q 3  still off, R 17  stops applying positive voltage to the base of Q 5 , which turns Q 5  off. With Q 5  off, circuit net REV B becomes positive through R 4 . These conditions create the second ⅓ of the internal staggered pulse signal sequence. 
     The turn on of Q 6  makes the anode of D 8  at −10 volts from NET C 1 , charging C 2  through R 9 . After about 33 milliseconds (about 66 milliseconds from the start of the select pulse), Q 3  turns on making circuit net FWD positive. The turn on of Q 3  applies positive voltage to the base of Q 5  through R 15 , turning on Q 5 . With Q 5  on, circuit net REV B is again close to supply ground. Q 3  is left in the on condition making circuit net FWD positive until the select pulse disappears. The net FWD is taken from the junction of C 3 , R 20 , and R 47  which delays the FWD signal to prevent it from being on at the same time as the REV B signal. Q 6  is still on making circuit net REV A close to supply ground. These conditions create the last ⅓ of the internal staggered pulse signal sequence. 
     Referring to FIG. 3, the REV A, REV B, and FWD staggered pulse signals, designated as  34 ,  36 , and  38  respectively, preferably have a pulse duration that is equal to or greater than the actuator switching time ratings of the actuators. This is preferred since the pulse duration of each enable signal matches the pulse duration of its corresponding staggered pulse signal, and the enable signal must be long enough to insure complete switching of the actuators. In the embodiments shown, the SEL  1  pulse duration is 100 milliseconds which, when split, provides a pulse duration of 33 milliseconds for each staggered pulse signal. Providing a 33 millisecond duration of the staggered pulse insures complete switching of all actuators since it somewhat exceeds 25 millisecond actuator switching time rating of each actuator. The staggered pulse signals do not need to have the same pulse duration as shown, and they can accordingly vary particularly when the switches have different actuator switching time ratings. 
     ACTUATOR SOLENOID DRIVER  1  AND STEERING LOGIC 
     FIG. 9 shows the actuator solenoid L 1  driver and steering logic. Q 7 , Q 8 , Q 13 , Q 14 , R 22 , R 23 , R 28 , R 29 , D 9 A, D 9 B, D 15 , D 16  and D 17  form the solenoid driver. Q 21 , Q 22 , R 35 , R 36 , R 44 , R 42 , R 48 , D 21 , D 22 , and D 23  form the steering logic. Diodes D 15 , D 16 , and D 17  are also part of the steering logic. 
     When select signal SEL  1  is activated, D 15  and D 23  will conduct while the other diodes function as open circuits. During the last ⅓ of the selection pulse the staggered pulse FWD is positive turning on Q 22  through R 42 . Q 22  makes the base of Q 14  negative through R 36  with respect to NET A. Q 14  and Q 8  are turned on making the right side of solenoid L 1  positive. The left side of solenoid L 1  is close to supply ground through D 15 . Under these conditions the solenoid L 1  moves to the on position during the last ⅓of the selection pulse. D 9 A and D 9 B protect the driver transistors by clamping the spikes generated by the solenoid when current through the solenoid is abruptly cut off. 
     ACTUATOR SOLENOID DRIVER  2  AND STEERING LOGIC 
     FIG. 7 shows the actuator solenoid L 2  driver and accompanying steering logic. Q 9 , Q 10 , Q 15 , Q 16 , R 24 , R 25 , R 30 , R 31 , D 1 OA, D 1 OB, D 18 , D 19  and D 20  form the solenoid driver. Q 23 , Q 24 , Q 19 , R 37 , R 34 , R 43 , R 40 , R 45 , R 49 , R 50 , D 24 , D 25 , D 26  form the steering logic. Diodes D 18 , D 19 , and D 20  are also part of the steering logic. 
     When select signal SEL  1  is activated, D 24  and D 19  conduct while the other diodes function as open circuits. During the first ⅓ of the selection pulse the staggered pulse REV A is positive turning on Q 23  through R 43 . Q 23  makes the base of Q 15  negative through R 37  with respect to NET A. Q 15  and Q 9  are turned on making the voltage on left side of solenoid L 2  positive. The right side of solenoid L 2  is close to supply ground through D 19 . Under these conditions the solenoid L 2  moves to the off position during the first ⅓ of the selection pulse. D 1 OA and D 1 OB protect the driver transistors by clamping the spikes generated by the solenoid when the current through the solenoid is abruptly cut off. 
     ACTUATOR SOLENOID DRIVER  3  AND STEERING LOGIC 
     FIG. 8 shows the actuator solenoid L 3  driver and accompanying steering logic. Q 11 , Q 12 , Q 17 , Q 18 , R 26 , R 27 , R 32 , R 33 , D 11 A, D 11 B, D 12 , D 13  and D 14  form the solenoid driver. Q 25 , Q 20 , R 38 , R 39 , R 46 , R 41 , R 51 , D 27 , D 28 , D 29  form the steering logic. Diodes D 12 , D 13 , and D 14  are also part of the steering logic. 
     When select signal SEL  1  is activated, D 27  and D 13  conduct while the other diodes function as open circuits. During the second ⅓ of the selection pulse the staggered pulse REV B is positive turning on Q 25  through R 46 . Q 25  makes the base of Q 17  negative through R 38  with respect to NET A. Q 17  and Q 11  are turned on making the left side of solenoid L 3  positive. The right side of solenoid L 3  close to supply ground through D 13 . Under these conditions the solenoid L 3  moves to the off position during the second ⅓ of the selection pulse. D 11 A and D 11 B protect the driver transistors by clamping the spikes generated by the solenoid when current through the solenoid is abruptly cut off. 
     The embodiment of FIG. 10 shows the multiple actuator control circuit configured to receive positive voltage select pulse signals. This embodiment is identical to that shown in FIG. 4 except that the polarity of the diodes and transistors reversed. 
     In the embodiments shown in FIGS. 4 and 10, the select signal is anticipated to be a direct current voltage pulse between 14 to 32 volts having a duration of approximately 100 milliseconds. As those in skilled in the art recognize the circuitry and sizing of the components can easily be adapted to account for any variety of direct current voltage pulses. By way of example, the select signals can comprise pulsed direct current signals having a pulse amplitude between about plus or minus 40 volts. 
     What has been described are preferred embodiments in which modifications and changes may be made without departing from the spirit and scope of the accompanying claims.