Actuator driving apparatus and method

Abstract

 An actuator driving apparatus (10) comprising at least one processing circuit (12) including: a first switching device (32) placed between an exciting coil (14) of an actuator and a dc power source (16,18) and operated by a pulse-width modulated signal (S4) generated so as to correspond to an overexciting period (T2) and a holding period (T3) subsequent to the overexciting period (T2) in a drive period (T1); a reflux circuit (36) connected in parallel to the exciting coil (14) and including a fly-wheel diode (44) and a second switching device (42) connected in series to the fly-wheel diode (44); and a disconnection signal generator (38) sending a disconnection signal (S5) to the second switching device (42) for a predetermined period after the termination of the drive period (T1). The fly-wheel diode (44) is provided so that a current generated from one end of the exciting coil (14) toward the other end when turning off the first switching device (32) can be recirculated. The second switching device (42) is turned off by the disconnection signal (S5) to be generated with the termination of the drive period (T1) to interrupt the flow of current to the exciting coil (14).

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to an actuator driving apparatus and an actuator driving method for efficiently driving the actuator.

Description of the Related Art

[0002] Patent documents 1, 2 and 3 describe relating to apparatus for driving an actuator, such as a solenoid as an inductive load, employed as a driving device in a fluid-jet loom.

[0003] A technique disclosed in Patent document 1 relates to an exciting circuit for a solenoid valve employed in a loom. More specifically, the exciting circuit includes a first switching device connected to an overexciting power source and controlled so as to close for a predetermined exciting time from the start of excitation, and a second switching device connected to a holding power source and controlled by an operation signal. An excitation coil is excited by a logical OR signal obtained from the output signals of the first and the second switching device.

[0004] This technique applies a voltage higher than a rated voltage and provided by the overexciting power source to the excitation coil for a predetermined time to activate the solenoid quickly, and then applies a voltage lower than the rated voltage and provided by the holding power source to the excitation coil to restrain the heat generation of the excitation coil.

[0005] Techniques disclosed in Patent documents 2 and 3 use a power circuit provided with a switching device for supplying power to the excitation coil of a solenoid and control the excitation coil by a pulse width modulation signal (PWM signal) to enhance the speed of response of the solenoid to an operation signal.

[Patent document 1]

[0006] JP-U 49367/1991 (Fig. 1, lines 28 to 31 in column 4 on page 2, and lines 28 to 31 in column 5 on page 3)

[Patent document 2]

[0007] JP-U 31884/1995 (paragraph No. 0002)

[Patent document 3]

[0008] JP-A 9945/1985

[0009] The technique disclosed in Patent document 1 needs the two power sources for overexcitation and holding, and the two switching devices. The manufacturing cost of the driving apparatus is therefore high. The high manufacturing cost of the driving apparatus is a serious problem in a loom provided with a plurality of apparatuses for driving solenoid valves for a plurality of picking nozzles of a picking device of an air-jet loom.

[0010] The techniques disclosed in Patent documents 2 and 3 do not use overexcitation for driving the solenoid and hence the solenoid cannot quickly be actuated. In particular, the slow response of the actuator is unignorable problems in the picking device of the loom in which the actuator is required to respond quickly.

SUMMARY OF THE INVENTION

[0011] Accordingly, it is an object of the present invention to provide an inexpensive actuator driving apparatus capable of driving an actuator for quick response.

[0012] According to a first aspect of the present invention, an actuator driving apparatus comprising at least one processing circuit including: a first switching device placed between an exciting coil of an actuator and a dc power source and operated by a pulse-width modulated signal generated so as to correspond to an overexciting period and a holding period subsequent to the overexciting period in a drive period; a reflux circuit connected in parallel to the exciting coil and including a fly-wheel diode and a second switching device connected in series to the fly-wheel diode; and a disconnection signal generator sending a disconnection signal to the second switching device for a predetermined period after the termination of the drive period; wherein the fly-wheel diode is provided so that a current generated from one end of the exciting coil toward the other end when turning on the first switching device can be recirculated; and wherein the second switching device is turned off by the disconnection signal to be generated with the termination of the drive period to interrupt the flow of current to the exciting coil.

[0013] According to a second aspect of the present invention, an actuator driving method to be carried out by an actuator driving apparatus comprising at least one processing circuit including: a first switching device placed between an exciting coil of an actuator and a dc power source and operated by a pulse-width modulated signal generated so as to correspond respectively to an overexciting period and a holding period subsequent to the overexciting period in a drive period; and a reflux circuit connected in parallel to the exciting coil and including a fly-wheel diode and a second switching device connected in series to the fly-wheel diode; and wherein the fly-wheel diode is provided so that an electric current generated from one end of the exciting coil toward the other end when turning off the first switching device can be recirculated; and wherein the method comprising steps of the second switching device is at least turned on when the pulse-width modulated signal is not outputted for the drive period to permit the reflux and turned off at the termination of the drive period to interrupt the reflux.

[0014] The first switching device is driven by a PWM signal generated so as to correspond to the overexciting period and the holding period subsequent to the overexciting period in the predetermined drive period, and the exciting coil of the actuator is connected electrically to the dc power source according to the PWM signal.

[0015] More specifically, the PWM signal corresponding to the holding period has a small duty factor as compared with that of the PWM signal corresponding to the overexciting period. Therefore, the voltage from the dc power source is applied for a long time to the exciting coil in the overexciting period and is applied for a short time to the exciting coil in the holding period. In the drive period, the current generated by the counterelectromotive force induced in the exciting coil when the PWM signal is stopped is permitted to flow through the fly-wheel diode to the exciting coil. Thus, the current generated by the exciting coil flows through the exciting coil after a power feed from the dc power source to the exciting coil has been stopped in the short holding period of the drive period. Consequently, a current lower than that of the current supplied to the exciting coil in the overexciting period is supplied to the exciting coil in the holding period. Thus, the dc power source is used as a common power source for supplying power for both overexciting and holding, the driving apparatus having less switching devices is capable of achieving overexciting and holding, and hence the driving apparatus is inexpensive.

[0016] Delayed off-action of an actuator is a problem to an industrial machine that requires the actuator to respond quickly. Therefore, the present invention holds the second switching device in an open state for a predetermined time subsequent to the drive period to prevent the reverse flow of the current to the exciting coil.

[0017] Even if an inductive electromotive force (hereinafter, referred to as "counterelectromotive force") is induced in the exciting coil when current supply to the exciting coil is stopped by opening the first switching device after the termination of the drive period, the reverse flow of the current through the fly-wheel diode to the exciting coil is interrupted by opening the second switching device. Consequently, the exciting coil can quickly be de-energized. The actuator can be turned on and turned off in an optimum mode because the exciting coil is driven for overexciting and holding only for the duration of the drive signal.

[0018] One end of the fly-wheel diode may be connected to one end of the exciting coil, and the other end of the fly-wheel diode may be connected only through the second switching device to the other end of the exciting coil.

[0019] As the second switching device, an n-channel FET may be used, one end of the exciting coil at which a current generated by counterelectromotive force induced in the exciting coil appears at the termination of the drive period may be connected to a drain terminal of the FET and may be connected through a resistor to a gate terminal of the FET. This configuration is able to reduce the number of circuit elements necessary for driving the FET.

[0020] The actuator driving apparatus may further include a surge absorber connected to the opposite ends of the exciting coil to absorb a current generated by counterelectromotive force induced at the termination of the drive period. The surge absorber reduces noise that may be generated upon interruption of the power feed to the exciting coil at the termination of the drive period.

[0021] The actuator driving apparatus includes a plurality of processing circuits respectively corresponding to a plurality of exciting coils, wherein one ends of the exciting coils at which currents generated by counterelectromotive force appear are connected electrically through diodes included in the processing circuits, respectively, to one end of the surge absorber, and the other ends of the exciting coils are connected electrically to the other end of the surge absorber. Thus, the single surge absorber is used effectively in combination with the plurality of processing circuits.

[0022] The actuator driving apparatus may be applied to driving an actuator included in the picking device of a fluid-jet loom. The actuator driving apparatus is capable of reducing a delay (drive period) in stopping driving the actuator after the receipt of a stop command. For example, when the actuator driving apparatus is applied to driving an actuator for opening and closing a valve for controlling the supply of a fluid to the main picking nozzle (or sub picking nozzle) of a loom, it is possible to prevent damaging the weft yarn by useless jetting of a picking fluid and wasting the picking fluid. When the actuator driving apparatus is applied to driving the actuator of a weft measuring-storing device (solenoid for operating a stopper pin), incorrect length measurement of the weft yarn due to delay in the operation of the stopper pin can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a schematic circuit diagram of an actuator driving apparatus in a preferred embodiment according to the present invention;

Fig. 2 is a schematic circuit diagram of an overcurrent detector included in the actuator driving apparatus shown in Fig. 1; and

Fig. 3 is a time chart of assistance in explaining the operation of the actuator driving apparatus shown in Fig. 1.

DETATILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Referring to Figs. 1 to 3, an actuator driving apparatus 10 in a preferred embodiment according to the present invention includes a plurality of processing circuits 12. Exciting coils 14 are connected to the processing circuits 12, respectively. The exciting coil 14 is a drive coil included in an actuator, such as a solenoid actuator, and acts as an inductive load. In this actuator driving apparatus 10, the exciting coils 14 are solenoids.

[0025] Actuators to be driven by the actuator driving apparatus 10 are supposed to be solenoid valves in the following description. Therefore, the exciting coils 14 are the drive coils of the solenoid valves.

[0026] The positive electrode 16 and the earth electrode (negative electrode) 18 of a direct current, i.e., dc power source are connected electrically to each processing circuit 12. A common surge absorber 20 is connected in parallel to the exciting coils 14 of the plurality of processing circuits 12. The supply voltage of the dc power source is, for example, in the range of 1.5 to 5 times the rated voltage of the exciting coils 14.

[0027] The terminals 22 and 24 of the surge absorber 20 are connected electrically to the positive electrode 16 and the processing circuits 12, respectively. In this embodiment, the terminal 22 is connected electrically through an overcurrent detector 26 to the positive electrode 16.

[0028] The surge absorber 20 is an electric device capable of consuming electric energy and converting the electric energy into thermal energy, such as a varistor or a CR circuit what is called a snubber circuit. If the surge absorber 20 is a varistor, the surge absorber 20 absorbs electric energy only when a surge occurs, which is very effective in saving electricity.

[0029] A loom controller, not shown, gives a drive signal S1 shown in Fig. 3(A) to each processing circuit 12. For example, if a picking device, included in an air-jet loom, has a main picking nozzle, and a plurality of sub picking nozzles arranged along the width of the air-jet loom to jet air sequentially into a shed, the drive signals S1 are given to the processing circuits 12 corresponding to the main picking nozzle and the sub picking nozzles at predetermined jetting times, respectively.

[0030] A pulse generator 28 generates a pulse signal S2 having a constant frequency, and sends the pulse signal S2 to the plurality of processing circuits 12. As shown in Fig. 3(C), the pulse signal S2 includes periodic pulses that are generated regardless of the HIGH(ON) and the LOW(OFF) state of the drive signal S1.

[0031] The drive signal S1 is applied to an overexcitation signal generator 30 included in each processing circuit 12. Each overexcitation signal generator 30 generates an overexcitation signal S3 that is held HIGH for a fixed period, such as a period in the range of 5 to 10 ms from the leading edge of the pulse of the drive signal S1 as shown in Fig. 3(B). Thus, the drive signal S1, the overexcitation signal S3 responsive to the drive signal S1 and the pulse signal S2 are give to each processing circuit 12.

[0032] Each processing circuit 12 includes an n-channel field-effect transistor (hereinafter, abbreviated to "FET") 32 as a switching device, a pulse-width modulated signal generator (PWM signal generator) 34 that generates a pulse-width modulated signal (PWM signal) S4 by pulse-width modulation on the basis of the drive signal S1, the pulse signal S2 and the overexciting signal S3, i.e., the input signal, a reflux circuit 36 connected in series to the FET 32, a disconnection signal generator 38 for electrically disconnecting the reflux circuit 36 from the exciting coil 14 according to the drive signal S1, and a diode 40 for preventing a reverse flow.

[0033] The exciting coil 14 has a terminal 46 electrically connected to the terminal 22 of the surge absorber 20, and a terminal 48 electrically connected through the diode 40 to the terminal 24 of the surge absorber 20. The diode 40 is connected to the terminal 48 at which a current generated by the counterelectromotive force appears and the terminal 22 of the surge absorber 20. More specifically, the anode terminal of the diode 40 is connected to the terminal 48 of the exciting coil 14 and the cathode terminal of the same is connected to the terminal 24 of the surge absorber 20.

[0034] The drain terminal D and the source terminal S of the FET 32 are connected electrically to the terminal 48 of the exciting coil 14 and the earth terminal 18, respectively, such that the FET 32 is connected in series to the exciting coil 14.

[0035] More specifically, the drain terminal D of the FET 32 is connected to the terminal 48 of the exciting coil 14, and the source terminal S of the same is connected to the earth terminal 18. The PWM signal S4 generated by the PWM signal generator 34 is applied to the gate terminal G of the FET 32, i.e., a first switching device. The FET 32 is turned on, i.e., the drain terminal D and the source terminal S are connected, when the PWM signal S4 goes HIGH. Consequently, a dc power source, not shown, is able to feed power to the exciting coil 14.

[0036] The PWM signal generator 34 generates a logical OR signal obtained by logical OR of the overexcitation signal S3 and the pulse signal S2 as the PWM signal S4 while the drive signal S1 is HIGH. The PWM signal S4 is applied to the gate terminal G of the FET 32 to turn on and off the FET 32. Consequently, the terminal 48 and the exciting coil 14 and the earth terminal 18 are electrically connected and disconnected.

[0037] The duty factor of the pulse signal S2 generated by the pulse generator 28 is 50% in the embodiment that will be descried later. The value of the duty factor may be a small value in the range of 20% to 60% suitable for maintain a holding state after overexcitation. Preferably, the overexcitation signal S3 generated by the overexcitation signal generator 30 is a pulse signal having a duty factor of 100% and remaining HIGH for a predetermined period. The duty factor of the overexcitation signal S3 may be smaller than 100% and larger than the duty factor of the pulse signal S2. For example, the duty factor of the overexcitation signal S3 may be in the range of 70% to 100%. The duty factors may be determined taking into consideration the response characteristic of the actuator, the condition of a holding operation and the heat generation of the exciting coil 14.

[0038] The reflux circuit 36 makes a current generated by the counterelectromotive force induced in the exciting coil 14 flow through the exciting coil 14. The reflux circuit 36 has a series circuit formed by connecting a FET 42 and a fly-wheel diode 44 in series, and connected in parallel to the exciting coil 14.

[0039] More specifically, the anode terminal of the fly-wheel diode 44 is connected to the terminal 48 of the exciting coil 14, and the cathode terminal of the same is connected to the drain terminal D of the FET 42. The source terminal S of the FET 42 is connected to the terminal 46 of the exciting coil 14. When a voltage is induced at the terminal 48 when the exciting coil 14 is de-energized and the FET 42 is in the on state, the reflux circuit 36 permits a current to flow from the terminal 48 toward the terminal 46.

[0040] The disconnection signal generator 38 generates a disconnection signal S5 shown in Fig. 3(E) that goes HIGH when the drive signal S1 is LOW, and goes LOW when the drive signal S1 is HIGH. The disconnection signal S5 is given to a switching circuit 56 included in a reflux controller 50.

[0041] The reflux controller 50 controls the flow of a current generated by the counterelectromotive force induced in the exciting coil 14. The reflux controller 50 includes a Zener diode 52, a resistor 54 connected in series to the Zener diode 52, and the switching circuit 56 connected in parallel to the Zener diode 52.

[0042] The series circuit consisting of the Zener diode 52 and the resistor 54 is connected in parallel to the series circuit of the FET 42 and the fly-wheel diode 44, and to the exciting coil 14. The joint of the Zener diode 52 and the resistor 54 is connected electrically to the gate terminal G of the FET 42.

[0043] The switching circuit 56 is connected electrically to the source and the gate of the FET 42, and the anode and the cathode of the Zener diode 52. More specifically, the anode and the cathode of the Zener diode 52 are connected to the source terminal S and the gate terminal G of the FET 42, respectively. The switching circuit 56 includes, for example, a contact or contactless switch. The output terminals of the switching circuit 56 are connected or disconnected according to the disconnection signal S5.

[0044] The switching circuit 56 connects the source and the gate of the FET 42 electrically to the anode and the cathode of the Zener diode 52 when the disconnection signal S5 goes HIGH, and disconnects the source and the gate of the FET 42 electrically from the anode and the cathode of the Zener diode 52 when the disconnection signal S5 goes LOW.

[0045] The resistance of the resistor 54 may be several kilohms. The resistor 54 generates a voltage difference across the drain terminal D and the source terminal S of the FET 42.

[0046] The terminal 48 of the exciting coil 14 is connected electrically through the fly-wheel diode 44 to the drain terminal D of the FET 42 and through the resistor 54 to the gate terminal G of the FET 42. The cathode of the fly-wheel diode 44 is connected electrically through the FET 42 to the terminal 46 of the exciting coil 14.

[0047] The Zener diode 52 is connected in parallel to the FET 42. The anode and the cathode of the Zener diode 52 are connected electrically to the terminal 46 of the exciting coil 14 and the resistor 54 connected to the gate terminal G of the FET 42, respectively.

[0048] The inductive electromotive force is induced in the exciting coil 14 when current supply to the FET 32 is stopped and a current generated by the inductive electromotive force appears at the terminal 48. Then, the potential of the terminal 48 rises sharply, causing the Zener diode 52 connected to the terminal 48 to breakdown. Consequently, the potential of the gate terminal G of the FET 42 rises beyond that of the source terminal S, the FET 42 is turned on, i.e., the drain terminal D and the source terminal S are connected, and the reflux circuit 36 is able to make the current generated by the inductive electromotive force flow from the terminal 48 through the fly-wheel diode 44 to the terminal 46.

[0049] When the output terminals of the switching circuit 56 are connected electrically by the disconnection signal S5, the potential of the gate terminal G of the FET 42 is equal to that of the source terminal S of the same even if the current generated by the inductive electromotive force at the stoppage of current supply to the exciting coil 14 appears at the terminal 48. Therefore, the FET 42 is turned off, i.e., the drain terminal D and the source terminal S are electrically disconnected, and the reflux circuit 36 is unable to make the current generated by the inductive electromotive force flow from the terminal 48 through the fly-wheel diode 44 to the terminal 46. Thus, the reflux controller 50 is able to use the inductive electromotive force, i.e., the counterelectromotive force, induced in the exciting coil 14 when power supply to the exciting coil 14 is stopped for operating the FET 42, and to control the flow of the current generated by the inductive electromotive force induced in the exciting coil 14 when current supply to the exciting coil 14 is stopped.

[0050] In the actuator driving apparatus 10, the plurality of exciting coils 14 are included in the plurality of processing circuits 12, respectively, and the exciting coils 14 can individually be driven. Preferably, the processing circuits 12 are provided with the diodes 40, respectively, and the single surge absorber 20 is common to all the processing circuits 12.

[0051] More specifically, the circuit shown in Fig. 1 is provided with the single surge absorber 20 for the plurality of processing circuits 12, one of the terminals of the surge absorber 20 is connected to the output terminal 22 of the overcurrent detector 26. The anode terminals of diodes 40 are connected to the terminals 48 of the corresponding exciting coils 14, respectively, and the cathode terminals of the same are connected collectively to the terminal 24 connected to the other terminal of the surge absorber 20.

[0052] Each diode 40 permits the flow of current from the terminal 48 of the exciting coil 14 through the terminal 24 to the surge absorber 20. Since the surge absorber 20 is common to all the processing circuit 12, the actuator driving apparatus 10 needs only the single surge absorber 20 and hence the actuator driving apparatus 10 can be manufactured at a low cost.

[0053] The overcurrent detector 26 is operative on excessive currents to protect the actuator driving apparatus 10. The overcurrent detector 26 may include a general current detecting circuit or a protective circuit.

[0054] Referring to Fig. 2, the overcurrent detector 26 may include a limiting circuit 58 capable of current monitoring and L-shaped current limitation, a closed circuit provided with a FET 60, a resistor 62 for voltage detection, and an overcurrent detecting circuit 64 for detecting excessive current on the basis of the voltage difference across the resistor 62.

[0055] The overcurrent detector 26 sends an overcurrent detection signal provided by the overcurrent detecting circuit 64 to a CPU included in the loom controller, not shown. Upon receipt of the overcurrent detection signal, the CPU of the loom controller applies a signal to the gate of the FET 60 to turn off the FET 60. Consequently, the power feed to the processing circuits 12 is interrupted.

[0056] The overcurrent detector 26 may internally be provided with a circuit (in the first processing circuit 12) that forcibly makes the PWM signal S4 go LOW to open the FET 32 in response to an overcurrent signal. The overcurrent detector 26 may externally be provided with such a circuit that gives an overcurrent signal to disconnect the dc power source from the actuator driving apparatus 10. The actuator driving apparatus 10 may be provided with a warning means that operates when an excessive current is detected to inform the operator to that effect.

[0057] The operation of the actuator driving apparatus 10 will be described with reference to Figs. 1 and 3.

[0058] When the exciting coil 14 does not need to be energized, the loom controller gives the LOW drive signal S1 to the processing circuit 12 including the exciting coil 14.

[0059] The PWM signal generator 34 is off while the drive signal S1 is LOW and hence the FET 32 is kept open. Consequently, any dc current is not supplied to the exciting coil 14 and hence the exciting coil 14 is not energized.

[0060] The disconnection signal generator 38 gives the HIGH disconnection signal S5 to the switching circuit 56 when the drive signal S1 is LOW. Consequently, the switching circuit 56 is closed to short-circuit the anode and the cathode of the Zener diode 52, and the source terminal S and the drain terminal D of the FET 42.

[0061] When the exciting coil 14 needs to be energized, the loom controller gives the HIGH drive signal S1 to the processing circuit 12 including the exciting coil 14. Thus, the PWM signal generator 34 is actuated to generate the overexcitation signal S3. Consequently, A drive period T1 and an overexcitation period T2 are started simultaneously

[0062] The disconnection signal S5 goes LOW when the drive signal S1 goes HIGH. Consequently, the switching circuit 56 opens to separate the anode and the cathode of the Zener diode 52 electrically.

[0063] The supply voltage of the dc power source is applied to the exciting coil 14, a current flows through the exciting coil 14, and the potential of the terminal 48 of the exciting coil 14 becomes lower than that of the terminal 46. As the voltage thus drops, a current flows from the anode toward the cathode of the Zener diode 52, the potential of the gate terminal G of the FET 42 drops below that of the source terminal S of the FET 42. Consequently, the FET 42 is turned off to disconnect the cathode of the fly-wheel diode 44 electrically from the terminal 46.

[0064] In the drive period T1, the FET 32 is turned on every time the PWM signal S4 goes HIGH. When the terminal 48 of the exciting coil 14 is thus connected electrically to the earth terminal 18, the exciting coil 14 is energized and a current flows in the direction of the arrow A. Since the PWM signal S4 is held HIGH during the overexcitation period T2, the exciting coil 14 is energized continuously in the overexcitation period T2. Thus, the dc power source feeds power of a voltage several times the rated voltage of the exciting coil 14 to the exciting coil 14 to keep the exciting coil 14 in an overexcited state for a predetermined period. Thus, the actuator operates quickly.

[0065] The actuator is supposed to be a solenoid valve and the exciting coil 14 is the solenoid of the solenoid valve in this embodiment. When the exciting coil 14 is energized, the valve element of the solenoid valve moves from a closing position to an opening position. In the overexcitation period T2 shown in Fig. 3(G), the exciting current decreases as impedance changes with the movement of the valve element. However, the exciting current is supplied continuously to the exciting coil 14 and the exciting coil 14 holds the solenoid valve in an open state.

[0066] The PWM signal S4 changes into a pulse signal that goes alternately LOW and HIGH after the termination of the overexcitation period T2. Thus, a holding period T3 follows the overexcitation period T2.

[0067] In the holding period T3, the PWM signal generator 34 generates, as the PWM signal S4, a pulse signal synchronous with the pulse signal S2. Consequently, the FET 32 is turned on and off alternately according to the PWM signal S4. In Fig. 3, reference characters a and b denote periods in which the PWM signal S4 is HIGH and those in which the PWM signal S4 is LOW, respectively.

[0068] When the FET 32 is turned off, counterelectromotive force is induced at the terminal 48 of the exciting coil 14 due to the sudden interruption of current. Since the FET 42 is turned off and hence the fly-wheel diode 44 is electrically disconnected from the terminal 46, the potential of the terminal 48 rises sharply and the counterelectromotive force is induced. A current generated by the counterelectromotive force flows through the resistor 54 and the Zener diode 52 in that order. Consequently, the voltage of the gate terminal of the FET is higher than that of the source terminal of the same, the FET 42 is turned on, and the current resulting from the counterelectromotive force flows through the fly-wheel diode 44 and the FET 42 in that order into the exciting coil 14 as indicated by the arrow B.

[0069] In the periods b shown in Fig. 3, the exciting current flowing through the exciting coil 14 falls gradually with time instead of falling sharply.

[0070] When the period a starts following the period b, the PWM signal S4 goes HIGH, the FET 32 is opened, and current flows into the exciting coil 14 as indicated by the arrow A in Fig. 1. Consequently, the exciting current flowing through the exciting coil 14 rises gradually with time in the period a.

[0071] The loom controller provides the LOW drive signal S1 between the termination of the drive period T1 and the start of the next drive period T1, i.e., in a predetermined period T4. Then; the disconnection signal generator 38 provides the HIGH disconnection signal S5 and the PWM signal generator 34 provides the LOW PWM signal S4.

[0072] Thus, the switching circuit 56 disconnects electrically the anode and the cathode of the Zener diode 52 to disconnect electrically the source and the drain of the FET 42. The PWM signal generator 34 does not provide any signal and the FET 32 is kept turned off.

[0073] At the termination of the drive period T1, current generated by induction, i.e., the so-called counterelectromotive force, generated at the interruption of the current flowing through the exciting coil 14 flows through the diode 40 into the surge absorber 20 as indicated by the arrow C in Fig. 1.

[0074] The power generated by the counterelectromotive force induced in the exciting coil 14 is internally consumed by the surge absorber 20 in a short period c (Fig. 3), and the current flowing through the exciting coil 14 decreases in a short time. Voltage that may appear across the exciting coil 14 and current that may flow through the exciting coil 14 under a condition where the disconnection signal generator 38 does not generate the HIGH disconnection signal S5 and the reflux current flows continuously through the fly-wheel diode 44 are indicate by dotted lines in Figs. 3(F) and 3(G) for comparison.

[0075] The present invention is applicable not only to the actuator driving apparatus for driving the solenoid valves of the picking device, but also to actuator driving apparatuses for driving the actuators, other than the solenoid valves, of the picking device, actuators of devices other than the picking device, and inductive loads of looms or devices associated with looms, such as solenoids and motors.

[0076] The actuators of the picking device, for example, are solenoid valves for controlling the air-jetting operation of the main picking nozzle and the sub picking nozzles, and solenoid actuators for operating the stopper pin and the clamper of the weft measuring-storing device. The present invention is applicable to an actuator driving apparatus for driving those actuators.

[0077] Actuators driven together with those of the picking device include, for example, the solenoid actuator and the motor for driving a weft-braking device for braking a picked weft yarn by bending the same, the solenoid valve of a tuck-in device for holding (tensioning) a picked weft yarn by air currents or for tucking in picked weft yarn by currents, and the solenoid actuator and the motor of a weft tensioning device for tensioning a picked weft yarn by pressing the picked weft yarn between pressing members or bending the picked weft yarn. The present invention is applicable to actuator driving apparatuses for driving those actuators. The present invention is applicable not only to looms, but also to a variety of industrial machines.

[0078] The present invention is applicable not only to the picking device of the loom, but also to the other devices of the loom, such as a braking system for braking the main shaft of the loom, and actuators associated with the picking motion of the loom. The present invention is applicable to actuator driving apparatuses for driving those actuators.

[0079] If noise that is generated when the actuator driving apparatus 10 de-energizes the exciting coils 14 does not affect the circuit, the surge absorber 20 may be omitted. The actuator driving apparatus 10 may be provided with a plurality of surge absorbers respectively in combination with the exciting coils 14 instead of the single common surge absorber 20. When the actuator driving apparatus 10 is provided with a plurality of surge absorbers, the diode 40 is omitted, and each of the surge absorbers is connected in parallel to the exciting coil 14.

[0080] Each processing circuit maybe provided with an overcurrent detector. The second switching device may be driven by power fed by the dc power source, or by the counterelectromotive force induced in the exciting coil 14 when the PWM signal S4 goes LOW.

[0081] The following modifications of the foregoing embodiment are possible. Both the FETs 32 and 42, i.e., the first and the second switching device, may be those of a type other than n-channel type. For example, the FETs 32 and 42 may be p-channel FETs. However, there are n-channel FETs of various types more than those of p-channel FETs available on the semiconductor market, and n-channel FETs are less expensive than p-channel FETs. The number of component parts, such as terminals, resistors and diodes, necessary for constructing the peripheral circuits of the actuator driving apparatus employing n-channel FETs is smaller than that of the peripheral circuits of the actuator driving apparatus employing p-channel FETs. The actuator driving apparatus comprising less component parts is less subject to circuit troubles and less expensive than that comprising more component parts.

[0082] Contact switching devices, such as relays, or noncontact switching devices, such as transistors, may be used as the first and the second switching device instead of the FETs.

[0083] The first switching device may be a high-side switch connected to the positive electrode of the dc power source instead of a low-side switch connected to the grounded side of the exciting coil 14 as shown in Fig. 1. When the first switching device is a high-side switch, the first switching device may be a semiconductor device, such as a transistor, other than an n-channel FET or a contact switching device capable of high-speed switching.

[0084] The circuit shown in Fig. 1 produces a potential difference necessary for operating the FET 42 in the reflux circuit 36 by effectively using the inductive electromotive force, i.e., the counterelectromotive force, induced when current supply to the exciting coil 14 is interrupted. Thus, the circuit is a desirable one in view of power saving. The circuit may be constructed such that a gate voltage developed according to the drive signal S1 is applied across the gate terminal G and the source terminal S of the FET 42.

[0085] Although the termination of a period for which the flow of current through the reflux circuit 36 is interrupted after the termination of the drive period T1 is delayed to the start of the next drive period T1 in the embodiment mentioned above in connection with Figs. 1 and 3, the termination of the period does not necessarily need to be delayed so and may be advanced provided that the advancement of the termination of the period does not affect adversely to the operation of the circuit. More concretely, the disconnection signal generator 38 may be constructed so as to measure time from the termination of the drive period T1 and to provide the LOW disconnection signal S5 upon elapse of a predetermined time, in which the flow of the current generated by the counterelectromotive force will be over, following the drive period T1.

[0086] The present invention is not limited in its practical application to the foregoing embodiment specifically described herein and many changes may be made therein without departing from the scope thereof.

Claims

1. An actuator driving apparatus (10) comprising at least one processing circuit (12) including:

a first switching device (32) placed between an exciting coil (14) of an actuator and a dc power source (16,18) and operated by a pulse-width modulated signal (S4) generated so as to correspond to an overexciting period (T2) and a holding period (T3) subsequent to the overexciting period (T2) in a drive period (T1);

a reflux circuit (36) connected in parallel to the exciting coil (14) and including a fly-wheel diode (44) and a second switching device (42) connected in series to the fly-wheel diode (44); and

a disconnection signal generator (38) sending a disconnection signal (S5) to the second switching device (42) for a predetermined period after the termination of the drive period (T1);

   wherein the flywheel diode (44) is provided so that a current generated from one end of the exciting coil (14) toward the other end when turning off the first switching device (32) can be recirculated; and
   wherein the second switching device (42) is turned off by the disconnection signal (S5) to be generated with the termination of the drive period (T1) to interrupt the flow of current to the exciting coil (14).

2. An actuator driving apparatus (10) according to claim 1, wherein one end of the fly-wheel diode (44) is connected to one end of the exciting coil (14), and the other end of the fly-wheel diode (44) is connected only through the second switching device (42) to the other end of the exciting coil (14).

3. An actuator driving apparatus (10) according to claim 1 or 2, wherein the second switching device (42) is formed by an n-channel FET, wherein one end of the exciting coil (14) at which a current generated by counter electromotive force induced in the exciting coil (14) appears at the termination of the drive period (T1) is connected to a drain terminal of the FET and is connected through a resistor to a terminal connected to a gate terminal of the FET.

4. An actuator driving apparatus (10) according to any one of claims 1 to 3 further comprising a surge absorber (20) connected to the opposite ends of the exciting coil (14) to absorb a current generated by the counter electromotive force induced at the termination of the drive period (T1).

5. An actuator driving apparatus (10) according to claim 4 further comprising a plurality of processing circuits (12) respectively provided in correspondence to a plurality of exciting coils (14),
   wherein one ends of the exciting coils (14) at which currents generated by counter electromotive force appear are connected electrically through diodes included in the processing circuits (12), respectively, to one end of the surge absorber (20), and the other ends of the exciting coils (14) are connected electrically to the other end of the surge absorber (20).

6. The actuator driving apparatus (10) according to any one of claims 1 to 5, which is used for driving an actuator included in a picking device mounted on a fluid-jet loom.

7. An actuator driving method to be carried out by an actuator driving apparatus (10) comprising at least one processing circuit (12) including:

a first switching device (32) placed between an exciting coil (14) of an actuator and a dc power source (16,18) and operated by a pulse-width modulated signal (S4) generated so as to correspond respectively to an overexciting period (T2) and a holding period (T3) subsequent to the overexciting period (T2) in a drive period (T1); and

a reflux circuit (36) connected in parallel to the exciting coil (14) and including a fly-wheel diode (44) and a second switching device (42) connected in series to the fly-wheel diode (44);

   wherein a fly-wheel diode (44) is provided so that an electric current generated from one end of the exciting coil (14) toward the other end when turning off the first switching device (32) can be recirculated; and
   the method comprising steps of at least turning on the second switching device (42) when the pulse-width modulated signal (S4) is not outputted for the drive period (T1) to permit the reflux and turned off at the termination of the drive period (T1) to interrupt the reflux.

Drawing