JP2006239186A - Motor control circuit for sewing machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the number of rotations of a motor by a method which is inexpensive and improved in safety. <P>SOLUTION: A signal can be transmitted and electricity is insulated between a driving output circuit 4A for a driving circuit 4 for supplying output from a power circuit 1 to a motor 3 and a driving control circuit 4B for generating an on/off control signal of the driving circuit and between a voltage detection circuit 2A for detecting counter voltage at both of the ends of the motor 3 and a detection control circuit 2B which obtains a signal from the voltage detection circuit 2A connected to both of the ends of the motor 3 to designate it to be a detection control signal. Consequently, even when the power circuit 1 supplies power supplied normally from primary power to the motor 3, the driving control circuit 4B and the driving output circuit 4A, and the voltage detection circuit 2A and the detection control circuit 2B are insulated from each other in the driving circuit 4 and a counter voltage detection circuit 2, so that there is no possibility that a circuit on a power side comes in contact with a light electrical control system circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sewing machine control circuit for controlling the rotational speed of a sewing machine motor, and more particularly, to detect the rotational speed of the sewing machine from the sewing motor and control the sewing machine to match a desired rotational speed. It relates to the circuit.

  The basic technical idea of a conventional sewing machine motor control circuit is that a photo interrupter and an encoder disk (100 pulses per rotation) are assembled as described in Patent Document 1 and Patent Document 2, and pulse width measurement, pulse A method of detecting the speed by measuring the number is adopted.

  Also, Patent Document 3 discloses a basic technical idea of a method for obtaining a speed from a voltage value by a counter electromotive force of a motor in a conventional sewing machine motor control circuit.

Both of these basic motor speed detection methods are known.
JP-A-8-150279 JP 2004-321771 JP 2000-354395 A

  However, the method of detecting the rotation speed by measuring the pulse width and the number of pulses in Patent Document 1 and Patent Document 2 requires components such as a photo interrupter and an encoder disk, and is expensive in cost. Absent. In addition, a counter driven with a high-accuracy clock pulse for pulse width measurement is also required, and in order to detect speed in a wide area from low speed to high speed, the capacity of the counter and memory for counting it increases, A high-speed processing circuit and a memory are indispensable. Even if the counter has a high-speed processing function and a high-speed processing circuit, the actual speed cannot be measured accurately unless a pulse shaped as the output of the photo interrupter arrives.

In addition, since the method for obtaining the rotation speed from the back electromotive voltage of the motor disclosed in Patent Document 3 is configured with a commercial power supply, the control circuit needs to employ an insulating circuit that is electrically insulated from the commercial power supply. Therefore, although it can be manufactured at low cost in Japan where the standard of double insulation structure (Class II) is not required, there is a problem in profit in a foreign country where the standard of double insulation structure is applied.

  The sewing machine motor control circuit disclosed in Patent Document 3, etc., detects the rotational speed by measuring the former pulse width and number of pulses because the motor speed control of the sewing machine depends on the surrounding environment (temperature, sewing machine torque, etc.). It is inferior to stabilization of rotation speed control than the method to do. However, since it can be realized with a configuration with a small number of parts, there is an advantage that an inexpensive configuration can be achieved. Another advantage is that measurement can be performed in real time for voltage detection.

  Therefore, the present invention has been made in consideration of these characteristics, and it is an object of the present invention to provide a motor control circuit for a sewing machine that can realize the detection of the rotational speed of the motor at a low cost and in a manner that improves safety. Is.

  The motor control circuit of the sewing machine according to claim 1 rotates the motor by turning on and off the output from the power supply circuit by the drive circuit, and the counter electromotive voltage (counter electromotive force) of the motor at that time is the counter electromotive voltage detection circuit. In the motor control circuit of a sewing machine that feeds back the difference between the actual speed detected by the back electromotive voltage detection circuit and the set speed set in the rotation speed instruction circuit to the drive circuit and controls the speed, the drive circuit Comprises a drive control circuit and a drive output circuit, and the back electromotive voltage detection circuit comprises a voltage detection circuit and a detection control circuit, and supplies the output from the power supply circuit to the motor via a switching circuit. The voltage detection circuit for detecting a back electromotive voltage of the drive output circuit and the motor generates a control signal for controlling on / off of the switching circuit of the drive output circuit. Between the detection control circuit to the control circuit and the voltage detection circuit variables of the controlled object the detected counter electromotive voltage is capable of signal transmission and those which are electrically insulated.

  Here, the rotation speed instruction circuit may be configured to input via an input means such as a variable resistor, a numeric keypad, and a changeover switch having a function of instructing the rotation speed of a motor as a drive source of the sewing machine. And the said power supply circuit can be made into an alternating current circuit by setting with the half wave rectifier circuit which supplies electric power to a motor, a full wave rectifier circuit, or another circuit structure.

  The drive circuit controls the output from the power supply circuit to supply power to the motor in accordance with an instruction from the rotation speed instruction circuit by on / off control of a switching circuit. The direct current can be controlled to be ON only at the timing of a predetermined half-wave of the circuit. The output of the half-wave rectifier circuit or the full-wave rectifier circuit can be a circuit that turns on the output at a predetermined timing.

  The counter electromotive voltage detection circuit detects the counter electromotive voltage based on the voltage between the terminals of the motor by turning off the output from the power supply circuit by the drive circuit. The rotation can also be detected from a dedicated coil for detecting the rotation of the motor.

  Further, the comparison circuit compares the number of revolutions instructed from the number of revolutions instruction circuit with the number of revolutions obtained from the detection circuit of the back electromotive voltage detection circuit. For example, the comparison result indicates the actual number of revolutions. When the number of rotations is smaller than that, feedback is provided to the drive circuit to increase the actual number of rotations, and a circuit for analog or digital processing can be obtained.

  Furthermore, the drive circuit is composed of a drive control circuit and a drive output circuit, and the drive output circuit is a circuit that supplies an output from the power supply circuit to the motor via a switching circuit, and the drive control circuit is It is a circuit for generating a control signal for controlling on / off of the switching circuit of the drive output circuit.

  The back electromotive voltage detection circuit is composed of a voltage detection circuit and a detection control circuit, the voltage detection circuit is a circuit for detecting a back electromotive voltage of the motor, and the detection control circuit is detected by the voltage detection circuit. The counter electromotive voltage is used as a variable proportional to the speed of the motor to be controlled.

  In addition, the signal transmission is possible and electrically insulated means that the circuit on the power side that supplies the output from the power supply circuit of the drive circuit to the motor and the on / off control of the drive circuit This means that an insulator made of an electrically non-conductive material is interposed between the circuit that generates the signal and the circuit that detects the counter electromotive voltage of the counter electromotive voltage detection circuit so that electrical continuity cannot be formed. .

  The signal transmission of the motor control circuit of the sewing machine according to claim 2 is possible, and electrical insulation is provided between the two as a photocoupler composed of a light emitting element and a light receiving element.

  Specifically, an on / off control signal generated by a drive control circuit that is a part of the drive circuit is transmitted from a light emitting element of the drive control circuit to a drive output circuit that drives a switching circuit that determines a motor current. It is optically coupled to the light receiving element. The back electromotive force of the motor has a detection circuit directly connected to the motor, and the light emitting element of the detection circuit and the light receiving element of the detection control circuit are optically coupled.

  In the motor control circuit of the sewing machine according to claim 1, between the drive output circuit of the drive circuit that supplies the output from the power supply circuit to the motor and the drive control circuit that generates the on / off control signal of the drive circuit. Signal transmission is possible and electrical insulation is provided. Further, the back electromotive voltage of the motor includes a voltage detection circuit for detecting a back electromotive voltage at both ends of the motor, a detection control circuit for obtaining a signal from the voltage detection circuit connected to both ends of the motor and using it as a detection control signal, Signal transmission is possible between the two, and electrical insulation is provided.

  Therefore, the power supply circuit is normally insulated from the drive control circuit and the drive output circuit, and the voltage detection circuit and the detection control circuit in the drive circuit and the back electromotive voltage detection circuit even if the power supplied from the commercial power supply is supplied to the motor. Therefore, there is no possibility that the power circuit and the control system circuit such as a microcomputer come into contact with each other. In addition, the number of components does not increase significantly, and it can be handled only by increasing the number of electronic components.

  In the motor control circuit of the sewing machine according to the second aspect, the electrical insulation can be provided with a photocoupler, so that the insulation can be provided between the two at a low cost.

  Next, a motor control circuit for a sewing machine according to an embodiment of the present invention will be described with reference to the drawings.

[Embodiment 1]
FIG. 1 is a conceptual diagram showing the configuration of a sewing machine motor control circuit according to an embodiment of the present invention. FIG. 2 is a specific circuit configuration diagram showing the configuration of a sewing machine motor control circuit according to an embodiment of the present invention. 3 is a waveform diagram of each circuit signal of the motor control circuit of the sewing machine according to the embodiment of the present invention. FIG. 4 is a motor of the counter electromotive voltage detection circuit of the motor control circuit of the sewing machine according to the embodiment of the present invention. It is a characteristic view of a rotation speed and a motor back electromotive force voltage signal.

  1 and 2, the power supply circuit 1 includes a commercial power supply 11 that supplies power to a motor 3 that is a DC motor and a rectifier circuit 10 thereof. As the rectifier circuit 10, a full-wave rectifier circuit or a half-wave rectifier circuit can be used. When the present invention is implemented, the present invention is not limited to the use of a rectifier circuit, and an AC circuit can be used if the drive circuit 4 described later has an AC switching characteristic.

  The back electromotive voltage detection circuit 2 is a circuit that detects the back electromotive voltage of the motor 3 at the timing when the output from the power supply circuit 1 is turned off by the drive circuit 4. And a detection control circuit for obtaining a variable (analog value) proportional to the actual rotational speed N (actual rotational speed) of the motor 3 to be controlled. 2B. The motor 3 is a DC motor and can be controlled in rotational speed by a control current such as a PWM signal.

  The drive circuit 4 controls the output from the power supply circuit 1 to be supplied to the motor 3 according to the instruction from the rotation speed instruction circuit 6 by on / off control. It can be controlled off. The drive circuit 4 generates a drive output circuit 4A that supplies the output from the power supply circuit 1 to the motor 3 via the switching element MOS, and a light control signal that controls on / off of the switching element MOS of the drive output circuit 4A. It consists of a drive control circuit 4B.

  Here, the switching element MOS constitutes the switching circuit of the present invention, and may be an element such as a transistor or a gate such as an analog gate.

  The rotation speed instruction circuit 6 is a circuit including input means for inputting the target rotation speed of the motor 3 as a driving source of the sewing machine as a variable resistor, a numeric keypad, and a changeover switch. Further, the comparison circuit 5 compares the target rotational speed instructed from the rotational speed instruction circuit 6 with the actual rotational speed N obtained from the back electromotive voltage detection circuit 2, and the comparison result indicates the actual target rotational speed. When the rotational speed is lower, the control amount is fed back to the drive circuit 4 to increase the actual rotational speed N. When the comparison result shows that the actual rotational speed N is higher than the target rotational speed, the actual rotational speed is supplied to the drive circuit 4. This is a circuit that feeds back a control amount to suppress N.

  Further, the drive output circuit 4A for supplying the output from the power supply circuit 1 to the motor 3 through the switching element MOS and the voltage detection circuit 2A for detecting the counter electromotive voltage of the motor 3 are switching of the drive output circuit 4A. A drive control circuit 4B that generates a control signal for controlling on / off of the element MOS and a detection control circuit 2B that obtains a back electromotive voltage detected by the voltage detection circuit 2A as a variable proportional to the rotational speed of the motor 3 to be controlled. Between them, the photocouplers 7 and 8 can transmit signals freely and are in an electrically insulated coupling state.

  Further, the description will be mainly based on the specific configuration of the motor control circuit of the sewing machine according to the present embodiment shown in FIG.

  In FIG. 2, the power supply circuit 1 includes a commercial power supply 11 and its full-wave rectifier circuit 12, and supplies the power to one terminal of the motor 3. The other terminal of the motor 3 is connected to the switching element MOS of the drive output circuit 4A, and power is supplied when the switching element MOS is on.

  The light receiving element 8b, the resistor R1, and the switching element MOS that are optically coupled constitute the drive output circuit 4A, and the terminal voltage of the resistor R1 is changed by the signal of the light receiving element 8b that is optically coupled to the switching element. The MOS is configured to perform a switching operation.

  Further, the back electromotive voltage of the motor 3 is detected as the light amount of the light emitting element 7a connected in series with the limiting resistor R2 connected between the terminals of the motor 3. The light emitting element 7a connected in series with the limiting resistor R2 connected between the terminals of the motor 3 constitutes a voltage detection circuit 2A that detects the counter electromotive voltage of the motor 3 as the light quantity of the light emitting element 7a.

  The light emitting element 7a constitutes the photocoupler 7 together with the light receiving element 7b. Light emission of the light emitting element 7a is detected by the light receiving element 7b, and a current corresponding to the light receiving timing is charged in the capacitor C1. The light reception timing is received only when the output of the drive circuit 4 is turned off, that is, when the output of the comparison circuit 5 is “H”, and when the transistor TR2 is turned on via the base resistor R7. Current flows in the parallel circuit of the element 7b, transistor TR2, capacitor C1 and discharge resistor R3, and charging of the capacitor C1 depends on the output of the light receiving element 7b. The capacitor C1 is discharged through the discharge resistor R3.

  Therefore, the circuit composed of the light receiving element 7b, the transistor TR2, the capacitor C1 and the discharge resistor R3 in parallel has a variable in which the back electromotive voltage detected by the voltage detection circuit 2A is proportional to the actual rotational speed N of the motor 3 to be controlled. The detection control circuit 2B is configured. The voltage of the capacitor C1 is connected to the analog input of the microprocessor functioning as the comparison circuit 5, where it is AD converted and digitally processed.

  The light receiving element 8b of the drive output circuit 4A is optically coupled so as to receive an optical signal from the light emitting element 8a connected in series with the transistor TR1 and the resistor R4. The light emitting element 8a and the light receiving element 8b constitute a photocoupler 8. The transistor TR1 is connected to the pull-up resistor R5 and the base resistor R6. When the comparison output of the microprocessor functioning as the comparison circuit 5 becomes "L", the transistor TR1 is turned on, causing the light emitting element 8a to emit light, When the comparison output of the comparison circuit 5 becomes “H”, the transistor TR is turned off and the light emitting element 8a stops emitting light.

  Here, the light emitting element 8a connected in series with the transistor TR1 and the resistor R4, the pull-up resistor R5 and the base resistor R6 of the transistor TR1 constitute a drive control circuit 4B.

  Incidentally, when the comparison output of the comparison circuit 5 becomes "L", the transistor TR1 is turned on, the light emitting element 8a emits light, and the switching element MOS is turned on by the voltage drop of the resistor R1 by the light receiving element 8b. At the same time, when the comparison output of the comparison circuit 5 becomes "L", the transistor TR2 is turned off, and the light emission of the light emitting element 7a becomes irrelevant to the charging of the capacitor C1. When the comparison output of the comparison circuit 5 becomes “H”, the transistor TR1 is turned off, the light emitting element 8a is turned off, and the switching element MOS is turned off. At the same time, when the comparison output of the comparison circuit 5 becomes “H”, the transistor TR2 is turned on, and the light emission of the light emitting element 7a contributes to the charging of the capacitor C1.

  The rotation speed instruction circuit 6 is a circuit that includes, as an input means, a numeric keypad having a function of instructing a target rotation speed of the motor 3 as a drive source for the sewing machine. The comparison circuit 5 is composed of a microcomputer having an analog input terminal, and digitally compares the digital value of the voltage of the capacitor C1 with the digital value of the target rotation speed input from the rotation speed instruction circuit 6, and the comparison result is the rotation speed instruction. When the actual rotational speed N is lower than the target rotational speed input from the circuit 6, the control circuit “H” and “L” control amounts of the comparison circuit 5 are fed back to the drive circuit 4 to increase the actual rotational speed N. Further, when the comparison result shows that the actual rotational speed N is higher than the target rotational speed input from the rotational speed instruction circuit 6, the comparison circuit 5 outputs “H”, “ The control amount of L ″ is fed back.

  The resistor R0 and the capacitor C0 which are inputs to the comparison circuit 5 are timing circuits for matching the timing of the waveform of the power supply circuit 1 and the output of the drive circuit 4.

  This timing circuit can also be detected from its own power supply voltage when the comparison circuit 5 is constituted by a microcomputer or the like. Further, it can be omitted by reducing the ripple rate of the rectifier circuit of the power supply circuit 1.

  Next, the motor control circuit operation of the sewing machine according to the present embodiment will be described using waveforms.

  The output waveform shown in FIG. 3A is obtained from the power supply circuit 1 by full-wave rectification. The target rotational speed is input by the rotational speed instruction circuit 6. The target rotational speed input by the rotational speed instruction circuit 6 is input to the comparison circuit 5. Further, the terminal voltage of the motor 3 shown in FIG. The terminal voltage of the motor 3 is supplied to the light emitting element 7a side of the photocoupler 7 through the limiting resistor R2, and the actual number of revolutions of the motor 3 is selected by selecting when no power is applied to the motor 3. A counter electromotive voltage corresponding to N can be applied to the light receiving element 7 b side of the photocoupler 7.

  Accordingly, the counter electromotive voltage signal e of the capacitor C 1 corresponding to the actual rotational speed N of the motor 3 is input to the comparison circuit 5 by the counter electromotive voltage detection circuit 2. As shown in FIG. 4, the motor back electromotive voltage signal e of the capacitor C1 becomes a low voltage at a low speed and a higher voltage at a high speed according to the actual rotational speed N of the motor 3 of the sewing machine. This motor counter electromotive voltage signal e is given as the actual rotational speed N of the motor 3.

  Here, the comparison circuit 5 compares the target rotational speed given as the rotational speed instruction signal with the actual rotational speed N obtained from the motor reverse voltage signal so that the sewing machine motor 3 is pulled to the target rotational speed. Further, the output is determined by the comparison circuit 5, and the motor drive signal shown in FIG. With this motor drive signal, the rotational speed of the motor 3 can be controlled to a constant rotational speed (target rotational speed). The motor driving signal shown in FIG. 3C is turned off when the timing T1 is “H” and turned on when the timing T2 is “L”.

  The motor back electromotive voltage signal e is a voltage generated between the terminals of the motor 3 and is connected in parallel through the light emitting element 7a and the light receiving element 7b of the photocoupler 7 and charged in parallel only when the transistor TR2 is turned on. And appear as an analog voltage of the discharge resistor R3 and input to the analog terminal of the comparison circuit 5. As shown in FIG. 4, the motor back electromotive voltage signal e of the capacitor C1 and the discharge resistor R3 connected in parallel becomes a low voltage at a low speed and a higher voltage at a high speed, as shown in FIG. .

  Here, during high-speed rotation, the back electromotive force increases, the current on the light emitting element 7a side of the photocoupler 7 increases, the current on the light receiving element 7b side of the photocoupler 7 also increases, and the capacitor C1 connected in parallel The voltage of the discharge resistor R3 connected in parallel increases. On the other hand, during low-speed rotation, the back electromotive force is reduced, the current on the light emitting element 7a side of the photocoupler 7 is reduced, the current on the light receiving element 7b side of the photocoupler 7 is also reduced, and the capacitor C1 connected in parallel The voltage of the discharge resistor R3 becomes low. That is, the actual rotational speed N of the motor 3 is output by the repeated integration value at the timing t shown in FIG.

  The motor back electromotive voltage signal e of the capacitor C1 is input to the comparison circuit 5, where it is compared with the target rotation speed input by the rotation speed instruction circuit 6, and from the comparison circuit 5 via the drive circuit 4, FIG. A motor drive signal is output so that the actual rotational speed N of the motor 3 shown in FIG. That is, the motor drive signal is transmitted to the transistor TR1, the photocoupler 8, and the switching element MOS of the drive control circuit 4B, and the switching element MOS is turned on / off by the motor drive signal shown in FIG. Is controlled, and as a result, the rotational speed of the motor 3 is controlled. Here, the switching element FET is off during the period T1 in FIG. 3C, and the switching element MOS is on during the period T2. Therefore, the voltage between the terminals of the motor 3 is as shown in FIG.

  The counter electromotive voltage detection circuit 2 described above generates a motor counter electromotive voltage depending on the rotation maintaining state of the motor 3 during the T1 period of FIG. 3C when the switching element MOS is turned off. This voltage is read by the integral value of the period, and the rotational speed is read as the actual rotational speed of the motor 3 of the sewing machine.

Here, the photocouplers 7 and 8 are configured to insulate the voltage detection circuit 2A and the drive output circuit 4A from the detection control circuit 2B and the drive control circuit 4B. The safety of the control circuit 2B and the drive control circuit 4B can be improved, and an inexpensive sewing machine control circuit can be realized. In particular, by using the photocouplers 7 and 8, it is possible to transmit only signals while insulating the detection control circuit 2B and the drive control circuit 4B that use a relatively low voltage.

  The motor control circuit of the sewing machine of the above embodiment includes a rotation speed instruction circuit 6 that instructs the rotation speed of the motor 3 that is a drive source of the sewing machine, a power supply circuit 1 that supplies power to the motor 3, and a power supply circuit 1 A drive circuit 4 consisting of a drive control circuit 4B and a drive output circuit 4A for controlling the output according to an instruction from the rotation speed instruction circuit 6 to be supplied to the motor 3 by on / off control, and a power supply circuit 1 The counter electromotive voltage detection circuit 2 comprising a voltage detection circuit 2A and a detection control circuit 2B for detecting the counter electromotive voltage of the motor when the output is turned off by the drive circuit 4, and the target rotational speed indicated by the rotational speed instruction circuit 6 A comparison circuit 5 for comparing the actual rotational speed N obtained from the back electromotive voltage detection circuit 2 and feeding back the comparison result to the drive circuit 4 is provided. The output from the power supply circuit 1 is supplied to the switching element MOS. The drive output circuit 4A supplied to the motor 3 and the voltage detection circuit 2A for detecting the back electromotive voltage of the motor 3 generate a control signal for controlling on / off of the switching element MOS of the drive output circuit 4A. And the detection control circuit 2B using the back electromotive voltage detected by the voltage detection circuit 2A as a variable proportional to the actual rotational speed N of the motor 3 to be controlled can transmit signals and be electrically insulated. It is what has been.

The motor control circuit of the sewing machine of the above embodiment includes a drive output circuit 4A that supplies an output from the power supply circuit 1 to the motor 3 via the switching element MOS, a voltage detection circuit 2A that detects a back electromotive voltage of the motor 3, A drive control circuit 4B that generates a control signal for controlling on / off of the switching element MOS of the drive output circuit 4A and a back electromotive voltage detected by the voltage detection circuit 2A is a variable that is proportional to the actual rotational speed N of the motor 3 to be controlled. The photocouplers 7 and 8 that are capable of transmitting signals and are electrically insulated are connected to the detection control circuit 2B used as the above. Therefore, a structure in which microcomputers such as the detection control circuit 2B, the drive control circuit 4B, and the comparison circuit 5 are insulated by the photocouplers 7 and 8 that can transmit signals and are electrically isolated can be maintained. The class II insulation structure, the safety of the detection control circuit 2B and the drive control circuit 4B, and an inexpensive sewing machine control circuit can be realized.

  In the above-described embodiment, the functions of signal transmission and electrical insulation are performed by the photocouplers 7 and 8, but in the case of implementing the present invention, an electromagnet, a Hall element, and the like. It can be a pair of magnetic sensors. Of course, it can also be configured as a separated light emitting element and light receiving element.

  In the above embodiment, the switching element MOS is used as the switching circuit. However, when the present invention is implemented, a gate circuit such as an analog gate and a semiconductor element such as a transistor can be used.

  The motor control circuit of the sewing machine of the above embodiment uses a microcomputer (microprocessor) as the comparison circuit 5. However, the AD conversion circuit, the comparison circuit 5, and the rotation speed instruction circuit 6 are actively processed in the microcomputer. It can be. Further, in the case of processing in the microcomputer, it is not necessary to input a signal that has obtained timing by itself from the outside.

  Although the present invention has been described as a sewing machine control circuit for controlling the rotational speed of a sewing machine motor, the present invention is not limited to a sewing machine and can be used for a general motor.

FIG. 1 is a conceptual diagram showing a configuration of a motor control circuit for a sewing machine according to an embodiment of the present invention. FIG. 2 is a specific circuit configuration diagram showing the configuration of the motor control circuit of the sewing machine according to the embodiment of the present invention. FIG. 3 is a waveform diagram of each circuit signal of the motor control circuit of the sewing machine according to the embodiment of the present invention. FIG. 4 is a characteristic diagram of the motor speed and the motor counter electromotive voltage signal of the counter electromotive voltage detection circuit of the motor control circuit of the sewing machine according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply circuit 2 Back electromotive voltage detection circuit 2A Voltage detection circuit 2B Detection control circuit 3 Motor 4 Drive circuit 4A Drive output circuit 4B Drive control circuit 5 Comparison circuit 6 Rotation speed instruction circuits 7 and 8 Photocoupler

Claims (2)

A rotation speed instruction circuit for instructing a target rotation speed of a motor serving as a drive source of the sewing machine;
A power supply circuit for supplying power to the motor;
A drive circuit for controlling the output from the power supply circuit to supply power to the motor in accordance with an instruction from the rotation speed instruction circuit by on / off control;
A counter electromotive voltage detection circuit that detects a counter electromotive voltage of the motor when an output from the power supply circuit is in an off state by the drive circuit;
A motor control circuit for a sewing machine comprising a comparison circuit that compares the target rotation speed indicated by the rotation speed instruction circuit with the actual rotation speed obtained from the counter electromotive voltage detection circuit and feeds back the comparison result to the drive circuit. In
The drive circuit includes a drive control circuit and a drive output circuit, and the counter electromotive voltage detection circuit includes a voltage detection circuit and a detection control circuit, and supplies an output from the power supply circuit to the motor via a switching element. The drive output circuit and the voltage detection circuit for detecting a back electromotive voltage of the motor are detected by a drive control circuit for generating a control signal for controlling on / off of a switching circuit of the drive output circuit and the voltage detection circuit. A signal can be transmitted and electrically insulated from a detection control circuit that processes the control amount as a variable proportional to the actual rotational speed of the motor to be controlled. Sewing machine motor control circuit. 2. The sewing machine motor control circuit according to claim 1, wherein the electrical insulation capable of signal transmission is a photocoupler.

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