JPS5947957B2 - Electric motor speed control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for an electric motor, and more particularly to an improvement in a speed control device capable of switching speeds.

Conventionally, a speed control device capable of switching between low and high speeds, which supplies current to a power machine via a semiconductor element with a control electrode, has a control device that controls a trigger voltage to the semiconductor element during speed switching. Some variable resistors are connected in series or in parallel with another variable resistor, thereby changing the variable range of the trigger voltage. In this case,
When the resistance is connected or disconnected by speed switching, the effective trigger voltage change range for the variable resistance change range, that is, the trigger voltage range sufficient to trigger the semiconductor control element, becomes narrower, thereby narrowing the speed control range. In other words, the position of the slider of the variable resistor changes when the trigger voltage reaches the trigger level of the semiconductor element, which narrows the range in which the effective trigger voltage can be controlled.Also, the starting position of the motor differs, making operation difficult. The drawback was that it was difficult to remove. The main objective of the invention is to eliminate the above-mentioned drawbacks.

A second object of the present invention is to provide a speed control device in which the effective change range of the trigger voltage does not change due to speed switching.

Other objects and features of the present invention, operations and effects of the speed control device according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments of the present invention. This will be clarified by reading the description.

Figure 1 shows speed control of an electric motor based on the present invention. FIG. 1 is a block diagram showing the basic components of a preferred embodiment of the device applied to an electric sewing machine capable of performing a single stitch;
The device connects an AC power source 1 to a main switch 2 and a semiconductor element 3 with a control electrode (for example, a thyristor, hereinafter simply referred to as a thyristor). a main motor circuit 5 for supplying motor current to the DC motor 4; a foot-operated motor speed controller 84 having a variable resistor; and a first trigger means for individually triggering each of the thyristors. 80, a second trigger means 81, a trigger disabling means 85 for disabling the second trigger means 81, a needle position detecting means 88 for detecting that the needle has come to a predetermined position, and the main switch 2. a first signal supply means 86 for supplying a first signal to enable the trigger disabling means 85 when turned on; a first control means 89 for disabling the first signal when activated; a second signal supply means 8T for supplying a second signal for enabling the trigger disabling means and a third signal for activating the first control means when the controller is depressed; a second control means 90 which is activated after a predetermined time has elapsed when the controller 84 is depressed to invalidate the second and third signals; and a second control means 90 which is activated when the controller is depressed. third control means 91 for disabling said first and second signals and being deactivated in response to actuation of said second control means; and alternatively selecting said first and second bias voltages. bias voltage supply means 83 for outputting a bias voltage; and automatic variable resistance means for automatically changing a resistance value according to one selected from the first and second bias voltages and the resistance value of the variable resistor. 82.

The first trigger voltage is controlled according to the resistance value of the automatic variable resistance means 82, and the switching means 92 disables the second and third control means when in the first state; When in the second state, the first trigger means 85 is deactivated, and when the needle position detection means 88 detects that the needle has come to a predetermined position, the first control means 89 is deactivated. has been done. Hereinafter, its configuration will be explained in detail with reference to FIG. 2. In FIG. 2, the traction motor circuit 10 includes a full-wave rectifier circuit consisting of four prism-connected silicon diodes 14, 15, 16, and IT. Power is supplied through the full-wave rectifier circuit. The first trigger means 80 includes a series circuit of a capacitor 45, a resistor 50 connected in parallel with the capacitor 43, and a capacitor 43. One terminal of the capacitor 43 is connected to the gate of the thyristor 3 via the diode 13, and the other terminal is connected to the gate of the thyristor 3. The terminal is connected to the cathode of the thyristor.

The capacitor 45 and the resistor 50 act as a phase shift circuit for the trigger voltage, and when the terminal voltage of the capacitor 45 reaches a predetermined potential, the diode 13 becomes conductive to discharge the charge in the capacitor 43 and trigger the thyristor 3. The second trigger means 81 includes a constant voltage element such as a neon discharge tube 40, a semi-fixed resistor 71 connected in parallel thereto, a backflow prevention diode 21, a resistor 50, and a capacitor 43 in series circuit. is connected to a full-wave rectifier circuit via a protective resistor 53. The full-wave rectified voltage is made into a constant voltage by the neon discharge tube 40, divided by the voltage dividing resistor 71, and then applied to the series circuit of the resistor 50 and the capacitor 43. Here, it is assumed that the value of the resistor 71 is adjusted so that the terminal voltage of the capacitor 43 is slightly larger than the break voltage of the diode 13 and the thyristor 3 is energized at an extremely small conduction angle. The controller 84 includes a switch 7 and variable resistors 72 and 73, and one end of the variable resistor 73 is connected to the full-wave rectifier circuit via the switch 7 and the resistor 48.

The switch 7 is linked to the slider C of the variable resistor 73,
When the resistance value of variable resistor 73 is maximum, that is, when slider C is at terminal a, switch 7 is open, and when it moves slightly toward terminal b, it is closed. The slider c is linked to, for example, a pedal (not shown), and when the pedal is depressed, the slider c moves from the terminal a to the terminal b side. The bias supply means 83 is a voltage dividing resistor 49
, 58, 59, 60 and the speed selection switch 8, a series circuit of resistors 49, 60, 59 is connected to the full-wave rectifier circuit.

When the switch 8 is released, the divided voltage of the series circuit of resistors 59 and 60 is supplied as the first bias voltage via the resistor 58, and when the switch 8 is closed, the divided voltage of the resistor 60 is supplied as the first bias voltage, which is lower than the first bias voltage. 2 bias voltage. The first bias voltage is for high speed, and the second bias voltage is for low speed. The automatic variable resistance means 82 consists of a transistor, for example, an NPN type transistor 33, whose base is connected to the resistor 58 of the bias supply means 83, and whose collector is connected to the resistor 58 of the bias supply means 83 through the reverse current prevention diode 20 and the single-pole double-throw switch 6. It is connected to the slider c of the controller, and its emitter is connected to the connection point between the capacitor 45 and the resistor 50 of the first trigger means.

The transistor 33 is a first transistor of the bias voltage supply means.
The conduction state is controlled by the second bias voltage, and the emitter current is controlled by the resistance value of the variable resistor 73.
Thereby, the terminal voltage of the capacitor 45 of the first trigger means is controlled. The trigger disabling means 85 includes a transistor 37, and its emitter collector circuit is connected in parallel to the series circuit of the neon discharge tube 40 and the variable resistor 71.

When the transistor 37 becomes conductive, it short-circuits the neon discharge tube 40 and disables the second trigger means. The second signal supply means 87 includes Zener diodes 29 and 30,
The anode of the Zener diode 29 is connected to the controller via a resistor 62 and a terminal d of the switch 6, and the anode of the Zener diode 30 is connected to the controller via a resistor 61 and a terminal e of the switch 6.

When the controller is depressed and the switch 7 is closed with the switch 6 connected to the terminal d, a rectified voltage is applied to the Zener diode 29, and the terminal voltage is applied to the transistor 3 via the diodes 23, 25 and the resistor 67.
It is applied as a second signal to the base of 7 to establish conduction, and is applied to the capacitor 47 via diode 27 as a third signal. When the switch 7 is closed with the switch 6 connected to the terminal e, a rectified voltage is applied to the Zener diode 30, and the terminal voltage is applied to the transistor 37 via the resistor 63, the diodes 26, 25, and the resistor 67.
is applied as a second signal to the base of diode 2, and diode 2
7 to the capacitor 47 as a third signal. The first signal supply means 86 has resistors 68 and 69, and when the main switch 2 is closed, the voltage between the terminals of the neon discharge tube 40 is applied to the transistor through the voltage dividing resistor 69 and the bias resistor 68. 37 as a first signal to establish continuity.

The needle position detection means 88 is, for example, the reed switch 38.
, 39, and the selection switch 9 for specifying the needle stop position.
including. The reed switches 38 and 39 are needles (not shown).
When the needle reaches a specified position, for example, top dead center, a permanent magnet (not shown) interlocked with the hand approaches the reed switch 38 and closes the reed switch 38, and when the hand reaches bottom dead center, the permanent magnet moves the lead. It is assumed that the reed switch 39 is configured to approach the switch 39 and close the reed switch 39. The second control means 89 includes a transistor 35 and a capacitor 46, and the base of the transistor 35 is connected to the bias resistor 6.
5 to the connection point between the resistor 64 and the capacitor 46, and its collector is connected to the connection point between the resistor 63 and the diode 26, and also to the base of the transistor 36 via the bias resistor 66. Resistor 64 and capacitor 4
6 forms a timer circuit, and when switch T is closed while switch 6 is on the terminal e side, the rectified voltage is applied to the resistor 61.
A constant voltage between the terminals of the Zener diode 30 charges the capacitor 46 via the resistor 64, and increases the terminal voltage at a predetermined time constant. Therefore, the transistor 35 is the capacitor 46
When the terminal voltage reaches a predetermined value, it becomes conductive, and
The current that has been supplied to the capacitor 4T via the diodes 26 and 2T, that is, the third signal, is temporarily cut off, and the current that flows through the diodes 26 and 25 and the resistor 6T, that is, the second signal, is temporarily cut off. do. The third control means 91 includes a transistor 36, the collector of which is connected to the paste of the transistor 3T, the emitter of which is grounded, and the paste of which is connected to the collector of the transistor 35 via a bias resistor 66.

In the transistor 36, the switch 6 is on the terminal e side, and when the switch T is closed, the terminal voltage of the Zener diode 30 is applied to the base via the resistors 63 and 66, making it conductive, and the base of the transistor 3T is grounded. to invalidate the first and second signals. Eventually, when the transistor 35 becomes conductive, the pace is grounded and becomes non-conductive. Therefore,
The transistor 36 becomes conductive when the switch T is closed, and becomes non-conductive after a predetermined time in response to the conduction of the transistor 35. The first control means 90 includes a transistor TO, the base of which is connected via a bias resistor T6 to the connection point between the capacitor 4T and the diode 2T, and also to the switch 9, and the collector of which is connected to the resistor 68, 69.
connection point and the emitter is grounded.

Capacitor 4T forms a time constant circuit with resistor T6, which connects switch 6 and diode 2 when switch T is closed.
charged by the third signal via 3, 26, 2T,
The voltage between the terminals turns on the transistor TO. When the switch T is opened, the charged charge is discharged through the resistor T6 and the transistor TO, and the transistor TO is kept conductive for a predetermined period of time. When the transistor TO becomes conductive, the resistor 68
, 69 are set to zero potential, thereby invalidating the first signal. The switching means 91 has a switch 6, and when it is on the terminal d side, that is, when it is in the first state, it deactivates the second and third control means, performs continuous sewing, and switches the terminal e to the terminal e. When the sewing machine is on the side, that is, when it is in the second state, the first trigger means is disabled and a single stitch is sewn.

The coils 10 and 11 and the capacitor 41 are used to prevent interference waves, and the resistor 24 and T5 are used to prevent the circuit from becoming high impedance when the switch 6 is turned on to the terminal e side and causing malfunction due to induced voltage. The diodes 23, 25, 26, and 2T are each used to prevent reverse current flow.
8 is a resistor 63 for quickly discharging the charge in the capacitor 46 when the switch T is opened.
is the diode 28 even when the transistor 35 is conductive.
A certain potential is held at the cathode of the resistor 6.
2 is a protective resistor for supplying an appropriate current to the Zener diode 29.

Next, the operation of the circuit will be explained with reference to FIG. First, the continuous sewing mode when the switch 6 is placed on the terminal d side will be explained. Now, if you close the main switch 2 without pressing the controller 84, that is, by opening the switch T and opening the speed selection switch 8 to select high speed, the full-wave rectified power supply voltage will be transferred to the resistor 53.
is applied to the neon discharge tube 40 via. The terminal voltage of the neon discharge tube 40 is applied on the one hand to the collector of the transistor TO via a resistor 69, while the terminal voltage of the transistor T
Since the base bias is not applied to O and it is in a non-conducting (off) state, the transistor 3 is connected via the bias resistor 68.
Applied to the base of T and turns on the transistor 31
do. On the other hand, the terminal voltage of the neon discharge tube 40 is applied to the semi-fixed resistor T1, but since the transistor 3T is in the on state, it is not applied to the series circuit of the diode 21, the resistor 50, and the capacitor 43, and therefore the capacitor 43 is The controller 8 is not charged and the thyristor 3 is kept non-conducting.
4, slightly move the slider c of the variable resistor T3 from the terminal a to the b side and close the switch T, the full-wave rectified voltage will be changed to the resistor 48, the switch T, the variable resistors T2, T3.
, are applied to the collector of the transistor 33 through the diode 20 via the terminal d of the switch 6. When the main switch 2 is closed, the transistor 33 is turned on because a full-wave rectified voltage is applied to the resistors 49, 60, and 59, and a voltage divided by the resistors 59 and 60 is applied to the base via the resistor 58. There is. Therefore, current flows for the first time through the collector-emitter circuit of transistor 33 and charges capacitor 45. Here, the charging current of the capacitor 45 is controlled by the resistance value of the variable resistor 73, and therefore the terminal voltage of the capacitor 45 is also controlled by the variable resistor 73. The capacitor 43 is charged via the resistor 50 by the charging voltage of the capacitor 45, but since the resistance value r between the slider c of the variable resistor 73 and the terminal b is close to the maximum value, the capacitor 45 is not charged. The voltage is low so that the voltage at the terminals of capacitor 43 does not reach the breakover voltage of diode 13 and thyristor 3 is not energized. Further, the full-wave rectified voltage is applied to the Zener diode 29 through the resistor 62 via the terminal d of the switch 6 to make it a constant voltage, and the constant voltage is applied to the transistor 3 via the diodes 23, 25 and the resistor 67.
7 (however, transistor 37 is biased through resistor 68 by closing main switch 7).

) along with the capacitor 47 via the diodes 23 and 27.
to charge. The charging voltage of capacitor 47 is applied as a bias to the base of transistor 70 via resistor 76. At this time, when the reed switch connected to the needle stop position selection switch 9 is closed, no bias is applied to the base, and when it is open, the bias is applied. When the base bias is applied and the transistor 70 is turned on, its collector potential becomes zero, and the bias applied to the transistor 37 via the resistor 68 is suddenly cut off, but the bias is applied to the transistor 37 via the resistor 67. It remains on because it is turned on. here.
A circuit including the transistor 32 and the capacitor 44 will be explained below.

The full wave rectified voltage passing through the diodes 14 and 15 is connected to the resistor 52.
, 54 to charge the capacitor 44. As the full-wave rectified voltage decreases from its maximum value with each half cycle of the supply voltage, capacitor 44 transfers its charge to resistor 5.
4. In order to discharge through the base-emitter circuit of the transistor 32 and turn on the transistor 32, the capacitor 4
3 is completely discharged through the collector-emitter circuit of the transistor 32 and the diode 22. In this way, the charge in the capacitor 43 is completely discharged every half cycle of the power supply voltage regardless of whether the diode 13 is conductive or not, so that intermittent breakdown of the diode 13 due to accumulation of residual charge in the capacitor 43 is prevented. Ru.
In order to achieve this effect, it is necessary to set the timing at which the charging voltage of the capacitor 44 reaches its maximum to be somewhat later than the timing at which the charging voltage of the capacitor 43 reaches its maximum. It is necessary to appropriately select the value of 54. Next, the feedback circuit including transistor 34 will be explained.

When a trigger voltage is applied to the capacitor 43 via the resistor 50, triggering the diode 13 and energizing the thyristor 3, the motor 4 is supplied with a pulsating full-wave rectified current. The diode 18 is a flywheel diode that circulates the magnetic energy in the field coil 74 when the thyristor 3 is cut off to increase the rotational electromotive force of the electric motor. Of the terminal voltage of the motor 4 including this rotating electromotive force, the terminal voltage when the thyristor 3 is energized is the Zener diode 3
1, the rotational electromotive force is sliced at a certain value (larger than the maximum rotational electromotive force) so that the rotational electromotive force can be easily detected, and the transistor 34
is added between the base emitters of.

At this time, the base resistor 56 is selected to amplify the change in rotational electromotive force caused by the change in load torque at low speeds, and this acts as a feedback signal, so the feedback effect is considerably greater than when the diode 18 is not inserted, and the rotational electromotive force changes at low speeds. This plays a major role in improving torque during rotation. now,
When the electric motor 4 is operating at a certain load torque rotational speed, as the load torque increases, the rotational speed decreases, so the rotational electromotive force generated proportionally decreases, and the base current of the transistor 34 decreases. Therefore, from resistance 50,
The current flowing through the collector-emitter circuit of the transistor 34 through the resistor 55 also decreases, and this decrease conversely becomes an increase in the charge charged in the capacitor 43, causing the dielectric 13 to increase.
The conduction phase angle (thyristor conduction phase angle) of thyristor is advanced, the amount of electric power supplied to the electric motor 4 is increased, and the rotation speed is increased. Conversely, when the load torque decreases, the rotational speed of the electric motor 4 increases and the rotational electromotive force also increases. Therefore transistor 3
The current flowing from the collector to the emitter of thyristor 4 also increases, and the current flowing to capacitor 43 decreases, delaying its charging voltage reaching the breakover voltage of diode 13, so that the conduction phase angle of thyristor 3 is delayed. Therefore, the amount of electric power supplied to the electric motor 4 decreases, and the rotation speed decreases. In this way, changes in load torque are detected using rotational electromotive force,
Feedback is performed so that the load torque remains constant. Next, when the controller 84 is further depressed to move the slider c toward the terminal b side and reduce the resistance value r of the variable resistor 13 to a predetermined value, the collector current of the transistor 33 increases and the charging voltage of the capacitor 45 increases. Therefore, the terminal voltage of the capacitor 43 reaches the brake over voltage of the diode 13 for the first time, triggering the diode and energizing the thyristor 3 at a certain small conduction angle, thereby starting the motor 4 and causing it to operate at a low speed.

When the resistance value r of the variable resistor T3 is further decreased, the charging voltage of the capacitor 45 increases, the energization phase of the thyristor 3 is advanced, and the motor is shifted to high-speed operation.

Incidentally, as the charging voltage of the capacitor 45 increases, the pace bias of the transistor 33 becomes shallower, but is it a variable resistor? The values of resistors 49, 60, and 59 are appropriately selected to provide a base bias that maintains the on state of transistor 33 even when the resistance value r of capacitor 3 is set to zero and the charging voltage of capacitor 4S is maximized. shall be taken as a thing.

Next, the operation when the electric motor is stopped will be explained.

When the controller 84 is gradually released to increase the resistance value r of the variable resistor T3, the speed of the motor decreases, and when the controller is completely released and the resistance value r is maximized, the switch T is opened. When the switch T is opened, the collector current of the transistor 33 is suddenly cut off, so that the charge in the capacitor 45 is discharged and the diode 13 is no longer triggered by the capacitor 45, and the motor rotates due to inertia. Further, by opening the switch T, the bias applied to the base of the transistor 3T via the resistor 6T is suddenly cut off. At the same time, the charging voltage applied to the capacitor 4T is cut off, but the reed switch connected to the switch 9 (reed switch 38 here)
is open, the capacitor 4T discharges its charge at a predetermined time constant via the resistor T6 and the base-emitter circuit of the transistor TO.
Keep it on. Accordingly, the pace bias of the transistor 3T is cut off and the transistor 3T shifts to the OFF state. Therefore, the terminal voltage of the neon discharge tube 40 is determined by the semi-fixed resistor T1 and the diode 2.
1 to the series circuit of resistor 50 and capacitor 43, triggers the diode 13, energizes the thyristor 3 at an extremely small conduction angle, and operates the motor at an extremely low speed with no inertia. The value of semi-fixed resistor T1 is adjusted to operate the motor at very low speed. When the needle bar eventually reaches the top dead center and the reed switch 38 closes, the capacitor 4T
The charged charge is quickly discharged through the resistor T6 and the reed switch 38 and is no longer added to the pace of the transistor TO, so the transistor TO is turned off.

Therefore, the voltage at the terminals of the neon discharge tube 40 is applied to the base of the transistor 3T via the resistors 69 and 68, turning on the transistor 3T and cutting off the thyristor 3, so the motor immediately stops and the needle bar reaches its upper limit. It will remain at the point. Thereafter, the capacitor 4T will completely discharge its charge, but the time from when the capacitor 4T starts discharging until it finishes discharging is such that if the controller 84 is suddenly released, the motor will run at high speed due to inertia. The needle bar should have at least the total time of the time required for the needle bar to gradually shift to ultra-low speed operation and the time required for the needle bar to make one round trip from the top dead center (or bottom dead center) after the needle bar changes to ultra-low speed operation. It is assumed that the capacitance of capacitor 4T and the resistance value of T6 are appropriately selected. In this manner, during continuous stitching, the needle bar is always stopped at the stop position selected by the needle stop position selection switch 9 when stopping. In the above example, the speed selection switch 8 was released and a high bias voltage was applied to the transistor 33, but when the switch 8 was closed, a low bias voltage was applied to the base of the transistor 33 and low speed operation was selected. . At this time, transistor 33 is immediately turned on. In this state, when the controller 84 is slightly depressed to open the switch T, the capacitor 45 is charged because the transistor 33 is turned on, and when the controller is further depressed to the same degree as when high speed is selected, the terminal voltage of the capacitor 43 changes to the switch T.
When the breakover voltage is reached, the thyristor 3 becomes conductive and the motor rotates at a low speed. As the controller is depressed, the charged voltage of the capacitor 45 increases, so the rotational speed of the motor increases, but at the same time, the base bias of the transistor 33 gradually becomes shallower, and when the controller is depressed close to the maximum, the bias becomes even shallower. A resistance appears between the collector and emitter of the transistor 33, which limits the increase in charging current. Therefore, when the controller is depressed to the maximum, the bias is at its shallowest level, but the transistor 33 continues to be turned on, causing the motor to rotate at its slow maximum speed. Here, the values of the resistors 49, 58, and 60 are as follows: when the controller is depressed the most, the transistor 33
It is assumed that the equivalent resistance between the emitter and the collector is appropriately selected to be such that the motor rotates at the specified maximum speed. In this way, when high-speed operation is selected, the bias of the transistor 33 becomes shallower as the controller 84 is depressed, but even when the bias is at its shallowest level when the controller 84 is depressed to the maximum, the bias of the transistor 33 becomes shallower.
Since no resistance appears between the three emitters and collectors, the motor is continuously controlled over the entire operating range of the controller from low speed to high speed. When low speed operation is selected, the speed control of the motor is the same as when high speed is selected until the controller is depressed halfway, but as the controller is depressed near the maximum, a resistance appears between the emitter and collector of the transistor 33, causing charging. Since it begins to limit the increase in current, the speed increase rate of the motor decreases, thus limiting the maximum speed. In other words, even if the speed is changed, the operating position of the controller (position of slider c) at which the motor starts moving
Since this does not change, the speed of the motor can be controlled over the entire operating range of the controller (the entire range of pedal strokes), and the pedal stroke of the controller can be used effectively and smoothly, and the motor can be started by switching the speed. It is easy to operate because there is no need to change the position of the controller. Next, the operation of sewing a single stitch will be explained.

First, the needle stop position selection switch 9 is connected to, for example, the reed switch 38, and when the needle bar is at the top dead center, the reed switch 38 is connected.
When the switch 6 is turned to the terminal e side and the controller 84 is depressed with the switch 6 closed, a full-wave rectified voltage is applied to the Zener diode 30 via the resistor 61. The constant terminal voltage of Zener diode 30 charges capacitor 46 through resistor 64 while biasing transistor 36 on through resistors 63 and 66, which in turn charges capacitor 47 through resistor 63 and diodes 26 and 27. to charge. When the transistor 36 is turned on, the current that had previously flowed to the base of the transistor 37 via the resistors 69 and 68 flows to the collector-emitter circuit of the transistor 36, and the transistor 37 is turned off, energizing the thyristor 3 and causing the motor to pass. Rotate at low speed. At this time, the transistor 37 is turned off regardless of whether the reed switch 38 is opened or closed. As the motor rotates, the needle bar begins to move from the top dead center, and when it eventually leaves the bottom dead center, the reed switch 38 opens and the charging voltage of the capacitor 47 is transferred to the resistor 76.
is applied to the base of transistor 70 to turn on transistor 70. Therefore, the current that was flowing to the collector of transistor 36 through resistors 68 and 69 flows to the collector of transistor 70 and continues to turn off transistor 37. On the other hand, when the charging voltage of the capacitor 46 rises after the switch 7 is closed and the transistor 35 is turned on, the potential on the anode side of the diode 26 is zeroed, the transistor 38 is turned off, and the charging current to the capacitor 47 is quickly cut off. do. However, at this time, the reed switch 38 is already open and the transistor 70 is turned on. Eventually, when the needle bar approaches the top dead center again from the bottom dead center, the reed switch 38 closes again and the transistor 70
In order to turn off the transistor 37, a bias is applied through the resistors 69 and 68, and the transistor 37 turns on.
is made non-conductive and the needle bar remains at the top dead center. In this way, one stitch is achieved. Here, the transistor 35 is not turned on until the needle bar leaves the top dead center after the switch 7 is closed and the reed switch 38 is opened. The capacitance of the capacitor 46 and the resistance 6 are set so that the capacitor 46 is turned on before the circuit is closed.
It is assumed that the value of 4 has been adjusted appropriately. Furthermore, it is necessary to press the controller 84, that is, to open the switch 7, at least until the transistor 35 is turned on, but after that, the controller 84 may be pressed continuously or the switch 7 may be released immediately. The next stitch is accomplished by stopping the needle, releasing the controller 84, and then depressing the controller again.

Also, since the charge in capacitor 4T is discharged via the reed switch immediately after the reed switch is closed, if the reed switch is forcibly opened by accidentally moving pulley 1 by hand after the needle bar has stopped. , no bias is applied to the base of transistor TO, so transistor 3T
is kept on, so the needle bar does not move and danger is prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a speed control device according to the present invention, and FIG. 2 is a detailed circuit diagram thereof.

Claims (1)

[Scope of Claims] 1. A foot-operated motor speed control controller having a main motor circuit that supplies a motor current from an AC power source to a motor via a main switch and a semiconductor element with a control electrode, and a variable resistor, The resistance of the variable resistor is changed by stepping on the controller, the switching means switching between a first state and a second state, and a first switching means for individually triggering the semiconductor element. and a second trigger means, a trigger disabling means for disabling the second trigger means when activated, a needle position detection means for detecting that the needle has reached a predetermined position, and the main switch. first signal supply means for supplying a first signal that, when turned on, causes the trigger disabling means to be inactivated;
a first control means that disables the first signal when actuated; a second signal that actuates the trigger disabling means when the controller is depressed regardless of the state of the switching means; a second signal supply means for supplying a third signal for activating the switching means; when the controller is depressed when the switching means is in the second state, the second signal supply means is activated after a predetermined period of time has elapsed to supply the second signal and the third signal; a second control means for disabling the first control means, which is actuated when the controller is depressed when the switching means is in a second state;
and a third control means that disables the second signal and is inactivated in response to the operation of the second control means, and a bias voltage that selectively selects and outputs the first and second bias voltages. supplying means; and automatic variable resistance means whose resistance value automatically changes according to one selected from the first and second bias voltages and a resistance value of the variable resistor, The trigger voltage is controlled according to the value of the variable resistor of the controller and the resistance value of the automatic variable resistance means, and the switching means disables the second and third control means when in the first state. and when in the second state, the first trigger means is inactivated, and when the needle position detection means detects that the needle has come to a predetermined position, the first control means is inactivated. An electric motor speed control device characterized by: 2. In claim 1, the automatic variable resistance means is a transistor, the base electrode of which is connected to the first
and a second bias voltage, the emitter collector circuit of which is connected to the alternating current power source via the variable resistor.