JPS6120229B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for a DC motor, and more particularly to an improvement in a speed control device for a DC motor that has extremely low speed fluctuation rate due to load fluctuations, etc.

Conventionally, in a speed control device that supplies a full-wave rectified current to a motor via a semiconductor element with a control electrode, changes in the voltage between the terminals of the motor are used to stabilize the rotational speed of the motor against load fluctuations. For example, Japanese Patent Application No. 52 filed by the same applicant uses an automatic variable resistance means whose resistance value changes according to the resistance value, and controls the conduction angle of a semiconductor element with a control electrode according to the change in the resistance value. It is disclosed in the specification No.-69679 and the specification No. 53-72962.

In the speed control device according to these prior inventions, as a means for supplying a trigger voltage to a control electrode of a semiconductor element, a charging element to which a set voltage of a variable voltage setting means is applied is brought into conduction when a terminal voltage of the charging element reaches a predetermined value. and a trigger element for discharging the charged charge of the charging element and applying it to the control electrode as a trigger voltage, an automatic variable voltage setting means connected to the charging element, and an automatic variable voltage setting means for controlling the charging current to the charging element. The current was divided according to the resistance value. However, because an automatic variable resistance means (transistor) is connected in parallel to the charging element (capacitor), the phase of the charging voltage of the charging element is delayed and the semiconductor element cannot be reliably turned on every half cycle of the power supply voltage. Operation is unstable as it may be triggered intermittently or unnecessarily.
In addition, since the automatic variable resistance means shunts the current to the charging element, the control current to other circuits (for example, the single-stitch stitch control circuit, etc.) is reduced, especially when the motor voltage is high and the resistance value of the automatic variable resistance means is small. When the shunt current is large, it decreases significantly and there is a risk that sufficient control may not be achieved.

The aim of the invention is to obviate the above-mentioned drawbacks.

In order to achieve such an object, the present invention connects a charging element and automatic variable means in series.

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.

FIG. 1 is a block diagram showing the basic components of a preferred embodiment of the electric motor speed control device according to the present invention applied to an electric sewing machine capable of sewing a single stitch. A foot-operated motor having a main motor circuit and a variable resistor for supplying motor current to a DC motor 4 via a main switch 2 and a semiconductor element 3 with control electrodes (for example, a thyristor, hereinafter simply referred to as a thyristor). A speed control controller 5, a first trigger voltage setting means 6 and a second trigger voltage setting means 7 for individually triggering the thyristor, respectively.
, trigger voltage supply means 8 for applying the voltage set by the first and second trigger voltage setting means to the control electrode of the thyristor as a trigger voltage;
A trigger disabling means 9 disables the trigger voltage setting means 7, a needle position detecting means 10 detecting that the needle has reached a predetermined position, and a trigger disabling means 9 is enabled when the main switch 2 is turned on. a first signal supply means 11 for supplying a first signal to trigger a signal; a first control means 12 for disabling the first signal when actuated; and a first control means 12 for disabling the first signal when the controller is depressed; and enabling the trigger disabling means when the controller is depressed. a second signal supply means 13 for supplying a second signal and a third signal for actuating the first control means; a switching means 14 for switching between a first and a second state; a second control means 14 which is activated after a predetermined time has elapsed when the controller is depressed to invalidate the second and third signals; and when the controller is depressed, which is activated to invalidate the first and second signals and the controller. third control means 15 which is deactivated in response to actuation of the second control means; means 16 for detecting motor voltage; automatic variable resistance means 17 whose value changes, the setting voltage of the first trigger voltage setting means 6 is controlled according to the resistance value of the variable resistor of the controller 5;
The switching means 14 disables the second and third control means when in the first state, and disables the first trigger means when in the second state, thereby disabling the needle position detection. When the means 10 detects that the needle is at a predetermined position, the first control means is inactivated, and the automatic variable resistance means controls the trigger voltage of the trigger voltage supply means according to the resistance value thereof. It is configured.

The configuration will be explained in detail below with reference to FIG.

In FIG. 2, the traction motor circuit consists of four bridge-connected silicon diodes 20, 2.
The electric motor 4 is supplied with power from the power source 1 via the main switch 2, the thyristor 3, and the full-wave rectifier circuit.

The main switch 5 includes a switch 24, a variable resistor 25, and a semi-fixed resistor 26, and one end of the variable resistor 25 is connected to a speed selection switch 28 and resistors 27, 29.
is connected to the full-wave rectifier circuit via. The switch 24 is linked to the slider C of the variable resistor 25, and when the resistance value of the variable resistor 25 is maximum, that is, the slider C is at the terminal d, the switch 24 is open and the switch 24 is connected to the terminal e side. It closes when moved a little. It is assumed that the slider c is linked to, for example, a depressable pedal (not shown), and when the pedal is depressed, the slider c moves from the terminal d to the terminal e side.

The first trigger voltage setting means 6 includes a constant voltage element such as a Zener diode 30 and a diode 3.
2. It includes a series circuit of a capacitor 33 and a transistor 38, and the cathode of a Zener diode 30 is connected to a full-wave rectifier circuit via a resistor 29, and also via a resistor 27, a switch 28, a controller 5, a switch 31, and a diode 32. and is connected to a capacitor 33 which is a charging element. The constant voltage between the terminals of the Zener diode 30 is the resistor 2
7. A first trigger setting voltage is applied via the controller 5 to the series circuit of the diode 32, capacitor 33, and transistor 38. The first trigger setting voltage is changed by changing the resistance value of the variable resistor 25 of the controller 5, and is changed by changing the resistance value of the variable resistor 25 of the controller 5.
The charging speed of the capacitor 33 is controlled by controlling the conduction state of the capacitor 33. The switch 28 is a switch for changing the maximum speed, and by closing it, a higher maximum speed can be selected.

The second trigger voltage setting means 7 includes a constant voltage element such as a Zener diode 91, a resistor 92 connected in series thereto, and a backflow prevention diode 93. The Zener diode 91 is connected to a full-wave rectifier circuit via a protective resistor 89. be done. The full-wave rectified voltage is made into a constant voltage by a Zener diode 91, divided by a voltage dividing resistor 92, and then applied to the capacitor 33 as a second trigger setting voltage. It is assumed here that the value of the resistor 92 is adjusted so that the voltage at the terminals of the capacitor 33 is slightly greater than the breakover voltage of the bidirectional diode, for example the diode 34, and energizes the thyristor 3 with a very small conduction angle.

The trigger voltage supply means 8 includes a capacitor 33,
It includes a diagonal 34 and a pulse transformer 35, the primary winding of the pulse transformer is connected in series with the diac 34, and the secondary winding is connected to the gate electrode of the thyristor 3.

The trigger disabling means 9 includes a transistor 79 whose emitter collector circuit is connected in parallel to a series circuit of a Zener diode 91 and a resistor 92. When the transistor 79 becomes conductive, it short-circuits the Zener diode 91 and disables the second trigger voltage setting means.

The needle position detection means 10 may be, for example, reed switches 87 and 88, and includes a selection switch 86 for specifying needle stop. Reed switch 87, 88
When the needle (not shown) reaches a specified position, for example, top dead center, a permanent magnet (not shown) interlocked with the needle approaches the reed switch 87, closes the reed switch 87, and the needle reaches the dead center. It is assumed that the permanent magnet is configured to approach the reed switch 88 and close the reed switch 88 when the reed switch 88 is reached.

The first signal supply means 11 includes resistors 84 and 90.
When the main switch 2 is closed, the voltage between the terminals of the Zener diode 91 is applied as a first signal to the base of the transistor 79 via the voltage dividing resistor 90 and the bias resistor 84 to establish conduction. .

The first control means 12 includes a transistor 85, the base of which is connected via a bias resistor 82 to the connection point between the capacitor 83 and the diode 76, and also to the switch 86, and the collector connected to the connection point between the resistors 84 and 90. point and the emitter is grounded. Capacitor 83 forms a time constant circuit with resistor 82, which when switch 24 is closed switches 31, diodes 64 or 7.
5. It is charged through the diode 76, and the voltage between its terminals makes the transistor 85 conductive. When the switch 24 is opened, the charged charge is discharged through the resistor 82 and the transistor 85, and the transistor 85 continues to be conductive for a predetermined period of time. When the transistor 85 becomes conductive, the potential at the connection point between the resistors 84 and 90 becomes zero potential, thereby invalidating the first signal.

The second signal supply means 13 includes Zener diodes 62 and 67, the cathode of the Zener diode 62 is connected to the controller via a resistor 61 and a terminal a of the switch 31, and the cathode of the Zener diode 67 is connected to the resistor 65 and the switch 31.
is connected to the controller via terminal b. When the controller is depressed and the switch 24 is closed with the switch 31 connected to the terminal a, a rectified voltage is applied to the Zener diode 62, and the terminal voltage is applied to the transistor 79 via the diodes 64, 77 and the resistor 78. is applied to the base of the capacitor 83 as a second signal for conduction, and is applied to the capacitor 83 via the diode 76 as a third signal. When the switch 24 is closed with the switch 31 connected to terminal b, a rectified voltage is applied to the Zener diode 67, and the terminal voltage is applied to the resistor 74, the diodes 75 and 77, and the resistor 78.
is applied as a second signal to the base of the transistor 79 via the diode 76, and is applied as a third signal to the capacitor 83 via the diode 76.

The second control means 14 includes a transistor 73 and a capacitor 69. The base of the transistor 73 is connected to the connection point between the resistor 70 and the capacitor 69 via a Zener diode 72 and a bias voltage resistor 71, and the collector is connected to the resistor. 74 and a diode 75, and also connected to the base of a transistor 81 via a bias resistor 80. The resistor 70 and the capacitor 69 form a timer circuit, and when the switch 24 is closed with the switch 31 on the terminal b side, the rectified voltage is applied to the Zener diode 67 via the resistor 65, A constant voltage across the terminals charges the capacitor 69 through the resistor 70, causing the terminal voltage to rise at a predetermined time constant. Therefore, the transistor 73 becomes conductive when the terminal voltage of the capacitor 69 reaches a predetermined value, and the current that has been supplied to the capacitor 83 via the diodes 75 and 76, that is, the third signal, is suddenly cut off. , and the current flowing through the diodes 75, 77 and the resistor 78, that is, the second signal, is cut off. The Zener diode 72 limits the base bias to the transistor 73 to a certain value.

The third control means 15 includes a transistor 81 whose collector is connected to the base of the transistor 79, whose emitter is grounded and whose base is connected to the collector of the transistor 73 via a bias resistor 80. In the transistor 81, the switch 31 is on the terminal b side, and when the switch 24 is closed, the terminal voltage of the Zener diode 67 is applied to the base via the resistors 74 and 80, making it conductive, and the base of the transistor 79 is grounded. The first
and invalidates the second signal. Eventually transistor 7
When 3 becomes conductive, its base is grounded and becomes non-conductive. Therefore, the transistor 81 becomes conductive when the switch 24 is closed, and becomes non-conductive in response to the conduction of the transistor 73 after a predetermined time period after the switch 24 is closed.

The switching means 14 has a switch 31, which disables the second and third control means when it is on the terminal a side, that is, when it is in the first state,
When continuous sewing is performed and the sewing machine is on the terminal b side, that is, when it is in the second state, the first bird disables the means and performs single stitch sewing.

The motor voltage detection means 16 includes a constant voltage element, such as a Zener diode 58, whose cathode is connected to the field winding 41 of the motor 4 via a resistor 56, and whose anode is connected to the transistor 38 via a resistor 52 and a diode 53. connected to the base. When the thyristor 3 is cut off, the residual magnetic energy of the coil 41 circulates through the flywheel diode 39, and the armature cuts off the magnetic field generated in the coil 41, causing an electromotive force (hereinafter simply referred to as rotational electromotive force) induced in the armature. ) is connected to a Zener diode 58 and a capacitor 59 via a resistor 56.
is applied to the parallel circuit of Zener diode 58
The voltage across the terminals of is applied as a reverse bias to the base of the transistor 38 via a resistor 52 and a diode 53. A capacitor 59 connected in parallel to the Zener diode 58 smoothes the rotational electromotive force of the motor.

The automatic variable resistance means 17 includes, for example, a transistor 38, the base of which is grounded via a resistor 54 and a bias adjustment semi-fixed resistor 55.
It is connected to the cathode of the diode 32 via the diode 53 and the voltage dividing resistor 51, and its collector is connected to the connection point between the capacitor 33 and the diode 34.
The emitter is grounded via a resistor 97. The transistor 38 is applied with the voltage set by the first or second trigger voltage setting means as a forward bias through the diode 32, the resistor 51, and the diode 53, and the rotational electromotive force detected by the Zener diode 58 is applied as a reverse bias. applied.

Incidentally, here the coils 94, 95 and the capacitor 96
is to prevent interference waves, and the diode 6
4, 75, 76, and 77 respectively prevent reverse current flow, and a diode 68 is connected to switch 2.
When resistor 74 is opened, the charge in capacitor 69 is quickly discharged.
is for maintaining a certain potential at the cathode of the diode 68 even when the transistor 73 is conductive, and the resistor 61 is a protective resistor for supplying an appropriate current to the Zener diode 62.

Next, the operation of the circuit will be explained with reference to FIG. First, the operation when the switch 31 is turned to the terminal a side and the continuous stitching mode is selected will be explained. Now, without pressing controller 5,
That is, when the main switch 2 is closed with the switch 24 open and the speed selection switch 28 closed to select high speed, the full-wave rectified power supply voltage is applied to the Zener diode 91 via the resistor 89. Ru. The terminal voltage of the Zener diode 91 is applied to the transistor 8 via the resistor 90 on the one hand.
5, but the transistor 85
is non-conducting (off) because no base bias is applied to
state, the voltage is applied to the base of transistor 79 via bias resistor 84, and transistor 7
9 becomes conductive (turned on). On the other hand, the terminal voltage of the Zener diode 91 is applied to the resistor 92, but since the transistor 79 is in the on state, it is not applied to the series circuit of the diode 93 and the capacitor 33, and therefore the capacitor 33 is not charged and the thyristor 3 is not charged. Keep non-conducting. In this way, the voltage set by the second transistor is invalidated by the conduction of the transistor 79.

Next, when the controller 5 is slightly depressed to slightly move the slider c of the variable resistor 25 from the terminal d to the e side and the switch 24 is closed, the full-wave rectified voltage is applied to the Zener diode 30 via the resistor 29. , the voltage between its terminals is determined by the switch 28 and the variable resistor 2.
5, semi-fixed resistor 26, switch 24, switch 3
It is applied to the resistor 52 and the diode 57 via the terminal a of 1, the diode 32, and the resistor 51, and
A bias is applied to the diode 53, the resistor 54, and the semi-fixed resistor 55 to apply a bias to the base of the transistor 38, turning the transistor 38 on. Here resistance 5
5 is for appropriately adjusting the bias. Therefore, a charging current flows through the capacitor 33 and connects the collector-emitter resistance of the transistor 38 and the capacitor 33.
The battery is charged with a time constant determined by the capacity of the battery. However, now, since the resistance value r between the slider c of the variable resistor 25 and the terminal e is close to the maximum value, the transistor 38
The bias voltage of the capacitor 33 is low, so the value of the semi-fixed resistor 26 is adjusted so that the charging voltage of the capacitor 33 does not reach the breakover voltage of the diode 34 and the thyristor 3 is not energized.

Further, the full-wave rectified voltage is applied to the Zener diode 62 through the resistor 61 via the terminal a of the switch 31 to become a constant voltage, and the constant voltage is applied to the transistor 7 via the diodes 64, 77 and the resistor 78.
9 (however, transistor 7
9 is biased through a resistor 84 when the main switch 2 is closed. ) with diode 6
4,76 to charge the capacitor 83. The charging voltage of capacitor 83 is applied as a bias to the base of transistor 85 via resistor 82. At this time, when the reed switch connected to the needle stop position selection switch 86 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 85 is turned on, its collector potential becomes zero, and the transistor 79 is turned on via the resistor 84.
Although the bias applied to the transistor 79 is suddenly cut off, the transistor 79 remains on because the bias is applied through the resistor 78.

Here, a circuit including the transistor 46 and the capacitor 43 will be explained. Diodes 20, 21
The full-wave rectified voltage passed through is divided by resistors 42 and 44, and the voltage between the terminals of resistor 44 is made trapezoidal with a constant maximum value by Zener diode 45 and is applied to capacitor 43. The capacitor 43 is rapidly charged through the diode 47, and when the terminal voltage of the Zener diode 45 begins to fall from a constant maximum value, the charged charge is transferred to the resistor 44 and the diode 4.
9. To discharge through the base-emitter circuit of the transistor 46 and turn on the transistor 46,
The charge in the capacitor 33 is completely discharged through the collector-emitter circuit of the transistor 46 and the diode 47. In this way, the charge in the capacitor 33 is completely discharged every half cycle of the power supply voltage, regardless of whether the diode 34 is conductive or not, thereby preventing intermittent breakdown of the diode 34 due to accumulation of residual charge in the capacitor 33. Ru. Note that the charging voltage of the capacitor 43 is discharged when the terminal voltage of the Zener diode 45 decreases from a constant maximum value, regardless of the capacitance of the capacitor 43 and the values of the resistors 42 and 44. The time when the voltage reaches its maximum is always a little earlier than the time when the charging voltage of the capacitor 43 reaches its maximum. Therefore, there is no need to adjust the capacitance of the capacitor 43 and the values of the resistors 42 and 44 as in the conventional case, and there may be some variation. Furthermore, resistance 4
Reference numerals 8 and 50 apply an appropriate bias to the base of the transistor 46 by the energizing voltage of the thyristor 3 to turn it on, thereby completely discharging the charging voltage of the capacitor 33.

Next, when the controller 5 is further depressed to move the slider c to the terminal e side and reduce the resistance value r of the variable resistor 25 to a predetermined value, the base bias of the transistor 38 increases and the collector current increases. The charging voltage increases, so that the terminal voltage of the capacitor 33 reaches the breakover voltage of the diode 34 for the first time near its maximum value, triggering the diode and supplying a trigger voltage to the gate of the thyristor 3 via the pulse transformer 35, which in turn 3 is energized at a certain small conduction angle, the electric motor 4 is started and operated at low speed.

When the resistance value r of the variable resistor 25 is further reduced, the base bias of the transistor 38 increases, the rise of the charging voltage of the capacitor 33 becomes more rapid, and the phase at which the breakover voltage of the diode is reached advances, advancing the energization phase of the thyristor 3. , the electric motor will shift to high-speed operation.

Next, the operation when the electric motor is stopped will be explained.
When the controller 5 is gradually released to increase the resistance value r of the variable resistor 25, the speed of the motor decreases, and when the controller is completely released and the resistance value r is maximized, the switch 24 is opened. By opening switch 24, the base bias applied to transistor 38 through diode 32 is now cut off, and capacitor 33 is no longer charged by the current flowing from the controller through diode 32. Also, by opening the switch 24, the resistor 7
The bias applied to the base of transistor 79 via transistor 8 is now cut off. At the same time, the charging voltage applied to the capacitor 83 is also cut off, but assuming that the reed switch (reed switch 87 here) connected to the switch 86 is open, the capacitor 83 transfers its charging charge to the resistor 82. The transistor 85 is kept on in order to discharge at a predetermined time constant via the base-emitter circuit of the transistor 85. Therefore, the base bias is not applied to the transistor 79 even through the resistor 84, the base bias is completely cut off, and the transistor 79 shifts to an off state. Therefore, Zener diode 9
1 terminal voltage is applied as a base bias to the transistor 38 via the resistor 92 and the diode 93, charges the capacitor 33, triggers the diode 34, energizes the thyristor 3 at an extremely small conduction angle, and operates the motor at an extremely low speed with no inertia. You will have to drive. The value of resistor 92 is adjusted to operate the motor at very low speeds.

Eventually the needle bar reaches top dead center and reed switch 8
7 is closed, the charge in the capacitor 83 is quickly discharged through the resistor 82 and the reed switch 87 and is no longer applied to the base of the transistor 85, so the transistor 85 is turned off. Therefore, the terminal voltage of the Zener diode 91 is
0 and 84 to the base of the transistor 79, turning on the transistor 79 and cutting off the trigger voltage to the thyristor 3, the motor immediately stops and the needle bar remains at the top dead center.

The time from when the capacitor 83 starts discharging until it finishes discharging is the time required for the motor to gradually shift from high-speed operation to ultra-low speed operation due to inertia when the controller 84 is suddenly released, and the time required for the motor to gradually shift from high-speed operation to ultra-low speed operation due to inertia. The capacitance of the capacitor 83 and the resistance value of the resistor 82 are appropriately selected so as to have at least the total time required for the rod to make one round trip from the top dead center (or bottom dead center) after it starts operating at a very low speed. It is assumed that In this manner, during continuous stitching, the needle bar is stopped at the stop position selected by the needle stop position selection switch 86 when the needle bar is stopped.

In addition, in the above example, the speed selection switch 28
is closed and a high bias voltage is applied to transistor 3.
However, when switch 28 is opened, a low bias voltage is applied to the base of transistor 38, selecting low speed operation.

Next, a feedback circuit including the transistor 38, which is a feature of the present application, will be explained. When the charging voltage of the capacitor 33 reaches a predetermined value, the dial 3
When the motor 4 is triggered and the thyristor 3 is energized, the motor 4 is supplied with a pulsating flow of full-wave rectified current. The diode 39 is a flywheel diode, which circulates the magnetic energy in the field coil 41 when the thyristor 3 is cut off, thereby increasing the circuit electromotive force of the motor. Further, the diode 37 prevents the thyristor from malfunctioning and prevents the surge voltage generated by the motor from being applied to the thyristor, and the diode 40 prevents the generation of flash voltage of the motor and prevents the thyristor from malfunctioning. It is. Diode 53 is transistor 3
Prevents reverse excessive voltage from being applied to the base of 8.
The diode 57 allows the charging voltage of the capacitor 59 to effectively act on the transistor 38, and the diode 6
0 allows the current to flow through the thyristor, but blocks the rotational electromotive force of the motor, effectively allowing the capacitor 59 to detect the rotational electromotive force.

A rotational electromotive force proportional to the rotational speed of the motor is applied via a resistor 56 to a constant voltage element, such as a parallel circuit of a Zener diode 58 and a capacitor 59.
The voltage across the terminals of the Zener diode 58 smoothed by the capacitor 59 is applied as a reverse bias voltage to the base of the transistor 38 via the resistor 52 and diode 53. Therefore, the transistor 38 has a forward bias voltage set by the controller 5 and applied through the resistor 51 and the Zener diode 58.
It is biased with the rotational electromotive force detected at , that is, the voltage difference from the bias voltage.

Now, when the electric motor 4 is operated at a constant speed with a certain constant load, the rotational speed at which the load increases decreases, and the rotational electromotive force also decreases in proportion to this. Therefore, the voltage between the terminals of the Zener diode 58 decreases and the reverse bias decreases, so the base bias of the transistor 38 increases, the collector current of the transistor 38 increases, the charging current to the capacitor 33 increases, and the conduction phase angle of the thyristor changes. Advance and increase the rotational speed of the electric motor. On the other hand, when the load decreases, the rotational speed of the motor increases and the rotational electromotive force increases, so the voltage between the terminals of the Zener diode 58 increases and the base bias voltage of the transistor 38 decreases. Therefore, the charging current of the capacitor 33 decreases and the energization phase angle of the thyristor is delayed, so that the rotational speed of the motor decreases. In this manner, by controlling the base bias of the transistor 38 in accordance with load fluctuations, the charging current of the capacitor 33 is controlled, and the speed of the motor is always kept constant. Further, due to the amplification effect of the transistor 38, fluctuations in the back electromotive force are sensitively detected, and a feedback effect is effectively achieved. In this circuit, the capacitor 33 and the collector-emitter circuit of the transistor 38 are connected in series, and the base bias is set to the voltage difference between the voltage set by the controller and the rotating electromotive force, so the charging voltage of the capacitor 33 is The phase of the thyristor is not delayed, the thyristor is reliably turned on every half cycle of the power supply voltage, and the thyristor is controlled extremely stably without unnecessary and intermittent triggering. Also, since the collector-emitter circuits of the capacitor 33 and the transistor 38 are connected in series, the transistor 3
The collector current of the capacitor 33 is the same as the charging current of the capacitor 33, and when the charging voltage of the capacitor 33 reaches the breakover voltage of the diode 34 and charging stops, the collector current also stops. Therefore, fluctuations in the control voltage to other circuits are extremely small, and control is performed stably.

Next, the operation of sewing a single stitch will be explained. First, the needle stop position selection switch 86 is connected to, for example, the reed switch 87, and with the needle bar at the top dead center and the reed switch 87 closed, the switch 31 is placed on the terminal b side and the controller 5 is depressed. A full-wave rectified voltage is applied to the Zener diode 67 via resistors 65 and 66. The constant terminal voltage of Zener diode 67 charges capacitor 69 via resistor 70, while biasing transistor 81 on via resistors 74 and 80, which in turn charges capacitor 83 via resistor 74 and diodes 75 and 76. to charge. By turning on the transistor 81, the resistors 90 and 84 or the diode 7
7. The current flowing to the base of the transistor 79 via the resistor 78 flows to the collector-emitter circuit of the transistor 81, so the transistor 79 is turned off, and as mentioned above, the thyristor 3 is energized and the motor rotates at an extremely low speed. let At this time, the transistor 79 is turned off regardless of whether the reed switch 87 is opened or closed. That is, if the switch 31 is turned on to the terminal b side, the thyristor is energized. As the motor rotates, the needle bar begins to move from the top dead center, and when it leaves the top dead center, the reed switch 87 opens, and the charging voltage of the capacitor 83 is applied to the base of the transistor 85 via the resistor 82. Turn on. Therefore, the current that was flowing to the collector of transistor 81 through resistors 90 and 84 flows to the collector of transistor 85, and continues to turn off transistor 79. On the other hand, when the charging voltage of the capacitor 69 rises after the switch 24 is closed and eventually reaches the breakover voltage of the Zener diode 72 and turns on the transistor 73, the potential on the anode side of the diode 75 becomes zero and the transistor 81 is turned off. The charging current to the capacitor 83 is cut off. However, at this time, the reed switch 87 is already open and the transistor 85 is turned on.

When the needle bar approaches the top dead center again from the bottom dead center, the reed switch 87 closes again and turns off the transistor 85. Therefore, the transistor 79 is turned on by being biased through the resistors 90 and 84, and the thyristor is turned on. 3 is made non-conductive and the needle bar remains at the top dead center. In this way, one stitch is achieved. Here, the transistor 73 is not turned on until the needle bar leaves the top dead center after the switch 24 is closed and the reed switch 87 is opened. It is assumed that the capacitance of the capacitor 69 and the value of the resistor 70 are appropriately adjusted so that the capacitor 69 is turned on before closing. Furthermore, it is necessary to press the controller 5, that is, to open the switch 24, at least until the transistor 73 is turned on.
After that, you can continue to step on it or release it immediately.

To sew the next stitch, stop the needle and press the controller 5.
This is achieved by pressing the controller again after releasing the button.

Furthermore, since the charge in the capacitor 83 is immediately discharged through the reed switch after the reed switch is closed, if the needle bar is stopped and the pulley is accidentally moved by hand to forcibly open the reed switch, Since no bias is applied to the base of transistor 85 and therefore transistor 79 remains on, 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 main motor circuit that supplies motor current from an AC power supply 1 to a motor 4 via a main switch 2, full-wave rectifier circuits 20 to 23, and a semiconductor device with control electrodes 3; and the full-wave rectifier. A foot-operated motor speed control controller connected to an output of a circuit and having a variable resistor 25, the resistance of the variable resistor being changed by depressing the controller; and a switching means. first trigger voltage setting means 29, 30, 32 for setting a variable trigger voltage and a second trigger voltage setting means for setting a constant trigger voltage, which are connected to the controller and individually trigger the semiconductor elements. Means 91-93
and trigger voltage supply means 33 to 35 that apply the voltage set by the first and second trigger voltage setting means to the control electrode of the semiconductor element as a trigger voltage, and when activated, disables the second trigger means. Trigger disabling means 79 for activating; needle position detecting means 86 to 88 for detecting that the needle of the sewing machine has reached a predetermined position; and disabling the trigger disabling means when the main switch 2 is turned on. a first signal supply means 84, 90 for supplying a first signal to trigger the trigger; a first control means 85 for disabling the first signal when activated; and a first control means 85 for disabling the trigger disabling means when the controller is depressed; second signal supply means 62, 67 for supplying a second signal to activate the first control means and a third signal to activate the first control means; second control means 69, 73 for disabling the third signal; and second control means 69, 73 that are actuated when the controller is depressed to disable the first and second signals and are inactivated in response to the actuation of the second control means. the switching means 31 which is switched between a first state instructing continuous stitching and a second state instructing single stitch stitching; and a capacitor connected in parallel to the electric motor. 59
and a Zener diode 58 in parallel circuit; and a voltage difference between the voltage set by the first or second trigger voltage setting means and the motor voltage detected by the motor voltage detection means. automatic variable resistance means 38 whose resistance value automatically changes according to the resistance value, the set voltage of the first trigger voltage setting means is controlled according to the resistance value of the variable resistor 25 of the controller 5; The switching means disables the second and third control means when in the first state;
When the needle position detecting means detects that the needle has come to a predetermined position, the first trigger means is inactivated; and when the needle position detection means detects that the needle is at a predetermined position, the first control means is inactivated; The trigger voltage is delayed when the motor voltage increases and is advanced when the transmission voltage decreases, and the trigger voltage supply means includes a first charging/discharging element 33 to which the voltage set by the first and second trigger voltage setting means is applied. , is connected to the first charging/discharging element and becomes conductive when the charging voltage of the first charging/discharging element reaches a predetermined value, discharging the charge of the first charging/discharging element and applying a trigger voltage to the control electrode of the semiconductor element. a trigger voltage supply element 34, whose collector is connected to one end of the first charging/discharging element, one end of which is connected to the output of the full-wave rectifier circuit, and the other end of which is connected to the emitter of the transistor. a second charging/discharging element 43 connected to the anode of the diode 47; and a constant voltage element 4 connected to one end of the second charging/discharging element.
5, and a resistor 44 connected in parallel to the constant voltage element.
The charge in the second charging/discharging element is discharged through the resistor and the base-emitter circuit of the transistor every half cycle of the AC power supply, and the automatic variable resistance means 38 is configured to control the first charging/discharging element. It is a transistor in which a collector-emitter circuit is connected in series to the element, and the voltage set by the first or second trigger voltage setting means is applied to the base of the transistor as a forward bias voltage, and the motor voltage is reverse biased. A speed control device for a DC motor, characterized in that: