JPH0683966B2 - Electric driver control circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control circuit for an electric driver having a clutch mechanism.

[Conventional technology]

An electric screwdriver with a conventional clutch mechanism receives a predetermined load when screw tightening is completed and automatically disengages the clutch to cut off the rotational force transmission of the drive motor, while cutting off the power supply to the drive motor. The drive motor was suddenly stopped by dynamic braking.

In this case, the operation switch provided in the circuit for supplying power to the drive motor is kept turned on, and the reset operation is performed after the drive motor is stopped.

[Problems to be Solved by the Invention]

In the above-mentioned conventional technique, when the electric screwdriver performs an erroneous operation such as turning the operation switch on and off at a high speed immediately after the tightening of the screw, the drive motor is short-circuited and the reset operation is performed while the generated braking current is flowing. The drive motor starts to be energized, and a short circuit without the drive motor is established to damage the circuit elements, and unnecessary continuous tightening,
There is a defect that a so-called double-strike phenomenon occurs and the screw and the screw hole are damaged.

Note that the above is a relatively erroneous operation that is likely to occur such as when the operation switch unintentionally turns off due to the reaction upon completion of tightening, or when the reaction switch causes the chattering phenomenon.

The present invention solves the problems of the prior art, and can prevent the circuit element, the screw, and the screw hole from being damaged by chattering of the operation switch or an erroneous operation that occurs immediately after the tightening of the screw is completed. The purpose is to provide.

[Means for Solving the Problems]

In the present invention, a capacitor (A) is provided in parallel with the thyristor to maintain the holding current of the thyristor during dynamic braking, and a capacitor (B) is further provided in the switching circuit so that the capacitor (B) operates to perform dynamic braking. While the current is flowing, even if an erroneous operation of the operation switch occurs, the state where the power supply to the motor is cut off is maintained.

[Action]

In the present invention, since the capacitor (A) is provided in parallel with the thyristor, even if the operation switch causes chattering immediately after the screw tightening is completed, the discharge current of the capacitor (A) maintains the holding current of the thyristor and does not extinguish the arc. . Therefore,
It is possible to prevent the formation of a short circuit loop of direct current that does not pass through the motor, while preventing continuous tightening of screws due to chattering.

Further, since the capacitor (B) is provided in the switching circuit, even if the operation braking switch is operated erroneously after the discharge current of the capacitor (A) is lost and the thyristor is extinguished, the capacitor ( By the operation of B), the state where the power supply to the motor is cut off can be maintained, and the formation of the short circuit loop of the direct current not passing through the motor can be prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a vertical sectional side view of the electric screwdriver according to the present embodiment.
In the figure, 1 is a drive motor, 2 is a reduction gear with a planetary gear mechanism, a sun gear 2a of the reduction gear 2 is mounted on an output shaft 1a of the motor 1, and the planetary gear 2a is rotatably supported by a fixed clutch 3. There is. The fixed clutch 3 has two rollers 4
Projectingly form a fixed cam. 5 is a driver shaft, 6 is a driver bit, 7 is a socket for holding a driver bit, 8 is a pin, 9 is a set screw, 10 is a rotating plate,
Reference numeral 11 is a steel ball, 12 is a movable clutch, and the movable clutch 12 is composed of a rotating plate 10 and a steel ball 11, and is attached to the driver shaft 5 by a key 13 so as to rotate by one body. 14 is a spring for adjusting the driver tightening force, 15 and 17 are sleeves, 16 is a push pin, and the steel balls 11 are housed so that they can project in and out from both ends of the rotating plate 10. Part of the steel ball 11 protrudes from the opposite sides of the fixed clutch 3 through the sleeves 15 and 17 and the push pin 16 by the pressing force of
Eleven protrusions are engaged with the outer peripheral surface of the roller 4. 18 is a gear cover, a reduction gear 2, a fixed clutch 3, a movable clutch 1
2, sleeve 15, push pin 16, etc. are stored. Reference numeral 19 is a pin, and 20 is a detection switch that detects the disengaged state of the movable clutch 12 when it disengages from the fixed clutch 3. The switch is held on a part of the outer side surface of the gear cover 18 via the pin 19 and is normally spring 14 The switch contact is opened by being pressed through the sleeve 17 by the pressing force of. Reference numeral 21 is a top cover that holds the spring 14, and 22 is an adjust ring that adjusts the pressing force of the spring 14.

FIG. 2 is an electric circuit diagram of the electric screwdriver shown in FIG. 1, in which 23 is a DC power source of the motor 1, 24 is an operation switch provided in the power supply circuit of the motor 1, and 25 is a tightening or loosening operation for screw tightening. The forward / reverse changeover switch of the motor 1 for selecting whether or not, 26 is a switching circuit provided in the control circuit of the motor 1, 27 is an NPN transistor of the switching circuit 27, and when the operation switch is turned on, the base is energized via the resistor 28. The motor 1 is turned on and the motor 1 is energized. 29 is an NPN transistor of the switching circuit 26, and 30 is a thyristor of the switching circuit 26, which conducts when the motor 1 is generated and brakes to form a short circuit loop of the motor 1. Reference numeral 31 is a thyristor which receives a gate signal by the closed circuit of the detection switch 20 and turns on to turn on the switching circuit 26. Thyristor
The anode terminals of 30, 31 are connected to the motor 1 via the operation switch 24.
The thyristor 31 has a cathode terminal connected through a diode 32 at one end to a capacitor (B) 33 and another end at the other end.
It is connected to the base of the NPN transistor 29 via a resistor 34. Further, a backup capacitor (A) is connected in parallel with the thyristor 31, the diode 32, and the capacitor 33. 36 to 40 are resistors and 41 and 42 are capacitors.

Next, the operation of the electric driver having the above configuration will be described.

When the operation switch 24 is turned on and the motor 1 is energized, the motor 1 is started, and its rotational force is transmitted to the fixed clutch 3 and the movable clutch 12 via the speed reducer 2, and the key is further pressed.
13, transmitted to the driver bit through the driver shaft 5, and tightens a screw (not shown). When the tightening force of the screw increases and reaches a predetermined value, a large load torque is applied to the motor 1 and the roller 4 of the fixed clutch 3 performs a cam operation to cause a steel ball.
11, the pressing force overcomes the pressing force of the spring 14 to push the steel ball 11 toward the sleeve 17, and the fixed clutch 3 and the movable clutch 12 are disengaged to the drive bit 6 of the motor 1. The transmission of the rotational force of is cut off.

Further, the steel ball 11 axially presses the sleeve 15 via the sleeve 17 and the push pin 16, and the push button 20 of the detection switch 20 is pressed.
Push a and close the switch contact. As a result, the gate signal enters the thyristor 31 via the resistor 36, arcs, charges the capacitor 33, and causes the NPN transistor 29 to conduct and the NPN.
The base and emitter of the transistor 27 are short-circuited to cut off the electric current to the motor 1.

Further, when the thyristor 31 is turned on, the thyristor 30 is simultaneously turned on.
Is arced and a braking current flows through the dynamic braking circuit by the motor 1 and the thyristor 31, the motor 1 suddenly stops, and the screw tightening work is completed.

3 (a) to 3 (f) are operation switches after screw tightening is completed.
FIG. 12 is a waveform diagram showing the state of the circuit elements when chattering and erroneous operation of 24 occur.

In this embodiment, the capacitor (A) is connected in parallel with the thyristor 31.
When 35 is provided and the operation switch 24 causes chattering, the holding current of the thyristor 31 is maintained by the discharge current of the capacitor (A) 35 as shown in FIGS. I have to.

Further, in this embodiment, a capacitor (B) 33 is provided between the base and emitter of the NPN transistor 29, and the operation switch 24
When the screw is turned off after a short time after the screw tightening is completed, and then turned on, the NPN transistor 29 is made conductive until the electric charge of the capacitor (B) 33 disappears as shown in FIGS. 3 (d) to (f). In this state, the NPN transistor 27 is cut off.

According to the present embodiment, by sufficiently increasing the capacity of the capacitor (B) 33, the NPN transistor 27 can be cut off while the braking current is flowing in the dynamic braking circuit.
Even if the operation switch 24 is turned on during that time, the thyristor 30,
A short circuit loop of the DC power supply 23 formed by the NPN transistor 27 not via the motor 1 is cut off, and damage to the circuit element due to the formation of the short circuit loop can be prevented. When chattering the operation switch 24, the thyristor 31
It is possible to prevent the formation of the above-mentioned short circuit loop by making the arc resistance, and to prevent continuous tightening of the screw and prevent damage to the screw and the screw hole.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, the problem of a prior art is solved and the damage of a circuit element, a screw, and a screw hole which arises by chattering of an operation switch which occurs immediately after the completion of screw tightening, or an incorrect operation can be prevented. A control circuit can be obtained.

[Brief description of drawings]

1 is a vertical sectional side view of an electric driver according to an embodiment of the present invention, FIG. 2 is an electric circuit diagram of the electric driver shown in FIG. 1, and FIG. 3 is a waveform showing a state of a circuit element shown in FIG. It is a figure. 1 is a motor, 2 is a speed reducer, 3 is a fixed clutch, 5 is a driver shaft, 6 is a driver bit, 12 is a movable clutch, 20 is a detection switch, 24 is an operation switch, 26 is a switching circuit, 27 and 29 are NPN transistors. , 30 and 31 are thyristors, 33 is a capacitor (B), and 35 is a capacitor (A).

Claims (1)

[Claims] 1. An operation switch provided in a circuit for supplying power to a motor, and a clutch mechanism for disengaging a clutch engagement when a load reaches a predetermined value when tightening a screw and interrupting transmission of a rotational force of the motor. When a detection switch closes when the above-mentioned detection switch is closed when the above-mentioned operation switch is closed, a thyristor that turns on by receiving a gate signal and a thyristor In a control circuit of an electric driver having a switching circuit that is energized by an arc to cut off the power supply to the motor, and suddenly stops the motor by dynamic braking, a capacitor (A) is provided in parallel with the thyristor to generate power. The holding current of the thyristor is maintained during braking, and a capacitor (B) is further provided in the switching circuit to While the generated braking current is flowing due to the operation of the sensor (B), control of the electric driver is characterized in that the state in which the power supply to the motor is cut off is maintained even if an erroneous operation of the operation switch occurs. circuit.