JPH0899270A - Screw fastening method and device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a screw tightening method and device capable of improving the efficiency of the entire screw tightening work. [Structure] A screw tightening device that tightens a screw by rotating a motor 10. The screw seating detection means 2 for detecting seating of a screw when the load of the motor 10 increases.
2 and the motor seating detection means 22 detects motor seating, the motor braking means SW1 for braking the motor 10;
Motor control means for rotating the motor 10 at a first rotation speed before the SW2 and the screw 10 are seated, and for rotating the motor 10 at a second rotation speed slower than the first rotation speed after the screw is seated. And 14 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw tightening method and device for tightening a screw by rotating a motor.

[0002]

2. Description of the Related Art Screw assembly work is the most basic of the assembly work in various industries such as precision equipment such as watches and cameras, electronic equipment such as computers and disk memory devices. This screw tightening work is performed using a screw tightening device that tightens the screw by motor power.

Generally, in screw tightening work, it is required to set the tightening torque to a preset value. The rotational speed of the motor is very important in order to securely tighten the screw with the set tightening torque. This is because if the rotation speed is too fast, the screws will be overtightened due to inertia, and if the rotation speed is too slow, the screw tightening time will be too long.

Therefore, in the conventional screw tightening device, the screw tightening is performed at the maximum number of rotations that does not cause overtightening of the screw in accordance with the type of screw to be tightened and the tightening torque. I'm trying to get the work done.

[0005]

However, in the conventional screw tightening device, the motor is rotated at the number of rotations in consideration of the excessive tightening of the screw even before the screw is seated where the excessive tightening of the screw cannot occur. There was a problem that the tightening work as a whole was not efficient. An object of the present invention is to provide a screw tightening method and device that can improve the efficiency of the entire screw tightening work.

[0006]

The above object is to provide a screw tightening method for tightening a screw by rotating a motor. Before the screw is seated, the motor is rotated at a first rotation speed to advance the screw. Then, the seating of the screw is detected by increasing the load of the motor, and when the seating of the screw is detected, the motor is braked, and after the seating of the screw, the motor is rotated at the first rotation speed. It is achieved by a screw tightening method characterized by rotating at a slower second rotation speed and tightening the screw.

In the screw tightening device for tightening the screw by rotating the motor, the screw seating detecting means for detecting seating of the screw due to an increase in the load of the motor, and the screw seating detecting means. When the seating of the screw is detected, motor braking means for braking the motor, before the seating of the screw rotates the motor at a first rotation speed, and after seating the screw, the motor is set to the first position. And a motor control unit that rotates at a second rotation speed that is slower than the first rotation speed.

[0008]

According to the present invention, before the screw is seated, the motor is rotated at the first rotation speed to advance the screw, the seating of the screw is detected by an increase in the load of the motor, and the seating of the screw is performed. , The motor is braked, and after the screw is seated,
Since the motor is rotated at the second rotation speed lower than the first rotation speed to tighten the screw, the work time before the screw is seated can be shortened. Moreover, since the motor is braked by detecting the seating of the screw, the motor can be braked at the optimum timing according to the screw tightening target.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A screw tightening device according to a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, a motor 10 is provided as a rotating means for tightening screws. One terminal of the motor 10 is grounded via the motor current detection resistor 12. By detecting the voltage of the motor current detection resistor 12, the value of the motor current flowing through the motor 10 can be detected.

The other terminal of the motor 10 has a switch SW.
It is connected to the motor drive unit 14 via 1. The switch SW1 is a normally-on type switch that is normally in a conductive state, and is turned off by a control signal from the switch controller 16 so that the motor 10 moves to the motor drive unit 1.
4 can be separated. Both terminals of the motor 10 are connected via a switch SW2. Switch SW2
Is a normally-off type switch that is normally in a cut-off state, and is made conductive by a control signal from the switch controller 16, and both terminals of the motor 10 can be short-circuited.

A microcomputer (not shown) is provided to control the entire screw tightening device, and the motor 10 is controlled based on various control signals from the microcomputer. The motor drive unit 14 drives and controls the motor 10 based on the motor drive signal. The motor drive signal is output from the microcomputer described above,
The motor 10 is set to rotate at a predetermined optimum constant speed rotation speed so that the screw tightening work can be performed efficiently.

The switch controller 16 switches the switch S based on the braking control signal from the microcomputer.
An on / off control signal for W1 and SW2 is generated and output. Details of the on / off control signal in the motor braking control will be described later. The D / A converter 18 converts the digital current setting signal from the microcomputer into an analog signal and outputs it to the motor current limiter 20.

The motor current limiter 20 is a D / A converter 1
The current setting signal from 8 and the voltage value of the motor current detection resistor 12 are compared to limit the motor current flowing through the motor 10 so as not to be larger than the current setting value. The output signal from the motor current limiter 20 is output to the motor driver 14 and the seating detector 22. The seating detection unit 22 detects the seating of the screw when the load on the motor increases, and in the present embodiment, the motor 10 reaches a stall torque and is seated by the output signal from the motor current limiting unit 20. That is detected and the seating detection signal is sent to the switch controller 1
6 is output.

The switch controller 16 switches the switches SW1 and SW1 at a predetermined timing based on the seating detection signal.
It generates and outputs an on / off control signal to SW2. Next, a screw tightening operation using the screw tightening device of this embodiment will be described with reference to FIGS. 1 and 2. Before tightening the screws,
As shown in FIG. 1A, the switch SW1 is turned on and the switch SW2 is turned off. In this state,
The motor 10 is drive-controlled by a motor drive unit 14.

First, when a power switch (not shown) is turned on, the motor 10 enters a constant speed rotation state in which it is rotated with a light torque. The rotation speed at this time is set to a rotation speed faster than the optimum rotation speed which is the maximum rotation speed at which the screws are not overtightened , for example, about 2 to 5 times the optimum rotation speed. Further, the current setting signal at the start is set to a value lower than the final set value at the time of screw tightening, as shown in FIG.

Next, a screw is chucked on the tip of a bit (not shown) provided on the rotating shaft of the motor 10 by vacuum. Since the motor 10 is rotating in the idle state, the groove of the head of the chucked screw automatically engages with the bit. Next, the screw chucked at the tip of the bit is aligned with the screw hole and the screw tightening is started.

Until the screw is seated, the motor 10 is rotated at a rotational speed faster than the optimum rotational speed and the load torque is small. Therefore, the female thread crest of the screw hole and the male thread crest of the screw mesh with each other and are screwed in at high speed. To go. When the screw is seated, the motor current signal begins to increase rapidly, as shown in FIG. The seating detector 22 detects the seating of the screw when the motor current signal exceeds the low set value of the current setting signal,
The seating detection signal is output to the switch controller 16.

As shown in FIG. 2, the switch controller 16 generates a one-shot signal activated by a seating detection signal. The switch controller 16 generates an on / off control signal for the switches SW1 and SW2 based on the one-shot signal. In synchronization with the rise of the one-shot signal, the switch SW1 is turned off to disconnect the motor drive unit 14, and the switch SW2 is turned on to short-circuit both terminals of the motor 10. At this time, as shown in FIG. 2, on / off control is performed at such a timing that the switch SW1 is turned off before the switch SW2 is turned on so that both terminals of the motor 10 are not short-circuited before the motor drive unit 14 is disconnected. Generate a signal.

The switch SW1 is cut off and the motor drive unit 1
When 4 is disconnected, the motor current becomes 0 as shown in FIG. 2, but when the switch SW2 is turned on and both terminals of the motor 10 are short-circuited, the motor 10 is rotating due to inertia. Electric power is generated by 10 and a motor current flows in the opposite direction, so that braking is rapidly performed. When the one-shot signal falls after the motor 10 has stopped rotating and the motor current has become 0, the current setting signal is changed from a low setting value to a normal setting value, as shown in FIG. Subsequently, the switch SW2 is turned off to cut off both terminals of the motor 10, and the switch SW1 is turned on to connect the motor drive unit 14. At this time, as shown in FIG. 2, the switch SW1 is turned on before the switch SW1 is turned on so that the motor drive unit 14 is not connected while both terminals of the motor 10 are short-circuited.
An on / off control signal is generated at a timing when 2 is cut off.

The switch SW1 is turned on to turn on the motor drive unit 1.
When 4 is connected, the motor drive control by the motor drive unit 14 is restarted, but the rotation speed at this time is lowered to the optimum rotation speed that is the maximum rotation speed at which the screws are not overtightened. When the screw driving control based on the optimum rotation speed is restarted by the motor drive unit 14, the motor current sharply increases and the screw tightening is performed. Finally, the screw is tightened with a predetermined torque, and when the motor current signal reaches the current setting signal, the seating detection unit 22 outputs the seating detection signal.

When the seating detection signal is output and, for example, it is detected from the pulse signal of the encoder (not shown) that the rotation of the motor 10 is stopped, the motor current is cut off for a short time and the stalled state is maintained. Then, the electric current of the motor 10 is cut off. This ends the screw tightening control. As described above, according to the present embodiment, at the start of screw tightening, the motor is rotated at a high speed, and when seating is detected, the motor is suddenly braked and temporarily stopped, and thereafter, the optimum rotation speed is selected according to the selected screw type and the like. Since the screw tightening control is performed, the work time before the screw is seated can be shortened. Moreover, since the motor is braked by detecting the seating of the screw, the motor can be braked at the optimum timing according to the screw tightening target.

A screw tightening device according to a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. The same components as those of the screw fastening device of the first embodiment shown in FIG. 1 are designated by the same reference numerals to omit or simplify the description. In the above-described first embodiment, the motor is braked by the dynamic braking method when the screw is seated, but this embodiment is characterized in that the motor is braked by the anti-phase braking method in which the anti-phase voltage is positively applied. There is.
The other basic screw tightening control is the same.

As shown in FIG. 1, one terminal of the motor 10 is grounded via a motor current detection resistor 12. By detecting the voltage of the motor current detection resistor 12, the value of the motor current flowing through the motor 10 can be detected. The other terminal of the motor 10 is connected to the motor drive unit 14 via the switch SW1. Switch S
W1 is a normally-on type switch that is normally in a conductive state, and is in a cutoff state by a control signal from the switch controller 16, and the motor drive unit 14 can be separated from the motor 10.

A switch SW3 is provided between both terminals of the motor 10.
It is connected to both terminals of the capacitor C1 via SW4 so as to have an opposite phase. The power supply side terminal of the motor 10 is connected to the ground side terminal of the capacitor C1 via the switch SW3, and the ground side terminal of the motor 10 is connected to the power supply side terminal of the capacitor C1 via the switch SW4.

The ground side terminal of the capacitor C1 is connected through the switch SW2 and the diode D1.
The switch SW2 is a normally-on type switch that is normally in a conductive state, and is turned off by a control signal from the switch controller 16 so that the capacitor C1 can be disconnected from the charging power source. The diode D1 is provided to prevent a reverse current from flowing from the ground side.

The charge amplifier 24 is an amplifier for charging the capacitor C1 and receives the voltage signal on the power source side of the motor 10 and the voltage signal on the power source side of the capacitor C1. The output end of the charge amplifier 24 is connected to the capacitor C1 via the current limiting resistor 26. The charge amplifier 24 adjusts the voltage of the power source side terminal of the capacitor C1 to the voltage of the power source side terminal of the motor 10,
The capacitor C1 is charged while monitoring the charging voltage of the capacitor C1.

The switch controller 16 switches the switch S based on the braking control signal from the microcomputer.
It generates and outputs an on / off control signal to W1, SW2, SW3, and SW4. Details of the on / off control signal in the motor braking control will be described later. Next, a screw tightening operation using the screw tightening device of the present embodiment will be described with reference to FIGS. 3 and 4.

Before tightening the screws, as shown in FIG.
The switches SW1 and SW2 are turned on, and the switch SW
3 and SW4 are turned off. In this state, the motor 1
0 is driven and controlled by the motor drive unit 14, and the capacitor C1 is charged by the charge amplifier 24 until it becomes equal to the terminal voltage of the motor 10. First, when a power switch (not shown) is turned on, the motor 10 enters a constant speed rotation state in which it is rotated with a light torque. The rotation speed at this time is set higher than the optimum rotation speed which is the maximum rotation speed at which the screws are not overtightened. Further, the current setting signal at the start is set to a value lower than the final set value at the time of screw tightening, as shown in FIG.

Next, a screw is chucked on the tip of a bit (not shown) provided on the rotating shaft of the motor 10 by vacuum. Since the motor 10 is rotating in the idle state, the groove of the head of the chucked screw automatically engages with the bit. Next, the screw chucked at the tip of the bit is aligned with the screw hole and the screw tightening is started.

Until the screw is seated, the motor 10 is rotated at a rotational speed higher than the optimum rotational speed and the load torque is small. Therefore, the female thread crest of the screw hole and the male thread crest of the screw mesh with each other and are screwed in at high speed. To go. When the screw is seated, the motor current signal begins to increase rapidly, as shown in FIG. The seating detector 22 detects the seating of the screw when the motor current signal exceeds the low set value of the current setting signal,
The seating detection signal is output to the switch controller 16.

As shown in FIG. 2, the switch controller 16 generates a one-shot signal activated by a seating detection signal. The switch controller 16 switches the switches SW1, SW2, SW based on the one-shot signal.
3. An on / off control signal for SW4 is generated. In synchronization with the rise of the one-shot signal, the switch SW1,
SW2 is turned off to disconnect the motor drive unit 14 and to disconnect the capacitor C1 from the ground. Also, switch SW
3, SW4 is turned on, and both terminals of the motor 10 are connected to both terminals of the capacitor C1 in reverse phase. At this time, as shown in FIG. 4, before the motor drive unit 14 and the capacitor C1 are separated, the switches SW3 and SW are arranged so that both terminals of the motor 10 are not connected to the capacitor C1.
The ON / OFF control signal is generated at such a timing that the switches SW1 and SW2 are cut off before the switch 4 is turned on.

When the switches SW1 and SW2 are cut off and the motor drive unit 14 is disconnected, the motor current becomes 0 as shown in FIG. 4, but the switches SW3 and SW4 are turned on and the capacitor C1 is connected to both terminals of the motor 10. When the two terminals are connected, a voltage of opposite phase is applied and the motor 10 is rapidly braked. When the one-shot signal falls after the motor 10 stops rotating and the motor current becomes 0, the current setting signal is changed from a low setting value to a normal setting value, as shown in FIG. Subsequently, the switches SW3 and SW4 are turned off to disconnect the capacitor C1 from both terminals of the motor 10, and the switches SW1 and SW2 are turned on to connect the motor drive unit 14. At this time, as shown in FIG.
The ON / OFF control signal is generated at such a timing that the switches SW3 and SW4 are cut off before the switches SW1 and SW2 are turned on so that the motor drive unit 14 is not connected while the capacitor C1 is connected to the motor 10.

When the switches SW1 and SW2 are turned on to connect the motor drive unit 14, the motor drive control by the motor drive unit 14 is restarted, but the rotation speed at this time is the maximum rotation speed at which the screws are not overtightened. It can be reduced to the optimum speed. When the screw driving control based on the optimum rotation speed is restarted by the motor drive unit 14, the motor current sharply increases and the screw tightening is performed. Finally, the screw is tightened with a predetermined torque, and when the motor current signal reaches the current setting signal, the seating detection unit 22 outputs the seating detection signal.

When the seating detection signal is output and, for example, it is detected from the pulse signal of the encoder (not shown) that the rotation of the motor 10 is stopped, the motor current is cut off for a short time and the stalled state is maintained. Then, the electric current of the motor 10 is cut off. This ends the screw tightening control. In addition,
During this time, the switches SW3 and SW4 are turned off, and the switch S
Since W1 and SW2 are on, charge amplifier 24
As a result, the capacitor C1 is charged, and the anti-phase braking is prepared for the next screw tightening.

As described above, according to this embodiment, at the start of screw tightening, the motor is rotated at a high speed, and when seating is detected, the motor is suddenly braked and temporarily stopped, and then the optimum screw type is selected. Since the screw tightening control is performed based on the number of rotations, it is possible to shorten the work time before the screw is seated. Moreover, since the motor is braked by detecting the seating of the screw, the motor can be braked at the optimum timing according to the screw tightening target. Further, since the reverse phase voltage is applied to the motor for braking, abrupt braking is possible, and it is possible to further speed up the rotation of the motor before starting screw tightening to improve efficiency.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above-described embodiment, the motor is braked and temporarily stopped when the screw seating is detected, but the motor may be decelerated to the optimum rotation speed without stopping, and the screw tightening control may be performed. Further efficient screw tightening control is possible. Further, in the above embodiment, the seating of the screw is detected by the increase of the current flowing through the motor, but when the seating of the screw increases the load and the rotation speed of the motor decreases, so that the EMF (electromotive force) of the motor decreases. The seating of the screw may be detected by detecting a decrease in the rotation speed of the motor or by directly detecting a decrease in the rotation speed of the motor with a tachometer, a rotary encoder, or the like. Alternatively, the seating of the screw may be detected by directly detecting an increase in load using a torque sensor, a mechanical sliding mechanism, a clutch, or the like.

[0037]

As described above, according to the present invention, before the seating of the screw, the motor is rotated at the first rotation speed to advance the screw, and the seating of the screw is increased by increasing the load of the motor. When it detects the seating of the screw, it brakes the motor,
After the screw is seated, the motor is rotated at the second rotation speed lower than the first rotation speed to tighten the screw, so that the work time before the screw is seated can be shortened. Moreover, since the motor is braked by detecting the seating of the screw, the motor can be braked at the optimum timing according to the screw tightening target.

[Brief description of drawings]

FIG. 1 is a block diagram of a screw tightening device according to a first exemplary embodiment of the present invention.

FIG. 2 is a time chart showing the operation of the screw tightening device according to the first exemplary embodiment of the present invention.

FIG. 3 is a block diagram of a screw tightening device according to a second exemplary embodiment of the present invention.

FIG. 4 is a time chart showing the operation of the screw tightening device according to the second exemplary embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Motor 12 ... Motor current detection resistance 14 ... Motor drive part 16 ... Switch controller 18 ... D / A conversion part 20 ... Motor current limiting part 22 ... Seating detection part 24 ... Charge amplifier 26 ... Current limiting resistance SW1, SW2, SW3 , SW4 ... Switch C1 ... Capacitor D1 ... Diode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Saburo Kojima 4-51-15 Izumi, Suginami-ku, Tokyo Inside Japan Technato Co., Ltd.

Claims (2)

[Claims] 1. A screw tightening method for tightening a screw by rotating a motor, wherein before the screw is seated, the motor is rotated at a first rotation speed to advance the screw, and the screw is seated. When the seating of the screw is detected by detecting an increase in the load of the motor, the motor is braked, and after the seating of the screw, the motor is rotated at a second rotation speed lower than the first rotation speed. A method for tightening a screw, wherein the screw is tightened by rotating the screw. 2. A screw tightening device for tightening a screw by rotating a motor, comprising: a screw seating detection unit that detects seating of the screw when the load of the motor increases; When the seating of the screw is detected, a motor braking unit that brakes the motor, before the seating of the screw rotates the motor at a first rotation speed, and after seating the screw, the motor operates as the first motor. And a motor control unit that rotates at a second rotation speed lower than the rotation speed.