JPH1080872A - Fastening device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fastening device which can reduce an overshoot of the fastening torque. SOLUTION: The limit value of a current fed to the motor of a fastening device is decided according to an expression: iL(t)=iT.exp -v(t)/K}. In which, iL(t) is a current limit value at the time t, iT is a current value to generate a target torque, v(t) is the rotational speed of the motor at the time t, and K is a constant. At first, a specific current is fed to the motor, a screw member is rotated at a specific high speed in the no-loading area so as to carry out a temporary fastening, and when the screw member is seated, and the rotational speed v(t) of the motor starts to reduce, the current limit value iL(t) begins to rise gradually according to the expression. As a result, the current value fed to the motor from a current amplifier is increased gradually, accordingly the rotational torque of the motor starts to rise. By increasing the current limit value iL(t) gradually according to the expression, no overshoot is generated, and the screw member is fastened adequately with a specific torque.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tightening device such as a nut runner for automatically tightening screw members such as bolts and nuts.

[0002]

2. Description of the Related Art In a tightening device such as an AC servo nut runner for automatically tightening a screw member such as a bolt or a nut, torque control of a motor serving as a driving source is performed to stabilize a tightening torque of the screw member. Will be
A stall method is an example of a torque control method. The stall method is described in, for example, Japanese Patent Application Laid-Open No. 2-4814.
No. 0 publication. In the stall method, as shown in FIG. 4, first, a constant current is supplied to a motor, and in a no-load region, a screw member is rotated at a constant high speed and temporarily tightened. When it falls, the supply current is increased and the tightening torque is increased to perform the tightening. Then, when the supply current reaches a predetermined stall current corresponding to the target tightening torque, the supply of the current is stopped to stop the rotation of the motor.

[0003]

However, in such a stall system, as shown in FIG. 4, an overshoot (overtightening) of the tightening torque always occurs. This overshoot is almost proportional to the rotation speed of the motor, and cannot be avoided by the stall method in which no limitation is imposed while the supply current is increasing, and the limitation is not reached until a predetermined stall current is reached. . In particular, since the screw member needs to be rotated at a high speed in order to increase the efficiency of the tightening process, there is a problem that the overshoot increases. Therefore,
SUMMARY OF THE INVENTION It is an object of the present invention to provide a tightening device capable of reliably reducing an overshoot of a tightening torque.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a first aspect of the present invention is a tightening device for rotating a socket by an electric motor to tighten a screw member. A tightening device has been created in which the magnitude of the drive current of the electric motor is continuously controlled in accordance with the rotation speed to perform the tightening. According to such a tightening device, the magnitude of the drive current of the motor is continuously controlled from the point in time when the rotation speed of the motor decreases due to the seating of the screw member, and the magnitude of the drive current smoothly increases. As described above, the magnitude of the drive current of the motor is continuously controlled until the magnitude of the drive current reaches the predetermined magnitude of the drive current corresponding to the target tightening torque. Become. In this way, in the present invention, by continuously changing the limit value of the magnitude of the drive current of the electric motor,
The present invention solves the problem of the related art in which the limit value of the magnitude of the drive current of the electric motor is constant, and provides a tightening device capable of reliably reducing the overshoot of the tightening torque.

According to a second aspect of the present invention, there is provided a tightening device for rotating a socket with a fluid pressure motor to fasten a screw member, wherein a fluid of the fluid pressure motor is changed in accordance with a rotation speed of the fluid pressure motor. We have created a tightening device that performs continuous tightening by controlling the flow rate per hour. According to such a tightening device, the flow rate per hour of the fluid of the fluid pressure motor is continuously controlled from the point in time when the rotation speed of the fluid pressure motor decreases due to the seating of the screw member, and the flow rate per time rises smoothly. As described above, since the flow rate of the fluid of the hydraulic motor is controlled continuously until the flow rate of the predetermined fluid corresponding to the target tightening torque is reached, overshoot occurs even when the target tightening torque is reached. Less likely to happen. Thus, in the present invention, the overshoot of the tightening torque can be reliably reduced even in the tightening device using the fluid pressure motor such as the air motor and the hydraulic motor.

Further, in the invention according to claim 3,
2. The tightening device according to claim 1, wherein the drive current of the electric motor has a negative exponential portion with respect to a decrease in the rotational speed of the motor, and the exponential portion includes the rotational speed of the motor. A tightening device characterized by controlling the magnitude of the drive current of the electric motor so as to rise. In this manner, the magnitude of the drive current of the motor is exponentially increased in the exponential part including the rotation speed of the motor, and the magnitude of the drive current is initially reduced. Since it rises sharply, the tightening torque also rises sharply following it. Then, the magnitude of the drive current gradually increases as approaching the magnitude of the predetermined drive current corresponding to the target tightening torque,
The tightening torque also gradually increases, and reaches the target tightening torque gradually without exceeding the target tightening torque. Thus, the tightening device can more reliably reduce the overshoot of the tightening torque.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment Next, a first embodiment of the present invention will be described with reference to FIGS. First, an overall configuration of a tightening device used in the present embodiment will be described with reference to FIG.
This will be described with reference to FIG. As shown in FIG. 1, a tightening device 1 of the present embodiment includes a nut runner 2 and a control device thereof. The nut runner 2 has a socket 4 to be fitted to a screw member such as a bolt or a nut.
The rotation shaft 6 of the socket 4 is connected to a motor 10 via a speed reduction mechanism 8. The motor 10 is provided with a speed detecting unit 12 for measuring a rotation speed.
The drive current for rotating 0 is supplied from the current amplifier 14.

The rotation speed data of the motor 10 measured by the speed detection unit 12 is input to an overall command unit 22. The overall command unit 22 limits the current to a current limiting unit 18 based on the input data as described later. Output the value. The speed command unit 20 outputs the value of the predetermined rotation speed of the motor 10 in the no-load region to the current command unit 16 as a command speed signal. The current command unit 16 calculates a current value corresponding to the value of the rotation speed, and supplies a current of this magnitude to the motor 10 via the current amplifier 14. The current limiter 18 constantly monitors the current value actually supplied from the current amplifier 14 to the motor 10 and adjusts the current command value so as not to exceed the current limit value input from the overall command unit 22 to the current limiter 18. Part 1
6 is interrupted.

Next, the tightening device 1 having such a configuration will be described.
A specific example of screw tightening according to the first embodiment will be described with reference to FIGS. FIG. 2 is a graph showing a specific example of screw tightening in the present embodiment.
, The limit value of the current supplied to the motor 10 and the rotation speed of the motor 10, and the horizontal axis indicates the passage of time. The current limiting value by the current limiting unit 18 in the present embodiment is determined by the following equation (1) also shown in FIG. iL (t) = iT.exp {-v (t) / K} (1) where iL (t) is a current limit value at time t, iT is a current value for generating a target torque, v
(T) is the rotation speed of the motor at time t, and K is a constant. As the value of the constant K, an appropriate value is selected according to the characteristics of the motor 10 and the characteristics of the screw member to be tightened.

In the screw tightening according to the present embodiment, first, a constant current is supplied to the motor 10, and in a no-load region, the screw member is rotated at a constant high speed to perform temporary tightening. At this time, the data of the rotation speed v (t) of the motor 10 measured by the speed detection unit 12
The rotation speed v (t)
And the current limit value iL according to equation (1) based on the data
(T) is calculated. The data of the calculated current limit value iL (t) is input to the current limiter 18 and the current limiter 18
Then, the current value actually supplied to the motor 10 from the current amplifier 14 is constantly monitored, and interrupt control is performed on the current command unit 16 so as not to exceed the current limit value iL (t). When the screw member is seated and the rotation speed v (t) of the motor starts to decrease, the current limit value iL (t) starts to gradually increase according to the equation (1). As a result, the current value supplied from the current amplifier 14 to the motor 10 gradually increases, and the rotational torque of the motor 10 also starts to increase.

As described above, by gradually increasing the current limit value iL (t) according to the equation (1), as shown in FIG. 2, the magnitude of the drive current sharply increases at the beginning of the rise. The tightening torque also follows this and rises sharply. Then, as the magnitude of the drive current gradually increases as the magnitude of the drive current approaches the magnitude of the predetermined drive current corresponding to the target tightening torque, the tightening torque also increases gradually, and the target tightening torque does not exceed the target tightening torque. Reach slowly. That is, the motor 10
The screw member is properly tightened with a predetermined torque without causing the rotation torque of the screw member to overshoot. Thus, the tightening device can reliably reduce the overshoot of the tightening torque.

In the present embodiment, the current limit value iL (t) is calculated from the rotation speed v (t) of the motor based on the equation (1).
Is calculated to control the rotation of the motor. However, the present invention is not limited to Expression (1), and any other appropriate relational expression may be used.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. Since the entire configuration of the tightening device used in the present embodiment is the same as that of the first embodiment, the description will be omitted with reference to FIG. In the present embodiment, the fastening device is controlled by fuzzy controlling the current limit value. FIG.
FIG. 7 shows a specific example of a membership function used for fuzzy control. By inputting such a membership function to the overall command section 22 and performing fuzzy control of the current limit value, the rotational torque of the motor 10 reaches the target torque without causing overshoot. by this,
The screw member is properly tightened with a predetermined torque.

In each of the above embodiments, the electric motor is controlled, but the present invention is also applicable to a fluid pressure motor such as an air motor or a hydraulic motor. That is, as shown in FIG. 2, the tightening torque rapidly increases in the initial stage of the increase, gradually increases as the tightening torque approaches the target tightening torque, and gradually increases to the target tightening torque without exceeding the target tightening torque. By controlling the flow rate per hour of the fluid of the fluid pressure motor so as to reach the above value, the screw member can be properly tightened with a predetermined torque without causing overshoot. The configuration, number, connection relationship, and the like of other parts of the fastening device are not limited to the above embodiments.

[0015]

According to the first to third aspects of the present invention, the overshoot of the tightening torque can be reliably reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a fastening device used in first and second embodiments of the fastening device according to the present invention.

FIG. 2 is a graph showing a specific example of screw fastening in the first embodiment of the fastening device.

FIG. 3 is a graph showing a specific example of a membership function in a second embodiment of the fastening device.

FIG. 4 is a graph showing a specific example of screw tightening in a conventional tightening device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tightening device 4 Socket 10 Motor

Claims (3)

[Claims] 1. A fastening device for tightening a screw member by rotating a socket with an electric motor, wherein the magnitude of a drive current of the electric motor is continuously controlled according to a rotation speed of the electric motor to perform the tightening. Performing tightening device. 2. A fastening device for fastening a screw member by rotating a socket with a fluid pressure motor, wherein a fluid flow rate per hour of the fluid pressure motor is continuously controlled according to a rotation speed of the fluid pressure motor. A tightening device that performs tightening. 3. The fastening device according to claim 1, wherein the drive current of the electric motor has a negative value in an exponential portion with respect to a decrease in the rotational speed of the motor, and the rotational speed of the motor is provided in the exponent portion. A tightening device, wherein the magnitude of the drive current of the electric motor is controlled so as to increase exponentially.