JPH1034555A - Method and device for controlling nut runner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method and a control device simultaneously tightening a plurality of bolts or nuts in a short time without tightening by two times in uniform tightening force by a multiaxial head of a nut runner. SOLUTION: In the case of simultaneously tightening a bolt 2 to a workpiece 3 by a multishaft head 1 of a nut runner, tightening operation is performed by turning on a switch 14 of a speed control loop 11 to drive a drive motor 4 at a prescribed rotational speed, when the bolt 2 is tightened by prescribed target tightening torque Ta, by detection of this target tightening torque Ta, the switch 14 is turned off, a switch 15 is turned on, to be switched to a torque control loop 12, a current of the drive motor 4 is controlled so as to hold the target tightening torque Ta, tightening is continued, and, in the point of time where all the heads 1 performs bolt tightening by the target tightening torque Ta, bolt tightening action of all the heads 1 is ended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method and a control apparatus for a multi-axis type nut runner which simultaneously automatically tightens a plurality of bolts or nuts on a work and simultaneously completes the tightening.

[0002]

2. Description of the Related Art When a plurality of bolts are tightened to a work such as an oil pan of an automobile engine with the same tightening force (axial force), the bolts are first tightened with a predetermined tightening torque due to a difference in the tightening timing of each bolt. The tightening force (axial force) of the bolts that were tightened is reduced by the tightening force of the bolts that were tightened later.
The bolting force of each bolt may vary. Therefore, in a nut runner provided with an automatic multi-axis head for automatically tightening a plurality of bolts on a work at the same time, for example, the following control method is adopted in order to avoid the above-mentioned phenomenon in which the tightening force varies. .

[0003] Each of the multi-axis heads provided with a drive motor rotates a bolt to seat the work, and starts tightening of all the bolts on the work at the timing when all the bolts are seated, so that each bolt is fixed to a predetermined position. When the motor is tightened with the tightening torque, the motor current at the moment of the tightening is kept constant, and the tightening force at the time of the tightening is maintained. Then, at the timing when all the bolts are tightened, the motor currents of all the multi-axis heads are cut off to complete the multi-axis bolt tightening.

As another control system, there is a system in which a plurality of bolts are tightened twice. That is, after tightening a plurality of bolts with a predetermined tightening torque, each bolt is slightly loosened and then tightened again to reduce the variation in the tightening force caused by the first tightening in the second tightening. .

[0005]

In the case of the above-mentioned control system in which the motor current is maintained constant when tightening the bolts, the final tightening force of each of the plurality of bolts is substantially uniform, but the bolts and the Some variation was observed depending on the material and type of the work. For example, FIG. 3 shows a graph showing the relationship between the time and the torque during the bolt tightening operation by the above-described current control method, and the relationship between the time and the motor current. The tightening torque increases in proportion to the increase in the motor current. When the applied torque reaches the preset target tightening torque Ta, the motor current Ia at this time is latched, and thereafter, the bolt tightening operation by the latched motor current Ia is completed by the time when the tightening of all bolts is completed. until t ₁ to continue.

As shown in FIG. 3, when the motor current Ia is held constant when tightening the bolt, if the tightening force of the bolt decreases, the bolt rotates with the motor current Ia and the decrease in the tightening force is suppressed. However, the actual tightening torque does not maintain the target tightening torque Ta, and as shown in the time-torque graph of FIG.
Fluctuates from Such fluctuations in the final tightening torque appear as variations in the tightening force of the multi-axis bolt, and particularly in the case of a work requiring an airtight and uniform tightening such as an oil pan, the reliability of the tightening force is not reliable. Is worse.

In the case of a control system in which a plurality of bolts are tightened twice, the variation in final tightening force of each bolt can be made relatively small, and the reliability of bolt tightening is improved. However, since each bolt is tightened twice, the cycle time for tightening all bolts once becomes longer,
It is difficult to improve the productivity of the bolting process.

Therefore, the object of the present invention is to
An object of the present invention is to provide a control method and a control device for simultaneously tightening a plurality of bolts or nuts with a more uniform tightening force in a short time without twice tightening a plurality of bolts or nuts with a multi-axis head of a nut runner.

[0009]

The technical means for achieving the above object of the present invention is to provide a nut runner having a multi-axial head with a built-in motor, in which a plurality of bolts or nuts are simultaneously tightened to a work and simultaneously tightened. In the control, when each head tightens a bolt or a nut with a predetermined target tightening torque, the motor current of each head is controlled by feedback-controlling the tightening torque so that the target tightening torque is kept constant. When all the heads tighten the bolts or nuts with the target tightening torque, the motor current of each head is cut off to complete the tightening.

Further, the present invention is an apparatus for implementing the above control method, wherein a speed control loop for tightening a bolt or a nut to a work to a predetermined target tightening torque by controlling the rotation of a drive motor of each head at a predetermined rotation speed. A torque control loop for controlling the motor current of each head so that each head maintains a constant target tightening torque at the time when each head tightens a bolt or nut to a work with a predetermined target tightening torque; and Alternatively, a loop switching means for switching the control system from the speed control loop to the torque control loop when the nut is tightened to the work with a predetermined target tightening torque is provided.

Here, the multi-axial head of the nut runner is
A general type having a torque sensor together with a drive motor, controls the current of the drive motor to tighten a bolt or a nut at a predetermined rotation speed (speed), and a tightening torque at this time is set to a predetermined target. When the torque is reached, the tightening by speed control is stopped, and then the motor current is controlled so that the tightening torque detected by the torque sensor maintains the target tightening torque, and the tightening is terminated. By performing such two-stage control of speed control and torque control on a plurality of heads, a plurality of bolts or nuts are unified to the same final tightening force based on a target tightening torque, and tightening is performed. Variation in power is suppressed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a description will be given with reference to a circuit block of the apparatus according to the present invention shown in FIG.

The nut runner multi-axis head 1 shown in FIG. 1 includes a DC drive motor 4, a speed reducer 5, a torque sensor 6, and an encoder (angle sensor) 7, respectively.
The drive motor 4 rotates the socket 8 via the speed reducer 5 to tighten the bolt (or nut) 2 fitted to the socket 8 to the work 3. The torque sensor 6 detects the tightening torque applied to the socket 8 at the time of this tightening, and the detected torque signal is fed back to the CPU 10 of the computer that controls the entire nut runner and used for speed control and torque control described later. Is done. The rotational speed of the socket 8 at the time of tightening is detected by the encoder 7, and the detected encoder signal is used as a feedback signal for tightening the bolt 2 by the speed control method.

The control method of the present invention is a control method for simultaneously tightening one bolt 2 on each of the plurality of heads 1 to the work 3 at the same time. When tightened with the torque Ta, the motor current of each head 1 is controlled so that the target tightening torque Ta is kept constant. When all the heads 1 tighten the bolts 2 with the target tightening torque Ta, each head 1 The bolt tightening operation 1 is completed. Accordingly, the final tightening force (axial force) of each bolt 2 that has been simultaneously started to be tightened by each head 1 and has been completed at the same time becomes more uniform based on the target tightening torque Ta.

The control system of the apparatus of the present invention shown in FIG. 1 for implementing such a control method is divided into a speed control loop 11 and a torque control loop 12, and these two loops 11, 12 are switched and used by loop switching means 13. . The loop switching means 13
For example, a first switch 14 for opening and closing the speed control loop 11
And a second switch 15 for opening and closing the torque control loop 12.
It consists of.

The speed control loop 11 controls the drive of the drive motor 4 of the head 1 at a constant rotation speed.
One speed control arithmetic circuit 17, a first switch 14, a current command circuit 20, a drive circuit 21, a drive motor 4, and an encoder 7 in which a speed command signal is input from 0 through a speed command circuit 16 in the order of one closed loop. Is configured. The torque control loop 12 includes a target tightening torque T when the head 1 tightens the bolt 2 to the work 3 with a predetermined target tightening torque Ta.
a for controlling the motor current of the drive motor 4 so as to maintain the constant a.
, A torque control arithmetic circuit 19 to which a torque command signal is input, a second switch 15, a current command circuit 20, a drive circuit 21, a drive motor 4, and a torque sensor 6 constitute one closed loop in this order.

The bolt tightening is performed in two stages by using the speed control loop 11 first and the torque control loop 12 later. First, the loop switching means 13
, The first switch 14 is turned on and the second switch 15 is turned off, so that only the speed control loop 11 becomes a closed loop, and the bolt 2 is fastened to the work 3 by the speed control method as follows.

A speed command signal from the CPU 10 is calculated by a speed control calculation circuit 17 into a current command value, and the first switch 1
4, the current command circuit 20 outputs a current command signal for driving the drive motor 4 to rotate at a predetermined rotation speed to the drive circuit 21 so that the drive motor 4 is driven. Tightening of the bolt 2 is started. An encoder signal, which is a rotation speed signal of the socket 8 detected by the encoder 7 during the bolt tightening operation, is transmitted to the speed control arithmetic circuit 1.
The speed is controlled so that the rotation speed of the socket 8 becomes constant. Further, a torque signal detected by the torque sensor 6 during the bolt tightening operation is transmitted to the CPU 10.
Is output to the torque control arithmetic circuit 19. When the CPU 10 detects that the input torque signal has reached the preset target tightening torque Ta, the CPU 10 operates the loop switching means 13 to turn off the first switch 14 and turn off the second switch 1.
Switch 5 on. With this switching, the speed control loop 11
Speed control ends, and the torque control loop 1
2 starts the bolt tightening operation by the torque control.

When the CPU 10 determines that the torque signal from the torque sensor 6 has reached the target tightening torque Ta,
The switch switching operation is performed by the loop switching means 13,
The torque command signal is output to the torque control operation circuit 19 via the torque command circuit 18 so that the torque signal maintains the target tightening torque Ta. The torque control calculation circuit 19 calculates C
It calculates a torque command signal from the PU 10 and outputs a current command signal to the current command circuit 20 via the second switch 15. The motor current is controlled by the current command signal, and the tightening torque detected by the torque sensor 6 becomes equal to the target tightening torque T.
The driving of the drive motor 4 is continued so as to maintain the value a.

The bolt tightening operation of the multi-axis head 1 is as follows.
The operation is performed simultaneously for a plurality of heads 1. Then, at time t ₂ the tightening torque has reached the target tightening torque Ta detected by the torque sensor 6 for all head 1, is cut off the motor current in all of the heads 1 is bolt tightening is completed. Results Each head 1 is tightening torque from tightening the bolt 2 to the target tightening torque Ta to tightening completion timing t _2, which is controlled to maintain the target tightening torque Ta as shown in FIG. 2 Then, the tightening forces of all the bolts 2 become values based on the target tightening torque Ta, and variations in the tightening force are reliably suppressed.

[0021]

According to the present invention, when a plurality of bolts or nuts are simultaneously tightened by a multi-axis head to reach a target tightening torque, the tightening is continued by a torque control method so as to maintain the target tightening torque. When all bolts or nuts have been tightened with the target tightening torque, simultaneous tightening is completed.Therefore, all bolts or nuts can be efficiently tightened in a minimum amount of time, and all bolts or nuts can be efficiently tightened. The tightening force is unified with the same target tightening torque, and the variation can be greatly suppressed, and the reliability of the tightening of the multi-axis bolts and the like is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a control device of the present invention.

FIG. 2 is a graph showing a relationship between time and torque during a bolt tightening operation by the nut runner of FIG. 1;

FIG. 3 is a graph showing a relationship between time and torque during a bolt tightening operation by a conventional nut runner control method.

[Explanation of symbols]

Reference Signs List 1 multi-axis head 2 bolt (or nut) 3 work 4 drive motor 11 speed control loop 12 torque control loop 13 loop switching means Ta Target tightening torque

Claims (2)

[Claims] 1. A method for controlling a nut runner having a multi-axial head with a built-in motor, in which a plurality of bolts or nuts are simultaneously tightened to a work and simultaneously tightened, wherein each head tightens a bolt or nut with a predetermined target tightening torque. At the time of tightening, the motor current of each head was controlled by feedback control of the tightening torque so that the target tightening torque was maintained constant, and all the heads tightened the bolts or nuts with the target tightening torque. A nutrunner control method, wherein the motor current of each head is interrupted at a point in time to complete the tightening. 2. A nut runner control device having a multi-axis head with a built-in motor for simultaneously tightening a plurality of bolts or nuts to a work and simultaneously completing the tightening, wherein the drive motor of each head is rotationally controlled at a predetermined rotation speed. And a speed control loop for tightening the bolt or nut to the work to the predetermined target tightening torque, and a target tightening torque at the time when each head tightens the bolt or nut to the work with the predetermined target tightening torque. A torque control loop for controlling the motor current of each head, and a loop switching means for switching the control system from the speed control loop to the torque control loop when each head tightens the bolt or nut to the work with a predetermined target tightening torque. A nutrunner control device, comprising: