JPH0248181A - Screw tightening with nut runner - Google Patents

Abstract

PURPOSE:To quickly and accurately respond to variation in turning speed and inhibit variation in result of detection at the time of seating by keeping the motor control current constant when a screw is tightened and thereafter detecting the positive seating point of variation in pulse frequency of the turning pulse signal. CONSTITUTION:The driving motor 4 of a nut runner 1 is controlled for the turning using both the turning pulse signal and the motor control current only and variation in pulse frequency of the turning pulse signal is monitored instead of variation in motor control current due to variation in turning mode caused when a screw is tightened. When the screw is tightened up to the seating point, the turning speed of the driving motor 4 is greatly reduced from the high speed to the low speed. The point when resulting variation in pulse frequency of the turning pulse signal exceeds the specified level is considered as the seating point of the screw so that the screw tightening may be detected accurately.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for tightening screws using a nut runner, and more particularly, to a method for automatically tightening screws using a simple nut runner having a rotation angle detector. It is.

[Conventional technology]

Nut runners used for automatic screw tightening are generally equipped with a torque transducer that detects the tightening torque that occurs during operation of the nut runner. In this type of nut runner, when a screw is tightened, the nut runner is driven and controlled based on a torque detection signal outputted from a torque transducer depending on the manner of screw tightening. However, the above-mentioned torque transducer is expensive, and therefore, when a nut runner having this torque transducer is used, there is a possibility that the cost of the screw-tightened product may increase.

Therefore, in recent years, a simple nut runner having a relatively inexpensive rotation angle detector has been gaining popularity in place of the expensive torque transducer.

This type of simple nut runner (1) has a drive motor (4) having a rotation angle detector (3) built into the nut runner body (2) as shown in FIG.
A screw tightening attachment (6) is connected to the output shaft (4a) of 4) via a reducer (5) that decelerates the rotation of the motor and generates a large torque.

When tightening screws with the nut runner (1), the through holes (7a) of the two members (7) and (8) to be screwed are
With the attachment (6) of the nut runner (1) fitted to the head of the nut runner (10), the nut runner body (
2) controls the rotation of the drive motor (4). During this screw tightening, the drive motor (4) is rotationally controlled by a rotation pulse signal FB fed back from the rotation angle detector (3) and a motor control current I based on the rotation pulse signal FB. When tightening screws by controlling the rotation of the drive motor (4), the time required for tightening is shortened by tightening the above-mentioned pole (10) at a high-speed constant rotation from the start of tightening of the drive motor (10) until the time of seating. , and from the time of seating to the time of completion of tightening, the torque is reduced by tightening (10) at a low speed constant rotation. In addition, in the no-load region (10) from the start of tightening to the time of seating, the motor control current ■ and the tightening torque are constant, and in the region of tightening from the time of seating to the time of completion of tightening, the motor control current Control current I and tightening torque both increase.

[Problem that the invention seeks to solve]

By the way, when tightening screws using the nut runner (1) as described above, the rotation of the drive motor (4) is controlled by the rotation pulse signal FB fed back from the rotation angle detector (3) and the motor control current I based on the rotation pulse signal FB. are doing.

In particular, until the seating point is reached by tightening the screws, even if the motor control current l is subject to slight fluctuations due to minute fluctuations in the load, the current fluctuations are corrected at high speed by feedback from the rotation pulse signal FB, and the drive motor ( 4) The rotational fluctuations are suppressed. When the screw tightening reaches the seating point and the load on the drive motor (4) changes greatly, the seating point is detected based on this while monitoring the load fluctuation by the motor control current (2). However, even if an attempt is made to detect the seating point by monitoring the fluctuations of the motor control current I in this way, since the motor control current I is controlled by feedback from the rotation pulse signal FB, the seating point due to the motor control current There is a tendency for timing detection to be delayed, and as a result, there has been a problem in that the accuracy of screw tightening is significantly reduced due to variations in the seating timing detection.

[Means for solving problems]

The present invention was proposed in view of the above-mentioned problems, and is a method for tightening screws while controlling the rotation of a drive motor for a Nando Lunch using a motor control current based on a rotation pulse signal detected from the drive motor. Therefore, when tightening the screws, the seating point is detected by the variation in the pulse cycle of the rotation pulse signal while correcting the variation in the motor control current due to rotation variation and keeping the motor control current constant. This method solves the above-mentioned problems by tightening screws using a nut runner.

[Effect]

In the method of the present invention, the rotation of the drive motor of the nut runner is controlled using only rotation pulse signals and motor control current, and when tightening screws, the fluctuations in the pulse cycle of the rotation pulse signal are used instead of the fluctuations in the motor control current due to rotational fluctuations. Monitor. - When the above-mentioned screw tightening reaches the seating point and the rotational speed of the drive motor shifts from high-speed rotation to low-speed rotation and decreases significantly, and as a result, the pulse period of the rotational pulse signal fluctuates and becomes larger than a certain level. can be detected without variation as the seating point.

〔Example〕

An embodiment in which the method of the present invention is applied to a simple nut runner shown in FIG. 6 will be described with reference to FIGS. 1 to 5. However, the same reference numerals are given to the same or equivalent parts as in FIG. 6, and the explanation thereof will be omitted. The above simple nut runner (
1) has a motor control system including a speed control section (11), a current control section (12), and a driver (13) using a PWM (pulse wide modulation) method, as shown in FIG.

When tightening screws with the nut runner (1), the rotation pulse signals fed back from the rotation angle detector (3), that is, the speed feed bank signal FBI and the current feedback signal FB2, and the speed and current feedback signals FBI, FB2 are used. Driver (based on
The rotation of the drive motor (4) is controlled by the motor control current (■0) sent from the drive motor (4). The screw tightening by controlling the rotation of the drive motor (4) is performed in the no-load region from the tightening start time t to the seating time 11 of (10) as shown in FIGS. 2 and 3. Drive motor (4)
is rotated at a constant high speed, and the bolt (10) is tightened with a constant torque. The tightening from the seating time t1 to the tightening completion time t2 is performed by the drive motor (4
) is rotated at a constant low speed, and the above-mentioned part (10) is tightened while increasing the torque and motor control current 1o.

This screw tightening is performed by comparing the speed feed bank signal FB sent from the rotation angle detector (3) with the desired speed setting value as shown in FIG. A control signal S1 is sent out, this is compared with a current feed bank signal FB2, a current control signal S2 is sent out from the current control section (12), and based on this, a current control signal S2 is sent out from a driver (13).
A motor control current IO is applied to the drive motor (4) from the motor control current IO. As a result, the motor control current Io due to rotational fluctuations
The motor control current Io is held constant while correcting fluctuations in the motor control current Io. The motor control system that maintains the motor control current 1o constant as described above has a drooping characteristic as shown by the solid line in FIG. Note that the broken line in the figure indicates normal motor characteristics. In a motor control system having such drooping characteristics, the range of variation in rotational speed is generally large for a stable current. Therefore, when tightening the screw, the fluctuation of the speed feed bank signal FB, which is a rotation pulse signal, is monitored. Motor control current Io with the above speed feed hack signal FBI
Since the motor control current is controlled at 1o as in the conventional
speed feedbank signal than to monitor fluctuations in the FBI
It is possible to respond more quickly to rotational fluctuations by monitoring fluctuations in rotation. The fluctuation of the speed feedback signal FB mentioned above corresponds to the fluctuation of the pulse period (interval) which is its inverse value, and the seating point is detected while monitoring the fluctuation of this pulse period. That is, as shown in Fig. 5, when tightening a screw, the pulse period decreases rapidly immediately after the start of tightening, and when the rotation of the drive motor (4) stabilizes at high speed, the pulse period becomes constant. is maintained. Then, when the seating time point t1 is reached, the rotational speed of the drive motor (4) rapidly decreases, and the pulse period increases rapidly. The above-mentioned seating time t1 is detected by the fluctuation of this pulse cycle, and from then on, as described above, the tightening moves to the area D2, and the screw tightening is performed at a constant pulse cycle to complete the tightening.

〔Effect of the invention〕

According to the method of the present invention, when tightening a screw, the motor control current is held constant and the seating point is detected by fluctuations in the pulse cycle of the rotation pulse signal. It is possible to respond more quickly and reliably to rotational fluctuations than by detecting the seating point, suppress variations in seating point detection, greatly improve tightening accuracy, and achieve highly reliable screw tightening.

[Brief explanation of the drawing]

Figures 1 to 5 are for explaining one embodiment of the method of the present invention. Figure 1 is a schematic configuration diagram showing the device for tightening screws using a nut runner, and Figure 2 is a diagram showing the tightening with respect to time. Figure 3 is a characteristic diagram showing the relationship between torque and tightening, Figure 4 is a characteristic diagram showing the drooping characteristics in the motor control system, and Figure 5 is a characteristic diagram showing the relationship between tightening and rotational speed. FIG. 3 is a characteristic diagram showing the relationship between pulse period and time. FIG. 6 is a schematic configuration diagram showing an example of the structure of the nut runner. (1) - Nut runner, (4) - Drive motor, FBI
- Rotation pulse signal (velocity feed hack signal), I. Motor control current, 1-at the time of seating. Patent applicant Sanyo Kiko Co., Ltd. Agent Shogo Ebara

Claims (1)

[Claims] (1) A method of tightening screws while controlling the rotation of a drive motor for a nut runner using a motor control current based on a rotation pulse signal detected from the drive motor, which controls the motor by rotational fluctuations when tightening a screw. A method for tightening screws using a nut runner, characterized in that the seating point is detected based on fluctuations in the pulse cycle of the rotation pulse signal, while correcting current fluctuations and keeping the motor control current constant.