JPH02284833A - Thread fastening method - Google Patents

Abstract

PURPOSE:To efficiently secure a competent screw state by moving at high speed a thread fastening bit until a thread fastening start position and controlling a pressurizing force according to the kind of a screw and the screw position until the thread fastening completion after the thread fastening starts. CONSTITUTION:The bit 1a of a thread fastening head 1 is rotated and driven by the motor 2 for rotating a bit consisting of a servomotor and the rotating position thereof is detected by an encoder 3. The thread fastening head 1 is guided freely liftably by a lift guide 4 and a nut 6 screwed with a lift screw shaft 5 is fixed as well. To the motor 7 for lift consisting of the servomotor rotating and driving the lift screw shaft 5 an encoder 8 for detecting the rotating position thereof is fitted, and the gear 9a fitted to the output shaft thereof and the gear 9b fitted to one end of the lift screw shaft 5 are linked via a toothed belt 10. The lift motor 7 is then driven and controlled via a driving circuit 12 based on the control signal output from the control circuit 11 of the lift motor 7 and the feeding of the thread fastening head 1 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a screw tightening method, and more particularly to a screw tightening head feed control method.

Conventional technology In conventional automatic screw tightening machines, an air cylinder device is generally used as a means to move the screw tightening head in the distance direction relative to the workpiece because it can easily apply a constant pressure force. It is being

In addition, for those that drive the screw tightening head with a motor,
The screw tightening head is configured to move at a constant speed with a buffer spring interposed between the bit and the screw tightening head main body.

Problem to be Solved by the Invention However, when using an air cylinder device, it is extremely difficult to change the speed during movement. becomes excessive. As a result, due to the frictional force generated by this pressurizing force, the tightening torque is affected, the tightening torque becomes unstable, and in some cases, the tightening operation ends with the screw floating, resulting in a screw-in failure. There is a problem that this may occur.

In addition, if the screw is moved at a constant speed by motor drive and a buffer spring is installed, the appropriate pressure cannot be applied unless the spring is replaced when tightening screws of various sizes. Similarly, there is a problem that screw-in failure may occur.

In view of the above conventional problems, the present invention aims to provide a screw tightening method that allows a screw tightening bit to be moved at high speed to a screw tightening starting position and that can ensure a proper screwed state.

Means for Solving the Problems In order to achieve the above object, the present invention provides a method for tightening a screw to a workpiece using a rotatable bit, the method comprising: a screw tightening process until the tip of the screw reaches the workpiece and the screw tightening is started; The bit is moved at a predetermined speed, and then the bit is moved by applying a predetermined pressing force depending on the type of screw and the screwing position until the screw is completely tightened onto the workpiece.

According to the present invention, the screw is moved as fast as possible within an appropriate range by speed control until it reaches the position where screw tightening is started, and the pressurizing force is applied depending on the type of screw and the screw position after screw tightening is started and until the screw tightening is completed. Since the screws are controlled and moved, the screws can be screwed in with a pressing force that is appropriate for the type of screw, and an appropriate screwing state can always be ensured efficiently regardless of the type of screw.

Embodiment Hereinafter, an embodiment of the present invention will be described based on FIGS. 1 and 2.

First, a schematic configuration of a lifting/lowering driving section of a screw tightening head in a screw tightening machine will be explained with reference to FIG. 1 is a screw tightening head, and la is its bit. The pill-1a is rotationally driven by a bit rotation motor 2 consisting of a servo motor, and its rotational position is detected by an encoder 3. This screw tightening head 1 is guided by an elevating guide 4 so as to be movable up and down, and a nut 6 screwed onto an elevating screw shaft 5 is fixed. Reference numeral 7 denotes an elevating motor consisting of a servo motor that rotationally drives the elevating screw shaft 5, and an encoder 8 is attached to detect the rotational position of the elevating motor. 11 is a control circuit for the lifting motor 7, in which a gear 9a attached to the output shaft of the lifting motor 7 and a gear 9b attached to one end of the lifting screw shaft 5 are connected via a toothed belt 10;
Based on the control signal output from the control circuit 11, the lifting motor 7 is driven and controlled via the drive circuit 12.

The control circuit 11 includes the output signals of the encoders 3 and 8 of the focusing rotation motor 2 and the lifting motor 7, the length of the screw to be tightened, the screw tightening height position, the screw diameter, the screw pitch, and the machine screw. Screw tightening data regarding types of screws such as types of screws, tamping screws, etc. is input.

Next, the operation will be explained with reference to FIG.

First, the screw tightening head 1 is positioned above the screw tightening position of the workpiece by means of an x-Y axis moving means (not shown).

Thereafter, the bit rotation motor 2 is controlled by a control circuit (not shown), and the preset tightening is rotationally driven based on screw tightening conditions such as torque and a screw tightening pattern depending on the type of screw.

On the other hand, the lifting motor 7 is started in the control circuit 11 via the drive circuit 12, and the screw tightening head l starts screwing into the workpiece from position 70, which is the origin position, as shown in FIG. 1(a). It descends at a high speed V toward the Z1 position, as shown in FIG. 1(b). During its descent, the screw is attracted and engages with the bit la.

The screwing start position Z1 is calculated from the screw length input in the control circuit 11 and the screwing height position of the workpiece. When the screw tightening head l reaches the Z1 position, the speed control is then switched to torque control and the lowering operation is controlled until the screw tightening is completed at position 22, as shown in FIG. 1(b). That is, as shown in FIG. 1(b) by a solid line, a broken line, a dashed line, etc., the screw is lowered with a torque corresponding to the screwing position based on a predetermined torque pattern corresponding to the type of screw to be tightened. Driven. The screwing position is detected based on a signal input from the encoder 3 of the bit rotation motor 2 to the control circuit 11. In this way, screw tightening is performed with a predetermined pressing force applied to the bit la depending on the type of screw and the screwing position.

In principle, the pressing force of the bit la is controlled by controlling the output torque of the lifting motor 7.
If you try to detect and control the output torque of the motor, you will need a torque detector, which will increase the cost. On the other hand, since current and torque are approximately proportional to each other, it is actually possible to control the pressurizing force by controlling the current. It's in control.

On the other hand, the bit rotation motor 2 is driven to rotate based on the predetermined screw tightening pattern as described above, but in the final stage, the current value is gradually increased to gradually increase the screw tightening torque, and when the screw tightening torque reaches the predetermined torque value, Screw tightening is completed by tightening with that torque for a predetermined time.

When the screw tightening is completed, the lifting motor 7 is driven in reverse,
One screw tightening operation is completed by returning to the home position Wizzo at high speed.

As described above, according to this embodiment, the screw can be lowered at high speed until the start of screwing, and then the screwing operation can be performed by applying an appropriate pressing force, and automatic screw tightening of precision and minute screws can also be performed reliably and stably.

Effects of the Invention According to the screw tightening method of the present invention, as is clear from the above explanation, the screw is moved as fast as possible within an appropriate range by speed control to the position where screw tightening is started, and after the screw tightening is started, Since the pressurizing force is controlled according to the type of screw and the screwing position until the screw is tightened, it is possible to efficiently tighten any type of screw, such as precision screws or micro screws, with the appropriate screwing state. It has a great effect.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention, and FIG. 1 (
a) and (b) are explanatory diagrams of the raising and lowering operation of the screw tightening head in the screw tightening process and its speed control, and FIG. 2 is a schematic diagram of the construction of the raising and lowering driving means. 1... Screw tightening head, 1a... Bit, 5... Lifting screw shaft, 7... Lifting motor, 11... control circuit. Agent: Patent attorney Shigetaka Awano and one other person Figure 1 Figure 2

Claims (1)

[Claims] A method of tightening a screw to a workpiece using a rotatable bit, in which the bit is moved at a predetermined speed to a position where the tip of the screw reaches the workpiece and screw tightening starts, and then the screw is tightened to the workpiece. A screw tightening method characterized in that the bit is moved by applying a predetermined pressing force depending on the type of screw and the screwing position until completion.