JPH0265975A - Loosening method for screw by automatic screw tightening machine - Google Patents

Abstract

PURPOSE:To effectively perform a screw loosening work by detecting the meshing of a bit and screw by loosening a screw. CONSTITUTION:In case of a bit getting into contact with a screw and biting with the head thereof, the rotation of the bit is stopped. Meanwhile, the output of an encoder E1 is monitored by a computer CP and the current value, the number of rotations and rotating direction equivalent to the screw loosening torque for the motor M1 for screw tightening are commanded with the elimination of the output by the rotation stoppage of the bit as timing. Accordingly, current is fed through a 1st controller C1 and the bit is going to rotate in the direction loosening the screw. The output of the encoder E1 is then monitored by the computer CP in advance and at the time when specified rotations are obtained in the reverse direction to the previous time the screw is decided to be loosened and a command is rendered so as to stop the operation of the motor M1 for tightening screw and the cylinder CL1 for pressing the bit.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention provides a method for loosening screws that have already been temporarily tightened or fully tightened when tightening screws on a workpiece using an automatic screw tightening machine. It is related to.

(Prior technology) When tightening screws on a workpiece using an automatic screwdriver, it is not only necessary to install and tighten new screws, but also to tighten screws that have already been temporarily or fully tightened on the workpiece. After loosening, it is often necessary to fully tighten again. Generally, when automatically assembling workpieces, temporary tightening is performed to prevent components from becoming separated before final tightening. During final tightening, work such as accurate positioning of components and addition of other components is required. .

In such cases, the bit of the automatic screw tightener is rotated in the direction of loosening the screw by applying it to the screw head, detecting whether the bit has engaged with the screw head by detecting changes in the current of the screw tightening motor, etc. It gives rotation for. However, when the temporary tightening torque is small, or when the difference between the temporary tightening torque and the frictional resistance torque when loosening is small, changes in the current value etc. are small, making it difficult to judge whether the bit and screw head have engaged. Alternatively, the bit may be rotated with enough torque to prevent the screw from loosening, pressing the bit against the screw, and when the rotation stops, it is determined that the bit has engaged with the screw head, but in this case, the screw has already loosened. It is possible that there are.

In this way, it was difficult to judge whether the bit had engaged with the screw head or not ((), which was an obstacle to tightening screws using an automatic screwdriver.

(Problem to be Solved) The problem of this invention is to use such an automatic screw tightening machine to reliably detect the engagement of a bit and screw when loosening a screw that has already been temporarily or fully tightened. The objective is to make the screw loosening work more efficient by doing so, and to make the entire screw tightening work including the loosening work more efficient.

(Means for Solving the Problems) In the present invention, when a workpiece to be screwed is set in a predetermined position, an automatic screw tightening machine is commanded to loosen the screw. The contents include the pressing of the bit of the automatic screw tightening machine against the screw head, and the torque and rotation direction for tightening the screw for the screw wire motor. Then, the bit of the screw tightening machine is pressed against the head of the screw to be loosened, and the screw wire motor rotates. Therefore, the output of the rotation detector connected to the screw wire motor is monitored, and when the output becomes zero, a command is given to loosen the screw.

The contents include the torque, rotation speed, and direction of rotation for loosening the screw. Then, the rotation direction and output of the rotation detector are monitored, and if the rotation direction and output are in the desired direction, the rotation of the screw tightening motor is stopped and the pressing of the bit is released.

(Example) An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 is a schematic plan view, in which the automatic screw tightening machine 1 is mounted on the lower surface of a bracket 3 of a Z-axis stand 2 that is movable in the Z-axis direction (perpendicular to the plane of the paper), and the two-axis stand 2 is It is attached to the frame 4 so as to be movable in the axial direction.

The automatic screw tightening machine 1 has a bit 5 attached to its tip for tightening screws, and a threaded wire motor M! attached to the rear. driven by.

Further, the bit 5 is moved forward and backward by a pit pressing cylinder 6 attached to the rear of the automatic screw tightening machine 1, and is pushed toward the tip by a spring (not shown) built in the tip of the automatic screw tightening machine 1. Forced.

On the other hand, the 27th workpiece 9 to which the first workpiece 7 is temporarily fixed with the screw 8 is positioned and held on the worktable 13 by the workpiece holders 10, 11, and 12.

The work table 13 is mounted on a pedestal 14 so as to be able to move upward in the X and Y directions and rotate within the XY plane by means of a mechanism and a motor (not shown).

Figure 2 is a block diagram of the control circuit for the screw wire motor M.
The output of the encoder Et connected to I is connected to a bus B to which is connected a computer C that has programmed the operation of the screw tightening operation. Also, screw wire motor M! connects the same bus B via the first controller CI supplying current
The bit pressing cylinder CLt is also connected to the bus B.

The screw tightening machine moving motor M2 moves the two-axis stand 2 on which the automatic screw tightening machine 1 is mounted in the Y-axis direction, and is connected to the bus B via the second controller C2. In addition, a motor for moving the bracket 3 of the two-axis stand 2 in two-axis directions, and a work table 13'? : A motor for moving or rotating is also connected to bus B, although not shown.

A first workpiece 7 temporarily fastened to a second workpiece 9 with screws 8 is carried onto a worktable 13 by a transport device (not shown), and is positioned and held by workpiece holders 10, 11, 12. Then, when the screw 8 and the automatic screw driver 1 face each other, the Y-axis direction position and rotational position of the work table 13 and the two-axis direction positions of the automatic screw driver are adjusted so that the screw 8 and the automatic screw driver 1 face each other. Then, by operating a switch (not shown),
A screw tightening operation is commanded.

Next, the second controller supplies current to the automatic screw tightening machine movement motor M2, and the screw tightening machine 1 moves in the Y-axis direction and enters from the sheltered position to a position directly facing the screw 8. .

Next, the extension of the bit pressing cylinder 6 and the current value and rotation direction corresponding to the screw tightening torque for the screw wire motor Ml are commanded, and the bit 5 approaches the screw 8 while rotating.

When the bit 5 contacts the screw 8 and further engages with its head,
50 rotations in the pit stop. During this time, the output of the encoder E1 is monitored by the computer CP, and the output of the encoder E1 is monitored by the pit 50.
When the output stops due to rotation stop, the current value, rotation speed, and rotation direction corresponding to the screw loosening torque are commanded to the screw wire motor M1.As a result, the current is supplied through the first controller. , the bit 5 attempts to rotate the screw 8 in the loosening direction.

Then, the output of the encoder E1 is monitored by the computer CP, and when a predetermined amount of rotation is obtained in the opposite direction to the previous one, it is determined that the screw 8 is loosened, and the screw wire motor M1 and the bit pressing cylinder are Retire.

If there are multiple screws, the same operation is performed for each screw, then predetermined operations such as accurate positioning of the two workpieces are performed, and normal screw tightening operations are performed one after another.

When loosening a screw, the rotational speed commanded to the threaded wire motor M1 is such that if the screw is only slightly loosened, the bit is rotated by about half a rotation, and is usually around this level. However, depending on the application, the rotation speed may be higher.

Note that at the beginning of the screw loosening operation, a torque slightly weaker than the predetermined screw loosening torque can be applied to the bit, and then the predetermined torque can be applied. In this way,
If the bit does not come off the screw head at all (in addition, if the screw loosens at this point, you can predict a problem.

This screw loosening method can also be used for screw tightening work using other types of screw tightening tools.

(Effects) As described above, according to the present invention, the bit of the automatic screw tightening machine and the screw head can be reliably engaged with a simple operation, so that the work of loosening the screw can be performed efficiently.
Automatic screw tightening work can be made more efficient.

[Brief explanation of the drawing]

The drawings show an embodiment of the invention, with FIG. 1 being a schematic plan view, FIG. 2 being a block diagram, and FIG. 3 being a flow diagram. In the drawing, 1 is an automatic screw tightening machine, 5 is a bit, 7 is a workpiece, 8 is a screw, 9 is a workpiece, Ml is a threaded wire motor, and E! is an encoder. Diagram

Claims (1)

[Claims] A method for loosening screws that have been temporarily tightened or fully tightened to a workpiece during the process of tightening screws to the workpiece by an automatic screw tightening machine, the method comprising: Applying screw tightening torque and rotation in the screw tightening direction to the screw tightening motor that rotates the bit of the automatic screw tightening machine to press the bit, and detect the rotation of the screw tightening motor. When it is determined that this rotation has stopped, the screw loosening torque and rotation of a predetermined number of rotations in the screw loosening direction are applied to the screw tightening motor, the rotation of the screw tightening motor is detected, and this rotation is detected. A method for loosening a screw in which the rotation of the screw tightening motor is stopped and the pressing of the bit is released when it is determined that the screw has rotated by a predetermined amount in the direction of loosening the screw.