JP2010201537A - Method of monitoring poor screw fastening - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein a conventional method of detecting poor screw fastening is adapted to determine pass/fail by measuring an overall rotation time and rotation angle, and the pass/fail is determined after passing a preset time and rotation angle, and therefore, the screw fastening is continued until reaching the set time and rotation angle, thus increasing the possibility of fracture of a screw or a workpiece, and taking considerable time to complete the pass/fail determination. <P>SOLUTION: In a method of monitoring poor screw fastening by a power screw fastening machine including a torque setting device, the time per unit rotation from the start of a screw fastening to the seating thereof is measured, and the screw fastening machine is stopped at the instant when the time per unit rotation departs from a set range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for monitoring a screw tightening failure in an electric or air-driven screw tightener equipped with a tightening torque setting device.

  Conventionally, for the purpose of tightening a screw with a predetermined torque, a power type torque driver equipped with a tightening torque setting device has been widely used. Some torque drivers stop mechanically or electrically when reaching a set tightening torque.

  In the screw tightening process, in addition to tightening the parts with a predetermined appropriate torque, the work is performed as designed, such as the type of screw and the presence or absence of a washer for quality control, or improper work such as diagonal tightening It is also necessary to determine whether or not there is any. For example, in the automatic screw tightening machine disclosed in Patent Document 1, a torque sensor and an encoder are provided to detect a tightening torque and a rotation angle of a main shaft of a driver, a driver bit, a socket, and the like to determine pass / fail. As the determination means, a control unit, storage means, input / output interface and the like are usually configured by a microcomputer, a sequencer, etc., so that various screw tightening operations can be handled.

In addition, the method for detecting galling in an automatic screw tightening machine shown in Patent Document 2 detects the occurrence of galling and reduces screw tightening defects by measuring the time and rotation angle from the beginning of screw tightening to seating. Yes.

JP-A-6-320357 Japanese Patent Laid-Open No. 6-099322

  The conventional screw tightening failure detection method is a method for determining pass / fail by measuring the overall rotation time and rotation angle. For this reason, there is a basic problem that it is not possible to judge pass / fail until after a preset time or rotation angle has elapsed.

Therefore, in the screw tightening process, the screw tightening is continued until the set time or rotation angle is reached. As a result, if there is a defect in the screw tightening, the determination is made, but the possibility of damaging the screw or the work is considerably increased. Moreover, a considerable amount of time elapses until the failure is judged, and it is a method that does not contribute at all to reduce damage or time loss in the case of a failure simply by detecting pass / fail. Met.

  Therefore, as a result of diligent research in view of the above-mentioned problems, the present inventor has achieved the present invention, which is characterized by monitoring screw tightening failure by a power screw tightener equipped with a torque setting device. A method is to measure each time per unit rotation from the beginning of screw tightening to seating, and to stop the screw tightening machine when each time per unit rotation is out of a set range.

  The term “powered screw tightening machine” as used in the present specification refers to a device for rotating a driver bit or a socket by an electric motor or an air motor, and tightening a screw, a bolt, a nut or the like. In the present invention, a power screw tightening machine equipped with a torque setting device is provided with a rotation angle sensor such as a rotary encoder and a timer linked to the rotation angle sensor so as to reduce the time per unit rotation of the driver bit and the socket. measure. The torque setting device is not particularly limited as long as it detects torque and stops mechanically or electrically.

  The screw tightening process is generally divided into temporary tightening, screwing, seating, tightening, and retightening. Temporary tightening is a state in which a screw is attached to a screw hole, and may be tightened by hand or by a screw tightening machine. Screwing is a process of tightening temporarily tightened screws at once with a screw tightening machine. Seating is a place where the head of the screw comes into contact with the workpiece and the torque increases rapidly, and the screw is tightened from here. When the tightening torque is accurately managed, retightening is performed.

  The screw tightening failure monitoring method according to the present invention determines that a screw tightening failure occurs when it deviates from the upper and lower limits of a preset range by measuring each time per unit rotation from the beginning of screw tightening to seating. This is a method of stopping the operation of the screw tightening machine. In other words, most of the screw tightening failures occur during the screwing process, and if the user sits within a predetermined rotation angle and time, the screw tightening is performed normally. In this case, it is not possible to determine whether the strength of the screw is insufficient, but it can be dealt with by using a method of measuring the entire rotation time and rotation angle until the completion of tightening.

For example, when there is an abnormality in a screw thread or a foreign object, it can be determined that the time per unit rotation is longer than the set time. Therefore, if the screw tightening failure is not judged by the method of the present invention, the problem is only the tightening from the seating. In most cases, the power screw tightening machine equipped with the torque setting device is tightened with a predetermined torque. It is possible to perform normally.

The screw tightening failure monitoring apparatus according to the present invention measures each time per unit rotation from the beginning of screw tightening to seating, and compares each time with a set time to determine screw tightening failure. If there is, the screw tightening process can be stopped at the earliest stage. Accordingly, it is possible to minimize damage to screws and workpieces due to defective portions, and to reduce time loss.
For this reason, even if it is not only a worker with little experience but a skilled worker, it has a very useful effect that damage to a work can be reduced and work efficiency can be improved.

It is a graph which shows the relationship between the rotation angle of the screw fastening process in the screw fastening defect monitoring method which concerns on this invention, and a torque. It is a graph which shows the time per unit rotation in the screwing process from the start of screw fastening to seating.

The screw tightening failure monitoring method according to the present invention solves the above problem by monitoring each time per unit rotation of the screwing process.

  As for the relationship between the rotation angle and the torque in the screw tightening process, the rotation angle of the screwing process occupies most of the entire process as shown in FIG. Basically, the torque in the screwing process is low, and tightening is performed at a relatively high rotational speed. In the tightening region after seating and tightening, tightening is performed at a low speed and high torque, and in the tightening process and the tightening process, in most cases, one rotation is not performed. Therefore, screw tightening defects such as screw thread anomalies, foreign object biting, screw length differences, and washer removal can be detected by monitoring the screwing process in detail.

  The screw tightening failure monitoring method according to the present invention is a method for detecting screw tightening failure by monitoring the time per unit rotation in the screwing process. FIG. 2 shows the rotation time (μ seconds) at each rotational speed when the M8 bolt is normally tightened from the start of screw tightening to the seating by a pneumatic screw tightener equipped with a torque setting device. Based on this rotation time, a screw tightening failure is determined by comparison with an actual screwing process. As determination means, a control unit, storage means, input / output, and the like can be configured by a commute microcomputer, a sequencer, or the like, so that various screw tightening operations can be handled.

  In the example of FIG. 1, the screwing process is from the time when the temporary fastening is completed to the seating. Temporary tightening may be performed by hand, tightened with a screw tightener, or may be automatically set. In order to increase the determination accuracy, it is necessary to make the screw tightening start time constant. For example, it is possible to make the screw tightening start constant by rotating the bolt reversely with a screw tightening machine and detecting the position and vibration when the bolt is fitted in the screw hole.

Claims (3)

  A method for monitoring a screw tightening failure by a power screw tightener equipped with a torque setting device, wherein each time per unit rotation is measured by measuring each time per unit rotation from the start of screw tightening to seating. A screw tightening failure monitoring method, wherein the screw tightening machine is stopped when the position is outside the set range.   The screw tightening failure monitoring method according to claim 1, wherein the tightening start of the screw is determined by detecting the position or vibration of the screw in the axial direction by rotating the screw in the reverse direction.   3. The screw tightening failure monitoring method according to claim 2, wherein the seating of the screw is determined by a rapid increase in time per unit rotation when the screw head is tightened.

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