JPH02198725A - Detecting device for fastening screw - Google Patents

Abstract

PURPOSE:To accurately detect the completion of screw fastening and a defective screw fastening by detecting the load torque increased according to the progress of a screw fastening from the motor current, in the screw fastening detecting device of an automatic screw fastening machine. CONSTITUTION:This screw fastening detection device is formed by a current monitoring means monitoring the motor current increased according to the load torque in a motor M for driving of the driver 2 for fastening a screw, and the position detecting means of the driver 2. The current monitoring means is composed of a current transformer and the decision circuit amplifying the output of the current transformer and deciding the current level thereof by comparing with a reference level as well and to the decision circuit variable resistor for setting the reference levels of high and low two kinds is connected. In this screw fastening machine, at the time when a signal, etc., informing of the member subjected to screw fastening coming to the necessary position are received, a cylinder 13 is actuated to start the descent of the driver 2 and the driver 2 is ascended by its restoring when the driver 2 reaches to the position where a limit switch 15 is driven by this descent.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a screw tightening detection device for detecting completion of screw tightening and failure of screw tightening in an automatic screw tightening machine.

[Conventional technology]

As an automatic screw tightening machine, there is a type shown in FIG. This is achieved by providing a pedestal 12 on the slide rail l that is slidable up and down via a linear belling 11,
An electric screwdriver 2 is attached to this frame 12, a cylinder 13 operated by hydraulic or pneumatic pressure is attached to the slide rail 1, a piston rod 14 of the cylinder 13 is attached to the frame 12, and the bit 20 attached to the driver 2 is attached to the front side. A screw chuck 21 for holding screws that are sequentially supplied one by one through a supply path 22 from a parts feeder (not shown) is provided. In this case, a limit switch 15 is arranged below the pedestal 12, and a metal sensor 23 is arranged in the middle of the supply path 22, so that the screws detected by the metal sensor 23 pass through the supply path 22 and the screws are screwed. chuck 21
Completion of screw tightening is detected by detecting that the driver 2 is lowered to the screw tightening completion position by the cylinder 13 and by detecting by the limit switch 15 that the screw driver 2 is lowered to the screw tightening completion position by being driven by the cylinder 13.

[Problem to be solved by the invention]

However, the above-mentioned method has a problem of low reliability because it does not directly detect whether the screw has been properly tightened. For example, even if a screw is not sent to the screw chuck 21 due to a blockage occurring after passing through the detection part by the metal sensor 23, the limit switch 15 indicates that the screwdriver 2 has descended to the required position. If it is output, it means that the screw tightening has been completed even though the screw tightening work was not actually performed. Furthermore, there is a problem in that it is not possible to detect failures in passage detection by the metal sensor 23 or clogging of screws in the screw chuck 21. The present invention has been made in view of these points, and its purpose is to provide a screw tightening detection device that can accurately detect the completion of screw tightening and the failure of screw tightening.

[Means to solve the problem]

Therefore, the screw tightening detection device according to the present invention is formed by current monitoring means for monitoring the motor current that increases in accordance with the load torque in the drive motor of the screw tightening screwdriver, and driver position detection means. It has characteristics. [Function] The load torque that increases as screw tightening progresses is detected from the motor current, and the screw tightening is determined depending on whether the detected load torque reaches the required value when the screwdriver reaches the required position. This is to detect that tightening has been completed. [Example] The present invention will be described in detail below based on the illustrated example. FIG. 1 shows an automatic screw tightening machine, which has almost the same form as that shown in the conventional example above. That is, the slide rail 1 is provided with a pedestal 12 that is slidable up and down via a linear belling 11, and the pedestal 12 is
An electric screwdriver 2 is attached to the screwdriver 2, a cylinder 13 operated by hydraulic pressure or pneumatic pressure is attached to the slide rail 1, a piston rod 14 of the cylinder 13 is attached to the frame 12, and in front of the bit 20 attached to the screwdriver 2, A screw chuck 21 is arranged to hold screws that are sequentially supplied one by one through a supply 2822 from a parts feeder (not shown). Also, pedestal 1
A limit switch 15 is arranged below the screwdriver 2 to detect when the screwdriver 2 has descended to the screw tightening completion position. As the drive motor M in the driver 2, a motor whose motor current increases according to the load torque as shown in FIG. 3, here a three-phase AC motor as shown in FIG. 2, is used. A current transformer 3 is attached to one phase of the power line of the motor M. The current monitoring means consists of this current transformer 3 and a determination circuit 4 that amplifies the output of the current transformer 3 and compares and determines the current level with a reference level. Setting variable resistors 41 and 42 are connected. However, in the above-mentioned screw tightening machine, when the screw tightening machine receives a signal indicating that the member to be tightened has arrived at the required position, it operates the cylinder 13 to start lowering the driver 2, and this lowering When the screwdriver 2 reaches the position where the limit switch 15 is driven by Detects defects in screw tightening. In other words, the determination circuit 4 is delayed by the time from the start of the descent of the driver 2 by the cylinder 13 in the screw tightening machine until the tip of the bit 20 engages with the head of the screw 5 and the screw tightening work actually starts. After that, the motor current monitoring operation starts. Here, the load torque (motor current) during tightening of the screw 5 increases as the tip of the screw 5 enters the object 6, and after the screw 5 has been screwed into the object 6 to a certain extent. , keeps a constant value for a while,
Then, the tightening of the screw 5 increases rapidly from just before completion. Now, the time point at which the above-mentioned operation of the determination circuit 4 starts is 8 in FIG.
If the motor current at this point has not reached the low-level side reference current level A set by the reference level setting variable resistor 42, the judgment circuit 4 will detect a screw missing error or bit 20'. Notify that a chip has occurred. Furthermore, if the high-level side reference current level All set by the reference level setting variable resistor 41 is exceeded between the time when the above-mentioned operation starts and the time when the limit switch 15 is activated, at this time, Abnormality of motor M or screw chuck 21
Notify of any abnormalities within the system. During the monitoring period, if the motor current level remains within the high and low reference current levels A, , AL, it is detected that the screws have been tightened properly. Note that the screw tightening detection device may operate only at one point in time immediately before the limit switch 15 operates. Furthermore, in the above method, the position of the driver 2 is detected indirectly based on the elapsed time from the start of its operation.
Direct detection may be performed using a limit switch or the like.

【Effect of the invention】

As described above, the screw tightening detection device of the present invention is formed of a current monitoring means for monitoring the motor current that increases according to the load torque in the drive motor of the screw tightening screwdriver, and a driver position detection means. , the load torque that increases as screw tightening progresses is detected from the motor current, and the load l detected when the driver reaches the required position.
・Since screw tightening is detected by whether or not the torque reaches the required value, screw tightening can be directly detected, and for this reason, accurate detection is required. Not only that, but it can also detect screw tightening failures and abnormalities.

[Brief explanation of the drawing]

Fig. 1 is a schematic side view of an automatic screw tightening machine equipped with an embodiment of the present invention, Fig. 2 is a block circuit diagram of the same as the above, Fig. 3 is a load torque-motor current characteristic diagram of the same as the above motor, and Fig. 4 is an explanatory diagram for explaining the same operation as above, and FIG. 5 is a schematic side view of the conventional example, in which 2 is a driver, 3 is a current transformer, 4 is a determination circuit, 5 is a screw, and M is a motor. Agent Patent Attorney Ishi 1) Chief 7116

Claims (1)

[Claims] (1) A screw tightening detection device comprising a current monitoring means for monitoring a motor current that increases in accordance with the load torque of a drive motor of a screw tightening screwdriver, and a driver position detection means.