JP2010172994A - Screw tightening device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that a member may be damaged due to flow of driving current to a member abutting to an end part of a motor cable with an open circuit since drive voltage is applied to the motor cable with an open circuit before an over-load state is detected in the conventional screw tightening device. <P>SOLUTION: In this screw tightening device, a drive control part 30 applies fine voltage for sending the predetermined fine current to the motor cable 2 before the motor 1 is started. Besides, the drive control part 30 determines whether the fine current flows to the motor cable 2 or not based on an output signal of a current detection sensor 31 input through an A/D converter 32, and detects an open circuit state of the motor cable 2 when determining that the fine current does not flow. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a screw tightening device, and in particular, before a drive voltage is applied to a motor cable by detecting a disconnection state of the motor cable when a weak current does not flow through the motor cable before the motor is started. The present invention relates to a novel improvement for enabling detection of disconnection of a motor cable and avoiding a drive current from flowing to other members.

  Since no patent application has been filed for in-house technology, no literature name is given, but this type of screw tightening device conventionally used is configured as shown in FIG. FIG. 1 is a block diagram showing a conventional screw fastening device. In the figure, a drive control unit 30 of a driver 3 is connected to a motor 1 that performs screw tightening driving via a three-phase motor cable 2 of U, V, and W. The drive control unit 30 is configured by an inverter or the like. The drive control unit 30 is connected to an external power source 4 that outputs three-phase AC power and an operation unit 5 that is operated by an operator. The drive control unit 30 starts to apply the drive voltage to the motor cable 2 when detecting the start command 5a from the operation unit 5, and controls the drive of the motor 1 by controlling the power supplied to the motor 1. To do.

  The drive control unit 30 applies a constant voltage to the motor cable 2 before starting the screw tightening in order to correctly control the screw tightening torque, and takes in the current flowing through the current detection sensor 31 through the A / D converter 32. When the current corresponding to the voltage applied to the motor cable 2 flows, it is determined that the current sensor 31 functions normally.

  For example, a rotation detector 6 such as a resolver or an encoder is connected to the motor 1, and an output 6 a of the rotation detector 6 is input to the drive control unit 30. Here, the rotational speed of the motor 1 is determined based on the drive voltage input to the motor 1. When the drive control unit 30 applies the drive voltage to the motor 1 to drive the motor 1, the drive control unit 30 obtains a speed difference between the command speed based on the drive voltage and the detected speed detected by the rotation detector 6. An overload condition is detected when the value exceeds a predetermined value. When detecting an overload state, the drive control unit 30 stops the application of the drive voltage and generates an overload alarm.

  When the motor cable 2 is disconnected, the drive current due to the drive voltage is not input to the motor 1, so that the speed difference between the command speed and the detected speed becomes large, and an overload alarm is generated. That is, in the conventional device, when an overload alarm occurs, a wiring check or the like is performed manually, and the disconnection of the motor cable 2 is found.

  In the conventional screw tightening device as described above, the application of the drive voltage is stopped when the overload state is detected based on the speed difference between the command speed and the detected speed. A drive voltage is applied to the motor cable 2 that has been disconnected. At this time, if any member is in contact with the end portion of the disconnected motor cable 2, a drive current flows and the member may be damaged.

  The present invention has been made in order to solve the above-described problems. The object of the present invention is to detect disconnection of the motor cable before the drive voltage is applied to the motor cable, and to drive the drive current to other members. It is providing the screw fastening apparatus which can avoid flowing.

  A screw tightening device according to the present invention includes a motor that performs screw tightening driving, and a drive control that is connected to the motor via a motor cable and controls electric power supplied to the motor to control driving of the motor. A current detection sensor that is provided in the motor cable and detects a current flowing through the motor cable; and an A / D converter connected to the current detection sensor. A predetermined weak current flows before starting, and whether or not the weak current flows through the motor cable is determined based on an output signal of the current detection sensor input via the A / D converter. When it is determined that the weak current is not flowing, the disconnection state of the motor cable is detected.

  According to the screw tightening device of the present invention, when a motor is started, a weak current is passed through the motor cable, and when it is determined that the weak current is not flowing, the disconnection state of the motor cable is detected. The disconnection of the motor cable can be detected before the current flows.

It is a block diagram which shows the screw fastening apparatus by the prior art and Embodiment 1 of this invention.

The best mode for carrying out the present invention will be described below with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a screw tightening device according to Embodiment 1 of the present invention. The same or equivalent parts as those of the conventional screw fastening device will be described using the same reference numerals. In the figure, a drive control unit 30 of a driver 3 is connected to a motor 1 that performs screw tightening driving via a three-phase motor cable 2 of U, V, and W. The drive control unit 30 is composed of an inverter or the like, and the drive control unit 30 is connected to an external power supply 4 that outputs three-phase AC power. The drive control unit 30 controls the drive of the motor 1 by starting the application of the drive voltage to the motor cable 2 and controlling the power supplied to the motor 1.

  For example, a rotation detector 6 such as a resolver or an encoder is connected to the motor 1, and an output 6 a of the rotation detector 6 is input to the drive control unit 30. Here, the rotational speed of the motor 1 is determined based on the drive voltage input to the motor 1. When the drive control unit 30 applies the drive voltage to the motor 1 to drive the motor 1, the drive control unit 30 obtains a speed difference between the command speed based on the drive voltage and the detected speed detected by the rotation detector 6. An overload condition is detected when the value exceeds a predetermined value. When detecting an overload state, the drive control unit 30 stops the application of the drive voltage and generates an overload alarm.

  The motor cable 2 between the drive control unit 30 and the motor 1 is provided with a current detection sensor 31 made of, for example, a shunt resistor or a Hall element. The current detection sensor 31 detects a current flowing through the U-phase and V-phase motor cables 2, and an output signal of the current detection sensor 31 is driven by a CPU or the like via an A / D converter 32. Input to the control unit 30.

  The drive control unit 30 applies a weak voltage for flowing a predetermined weak current to the motor cable 2 before the motor 1 is started. Specifically, the drive control unit 30 applies a weak voltage to the motor cable 2 when detecting the activation command 5a from the operation unit 5 operated by the operator. Further, the drive control unit 30 determines whether or not the weak current flows through the motor cable 2 based on the output signal of the current detection sensor 31 input via the A / D converter 32. Note that the weak voltage is for flowing a weak current that does not allow the motor 1 to move, and is a voltage smaller than the drive voltage.

  When the drive control unit 30 determines that the weak current is flowing, the drive control unit 30 detects the non-disconnection state of the motor cable 2 and starts applying the drive voltage to the motor cable 2.

  Moreover, when it determines with the said weak electric current not flowing, the drive control part 30 detects the disconnection state of the said motor cable 2, and generates a disconnection alarm. That is, when the disconnection state is detected, the drive voltage is not applied to the motor cable 2. As a result, the disconnection of the motor cable 2 can be detected before the drive voltage is applied to the motor cable 2, and the drive current can be prevented from flowing to other members.

DESCRIPTION OF SYMBOLS 1 Motor 2 Motor cable 30 Drive control part 31 Current detection sensor 32 A / D converter

Claims (1)

A motor (1) for driving screw tightening;
A drive control unit (30) connected to the motor (1) via a motor cable (2) and controlling the drive of the motor (1) by controlling the power supplied to the motor (1);
A current detection sensor (31) provided on the motor cable (2) for detecting a current flowing through the motor cable (2);
An A / D converter (32) connected to the current detection sensor (31),
The drive control unit (30) allows a predetermined weak current to flow before the motor (1) is started, and also inputs the current detection sensor (31) via the A / D converter (32). It is determined whether or not the weak current has flowed through the motor cable (2) based on the output signal, and when it is determined that the weak current is not flowing, the disconnection state of the motor cable (2) is detected. A screw fastening device characterized by that.

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