JP2006043852A - Automatic screw fastening machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic screw fastening machine capable of accurately detecting the revolution angle during screw fastening work. <P>SOLUTION: The machine in this invention is equipped with a driver bit 31, which revolves due to the driving of an AC servo motor 30; an encoder 30a, which can issue revolving signals in accordance with the driving of the motor 30; a distortion member 32, which is installed in connection with the motor 30 and can be elastically deformed to the revolving direction or counter-revolving direction of the driver bit 31 depending on screw fastening torque applied on the driver bit 31; a distortion gauge 34, which issues signals in accordance with an elastic deformation amount of the distortion member 32; and a control unit 4, designed to compensate information about the revolution angle of the motor 30 due to the revolution signals for the encoder 30a based on signals from the distortion gauge 34. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an automatic screw tightening machine for tightening a screw on a workpiece, and more particularly, to an automatic screw tightening machine capable of detecting a screw tightening torque by distortion of a strain generating member.

  Conventionally, as an automatic screw tightening machine with a torque sensor having a function of detecting a screw tightening torque, there is one described in Patent Document 1. This patent document 1 shows a nut runner, which is configured by installing a mechanism portion attached to a support plate. The mechanism is configured by connecting an output shaft having a socket that can be engaged with a screw member to a rotation driving means, and connecting the rotation driving means and the support plate with a torque sensor. The torque sensor is configured by attaching a strain gauge to a thin cylindrical main body and connecting the strain gauge to a detection unit. In this configuration, when the rotation driving means is driven to transmit the rotation to the socket and the screw member engaged therewith is tightened, the cylindrical body is distorted by the tightening reaction force at this time, and a voltage corresponding to the distortion is generated. Output from strain gauge. From this output voltage, the torque generated by tightening the screw member is detected by the detection unit.

Japanese Patent Laid-Open No. 11-347856

  In tightening the screw, a tightening method using a so-called torque method is effective in which the tightening torque of the screw is monitored and the screw is tightened until the torque reaches a predetermined torque. The problem with tightening screws using this torque method is that if excessive torque is generated when the screw does not properly bite into the female screw, etc., screw tightening is completed even during screw tightening. It is to do. In order to cope with this, for example, a so-called angle-type tightening method in which the rotation angle of the screw from the tightening start position is monitored to check whether or not the rotation angle has reached a predetermined rotation angle is also employed. By using both the torque method and the angle method, it is possible to perform screw tightening with higher accuracy (with less occurrence of tightening failure). However, in the case of the structure such as the nutrunner, the rotation driving means itself also rotates with the distortion (twisting) of the cylindrical main body. Therefore, when the rotation angle is obtained from the output signal of the encoder of the rotation driving means, this rotation An error has occurred between the angle and the actual rotation angle of the screw, causing problems such as inability to accurately manage the angle.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an automatic screw tightening machine capable of accurately detecting a rotation angle at the time of screw tightening. In order to achieve this object, the present invention provides a rotation drive means, a driver bit that rotates by receiving the rotation drive means, and a rotation detection means capable of transmitting a rotation signal in accordance with the drive of the rotation drive means. A strain generating member coupled to the rotation driving means and elastically deformable in the rotational direction of the driver bit or in the opposite direction in accordance with a tightening torque of a screw acting on the driver bit, and elastic deformation of the strain generating member Distortion detection means for emitting a signal corresponding to the amount, and a control unit for correcting rotation angle information based on the rotation signal of the rotation detection means based on the signal of the distortion detection means.

  The automatic screw tightening machine according to the present invention corrects the rotation angle information obtained from the signal of the rotation detecting means according to the strain of the strain generating member. Therefore, when the strain generating member is connected to the rotation driving means, even if the rotation driving means rotates integrally with the strain generating member, the rotation angle obtained from the signal of the rotation detecting means such as an encoder provided in the rotation driving means can be obtained. It is possible to match the actual rotation angle of the screw. Thus, there is an advantage that extremely accurate screw tightening can be realized by using the angle method together with performing tightening by the torque method with high accuracy using the strain generating member.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes an automatic screwing machine, which includes a reciprocating drive unit 2, a tool unit 3 connected to the reciprocating drive unit 2, and a control unit 4 that controls the tool unit 3.

  The reciprocating drive unit 2 includes a ball screw mechanism 21 connected to an AC servo motor 20 (hereinafter simply referred to as a motor 20) having an encoder 20a, and a tool table 22 connected to a nut member 21a of the ball screw mechanism 21. It consists of and. The tool unit 3 is installed on the tool table 22. A dedicated ASIC circuit (not shown) is incorporated in the motor 20 of the reciprocating drive unit 2 so that the number of pulse signals generated by the encoder 20a can be measured.

  The tool unit 3 includes an AC servomotor 30 (hereinafter simply referred to as a motor 30) as a rotation driving unit. The motor 30 is provided with an encoder 30a which is an example of rotation detection means. When the motor 30 is driven and its drive shaft 30b rotates, a pulse signal is generated from the encoder 30a as a rotation signal corresponding to this. It is done. Further, the lower part of the motor 30 is a speed reducer 30c, and the drive shaft 30b rotates at the number of rotations decelerated by the speed reducer 30c. The motor 30 also incorporates a dedicated ASIC circuit (not shown), and is configured to measure a pulse signal generated by the encoder 30a. A driver bit 31 is coupled to the drive shaft 30b of the motor 30 so as to rotate integrally. The driver bit 31 has a tip shape that engages with a cross-shaped drive hole recessed in the head of the screw. Further, one end of a thin cylindrical strain generating member 32 is connected to the lower portion of the speed reducer 30 b of the motor 30 so as to include the driver bit 31. The other end of the strain generating member 32 is fixed to a flange member 33 for installing the tool unit 3 on the tool table 22. Further, as an example of a strain detecting means for generating a signal corresponding to the amount of elastic deformation of the strain generating member 32, four strain gauges 34. It is. These strain gauges 34 have output voltage signals that change in accordance with the amount of elastic deformation of the strain-generating member 32, and as shown in FIG. 2, these are the same Wheatstone bridges disclosed in Patent Document 1. A circuit is configured and connected to a later-described measurement unit 47 of the control unit 4 via an amplifier 35 and an analog / digital conversion unit 36 (hereinafter referred to as an A / D conversion unit 36).

  The control unit 4 includes a control unit 40, a motor drive unit 41 that controls a load current value to the motor 20, a motor drive unit 42 that controls a load current value to the motor 30, and an encoder 30a for tightening torque. A storage unit 43 storing various programs and parameters necessary for control of the tool unit 3 including a correction value of the number of pulse signals, an operation unit 44 for inputting various information and signals, and various information are displayed. It comprises a display unit 45, an input / output unit 46 connected to the ASIC circuit of each of the motors 20 and 30, and a measurement unit 47 for determining the tightening torque from the output voltage signal of the strain gauges 34.

As shown in FIG. 3 and FIG.
S01: Waiting for input of start command signal.
S02: Both the first flag and the second flag are turned off.
S03: A drive command signal is transmitted to the motor drive unit 41.
S04: The number of pulse signals of the encoder 20a is read.
S05: Check whether the number of pulse signals of the encoder 20a has reached the target value. If not, jump to S04.
S06: A drive command signal is transmitted to the motor drive unit 42.
S07: The number of pulse signals of the encoder 30a is read.
S08: The tightening torque is read from the measuring unit 47.
S09: The correction value of the number of pulse signals corresponding to the tightening torque is read from the storage unit 43.
S10: Increase / decrease the number of pulse signals using the correction value to make it appropriate.
S11: Check whether the number of corrected pulse signals has reached the target value range. If not, jump to S13.
S12: The first flag is turned on.
S13: Check whether the tightening torque has reached the target tightening torque. If not, jump to S15.
S14: Turn on the second flag.
S15: If both the first flag and the second flag are OFF, jump to S07.
S16: A stop command signal is transmitted to the motor drive unit 42.
S17: A stop command signal is transmitted to the motor drive unit 41.
S18: If both the first flag and the second flag are ON, jump to S20.
S19: An abnormal completion display command signal is transmitted to the display unit 45, and the process jumps to S21.
S20: A normal completion display command signal is transmitted to the display unit 45.
S21: A reverse drive command signal is transmitted to the motor drive unit 41.
S22: The number of pulse signals of the encoder 20a is read.
S23: If the number of pulse signals of the encoder 20a is not 0, jump to S22.
S24: A stop command signal is transmitted to the motor drive unit 41.
S25: End.
The screw tightening control is executed.

Next, the operation of the automatic screw tightening machine according to the present invention will be described.
A start switch (not shown) of the operation unit 44 is inputted and a start command signal is inputted to the control unit 40 in a state where the screw held by the holding means (not shown) is arranged immediately above the female screw of the workpiece. Then, first, the motor 20 is driven. Thereby, the nut member 21a of the ball screw mechanism 21 moves downward in the figure, and the tool table 22 and the tool unit 3 are lowered. As a result, the screw held by the holding means is pushed out onto the female screw of the workpiece by the driver bit 31. When the driver bit 31 is lowered so far, the number of pulse signals of the encoder 20a reaches the target value, and the motor 30 is driven in response to this. As a result, the driver bit 31 engages with the screw drive hole and rotates to tighten the screw into the female screw.

  Simultaneously with the start of driving of the motor 30, measurement of a pulse signal generated by the encoder 30a is started. On the other hand, when the tightening torque is increased by, for example, the screw being seated on the workpiece surface, the reaction force of this tightening torque is transmitted to the strain generating member 32, and the strain generating member 32 accordingly receives the flange member 33 side. Is elastically deformed (twisted) in the rotational direction of the driver bit 31 with reference to As a result, the motor 30 itself also rotates, so that the rotation angle of the drive shaft 30b of the motor 30 that can be obtained from the number of pulse signals of the encoder 30a does not exactly match the actual rotation angle of the screw. . In order to deal with this, the control unit 40 reads the tightening torque from the measurement unit 47 and reads the correction value of the number of pulse signals corresponding to the tightening torque from the storage unit 43. Then, the number of pulse signals measured by the encoder 30a is increased / decreased by this correction value to be optimized. As a result, the rotation angle of the drive shaft 30b of the motor 30 and the rotation angle of the screw can be exactly matched, and the rotation angle of the screw can be properly managed.

  When the screw tightening torque increases and reaches the target tightening torque preset in the storage unit 43 or the number of pulse signals reaches the target value range preset in the storage unit 43, the motors 20 and 30 Driving stops. At this time, when the tightening torque has reached the target tightening torque and the number of pulse signals has also reached the target value range, the LED indicating the normal completion state is turned on by the display unit 45. If either one has not reached, the display unit 45 turns on the LED indicating the abnormal completion state. Thus, after each tightening completion state is displayed on the display unit 45, the motor 20 is driven in reverse to return the tool table 22 and the tool unit 3 to the origin position and prepare for the next operation.

  In the above description, the example in which the strain generating member is elastically deformed in the rotation direction of the driver bit (screw tightening direction) has been introduced.

The block explanatory view of the automatic screw fastening machine concerning the present invention. The block explanatory view of the principal part of the automatic screw fastening machine concerning the present invention. The flowchart of the screw tightening control front stage of the automatic screw tightening machine which concerns on this invention. The flowchart after the screwing control of the automatic screwing machine which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Automatic screwing machine 2 Reciprocating drive unit 3 Tool unit 4 Control unit 20 AC servo motor 20a Encoder 21 Ball screw mechanism 30 AC servo motor 30a Encoder 31 Driver bit 32 Strain generating member 34 Strain gauge

Claims (1)

  Rotation drive means, a driver bit that rotates in response to the drive of the rotation drive means, a rotation detection means that can send a rotation signal in accordance with the drive of the rotation drive means, and the rotation drive means, and this driver A strain-generating member that can be elastically deformed in the rotational direction of the driver bit in the rotational direction of the driver bit according to the tightening torque of the screw acting on the bit or the opposite direction; An automatic screw tightening machine comprising: a control unit that corrects rotation angle information based on a rotation signal of the rotation detection means based on a signal of the distortion detection means.

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