JP4481960B2 - Automatic screw tightening device - Google Patents

Description

  The present invention relates to an automatic screw fastening device that controls a thrust applied to a screw when the screw is fastened to a workpiece.

  2. Description of the Related Art Conventionally, a screw fastening device as shown in Patent Document 1 is known as a device used when fastening a screw to a workpiece. This screw tightening device has a driver tool having a driver bit that rotates in response to the driving of a tightening motor, and this driver tool is integrated with a nut member of a ball screw mechanism driven by a moving servo motor. It is configured to reciprocate in the axial direction. In this screw tightening device, after the screw is engaged with the tip of the driver bit, the tightening motor is driven to rotate the driver bit, and the rotation is transmitted to the screw by the driver bit, and the screw is tightened to the workpiece. During this time, the rotational speed control and torque control of the moving servo motor are performed, and by these controls, the force with which the driver tool presses the screw upon completion of tightening, the so-called thrust, is arbitrarily changed.

Japanese Patent No. 2894198

  In recent years, various devices such as various electric devices have been miniaturized, and along with this, the size of screws used for assembling them has also been minimized. Especially for digital devices that are remarkably miniaturized, screws with a nominal diameter of around 1 mm are widely used. When tightening such an ultra-small screw, not only tightening torque but also low thrust is required. This is because if an excessive thrust is applied, the female screw and the male screw are destroyed, or seizure occurs due to excessive friction between the screw threads. The proper thrust for tightening such a microscrew is several tens to several hundreds of grams. However, in the above conventional screw tightening device, it is not possible to apply a thrust in a low region below a thrust based on the mass of a driver tool or a nut member of a ball screw mechanism to the screw. Therefore, the thrust in the low area required for tightening the micro screw cannot be controlled, and when used for tightening the micro screw, excessive thrust is applied to the screw, causing screw tightening failure due to the above problems. There was a problem such as.

The present invention has been created in view of the above problems, and provides excellent screw tightening by applying an accurate thrust when tightening a screw that needs to be tightened under a low thrust, such as a micro screw. An object of the present invention is to provide an automatic screw tightening device capable of performing the above. In order to achieve this object, the present invention includes a driver tool configured to rotate a driver bit by a rotation driving source for tightening, and a moving position control mechanism having a moving unit that moves integrally with the driver tool, The moving position control mechanism is an automatic screw tightening device that is configured to raise and lower the moving unit by a screw shaft that rotates in response to the rotation of the moving rotational drive source,
While connecting a rotational drive source for supporting force to the screw shaft and providing an output torque in a direction in which the moving part rises from the rotational drive source for supporting force to the screw shaft,
The upper limit torque of the rotational drive source for movement is made larger than the output torque of the rotational drive source for supporting force.

  In the present invention, in order to achieve the above object, the screw shaft can be a ball screw shaft.

  In the automatic screw tightening device of the present invention, the moving rotary drive source is driven and the moving part is lowered while receiving position movement control, and the screw supplied to the tip of the driver bit is lowered integrally. During this time, an output torque is generated so that the rotational force source for supporting force is driven and the screw shaft is rotated in the direction in which the moving part is raised. Although the moving portion receives a force in the upward direction by this output torque, since the rotational drive source for movement is controlled in moving position, the output torque rises to the upper limit torque, and the upper limit torque at that time and the rotational drive source for supporting force The moving part descends with a difference from the output torque of. At this time, by setting so that the pressing force corresponding to the driver tool and the moving part's own weight can be obtained from the output torque of the supporting force rotation drive source, the thrust due to the driver tool's own weight is canceled out. The moving part can be lowered. Therefore, the screw can be tightened by the driver bit using only the pressing force generated by the moving rotational drive source as a thrust, and the thrust can be controlled in a very low region. Moreover, even if the screw shaft is replaced with a ball screw shaft, the same effect can be obtained.

  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 screw tightening device, which is composed of a moving position control mechanism 2, a driver tool 4 whose movement is controlled by the moving position control mechanism 2, and a control unit 5 for controlling them. .

  The moving position control mechanism 2 has a base 21 composed of an upper plate 21a, a lower plate 21b, and an upright plate 21c, and a moving AC servomotor 23 (hereinafter referred to as an example of a rotational drive source for movement) installed on the upper plate 21a. , A moving motor 23), a ball screw shaft 24, which is an example of a screw shaft that is connected to the drive shaft 23 a via a coupling mechanism 27 a and rotates integrally therewith, and is screwed into a spiral groove of the ball screw shaft 24. And a nut member 25 having a bearing (not shown). The moving motor 23 can output an upper limit torque larger than the output torque of the supporting force motor 31 to be described later, and is always driven with a set output torque lower than the upper limit torque, and the nut member 25 together with the driver tool 4 has a predetermined speed. It is comprised so that it may descend | fall. The moving motor 23 includes a moving pulse encoder 23b (hereinafter referred to as a moving encoder 23b) that can output a pulse signal corresponding to the rotation of the drive shaft 23a. The rotational speed of the moving motor 23 and the moving distance of the nut member 25 are feedback-controlled.

  The nut member 25 is guided by a linear rail 26 attached to the upright plate 21c, reciprocates in the axial direction as the ball screw shaft 24 rotates, and the moving position control mechanism 2 together with the driver base 4a described later. The moving part 2a is configured. Further, the driver tool 4 is attached to the nut member 25 via the driver base 4a, and is configured to move integrally with the movement of the nut member 25. The driver tool 4 includes a tightening AC servo motor 41 (hereinafter referred to as a tightening motor 41), which is an example of a tightening rotation drive source installed on the driver base 4a, and a driver bit 42 coupled to the drive shaft 41a. It has. The drive shaft 41a and the driver bit 42 are directly connected via a coupling mechanism 27c, and are configured such that a force accompanying the movement of the driver base 4a, that is, a thrust is transmitted to the tip of the driver bit 42. Further, like the moving motor 23, the tightening motor 41 includes a tightening pulse encoder 41b (hereinafter referred to as a tightening encoder 41b) capable of outputting a pulse signal according to the rotation of the drive shaft 41a. A pulse signal is sent to the control unit 51 so that the rotational speed of the tightening motor 41 is controlled.

  On the other hand, on the lower surface of the lower plate 21b, a supporting force AC servo motor 31 (hereinafter referred to as a supporting force motor 31), which is an example of a supporting force rotation drive source, has its drive shaft 31a facing upward and the lower plate 21b. The ball screw shaft 24 is connected to the drive shaft 31a via a coupling mechanism 27b. The supporting force motor 31 includes a supporting force pulse encoder 31b (hereinafter referred to as a supporting force encoder 31b) that can output a pulse signal corresponding to the rotation of the drive shaft 31a. And the output torque of the supporting force motor 31 is feedback-controlled. Further, the supporting force motor 31 is configured so as to be able to set a predetermined output torque so that an output torque capable of obtaining a pressing force corresponding to the weight of the nut member 25, the driver base 4a, and the driver tool 4 can be output. It is configured. Moreover, the output torque of the supporting force motor 31 is set to be smaller than both the set output and the upper limit torque of the moving motor 23, and the set thrust is calculated from the difference from this upper limit torque. ing.

  The control unit 5 includes a control unit 51, a moving servo controller 52a for controlling the moving motor 23, a supporting force servo controller 52b for controlling the supporting force motor 31, and a tightening motor 41. It has a tool controller 53 for controlling, and each controller is driven by various command signals sent from the control unit 51. When receiving a start signal from a start switch (not shown), the controller 51 sends a movement command signal at a predetermined speed to the movement servo controller 52a, while receiving a pulse signal from the movement encoder 31b. A position immediately before the screw supplied to the tip of the driver bit 42 abuts against a workpiece (not shown) is detected. When the controller 51 detects the position immediately before the seating, it sends a support force generation command signal to the support force servo controller, drives the support force motor 31 and receives a pulse signal from the support force encoder 31b. Thus, the output torque is controlled to be constant. Further, when receiving a start signal, the control unit 51 is configured to send a high-speed drive command signal to the tool controller 53, while outputting the support force generation command signal and simultaneously sending a low-speed drive command signal to the tool controller 53. .

  The control unit 51 receives a pulse signal from a tightening encoder 41b, which will be described later, and controls the speed of the tightening motor 41 to apply a preset torque to the driver bit 42 and perform tightening. It is configured to detect the completion of screw tightening when it rotates a predetermined rotation angle after sitting. The controller 51 is configured to send a stop command signal to the tool controller 53, the moving servo controller 52a, and the supporting force servo controller 52b at the same time as detecting the completion of screw tightening. Further, the control unit 51 sends a reverse rotation command signal to the movement servo controller 52a following the stop command signal, while waiting for the nut member 25 to return to the upper limit, and sends a stop command signal to the movement servo controller 52a. It is configured.

  When the movement servo controller 52a receives the movement command signal, it supplies power to the movement motor 23 and rotates it with the set output torque, while receiving the pulse signal of the movement encoder 23b, The speed and the moving distance of the nut member 25 are feedback-controlled. When the movement servo controller 52a receives a reverse rotation command signal, the movement servo controller 52a supplies power to the movement motor 23 and reverses it to return the moving table to the upper limit position. The power supply is configured to be stopped.

  When receiving the support force generation command signal, the support force servo controller 52b drives the support force motor 31 to feedback control the output torque, and outputs the output torque in the direction in which the nut member 25 is pushed up. The nut member 25, the driver base 4a, and the driver tool 4 are configured to obtain a pressing force corresponding to their own weight. Further, the support force servo controller 52b is configured to stop the power supply to the support force motor 31 and release the restraint of the ball screw shaft 24 when receiving the stop command signal.

  The tool controller 53 is configured to rotate the tightening motor 41 at a predetermined high speed when receiving a high-speed drive command signal, and to rotate the tightening motor 41 at a predetermined low speed when receiving a low-speed drive command signal. Has been. Further, the tool controller 53 is configured to stop the power supply to the tightening motor 41 and stop the driver bit 42 when receiving the stop command signal.

  In the automatic screw tightening device, when a screw is supplied to the tip of the driver bit 42 and a start command signal is input to the control unit 51, a high-speed rotation drive command signal is sent from the control unit 51 to the tightening motor 41, The tightening motor 41 rotates at a predetermined high speed. At the same time, a movement command signal is output from the controller 51 to the movement servo controller 52a, and the movement servo controller 52a drives the movement motor 23 at a preset speed. Therefore, the nut member 25 screwed to the ball screw shaft 24 is lowered along the ball screw shaft 24 while the movement distance is controlled. As the nut member 25 descends, the driver tool 4 descends integrally and reaches the position immediately before the screw at the tip of the driver bit 42 bites into the work hole of the work, and the controller 51 rotates the tool controller 53 at a low speed. A command signal is sent, and the moving motor 23 rotates at a preset low speed. At the same time, a support force generation command signal is sent from the control unit 51 to the support force servo controller 52b, and the support force motor 31 is driven. At this time, the supporting force motor 31 outputs an output torque so as to generate a pressing force in the direction in which the nut member 25 is raised, so that the nut member 25 receives this pressing force and receives the nut member 25, the driver base 4a, and the driver. The thrust applied to the driver bit 42 by the weight of the tool 4 is canceled out.

  Further, while the supporting force motor 31 is driven, the moving motor 23 outputs an output torque larger than the output torque of the supporting force motor 31, so that the ball screw shaft 24 rotates against the supporting force motor 31. Then, the nut member 25 is lowered together with the driver tool 4. At this time, since the movement motor 23 is controlled in the movement position, the output torque increases and reaches the upper limit torque. The difference between the upper limit torque and the output torque of the supporting force motor 31 causes the movement motor 23 to The nut member 25 is advanced by rotating. Therefore, the thrust due to the weight of the nut member 25, the driver base 4a, and the driver tool 4 is not applied to the driver bit 42 that rotates in response to the rotation of the tightening motor 41, and the upper limit torque of the moving motor 23 and the supporting force motor Only the pressing force generated from the difference between the output torques 31 can be applied to the driver bit 42 as a thrust, and the thrust in a very low region can be controlled.

  After that, when the control unit 51 receives the pulse signal from the tightening encoder 41b and the screwdriver bit 42 detects the completion of screw tightening by rotating a predetermined rotation angle from the time of screw seating, a stop command signal is sent to each controller 52a, 52b, 53. The feeding and tightening motor 41, the moving motor 23 and the supporting force motor 31 are stopped. Further, after the moving motor 23 is stopped, a reverse rotation command signal is sent from the control unit 51 to the moving servo controller 52a, the moving motor 23 is reversely rotated and the nut member 25 is raised and returned. When the nut member 25 returns to the upper limit, a stop command signal is sent from the controller 51 to the moving servo controller 52a, the moving motor 23 is stopped, and the screw tightening operation can be completed.

  In the embodiment, the output torque of the moving motor 23 at the start of screw tightening is made larger than the output torque of the supporting force motor 31, but it may be made smaller. In this case, the nut member 25 is lowered by the moving motor 23 until the supporting force motor 31 is rotated. However, when the supporting force motor is driven, the torque of the moving motor 23 is increased to increase the supporting force. Since the moving motor 23 does not rotate until it becomes larger than the output torque of the motor 31, the nut member 25 stops at that position. After that, since the movement motor 23 has been subjected to movement position control, the output torque of the movement motor 23 increases, and when the output torque of the supporting force motor 31 is exceeded, the nut member 25 can resume descent. .

It is block explanatory drawing of the automatic screw fastening apparatus which concerns on this invention.

Explanation of symbols

1 Automatic screw tightening device 2 Moving position control mechanism 2a Moving part

4 Driver tool 4a Driver stand 5 Control unit

21 Base 21a Upper plate 21b Lower plate 21c Upright plate 23 AC servomotor 23a for movement Drive shaft 23b Pulse encoder 24 for movement Ball screw shaft 25 Nut member 26 Linear rail 27a, 27b, 27c Coupling mechanism

31 Support Servo AC Servo Motor 31a Drive Shaft 31b Support Force Pulse Encoder

41 Tightening AC servomotor 41a Drive shaft 41b Tightening pulse encoder 42 Driver bit

51 Control Unit 52a Movement Servo Controller 52b Support Force Servo Controller 53 Tool Controller

Claims (2)

A driver tool configured to rotate a driver bit by a tightening rotation drive source, and a movement position control mechanism having a moving unit that moves integrally with the driver tool, the movement position control mechanism being a rotation drive source for movement. An automatic screw tightening device that is configured to raise and lower the moving part by a screw shaft that rotates in response to rotation,
While connecting a rotational drive source for supporting force to the screw shaft and providing an output torque in a direction in which the moving part rises from the rotational drive source for supporting force to the screw shaft,
An automatic screw tightening device, wherein an upper limit torque of the rotational drive source for movement is made larger than an output torque of the rotational drive source for supporting force. 2. The automatic screw tightening device according to claim 1, wherein the screw shaft is a ball screw shaft.

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