JP2007038384A - Automatic thread fastening device and thread fastening device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform favorable thread fastening by applying accurate thrust force in thread fastening which requires thread fastening with low thrust force as in a very small screw. <P>SOLUTION: This automatic thread fastening device includes: a driver tool 4 for driving a driver bit 42 engaged with a screw head in rotation by an AC servo motor 41; and a thrust control mechanism 3 for changing the thrust given to the screw from the driver bit 42 in screwing the screw in a work. The thrust control mechanism 3 generates dead load support force, which supports the dead load of a member for applying load of the driver tool 4 or the like based upon the mass to the screw, and on the other hand, generates the pressing force for pressing the screw in the reverse direction to the dead load support force, which is larger than the dead load support force in screwing the screw in the work. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an automatic screw tightening device and a screw tightening method used when tightening a screw on a workpiece, and more particularly to an automatic screw tightening device and a screw tightening method for controlling a thrust applied to a screw.

  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 motor, and is configured so that the driver tool can be reciprocated in the axial direction of the driver bit by a ball screw mechanism driven by a servo motor. It is a thing. In this screw tightening device, the screw is engaged with the tip of the driver bit to drive the motor and transmit the rotation to the screw to tighten the screw to the workpiece. At that time, the rotation of the servo motor of the ball screw mechanism Speed control and torque control are performed, whereby the force with which the driver tool presses the screw, so-called thrust, is changed.

Japanese Patent No. 2894198

  In recent years, various devices including various electric devices have been miniaturized, and along with this, the size of screws used for assembling them has been miniaturized. Especially for digital devices that are remarkably miniaturized, screws with a nominal diameter of around 1 mm are widely used. When tightening such a micro screw, it is required to have a low thrust as well as a tightening torque. This is because if excessive thrust is applied, the female screw and the male screw are destroyed, or seizure occurs due to excessive friction between the screw threads. An appropriate thrust for tightening such a micro screw is several tens to several hundreds of grams. However, in the conventional screw tightening device, it is impossible 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 control in the low area required for tightening the micro screw cannot be performed, and when used for tightening the micro screw, excessive thrust is applied to the screw, causing screw tightening failure due to the above-mentioned problems. There was a problem such as.

  The present invention has been created in view of the above problems, and in the tightening of a screw that needs to be tightened under a low thrust, such as a microminiature screw, an accurate thrust is applied to achieve a good screw tightening. An object of the present invention is to provide an automatic screw tightening device and a screw tightening method that can be performed. In order to achieve this object, the present invention provides a driver tool configured to rotationally drive a screwdriver bit engageable with a screw head by a rotary driving source, and the screwdriver bit is applied to the screw when screwed into a workpiece. An automatic screw tightening device comprising a thrust control mechanism for changing a thrust to be generated, wherein the thrust control mechanism includes the driver tool and can support the weight of other members that apply a load based on mass to a screw to be tightened. A supporting force generating unit that generates a supporting force; and a pressing force generating unit that generates a pressing force that presses the screw in a direction opposite to the self-weight supporting force when the screw is screwed into the workpiece. It is characterized by comprising. In addition, it is desirable that the pressing force generator is configured to generate pressing forces with different strengths.

  In order to achieve the above object, the present invention provides a driver tool configured to rotationally drive a driver bit engageable with a screw head by a rotational drive source, and a screw from the driver bit when the screw is screwed into a workpiece. A screw control method for changing the thrust applied to the screw, and rotating a driver bit engaged with the screw head to tighten the screw on the work. The thrust control mechanism generates a self-weight support force. The driver tool supports its own weight, and in this state, the thrust control mechanism generates a pressing force that is greater than its own weight supporting force and reverse to its own weight supporting force, and is the difference between the pressing force and its own weight supporting force. It is also characterized in that the screw is screwed into the workpiece while applying thrust to the screw. In this case, it is desirable to change the pressing force applied from the thrust control mechanism when the screw is screwed to a predetermined position.

  In the automatic screw tightening device of the present invention, in a state in which a self-weight support force capable of supporting the self-weight of a member that applies a load based on the self-weight to a screw to be tightened is generated, A pressing force is generated in a direction in which the screw is pressed, and a thrust, which is a difference between the pressing force and the own weight support force, is applied to the screw. For this reason, it is possible to prevent the thrust based on the weight of the driver tool, etc., from acting on the screw when tightening the screw, and it is possible to control the thrust in an extremely low region below the thrust based on the weight of the driver tool, etc. Even when a screw such as a screw that requires a very low thrust is used for tightening, the thrust can be controlled appropriately to achieve good screwing and tightening. In addition, since the pressing force is changed according to the screwing position of the screw, for example, screwing is performed with a low thrust to the position immediately before the seating, and from the position immediately before the seating to the tightening completion position, in order to prevent a cam-out. There is an advantage that thrust control according to the screw tightening process, such as tightening with high thrust, can be realized even in a low thrust region.

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. The automatic screw tightening device includes a moving position control mechanism 2, a thrust control mechanism 3 connected to and supported by the moving position control mechanism 2, and the thrust control mechanism 3. It comprises a supported driver tool 4 and a control unit 5 for controlling them.

  The moving position control mechanism 2 has a ball screw mechanism 22 disposed on a base 21. The ball screw mechanism 22 includes an AC servomotor 23 (hereinafter simply referred to as the motor 23) installed on the upper portion of the base 21, a screw shaft 24 that is connected to a drive shaft 23a of the motor 23 and can rotate integrally, The nut member 25 is screwed into the spiral groove of the screw shaft 24 and can reciprocate in the axial direction as the screw shaft 24 rotates.

  The motor 23 includes a rotary encoder 23b (hereinafter simply referred to as an encoder 23b) that can output a pulse signal corresponding to the rotation of the drive shaft 23a. The nut member 25 is slidably guided by a guide rail 26 disposed on the back surface of the base 21 so as to extend in parallel with the screw shaft 24. The nut member 25 is supported by the thrust control mechanism 3. The plate 31 is fixed integrally.

  The thrust control mechanism 3 includes a support plate 31, a low friction guide rail 32 (hereinafter simply referred to as a low friction rail 32) fixed to the front surface of the support plate 31 so as to extend in parallel with the guide rail 26, A tool table 33 slidably disposed along the friction rail 32, a low friction air cylinder 34 (hereinafter simply referred to as a cylinder 34) having a piston rod 34 a connected to the tool table 33, and a port 34 b of the cylinder 34. , 34c, and an air control unit 35 for controlling the supply of compressed air to 34c.

  The cylinder 34 has a general structure in which the inside of the cylinder tube 34d is partitioned into two air chambers by a piston (not shown) integrated with the piston rod 34a. The cylinder tube 34d is fixed to the support plate 31; It is configured to be movable together. The cylinder 34 is a low friction type air cylinder designed so that the sliding resistance and the like related to the operation of the movable portion such as the piston rod 34a and the piston is extremely small. The stroke of the piston rod 34a is applied to the workpiece. It is set sufficiently longer than the length of the screw to be screwed. The low friction rail 32 and the tool table 33 are also designed so that the sliding resistance between them is extremely small.

  The air control unit 35 includes an electropneumatic regulator 353 and a precision regulator 354 connected to compressed air supply sources 351 and 352 having different air pressures. The electropneumatic regulator 353 moves the piston rod 34 a of the cylinder 34. The precision regulator 354 is connected to the port 34b leading to the air chamber to be advanced (elongated), and the port 34c leading to the air chamber to retract the piston rod 34a by the shortest path. Further, surge tanks 355 and 356 are arranged on the pipelines connecting the regulators 353 and 354 and the ports 34b and 34c of the cylinder 34, respectively.

  The driver tool 4 includes an AC servo motor 41 (hereinafter simply referred to as a motor 41) installed on the tool table 33, and a driver bit 42 integrally connected to a drive shaft 41a of the motor 41. The drive shaft 41a and the driver bit 42 are directly connected without a buffer mechanism, and are configured such that a force accompanying the movement of the tool table 33, that is, a thrust is transmitted from the tip of the driver bit 42 to the screw. Yes. Similarly to the motor 23, the motor 41 includes a rotary encoder 41b (hereinafter simply referred to as an encoder 41b) that can output a pulse signal in accordance with the rotation of the drive shaft 41a. Further, the driver bit 42 has a cross-shaped cross section at the tip, and can be engaged with a cross-shaped drive hole formed in the screw head. The tip of the driver bit 42 is magnetized so that the engaged metal screw can be magnetically held.

  The control unit 5 includes a control unit 51, a servo controller 52 for driving and controlling the motor 23, and a tool controller 53 for driving and controlling the motor 41.

  In the precision regulator 354, the piston rod 34a exerts a force greater than or equal to the force represented by {(mass of the driver tool 4 + mass of the piston rod 34a) × gravity acceleration—frictional force of each operating part of the thrust control mechanism 3}. It is set so that air of a pressure that can be generated is supplied to the cylinder 34. The air supplied from the precision regulator 354 generates a force in the direction of retreating the piston rod 34a (hereinafter referred to as a self-weight support force), and thereby a load based on the self-weight of the driver tool 4, the piston rod 34a, etc. Offset. The electropneumatic regulator 353 is configured to adjust the air pressure in accordance with a command signal from the control unit 51. By adjusting the air pressure by the electropneumatic regulator 353, the force in the direction of moving the piston rod 34a forward can be changed.

  Next, an operation when the screw is fastened to the workpiece while the screw is engaged and held at the tip of the driver bit 42 will be described. First, the air whose pressure is adjusted by the precision regulator 354 is always supplied to the cylinder 34, so that the piston rod 34a always exhibits its own weight support force. From this state, when a start command signal is input to the control unit 51 by a start switch or the like (not shown), the control unit 51 gives a high-speed movement command signal to the servo controller 52. As a result, the servo controller 52 drives the motor 23 to rotate at high speed, and lowers the nut member 25 or the driver tool 4 at a high speed downward in the figure. At this time, the pulse signal of the encoder 23b is fed back from the servo controller 52 to the control unit 51 and integrated.

  Next, the control unit 51 gives an operation command signal to the electropneumatic regulator 353. As a result, the electropneumatic regulator 353 generates air with a pressure at which the piston rod 34a is approximately 10% larger than its own weight support force and exerts a force opposite to its own weight support force (hereinafter, this force is referred to as a pressing force). This is supplied to the port 34b of the cylinder 34. As a result, the piston rod 34a extends and pushes down the driver tool 4. In this state, when the driver tool 4 moves to a position corresponding to the position immediately before the tip of the screw reaches the female screw entrance of the workpiece (a position before 1 cm), the integrated value of the pulse signal output from the encoder 23b becomes a predetermined value. Reach. In response to this, the control unit 51 sends a drive stop command signal to the servo controller 52 to place the motor 23 in a drive stop state and temporarily stop the driver tool 4 at the position.

  Subsequently, the control unit 51 provides a low speed movement command signal to the servo controller 52 and a constant speed rotation command signal to the tool controller 53. As a result, the tool controller 53 drives and controls the motor 41 at a constant rotational speed, and the pulse signal generated by the encoder 41b is fed back to the control unit 51 and integrated. Further, the servo controller 52 that has received the low speed movement command signal screwed into the female screw of the screw obtained from the thread lead of the screw to be tightened and the rotation speed of the motor 41 based on the rotation command signal given to the tool controller 53. The speed of the motor 23 is controlled so that the support plate 31 descends at a speed slightly higher than the speed.

  As a result, the screw reaches the female screw inlet of the workpiece while rotating, and is pressed against the female screw inlet of the workpiece with a light force that does not act on its own weight component such as the driver tool 4. By doing so, the screw tip can be accurately screwed into the female screw of the workpiece.

  Thereafter, the servo controller 52 moves the motor 23 so that the support plate 31 descends at a slightly higher speed than the screwing speed obtained from the lead of the screw thread and the rotational speed of the motor based on the rotation command signal to the tool controller 53. Keep speed control. When detecting that the support plate 31 has moved to a position corresponding to the screw tightening completion position from the number of accumulated pulse signals of the encoder 23b, the control unit 51 sends a drive stop command signal to the servo controller 52 to drive the motor 23. In a stopped state, the nut member 25 and the support plate 31 are stopped at this position. As described above, even if the support plate 31 is lowered at a speed slightly higher than the screwing speed, the cylinder 34 serves as a shock absorber, so that the thrust generated by the operation of the ball screw mechanism 22 acts on the screw from the driver tool 4. There is no. Even if the piston rod 34 and the cylinder tube 34d are pushed by the thrust generated by the operation of the ball screw mechanism 22 at this time, and negative pressure is generated in the air piping, this can be absorbed by the surge tanks 355 and 356. There is no 354 pressure fluctuation.

  After supplying a constant speed rotation command signal to the tool controller 53, when a necessary and sufficient time has elapsed for the screw tip to be screwed into the female screw inlet, the control unit 51 gives a pressurization command signal to the electropneumatic regulator 353. Thereby, the pressure of the air supplied from the electropneumatic regulator 353 to the cylinder 34 is slightly increased. As a result, the screw can be pushed into the female screw with the optimum thrust for screwing. Also at this time, due to the action of the self-weight support force, the thrust generated by the self-weight component of the driver tool 4 or the like is not affected by the screw, and the necessary thrust can be accurately applied to the screw.

  When it is detected from the increase in the number of pulse signals of the encoder 41b and the load current value of the motor 41 that the screw is screwed until the head seating surface of the screw is seated on the workpiece, the control unit 51 causes the tool controller 53 to generate high torque. A rotation command signal is given and a pressure command signal is given to the electropneumatic regulator 353. As a result, the motor 41 is switched to low-speed rotation and high-torque driving, and on the other hand, the thrust applied to the screw is increased to a level at which no cam-out occurs even when the driver bit 42 rotates at a high torque corresponding to the target tightening torque. It is done.

  Thereafter, when the number of pulse signals of the encoder 41b reaches a value indicating that the screw has been tightened to a predetermined rotation angle, or the load current value of the motor 41 increases to the target tightening torque of the screw, the control unit 51 Then, a drive stop command signal is given to the tool controller 53. At this time, when the screw is tightened to a predetermined rotation angle and a target tightening torque, the control unit 51 displays a screw tightening normal end display by a display unit (not shown). When the screw is screwed in at a predetermined rotational angle and a target tightening torque, the control unit 51 displays a screw tightening abnormal end display on the display unit. Further, the control unit 51 gives a stop command signal to the electropneumatic regulator 353. As a result, the operation of the electropneumatic regulator 353 is stopped, and only the air pressure from the precision regulator 354 is applied to the cylinder 34. Therefore, the piston rod 34a is retracted, and the driver bit 42 is detached from the screw.

  Thereafter, the control unit 51 gives a motor reverse rotation drive command signal to the servo controller 52, whereby the motor 23 is reversely driven to raise the driver tool 4 and the like. When the controller 51 confirms that the driver tool 4 and the like have returned to the original position from the number of pulse signals of the encoder 23b, the controller 51 gives a drive stop command signal to the servo controller 52 to stop the motor and perform a series of screw tightening operations. Complete.

  As described above, the automatic screw tightening device 1 cancels the thrust (load) based on the mass of the driver tool 4 and the like by the self-weight support force constantly applied to the cylinder 34 during the screw tightening operation. For this reason, for example, when assembling various small precision devices using an extremely small screw having a nominal diameter of 1 mm or less, it is necessary to control the thrust applied to the screw in a region smaller than the force based on the weight of the driver tool 4 or the like. Even in this case, it is possible to perform a screw tightening operation by applying a very accurate thrust to the screw, and it is possible to prevent the occurrence of defects such as screw breakage and workpiece deformation. In the present embodiment, the support force generation unit described in the claims is realized by the precision regulator 354 and the cylinder 34. Similarly, the pressing force generator is realized by the electropneumatic regulator 353 and the cylinder 34.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Automatic screw fastening apparatus 2 Movement position control mechanism 3 Thrust control mechanism 4 Driver tool 5 Control unit 22 Ball screw mechanism 23 AC servo motor 24 Screw shaft 25 Nut member 26 Guide rail 31 Support plate 32 Low friction guide rail 33 Tool table 34 Low Friction air cylinder 34a Piston rod 35 Air control unit 41 AC servo motor 42 Driver bit 51 Control unit 52 Servo controller 53 Tool controller 353 Electropneumatic regulator 354 Precision regulator

Claims (4)

A driver tool configured to rotationally drive a driver bit engageable with a screw head by a rotational drive source, and a thrust control mechanism that changes a thrust applied to the screw from the driver bit when the screw is screwed into a workpiece. Automatic screw tightening device,
The thrust control mechanism is
A support force generating unit that generates a self-weight support force that can support the self-weight of another member that includes the driver tool and applies a load based on mass to a screw to be tightened;
An automatic screw tightening device comprising: a pressing force generator that generates a pressing force that presses a screw that is larger than the self-weight supporting force when the screw is screwed into a workpiece and is opposite to the self-weight supporting force. .   The automatic screw tightening device according to claim 1, wherein the pressing force generator is configured to generate pressing forces having different strengths. A driver tool configured to rotationally drive a driver bit engageable with a screw head by a rotational drive source, and a thrust control mechanism that changes a thrust applied to the screw from the driver bit when the screw is screwed into a workpiece. ,
A screw tightening method in which a screwdriver bit engaged with a screw head is rotationally driven to tighten a screw on a workpiece,
The thrust control mechanism generates its own weight support force to support the driver tool's own weight. In this state, the thrust control mechanism generates a pressing force that is greater than the self-weight support force and in the direction opposite to the self-weight support force. A screw tightening method characterized in that a screw is screwed into a workpiece while a thrust, which is a difference between pressure and its own weight support force, is applied to the screw.   The screw tightening method according to claim 3, wherein when the screw is screwed to a predetermined position, a pressing force applied from the thrust control mechanism is changed.

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