JP2010099791A - Screw fastening screwdriver unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw fastening screwdriver unit preventing force in a loosening direction from acting on a screw by the reaction due to the torsion of a transmission shaft transmitting the drive of a rotational driving source to a driver bit. <P>SOLUTION: The screw fastening screwdriver unit 1 includes: a rotation driving means 12; the transmission shaft 15 integrally rotatably connected to a drive shaft 12a of the rotation driving means 12 and having a screw fastening tool 17 engageable with the head of a screw at its tip; a torque sensor 16 detecting the torsion of the transmission shaft 15 over the whole of screw fastening work; and a control unit 20 accumulating the detected data by the torque sensor 16, determining damped vibration caused by the twisted transmission shaft 15 based on the accumulated data, and giving a gradual decrease command signal calculated on the basis of the determined result to the rotation drive means 12 after reaching the target of screw fastening torque to gradually decrease the rotation of the transmission shaft 15. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a screw tightening driver unit that prevents a force in a loosening direction from acting on a screw due to a reaction caused by twisting of a transmission shaft that transmits a drive of a rotary drive source to a driver bit during a screw tightening operation. .

  Conventionally, in the screw tightening operation by the screw tightening driver unit, when the seat surface of the screw head is seated on the object to be fastened and the tightening torque reaches a preset target tightening torque, the drive of the rotary drive source is stopped and the screw is tightened. The tightening operation is completed. However, in the drive control that immediately stops such a rotational drive source, the transmission shaft interposed between the drive shaft of the rotational drive source and the driver bit is twisted, and the twisted transmission shaft is instantaneously opened. The force causes a phenomenon that the driving shaft of the motor is attenuated forward and backward in a damping manner. At this time, since the reverse drive of the rotation drive source acts in the direction of loosening the screw, there is a problem that the screw is loosened even though the screw tightening operation is completed. Therefore, in the screw tightening driver unit shown in Patent Document 1 (Japanese Patent Laid-Open No. 2007-229853), when the seating surface of the screw head is seated on the object to be fastened and the tightening torque reaches the target tightening torque, the rotation drive source outputs The drive is controlled so as to gradually reduce the torque. By this drive control, the twist of the transmission shaft is gradually reduced to prevent the forward and reverse rotation of the rotational drive source from occurring, and the torque (transmission in the loosening direction) is transmitted to the screw that has been tightened to the target tightening torque. (Reaction force due to twisting of the shaft) is prevented from acting.

JP 2007-229853 A

  However, in the screw tightening driver unit, it is possible to substantially eliminate the twist of the transmission shaft and prevent the torque from being generated in the loosening direction by the above-described configuration. As shown in FIG. 3, the generated vibration of the drive shaft varies depending on the rigidity of the transmission shaft, the material of the workpiece, the type of screw, etc., and thus it is impossible to completely remove the twist of the transmission shaft.

  The present invention has been made in view of the above problems, and is a screw driving tool that is rotatably connected to a rotation driving means and a drive shaft of the rotation driving means so as to be engageable with a screw head at the tip. A transmission shaft, a torque sensor that detects torsion of the transmission shaft throughout the entire screwing operation, and attenuation caused by the twisted transmission shaft on the basis of the accumulated data detected by the torque sensor. And a control unit that determines vibration and issues a gradual decrease command signal calculated based on the determination result to the rotation driving means after reaching the target tightening torque to gradually decrease the rotation of the transmission shaft.

  Further, the control unit accumulates data detected by the torque sensor, determines whether the twisted transmission shaft is damped or overdamped based on the accumulated data, and only when it is determined to be damped. A gradual decrease command signal is generated.

  According to the first aspect of the present invention, the rotational drive source is controlled by a gradual decrease command signal corresponding to the twist of the transmission shaft that varies depending on the rigidity of the transmission shaft, the material of the workpiece, the type of screw, and the like. With this configuration, it is possible to prevent the torque in the loosening direction from acting on the screw after the screw tightening is completed.

  According to the second aspect of the present invention, since the gradual decrease command signal is not issued for the overdamped vibration in which the rotation angle of the drive shaft is not displaced in the direction of loosening the screw, the screw tightening time can be shortened.

  The best mode for carrying out the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a screw tightening driver unit, which includes a tool unit 10 and a control unit 20 that controls the tool unit 10.

  The tool unit 10 is covered with a housing 11, and an AC servo motor 12 (hereinafter simply referred to as a motor) is assembled in the housing 11 as an example of a rotation driving means. The motor 12 is assembled with an encoder 13 which is an example of a first rotation angle detection means, and is configured to always detect the rotation angle of the drive shaft 12a of the motor 12. In addition, a transmission shaft 15 is connected to the drive shaft 12 a via a speed reducer 14, and a torque sensor 16 that detects torsion of the transmission shaft 15 is attached to the transmission shaft 15. Further, a screw tightening tool 17 having a tip shape connectable to a cross-shaped drive hole of a screw (not shown) is connected to the tip of the transmission shaft 15 so as to rotate integrally with the transmission shaft 15. Yes.

  The torque sensor 16 has a cylindrical strain tube 18 fixedly disposed on the housing 11 so as to cover the periphery of the transmission shaft 15, and is attached to the strain tube 18 to twist the strain tube 18. And a strain gauge 19 for detecting a strain corresponding to the above as an electric signal. With this configuration, the strain generating tube 18 is twisted by the rotational resistance generated in the process in which the screw engaged with the tip of the screw tightening tool 17 is screwed into the workpiece (not shown), and the strain gauge 19 detects this twist. . The torque sensor 16 is configured to continuously detect the torsion of the strain-inducing tube 18, and the detection data is configured to be accumulated in the control unit 20.

  The control unit 20 accumulates twist detection data by the torque sensor 16 and stores various data such as a tightening torque corresponding to the twist of the transmission shaft 15 detected by the torque sensor 16 and a target tightening torque. 21, a control unit 22 that analyzes the twist detection data stored in the storage unit 21 and calculates a gradual decrease command signal that will be described in detail later, and a motor drive that drives and controls the motor 12 based on the gradual decrease command signal Part 23. The control unit 22 is also configured to calculate the rotation angle of the screw tightening tool tip 17 from the twist of the transmission shaft 15 and the rotation angle of the drive shaft 12a.

  Next, the screw tightening process of the screw tightening driver unit 1 of the present invention will be described along the flowchart shown in the drawing. As shown in FIG. 2, when a start command signal is input from an external device controller (not shown), a drive command signal is issued to the motor 12 to drive the motor 12 (step S01). When a screw engaged with the tip of the screw tightening tool 17 is screwed into the workpiece, a tightening torque (rotational load) when the screw is screwed into the screw tightening tool 17 and the transmission shaft 15 acts as a rotational resistance. . Therefore, a difference occurs in the rotation angle between the screw tightening tool 17 and the drive shaft 12a according to the tightening torque, the transmission shaft 15 is twisted, and this is detected by the torque sensor 16 (step S02). The control unit 20 calculates a tightening torque corresponding to the twist (step S03) and determines whether or not the tightening torque has reached the target tightening torque (step S04). If this does not reach the target tightening torque, a tightening torque corresponding to a new rotation angle difference is obtained, and comparison between this and the target tightening torque is repeated.

  Thereafter, when the screw head seating surface is seated on the workpiece and the tightening torque reaches the target tightening torque, the control unit 20 determines whether or not the twisted transmission shaft 15 oscillates (step S05). When vibrating, the control unit 22 issues a gradual decrease command signal corresponding to the twist of the transmission shaft 15 to the motor drive unit 23 (step S06), and the motor 12 is driven with an output torque based on the gradual decrease command signal. Finally stop. That is, upon receiving the torque gradual decrease command signal from the control unit 22, the motor drive unit 23 gradually decreases the load current value of the motor 12 based on the various gradual decrease command signals from that point to 0 (zero) (step S07). ). On the other hand, when the control unit 20 determines that the twisted transmission shaft 15 is overdamped, the control unit 20 does not issue a gradual decrease command signal to the motor 12 and reaches the target tightening torque. Then, the load current value of the motor 12 is set to 0 (zero) to complete the screw tightening.

Hereinafter, the damped vibration of the transmission shaft 15 shown in FIG. 3 will be described. The following Equation 1 is an equation of motion of damped vibration caused by twisting the transmission shaft of mass m.

Here, x represents the rotation angle of the rear end of the transmission shaft 15, and corresponds to the rotation angle of the drive shaft 12a connected to the rear end of the transmission shaft 15. In addition, k is an elastic constant of the transmission shaft 15 and kx is a restoring force of the twisted transmission shaft 15. Further, 2γ is a constant proportional to the rotational speed and mass of the transmission shaft 15, and 2γm · dx / dt is a resistance force acting on the transmission shaft 15 during the damped vibration. In addition, when this resistance force is 0 (zero), it is a single vibration. The resultant force F of the restoring force and the resistance force is a force acting on the transmission shaft 15 during the damped vibration. Dividing both sides of the above equation by m gives the following equation.

Here, ω ₀ ² = k / m. It should be noted that the condition under which the elastic body (the transmission shaft 15 corresponds to this in the present invention) undergoes damped vibration is ν ² <ω ₀ ² , while if ν ² > ω ₀ , it oscillates excessively.

FIG. 3 also shows in time series the displacement of the rotation angle of the drive shaft connected to the transmission shafts A and B having different rigidity so as to be integrally rotatable. The waveform under the condition of vibration (ν ² <ω ₀ ² ) is shown. Further, the elastic coefficient ka of the transmission shaft A and the elastic coefficient kb of the transmission shaft B are ka> kb, and the transmission shaft A has a larger amplitude than the transmission shaft B and repeats many vibrations until it becomes stable. As shown in FIG. 3, the rotation angle of the drive shaft 12a changes with time due to the twisting of the transmission shafts A and B, and until the target tightening torque is reached, the rotation angle of the drive shaft 12a returns to the position of the rotation angle of the screw tightening tool 17 tip. The displacement of the rotation angle at the tip of the tightening tool 17 remains when the target tightening torque is reached. When the rotation angle of the drive shaft 12a is returned to a position exceeding the rotation angle of the tip of the screw tightening tool 17 when the target tightening torque is reached, as shown in A1 of FIG. The screw is displaced in the loosening direction, and the screw is loosened by the displacement amount A1. Subsequently, the screw is loosened in the order of the displacement amounts A2 and A3 due to repeated damping vibration. Further, in the transmission shaft B shown in FIG. 3, the displacement amount B1 of the force acting in the loosening direction is smaller than that of the transmission shaft A, but the screw tightening tool 17 rotates as the rotational angle of the drive shaft 12a is returned. The rotation angle of the tip is displaced in the direction of loosening the screw.

On the other hand, the transmission axis C shown in FIG. 3 shows a waveform under the condition of overdamped vibration (ν ² > ω ₀ ). This overdamped vibration is caused when the rotational load applied to the transmission shaft C satisfies a predetermined condition (ν ² > ω ₀ ), and is interposed, for example, on the drive transmission path of the motor 12. A reduction gear or the like applies the rotational load. In this overdamped vibration, as shown by the waveform of the transmission shaft C in FIG. 3, the drive shaft 12a is not returned to a position exceeding the rotation angle of the tip of the screw tightening tool 17, that is, the rotation angle of the drive shaft 12a loosens the screw. The screw does not loosen because it is not displaced in the direction.

  In the control unit 20, the storage unit 21 is configured to detect and accumulate the rotational angle displacement of the drive shaft 12a from the start of twisting until the target tightening torque is reached, while the control unit 22 accumulates this. Whether the transmission shaft 15 vibrates damped or excessively damped based on the obtained data is determined by analysis based on Formula 1 and Formula 2.

  When the control unit 20 determines that the vibration is damped, a gradual reduction command signal corresponding to the twist of the transmission shaft 15 is generated depending on the rigidity of the transmission shaft 15, the material of the workpiece, the type of screw, and the like. Hereinafter, calculation of the gradual decrease command signal corresponding to the twist of the transmission shaft 15 will be described. As shown in FIG. 3, in the transmission shafts A and B having different rigidity, the displacement of the rotation angle of the drive shaft 12a from the start of twisting to reaching the target tightening torque is different, that is, the twisting amount is different. The storage unit 21 of the present invention is configured to detect and store the displacement of the rotational angle of the drive shaft 12a from the start of twisting until the target tightening torque is reached, while the control unit 22 stores the accumulated data in the stored data. The elastic characteristics of the transmission shaft are analyzed based on Formulas 1 and 2, and the waveform of the damped vibration caused by the elastic energy stored in the transmission shaft 15 is calculated when the target tightening torque is reached. Yes. From the calculated waveform, the torque of the drive shaft 12a rotating in the loosening direction after reaching the target tightening torque is calculated. In other words, the control unit 22 detects the displacement of the rotation angle of the drive shaft 12a from the start of twisting until the target tightening torque is reached in time series, and analyzes this based on the equations 1 and 2 to achieve the target tightening torque reaching time. From the time until the rotation angle of the drive shaft 12a coincides with the tip angle of the screw tightening tool 17, the torque of the drive shaft 12a that is different at each point and acts in the loosening direction can be acquired in advance. The force acting in the loosening direction is the resultant force F of Equation 1 described above, and a signal that outputs a torque that balances this resultant force F is a gradually decreasing command signal.

  The motor drive unit 23 issues this gradual decrease command signal to the motor 12 and outputs a torque balanced with the torque of the drive shaft 12a acting in the loosening direction to the drive shaft 12a, while maintaining this balance. Is controlled to rotate at a constant speed in the loosening direction. The displacement of the rotation angle of the drive shaft 12a drawn by this control is as shown by the broken line in FIG. 3, and it can be confirmed that the rotation angle of the drive shaft 12a does not displace the screw in the loosening direction.

  On the other hand, the transmission shaft C shown in FIG. 3 causes overdamped vibration as described above, and it can be confirmed from the waveform that the rotation angle of the drive shaft does not displace in the loosening direction without gradually decreasing. Therefore, the control unit 20 does not issue a gradual decrease command signal to the motor 12, and when the target tightening torque is reached, the load current value of the motor 12 is set to 0 (zero) to complete the screw tightening.

  In the screw tightening driver unit of the present invention, the torque sensor 16 is used as a means for detecting the twist of the transmission shaft 15. Instead, the twist of the transmission shaft 15 is detected from the load current value of the motor 12. You may do it.

  According to the present invention, the motor 12 is controlled by a gradual decrease command signal corresponding to the torsion of the transmission shaft that varies depending on the rigidity of the transmission shaft 15, the material of the workpiece, the type of screw, and the like. With this configuration, the screw does not loosen since the drive shaft is not displaced in the direction of loosening the screw after the screw tightening is completed. Further, since the gradual decrease command signal is not issued for the overdamped vibration in which the rotation angle of the drive shaft 12as is not displaced in the direction of loosening the screw, the time required for screw tightening can be shortened.

It is a block explanatory view of the screw tightening driver unit of the present invention. It is a flowchart which shows the screwing process of the screwing driver unit of this invention. It is a figure which shows the damped vibration and the overdamped vibration which various transmission shafts cause.

Explanation of symbols

1 Screw tightening driver unit

DESCRIPTION OF SYMBOLS 10 Tool unit 11 Housing 12 Motor 12a Drive shaft 13 Encoder 14 Reducer 15 Transmission shaft 16 Torque sensor 17 Screw tightening tool 18 Strain tube 19 Strain gauge

20 control unit 21 storage unit 22 control unit 23 motor drive unit

Claims (2)

Rotation drive means;
A transmission shaft having a screw tightening tool that is rotatably coupled integrally with the drive shaft of the rotation driving means and engageable with the head of the screw at the tip;
A torque sensor that detects the torsion of the transmission shaft throughout the entire screwing operation;
Based on the accumulated data detected by the torque sensor, the damping vibration caused by the twisted transmission shaft is determined based on the accumulated data, and the gradual decrease command signal calculated based on the determination result is used to reach the target tightening torque. A screw tightening driver unit comprising: a control unit that later emits to the rotation driving means to gradually reduce the rotation of the transmission shaft.   The control unit accumulates detection data from the torque sensor, determines whether the twisted transmission shaft is damped or overdamped based on the accumulated data, and only decreases the command when it is determined that the damped vibration is detected. 2. The screw tightening driver unit according to claim 1, which emits a signal.

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