JP2011031369A - Impact type screwing device - Google Patents

Abstract

【Task】
An impact-type screw tightening device capable of performing tightening with high accuracy based on a set hitting torque is provided.
[Solution]
In an impact-type screw tightening device that has a brushless DC motor and a torque sensor that detects the occurrence of impact torque, and that uses the torque sensor output to tighten the tip tool with a specified tightening torque. Until it is completed, it is divided into three modes, section A, section B, and section C. In section A, the number of rotations of the motor is limited and tightened at a constant number of rotations lower than the maximum number of rotations. rotational speed N _{(target value)} = N _{(previous value)} + _{G 1} × _{(T (target value)} -T _{(detected value))} clamped by the clamping rotational speed N from dropping once rpm After achieving 70% of the torque _{(Target value)} = N _{(Previous value)} + G ₂ × (T _{(Target value)} −T _{(Detected value)} ), (G ₁ > G ₂ ) and tighten (T: Torque value (N・ M), _G1,2 : Gain constant).
[Selection] Figure 3

Description

  The present invention relates to an impact-type screw fastening device that is driven to rotate by a motor and tightens a fastening member such as a bolt using an intermittent impact force generated by an oil pulse unit, and in particular, with high accuracy based on a set impact torque. The present invention relates to an impact-type screw fastening device capable of fastening.

  Various methods have been proposed for preventing a so-called torque overrun in which a screw tightening device that tightens a screw, a bolt, or the like with a constant torque using a torque sensor is tightened beyond a set torque value. For example, Patent Document 1 describes that, in an AC nutrunner that is tightened to a constant torque using a torque sensor, the rotational speed of the AC motor is decreased as the tightening torque is increased to prevent torque overrun. Has been. Patent Document 2 discloses a nut runner that reduces the rotation speed of the output shaft in three stages in accordance with the tightening torque in order to shorten the work time while preventing torque overrun.

  On the other hand, a device using an oil pulse unit that generates a striking force using hydraulic pressure is known as a screw tightening device. A screw tightening device using an oil pulse unit has a feature that operation noise is low because there is no collision between metals. As an example of disclosing such an impact-type screw fastening device, for example, there is Patent Document 3, an air motor is used as power for driving the oil pulse unit, and an output shaft of the air motor is directly connected to the oil pulse unit. When the trigger switch is pulled, air is supplied to the air motor, and it is detected using the output from the torque sensor and rotation detector that the tightening has been performed with the specified tightening torque. Stops.

Japanese Patent Laid-Open No. 63-39972 JP-A-1-171777 JP-A-7-186060

  In recent years, brushless DC motors have been used as motors for screw fastening devices. Brushless DC motors have the advantage that there are no noises due to brush friction, no sparks or electrical noise, no wear, and no faults such as poor contact. By driving the oil pulse unit using a brushless DC motor, it is possible to realize an impact-type screw tightening device with low power consumption and high work efficiency. Also in this screw tightening device, it is an important problem to prevent torque overrun. However, when the technique of Patent Document 1 is applied to an impact-type screw fastening device using a brushless DC motor, there is a characteristic that the torque applied to the nut is reduced when the motor rotation speed is reduced, so that a sufficient fastening torque can be obtained. There is a risk of disappearing.

  Moreover, the technique of patent document 2 is also related to the nutrunner, and is not suitable for application to an impact-type screw tightening device, similarly to the technique of patent document 1.

  The present invention has been made in view of the above background, and an object of the present invention is to provide an impact type screw tightening device that can perform tightening with high accuracy based on a tightening torque value set without torque overrun. is there.

According to one aspect of the present invention, a brushless DC motor, a control circuit for controlling rotation of the motor, an oil pulse unit driven by the motor, and a tip tool connected to the shaft of the oil pulse unit are mounted. An impact-type screw tightening device that has a torque sensor that detects the occurrence of impact torque on the output shaft and that tightens the tip tool with a predetermined tightening torque using the output of the torque sensor.
(1) The control circuit is divided into three modes, section A, section B, and section C, from the start to the completion of screw tightening.
(2) In section A, the number of rotations of the motor is limited and tightened at a constant number of rotations lower than the maximum number of rotations.
(3) When the first impact is made in the oil pulse unit, the control is shifted to the control of the section B, the target rotational speed of the motor is set by the following formula,
N _{(target value)} = N _{(previous value)} + G ₁ × (T _{(target value)} −T _{(detected value)} )
Here, N: motor rotation speed (rpm), T: torque value (N · m), G ₁ : gain constant The duty to the inverter circuit supplied to the motor at this target rotation speed is expressed by the following equation: Set
Duty _{(target value)} = Duty _{(previous value)} + G ₂ × (N _{(target value)} −N _{(detected value)} )
Here, G ₂ : Gain constant (4) When the detection value of the torque sensor when the impact is made in the oil pulse unit reaches a predetermined value of the set tightening torque, the rotational speed is once lowered, and then the section Shift to the control of C, and if it is below the predetermined value, repeat the control of section B,
(5) In the section C, the target rotational speed of the motor is set by the following formula,
N _{(target value)} = N _{(previous value)} + G ₃ × (T _{(target value)} −T _{(detected value)} )
Here, G ₃ : gain constant (where G ₃ <G ₁ )
At this target rotational speed, set the duty to the inverter circuit to be supplied to the motor using the following formula,
Duty _{(target value)} = Duty _{(previous value)} + G ₄ × (N _{(target value)} −N _{(detected value)} )
Here, G ₄ : gain constant (where G ₄ <G ₂ )
(6) If the detection value of the torque sensor when the oil pulse unit is hit does not reach the set tightening torque, the control in section C is repeated, and if the set torque is exceeded, the motor is stopped. I did it.

According to another aspect of the present invention, the transition from the section B to the section C is performed when it reaches 70% of the set tightening torque value. Further, in section C, an upper limit value of the motor speed is set, and when N _{(target value)} according to the above formula exceeds the upper limit value, the motor is rotated at the upper limit speed. . A microcomputer is provided in the control circuit, and the rotation control of the motor in the sections A to C is performed by the microcomputer.

  According to the first aspect of the present invention, when the torque value detected by the torque sensor exceeds a predetermined value, the rotational speed is reduced, and the target torque is reached by striking while controlling the rotational speed according to the formula described in the first aspect. Since tightening is performed, it is possible to prevent tightening exceeding the target torque significantly.

  According to the invention of claim 2, the transition from the section B to the section C is performed when it reaches 70% of the set tightening torque value. Since the impact is made with high accuracy and certainty, tightening can be performed with an ideal torque increase / decrease value.

According to the invention of claim 3, in section C, an upper limit value of the motor speed is set, and when N _{(target value)} according to the above formula exceeds the upper limit value, the upper limit value is set. Since the motor is rotated, it is possible to prevent tightening beyond the tightening torque value.

  According to the invention of claim 4, since the control circuit has a microcomputer and the rotation control of the motor in the sections A to C is performed by the microcomputer, the tightening can be performed with high accuracy.

  The above and other objects and novel features of the present invention will become apparent from the following description and drawings.

It is sectional drawing which shows the whole impact type screw fastening apparatus which concerns on embodiment of this invention. It is a block diagram which shows the control circuit of the impact type screw fastening apparatus 1 concerning embodiment of this invention. It is a figure for demonstrating clamping | tightening control in embodiment of this invention. It is a flowchart which shows operation | movement of the impact type screw fastening apparatus which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an impact type screw tightening apparatus according to an embodiment of the present invention. The impact type screw tightening device 1 drives a motor 3 by using electric power supplied from a power supply box 30 by a cable or the like, drives an oil pulse unit 10 by the motor 3, and an output shaft connected to the oil pulse unit 10. Rotating force and impact force are applied to a tip tool (not shown) such as a hexagon socket to transmit the rotational impact force continuously or intermittently to perform screw tightening operations such as nut tightening and bolt tightening.

  As the motor 3, for example, a known brushless DC motor having a rotor having a permanent magnet and a stator having a winding wound around an iron core is used. A rotation position detection element (not shown) for detecting the rotation position of the rotor is mounted on the motor 3, and the rotation control of the motor 3 is performed by the motor drive circuit 7 based on the detected position. The motor drive circuit 7 includes an inverter circuit composed of semiconductor elements such as transistors and MOSFETs, and supplies a pulse width modulation signal (PWM signal) to the inverter circuit to change the pulse width (duty ratio) of this signal. The amount of electric power supplied to the motor 3 is adjusted by rotating the motor 3 at a desired rotation speed.

  A trigger switch 8 is disposed in the grip portion 11 of the impact type screw tightening device 1, and a signal proportional to the amount by which the trigger switch 8 is pulled is transmitted to the control circuit 2. Further, an LED 15 is provided below the grip portion 11 and on the surface of the housing opposite to the end tool. The LED 15 is, for example, two types of LEDs, green and red. The LED (first display state: for example, the green lamp is lit) indicating that the screw tightening operation has been normally completed, and the screw tightening operation is normal. LED (second display state: red lamp blinking, for example) indicating that the operation has not been performed. Furthermore, you may provide LED (3rd display state: For example, blue lamp blinking) which shows a communication state with an external apparatus separately.

  The oil pulse unit 10 can be a known one, and is mainly composed of two parts, a drive part that rotates in synchronization with the motor 3 and an output part that rotates in synchronization with the tip tool. The closed space formed by the output portion is filled with oil (hydraulic oil) for generating torque.

  When the trigger switch 8 is pulled and the motor 3 is started, the control circuit 2 sets the target rotational speed of the motor 3 according to the amount pulled by the trigger switch 8 and the set tightening torque value. The control circuit 2 calculates the pulse width (duty ratio:%) of the PWM signal so as to rotate at the rotation speed, and controls the inverter circuit of the motor drive circuit 7 according to the calculated value. When the motor 3 rotates, the rotational force is transmitted to the oil pulse unit 10. The oil pulse unit 10 rotates almost in synchronism with the rotation of the motor 3 only by the resistance of the oil when no load is applied to the output shaft or when the load is small. When a strong load is applied to the output shaft, the rotation of the output shaft stops. Therefore, only the liner on the outer peripheral side of the oil pulse unit 10 continues to rotate, and the oil pressure is maintained at a position where the oil provided at one place per one rotation is sealed. It suddenly rises to generate an impact pulse (hit), and the output shaft is rotated by a strong spire-like torque. Thereafter, the generation of the same shock pulse is repeated several times.

  A torque sensor 9 such as a strain gauge is attached to the output shaft of the oil pulse unit 10, and the control circuit 2 detects the tightening torque value when the shock pulse is generated, and rotates the motor 3 when the set tightening torque is reached. Stop.

  Next, the control circuit of the impact type screw fastening apparatus 1 will be described with reference to the block diagram of FIG. In the present embodiment, the motor 3 is a three-phase brushless DC motor, and includes a rotor that includes a permanent magnet and a star-connected three-phase stator windings U, V, and W. And a rotational position detecting element for detecting the rotational position of the rotor. Based on the position detection signal from the rotational position detection element, the ratio (duty ratio) of the energizing direction and energizing time to the stator windings U, V, W is controlled, and the motor 3 rotates.

  The motor drive circuit 7 includes an inverter circuit including six switching elements such as FETs (Field Effect Transistors) connected in a three-phase bridge format. The inverter circuit detects the rotational speed of the motor 3 and sends it to the rotational speed control circuit 17, receives a switching element drive signal from the rotational speed control circuit 17, performs a switching operation, and is supplied from an external power supply box 30. Is converted into three-phase (U-phase, V-phase and W-phase) voltages Vu, Vv, Vw and supplied to the stator windings U, V, W. In addition, since the well-known methods, such as a PWM (Pulse Width Modulation) system, can be used for the concrete drive method of an inverter circuit, the description is abbreviate | omitted here.

  Although not shown, the microcomputer 16 is a central processing unit (CPU) for outputting a drive signal based on the processing program and data, a ROM for storing the processing program and control data, and a temporary storage for data. It includes a RAM, a timer having a clock function, and the like.

  A full-wave rectifying / smoothing circuit 31 is provided in the power supply box 30. The full-wave rectifying / smoothing circuit 31 is, for example, a combination of a rectifying circuit in which four rectifying elements are connected in a bridge shape and a smoothing circuit using a capacitor. In this embodiment, a transformer is not used. It is in a non-insulated state. The full-wave rectifying / smoothing circuit 31 converts the voltage into, for example, 140V DC, and the high-voltage DC is supplied to the motor drive circuit 7 and the 18V constant voltage circuit 18. The 18V constant voltage circuit 18 creates a DC voltage of 18V from a DC 140V power supply, and may be configured with a known chopper circuit or a known constant voltage circuit combining a Zener diode and a transistor. Also good. Next, the output of the 18V constant voltage circuit 18 is input to a ± 12V power source 19. The ± 12V power source 19 generates + 12V and −12V voltages. −12V is used for driving the strain gauge 12. A power line from the ± 12 V power source 19 to the strain gauge 12 is not shown. The output of the ± 12V power source 19 is input to the constant voltage circuit 20, and the constant voltage circuit 20 generates an operating voltage Vdc for operating the microcomputer 16, for example, 5V DC and 3.3V DC.

  A transmission signal from the transmission circuit 21a of the torque detection circuit 21 is supplied to the strain gauge 12 via the input transformer 22a. At the same time, the reference amplitude from the transmission circuit 21a is also sent to the microcomputer 16. This is because the microcomputer 16 cannot detect distortion from the torque waveform without inputting the reference amplitude. When tightening torque is generated by the oil pulse unit 10 on the output shaft 5, the resistance value of the strain gauge 12 changes, and the reference amplitude signal changed by the change in resistance value is transmitted to the detection circuit 21b via the output transformer 22b. It is detected. Since the offset adjustment signal is sent from the microcomputer 16 to the detection circuit 21b, the detection signal corrected for offset is output to the microcomputer 16. The microcomputer 16 uses the output value of the strain gauge 12 to calculate how much torque value has been tightened (tightening torque).

  At this time, the microcomputer 16 determines the rotation speed of the motor 3 according to the set tightening torque. Further, when the microcomputer 16 determines that the tightening has been normally completed with the set tightening torque value, the microcomputer 16 stops the motor 3 and lights the LED 15. The operator can recognize that the motor 3 has automatically stopped and whether the tightening operation has been completed normally or abnormally by turning on the LED 15. In this embodiment, three LEDs are used as the LEDs 15. The first one is a green LED 15a indicating "complete tightening", and the operator can recognize that the tightening has been normally completed based on the target tightening torque set by the display of the green LED 15a. Further, the green LED 15a also has a meaning as a lamp for informing that “tightening is completed” indicating that the tightening is completed. Therefore, the operator can return the trigger switch 8 when the lamp is attached.

  The second is a red LED 15b indicating "tightening abnormality". The red LED 15b is turned on instead of the green LED 15a, and is turned on immediately when the microcomputer 16 detects an abnormality. In order to make the operator recognize that there is an abnormality, it is preferable to make the operator blink instead of simply lighting. The third is the blue LED 15c indicating “communication abnormality”. This blue lamp is turned on when an abnormality is detected in the communication state between the microcomputer 16 and the external communication device.

  FIG. 3 is a diagram for explaining a method of performing torque control in the present embodiment. At the time of screw tightening according to the present embodiment, the motor 3 is controlled in three stages according to the tightening state. The upper graph of FIG. 3 plots the relationship between the passage of time and the tightening torque with the torque at the time of impact in the oil pulse unit 10, the horizontal axis is time t (s), and the vertical axis is the torque value T. (N · m). The lower graph of FIG. 3 is a diagram showing the relationship between time t (s) and the number of rotations (rpm) of the motor. In order to make the upper and lower graphs correspond to each other, the interval between the horizontal axes is made common.

  First, a set torque value (N · m) for tightening is set in the microcomputer 16 before tightening the bolt. The setting method may be set by an operation button provided in the impact type screw tightening device 1 or an instruction may be issued from an external device to the microcomputer 16 through a signal cable (not shown). When an operator sets a bolt, a nut, or the like on the tip tool and positions the tip tool on the material to be fastened and pulls the trigger switch 8, the microcomputer 16 rotates the motor 3 according to the drawn stroke (section A). ). However, in section A, the upper limit rotational speed 41 is set in advance by the microcomputer 16, and even if the trigger switch 8 is pulled with a stroke equal to or higher than the upper limit rotational speed 41, it is limited to rotate while maintaining the upper limit rotational speed 41. The As described above, in the section A, by limiting the rotation speed, the rotation speed of the motor 3 is limited so as not to suddenly exceed the target torque (cut torque) at the first impact. The limiting method can be limited by the duty ratio of the pulse width modulation signal supplied to the inverter circuit.

  When the bolt is tightened by the rotation of the section A and the first impact 51 by the oil pulse unit 10 is performed, the microcomputer 16 that has detected it shifts to the rotation control of the motor 3 in the section B. The first hit 51 is detected by monitoring the output of the strain gauge 12.

In the section B, control is performed in a so-called soft joint region. The control feature in this region is not to rotate the motor 3 in proportion to the stroke amount of the trigger switch 8, but to use the following equation: The target rotational speed of the motor 3 is determined and controlled.
N _{(target value)} = N _{(previous value)} + G ₁ × (T _{(target value)} −T _{(detected value)} )
Here, N: motor rotation speed (rpm), T: torque value (N · m), G ₁ : gain constant The duty at this target rotation speed is controlled using the following equation.
Duty _{(target value)} = Duty _{(previous value)} + G ₂ × (N _{(target value)} −N _{(detected value)} )
Where N: motor rotation speed (rpm), G ₂ : gain constant

  In the section B, when the target rotational speed is controlled while resetting every time an impact is made, the target rotational speed is determined as 42 to 44 in the figure. Further, hits 52 to 54 are performed while the motor 3 rotates at the target rotation speed. Here, since 70% of the cut torque was exceeded when the hit 54 was performed, the motor speed in the section C is shifted to after the motor speed is decreased by a predetermined number. The reason for reducing the rotational speed of the motor 3 during the transition to the section C is that if the method of determining the target rotational speed is continued in the section B, the target torque will be exceeded at the next impact depending on the target rotational speed. This is because there is a risk of tightening with a torque that is higher than the set torque in some cases. Therefore, when the predetermined torque value, in this embodiment, the tightening torque value becomes 70%, the rotational speed is decreased and the control is switched to the control of section C. In this embodiment, it is assumed that the soft joint method is tightened, and the bolt is seated in the vicinity of 70%. However, the switching timing from the section B to the section C can be appropriately set based on various factors such as a tightening target, a target torque value, a soft joint, and a hard joint. Further, the number of revolutions to be dropped when shifting from the section B to the section C may be appropriately set in consideration of the initial target rotational speed that will be set in the section C.

  In the section B, the trigger switch 8 is used as a simple trigger for ON / OFF control. If the trigger switch 8 is pulled even a little, the rotation speed set by the microcomputer 16 regardless of the stroke amount. It is good to make it rotate with. On the other hand, when the trigger switch 8 is released, that is, when the stroke becomes zero, the motor 3 is stopped. If it does in this way, it can prevent that an operator adjusts the amount of strokes and adjusts the rotational speed of the motor 3, and it can prevent that a fastening state varies.

  The setting of the target rotational speed is recalculated every time a hit is made. For example, when the hit 51 is performed, the target rotational speed 42 is calculated by the above formula, and the motor 3 is rotated by setting the duty ratio corresponding to the calculated target rotational speed. Thereafter, the control of the section B is repeated until the impact torque value detected by the strain gauge 12 reaches a predetermined ratio of the cut torque, for example, 70%.

When it reaches 70% of the cut torque, the control shifts to the control in the section C, the rotational speed of the motor 3 is set lower than that in the section B, and the control is performed using the following formula.
N _{(target value)} = N _{(previous value)} + G ₃ × (T _{(target value)} −T _{(detected value)} )
Here, N: motor rotation speed (rpm), T: torque value (N · m), G ₃ : gain constant The duty at this target rotation speed is controlled using the following equation.
Duty _{(target value)} = Duty _{(previous value)} + G ₄ × (N _{(target value)} −N _{(detected value)} )
Where N: motor rotation speed (rpm), G ₄ : gain constant

As can be understood from the slopes 45 to 46 in FIG. 3, the gain constants have a relationship of G ₁ > G ₃ and G ₂ > G ₄ . The value of the gain constant is preferably set in the microcomputer 16 in advance. In section C, the upper limit rotational speed is set so that the tightening torque value does not exceed the specified value, and control is performed to keep it. In 48 of FIG. 6, since the rotation speed by the above formula exceeds the upper limit rotation speed, the rotation speed is not the calculated value by the above formula but the upper limit rotation speed.

  In this way, in the present embodiment, in the section B, the bolt is fastened at an early rotational speed, and after exceeding 70% of the target torque, the rotational speed of the motor 3 is limited so as not to overtighten the bolt. By controlling to, it is possible to tighten with a target torque with high accuracy. In FIG. 3, since the target torque has been achieved by the impact 58, the microcomputer 16 detects it and stops the rotation of the motor 3.

  Next, the control procedure by the control circuit 2 will be described with reference to FIG. FIG. 4 is a flowchart showing the operation of the impact type screw fastening device 1 according to the present embodiment. The procedure according to this flowchart is executed by the microcomputer 16 included in the control circuit 2. First, before starting the tightening operation, the microcomputer 16 acquires a target torque value that is a set value of the tightening torque (step 61). Next, it is detected whether or not the trigger switch 6 has been pulled by the operator, and if pulled, the process proceeds to step 63 (step 62). When the trigger switch 62 is pulled, the operation mode is set (step 63). Immediately after the trigger switch 62 is pulled, the operation mode of the section A is set. When the motor 3 rotates, the bolt rotates until the first impact is made, as indicated by 51 in FIG.

  When the first impact is made, a tightening torque value at the time of impact is detected (step 65). This detection is performed using the strain gauge 12. This detected value is evaluated by the microcomputer 16 to determine whether the tightening has been performed normally or abnormally (step 66). Here, the tightening abnormality is a case where the target torque value is achieved within the assumed number of hits (for example, when the target torque is suddenly achieved by the first hit) or a torque value significantly higher than the target torque value. It is tightened and tightened at an allowable upper limit torque (MAX) or more, or it does not reach the target torque indefinitely.

  If it is determined that there is no abnormality in tightening, it is determined whether or not the operation mode switching condition is satisfied (step 67). That is, in the case of the first hit 51, the operation mode needs to be changed from the section A to the section B control. Further, when the operation mode is section B, it is determined whether or not the tightening torque value detected in step 65 is 70% of the target torque value. A change to C control is required. If a change is necessary, the process returns to step 63 (step 67).

  Next, it is determined whether or not the detected tightening torque value exceeds the target torque (step 68). If not reached, the process returns to step 64. If reached, the rotation of the motor 3 is stopped (step 69), and normal tightening is performed. The LED 15a (green) indicating the above is turned on (step 70). Thereafter, the process returns to step 62 to prepare for the next bolt tightening operation.

  If it is determined in step 66 that the tightening is abnormal, the rotation of the motor 3 is stopped (step 71), the LED 15b (red) indicating abnormal tightening is blinked (step 72), and the process is terminated. In addition, in the flowchart of FIG. 4, although it does not mention about lighting of LED15c which shows generation | occurrence | production of communication abnormality, it is not necessary to make it interlock | cooperate with a rotation and a striking state, and if communication abnormality generate | occur | produces, it will light or blink at arbitrary timings. This is because it is only necessary to do so.

  According to the above-described embodiment, it is possible to perform tightening with high accuracy based on the set impact torque without performing torque overrun.

  As mentioned above, although demonstrated based on embodiment which shows this invention, this invention is not limited to the above-mentioned form, A various change is possible within the range which does not deviate from the meaning. For example, in this embodiment, the trigger switch 8 is used as a simple trigger for ON / OFF control in the section B. However, the control of the sections A to C is performed when the trigger switch 8 is pulled even a little by omitting the OFF control. Even if the trigger switch 8 is returned, the operation until the tightening of the screws and bolts is completed may be performed.

DESCRIPTION OF SYMBOLS 1 Impact type screw fastening apparatus 2 Control circuit 3 Motor 7 Motor drive circuit 8 Trigger switch 9 Torque sensor 10 Oil pulse unit 11 Grip part 12 Strain gauge 14 Switch circuit board 15 LED
16 microcomputer 17 rotation speed control circuit 18 18V constant voltage circuit 19 ± 12V power supply 20 constant voltage circuit 21 torque detection circuit 21a transmission circuit 21b detection circuit
22a, 22b Transformer 29 AC commercial power supply
30 Power supply box 31 Full wave rectification smoothing circuit 41 to 48 Target rotation speed 51 to 58

Claims (4)

Brushless DC motor, control circuit for controlling the rotation of the motor, an oil pulse unit driven by the motor, an output shaft connected to a shaft of the oil pulse unit and mounted with a tip tool, and the output In an impact-type screw tightening device that has a torque sensor that detects the occurrence of impact torque in the shaft, and that tightens the tip tool with a predetermined tightening torque using the output of the torque sensor,
(1) The control circuit is divided into three modes, section A, section B, and section C, from the time of startup until the completion of screw tightening.
(2) In section A, the number of rotations of the motor is limited and tightened at a constant number of rotations lower than the maximum number of rotations;
(3) When the first impact is made in the oil pulse unit, the control is shifted to the control of the section B, and the target rotational speed of the motor is set by the following formula,
N _{(target value)} = N _{(previous value)} + G ₁ × (T _{(target value)} −T _{(detected value)} )
Here, N: motor rotation speed (rpm), T: torque value (N · m), G ₁ : gain constant The duty to the inverter circuit supplied to the motor at this target rotation speed is expressed by the following equation: Set using
Duty _{(target value)} = Duty _{(previous value)} + G ₂ × (N _{(target value)} −N _{(detected value)} )
Here, G ₂ : Gain constant (4) When the detection value of the torque sensor when the oil pulse unit is hit reaches a predetermined value of the set tightening torque, the rotational speed is once lowered. To the control of the section C, and if it is below the predetermined value, the control of the section B is repeated,
(5) In the section C, the target rotational speed of the motor is set by the following formula,
N _{(target value)} = N _{(previous value)} + G ₃ × (T _{(target value)} −T _{(detected value)} )
Here, G ₃ : gain constant (where G ₃ <G ₁ )
The duty to the inverter circuit to be supplied to the motor at this target rotational speed is set using the following equation:
Duty _{(target value)} = Duty _{(previous value)} + G ₄ × (N _{(target value)} −N _{(detected value)} )
Here, G ₄ : gain constant (where G ₄ <G ₂ )
(6) If the detection value of the torque sensor when the oil pulse unit is hit does not reach the set tightening torque, the control in the section C is repeated, and if the set torque is exceeded. Stopping the motor;
An impact type screw fastening device characterized by that.   The impact type screw tightening device according to claim 1, wherein the transition from the section B to the section C is performed when 70% of the set tightening torque value is achieved. In the section C, an upper limit value of the rotational speed of the motor is set, and when the N _{(target value)} according to the above formula exceeds the upper limit value, the motor is rotated at the rotational speed of the upper limit value. The impact type screw fastening device according to claim 1 or 2, wherein the impact type screw fastening device is provided.   The impact type screw fastening apparatus according to any one of claims 1 to 3, wherein the control circuit includes a microcomputer, and the rotation control of the motor in the sections A to C is performed by the microcomputer.

Images