JPH0478421B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention provides an automatic screwdriver configured to eliminate the influence of inertia of a driver bit when screw tightening is completed and to reliably tighten screws with a desired screw tightening torque. The present invention relates to a tightening defect detection device for a tightening machine.

Prior Art Generally, when controlling screw tightening torque, a driver bit is rotated by a motor, the load current of the motor is detected, which fluctuates according to the load applied to the driver bit, and when this detected value reaches a set value, , a device that stops the motor after a certain period of time from that point, and a device that detects the reaction torque applied to the driver bit using a torque detection unit such as a strain gauge, and stops the motor when this reaches a certain value. In these devices, if the set value of the screw tightening torque is low, the tightening torque will be far from the set value due to the influence of the inertia of the rotary drive unit when the screw tightening is completed, making it impossible to accurately tighten the screw with the desired tightening torque. Therefore, there is a need for a screw tightening machine that can accurately tighten screws even at a low set tightening torque.

In line with this demand, new automatic screw tightening machines have been developed. As shown in FIGS. 3 to 5, this automatic screw tightening machine has a driver stand 3 that is raised and lowered by the operation of a cylinder 2. A motor stand 4 is fixed to the driver stand 3 via a rod 3a, and a motor 4a is attached to the motor stand 4 with its drive shaft facing downward. An automatic transmission 15 is connected to the drive shaft of the motor 4a. This automatic transmission 15 is connected to the motor 4.
The input disk 5 has an input disk 5 which is rotated by a rotation angle a, and a plurality of planetary cones 6 are arranged on the outer periphery of the input disk 5 so as to be frictionally engaged and rotated. A flat surface 6b located on the back surface of the conical surface 6C of the planetary cone 6
A cam disk 7 that rotates concentrically with the input disk 5 is arranged to frictionally engage with the input disk 5, and the gear ratio can be continuously changed by the frictionally engaged position between the gearshift ring 9 and the planetary cone 6, which will be described later. It is configured to change the Further, a driver bit (not shown) is connected to the cam disc 7 via a connecting mechanism 16 that rotates together with the cam disc 7, and the motor 4a
The rotation of the driver bit is transmitted to the driver bit.

Further, the driver stand 3 includes the motor stand 4.
A gear case 13 is rotatably disposed between the input disk 5 and the input disk 5, and the gear case 13 is configured to enclose the input disk 5, the planetary cone 6, and the cam disk 7. Further, an arm 12 is rotatably locked in the gear case 13 via a fixture 11, and a speed change ring 9 is rotatably supported at the upper end of the arm 12. It is configured to be movable along a conical surface.
The speed change ring 9 is biased by a spring 14 so that its frictional engagement position is located on the high speed side,
This spring 14 and the arm 12 are connected to the speed change ring 9
It is configured to regulate the maximum value of the reduction ratio and the tightening torque determined by the frictional engagement position of. Furthermore, the gear case 13 is connected to an elastically deformable member, such as a strain gauge tube 17, and is configured such that its rotation is transmitted to the upper end of the strain gauge tube 17 placed on the driver stand 3. A strain gauge 10 serving as a torque detection section is attached to the strain gauge tube 17, and the structure is such that the quality of the tightening is determined based on the detected value.

Problems to be Solved by the Invention In the automatic screw tightening machine described above, during normal screw tightening, the load applied to the driver bit is small and almost constant until the screw seating surface comes into contact with the workpiece. There is almost no movement of the screwdriver bit 9, and the driver bit can rotate at high speed to tighten the screw. After that, when the seat surface of the screw comes into contact with the workpiece, the load on the driver bit increases rapidly. At the same time, the speed change ring 9 receives a reaction torque according to the load on the driver bit, and rotates in the opposite direction to the driver bit. At this time, since the gear ring 9 is held by the arm 12, the planetary cone 6
The position of frictional engagement with the motor changes, and the reduction ratio rapidly increases. Therefore, as shown in Fig. 6, the rotation of the driver bit is rapidly decelerated, the rotation reaches zero rotation, and screw tightening is completed, accurately and without being affected by the inertia of the rotating part of the motor 4a. It is now possible to tighten quickly.

However, with this automatic screw tightening machine 1, if a screw with a large leg diameter is screwed into the pilot hole of the workpiece, or if the screw chafes diagonally during screw tightening, the seating surface of the screw may Before contacting the workpiece, the reaction torque of the driver bit begins to gradually increase. As this reaction torque increases, the speed change ring 9 moves quickly, the reduction ratio increases quickly, and the rotation of the driver bit decreases. Therefore, the tightening speed becomes extremely slow before the seat surface of the screw comes into contact with the workpiece, making it impossible to complete tightening within a predetermined time, resulting in poor tightening. The only way to detect this defective tightening is to use a statistical method to set the machine cycle time required from the start of work to the completion of tightening, and to determine whether or not tightening is completed within this set time. With this method, it is not possible to immediately detect the diagonal biting of a screw, and there is a need for a device that can directly detect this when a tightening failure occurs.

Means for Solving the Problems The present invention was created in accordance with the above-mentioned demands.
It has a driver stand that moves up and down by the operation of a cylinder. A motor is fixed to this driver stand so that it moves up and down as a unit, and this motor includes an input disk that rotates in response to the rotation of the motor, a planetary cone that frictionally engages with the outer periphery of the input disk, and a planetary cone that frictionally engages with the input disk. A driver bit is connected via a cam disk. Further, a fixture is provided on the driver stand via an elastically deformable member, and an arm is rotatably locked to this fixture. This arm rotatably holds the speed change ring in a position where it is frictionally engaged with the conical surface of the planetary cone, and the speed change ring is biased toward the high speed side by a spring.

Furthermore, the elastically deformable member is provided with a torque detection section that detects the amount of strain thereof, and furthermore, a torque comparison section that compares the detected value with a torque setting value.

On the other hand, the motor is connected to a current detection section that detects the load current, and the detected value of this current detection section is detected by the current comparison section, and when the reaction torque applied to the driver bit reaches the desired torque, the current is applied to the motor. The current value ia is configured to be compared with a current set value ib lower than the current value ia. Further, the output of the current comparison section is connected to a delay section, and the output signal is configured to be transmitted from the delay section after a predetermined time TB. Further, the output signal of the delay section is configured to send the output of the torque comparison section to the tightening quality determination section.

Function In the automatic screw tightening machine described above, when voltage is supplied to the motor, the rotation of the motor is transmitted to the driver bit at a reduction ratio determined by the frictional engagement position of the speed change ring with respect to the conical surface of the planetary cone, and the screw is tightened into the workpiece. is tightened into place. When the screw is tightened and the speed change ring rotates in response to the reaction torque of the driver bit, the arm tilts, the speed change ring moves in its axial direction, and its reduction ratio increases. When the seat surface of the screw comes into contact with the workpiece, the load on the driver bit increases rapidly, so the reduction ratio increases rapidly and finally reaches infinity, and the rotation of the driver bit stops, completing tightening. do.
At the same time, the reaction torque of the driver bit, which increases rapidly with the load on the driver bit, is detected by the torque detection section.

On the other hand, the load current of the motor is small and almost constant until the seat of the screw comes into contact with the workpiece.
When the screw seat surface contacts the workpiece, the load current increases rapidly in the same way as the load applied to the driver bit. This load current is detected by the current detection section, and when the detected value reaches the current set value ib, an output signal is generated from the current comparison section and the delay section is activated. An output signal is generated from the delay section after a predetermined time TB has elapsed, and the output signal of the torque comparison section is determined based on this output signal. At this time, since the detected value of the torque detection section has already reached the torque setting value within a predetermined time after the load current reaches the set value ib, an output signal is sent from the torque comparison section to the tightening quality judgment section. , the tightness is determined and displayed.

Furthermore, if the threaded screw bites into the workpiece obliquely, the load applied to the driver bit gradually increases before the seating surface of the screw comes into contact with the workpiece. Therefore, the rotational speed of the driver bit is rapidly reduced before the seat surface of the screw contacts the workpiece, and the tightening speed is rapidly reduced even before the seat surface of the screw contacts the workpiece. At this time, the load current of the motor increases rapidly, almost in the same way as when the screw seat surface contacts the workpiece, so that the load current reaches the current set value ib. Therefore, an output signal is transmitted from the current comparison section, and similarly to the above, after a predetermined time TB, an output signal from the torque comparison section that compares the detection value of the torque detection section and the torque setting value is sent to the tightening quality determination section. At this point, the rotational speed of the driver bit has been rapidly reduced before the screw seating surface contacts the workpiece, so the screw seating surface is not in contact with the workpiece. Therefore, the detection value of the torque detection section does not reach the torque setting value, no output signal is generated from the torque comparison section, and the tightening quality determination section can determine that the tightening is defective.

Embodiments Hereinafter, embodiments will be described with reference to the drawings. In FIG. 1, A indicates the rotation of the motor 4a through the automatic transmission 1.
This is a control device for the automatic screw tightening machine 1, which is configured to transmit information to the driver bit 8 via the driver bit 5, and is configured to control the motor 4a. This control device A has a work start section 20, which includes a cylinder 2 serving as a lifting means for the automatic screw tightening machine 1, and a timer TA to be described later.
and is configured to operate the reset pulse circuit 21. Further, the work start section 20 operates the speed command section 22 and the forward/reverse switching command section 23, respectively, and operates the forward/reverse switching means 24 of the motor 4a.
It is configured to switch the motor 4a to the forward rotation side, and to rotate the motor 4a by giving a command to the motor 4a to rotate at the necessary rotation speed during the normal rotation. Further, a voltage supply section 25 is connected to the motor 4a via the forward/reverse switching means 24, and the motor 4a is configured to rotate upon receiving the voltage from the voltage supply section 25. A current detection section 26 is connected to the motor 4a to detect the load current thereof. This current detection section 26 includes a resistor 26b connected to the armature winding of the motor 4a, a first filter 26a, a first amplification section 27, and a gain correction section 28.
It is connected to a tightening completion detection section 29 that detects the completion of screw tightening. This tightening completion detection section 29 includes a current setting section 30 that sets a current setting value ib lower than the current value ia of the motor 4a when screw tightening is normally completed with a desired tightening torque;
A current comparator 31 that compares the current set value ib with the detected value; an AND circuit 32 that passes the output signal of the current comparator 31 according to the output signal of the timer TA;
It consists of a timer TB forming a delay section 33 which transmits an output signal after TB. This delay section 33 is configured to send a conversion command signal to an A-D conversion section 34, which will be described later.

Also, the timer TB of the tightening completion detection section 29
The output signal is sent to the timer TC, and the time TC required for the A-D converter 34 to complete the conversion is
has passed, the output signal is sent to the speed command section 2.
2 and the forward/reverse switching command unit 23, and the motor 4a
At the same time, the forward/reverse switching means 24 is configured to be switched to the reverse direction. Moreover, the output signal of the timer TC is sent to the timer TD, and after the time TD required for the motor 4a to completely stop has elapsed, the speed command section 22 is activated to control the motor 4a at a predetermined rotation speed. It is configured to reverse only the time. At the same time, the output signal of this timer TD is sent to the machine cycle completion section 35.
The cylinder 2 is configured to be returned to its original position by a cycle completion signal issued from the cylinder 2.

On the other hand, the detected value of the rejection gauge 10 is sent to a peak hold circuit 38 via a second filter 36 and a second amplification section 37, and is displayed on a display section 39 via an A-D conversion section 34. It is configured.
The A-D converter 34 is connected to the tightening completion detector 2.
The output signal of timer TB 9 is used as the operation timing, and the detection value at this point is converted into a digital value, which is displayed on the display section 39.

Moreover, the output of the A-D conversion section 34 is sent to a first torque comparison section 40 and a second torque comparison section 41, and the lower limit digital torque set by the first torque setting section 43 and the second torque setting section 44, respectively. The set value is configured to be compared with the upper limit digital torque set value. The first torque comparison section 4
0 and the output signal of the second torque comparison section 41 are sent to a tightening quality determination section 45, which determines whether the digital detection value is within a predetermined range, and displays whether the tightening quality is good or not. There is.

Further, the output of the second amplification section 37 is sent to a third torque comparison section 46, where it is compared with the lower limit analog torque set value set by the third torque setting section 47, and the conversion of the A-D conversion section is completed. If there is a decrease in the analog detection value later, it is configured to be able to detect this.

In the control device A of the automatic screw tightening machine described above, the second A
As shown in Figures a, b, and c, the output signal from the work start section 20 activates the cylinder 2, which serves as a means for raising and lowering the driver bit 8, and the driver bit 8 is lowered. At the same time, the output signal of the work start section 20 activates the timer TA, as shown in FIG. 2A e.
After a predetermined time TA, the peak hold circuit 38 is set and the AND circuit 32 is opened. Moreover,
The work start section 20 is a reset pulse circuit 21
and reset each part. Furthermore, the work start section 20 operates the speed command section 22, the forward/reverse switching command section 23, and the forward/reverse switching means 24 to rotate the motor 4a forward at a predetermined rotation speed. As the motor 4a rotates in the forward direction, the motor 4a rotates through the automatic transmission 15 consisting of an input disc (not shown), a planetary cone (not shown), a cam disc (not shown), and a speed change ring (not shown). The driver bit 8 rotates, and the tightening work is started. When the screw is screwed into the workpiece normally, the load applied to the driver bit 8 is small and almost constant until the seat surface of the screw comes into contact with the workpiece, so the movement of the speed change ring is small and the reduction ratio is small. Bit 8 rotates at high speed.

When the screw seat surface comes into contact with the workpiece, the load on the driver bit 8 increases rapidly as shown in FIG. 2A, and the reaction torque applied to the driver bit 8 also increases rapidly. Therefore, the speed change ring rotates greatly, and its reduction ratio increases continuously, until finally, the reduction ratio reaches infinity, and the rotation of the driver bit 8 stops, completing the tightening. At the same time, the reaction torque applied to the driver bit 8 at this time is detected by the strain gauge 10.

On the other hand, the load current of the motor 4a increases rapidly as the load of the driver bit 8 increases, as shown in FIG. 2A (d). This load current is detected by the current detection section 26, and the detected value is compared with the current setting value ib of the current setting section 30. When the detected value matches the current set value ib,
As shown in i and j, timer TC and timer TD are sequentially activated after a predetermined time TB from that point, and a conversion command signal is supplied to the AD converter 34. The A-D converter 34 converts the detected value of the strain gauge at that time into digital data,
After the conversion completion signal is transmitted as shown in FIG. 2A, g, this digital data is sent to the display section 39, where it is displayed.

At the same time, the digital data is compared with the upper and lower limit torque setting values of the first torque setting section 43 and the second torque setting section 44. At this time, the rotation of the driver bit 8 is completely stopped, and the reaction torque is
As shown in Figure A h, since the tightening has already been completed, the first torque comparison section 40 and the second torque comparison section 41 are increased by the time-up signal of the timer TC, as shown in Figure 2A h. Depending on the output signal, the tightening quality determination section 45 can determine whether the reaction torque applied to the driver bit 8 is within the torque setting value range, and can display the quality of the tightening at the timing shown in FIG. 2Ak.

On the other hand, when the screw is bitten into the work piece diagonally and is screwed in, the load applied to the driver bit 8 is applied even before the bearing surface of the screw comes into contact with the work piece, as shown in Fig. 2Bh.
It gradually increases as shown in . Therefore, as shown in Fig. 6, the automatic transmission 15 increases the reduction ratio according to the load, and the rotational speed of the driver bit 8 suddenly decreases even before the seat surface of the screw contacts the workpiece. and the screws are tightened.
On the other hand, the load current applied to the motor 4a is
As the characteristic curve in Figure 7 shows, driver bit 8
When the load is small, if the current increases even slightly, the current increases rapidly and settles down to a certain value. Therefore, the second
As shown in Fig. B, d, the detected value of the current detection unit 26 reaches the current set value immediately before the seat surface of the screw comes into contact with the workpiece. Therefore, as shown in Fig. 2B, f, the timer TB operates in the same manner as described above, and
After TB, the detected value of the strain gauge 10 is converted by an A-D converter, and the digital values are compared by a first torque comparator 40 and a second torque comparator 41. At this time, the detected value detected by the strain gauge 10 is due to the fact that the driver bit 8 rotates slowly and takes time to tighten the screw.
After TB has elapsed, the driver bit 8 is still rotating, and the reaction torque applied thereto has not reached the predetermined value as shown in FIG. 2B h. Therefore, the output signals of the first torque comparison section 40 and the second torque comparison section 41 are not generated, and as shown in FIG. 2B k, the tightening quality determination section 45 determines that the detected value is not within the predetermined range. , it is determined that the tightening is defective and that the screw is loose during tightening.

Thereafter, as shown in Figures 2A and 2B, i and j, the output signal of the timer TB is sent to activate the timer TC, and a time-up signal after a predetermined time TC stops the motor 4a and switches the forward/reverse switching means 24. Switch to the reverse side. At the same time, the time-up signal of the timer TC activates the timer TD, and the time-up signal after a predetermined time TD causes the speed command unit to
2 is activated to reverse the motor 4a at a predetermined rotation speed for a predetermined time. As a result, driver bit 8
The chamfering between the screw and the automatic transmission 15 is released.
returns to its original position.

Further, the time-up signal of the timer TD is sent to the machine cycle completion detection section 35, and the cylinder 2 moves back in response to the completion signal from the machine cycle completion detection section 35 to prepare for the next work.

Effects of the Invention As explained above, the present invention transmits the rotation of a motor to a driver bit through an automatic transmission consisting of an input disk, a planetary cone, a cam disc, and a speed change cylinder, and also transmits the reaction torque applied to the driver bit. A torque detection unit is provided to detect the load current of the motor, and when the detected value reaches a set value for detecting completion of tightening and a tightening completion signal is issued, the detection value of the torque detection unit is Since it is configured to determine whether a predetermined value has been reached, not only can the screw be tightened without being affected by the inertia of the motor, but even if a tightening defect such as a screw chamfering occurs diagonally, this will not occur. It is possible to detect a decrease in the tightening speed caused by the machine and immediately detect a tightening defect, and it is possible to prepare for the next operation early without waiting until the machine cycle time has elapsed, thereby providing an efficient tightening defect detection device. There are advantages such as

In the embodiment, a strain gauge tube and a strain gauge are used as the torque detection section, but these can be replaced with a position sensing device.
Further, although the detection value of the torque detection section is configured to be held by the peak hold circuit, it may also be held by a sampling circuit.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the present invention, Figures 2A and B are signal waveform diagrams at each point in Figure 1, Figure 3 is an overall explanatory diagram of the automatic screw tightening machine according to the present invention, and Figure 4 is the Fig. 5 is an enlarged cross-sectional view of the main parts of the automatic transmission according to the present invention, and Figs. 6 and 7 are respectively the torques possessed by the output shaft of the automatic transmission according to the present invention. - A rotation speed characteristic curve diagram and a torque-load current characteristic curve diagram. A...Control device, 1...Automatic screw tightening machine, 2...Cylinder, 3...Driver stand, 3a...Rod, 4...Motor stand, 4a...Motor, 5...Input disk, 6...Planetary cone, 6a...Circumferential groove , 6b...flat surface, 6c...conical surface, 7...cam disk, 8...driver bit, 9
...speed change ring, 10...strain gauge, 11...fixture, 12...arm, 13...gear case, 14...spring, 15...automatic transmission, 16...coupling mechanism, 17...
Strain gauge tube, 20...Work start section, 21...Reset pulse circuit, 22...Speed command section, 23...
Forward/reverse switching command section, 24... Forward/reverse switching means, 25... Voltage supply section, 26... Current detection section, 26a... First filter, 26b... Resistor, 27... First amplifying section, 28...
Gain correction section, 29...Tightening completion detection section, 30...
Current setting section, 31... Current comparison section, 32... AND circuit, 33... Delay section, 34... A-D conversion section, 35...
Machine cycle completion detection section, 36... second filter, 37... second amplification section, 38... peak hold circuit, 39... display section, 40... first torque comparison section, 4
DESCRIPTION OF SYMBOLS 1...Second torque comparison section, 42, 43...First torque setting section, 44...Second torque setting section, 45...Tightening quality determination section, 46...Third torque comparison section, 47...Third torque setting section.

Claims (1)

[Claims] 1. A driver stand 3 is provided which is raised and lowered by the operation of the cylinder 2, and a motor 4a is attached to the driver stand 3 so as to move up and down together with the driver stand 3.
The driver bit 8 is connected via the input disk 5 which rotates in response to the rotation, the planetary cone 6 which frictionally engages with the outer periphery of the input disk 5, and the cam disk 7 which frictionally engages with the input disk 5.
At the same time, a fixture 11 is provided on the driver stand 3 via an elastic deformable member, and this fixture 1
1, an arm 12 is rotatably locked to the arm 12, a speed change ring 9 is rotatably held by the arm 12, and this speed change ring 9 is placed in frictional engagement with the outer periphery of the planetary cone 6. The speed change ring 9 is biased toward the high speed side by the spring 14, while a torque detection section for detecting the amount of displacement of the elastic deformation member is disposed, and a torque comparison section is provided for comparing the detected value with a torque setting value. A current detection section 26 is provided to detect the load current of the motor 4a, and the detection value of the current detection section 26 and the reaction torque applied to the driver bit 8 are lower than the current value ia flowing through the motor 4a when the desired torque is reached. A current comparison section 31 is provided to compare the current setting value ib with a current setting value ib, a delay section 33 is provided which is activated by the output signal of the current comparison section 31, and the output of the torque comparison section is determined based on the output signal of the delay section 33. A tightening defect detection device for an automatic screw tightening machine, characterized in that a quality determining section 45 is provided.