JPH0724991B2 - Automatic screw tightener - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a box bit or a driver bit that rotates in response to the rotation of a motor to tighten a bolt, a nut or a screw on a work without being affected by the inertia of the motor. The present invention relates to an automatic screw tightener configured to perform tightening without being affected by a shocking reaction force torque when a workpiece collides with a work and to accurately detect the tightening torque from an axial force applied to a driver bit.

[0002]

2. Description of the Related Art Generally, when controlling the tightening torque of bolts, nuts, screws, etc., a motor rotates a box bit or a driver bit (hereinafter, the driver bit will be described), and Addition to a device or a driver bit that is configured to stop the motor after a certain time from the time when a detection unit that detects the load current of the motor that fluctuates according to the applied load is provided and the detected value reaches the set value A general device is configured such that the reaction torque is converted into a strain amount by a strain tube, the strain amount is detected again by a detection unit such as a strain gauge, and the motor is stopped if the strain amount reaches a constant value. In these devices, if a shocking reaction force torque is generated when the head seat surface of the screw comes into contact with the work immediately before the completion of tightening, this is detected by the detection unit, and sometimes the detected value reaches the set value. However, there are drawbacks such as the completion of tightening. In addition, in these devices, if tightening is started and the detected value reaches the set tightening torque, the actual tightening torque is always the set tightening torque due to the influence of inertia when the motor is stopped because the motor is stopped. However, there are drawbacks such as not being able to perform accurate tightening work. As a device for eliminating these drawbacks, an automatic screw tightener equipped with an automatic transmission that stops the rotation of the driver bit when a set tightening torque is reached is known. As shown in FIG. 2, an automatic transmission 10 of the automatic screw tightener 1 includes an input disc 11 that is rotationally driven by a motor 9 and a plurality of planet cones 12 having a circumferential groove 12a that frictionally engages the input disc 11. A cam disk 13 frictionally engaged with a flat surface 12c on the back surface thereof, a speed change ring 14 frictionally engaged with the conical surface 12b of the planetary cone 12, an arm 15 rotatably holding the ring 15, and a speed change gear. It is composed of a spring 17 for urging the ring 14 toward the high speed side. When the speed change ring 14 is rotated and the arm 15 is inclined, the friction engagement position between the speed change ring 14 and the planetary cone 12 is changed to reduce the speed reduction ratio. Is configured to be continuously changed.

[0003]

In the automatic screw tightener 1 having the automatic transmission 10 as described above, the head seat surface of the screw (not shown) is the work (not shown) immediately before the completion of tightening.
Even if a shocking reaction force torque is generated when it comes into contact with the motor 9, it is absorbed by the rotation of the transmission ring 14 and is not transmitted to the motor 9 side, and this shocking reaction force torque is applied to the motor 9. It does not appear as torque. Further, when the speed change ring 14 of the automatic transmission 10 moves to the larger diameter side along the conical surface 12b of the planetary cone 12 and the reduction ratio becomes infinite, the tightening is completed when the tightening is completed. Since the rotation of the driver bit (not shown) is stopped even when the motor 9 is rotating, the tightening can be performed without being affected by the inertia of the motor 9. 1 has been highly evaluated as a highly accurate screw tightener. However, in this automatic screw tightening machine 1, when the tightening torque of the screw tightened by the driver bit is detected as shown in FIG. 3, the motor 9 is held rotatably with respect to the driver base 2 side. The reaction torque applied is detected as a tightening torque by a sensor 26 such as a strain gauge attached to the strain tube 25. Therefore, in the case of performing the tightening work by rotating the motor 9 at high speed at no load, if the rotation of the motor 9 at no load is excessively increased, the reaction torque applied to the motor 9 due to the influence of inertia at that time will occur. If the motor 9 increases and is detected by the sensor 26, or conversely, the weight of the motor 9 becomes too heavy, even if the motor 9 receives a reaction force during tightening, this may not be detected by the sensor 26. There is a defect that the magnitude of the inertia moment on the input side of the sensor affects the response speed and detection accuracy of the sensor 26. Further, because the reaction force type torque detection means of this kind is used, the detection speed of the torque is slow, the reduction ratio of the automatic transmission 10 becomes infinite, and the rotation of the driver bit is stopped. That is, when the set tightening torque is set so that the tightening is completed while the tightening torque is fluctuating, the torque fluctuates at high speed especially when the motor 9 rotates at high speed under no load. Therefore, the tightening torque cannot be detected in time, and accurate tightening cannot be performed, which is not suitable for this type of dynamic torque detection.

The present invention is intended to eliminate the above-mentioned drawbacks, is not affected by the inertia of the motor at the time of completion of tightening, is not affected by the shocking torque immediately before the completion of tightening, and has a tightening torque. It is an object of the present invention to provide an automatic screw tightening machine that can detect the tightening torque at high speed and accurately control the tightening torque even if the tightening work is finished while the torque varies.

[0005]

There is provided a driver stand that moves up and down by the operation of a lifting drive source, and a case is arranged so as to move integrally with the driver stand.
A bottom lid having a sleeve portion protruding inward is fixed to the bottom of the case, and the case is configured to be filled with lubricating oil. Also,
Inside the case, there are arranged an input disc rotated by rotational driving of a motor, a plurality of planet cones having circumferential grooves frictionally engaged with the disc, and a cam disk frictionally engaged with the back surface thereof. There is. A speed change ring is arranged in frictional engagement along the conical surface of the planet cone, and the speed change ring is rotatably held by an arm whose one end is locked to the driver base side. The speed change ring is urged toward the high speed side by a spring, and an automatic transmission is constructed in which the reduction gear ratio is continuously changed by the rotation of the speed change ring.

Further, an output shaft is connected to the cam disk, and a driver bit that integrally rotates is connected to the output shaft via a detection shaft which is a part of the magnetostrictive sensor. A magnetostriction generator is provided on the peripheral surface of the detection shaft, and an excitation coil and a magnetic detection coil that generate a predetermined magnetic field are arranged around the magnetostriction generator. Both ends of this magnetic detection coil are connected to the torque converter,
It is configured to detect a change in magnetic permeability appearing in the magnetostriction generating portion and detect an axial force applied to the detection shaft as a tightening torque.

Further, the magnetostriction generating portion may be composed of two detection grooves which are provided so as to be inclined in opposite directions.
In this case, an exciting coil and a magnetic detection coil that generate a predetermined magnetic field are arranged around the detection grooves of each stage, and both ends of each of the magnetic detection coils are connected to the torque conversion unit to connect the detection grooves of each of the two stages. The axial force applied to the detection shaft is detected as the tightening torque from the ratio of the magnetic permeability.

[0008]

In the above automatic screw tightener, when the speed of the motor is increased at no load, the inertial force of the motor becomes large, the driver bit outputs a large torque, and the reaction torque applied to the motor becomes relatively large. However, since the driver bit in which the magnetostrictive sensor for detecting the tightening torque is arranged is not distorted at all, the reaction torque is not detected as the tightening torque. If tightening is performed in this state, the head seat surface of the screw contacts the work just before the tightening is completed, and shocking reaction torque is applied. This reaction force torque is transmitted to the automatic transmission through the output shaft, and the reaction ring torque is absorbed by the rotation of the speed change ring, and the shocking reaction force torque does not cause distortion of the detection shaft. Not affected. Also, when setting the time when the speed change ring of the automatic transmission moves to the large diameter side of the conical surface of the planet cone and its reduction ratio becomes infinite as the tightening completion time,
Although the motor is rotating when tightening is completed,
Due to the driver bit stopping, tightening is completed without being affected by the inertia of the motor.

Further, when the tightening is completed just before the speed change ring of the automatic transmission moves to the large diameter side of the conical surface of the planet cone and its reduction ratio becomes infinite, that is, the driver bit is rotating. Even if the set tightening torque is set so that the completion of tightening is detected while the tightening torque is fluctuating, the strain generated in the detection axis is detected as the change in the magnetic permeability in the magnetostriction generator, and the torque converter The tightening torque can be detected at high speed, and the tightening torque can be accurately detected even when the motor is set at a high speed with no load and the setting torque is dynamic. it can.

[0010]

Embodiments Embodiments will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes an automatic screw tightening machine, which is a driver base 2 that is moved up and down by the operation of a cylinder (not shown), which is an example of an elevation drive source, and a chuck base that is integrally lowered to a predetermined position with a predetermined distance. (Not shown). A mounting base 4 is fixed to the upper surface of the driver base 2 via a cesar base 3, and a bottom cover 6 having a sleeve portion 6a for rotatably guiding an output shaft 5 described later is mounted on the mounting base 4. Is fixed. Further, a case 7 is fixed to the bottom cover 6, and an upper cover 8 is fixed to the upper part of the case 7 so that the case 7 is filled with lubricating oil. A motor 9 is attached to the upper lid 8 via a bracket 8a integrally attached, and its rotation is transmitted to an input disc 11 of an automatic transmission 10 built in the gear case 7. Has been done.

The automatic transmission 10 has a drive shaft 9 of a morch 9.
A plurality of planet cones 12 each having an input disk 11 that rotates upon receiving the rotation of a, and a circumferential groove 12a that frictionally engages the outer circumference of the input disk 11, and a cam disk 13 on each of the planet cones 12. The cone 12 is arranged so as to be frictionally engaged with the flat surface 12c located on the rear surface of the conical surface 12b and to rotate concentrically with the input disk 11. Further, a speed-change ring 14 is rotatably arranged on the conical surface 12b of the planetary cone 12 by frictionally engaging it, and the speed reduction ratio is determined by the frictional engagement position between the speed-change ring 14 and the planetary cone 12. It is configured to change continuously. Further, the speed change ring 14 is engaged with one end of an arm 15 at a plurality of positions on the outer circumference thereof, and the other end of the arm 15 is locked to a fixed ring 16 attached to the bottom cover 6 so that the speed change ring 14 Is configured to limit the amount of movement on the high speed side. Moreover, the speed change ring 14 is biased upward by a spring 17 held by a spring pressure adjusting means (not shown) so that the arm 15 is always upright.

An output shaft 5 rotatably guided to the sleeve portion 6a of the bottom cover 6 is connected to the cam disk 13 via a pressure adjusting mechanism 18, and the output shaft 5 is connected to the output shaft 5. Connecting shaft 1 rotatably held on the mounting base 4
9 are connected. The magnetostrictive sensor 2 is attached to the connecting shaft 19.
A detection shaft 21 forming a part of 0 is connected, and a driver bit 22 is integrally rotated at the lower end of the detection shaft 21 via a transmission mechanism (not shown). As an example of a magnetostriction generator, detection grooves 21a and 21b are provided in the center of the detection shaft 21 and are inclined in opposite directions in two steps. Detection groove 2 of each step
An excitation coil 23 and a magnetic detection coil 24 that generate a constant magnetic field are arranged around 1a and 21b, and are configured to detect a change in magnetic permeability of each detection groove 21a and 21b as a current value. There is. The magnetic detection coil 24 is connected to a torque conversion unit (not shown), detects the amount of strain generated in the detection shaft 21 from the ratio of the respective current values, and tightens the axial force applied to the detection shaft 21 from this. It is configured to detect as torque. Incidentally, the magnetostriction generating portion need not be a detection groove provided on the detection shaft,
The same effect can be obtained by applying or sticking a substance that shows a marked change in magnetic permeability.

In the above automatic screw tightener, when the motor 9 is driven and tightening is started, the speed change ring 14 of the automatic speed changer 10 follows the conical surface 12b of the planetary cone 12 in accordance with the load applied to the driver bit 22. Rotate. Therefore, the arm 15 is tilted to move the transmission ring 14 to the larger diameter side of the planet cone 12, and the friction engagement position between the planet cone 12 and the transmission ring 14 is changed. Therefore, the speed reduction ratio of the automatic transmission 10 increases and the rotation speed of the driver bit 22 gradually decreases. When the bearing surface of the screw (not shown) reaches the work (not shown) and the load on the driver bit 22 suddenly increases, and a shocking reaction torque is applied to the driver bit 22, the transmission ring 14 further rotates. However, this shocking reaction force torque is absorbed and the detection shaft 21 of the magnetostrictive sensor 20 is absorbed.
Is not twisted by this shocking reaction torque.

Moreover, the rotation of the transmission ring 14 increases the inclination of the arm 15 to increase the inclination of the transmission ring 14 and the planetary cone 1.
In the case where the tightening is completed at the time when the frictional engagement position with 2 moves toward the larger diameter side and the reduction ratio of the automatic transmission 10 becomes infinite, that is, the input disc 11 is rotating. If the cam disk 13 and the driver bit 22 integrated with the cam disk 13 do not rotate,
A constant output torque determined by the elastic force of the spring 17 and the speed change mechanism is output to the driver bit 22, and the screw is tightened at this output torque, that is, a desired set tightening torque without being affected by the inertia of the motor 9. To be

On the other hand, the friction engagement position is the planet cone 12
When the tightening torque immediately before moving to the larger diameter side of the automatic transmission 10 and the reduction ratio of the automatic transmission 10 becomes infinite is set as the tightening torque, that is, while the driver bit 22 is rotating and the tightening torque is changing. When the set tightening torque is reached, if the detection shaft 21 is distorted by the reaction torque applied to the driver bit 22, the detection grooves 21a, 21b
The change in magnetic permeability is immediately detected as a current value by the magnetostrictive sensor 20, and the axial force applied to the detection shaft 21 is detected as a tightening torque from the ratio. Therefore, if a strain is applied to the detection shaft 21, the tightening torque can be immediately obtained, the tightening torque can be detected at high speed, and even when the motor 9 with no load is rotated at high speed, the dynamic torque is increased. Even with tight tightening torque control, tightening with the set tightening torque can be performed accurately.

[0016]

As described above, according to the present invention, the input disc, the planetary cone that rotates by the rotation thereof, the cam disk that frictionally engages with the flat surface of the back surface thereof, and the frictional engagement with the conical surface of the planetary cone. The automatic transmission consisting of a gearshift ring, a rotatably holding arm and a spring that biases the gearshift ring so that the arm is always upright, and the output shaft of the automatic transmission has a detection shaft of a magnetostrictive sensor. Since the driver bit is connected to rotate integrally with the motor, the torque conversion part that detects the axial force applied to the detection shaft from the output of this magnetostrictive sensor as the tightening torque is provided. When the speed is increased, the inertial force of the motor increases and the reaction torque applied to the motor increases, but the detection axis of the magnetostrictive sensor does not become distorted and No effect on the detection of the tightening torque of the bit. Further, according to the present invention, even if the head seat surface of the screw comes into contact with the work immediately before the completion of tightening and the shocking reaction torque is applied, this shocking reaction torque does not cause the rotation of the speed change ring of the automatic transmission. It is absorbed by the motion, and the shocking reaction torque does not cause distortion of the detection shaft.
The output of the magnetostrictive sensor is not affected at all, and only the reaction torque applied to the driver bit can be accurately detected to accurately detect the tightening torque. Further, according to the present invention, if the time when the speed change ring of the automatic transmission moves toward the large diameter side of the conical surface of the planet cone and its reduction ratio becomes infinite is the time point when the tightening is completed, the motor will be operated when the tightening is completed. Despite the rotation, the driver bit stops, so it is not affected by the inertia of the motor.
The tightening can be completed. Moreover, according to the present invention, when the tightening is completed just before the speed change ring of the automatic transmission moves to the large diameter side of the conical surface of the planet cone and its reduction ratio becomes infinite, that is, the driver bit rotates. Even if the tightening torque is set so that the completion of tightening is detected while the tightening torque is fluctuating, tightening is performed based on the ratio of the magnetic permeability generated in each detection groove due to the strain generated in the detection shaft. Since the torque is detected, the tightening torque can be detected at high speed, and even if the tightening torque fluctuates drastically when the motor is rotating at high speed with no load, tightening the set tightening torque is accurate. Can be done.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram illustrating a main part of the present invention.

FIG. 2 is a longitudinal sectional view of an essential part of the automatic transmission according to the present invention.

FIG. 3 is a schematic explanatory diagram illustrating a main part of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Automatic screw tightener 2 Driver stand 3 Sensor stand 4 Mounting stand 5 Output shaft 6 Bottom cover 6a Sleeve part 7 Gacase 8 Top cover 8a Bracket 9 Motor 9a Drive shaft 10 Automatic transmission 11 Input disk 12 Planetary cone 12a Circular groove 12b Conical surface 12c Flat surface 13 Cam disk 14 Speed change ring 15 Arm 16 Fixed ring 17 Spring 18 Pressure adjusting mechanism 19 Connecting shaft 20 Magnetostrictive sensor 21 Detection shafts 21a, 21b Detection groove 22 Driver bit 23 Excitation coil 24 Magnetic detection coil 25 Strain tube 26 Sensor

Claims (2)

[Claims] 1. A case is arranged so as to move integrally with a driver stand that is moved up and down by the operation of an up-and-down drive source, and a bottom cover having a sleeve portion projecting inward is fixed to the bottom of the case and fixed inside the case. An input disc that is configured to be filled with lubricating oil and that is rotated by the rotational drive of a motor in the case, a plurality of planet cones having a circumferential groove that frictionally engages with the input disc, and a friction member on the back surface thereof. A mating cam disk is arranged, and further, a transmission ring is arranged in friction engagement along the conical surface of the planetary cone,
The transmission ring is rotatably held by an arm whose one end is locked to the driver base side and is urged toward the high speed side by a spring, while the output shaft is integrally connected to the cam disk. Is connected to a driver bit that rotates integrally through the detection axis of the magnetostrictive sensor, and a magnetic strain generation section is provided on the peripheral surface of the detection axis, and an excitation coil and a magnetic detection coil are arranged around this magnetic strain generation section. An automatic screw tightener is provided with a torque conversion unit that detects a change in magnetic permeability appearing in the magnetic strain generation unit from both ends of the magnetic detection coil and detects an axial force applied to the detection shaft. 2. The magnetostriction generating section is composed of two-step detection grooves that are inclined around the detection axis in opposite directions, and an exciting coil and a magnetic detection coil are arranged around each detection groove. The torque conversion unit for detecting a change in magnetic permeability appearing in the detection groove at both ends of the magnetic detection coil and detecting an axial force applied to the detection shaft from the ratio of the change in magnetic permeability is provided. Automatic screw tightening machine described.