JPH03136729A - Automatic screw driving device and its control method - Google Patents

Abstract

PURPOSE:To easily perform automization of screw driving operation with a robot by making fastening torque proportional to a displacement of a torque spring, whose characteristics does not depend upon operator's working attitude, and by constituting a device so as to detect the displacement of the torque spring as an axial displacement of a nut of a ball screw having high stiffness. CONSTITUTION:When a load is applied to a ball screw shaft 6, a ball screw nut 5 moves axially while rotating. As the result, a torque spring 7 deforms, and axial load increases with the displacement of the torque spring 7. Because torque of a ball screw 61 is proportional to the axial load of the ball screw 61, the torque is produced in proportion to the displacement of the torque spring 7. The ball screw shaft 6 is rotated by this torque. A movable dog 71 moves with this rotation according to the displacement of the torque spring 7. The position of the movable dog 71 is detected by a displacement sensor 8, and a required fastening torque, which is proportional to the required displacement, is detected. On the basis of the detected value of the sensor 8 and the set value of the torque spring 7, a driver motor 2 is controlled so as to fasten a screw with the required torque.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tool for automatically tightening a nut to a bolt, and also relates to a tool that can adjust the torque and control the tightening operation.

[Prior Art] Conventionally, in order to obtain torque for predetermined tightening, the bolt elongation is detected and the drive motor of the socket is controlled (for example, Japanese Utility Model Application Publication No. 1-74029); It can be detected by the current value of the drive motor (for example,
No. 23830), those that control the rotation of the socket by detecting it with a torque detector installed on the drive shaft of the socket (for example, Japanese Utility Model Application Publication No. 1983-728), and those that detect tightening torque using a strain gauge. However, a method has been disclosed in which a motor is controlled using this detection signal.

[Problems to be Solved by the Invention] By the way, in order to detect the elongation of a bolt, a receiving and transmitting device for ultrasonic waves, light, etc. is required, and the device is complicated.

In addition, even for devices that control the rotation of the socket by detecting torque based on the current value of the drive motor, it is necessary to improve the accuracy of the correlation between the torque and the detected value and increase the responsiveness of the control device when tightening the motor. Coasting may occur, resulting in excessive tightening torque. In addition, in a device that controls torque using a strain gauge, tightening is controlled by a signal after the torque is reached, so the tightening torque may become excessive due to a delay in response of the motor or inertia of the mechanism.

Furthermore, when attached to the wrist of an industrial robot whose operating posture changes in a complex manner, sufficient reliability against vibration and acceleration is required, and the device with the above configuration is unable to meet these requirements. had disadvantages such as complicated structure and high cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic screw tightening device that can set the necessary torque by an external command, has a simple configuration, and is inexpensive.

[Means for Solving the Problems] The present invention provides a tool mounting system that is driven via a drive motor provided inside one end of a hollow frame and a clutch with a brake coupled to the output shaft of the drive motor. In an automatic screw tightening device having a part, a spline shaft is fixed to the output side of the clutch with a brake, a hollow part is formed at the other end, and a spline shaft is provided inside the hollow part of the spline shaft. Spline teeth, a bearing that supports the spline shaft in a frame so as to be rotatable and not move in the axial direction, a ball screw nut having external teeth on its outer periphery that mesh with the spline teeth, and a ball screw nut that meshes with the ball screw nut. A ball screw is provided, and the tool mounting is provided between a ball screw shaft connecting the parts, a bracket provided at the other end of the frame, and an intermediate portion of the ball screw shaft and the bracket, and the tool mounting is provided between the ball screw shaft and the bracket, and the tool mounting is provided between the ball screw shaft and the bracket, and the tool mounting is provided between the ball screw shaft that connects the parts, and the bracket provided at the other end of the frame, and the tool mounting is provided between the ball screw shaft and the bracket. and a bearing supported so as not to move in an axial direction, a torque spring inserted through a thrust bearing between the bracket and the ball screw nut, and a movable dog that moves according to displacement of the torque spring. and a displacement detector for detecting displacement of the movable dog.

Further, a control method includes providing a displacement setting device for setting a displacement of the torque spring corresponding to a desired torque of the ball screw shaft, and controlling the drive motor based on a detected value of the displacement detector and a set value of the displacement setting device. It is.

[Operation] When a load is applied to the ball screw shaft, the ball screw nut moves in the axial direction while rotating. As a result, the torque spring is displaced and the axial load increases in proportion to the displacement of the torque spring. Since the torque of the ball screw is proportional to the axial load, a torque proportional to the displacement of the torque spring is generated,
The torque, or tightening, rotates the ball screw shaft.

In addition, when the ball screw shaft rotates, the movable dog moves according to the displacement of the torque spring, but the position of the movable dog is detected by a displacement detector, and the torque for a predetermined tightening that is proportional to the predetermined displacement is detected. .

Further, by comparing the detected value of the displacement detector and the set value of the displacement setter, it can be known that the tightening torque has reached the set value.

[Example] The present invention will be described with reference to embodiments shown in the drawings.

FIG. 1 is a side sectional view of an embodiment of the present invention, in which a drive motor 2 is fixed inside one end of a hollow frame l, and an input side of a clutch with a brake 3 is attached to an output shaft 21 of the drive motor 2. ing. A fixed portion of the clutch with brake 3 is fixed to a frame l, and one end of a spline shaft 4 is fixed to the output side of the clutch with brake 3. A hollow portion 41 is formed at the other end of the spline shaft 4, and is rotatably supported by the frame 1 via a bearing 11, and movement in the axial direction is stopped. Spline teeth 42 are provided inside the hollow portion 41, and are engaged with external teeth 51 provided on the outer periphery of the ball screw nut 5. A ball screw 61 is engaged with the ball screw nut 5 and is provided from one end of the ball screw shaft 6 to approximately the middle portion. An intermediate portion of the ball screw shaft 6 is rotatably supported by a bracket 13 provided at the other end of the frame 1 via a bearing 12, and movement in the axial direction is stopped. A thrust bearing 5 is provided between the bracket 13 and the ball screw nut 5.
A torque spring 7 is inserted through 2. Furthermore, a movable dog 71 that moves according to the displacement of the torque spring 7 is fixed to the thrust bearing 52. A displacement detector 8 such as a proximity switch for detecting displacement of the movable dog 71 is provided near the other end of the frame l. The other end of the ball screw shaft 6 is provided with a flange portion 91, and a tool mounting portion 9 is provided.
is provided to slide in the axial direction, and the flange portion 91
A pressure spring 92 is provided between the nut and the bearing 12 to generate pressure applied in the axial direction when tightening the nut.

Here, the relationship between the torque T of the ball screw and the axial load F is expressed by the following equation (1).

T=F-1/2π·η (1) Here, β is the lead of the ball screw, and η is the efficiency of the screw.

Therefore, if the efficiency η of the lead 11 screw is constant,
The torque T of the ball screw is proportional to the axial load F.

Now, when the tool is attached by attaching a nut to the part 9 and rotating the drive motor 2, the spline shaft 4 is rotated via the clutch 3 with a brake.

When there is no load, the ball screw nut 5 rotates together with the spline shaft 4 without moving in the axial direction, and the ball screw shaft 6 also rotates together with the spline shaft 4 due to the friction torque of the ball screw.

When a load is applied to the nut, a force acting to stop the rotation of the ball screw shaft 6 is applied to the tool attachment via the portion 9, and the ball screw nut 5 moves in the axial direction while rotating. As a result, the torque spring 7 is displaced, and an axial load proportional to the displacement is generated on the ball screw. Therefore, the expression (
As expressed by 1), a torque proportional to the axial load is generated, and the ball screw shaft 6 is rotated by the torque, that is, the tightening torque.

By rotating the ball screw shaft 6, the movable dog 71 moves according to the displacement of the torque spring 7. When the position of the movable dog 71 is detected by the displacement detector 8 and a predetermined displacement is detected, the predetermined tightening is performed. Torque can be obtained. Furthermore, when a predetermined tightening is performed, the clutch with brake 3 is operated by the detection signal of the displacement detector 8 when torque is obtained, and the rotation of the ball screw shaft 6 is stopped.

Note that the drive motor 2 can be constituted by a servo motor with good responsiveness, and the drive motor can be directly controlled by a control device 22 shown in FIG. 2 based on a detection signal from the displacement detector 8.

That is, the displacement detector 8 has a plurality of proximity switches arranged in the axial direction, detects the displacement corresponding to the torque of a plurality of set tightenings, and instructs the clutch with brake 3 or the drive motor 2 to perform the required operation. do.

In this case, the control device 22 is provided with a first displacement setting device 221 that sets the displacement of the torque spring 7 when the required torque is small, for example, the displacement corresponding to the torque generated when the screw rotates two to three times and starts biting. The set low torque displacement value and the output of the displacement detector 8 are compared by the comparator 222, and when they match, the low speed command 223 controls the drive motor 2 by the controller 225 via the selection switch 224. To control the rotation speed to a low speed to make the screw start to bite smoothly.

Further, a second displacement setter 226 is provided to set the displacement of the torque spring 7 corresponding to the required torque when screwing the screw, and a displacement value of the set screw tightening torque and a displacement detector 8 are provided.
The comparator 227 compares the outputs of the drive motor 2 with the output of the drive motor 2, and when they match, the high speed command 228 causes the controller 225 to increase the rotational speed of the drive motor 2 via the selection switch 224 to tighten the screws.

Furthermore, a third displacement setter 229 is provided to set the displacement of the torque spring 7 corresponding to the required torque when tightening the screw, and a comparator is used to compare the displacement value of the set tightening torque and the output of the displacement detector 8. 230 and when they match, the controller 225 controls the rotation speed of the drive motor 2 to a low speed rotation via the selection switch 224 using the low speed command device 231.

Note that the timer 232 sets the time during which the tightening torque is applied.
The controller 225 controls the drive motor 2 so that the drive motor 2 is stopped by the stop command device 233 before an overload occurs.

Further, a rotation speed detector 234 that detects the rotation speed of the ball screw shaft 6 and a rotation speed setting device 235 that sets the 2 to 3 rotations at which the screw starts biting are provided, and the output of the rotation speed detector 234 and the rotation speed setting are provided. The set value of the device 235 is compared by the comparator 236. In this case, the spline shaft 4 and the output shaft 21 of the drive motor 2 are made hollow, and the detection shaft 62 fixed concentrically to one end of the ball screw shaft 6 is passed through, and the detection shaft 62 is connected to the rotation speed detector 234. Let's combine them.

The detection shaft 62 along with the ball screw shaft 6 is driven by the drive motor 2.
When the output of the rotation speed detector 234 and the setting value of the rotation speed setting device 235 match, the third displacement setting device 229
When the displacement corresponding to the set tightening torque is output, an overload signal is output to the stop command device 233 via the multiplier 237, and the drive motor 2 is stopped by the controller 225.

That is, if the torque spring 7 is displaced less than the displacement corresponding to the tightening torque at a predetermined rotation speed of the ball screw shaft 6, it is determined to be normal; If the displacement is reached, it is determined that the screws are engaged in an abnormal state, so that it is possible to detect an abnormality when the screws start to bite.

In this way, by providing the displacement detector 8 and the above-mentioned control device 22, highly reliable program control of screw tightening work without overload can be performed.

Alternatively, a differential transformer or a linear pulse generator may be used instead of the proximity switch, and predetermined tightening may be detected by setting the torque steplessly.

Moreover, if instead of the drive motor 2, a wrist torsion drive motor attached to the arm of the industrial robot is directly connected to a clutch with a brake or a spline shaft, a compact screw tightening robot can be constructed.

[Effects of the Invention] As described above, according to the present invention, tightening is performed by making torque proportional to the displacement of a torque spring whose characteristics do not change even if the operating posture changes, and by applying the displacement to a highly rigid ball screw nut. Since the detection is based on axial displacement, a simple, reliable, and inexpensive automatic screw tightening device is provided.

In addition, by providing a displacement detector that detects the displacement of the torque spring and a control device that controls the drive motor based on the detected displacement value, screw tightening work can be program controlled, so industrial robots can perform screw tightening work. This has the effect of making automation easier.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an embodiment of the present invention, and FIG. 2 is a block diagram of a control device. l... Frame, 2... Drive motor, 3... Clutch with brake, 4... Spline shaft, 5... Ball screw nut, 6... Ball screw shaft, 61... Ball screw, 62 ...Detection axis, 7...Torque spring, 8
...Displacement detector, 22...Control device, 221...
First displacement setter, 226...Second displacement setter, 229
...Third displacement setter, 234...Rotation speed detector, 2
35...Rotation speed setting device Fig. 1 Fig. 2

Claims (1)

[Scope of Claims] 1. An automatic screw tightening device comprising a drive motor provided inside one end of a hollow frame, and a tool mounting portion driven by an output shaft of the drive motor, wherein one end is provided inside the one end of the hollow frame. a spline shaft connected to an output shaft of a drive motor and having a hollow portion formed at the other end; spline teeth provided inside the hollow portion of the spline shaft; A bearing for stopping and supporting directional movement, a ball screw nut having external teeth on the outer periphery that mesh with the spline teeth, and a ball screw meshing with the ball screw nut,
A ball screw shaft that connects the tool mounting portion, a bracket provided at the other end of the frame, and a bracket provided between an intermediate portion of the ball screw shaft and the bracket, which allows the ball screw shaft to rotate freely and in the axial direction. a torque spring inserted through a thrust bearing between the bracket and the ball screw nut; a movable dog that moves according to the displacement of the torque spring; and a displacement of the movable dog. An automatic screw tightening device characterized by being equipped with a displacement detector that detects. 2. The automatic screw tightening device according to claim 1, comprising: a clutch with a brake coupled to the output shaft of the drive motor; and the spline shaft coupled to the clutch with brake. 3. The automatic screw tightening device according to claim 1 or 2, wherein the displacement detector comprises a plurality of proximity switches arranged in the axial direction. 4. The automatic screw tightening device according to claim 1 or 2, wherein the displacement detector is a stepless displacement detector. 5. A displacement setter is provided for setting a displacement of the torque spring corresponding to a desired torque of the ball screw shaft, and the drive motor is controlled by a detected value of the displacement detector and a set value of the displacement setter. Features: Control method for automatic screw tightening device. 6. A first displacement setting device is provided for setting the displacement of the torque spring corresponding to the torque generated when the screw starts biting,
a second displacement that lowers the rotational speed of the drive motor based on the detected value of the displacement detector and the set value of the first displacement setter, and sets the displacement of the torque spring corresponding to the torque generated during screwing; A setting device is provided, and the rotation speed is increased to a predetermined value based on the detected value of the displacement detector and the setting value of the second displacement setting device, and the displacement of the torque spring corresponding to the torque generated when tightening the screw is set. 6. The method for controlling an automatic screw tightening device according to claim 5, wherein a third displacement setting device is provided, and the speed is controlled to be reduced based on the detection value of the displacement detector and the setting value of the third displacement setting device. 7. A rotation speed detector for detecting the rotation speed of the ball screw shaft and a rotation speed setting device capable of setting a predetermined rotation speed are provided, and when the rotation speed is set by the rotation speed setting device, the third displacement setting is performed. If the displacement is equal to or less than the set value of the device, it is determined to be normal and the control of the drive motor described in paragraph 6 is continued, and when the set rotation speed is reached, the set value of the third displacement setter is reached. 7. The method of controlling an automatic screw tightening device according to claim 6, wherein if this occurs, it is determined that the screws are engaged in an abnormal state, and the drive motor is stopped.