JPS62246482A - High-precision axial tension control method in screwing - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for controlling the axial force of a screw with high precision, in addition to screw tightening.

[Conventional technology]

As a conventional tightening method for a screw tightening device, there is
As described in Japanese Patent No. 51084, a torque method in which tightening is terminated when a certain torque value is reached is widely used. However, this torque method is greatly affected by the frictional resistance of the screw seating surface and threaded surface, and that frictional resistance is not constant.

It was difficult to control the fastening force of the screw, that is, the axial force, with high precision. Further, as described in Japanese Patent Application Laid-Open No. 58-40274, the rotation method in which the axial force of the screw is managed by turning the screw by a certain rotation angle is based on the starting point of one rotation.

In other words, it was difficult to find the point where the threaded surface came into close contact with the object to be fastened. Furthermore, as an application of the above two methods, as described in Japanese Patent Application Laid-Open No. 58-56776,
Torque that controls the fastening force by tightening with a constant torque (this is called snap torque) until the threaded surface comes into close contact with the object being fastened, and then turning it by a predetermined rotation angle.
Rotation angle method, also.

JP-A No. 58-56773, JP-A No. 58-5677
There are methods of managing axial force based on the ratio of one rotation angle to torque, as described in Publication No. 4, but none of these methods.

This method takes advantage of the fact that within the elastic range of the screw, the relationship between the rotation angle of the screw and the axial force is linear and constant.

[Problem that the invention seeks to solve]

The conventional techniques, the torque method, the one-rotation angle method, and the torque-rotation angle method, all have advantages and disadvantages, and it is difficult to perform highly accurate axial force management.Especially, as with the torque-rotation angle method, For screws that utilize the fact that the axial force is linear with respect to the rotation angle within the elastic range, the starting point of tightening is determined based on the torque value, and the fluctuation of the torque value and torque - rotation angle Since this method does not take into account errors caused by changes in the characteristics of the system, there are problems with the accuracy and stability of determining the starting point.

The object of the present invention is to determine a stable tightening starting point for each screw in the torque-rotation angle method, and to achieve the target tightening by turning the screw by a certain rotation angle based on this point. The object of the present invention is to provide a high-precision axial force management method that can control applied force, that is, axial force, with high precision.

Means for Solving Problem c] The above object is achieved by calculating and estimating the torque-rotation angle characteristics during screw tightening to determine the tightening starting point.

For this reason, the present invention provides a sensor that can sense the rotation angle of the screw and the screw tightening torque at that rotation angle when tightening the screw, and a computer that can process the data from the sensor at high speed. Furthermore, in a device consisting of a screw tightening mechanism that can be turned by an arbitrary rotation angle, the rotation angle-torque characteristic was investigated based on the rolling angle and torque data from the sensor, and the linear region in this characteristic was calculated. The rotation angle of this linear region,
Torque data is approximated to the least squares and expressed as a linear equation. Using this linear equation, the point where the torque becomes O is estimated as the tightening starting point, and the screw is tightened by a predetermined tightening angle from this point. It is.

FIG. 1 is a flowchart showing the control processing procedure according to the method of the present invention.

[Effect]

The rotation angle of the screw is converted into an electrical signal by, for example, a rotary encoder, and then transferred to a computer. Further, the tightening torque of the screw is converted into an electric signal by a torque converter or the like, and then transferred to a computer.

Then, we sample the rotation angle and torque data above a certain torque value, or the rotation angle and torque when the rate of change of the torque value with respect to the rotation angle becomes almost constant, and make one rotation based on the sampling data. Use a computer to find the optimal straight line equation that represents the relationship between angle and torque using the method of least squares. Using this formula, find the rotation angle when the torque becomes O, and use this as the tightening starting point. By tightening the screw based on this tightening starting point, it is possible to determine whether the screw has reached a predetermined axial force by looking at the rotation angle of the screw.

According to the method of the present invention, even when the rotation angle-torque characteristics change, the tightening starting point (that is, the point where the screw is in close contact with the object to be fastened) can be accurately found, and the torque The influence of errors, etc. can be minimized by calculating a linear equation using the least squares method based on a large amount of data, making it possible to stably find the tightening starting point and improve this tightening process. By tightening the screw at a predetermined rotation angle based on the starting point, it is possible to tighten the screw while accurately controlling the axial force.

Here, one aspect of the present invention will be explained in detail. Figure 2 is.

It is a characteristic diagram of rotation angle-torque and rotation angle-axial force. In FIG. 2, the horizontal axis indicates the rotation angle, that is, the tightening angle θ, the upward axis of the vertical axis indicates the tightening torque T, and the downward axis of the vertical axis indicates the axial force At of the screw. As shown in this figure, the axial force At of the screw has a linear relationship with its tightening angle (rotation angle O) within the elastic range.

This is clear from the fact that the axial force is proportional to the elongation of the screw, and the elongation is proportional to the tightening angle. Furthermore, if the elastic modulus of the screws is equal, the change in axial force with respect to the change in tightening angle, that is, the slope of the axial force graph will be constant. Therefore, if the screws are of the same type with the same elastic modulus, the axial force will be O
The starting point θ of tightening is θ. If it is possible to accurately find the axial force, it is possible to accurately manage the axial force using the rotation angle.1 The present invention stably and accurately finds the starting point of tightening where the axial force becomes O, and This method provides a method for managing axial force with high precision by tightening at a certain angle based on .

Now, if we look at the characteristic of one rotation angle vs. torque in Fig. 2, we can see that even before the bearing surface of the screw comes into close contact with the object to be fastened, the torque value does not become O due to friction on the screw surface, etc. However, Assuming an ideal case where there is no friction on the screw surface, the torque will be O until the screw seating surface comes into close contact with the object to be fastened. Torque should be generated for the first time at the point where Therefore, by using the characteristic of this graph that the rotation angle-torque characteristic after the axial force is generated is almost a straight line, as shown in Fig. 3, the linear part of the graph of the rotation angle-torque characteristic is converted into torque, Based on the rotation angle data, linear approximation is performed using the least squares method. Then, in this linear equation, the point where the torque becomes O coincides with the point where the axial force becomes O, and this may be the starting point for tightening.

Here, we will briefly discuss how to obtain this linear equation. In Fig. 3, the data of the linear part of the rotation angle-torque characteristic is (θi, Ti), and the equation of the straight line to be found is T=ko+t, ......(1
), so the sum of squares of the distances to this set of data (θi, 'ri) is.

In the least squares method, k and t are determined so as to minimize q. The necessary conditions for q to be minimum are and. Rearranging the above equation, we should obtain t, where, n is the rotation angle and torque data (on θ, Ti
) is calculated using equations (6) and (7), which represents the number of pairs of t
, and equation (1), the rotation angle θ at which the torque T becomes O.

is lI θ. 8-1...This θ becomes song (9). By using this as the starting point for tightening and tightening the screw at a predetermined rotation angle based on this point, it becomes possible to tighten the screw with any axial force.

Next, a method for collecting data on the linear portion of the one rotation angle-torque characteristic will be described.

The first method, as shown in Figure 4, uses a torque T that is slightly larger than the minute torque generated by friction on the thread surface.
s is determined in advance, and data (+)i, Ti) that is larger than this Tss, that is, Ti>Ts, is taken as data in the linear region. The second method is the fifth
As shown in the figure, the rate of change of torque with respect to the rotation angle becomes larger than a predetermined constant value m,
That is, Δi≧m (
11), and the difference between the rate of change and the previous rate of change is smaller than a small constant value E, that is, 1Δi−Δ1−11≦ε (1
2) This is a method in which the data (θi, Ti) is set as data in a linear region. In addition to these two methods.

There is a method of giving an approximate rotation angle and collecting data from points larger than that angle. No matter which method is used, the present invention can be realized as long as a linear region can be determined and its data can be collected.

〔Example〕

Next, some embodiments of the present invention using the above principle will be described.

FIG. 6 is a block diagram showing a screw tightening device used in an embodiment of the present invention. In FIG. conclude. The rotation angle of the screw is converted into an electrical signal by the rotary encoder 2, and transmitted to the control unit @U through the counter 9. Further, the torque applied to the screw is converted into an electric signal by a torque converter 3, which passes through an amplifier 1o and is A/D converted by an A/D converter 11 to a control device.

The control device used here has the simplest configuration and is transferred to the central processing bag @4. Memory 5, I
It consists of 10 devices 6. - Based on the rotation angle data and torque data obtained from the rotary encoder 2 and torque converter 3 mentioned above, the control device sequentially executes predetermined calculations according to the flowchart shown in FIG. A signal as a speed command value or a position command value to 1 is D/A converted by a D/A converter 12 and then sent to a servo amplifier 7 to control the rotation of the servo motor 1.

Further, the servo motor 1 receives current feedback from a tacho generator 13 that is directly connected to the servo motor 1.
Stable rotation control is possible. Further, predetermined calculation procedures and processing methods are stored in the memory 5 mentioned above.

Next, the operation of this embodiment will be explained with reference to the flowchart shown in FIG. First, initial values are set in the memory 5.

The initial values include the tightening angle (change in angle) Δθe necessary to obtain the appropriate axial force, various coefficients ε1m necessary to obtain the linear part of the rotation angle-torque characteristic, and various other constants. Set 29 etc. in advance (Step 10)
1) Next, select a data extraction method for the linear part of the rotation angle-torque characteristic described above, and then issue command data to rotate the servo motor 1 at a low speed, and the servo motor 1 starts rotating. (Step 101).

At this time, it is natural to select a data extraction method for the linear part of the rotation angle-torque characteristic that can collect rotation angle data and torque data from the rotary encoder 2 and torque converter 3 in real time. Collect data for the linear part according to the method described in step 11.
1 to 113 or step 114, and data collection is started by either one. After this,
Collect some predetermined data numbers from the linear part as rotation angle and torque monitors (steps 120 and 121)
, Using these data, calculate the constant of equation (1) directly using equations (6) and (7) using the least squares method, and obtain (
1) Calculate the equation (step 122). Next, from equation (1) of this straight line, find the angle θ at the starting point of tightening, which is the angle at which the torque becomes 0. is calculated using equation (9) (step 123). Based on the angle 0° of the starting point of tightening determined in this way, has the difference from the current rotation angle 0, (θ - θ.), reached the tightening angle Δθe necessary to generate the predetermined axial force? When ΔθC is reached, the servo motor 1 is stopped to complete screw fastening with the desired axial force (Step 125).

The above describes the simplest control procedure centered on the main steps, and various measures have also been taken to counter noise caused by torque, and the effects of inertia when the motor is running and stopped. .

For example, in step 114 of FIG. 6, as a countermeasure against the noise riding on the torque T, as shown in FIG. If it is assumed that this condition is met, it is possible to prevent the influence of noise. This method can be performed in exactly the same way for steps 112 and 113. In addition, as a countermeasure against driving the motor, as shown in the flowchart in Fig. 8, the servo motor 1 is rotated at high speed until the 1 rotation angle-torque characteristic becomes linear, and after the linear condition is established, the servo motor 1 is rotated at low speed. By doing so, it is possible to shorten the fastening time, collect data in a low-speed rotation state, and perform highly accurate data processing.

Furthermore, the rotation angle θ at the end of fastening is the angle 0. When θX=ΔOe can be calculated, θX=ΔOe10.

It is possible to obtain it as Therefore, it is possible to accurately stop the servo motor 1 at the rotation angle θX by decelerating the rotation speed of the servo motor 1 according to an appropriate deceleration pattern as shown in FIG. 10 until reaching one rotation angle Ox. Become. The flowchart of the above processing procedure is shown in
As shown in the figure.

The embodiments described above use a screw tightening device having a drive system such as a servo motor.

Next, a description will be given of an embodiment in which the present invention is realized by tightening screws by one person's hands. FIG. 11 is a perspective view showing the overall appearance of an apparatus used to manually implement the present invention. This takes the form of a torque wrench, and the block diagram of its internal configuration is shown in FIG. 12.The block diagram of this embodiment is as follows from the block diagram shown in FIG. D/A conversion @12. Remove the tachogenerator 13 and replace it with a lever 32. Indicator 30 for displaying the tightening condition. Keyboard 3 for initial value setting
1 is attached. Therefore, the processing procedure is almost the same as the above-mentioned embodiment, and the command to the servo motor given in the above-mentioned embodiment is notified to the operator by the display 30, alarm sound, or voice. It can be achieved in exactly the same way. However, in order to obtain the rotation angle here, it is necessary to fix a part of the device. In the example shown in FIG. 11, the external ring part of the rotary encoder 2 is fixed by hand, or in the example shown in FIG. Fixing lever 3
The details of each part and operation of this embodiment are almost the same as those of the above-mentioned embodiment, so they will not be described here. The explanation will be omitted.

Further, as another embodiment, the control device i35 can be compactly integrated, and the rotary encoder 2. The external appearance of the device integrated with the torque converter 3 etc. is shown in Fig. 14.
Since each component and operation are almost the same as in the previous embodiment, description thereof will be omitted.

〔Effect of the invention〕

According to the present invention, based on data of rotation angle and torque in a linear region of rotation angle-torque characteristics of a screw tightening device, this linear relationship is expressed by a linear equation using the least squares method, and in this linear equation, the torque The rotation angle at the point where is 0 is 1 rotation angle -
Since it can be calculated stably regardless of changes that occur in the torque characteristics, the axial force of the screw can be managed with high precision by using this point as the tightening starting point and controlling the tightening rotation angle of the screw. can.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a control processing procedure according to the method of the present invention, FIGS. 2 to 5 are diagrams for explaining the present invention in detail, and FIG. 6 is a configuration of an apparatus used in an embodiment of the present invention. 7 to 9 are partial views of an improved flowchart of FIG. 1, FIG. 10 is a deceleration pattern diagram of the servo motor, and FIG. 11 is a perspective view of a device used in another embodiment of the present invention. 12 are block diagrams showing the configuration of the device, and FIGS. 13 and 14 are perspective views showing modifications of the device. Explanation of symbols 1...Servo motor 2...Rotary encoder 3...Torque converter 4...Central processing unit 5
...Memory 6...I10 device 7...
・Servo amplifier 8...Bit 9...Counter lO...Amplifier 11...A/D converter
12...D/A converter 13...Tachogenerator U...Control device 30...Display device 3
1...Keyboard 32...Lever 33
...Fixed A-River...Control display

Claims (1)

[Claims] 1. A measuring device that measures the torque and rotation angle applied to a screw, a control device that can process data on the measured torque and rotation angle, and a screw tightening device according to instructions from the control device. In a method of controlling axial force with high precision in screw tightening using a screw tightening machine consisting of a mechanism for tightening,
Identify the region in the rotation angle-torque characteristics of the screw where the relationship between the two is linear, sample the torque and rotation angle data within the linear region, and use this data to determine whether the seat surface of the screw is attached to the fastened object. A high-precision shaft for screw tightening that is characterized by the ability to control the axial force of a screw with high precision by estimating a close tightening starting point and tightening the screw at a constant angle based on the tightening starting point. Power management method. 2. In the high-precision axial force management method for screw tightening described in claim 1, the tightening starting point is estimated using torque and rotation angle data in a linear region of the rotation angle-torque characteristic of the screw. A high-precision axis for screw tightening, which is characterized by linearly approximating the relationship between rotation angle and torque using the least squares method, and calculating the rotation angle when the torque becomes 0 using this linear equation. Power management method. 3. In the high precision axial force management method for screw tightening according to claim 1 or 2, the rotation angle of the screw -
The linear region of torque characteristics is identified by finding that the rate of change of torque with respect to the rotation angle is greater than a predetermined value, and the difference between the rate of change and the previous rate of change is less than a small constant value. A high-precision axial force management method for screw tightening, which is characterized by the following: 4. In the high precision axial force management method for screw tightening according to claim 1 or 2, the rotation angle of the screw -
A high-precision axial force management method in screw tightening, characterized in that the linear region of torque characteristics is identified by setting a minute torque value in advance, and defining the region equal to or greater than the torque value as the linear region.