JP2000141240A - Screw fastening axial tension measuring method, screw fastening method using this measuring method and their devices - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely measure a value corresponding to fastening axial tension in case of fastening a screw to a plastic region and to properly control screw fastening force in accordance with this measured value. SOLUTION: These are a screw fastening axial tension measuring method constituted to measure screw fastening axial tension corresponding to a measured value of a fastening angle from relation of the previously found fastening angle and the fastening axial tension by finding a measuring standard angle of the fastening axial tension except for screw plastic deforming quantity in accordance with a torque rate after finding the torque rate consisting of a ratio of variation of fastening torque in an elastic region of this screw and variation of the fastening angle in a fastening process of the screw using a screw fastening means consisting of a nut runner 6 and measuring the screw fastening angle at a measuring point of time of the fastening axial tension with this measuring standard angle as a basic point, a screw fastening method using this measuring method and their devices.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a screw tightening axial force, a screw tightening method using the measuring method, and an apparatus therefor.

[0002]

2. Description of the Related Art The most important factor for judging whether a screw is properly tightened is a tightening axial force acting by tightening a screw. This tightening axial force is directly measured. Is difficult to do. For this reason, conventionally, a torque control method that controls the tightening state of the screw while monitoring the torque of the drive motor that acts when the screw is tightened with a torque transducer or the like, or a detection signal of an encoder that detects the tightening angle is used. When the screw is confirmed to have further rotated from a constant torque to a predetermined angle, the tightening of the screw is terminated by controlling the tightening state of the screw by a constant torque / rotation angle control method that terminates the tightening of the screw. It has been practiced to set an axial force within an elastic range.

[0003] Since the torque control system is configured to control the tightening state of the screw irrespective of the friction coefficient between the seat surface of the screw and the surface to be tightened, the torque control method varies according to the friction coefficient. The control of the tightening axial force cannot be executed. The constant torque / rotation angle control method is also affected by the coefficient of friction between the seat surface of the screw and the surface to be tightened until the torque becomes constant. Will fluctuate.

In tightening a screw, a torsional stress acts on the screw due to friction between the seat surface of the screw and the surface to be tightened together with the tightening stress. Therefore, when the torsional stress is high, that is, when the friction coefficient is high, the screw yields with a low fastening axial force. In order to control the torque so that the screw does not yield, the torque is controlled in consideration of the case where the above-mentioned friction coefficient is low. There is a problem that force cannot be applied. On the other hand, in the constant torque / angle control method, the tightening axial force after the tightening greatly varies depending on the set value of the constant torque, and there has been a problem that it is difficult to tighten the screw to the limit of the capability of the screw.

For this reason, for example, Japanese Patent Publication No. 261962
As shown in No. 8, in the first stroke, a torque rate corresponding to the friction coefficient between the seat surface of the screw and the surface to be tightened is determined during the tightening of the screw, and in the second stroke, The theoretical seating point is calculated from the torque rate, and in the third stroke, the theoretical increase from the theoretical seating point to the elastic limit point is performed based on the screw size and the tightening coefficient determined by the spring constant of the tightened body. By calculating the squeezing angle and controlling the screw tightening angle based on the theoretical increasing angle in the fourth stroke, the screw capacity is sufficiently utilized to obtain a high tightening axial force. Is known.

[0006]

As shown in the above-mentioned publication, a torque rate corresponding to the above-mentioned friction coefficient is obtained during the tightening of the screw, and a theoretical seating point is calculated from the torque rate to calculate the torque rate. If the configuration is such that the theoretical expansion angle from the theoretical seating point to the elastic limit point is set, within the elastic range of the screw, it is not affected by the coefficient of friction between the screw seat surface and the tightened surface. Since the fastening axial force can be set, the fastening axial force acting on the screw can be appropriately controlled.

[0007] However, in order to obtain a high tightening axial force by making full use of the capability of the screw, a configuration is adopted in which the tightening axial force is set in a plastic range exceeding the elastic limit of the screw. In this plastic region, it is known that the relationship between the screw tightening angle and the tightening axial force greatly changes according to the friction coefficient, so that a preset tightening axial force is obtained. There is a problem that it cannot be controlled.

[0008] That is, the axial yield force Fy of the screw is JIS
It is expressed by the following equation (Equation 1) defined in B1083. From this equation (Equation 1), as shown in FIG. 7, when the screw is tightened beyond the elastic limit of the screw to the plastic region, the screw tightening angles are equal. Also in this case, it can be seen that the smaller the friction coefficient μ, the larger the fastening axial force F acting on the screw. In the following equation (Equation 1), σy is the yield axial force of the screw, As
Is the effective area of the screw, p is the pitch of the screw, ds is the effective diameter of the screw, and U is the full angle of the thread.

[0009]

(Equation 1)

In view of such circumstances, the present invention can accurately measure a value corresponding to a screw axial force even when a screw is tightened to a plastic region,
An object of the present invention is to provide a screw tightening axial force measuring method, a screw tightening method using the measuring method, and a device for properly controlling the screw tightening force based on the measured value.

[0011]

The invention according to claim 1 is
In the process of tightening the screw using the screw tightening means, a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in an elastic range of the screw is obtained, and then, based on the torque rate, Calculate the reference angle for tightening axial force excluding the amount of plastic deformation of the screw, and measure the tightening angle of the screw at the time of measuring the tightening axial force as a base point for this measuring reference angle. The fastening axial force of the screw corresponding to the measured value is measured from the relationship between the previously determined fastening angle and the fastening axial force.

[0012] According to this configuration, the elastic deformation of the screw at the time of measuring the tightening axial force is based on the measurement reference angle of the tightening axial force excluding the plastic deformation of the screw obtained according to the torque rate. The tightening angle corresponding to the amount is determined, and the tightening axial force corresponding to this tightening angle is measured, so that even when the screw is tightened to the plastic range, the tightening axial force of the screw can be accurately determined. Will be required.

According to a second aspect of the present invention, in the method of the first aspect, the tightening torque corresponding to at least two tightening angles in the elastic range of the screw to be tightened is reduced from the torque rate. Is obtained.

According to this configuration, within the elastic range of the screw in which the tightening angle of the screw and the tightening torque are proportional,
Since the torque rate, which is the ratio of the change in the tightening torque to the change in the tightening angle, can be easily and appropriately determined, the plastic deformation of the screw corresponding to the elastic deformation of the screw is excluded based on this torque rate. The measurement reference angle of the tightened axial force is accurately obtained.

According to a third aspect of the present invention, there is provided the method for measuring a fastening axial force according to the first or second aspect, wherein the measurement is performed through a measuring point of a coordinate system having a fastening angle and a fastening torque of the screw as a coordinate axis. An intersection of a line extending parallel to the torque gradient in the elastic range of the screw and a line where the tightening torque of the coordinate system is 0 is determined, and the tightening angle at this intersection is set as a reference angle for measuring the tightening axial force. It is configured as follows.

According to this configuration, the measurement reference angle excluding the plastic deformation of the screw can be easily and appropriately obtained from the coordinate system using the screw tightening angle and the tightening torque as coordinate axes. The tightening angle corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening axial force can be accurately obtained based on.

According to a fourth aspect of the present invention, there is provided a method for measuring a tightening axial force according to any one of the first to third aspects, wherein
Obtain the intersection of the extension line of the torque gradient in the elastic range of the screw displayed in the coordinate system with the tightening angle and the tightening torque of the screw as the coordinate axes and the line where the tightening torque of the coordinate system becomes 0, After setting the coordinates of the intersection as the theoretical seating point, measure the tightening angle at the time of measuring the tightening axial force based on the theoretical seating point, obtain the measurement reference angle, and measure the tightening angle. By subtracting the measurement reference angle from, the tightening angle of the screw at the time of measuring the tightening axial force based on the measurement reference angle is obtained.

According to this configuration, the amount of plastic deformation of the screw at the time of measuring the tightening axial force is removed from the coordinate system using the tightening angle and the tightening torque of the screw as coordinate axes, with the theoretical seating point as a base point. The tightening angle is easily and appropriately determined, and the tightening axial force corresponding to the amount of elastic deformation of the screw is accurately determined based on the tightening angle.

According to a fifth aspect of the present invention, in the process of tightening a screw using the screw tightening means, the torque is defined by a ratio of a change amount of a tightening torque to a change amount of a tightening angle in an elastic range of the screw. After obtaining the rate, the reference angle for measuring the tightening axial force excluding the amount of plastic deformation of the screw is determined based on the torque rate, and the screw tightening at the time of measuring the tightening axial force is determined based on the measurement reference angle. The fastening angle is measured, and based on the measured value of the fastening angle, the screw fastening state is controlled so that a preset fastening axial force is obtained.

According to this configuration, the measuring reference angle of the tightening axial force excluding the amount of plastic deformation of the screw is obtained based on the torque rate, and the tightening shaft is determined using the measuring reference angle as a base point. The tightening angle corresponding to the amount of elastic deformation of the screw at the time of the force measurement is easily and appropriately determined, and the tightening state of the screw is controlled based on the measured value of the tightening angle, so that the screw reaches the plastic range. Even when the screw is tightened, the tightening axial force of the screw is adjusted so as to be a preset appropriate value.

According to a sixth aspect of the present invention, after the tightening of the screw using the screw tightening means is completed, the ratio of the change amount of the tightening torque to the change amount of the tightening angle in the elastic range of the screw is determined. A torque reference rate is obtained, and a reference angle for measuring the tightening axial force excluding the amount of plastic deformation of the screw is determined based on the torque rate, and the screw is tightened at the time of measuring the tightening axial force based on the measurement reference angle. After measuring the tightening angle and measuring the tightening axial force of the screw corresponding to the measured value of the tightening angle from the relationship between the previously determined tightening angle and the tightening axial force, measuring the tightening axial force This is to determine whether the screw is properly tightened based on the value.

According to this configuration, at the end of the tightening of the screw, the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw is determined based on the measurement reference angle obtained according to the torque rate. At the same time, the tightening angle corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening axial force can be easily and appropriately determined based on the measurement reference angle, and the tightening shaft corresponding to the measured value of the tightening angle can be obtained. By obtaining the force, even when the screw is tightened to the plastic region, the tightening axial force of the screw can be accurately determined, and based on the measured value of the tightening axial force, the tightening state of the screw is appropriate. It will be accurately determined whether or not there is.

According to a seventh aspect of the present invention, in the process of tightening a screw using the screw tightening means, the torque is defined by a ratio of a change amount of a tightening torque to a change amount of a tightening angle in an elastic range of the screw. A torque rate calculation unit for obtaining a rate, a reference angle calculation unit for obtaining a measurement reference angle of a tightening axial force excluding a plastic deformation amount of the screw based on the calculation value of the torque rate, and a reference angle calculation unit for obtaining a reference angle calculation unit. A tightening angle measuring unit for measuring the tightening angle of the screw at the time of measuring the tightening axial force based on the measured reference angle, and a tightening axial force corresponding to the measured value of the tightening angle are determined in advance. And a tightening axial force measuring unit which is obtained from a relationship between the mounting angle and the tightening axial force.

According to this configuration, the reference angle calculation unit obtains the measurement reference angle of the tightening axial force excluding the plastic deformation of the screw based on the torque rate obtained by the torque rate calculation unit. The tightening angle corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening axial force based on the measurement reference angle is accurately and easily determined by the tightening angle measuring unit, so that the screw is tightened to the plastic region. Even in this case, the tightening axial force corresponding to the tightening angle obtained by the tightening angle measuring unit can be accurately obtained by the tightening axial force measuring unit.

According to an eighth aspect of the present invention, in the screw tightening axial force measuring device according to the seventh aspect, the tightening torque corresponding to at least two tightening angles within the elastic range of the screw to be tightened is reduced to the torque. It is configured so that the torque rate is obtained by a rate calculation unit.

According to this structure, the torque defined by the ratio of the change amount of the tightening torque to the change amount of the tightening angle within the elastic range of the screw in which the tightening angle of the screw is proportional to the tightening torque. The rate is properly obtained in the torque rate calculation unit.

According to a ninth aspect of the present invention, in the screw tightening axial force measuring device according to the seventh or eighth aspect, the measuring point of the coordinate system using the screw tightening angle and the tightening torque as a coordinate axis. A reference angle calculation unit obtains a tightening angle at an intersection of a line passing through the screw and extending in parallel with the torque gradient in the elastic region and a line at which the tightening torque of the coordinate system is zero.
The tightening angle at the intersection is set as a measurement reference angle of the tightening axial force.

According to this configuration, the measurement reference angle of the tightening axial force excluding the plastic deformation of the screw can be easily and appropriately obtained from the coordinate system using the tightening angle and the tightening torque of the screw as coordinate axes. The tightening angle corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening angle with the measurement reference angle as a base point can be accurately obtained.

The invention according to claim 10 is the invention according to claims 7 to
The screw tightening axial force measuring device according to claim 9, wherein an extension line of a torque gradient in an elastic region of the screw, which is displayed in a coordinate system having the screw tightening angle and the tightening torque as coordinate axes, An intersection with the line where the tightening torque of the coordinate system becomes 0 is determined, the coordinates of this intersection are set as a theoretical seating point, and the tightening angle at the time of measuring the tightening axial force is determined based on the theoretical seating point. The measurement reference angle is measured by the attachment angle measurement unit, the measurement reference angle is obtained by the reference angle calculation unit, and the measurement reference angle of the fastening axial force is subtracted from the measurement value of the fastening angle to obtain the measurement reference angle as a base point. The configuration is such that the tightening angle at the time of measuring the tightening axial force is obtained.

According to this configuration, the tightening axial force excluding the amount of plastic deformation of the screw is measured from a coordinate system using the tightening angle and the tightening torque of the screw as coordinate axes with the theoretical seating point as a base point. The tightening angle at the time is easily and properly measured by the tightening angle measuring unit, and based on the measured value of the tightening angle, the tightening axial force corresponding to the amount of elastic deformation of the screw is determined by the tightening axial force measuring unit. Therefore, even when the screw is tightened to the plastic region, the tightening axial force of the screw can be accurately obtained.

According to an eleventh aspect of the present invention, in the process of tightening a screw using the screw tightening means, a torque which is a ratio of a change amount of a tightening torque to a change amount of a tightening angle in an elastic range of the screw is used. A torque rate calculation unit for obtaining a rate, a reference angle calculation unit for obtaining a measurement reference angle of a tightening axial force excluding an amount of plastic deformation of a screw based on the calculation value of the torque rate, and a reference angle calculation unit for obtaining a reference angle calculation unit. A tightening angle measuring unit that measures the screw tightening angle at the time of measuring the tightening axial force based on the measured order angle as a base point, and obtains a preset tightening axial force based on the measured value of the tightening angle. And a tightening state control unit for controlling the tightening state of the screw so that the screw can be tightened.

According to this configuration, based on the torque rate obtained by the torque rate calculator, a reference angle for measuring the tightening axial force excluding the amount of plastic deformation of the screw is obtained by the reference angle calculator. The tightening angle corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening axial force is easily and properly measured by the tightening angle measuring unit with the measurement reference angle obtained by the reference angle calculating unit as a base point, By controlling the tightening state of the screw based on the measured value of the tightening angle by the tightening state control unit, even when the screw is tightened to the plastic region, the tightening axial force of the screw is set in advance. It will be adjusted to be a proper value.

According to a twelfth aspect of the present invention, in the process of tightening a screw using the screw tightening means, the torque is determined by the ratio of the change amount of the tightening torque to the change amount of the tightening angle in the elastic range of the screw. A torque rate calculator for calculating the rate, a reference angle calculator for calculating a measurement reference angle of the tightening axial force excluding a plastic deformation of the screw based on the calculated value of the torque rate, and a reference angle calculator for calculating the reference angle. The tightening angle measuring unit that measures the tightening angle of the screw when measuring the tightening axial force with the measurement reference angle as the base point, and the tightening axial force of the screw corresponding to the measured value of the tightening angle is obtained in advance. A tightening axial force measuring unit that measures from the relationship between the tightening angle and the tightening axial force, and the screw tightening state is appropriate based on the screw tightening axial force measured by the tightening axial force measuring unit. With a tightening state determining unit for determining whether or not A.

According to this configuration, based on the torque rate obtained by the torque rate calculator, a reference angle for measuring the tightening axial force excluding the amount of plastic deformation of the screw is obtained by the reference angle calculator. After the tightening angle of the screw corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening axial force is measured by the tightening angle measuring means based on the calculated value of the measurement reference angle, Measurements and
Even if the screw is tightened up to the plastic region, whether the screw is properly tightened is determined by comparing the preset target value of the tightening axial force with the tightening state determination unit. It will be determined accurately.

According to a thirteenth aspect, in the twelfth aspect,
The screw tightening device according to the above, further comprising a display unit for displaying a result of the determination of the screw tightening state by the tightening state determining unit.

According to the above configuration, it is possible to easily and appropriately determine whether or not the screw tightening state is appropriate according to the result of the determination of the screw tightening state displayed on the display means.

[0037]

FIG. 1 shows an embodiment of a screw tightening device according to the present invention. The tightening device for this screw includes:
A socket 1 engaged with a head of a screw;
A torque transducer 2 for adjusting a torque applied to a screw by a screw, and a tightening torque detector 3 for detecting a tightening torque of the screw tightened by the socket 1
A screw tightening means comprising a nut runner 6 having a drive motor 4 for rotating and driving the socket 1 and an angle encoder 5 for measuring a screw tightening angle by detecting a rotation angle of the drive motor 4. Is provided.

Further, the screw tightening device includes a first tightening torque setting device 7 for setting a first tightening torque in the elastic range of the screw, and a first tightening torque larger than the first tightening torque in the elastic range of the screw. A second tightening torque setting device 8 for setting a second tightening torque of the value, a screw tightening torque detected by the tightening torque detector 3 and a first tightening torque setting device 7. A first comparator 9 for comparing the first tightening torque with the second tightening torque and outputting a coincidence signal of the two torques; a screw tightening torque detected by the tightening torque detector 3 and the second tightening torque setting device 8; A second comparator 10 that compares the second tightening torque set by the second comparator 10 and outputs a coincidence signal of the two torques, and a CPU 11 that outputs a control signal corresponding to the coincidence signal output from the first and second comparators 9 and 10 to the CPU 11. Output to The first, the second analog switch 1
2 and 13.

Further, the screw tightening device includes a target tightening angle setting section 14 for setting a target tightening angle corresponding to a target value of a tightening axial force generated by tightening the screw.
An angle gate 15 for inputting a control signal for measuring a detection angle of the angle encoder 5 at the time when the control signal is output from the first and second analog switches 12 and 13 to the CPU 11, and a control output from the CPU 11 Servo amplifier 1 that controls the drive motor 4 according to a signal
6 and display means 17 for displaying the tightening axial force of the screw in accordance with a control signal output from the CPU 11.

Further, in the CPU 11, in the process of tightening the screw by the nut runner 6, a torque rate for obtaining a torque rate based on a ratio of a change amount of the tightening torque to a change amount of the tightening angle in the elastic range of the screw is provided. A calculating unit 18, a reference angle calculating unit 19 for obtaining a measuring reference angle of the tightening axial force excluding the plastic deformation of the screw based on the torque rate obtained by the torque rate calculating unit 18, and a reference angle calculating unit A tightening angle measuring unit 20 for measuring the tightening angle of the screw at the time of measuring the tightening axial force based on the measurement reference angle obtained in step 19, and a tightening angle measured by the tightening angle measuring unit 20. A tightening axial force measuring unit 2 for measuring a corresponding tightening axial force from a relationship between a previously determined tightening angle and a tightening axial force.
1 and a tightening state control unit 22 that controls the tightening state of the screw based on the tightening angle measured by the tightening angle measuring unit 20.

FIGS. 2 and 3 show a method for measuring a screw tightening axial force which is performed when the screw is tightened by the screw tightening device and a screw tightening method using this measuring method.
This will be described with reference to the flowchart shown in FIG. First, in step S1, in response to the operation of an input switch (not shown), the drive motor 4 of the nut runner 6 is rotated to start screw tightening. Then, in step S2, an input is made by an input means such as a keyboard (not shown). The first tightening torque T1 corresponding to the size of the set screw is set by the first setting device 7. Next, in step S3, the first tightening torque T1 is compared with the screw tightening torque T detected by the tightening torque detecting means 3 and the first tightening torque T1 to determine whether the two torques T and T1 are equal. Determine whether or not.

If YES is determined in the step S3, the angle gate 15 is turned ON in a step S4, a measured value of the screw tightening angle θ1 at this time is input, and in a step S5, the measured value of the screw The second tightening torque T2 corresponding to the size etc.
Set by the setting device 8. Next, in step S6, the tightening torque T of the screw detected by the tightening torque detecting means 3 and the second tightening torque T2 are compared with the second tightening torque T2.
A comparison is made by the comparator 10 to determine whether the two torques T and T2 are equal.

If YES is determined in step S6, the angle gate 15 is turned off in step S7.
In this state, the measured value of the screw tightening angle θ2 at this time is input, and in step S8, the first and second tightening torques T1 and T2 and the screw tightening angles θ1 and θ2 are detected. Based on the value, the torque rate C, which is the ratio of the change amount ΔT (= T2−T1) of the tightening torque T in the elastic range of the screw to the change amount Δθ (= θ2−θ1) of the tightening angle θ, is calculated as described above. The torque rate is calculated by the torque rate calculator 18. Then, in step S9, the reference angle calculation unit 19 calculates the theoretical seating point θO of the screw based on the torque rate C.

That is, at the beginning of the tightening of the screw, after a certain slip corresponding to the coefficient of friction between the seat surface of the screw and the surface to be tightened occurs, within the elastic range, as shown in FIG. Since the tightening torque T increases in proportion to the screw tightening angle θ, the change amount ΔT of the tightening torque T (= T2−T1) and the change amount Δθ of the tightening angle θ (= θ2−θ1) And the torque rate C (= ΔT / Δθ) is calculated. The torque gradient α in the elastic range of the screw, which is displayed in the coordinate system shown in FIG. 4 using the screw tightening angle θ and the tightening torque T as coordinate axes, that is, the torque rate C is calculated in the elastic range. Straight line α indicating the changed state of the tightening torque T
By obtaining the intersection between the extension line of the above and the line where the tightening torque T of the coordinate system becomes 0, that is, the horizontal axis of the coordinate system, and setting the coordinates of this intersection as the theoretical seating point θO, A theoretical seating point assuming that there is no slippage between the surface and the surface to be fastened is determined.

Next, in step S10, the detected value TB of the tightening torque T at the time when the tightening axial force is measured.
And the detected value θB of the tightening angle θ, and in step S11, the screw passes through the measuring point B of the coordinate system shown in FIG. 4 using the screw tightening angle θ and the tightening torque T as coordinate axes. The intersection between the line β extending parallel to the torque gradient α in the elastic range of the above and the line (horizontal axis) where the tightening torque T of the coordinate system becomes 0 is calculated by the reference angle calculator 19, and this intersection is obtained. Is set as the measurement reference angle θA of the tightening axial force.

In step S12, the tightening angle measuring unit 20 calculates and calculates a change amount ΔθA (= θB−θA) of the tightening angle θ from the measurement reference angle θA to the current tightening angle θB. After setting the change amount ΔθA as the tightening angle ΔθA at the time of measuring the tightening axial force, in step S13, the tightening axial force FA of the screw corresponding to the tightening angle ΔθA is set to a predetermined tightening angle. The tightening axial force F is measured by the tightening axial force measuring unit 21 from the relationship between θ and the tightening axial force F, and the tightening axial force FA is displayed on the display unit 17.

That is, assuming that screw tightening is started from the theoretical seating point θO of the screw, within the elastic range of the screw, as shown in FIG. 5, tightening is performed in proportion to the screw tightening angle θ. When the axial force F changes, the screw tightening axial force F
Exceeds the elastic range FC, plastic deformation occurs in the screw, so the proportional relationship between the screw tightening angle θ and the tightening axial force F is broken, and the tightening axial force F increases with the increase in the tightening angle θ. Large quantities tend to drop gradually. And, the elastic region FC
After the screw is tightened until the tightening axial force FA slightly exceeds the above, when the tensile load is removed from the plastic region of the screw, the screw is tightened along a line β1 parallel to the screw displacement line α1 in the elastic region. The axial force F decreases,
Plastic deformation corresponding to the change amount ΔθO of the tightening angle θ from the theoretical seating point θO to the tightening angle θA at the intersection of the line β1 and the horizontal axis of the coordinate system shown in FIG. 5 occurs.

When the screw is tightened until the tightening axial force FA slightly exceeds the elastic range FC as described above, the measurement of the tightening axial force F excluding the amount of plastic deformation ΔθO of the screw is performed. The tightening axial force F changes in proportion to the screw tightening angle based on the reference angle θA. Then, within the elastic range of the screw, there is a relationship represented by the following equation (Equation 2). From this equation (Equation 2), a fastening axial force F corresponding to the fastening angle θ is obtained from the equation or obtained in advance. The above-mentioned fastening axial force F can be estimated from experimental data. In the following equation (2), p is the pitch of the screw, Kb is the tension spring constant of the screw, and Kc is the compression spring constant of the tightened member.

[0049]

(Equation 2)

Therefore, in the coordinate system shown in FIG.
An intersection point of a line β extending parallel to the torque gradient α in the elastic range of the screw through the measurement point B and a line where the tightening torque T of the coordinate system becomes 0 is determined, and a tightening angle θ of the intersection point is obtained.
Is set as a measurement reference angle θA of the tightening axial force F, a change amount ΔθA of the tightening angle θ from the measurement reference angle θA to the current tightening angle θB is obtained, and this change amount ΔθA is calculated by the measurement reference angle. By setting the tightening angle ΔθA at the time of measurement based on θA, this tightening angle Δθ
The current fastening axial force F can be obtained based on A and the above equation (Equation 2). That is, the theoretical seating point θO
By subtracting the plastic deformation amount ΔθO of the tightening angle θ obtained from the theoretical seating point θO from the change amount ΔθB of the tightening angle θ at the current time measured based on
A change amount ΔθA of the tightening angle θ from the axial force reference angle θA to the current tightening angle θB is obtained, and the tightening axial force FA can be indirectly measured based on the change amount ΔθA.

Next, in step S14, the target tightening angle θa initially required for the tightening component is set by the target tightening angle setting unit 14 based on the screw size and the like input by the input means. In step S15, by comparing the target tightening angle θa with the tightening angle ΔθA based on the measurement reference angle θA obtained in step S12, the tightening axial force F of the screw becomes the target value. The tightening state control unit 22 determines whether or not it has occurred.
If the determination in step S15 is NO, the process returns to step S10 to continue the screw tightening operation.

Then, YES is determined in the step S15, and the tightening angle ΔθA based on the measurement reference angle θA corresponding to the tightening axial force F at the present time becomes equal to the target tightening angle θa, When it is confirmed that the screw tightening axial force F has reached the target value, step S16
In the above, a control signal for stopping the drive motor 4 of the nut runner 6 constituting the screw tightening means is output from the tightening state control unit 22 to the servo amplifier 16 to terminate the screw tightening operation.

In the process of tightening the screw using the screw tightening means including the nut runner 6, the ratio between the change ΔT of the tightening torque T and the change Δθ of the tightening angle θ in the elastic range of the screw is obtained. After obtaining the torque rate C, the measurement reference angle θA of the tightening axial force F obtained by subtracting the plastic deformation amount ΔθO of the screw from the torque rate C is obtained, and the tightening shaft is set based on the measurement reference angle θA. The screw tightening angle ΔθA at the time of measuring the force F is measured, and the tightening angle Δθ
Since the tightening axial force F of the screw corresponding to A is measured by the tightening axial force measuring unit 21 from the relationship between the previously determined tightening angle θ and the tightening axial force F, the elastic limit of the screw is limited. Even when the screw is tightened beyond the plastic region, the tightening axial force F of the screw can be accurately measured, and the tightening state of the screw can be properly determined based on the measured value of the tightening axial force F. Can be controlled.

That is, for a screw of the same size, as shown in FIG. 6, a screw H having a high coefficient of friction between a screw bearing surface and a surface to be tightened and a screw L having a low coefficient of friction are elastically connected. When the screw H is tightened to the plastic region beyond the limit, the screw H having a high friction coefficient requires a larger tightening torque T to tighten the screw than the screw L having a low friction coefficient,
Since the elastic limit tends to be exceeded early, the amount of plastic deformation ΔθO generated after the tightening by the angle control from θO
Also tend to be large. When the screw is tightened until the tightening axial force F slightly exceeds the elastic range as described above, the measurement reference angle θA of the tightening axial force F excluding the plastic deformation amount ΔθO of the screw is obtained. Screw tightening angle θ as the base point
Since it is known that the tightening axial force F changes in proportion to the above, the measurement reference angle θA of the tightening axial force F excluding the plastic deformation amount ΔθO is obtained, and the measurement reference angle θA is used as a base point. Screw tightening angle ΔθA at the time of measurement of tightening axial force F
By measuring the tightening angle ΔθA of this screw,
From the relationship between the previously determined tightening angle θ and the tightening axial force F, the tightening axial force F can be properly obtained in the screw tightening process.

Therefore, based on the change amount ΔθA of the tightening angle θ which is a value obtained by subtracting the plastic deformation amount ΔθO from the change amount ΔθB of the tightening angle from the theoretical seating point θO to the time point when the tightening axial force F is measured. The tightening axial force F measured by the tightening axial force measuring unit 21 is displayed on the display means 17, and by controlling the tightening state of the screw while watching the display, the screw having a high friction coefficient is displayed. In H, the screw tightening amount can be adjusted so that the performance of the screw is maximized. Further, by controlling the screw tightening state of the screw L having a small friction coefficient so that the target tightening axial force is set to the same value as the screw H having the high friction coefficient, the screw H and the screw H are controlled. By setting the same tightening axial force, the ability of the screw can be fully exhibited.

After the screw tightening operation is completed, it is determined whether or not the screw is properly tightened according to the tightening axial force F displayed on the display means 17, and the tightening shaft is determined. If the force F is smaller than the target value, the screw is further tightened to retighten. On the other hand, if the tightening axial force F is larger than the target value, it is determined that the screw tightening amount is excessive. It is possible to reliably prevent the occurrence of a screw tightening failure, such as replacing the screw with a new one upon judgment.

Further, in the above embodiment, at least two fastening angles θ in the elastic range of the screw to be fastened.
1 and θ2, the torque rate C is determined from the tightening torques T1 and T2.
And the tightening torque T, within the elastic range of the screw, which is proportional to the tightening torque, the change amount ΔT of the tightening torque and the change amount Δ
and the torque rate C, which is a ratio to the angle θ, can be easily and appropriately obtained. Based on the torque rate C, the measurement reference angle θB of the tightening axial force F excluding the plastic deformation amount ΔθO of the screw is accurately obtained. be able to.

Further, in the above-described embodiment, the measuring point B in the coordinate system using the screw tightening angle θ and the tightening torque T as coordinate axes.
Of the line β extending parallel to the torque gradient α in the elastic region of the screw through the line and the line where the tightening torque of the coordinate system becomes 0, and the tightening angle θ at this intersection is determined by the tightening axial force F. Since the measurement reference angle θA is set as the measurement reference angle θA, the measurement reference angle θA excluding the amount of plastic deformation θA of the screw can be easily and appropriately obtained from the coordinate system. The tightening angle ΔθA of the screw at the time of measuring the applied axial force F can be accurately obtained.

Further, as shown in the above embodiment, an extension line of the torque gradient α in the elastic range of the screw displayed on the coordinate system using the screw tightening angle θ and the tightening torque T as coordinate axes; Is determined as the theoretical seating point θO, and then the tightening angle θB at the time of measurement of the tightening axial force F is determined based on the theoretical seating point θO. And measuring the measurement reference angle θA based on the theoretical seating point θO, and subtracting the measurement reference angle θA from the measured value of the tightening angle θB, thereby removing the plastic deformation amount ΔθO of the screw. When the configuration is such that the tightening angle ΔθA is obtained, the tightening angle θ measured with the same seating point θO as a base point.
Based on the above, the screw tightening angle ΔθA excluding the plastic deformation amount ΔθO of the screw can be easily and appropriately measured.

In the above embodiment, the torque rate C
The measurement reference angle θA of the tightening axial force F excluding the plastic deformation amount ΔθO of the screw is obtained by the reference angle calculation unit 19 based on the calculation value of the above, and the measurement reference angle θA obtained by the reference angle calculation unit 19 is obtained. As the base point, the tightening angle ΔθA of the screw at the time of measuring the tightening axial force F is determined by the tightening angle measuring unit 2.
0, and based on the measured value of the tightening angle ΔθA, the tightening state of the screw is controlled by the tightening state control unit 22 so that a preset tightening axial force F is obtained. The control unit 22 is configured to compare the measured value of the tightening angle ΔθA with a preset target tightening angle θa and terminate the screw tightening operation when the two agree with each other. The tightening operation can be automated and the amount of screw tightening can be properly controlled.

Instead of the above-described embodiment, a tightening state for judging whether or not the screw is properly tightened based on the tightening axial force F of the screw measured by the tightening axial force measuring unit 21. A determination unit is provided. The tightening state determination unit compares the measured value of the tightening axial force F with a preset target value of the tightening axial force F. The structure may be provided with a tightening state control unit for ending the tightening operation. With such a configuration, the tightening state of the screw can be controlled more accurately based on the tightening axial force F of the screw.

A display means for displaying the result of the determination of the tightening state of the screw by the tightening state determining section 22 is provided. According to the determination result of the tightening state displayed on the display means, the tightening state of the screw is determined. May be configured so that an operator determines whether or not is appropriate.

Further, based on the measured value of the tightening angle ΔθA based on the measurement reference angle θA as described above, the tightening state of the screw is controlled so that a preset tightening axial force F is obtained. In the screw tightening device provided with the attaching state control unit 22, a friction coefficient measuring unit for measuring a friction coefficient at the time of tightening of the screw is provided, and based on the measured value of the friction coefficient, the screw corresponds to a yield axial force of the screw. The target tightening angle of the screw may be set by the target tightening angle setting unit 14.

That is, as shown in FIG. 6, the relationship between the tightening angle θ of the screw and the tightening torque T changes according to the coefficient of friction, and the friction at the time of tightening the screw is determined based on this relationship. The coefficient may be measured by a friction coefficient measuring unit. Then, as shown in the above equation (Equation 1), since the yield axial force Fy of the screw changes based on the friction coefficient μ, the capacity of the screw is maximized according to the yield axial force Fy of the screw. By setting the target tightening angle in such a manner, the screw tightening control corresponding to the friction coefficient μ can be properly executed.

A tightening state determining unit for determining whether the tightening state of the screw is appropriate based on the tightening axial force F of the screw measured by the tightening axial force measuring unit 21 as described above. A friction coefficient measuring unit for measuring a coefficient of friction at the time of screw tightening, and a target tightening shaft of the screw corresponding to a yield axial force of the screw based on the measured value of the coefficient of friction. The structure may be provided with a target tightening axial force setting unit for setting the force. Also in this case, the fastening axial force F, which serves as a criterion for judging whether or not the screw is properly tightened, is based on the yield axial force Fy of the screw that changes according to the friction coefficient μ.
By properly setting the target value of friction coefficient μ
Can be properly performed.

[0066]

As described above, according to the method and the apparatus for measuring the screw axial force of a screw according to the present invention, in the process of tightening the screw using the screw tightening means, the screw is tightened in the elastic range. After obtaining a torque rate consisting of a ratio of a change amount of the torque to a change amount of the tightening angle, a measuring reference angle of the tightening axial force excluding a plastic deformation amount of the screw is obtained based on the torque rate, and Measure the tightening angle of the screw at the time of measuring the tightening axial force based on the measurement reference angle, and determine the tightening axial force of the screw corresponding to the measured value of the tightening angle with the previously determined tightening angle and tightening angle. Since the measurement is performed based on the relationship with the axial force, even when the screw is tightened to the plastic region beyond the elastic limit of the screw, the tightening axial force of the screw can be accurately measured.

Further, in the screw tightening method and the screw tightening device according to the present invention, during the screw tightening process using the screw tightening means, the change amount of the tightening torque and the tightening angle in the elastic range of the screw are improved. After obtaining the torque rate based on the ratio to the change amount, determine the measuring reference angle of the tightening axial force excluding the amount of plastic deformation of the screw based on the torque rate, and use the measuring reference angle as the base point to determine the tightening shaft. Because the screw tightening angle at the time of force measurement is measured, and based on the measured value of the tightening angle, the screw tightening state is controlled so as to obtain a preset tightening axial force. Even when the screw is tightened to the plastic region beyond the elastic limit of the screw, the screw tightening state can be easily and accurately controlled so that the screw axial force of the screw becomes an appropriate value.

Further, according to the screw tightening method and the screw tightening apparatus according to the present invention, after the screw tightening using the screw tightening means is completed, the amount of change in the tightening torque in the elastic range of the screw and the tightening torque are determined. After obtaining the torque rate based on the ratio of the change in the angle, the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw is calculated based on the torque rate, and the tightening is performed based on the measurement reference angle. The tightening angle of the screw at the time of measuring the axial force is measured, and the axial force of the screw corresponding to the measured value of the tightening angle is determined from the relationship between the previously obtained tightening angle and the axial force. However, since it is configured to determine whether the screw is properly tightened based on the tightening axial force, even if the screw is tightened to the plastic range beyond the elastic limit of the screw, Easy and accurate whether the tightening axial force is appropriate There is an advantage that can be determined.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a screw tightening device according to the present invention.

FIG. 2 is a flowchart showing a first half of a screw tightening control operation.

FIG. 3 is a flowchart showing a latter half of a screw tightening control operation.

FIG. 4 is a graph showing a correspondence between a screw tightening angle and a tightening torque.

FIG. 5 is a graph showing a correspondence relationship between a screw tightening angle and a tightening axial force.

FIG. 6 is a graph showing a correspondence between a tightening angle of a screw and a tightening torque when screws having different friction coefficients are tightened.

FIG. 7 is a graph showing a correspondence relationship between a screw tightening angle and a tightening axial force when screws having different friction coefficients are tightened.

[Explanation of symbols]

 6 Nut runner (screw tightening means) 14 Target tightening angle setting unit 18 Torque rate calculating unit 19 Reference angle calculating unit 20 Tightening angle measuring unit 21 Tightening axial force measuring unit 22 Tightening state control unit

Claims (13)

[Claims] In the process of tightening a screw using a screw tightening means, a torque rate comprising a ratio between a change amount of a tightening torque and a change amount of a tightening angle in an elastic range of the screw is obtained. Based on the torque rate, determine the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw, and measure the tightening angle of the screw at the time of measuring the tightening axial force based on the measurement reference angle, A method for measuring a tightening axial force of a screw, comprising measuring a tightening axial force of the screw corresponding to the measured value of the tightening angle from a relationship between a previously determined tightening angle and the tightening axial force. 2. The method according to claim 1, wherein the torque rate is calculated from a tightening torque corresponding to at least two tightening angles within an elastic range of the screw to be tightened. A method for measuring a tightening axial force of a screw, characterized in that: 3. A torque gradient in an elastic region of a screw through a measuring point of a coordinate system having a tightening angle and a tightening torque of a screw as coordinate axes, according to the method of measuring a tightening axial force according to claim 1. An intersection of a line extending in parallel with the line and a line at which the tightening torque of the coordinate system becomes 0 is obtained, and the tightening angle at this intersection is set as a measurement reference angle of the tightening axial force. A method for measuring the tightening axial force of a screw. 4. The tightening axial force measuring method according to claim 1, wherein the tightening angle and the tightening torque of the screw are displayed in a coordinate system using a coordinate system as a coordinate axis. The intersection of the extension line of the torque gradient and the line where the tightening torque of the coordinate system becomes 0 is determined, the coordinates of this intersection are set as the theoretical seating point, and the tightening axial force is set based on the theoretical seating point. By measuring the tightening angle at the time of the measurement, obtaining the measurement reference angle, and subtracting the measurement reference angle from the measurement value of the tightening angle, the measurement of the tightening axial force based on the measurement reference angle is performed. A method for measuring a tightening axial force of a screw, characterized in that a tightening angle of the screw at a point in time is obtained. 5. In a process of tightening a screw using a screw tightening means, after obtaining a torque rate comprising a ratio of a change amount of a tightening torque and a change amount of a tightening angle in an elastic range of the screw, Based on the torque rate, determine the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw, and measure the tightening angle of the screw at the time of measuring the tightening axial force based on the measurement reference angle, Screw tightening using a screw tightening axial force measuring method, wherein the screw tightening state is controlled so that a preset tightening axial force is obtained based on the measured value of the tightening angle. Method. 6. After completion of the tightening of the screw using the screw tightening means, a torque rate comprising a ratio of a change amount of the tightening torque to a change amount of the tightening angle in an elastic range of the screw is obtained. Based on the torque rate, determine the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw, and measure the tightening angle of the screw at the time of measuring the tightening axial force based on the measurement reference angle, After measuring the tightening axial force of the screw corresponding to the measured value of the tightening angle from the relationship between the previously determined tightening angle and the tightening axial force, the screw is tightened based on the measured value of the tightening axial force. A screw tightening method using a screw tightening axial force measuring method, wherein it is determined whether or not a tightening state is proper. 7. A torque rate calculation for obtaining a torque rate based on a ratio of a change amount of a tightening torque and a change amount of a tightening angle in an elastic range of the screw in a screw tightening process using the screw tightening means. Part, a reference angle calculator for obtaining a measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw based on the calculated value of the torque rate, and a measurement reference angle obtained by the reference angle calculator as a base point. A tightening angle measuring unit that measures a screw tightening angle when measuring a tightening axial force, and a tightening axial force corresponding to a measured value of the tightening angle, a tightening angle determined in advance and a tightening shaft. A tightening axial force measuring device for a screw, comprising: a tightening axial force measuring unit which is determined from a relationship with a force. 8. The screw axial force measuring device according to claim 7, wherein the torque rate calculating unit calculates a torque rate from a tightening torque corresponding to at least two tightening angles in an elastic range of the screw to be tightened. A screw tightening axial force measuring device characterized in that it is configured to obtain the screw tightening axial force. 9. The screw tightening axial force measuring device according to claim 7, wherein the screw tightening angle and the tightening torque pass through a measuring point of a coordinate system having a coordinate axis as a coordinate axis and are measured in an elastic region of the screw. A tightening angle at an intersection of a line extending in parallel with the torque gradient and a line at which the tightening torque of the coordinate system is 0 is obtained by a reference angle calculation unit, and the tightening angle at the intersection is used as a standard for measuring the tightening axial force. A screw tightening axial force measuring device, characterized in that the angle is set as an angle. 10. The screw tightening axial force measuring apparatus according to claim 7, wherein the elasticity of the screw is displayed in a coordinate system using the tightening angle and the tightening torque of the screw as coordinate axes. The intersection of the extension line of the torque gradient in the area and the line where the tightening torque of the coordinate system becomes 0 is set, the coordinates of this intersection are set as the theoretical seating point, and the tightening axial force is set based on the theoretical seating point. The tightening angle at the time of the measurement is measured by the tightening angle measuring unit, the measuring reference angle is obtained by the reference angle calculating unit, and the measuring reference angle of the tightening axial force is subtracted from the measured value of the tightening angle. Wherein the tightening angle at the time of measuring the tightening axial force based on the measurement reference angle is obtained. 11. A torque rate calculation for obtaining a torque rate based on a ratio of a change amount of a tightening torque to a change amount of a tightening angle in an elastic range of the screw in a screw tightening process using the screw tightening means. Part, a reference angle calculation unit for obtaining a measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw based on the calculation value of the torque rate, and a measurement reference angle calculated by the reference angle calculation unit as a base point. A tightening angle measuring unit for measuring the tightening angle of the screw at the time of measuring the tightening axial force, and tightening the screw such that a preset tightening axial force is obtained based on the measured value of the tightening angle. A screw tightening device, comprising: a tightening state control unit that controls a tightening state. 12. A torque rate calculation for obtaining a torque rate based on a ratio of a change amount of a tightening torque and a change amount of a tightening angle in an elastic range of the screw in a screw tightening process using the screw tightening means. Part, a reference angle calculation unit for obtaining a measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw based on the calculation value of the torque rate, and a measurement reference angle calculated by the reference angle calculation unit as a base point. A tightening angle measuring unit that measures the tightening angle of the screw when measuring the tightening axial force, and the tightening axial force of the screw corresponding to the measured value of the tightening angle is determined by the previously determined tightening angle and tightening angle. A tightening axial force measuring unit that measures from the relationship with the attached axial force, and whether the screw is properly tightened based on the tightening axial force of the screw measured by the tightening axial force measuring unit. And a tightening state determining unit for determining the tightening state. apparatus. 13. The screw tightening device according to claim 12, further comprising display means for displaying a result of the determination of the screw tightening state by the tightening state determining unit. .