TW200925599A - Fatigue testing device - Google Patents

Abstract

Provided is a fatigue testing device which can acquire such an amplitude of the angle of an axis of rotation of a servomotor automatically and quickly as to be set when a test is done with the fluctuation widths of a force to be applied to a work being adjusted constant. The fatigue testing device comprises deformation detecting means for measuring the deformation of the work, force measuring means for measuring the magnitude of the force to be applied to the work, spring constant calculating means for calculating the spring constant of the work, while increasing the amplitude of the angle of the rotation axis of the servomotor gradually, on the basis of the measurement results of the deformation detecting means and the force measuring means, and control means for controlling the servomotor on the basis of the spring constant calculated by the spring constant calculating means, so that the amplitude of the magnitude of the force to be applied to the work may be a predetermined magnitude.

Description

200925599 VI. Description of the Invention: [Technical Field] The present invention relates to a fatigue testing device for applying a reverse load in a torsion, tension, compression, and bending direction to a workpiece. [Prior Art] A fatigue tester that measures the fatigue strength of a material by applying a load to a material is used by a motor that is described in Japanese Laid-Open Patent Publication No. S63-37233. The feeding motor moves the phase of the rotating shaft of the servo motor to its angle by inputting the target angle (target angle) into the servo amplifier. The servo motor is provided with a rotary encoder for detecting a phase change of the rotary shaft, and the servo amplifier sets the drive power applied to the servo motor based on the difference between the phase of the rotary shaft determined from the detected value of the rotary encoder and the target angle. The torque test device for performing the torque test is provided to the workpiece by amplifying the torque of the servo motor by a speed reducer (reduction gear or the like) provided between the chuck at one end of the gripping workpiece and the rotary shaft of the servo motor. Further, the universal testing device for performing the stretching, compression, and bending tests is to provide a linear motion converter such as a feed screw mechanism on the rotary shaft of the servo motor, and convert the rotary motion of the servo motor into a linear motion. SUMMARY OF THE INVENTION In such a fatigue test apparatus, a variable load (torque or load), a displacement, a speed, or an acceleration fluctuation range (upper limit and/or a lower limit) is kept constant, and a reverse load is applied to a workpiece. However, since the servo motor controls the angle of the rotation axis, when the test is performed while the fluctuation range of the applied force is kept constant, the operator performs the repeated test at 200925599: 2, and the operator applies the palladium with the manual operation. Battle on the artifact, estimated for action). If you want to do this kind of trial with a manual operation, you need the servo motor rotation axis. c In addition, if the force is excessively applied to the workpiece, it may be damaged for a long time. The present invention has been made in order to solve the above problems. The purpose of the present invention is to provide a fatigue-reducing device, that is, the present invention will: maintain the variation of the force applied to the workpiece - at speed = when it is required Angle vibration of the rotating shaft of the motor = binding test In order to achieve the above purpose, the force measuring means, the system is two ====: which makes the angle of the rotating shaft of the servo motor vibrate; According to the uniform motor money to turn to the New York tester, the force applied to the workpiece and the rotation of the servo motor are often used; and the control method is based on a proportional constant calculated by the proportional* number of nose means to control the servo motor. The amplitude of the force applied to the workpiece is a specified size. With this configuration, the proportionality constant can be automatically and quickly determined, and the servo motor can be driven with an appropriate angular amplitude in accordance with the proportional constant. In addition, since the angular amplitude of the rotating shaft of the servo motor is gradually increased, excessive force is not inadvertently applied to the workpiece, and the workpiece is broken. Further, the 'proportional constant calculation means should be based on the angle of the rotating shaft of the servo motor. The proportional constant is calculated by changing the rotation angle of the rotating shaft of the servo motor and the measurement result of the force measuring means when the fluctuation is stopped. That is, because the angular velocity of the rotating shaft of the servo motor is fast, that is, the deformation of the workpiece 4 200925599, the speed is easy. Since the measurement error occurs, the proportional constant can be calculated by calculating the proportionality constant when the deformation speed of the workpiece is low, that is, the magnitude of the force applied to the workpiece and the rotation angle of the rotation axis of the servo motor in a state where the workpiece is substantially stationary. The angular amplitude of the servo motor is determined. In addition, the force measuring means should be configured to measure the magnitude of the force applied to the workpiece at least twice, and the proportional constant calculation means should constitute the rotation angle of the rotating shaft of the servo motor during the first measurement. The difference between the rotation angles of the rotary axes of the servo motor during the second measurement, except the first count The value of the difference between the magnitude of the force and the force of the second measurement, as the elastic constant of the workpiece. For example, in the tensile test and the compression test, because the workpiece is mounted on the test device, it will be on the workpiece. Warpage occurs. The rotation angle of the rotating shaft of the servo motor does not necessarily correspond to the amount of deformation in the natural state. According to the present invention, the difference between the amount of deformation and the magnitude of the force when the workpiece is deformed by different forces is used. In addition, the fatigue test device should be configured to be both movable along the first direction and the second direction opposite to the first direction, and a load is applied to the workpiece, and the proportional constant operation means the workpiece is calculated. a first proportional constant when deforming in one direction, and a second proportional constant when the workpiece is deformed in the second direction, and the control means controls the servo motor to divide the first proportional constant by a specified size when the workpiece is deformed in the first direction The obtained deformation amount becomes the upper limit of the deformation amount of the workpiece, and controls the aforementioned servo horse violation. When the workpiece is deformed in the first direction, the second ratio is often In addition to the amount of deformation of the specified size to obtain the deformation amount becomes the upper limit of the workpiece. That is, as in the fatigue test in which a tensile load is applied to the workpiece, when the workpiece is deformed in the stretching direction (first direction), and when the load is released from the state (the workpiece is deformed in the second direction), The salt ratio constant is different. Therefore, as in the constitution of the present invention, the first proportional constant and the second proportional constant should be separately determined. 200925599 In addition, a fatigue testing device is a torque testing device that applies a torsional load on a workpiece, and the force applied to the workpiece is the moment around the rotating shaft of the workpiece. Alternatively, the fatigue testing device is a universal testing device that applies a tensile, compressive or bending load to the workpiece via a feed screw mechanism, and the force applied to the workpiece is fed by a feed screw mechanism applied to the load of the workpiece. Directional component. As described above, according to the present invention, it is possible to automatically and quickly obtain a fatigue test apparatus which can set the angular amplitude of the rotary shaft of the servo motor when the fluctuation range of the force applied to the workpiece is kept constant. [Embodiment] Hereinafter, embodiments of the present invention will be described in detail using the drawings. The first figure shows a block diagram of the fatigue test apparatus of the first embodiment of the present invention. The fatigue testing device of this embodiment is a fatigue testing device that can repeatedly apply a torsional load on a test piece (workpiece). As shown in the first figure, the fatigue testing apparatus of the present embodiment has a device body 10 for applying a torsional load on the workpiece W, a servo amplifier 20 for driving the servo motor 12 of the apparatus body 10, and a servo amplifier 20 for controlling Control unit 30. The apparatus body 10 has chucks 11a, lib, a servo motor 12, a speed reducer 13, a torque sensor 14, and an angle sensor 15. The chucks 11a and 11b hold the workpiece W from both ends. The speed reducer 13 is disposed between the drive shaft of the servo motor 12 and one of the chucks 11a, and increases the torque of the drive shaft of the servo motor 12 to be applied to the workpiece W. Further, the other chuck lib is fixed to the frame of the apparatus body (not shown) via the torque sensor 14. In the configuration described above, when the servo motor 12 is driven, the torque is applied to the workpiece w held by the 200925599 chucks 11a, 11b, and is measured by the torque sensor 14. In addition, the angle of the salty crying speed (four) of the output shaft 'detected at the chuck lla4 = ; at the force reduction angle. The twist of the workpiece W of % is controlled by the servo amplifier 20. Also, the _ amplifier 20 is based on the set angle transmitted from the control unit 30.

The rotation axis angle of the servo motor generates driving power for driving the servo horse, and sends it to the servo motor 12 to drive the servo motor 12 to be provided with a rotating shaft for detecting the servo motor 12. Rotary encoder 12a of number of revolutions and angles. The signal encoder of the rotary encoder i2a is connected to the feeding amplifier 20'. The servo amplifier 20 performs feedback control of the driving power in accordance with the measurement result of the rotary encoder 12a. The configuration of the control unit 30 will be described for a long time. The second drawing is a block diagram of the control unit 30 of the present embodiment. As shown in the second figure, the control unit 30 of the present embodiment includes a controller 31, a signal conversion means 32, an a/d conversion means 33, a torque sensor amplifier 34a, an angle sensor amplifier 34b, an operation means 35, The waveform generating circuit 36, the floppy disk drive (FDD) 37, the memory 38, and the analog 埠39. Further, in the first diagram and the second diagram, the control unit 30 describes one block, but actually it is formed by a plurality of units. For example, the torque sensor amplifier 34a and the angle sensor amplifier 34b are formed as separate units. Further, the operation means 35 is provided on the control panel on the side of the casing of the unit including the controller 31, but may be a separate unit (e.g., a personal computer) connected to the controller 31 via electric power. The control unit 30 of the present embodiment refers to the moment and angle of the workpiece W detected by the torque sensor 14 and the angle sensor 15 (both as shown in the first figure), and displays the hope with time or time of the moment or angle. In the manner of the waveform, the set angle is transmitted to the servo amplifier 20 (first figure). 200925599 The waveform that gives the action w (load and deformation amount) of the workpiece w is set by means 35. The operation means 35 includes a means for inputting a keyboard or the like, and a display means for confirming the input result of the input means. The operator of the fatigue test apparatus of the present embodiment can operate the operation means X to set the reverse torque test. The range of moments, angles or angular velocities. For example, the amplitude of the angular change when the back and forth torque motion is performed in a sinusoidal wave shape can be set. The setting result of the operation means 35 is transmitted to ^ and stored in the memory 38. Two ‘ ❹

Further, the waveform generating circuit 36 is a circuit that generates signal waveforms such as sine waves, triangular waves, and rectangular waves in a desired cycle and timing. More specifically, when f(1) is a function of the time t as a self-variable, the value s expressed by the equation s=f(t) is sequentially output to the controller 31. Further, in the above formula, if the waveform is a sine wave, the period is set to τ, and the phase is set to = then 'f(t) = sin(27t(t - a) / T). At this time, the period τ and the phase a can be set to an arbitrary value by the operation operation means 35. The controller 31 transmits the value from the waveform generation circuit 36 to the controller 31 = value multiplied by the operation means 35 to calculate the target wave = and calculates the set value to be sent from the target waveform to the servo amplifier 20. Then, the calculated set angle set by the operating means 35 is transmitted to the servo amplifier 2 via the signal converting means 32.

According to the above configuration, the servo motor 12 can be driven to vary the workpiece W = torque angle by a predetermined waveform of a sine wave, a triangular wave or a rectangular wave. The fatigue test apparatus 1 of the present embodiment is set to perform the operation of | The amplitude of the torque (set torque amplitude) can automatically set the amplitude of the angular variation of the servo motor 1 on the rotating shaft when the fatigue test of the load over the workpiece w is applied. For the procedure, refer to the third figure for the day; in addition, the second graph is the time axis t, the vertical axis is the servo horse i; 8 200925599 12 is the angle θ of the rotation axis. In order to apply a force to the workpiece w to apply a load to the load w as described above, in the present embodiment, the spring constant of the workpiece ^ is measured before the fatigue test. Next, the specific measurement method will be described. First, the workpiece w is attached to the chucks 11a and ub, and after the servo motor is driven, the rotary shaft of the servo motor 12 is driven with a sufficiently small amplitude at the beginning of the start of driving of the servo motor. Thereafter, the amplitude of the wide angle is gradually increased. At this time, the moment applied to the workpiece w by the torque sensor 14 ❹ 。. Further, the change in the angle of the rotation axis, T-set, is independent of the amplitude. Weeks 12 A, Fb, 匕, ~ and the angle Θα, Θβ, %, θ〇 of the servo motor H疋 shaft at this time. At this time, when the point A $ "Iff starts to test, the angle of the rotation axis 〇 changes in the positive direction of the direction 2", the measurement is performed, and the point β t changes toward the direction opposite to the positive direction (hereinafter, For the change, the measurement is performed. ; Universal direction) The second sub-point * Only in the example of the third example, the control shaft rotation axis (four) movement becomes a sinusoidal wave. Therefore, the elapsed time from the scraping: T/4+ After nT(n: natural number), the angular velocity of the 'rotation axis' on the positive side is 0 = 3Τ/4 + 方向 between the directions, and in the positive square 过 ^ 细 , , , , , , , , , , , , , , , 4 is set to point A, . , , after 11T/4, set to point B, will be set after 15T/4, point will be red, 137/4, then 5 is point C, workpiece 5 people two The measured values of A to D are the proportional constants sP and sN of the ratio of the torque in the positive and negative directions to the rotation of the feeding motor ^ = 200925599 by the formula 1 [S1] sP=^ θ, -θ, c — Fd -Fb

Then, based on the measured SP and SN, the upper limit and the lower limit of the angular variation of the rotational axis of the servo motor 12 for the reverse load are applied to the workpiece W by the set torque amplitude. In other words, the set torque amplitude on the positive side is FSP, the set torque amplitude on the negative side is FSN, and the upper and lower limits of the angular variation of the rotational axis of the servo motor 12 are respectively set. ΘΡ, ΘΝ, and ΘΡ, ΘΝ by the following formula 2. [Expression 2]

a _ ^SN

ΘΝ—T

Then, according to the obtained θρ, ΘΝ, the angle variation of the rotation axis of the servo motor 12 satisfies the formula 3, and by changing the set angle 赋予 given to the servo amplifier 20, the workpiece amplitude can be set according to the desired torque amplitude. Give a repeat load. [Expression 3] 200925599 Apparatus ‘: The first embodiment of the invention is related to the torque test. Even if it is: the non-conformity is determined by the above-mentioned constituents. That is, the fatigue test apparatus 2 of the other type which is still available in the center can be used for the fatigue measurement of the second embodiment of the present invention. The so-called universal test package for compressing or testing the load is shown in the third section of the fatigue test device igi of the present embodiment.

The fatigue test device of the example can repeatedly apply tensile, compressive or bending loads on the test piece (workpiece). As shown in the fourth figure, the test apparatus 101 of the present embodiment has a device body 11A that applies a load on the workpiece W, and is used to drive the apparatus body: a servo amplifier 12A of the feeding motor 112, and The control unit 13 of the servo amplifier 120 is controlled. The apparatus body 〇 has a frame ln, a servo motor 112, a linear motion converter 113, a load sensor U4, a displacement sensor 115, and adapters 118a and 118b. The linear motion converter 113 is for converting the known rotational motion of the rotational axis of the servo motor 112 into a motion in the straight forward direction. Further, it has a feed screw 113a, a nut 113b, a pair of guide rails 113c, and a moving block 113d corresponding to the guide rail 113c. The nut U3b is coupled to the feed screw 113a. Further, the moving block 113d is fixed to the nut 113b. The moving block 113d is movable along the corresponding guide rail 113c and cannot be moved in the other direction. Thus, the movement of the moving block 113d and the nut 113b is limited to one degree of freedom in the direction in which the guide 113c protrudes. Furthermore, since the axial direction of the feed screw 113a is parallel to the direction in which the guide rail 113 () protrudes (i.e., the up and down direction), when the feed screw 113& is rotated by the servo motor 112, the nut 113b is along the guide rail. I13c moves. As shown in the fourth figure, the servo motor 112 is fixed to the platform portion U1 of the frame m, and the 11 200925599 outer 'rail 113c is fixed to the platform portion ma. Move up and down on the platform. The lower adapter 118a for holding the workpiece w is placed over the nut. The upper stage 116 is provided with a top plate 111b of the frame ηι. This is provided on the upper surface of the platform portion ma with the upper and lower side guide bars 117C extending from the figure. A through hole 116a that is perforated in the direction is formed at an end portion of the upper stage 116 in the left-right direction, and the guide rod 117c passes through the through hole 11, for example. Thus, the upper stage 116 can be in the up and down direction along the guide bar 117c

❹ & amp t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t上 An upper adapter U8b for holding the workpiece w from above is mounted under the upper stage 116. In the present embodiment, the nut 113b is moved up and down in a state where the workpiece W is held between the upper adapter U8b and the lower adapter 118a, and a load can be applied to the workpiece w. Further, each of the crotch portion and the lower adapters 118a and 118b is configured to be detachable from the upper stage 116 and the nut 113b, and an appropriate adapter can be selected depending on the type of load applied to the workpiece w. Since the fourth figure is a configuration in which a compressive load is applied to the workpiece w, the lower surface of the upper adapter U8b and the upper surface of the lower adapter are formed in a planar shape. When the tensile load is applied to the workpiece w, the adapters 118a and li8b provided with the chuck for holding the workpiece W are used. When the three-point bending test is performed, the adapter for the combined compression test and the three-point fastener are used. Further, the upper stage 116 is suspended from the top plate U1b of the frame 111 by a feed screw 117a. A nut (not shown) that can be rotated in conjunction with the feed screw 117a is embedded in the top plate 111b. The nut is rotationally driven by a motor 117b disposed on the top plate U1b. Further, by connecting the link of the feed screw 117a and the upper stage 116, the feed screws 117a 12 200925599 rotate the upper stage 116 around its axis. Therefore, when the bolt of the upper stage 116 is loosened and the upper stage 116 is moved, the nut is rotated by the motor 117b, and the feed screw 117a can be driven in the up-and-down direction and coupled to the feed screw 117a. Upper stage 116. This function is used to adjust the spacing of the adapters 118a, 118b in accordance with the size of the workpiece w. That is, when the test is performed, the bolt is tightened, and the upper stage 116 is fixed to the guide rod 117c. In the above-described configuration, when the workpiece W is held by the adapters 118a and 118b and the servo motor 1·12 is driven, a tensile, compressive or bending load is applied to the workpiece w, and the magnitude thereof is measured by the load cell 114. Further, the displacement sensor 115 detects a displacement of the lower adapter, that is, a sensor that detects the amount of deformation of the workpiece W (e.g., a dial gauge inserted into the rotary encoder). The servo motor 112 is controlled by the servo amplifier 120 as in the first embodiment. That is, the servo amplifier 12 generates driving power for driving the servo motor 112 in accordance with the target value transmitted from the control unit 13 (the rotation axis angle of the target servo motor), and sends it to the servo motor 112 to cause it. drive. The servo motor ip is provided with a rotary encoder U2a for detecting the number of revolutions, the angle, and the like of the rotary shaft of the servo motor 112. The signal output of the rotary encoder 112a is connected to the servo amplifier 12A, and the servo amplifier 120 performs feedback control based on the measurement result of the rotary encoder i12a. Next, the configuration of the control unit 130 will be described. The fifth diagram is a block diagram of the control unit 130 of the present embodiment. As shown in the figure, the control unit 130 of the present embodiment can be used in addition to the torque sensor instead of the torque sensor, and the displacement sensor instead of the angle sensor, and the present invention shown in the third figure. The first embodiment is the same. Therefore, in the control unit 130, the same or similar constituent elements as those of the first embodiment of the present invention are denoted by the same reference numeral 13 200925599, and the detailed description of the control unit 13A is omitted. The control unit 130 of the embodiment refers to the load and deformation of the workpiece w detected by the load sensor ι 4 and the displacement sensing "15 (all recorded in the fourth figure), and displays the load or the amount of deformation with time. The desired waveform mode is 'transmitted to the feeding amplifier 12 〇 (first figure). - The waveform imparted to the workpiece w is set by the operating means 35. The operator of the testing apparatus 101 of the present embodiment can Operational means

❹ 35 ’ Set the amplitude of the load, the amount of deformation, etc. during the repeated test. For example, the displacement amplitude when a sinusoidal reverse compression displacement is applied to the workpiece W can be set. The controller 31 multiplies the value set by the operation means 35 by the value transmitted from the waveform generating circuit 36 to the controller 31, calculates the target value, compares the target value with the load detected by the load sensor 114, or compares it. The amount of deformation detected by the bit sensor 115 (or the deformation rate of the time differential value) is calculated and sent to the set angle of the servo amplifier 120. The calculated set angle is transmitted to the servo amplifier 120 via the signal conversion means 32. According to the above configuration, the servo motor 112 can be driven such that the load applied to the workpiece W or the deformation amount of the workpiece W fluctuates according to a predetermined waveform of a sine wave, a triangular wave or a rectangular wave. Further, in the same manner as the first embodiment, the universal testing device 101 of the present embodiment can automatically set the feeding service when the fatigue test of the load is applied to the workpiece w by the amplitude of the load set by the operator (set load amplitude). The angular variation amplitude of the rotation axis of the motor 12. This configuration is substantially the same as the embodiment of the present invention described with reference to the third drawing. Therefore, this embodiment is also described with reference to the third figure. In order to apply the 14200925599 reverse load to the workpiece W with the set torque amplitude as described above, in this embodiment, the spring constant of the workpiece w is measured before the fatigue test. The specific measurement methods are described below. First, the workpiece W is mounted on the test device 101, and the servo motor 12 is driven next. Then, at the beginning of the start of driving of the servo motor 12, the rotation shaft of the servo motor 12 is driven at an amplitude that is sufficiently small to vary. Thereafter, the angular amplitude of the rotating shaft is gradually increased. At this time, the moment applied to the workpiece W is detected by the torque sensor 14. Further, the fluctuation period T of the angle of the rotation axis is constant regardless of the amplitude. Next, the points A, B, C, and D at four points in the third figure measure the loads PA, PB, Pc, PD applied to the workpiece W and the angles 旋转α, Θβ, 〇c of the rotation axis of the servo motor 12 at this time. , 〇d. At this time, the angles of the points A and C are measured from the angle 0 of the rotation axis at the start of the test in one direction (hereinafter, defined as a positive direction), and the angles of the points B and D are opposite to the positive direction. When the direction (hereinafter referred to as the negative direction) changes, the measurement is performed. Further, each of the points A to D is a point at which the fluctuation of the rotation axis of the servo motor 12 is substantially stopped. In the present embodiment, as shown in the third figure, the fluctuation of the rotation axis of the servo motor 12 is controlled to be sinusoidal. Therefore, after the elapsed time T/4 + nT (η : natural number) from the test β, the angular velocity of the rotating shaft is 0 on the positive side. Similarly, after the elapsed time from the start of the test, 3 Τ / 4 + η , , the angular velocity of the rotary shaft is 0 on the positive direction side. In this embodiment, it will be set to point A after 9Τ/4 from the start of the test, to point B after 11T/4, to point C after 13T/4, and to the point after 15T/4. D. Next, using the measured values at points A to D, the elastic constants SP and SN of the workpiece W in the positive and negative directions are calculated by the equation 4. [Expression 4] 15 200925599

Pc-Pa P θ.-θκ

PD - PB N ΘΌ - ΘΒ Next, based on the measured SP and SN, the upper limit and the lower limit of the angular variation of the rotational axis of the servo motor 12 for applying the load to the workpiece W are determined by setting the load amplitude. In other words, the set load amplitude on the positive side is PSP, the set load amplitude on the negative side is PSN, and the upper and lower limits of the angular variation of the rotational axis of the servo motor 12 are respectively set. ΘΡ, ΘΝ, and ΘΡ, ΘΝ by the following formula 5. [Expression 5] Then, according to the obtained θρ, ΘΝ, the angular variation of the rotation axis of the servo motor 12 satisfies the above Expression 3, and the setting angle 赋予 given to the servo amplifier 20 can be changed according to the desired setting. The load amplitude gives a repetitive load on the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS The first figure shows an outline of a fatigue testing apparatus according to a first embodiment of the present invention. The second drawing is a block diagram of the control unit of the fatigue testing apparatus of the first embodiment of the present invention. The third figure shows an angle variation diagram of the rotation axis of the servo motor of the servo motor of the first and second embodiments of the present invention. The fourth figure shows an overview of the fatigue testing apparatus of the second embodiment of the present invention. Fig. 5 is a block diagram of a control portion of the fatigue testing device of the second embodiment of the present invention. [Explanation of main component symbols] 1 Fatigue test device 10 Device body 12 Servo motor 20 Servo amplifier 30 Control unit 31 Controller 33 A/D converter 35 Operating means 37 Disk drive (FDD) W Workpiece 17

Claims (1)

200925599 VII. Patent application scope: 1. A fatigue testing device, which applies a reverse load on a workpiece by a servo motor, and has: a force measuring means for measuring the magnitude of a force applied to the workpiece; The driving angle of the rotating shaft of the servo motor is gradually increased and the driving is reversed. The rotation of the servo motor and the measurement result of the force measuring means are used to calculate the force applied to the workpiece and the rotation of the servo motor. a proportionality constant of a ratio of a rotation angle of a shaft; and a control means for controlling the servo motor based on a proportionality constant calculated by the proportional constant calculation means to specify an amplitude of a force applied to the workpiece The size. 2. The fatigue test apparatus according to claim 1, wherein the proportional constant calculation means is based on a rotation angle of the rotation axis of the servo motor when the angular rotation of the rotation axis of the servo motor is substantially stopped, and the force measurement means The measurement result is used to calculate the proportionality constant. 3. The fatigue testing device according to claim 1, wherein the force measuring means measures the magnitude of the force applied to the workpiece at least twice, and the proportional constant calculating means rotates the servo motor in the first measurement. The ratio of the difference between the rotation angle of the shaft and the rotation angle of the rotation axis of the servo motor in the second measurement is the difference between the magnitude of the force at the time of the first measurement and the magnitude of the force at the second measurement. constant. 4. The fatigue testing device of claim 1, wherein the fatigue testing device is capable of applying a load on the workpiece along both the first direction and a second direction opposite the first direction, 18 200925599 The proportional constant calculation means calculates a first proportional constant of the workpiece when deformed in the first direction, and a second proportional constant when the workpiece is deformed in the second direction, and the control means controls the servo motor to be in the first When the direction is deformed, the deformation amount obtained by dividing the first proportional constant by the specified size becomes the upper limit of the deformation amount of the workpiece, and controls the servo motor, and when the workpiece is deformed in the second direction, the second The amount of deformation obtained by dividing the proportional constant by the specified size becomes the upper limit of the amount of deformation of the workpiece. 5. The fatigue testing device of claim 1, wherein the fatigue testing device is a torsion testing device that applies a torsional load on the workpiece, and the force applied to the workpiece is a moment around a rotating shaft of the workpiece. 6. The fatigue testing device of claim 1, wherein the fatigue testing device applies a universal testing device for tensile, compressive or bending loads on the workpiece via a feed screw mechanism, and applies to the workpiece. The force applied to the load of the workpiece is the feed direction component of the feed screw mechanism. 19