Workpiece mass estimation device

Abstract

The purpose of the present invention is to facilitate confirmation of whether calculations have been processed normally or not. This workpiece mass estimation device is a device for a machine. The machine includes a motor that drives a workpiece loading unit and a sensor that detects the state of the motor. The workpiece mass estimation device is provided with an identification unit, a storage unit, an estimation unit, and a display. The identification unit: identifies the value of a physical parameter of a driven object driven by the output of the motor based on the state of the motor detected by the sensor; and continuously updates the identified value through repeated calculation. The storage unit stores the value of the physical parameter being updated.The estimation unit estimates the mass of a workpiece based on the final value of the physical parameter being updated. The display shows a graph indicating the history of the physical parameter values based on data stored in the storage unit and displays the mass estimated by the estimation unit.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a workpiece mass estimation device that estimates the mass of a workpiece loaded on various machines such as machine tools. TECHNICAL BACKGROUND

[0002] Some machines, such as machine tools, each include a workpiece loading unit, a motor, a sensor, and a motor control unit. Workpieces are loaded onto the workpiece loading unit. The motor drives the workpiece loading unit. The sensor detects the state of the motor. The motor state includes, for example, a current value and a motor speed. The motor control unit performs feedback control of the motor based on the detected state of the motor. List of citationsPatent document

[0003] Patent Document 1: Unexamined Japanese Patent Application, Publication No. 2015-55923 DISCLOSURE OF THE INVENTION Problems to be solved by the invention

[0004] The total mass of the driven object driven by the motor varies depending on the mass of the workpiece loaded on the workpiece loading unit. Therefore, the inertia of the driven object also varies depending on the mass of the workpiece. The acceleration / deceleration of the driven object by the motor is changed by the change in inertia. Excessive acceleration / deceleration imposes excessive load on the machine, etc., leading to machine failure, while insufficient acceleration / deceleration reduces the working efficiency of the machine. Therefore, it is necessary to adjust the acceleration / deceleration of the driven object by the motor to the optimal acceleration / deceleration. Therefore, some machines adjust the acceleration / deceleration of the driven object by the motor to the optimal acceleration / deceleration based on the workpiece mass input by the operator.

[0005] According to such a technique, although the acceleration / deceleration of the driven object can be adjusted, it requires the operator to manually input the mass of the workpiece each time. Therefore, it has been proposed to automatically estimate the mass of the workpiece in the following way. First, a predetermined operation command is sent to the motor control unit of the machine to cause the motor to drive the driven object. The inertia of the driven object at this time is identified based on a current feedback value, a speed feedback value, etc., detected by the sensor. The inertia of the workpiece is calculated by subtracting the inertia caused by factors other than the workpiece from the identified inertia of the driven object, and the mass of the workpiece is estimated.

[0006] However, the present disclosers have focused on the fact that the following problem may arise in such a configuration.

[0007] During the process of estimating the mass of the workpiece, the physical parameter values ​​can be updated sequentially through repetitive operations such as a steepest descent method. The physical parameters include the inertia of the driven object and parameters for calculating the inertia. The estimated mass of the workpiece is calculated based on the final values ​​of the physical parameter values ​​that have been updated. Therefore, the estimated mass of the workpiece depends on the final values.

[0008] If the repetitive operations are processed normally, there will be no particular problem. However, if the repetitive operations are not processed normally, the physical parameter values ​​will not converge within the time limit, and the final values ​​will be incorrect. As a result, a discrepancy will occur between the estimated mass of the workpiece and the actual mass of the workpiece.

[0009] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to make it easy to check whether repetitive operations are processed normally. Means to solve the problems

[0010] A workpiece mass estimation device of the present disclosure is a device for estimating a mass of a workpiece for a machine, including: a workpiece loading unit on which the workpiece is loaded; a motor for driving the workpiece loading unit; a sensor for detecting a state of the motor; and a motor control unit for controlling the motor based on the detected state of the motor. The workpiece mass estimation device includes: an identification unit configured to identify a value of a physical parameter of a driven object driven by an output of the motor based on the detected state of the motor and to update the identified value through a repetitive operation; a storage unit configured to store the value of the physical parameter whenever the value is updated; an estimation unit configured to estimate the mass of the workpiece based on a final value of the physical parameter values ​​that have been updated; and a display configured to display a graph indicating a transition of the value of the physical parameter based on data stored in the storage unit and to display the mass estimated by the estimation unit. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a workpiece mass estimating apparatus and a machine tool according to a first embodiment; Fig. 2 is a flowchart showing a process of mass estimation of a workpiece; Fig. 3 shows a normal pattern displayed on a display; Fig. 4 shows a first abnormal pattern shown on the display; Fig. 5 shows a second abnormal pattern shown on the display; Fig. 6 shows a third anomalous pattern shown on the display; and Fig. 7 shows a fourth anomalous pattern shown on the display. PREFERRED MODE FOR IMPLEMENTING THE INVENTION [First Embodiment]

[0011] As in Fig. 1, a workpiece mass estimation device 100 of the present embodiment is installed on a machine tool 200. The machine tool 200 includes a motor control unit 50, a sensor 60, a motor 70, a transmission mechanism 80, and a workpiece loading unit 90.

[0012] The workpiece loading unit 90 is provided to be movable in a rotational direction or a linear direction. A workpiece W is loaded on the workpiece loading unit 90. The motor 70 includes a rotor 78 and a stator 76 that rotates the rotor 78. Hereinafter, the output from the stator 76 to the rotor 78 is referred to as "motor output Mo." The transmission mechanism 80 transmits the motor output Mo from the rotor 78 to the workpiece loading unit 90. The transmission mechanism 80 may include a reduction gear such as a gear box.

[0013] Hereinafter, the part of the machine tool 200 that transmits the motor output Mo to the workpiece loading unit 90 is referred to as the "transmission system." The transmission system includes a transmission mechanism 80 and its periphery. Hereinafter, the component group driven by the motor output Mo is referred to as the "driven object Dv." The driven object Dv includes the rotor 78, the transmission mechanism 80, the workpiece loading unit 90, and the workpiece W. Hereinafter, the component group excluding the workpiece W from the driven object Dv is referred to as the "general driven object."

[0014] The sensor 60 detects motor information Mi indicating the state of the motor 70. The motor information Mi includes a current value of the motor 70 and a rotational speed of the rotor 78. The motor control unit 50 performs feedback control of the motor 70 based on the motor information Mi detected by the sensor 60.

[0015] Next, the workpiece mass estimation device 100 will be described. The workpiece mass estimation device 100 is a device for estimating the mass of the workpiece W. Hereinafter, the estimation of the mass of the workpiece W is simply referred to as "mass estimation," and the mass estimated by the mass estimation is simply referred to as "estimated mass."

[0016] The workpiece mass estimation device 100 includes an identification unit 10, a storage unit 20, an estimation unit 30, and a display 40. The identification unit 10, the storage unit 20, and the estimation unit 30 are configured, for example, mainly by the same computer. The display 40 mainly includes, for example, the above-described computer and a display. The computer includes, for example, a CPU, a ROM, a RAM, and a memory. Fig. 1, the workpiece mass estimation device 100 and the machine tool 200 are shown separately, but the workpiece mass estimation device 100 may be integrated into the machine tool 200.

[0017] The identification unit 10 identifies the physical parameters of the driven object Dv based on the motor information Mi detected by the sensor 60 and updates the identified values ​​sequentially through repetitive operations such as a steepest descent method. The physical parameters include the inertia of the driven object Dv, a viscous friction coefficient in the transmission system, a Coulomb friction coefficient in the transmission system, and a spring constant in the transmission system. Hereinafter, the viscous friction coefficient in the transmission system is simply referred to as "viscous friction coefficient," the Coulomb friction coefficient in the transmission system is simply referred to as "Coulomb friction," and the spring constant in the transmission system is simply referred to as "spring constant."The inertia of the driven object Dv is calculated taking into account the viscous friction coefficient, the Coulomb friction coefficient and the spring constant.

[0018] The storage unit 20 stores the values ​​of the physical parameters as soon as the values ​​are updated by the identification unit 10.

[0019] If the final value of the physical parameter values ​​updated by the identification unit 10 is within a predetermined range, the estimation unit 30 performs mass estimation based on the final value. Specifically, the estimation unit 30 calculates the inertia of the workpiece W by subtracting the inertia of the general driven object from the final value of the inertia of the driven object Dv identified by the identification unit 10. The inertia of the general driven object is calculated, for example, based on the mass of the general driven object input in advance. The estimation unit 30 performs mass estimation based on the calculated inertia of the workpiece W.On the other hand, if the final value of the physical parameter values ​​updated by the identification unit 10 falls outside the predetermined range, the estimation unit 30 does not perform mass estimation.

[0020] As in Fig. As shown in Figures 3 to 7, the display 40 displays a graph 41 showing the transition of the values ​​of the physical parameters based on the data stored in the storage unit 20. The graph 41 includes an inertia graph 41a showing the transition of inertia, a viscous friction coefficient graph 41b showing the transition of the viscous friction coefficient, a Coulomb friction coefficient graph 42c showing the transition of the Coulomb friction coefficient, and a spring constant graph 42d showing the transition of the spring constant.

[0021] When the mass estimation is performed by the estimation unit 30, the display 40 shows while displaying the diagram 41 as in Fig. 3, the display 40 displays mass information 42 indicating the estimated mass. However, if the mass estimation is not performed, that is, if the final value of the physical parameter falls outside the predetermined range, the display 40 displays an alarm 42A such as "ERR" instead of displaying the mass information 42, as shown in Fig. 4 to 7. That is, the display 40 shows the alarm 42A while the diagram 41 is being displayed.

[0022] As in Fig. 3 to 7, the display 40 displays a switching area 43, an operation pattern selection area 44, a drive amount selection area 45, status information 46, date and time information 47, and temperature information 48 while displaying the graph 41.

[0023] The switching area 43 is a part for performing an operation of switching between the execution and suspension of a mass estimation. The switching area 43 also serves as a reset area for initializing the estimated mass. The switching area 43 is configured to be selectable between "SET" and "RESET" by an operator. When "SET" is selected, execution of a mass estimation is selected. On the other hand, when "RESET" is selected, the execution of a mass estimation is suspended and the estimated mass is initialized. In the case where "SET" is selected, the selection returns as in Fig. 4 to 7 automatically returns to “RESET” when an error occurs such as the final value of the physical parameter falling outside the predetermined range.

[0024] The operation pattern selection section 44 is a part for selecting an operation condition of the driven object Dv in a mass estimation. The drive amount selection section 45 is a part for selecting the drive amount of the driven object Dv in a mass estimation.

[0025] The status information 46 is information indicating whether the mass estimation is completed normally. That is, if the mass estimation is completed normally, as in Fig. 3, a message indicating that the mass estimation is completed is displayed as the status information 46, such as "Adjustment completed." If the mass estimation is not completed normally, as shown in Fig. 4 to 7, a message indicating that the mass estimation is incomplete is displayed as the status information 46, such as “Adjustment failed”.

[0026] The date and time information 47 is information indicating the date and time (year, month, day, time, etc.) at which the mass estimation is completed. The temperature information 48 is information indicating the temperature of a predetermined part of the engine 70 in real time. The predetermined part is a part of the engine 70 where the temperature affects the mass estimation.

[0027] Next, with reference to Fig. 2 describes a flow of mass estimation by the workpiece mass estimation device 100. Note that an "S" shown below is an abbreviation for "step." First, in S1, it is determined whether mass estimation is being performed. If a negative determination N (No) is made, the determination of S1 is repeated. Conversely, if an affirmative determination J (Yes) is made in S1, the processing proceeds to S2.

[0028] In S2, the identification unit 10 acquires the engine information Mi from the engine control unit 50.

[0029] In S3, the identification unit 10 identifies the values ​​of the physical parameters based on the engine information Mi. In S4, the storage unit 20 stores the identified parameter information. In S5, it is determined whether the duration of the estimation processing has reached a time limit. If a negative determination N is made, processing returns to S3. As a result, the repetitive operations by the identification unit 10 continue. Conversely, if a positive determination J is made in S5, processing proceeds to S6.

[0030] In S6, it is determined whether the final value of the identified physical parameter is within a preset predetermined range. If an affirmative determination J is made, processing proceeds to S8. In S8, the estimation unit 30 estimates the mass of the workpiece W based on the final value of the identified physical parameter. In S9, while displaying the diagram 41 based on the data stored in the storage unit 20, the display 40 displays the estimated mass estimated by the estimation unit 30 as the mass information 42.

[0031] If a negative determination N is made in S6, that is, if the identified final value of the physical parameter is not within the preset predetermined range, processing proceeds to S9. In S9, the display 40 displays the alarm 42A while displaying the graph 41 based on the data stored in the storage unit 20.

[0032] Next, with reference to Fig. 3 to 7 describe the display patterns shown on the display 40.

[0033] The Fig. The normal pattern Np shown in Figure 3 represents a case where the repetitive operations are processed normally. In the normal pattern Np, all physical parameters converge. Therefore, in each of the inertia diagram 41a, the viscous friction coefficient diagram 41b, the Coulomb friction coefficient diagram 41c, and the spring constant diagram 41d, a behavior in which the value of the physical parameter converges appears.

[0034] In the Fig. In the first anomalous pattern Ap1 shown in Figure 4, the repetitive operations are not processed normally for all physical parameters. Therefore, a behavior in which the value diverges appears in each of the inertia diagram 411, the viscous friction coefficient diagram 412, the Coulomb friction coefficient diagram 413, and the spring constant diagram 414.

[0035] In the Fig. In the second anomalous pattern Ap2 shown in Fig. 5, a wavy waveform appears in the inertia diagram 411 due to unstable fixation of the workpiece W or unsteady disturbance.

[0036] In the Fig. In the third abnormal pattern Ap3 shown in Fig. 6, a protrusion-like waveform appears in the Coulomb friction coefficient diagram 41c due to wear deterioration of the sliding parts in the transmission system.

[0037] In the Fig. In the fourth anomalous pattern Ap4 shown in Figure 7, the spring constant changes due to a change from elastic deformation to plastic deformation in parts of the transmission system. As a result, an irregularly divergent waveform appears in the spring constant diagram 41d.

[0038] From the above, the operator can determine whether the repetitive operations were processed normally based on the diagram 41. Furthermore, if the repetitive operations were not processed normally, the cause can be determined based on the waveform appearing in the diagram 41. That is, the operator can determine the cause of the mass estimation failure by determining which shape Fig. 4 to 7 resembles the behavior appearing in diagram 41.

[0039] The following summarizes the features and effects of the present embodiment.

[0040] The display 40 displays the chart 41 and the mass information 42. Therefore, the operator can check whether the repetitive operations are being processed normally based on the chart 41 and check the estimated mass based on the mass information 42. Furthermore, if the repetitive operations have not been processed normally, the cause can be determined based on the waveform appearing in the chart 41. This makes it easier for the operator to perform the next appropriate process.

[0041] Specifically, diagram 41 includes the inertia diagram 41a, the viscous friction coefficient diagram 41b, the Coulomb friction coefficient diagram 41c, and the spring constant diagram 41d. If the repetitive operations are not processed normally, the Fig. 4 to 7, the behavior shown in diagrams 41a to 41d. Therefore, the operator can determine the cause of the mass estimation failure by determining which form this behavior approximates.

[0042] The display 40 displays the switching area 43 while displaying the chart 41. Therefore, the operator can switch between the execution and suspension of the mass estimation by means of the switching area 43 while checking the trend of the repetitive operations, etc., based on the chart 41.

[0043] The display 40 displays the date and time information 47 while displaying the chart 41. Therefore, the operator can check the cause of the mass estimation failure based on the chart 41 while checking the date and time at which the mass estimation is completed based on the date and time information 47 when the repetitive operations are not processed normally.

[0044] The display 40 displays the temperature information 48 in real time while displaying the chart 41. Therefore, the operator can check the cause of the mass estimation failure based on the chart 41 while checking the temperature of the motor 70 based on the temperature information 48 when the repetitive operations are not processed normally.

[0045] The display 40 displays the operation pattern selection area 44 while displaying the chart 41. Therefore, by means of the operation pattern selection area 44, the operator can, for example, change the operating condition of the driven object Dv while checking the cause of the mass estimation failure based on the chart 41 when the repetitive operations are not processed normally.

[0046] The display 40 displays the drive amount selection area 45 while displaying the chart 41. Therefore, the operator can, for example, change the drive amount of the driven object Dv using the drive amount selection area 45 while checking the cause of the mass estimation failure based on the chart 41 when the repetitive operation is not processed normally.

[0047] If the mass estimation is not completed normally, the display 40 displays a message indicating that the mass estimation is incomplete as the status information 46 while displaying the chart 41. Therefore, the operator can quickly recognize that the mass estimation is incomplete based on the status information 46 and check the cause of the mass estimation failure based on the chart 41.

[0048] The switching area 43 also serves as a reset area for initializing the estimated mass. That is, the display shows the reset area while displaying the graph 41. Therefore, the operator can reset the estimated mass using the reset area if necessary while checking the trend of repetitive operations, etc., based on the graph 41.

[0049] If the identified physical parameter falls outside the predetermined range, the display 40 displays the alarm 42A while displaying the graph 41. Therefore, the operator can quickly detect the mass estimation failure based on the alarm 42A and check the cause of the failure based on the graph 41. [Other embodiments]

[0050] The above-described embodiment can be modified, for example, as follows. The workpiece mass estimation device 100 can be installed for a machine other than the machine tool 200. Regarding the diagram 41, some of the four diagrams 41a to 41d described above can be omitted, or an additional diagram can be added. The inertia diagram 41a can indicate the transition of the inertia of the workpiece W instead of the transition of the inertia of the driven object Db. Some of the individual information 42A and 43 to 48 displayed together with the diagram 41, except for the mass information 42, can be omitted, or additional information can be added. The switching area 43, the operation pattern selection area 44, the drive amount selection area 45, etc., can be displayed in a manner other than those shown in Fig. 3 to 7 are displayed.

[0051] According to the above embodiments, the workpiece mass estimating devices (100) of Additional Notes 1 to 9 described below can be realized. [Additional Note 1]

[0052] A workpiece mass estimation device (100) for estimating a mass of a workpiece (W), for a machine (200), comprising: a workpiece loading unit (90) on which the workpiece (W) is loaded; a motor (70) for driving the workpiece loading unit (90); a sensor (60) for detecting a state of the motor (70); and a motor (70) control unit for controlling the motor (70) based on the detected state of the motor (70), wherein the workpiece mass estimation device (100) comprises: an identification unit (10) configured to identify a value of a physical parameter of a driven object (Dv) driven by an output of the motor (70) based on the detected state of the motor (70) and to update the identified value through a repetitive operation; a storage unit (20) configured to store the value of the physical parameter as soon as the value is updated; an estimation unit (30) configured to estimate the mass of the workpiece (W) based on a final value of the values ​​of the physical parameter that have been updated; and a display (40) configured to display a graph (41) indicating a transition of the value of the physical parameter based on data stored in the storage unit (20) and to display the mass (42) estimated by the estimation unit (30). [Additional Note 2]

[0053] A workpiece mass estimation device (100) according to Additional Note 1, wherein the display (40) displays, during display of the diagram (41), a switching area (43) for performing an operation of switching between execution and suspension of estimation of the mass. [Additional Note 3]

[0054] A workpiece mass estimation device (100) according to additional note 1 or 2, wherein the display (40) displays, while displaying the diagram (41), the date and time (47) at which an estimation of the mass is completed. [Additional Note 4]

[0055] A workpiece mass estimation device (100) according to any one of additional notes 1 to 3, wherein the display (40) displays a temperature (48) of the motor (70) in real time while displaying the graph (41). [Additional Note 5]

[0056] A workpiece mass estimating device (100) according to any one of Additional Notes 1 to 4, wherein the display (40) displays an operation pattern selection area (44) for selecting an operation condition of the driven object (Dv) while displaying the diagram (41). [Additional Note 6]

[0057] A workpiece mass estimation device (100) according to any one of additional notes 1 to 5, wherein when an estimation of the mass of the workpiece (W) is not completed normally, the display (40) displays a message (46) that the estimation of the mass is incomplete while displaying the diagram (41). [Additional Note 7]

[0058] A workpiece mass estimation device (100) according to any one of additional notes 1 to 6, wherein the display (40) displays a reset area (43) for initializing the estimated mass while displaying the diagram (41). [Additional Note 8]

[0059] A workpiece mass estimation device (100) according to any one of additional notes 1 to 7, wherein when the identified physical parameter falls outside a predetermined range, the display (40) displays an alarm (42A) while displaying the graph (41). [Additional Note 9]

[0060] Workpiece mass estimation device (100) according to one of the additional notes 1 to 8, where diagram (41) includes: an inertia diagram (41a) showing a transition of an inertia of the driven object (Dv); a viscous friction coefficient diagram (4b1) showing a transition of a viscous friction coefficient in a transmission system for transmitting an output of the motor (70) to the workpiece loading unit (90); a Coulomb friction coefficient diagram (41c) showing a transition of a Coulomb friction coefficient in the transmission system; and a spring constant diagram (41d) showing a transition of a spring constant in the transmission system.

[0061] According to the workpiece mass estimating devices (100) of Additional Notes 1 to 9, it is possible to easily check whether the repetitive operations are processed normally.

[0062] Although the present disclosure has been described in detail above, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial omissions, and the like can be made to these embodiments without departing from the gist of the present disclosure or spirit of the present disclosure, which is evident from the contents recited in the claims and the equivalents thereof. These embodiments can also be implemented in combination. For example, in the embodiments described above, the order of each operation and the order of each process are exemplified, and the present disclosure is not limited thereto. The same applies to the case where numerical values ​​or equations are used in the descriptions of the embodiments described above. List of reference symbols 10 Identification unit 20 storage units 30 estimation units 40 ad 41 Diagram 41a Inertia diagram 41b Diagram of the viscous friction coefficient 41c Diagram of the Coulomb friction coefficient 41d Spring constant diagram 42 Mass 42A Alarm 43 Switching range 44 Operating pattern selection area 46 Status information 47 Date and time information 48 Temperature information 50 Engine control or regulation unit 60 sensors 70 engine 90 workpiece loading unit 100 workpiece mass estimation device 200 machine tool (machine) W workpiece QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2015-55923

[0003]

Claims

[1] A workpiece mass estimation device for estimating a mass of a workpiece, for a machine comprising: a workpiece loading unit on which the workpiece is loaded; a motor for driving the workpiece loading unit; a sensor for detecting a state of the motor; and a motor control unit for controlling the motor based on the detected state of the motor, the workpiece mass estimation device comprising: an identification unit configured to identify a value of a physical parameter of a driven object driven by an output of the motor based on the detected state of the motor and to update the identified value through a repetitive operation; a storage unit configured to store the value of the physical parameter whenever the value is updated; an estimation unit configured to estimate the mass of the workpiece based on a final value of the physical parameter values ​​that have been updated; and a display configured to display a graph indicating a transition of the value of the physical parameter based on data stored in the storage unit and to display the mass estimated by the estimation unit. [2] A workpiece mass estimating device according to claim 1, wherein the display, during displaying the diagram, displays a switching area for performing an operation of switching between execution and suspension of estimation of the mass. [3] A workpiece mass estimating device according to claim 1 or 2, wherein the display, while displaying the diagram, displays the date and time at which an estimation of the mass is completed. [4] A workpiece mass estimating device according to any one of claims 1 to 3, wherein the display displays a temperature of the motor in real time while displaying the graph. [5] A workpiece mass estimating device according to any one of claims 1 to 4, wherein the display displays an operation pattern selection area for selecting an operation condition of the driven object while displaying the diagram. [6] A workpiece mass estimating device according to any one of claims 1 to 5, wherein when an estimation of the mass of the workpiece is not completed normally, the display displays a message that the estimation of the mass is incomplete during the display of the diagram. [7] A workpiece mass estimating device according to any one of claims 1 to 6, wherein the display displays a reset area for initializing the estimated mass while displaying the diagram. [8] A workpiece mass estimating apparatus according to any one of claims 1 to 7, wherein when the identified physical parameter falls outside a predetermined range, the display displays an alarm while displaying the graph. [9] A workpiece mass estimating device according to any one of claims 1 to 8, wherein the diagram comprises: an inertia diagram showing a transition of inertia of the driven object; a viscous friction coefficient diagram showing a transition of a viscous friction coefficient in a transmission system for transmitting an output of the motor to the workpiece loading unit; a Coulomb friction coefficient diagram showing a transition of a Coulomb friction coefficient in the transmission system; and a spring constant diagram showing a transition of a spring constant in the transmission system.

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