JP2016148978A - Position controller and position control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which it takes a time for a position controller which performs friction compensation using a data base to update all data of the database so as to reduce an influence of secular change in friction characteristics.SOLUTION: As one embodiment of the present invention, there is provided a position controller which drives a movable part of a rolling stage with driving force of a linear motor, the position controller being configured: to specify an inversion position of the movable part from a processing program in which positions of the movable part in machining processing on a work are described; to calculate a displacement and a speed of the movable part from the inversion position; to extract driving force corresponding to the displacement and speed from a database; to generate a position command from the inversion position corresponding to a condition for the driving force; to drive the movable part of the rolling stage on the basis of the position command; and to update the database on the basis of measurement results of the displacement, speed and driving force of the movable part at this time.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a position control device that reduces deviation caused by friction in various industrial machines in which friction acts on bearings and guide surfaces.

  Precision processing machines and precision measuring machines are equipped with stages with high-precision positioning performance. In general, the linear guide used for the stage includes a rolling guide, a sliding bearing, and a static pressure bearing. Among them, the rolling guide is most widely used. Since the rolling guide is inexpensive and easy to install, there is an advantage that it is easy to use.

  On the other hand, since spherical or cylindrical rolling elements are used for the guide portion of the rolling guide, friction due to contact exists between the rolling elements and the rolling surface. It is known that due to the friction, there is a region where the rolling element does not roll when the rolling direction of the rolling element is reversed (non-patent document 1). Due to this friction characteristic, there is a problem that a projection-like deviation occurs when the moving direction of the stage is reversed. This protrusion-like deviation is generally called a quadrant protrusion, and it is difficult to eliminate even if closed-loop control that feeds back the stage position is used.

  The non-linear friction characteristic that is the cause of the quadrant projection will be described. Normally, lubricating oil is inserted between the rolling element and the rolling surface to prevent solid contact, but in situations where the speed is almost zero, the oil film becomes thin and the rolling element and the rolling surface A large frictional force is generated because solid contact occurs. When the displacement from the reversal position is in the range of zero to several hundred μm, the frictional force (strictly, the elastic deformation force) is increased by elastically deforming the rolling elements without rolling. Further, when the displacement increases and becomes an area of several hundred μm or more, the rolling element starts to roll, and is released from elastic deformation to reduce the frictional force.

  However, this friction characteristic cannot be explained simply by depending on the displacement of the stage. Since the rolling element starts to roll as the stage speed increases from zero, an oil film layer is formed between the rolling element and the rolling surface, and the frictional force is reduced by lubrication of the oil film layer. In addition, since the formation of the oil film layer changes depending on the speed, the frictional force between the rolling element and the rolling surface also depends on the speed.

  It is known that the viscous force of the lubricating oil increases and becomes a resistance in a region where the speed is high, but as described above, the frictional force between the rolling element and the rolling surface is also in a region where the stage speed is extremely slow. It is not well known that it depends on speed. Thus, the frictional force between the rolling element and the rolling surface is not independent of both the displacement and the speed, complicating the frictional characteristics. The difficulty of the problem of reducing is increased.

  Patent Document 1 discloses a technique for determining an optimum parameter used for quadrant protrusion correction with high efficiency and high accuracy. Patent Document 2 discloses a technique for automatically adjusting a control parameter to an appropriate value when the control characteristics of the moving mechanism change over time.

JP-A-11-231921 JP 2011-134169 A

Study on friction model of linear motor ball guide for precise positioning control (2nd report) Tanaka, Oiwa, Otsuka Journal of Precision Engineering Vol. 73, No4, 2007

  In a position control device that performs friction compensation using a friction compensation database, the friction compensation database and the actual friction generated when used due to the secular change in friction characteristics between the rolling elements and the rolling surface. Deviation may occur between the two. A deviation occurs in the friction compensation database, and the compensation value of the frictional force is incorrect. In order to solve this problem, it is conceivable to update the friction compensation database before using the apparatus. However, since the update takes time, the operation rate of the apparatus is reduced.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a position control device and a position control method for reducing the time required for updating a friction compensation database used for feedforward control of a rolling stage.

  One embodiment of the present invention is a position control device that drives a movable part of a rolling stage by a driving force of a linear motor, and is used for feedforward control of the movable part, and a reverse position where the moving direction of the movable part is reversed. The database part that stores the database related to the displacement and the driving force with respect to speed, and the reversal position of the movable part from the machining program that describes the position of the movable part in the workpiece machining process, and the displacement of the movable part from the reversal position And a command generation unit that calculates the speed, a driving force corresponding to the displacement and speed calculated by the command generation unit is extracted from the database, a condition corresponding to the extracted driving force is specified, and an inversion position corresponding to the condition is The position command is created, and the movable part is driven based on the created position command, and the data based on the measurement results of the displacement, speed and driving force of the movable part at that time To provide position control device and a database creation unit that updates the over scan.

  Another embodiment of the present invention is a position control method for a movable part of a rolling stage that is driven by a driving force of a linear motor, and the position of the movable part is determined from a machining program that describes the position of the movable part in a workpiece machining process. A step of specifying a reversal position where the moving direction is reversed, a step of calculating a displacement and a speed of the movable part from the reversal position, and a step of extracting a driving force according to the displacement and speed calculated from the database, The database is a database related to the driving force with respect to the displacement and speed from the reversal position of the movable part, which is used for feedforward control of the movable part, and a step for specifying a condition corresponding to the extracted driving force, The step of creating a position command from the corresponding reverse position, and the movable part is driven based on the created position command. Displacement of the moving part, provides a position control method comprising the steps of updating the database based on the measurement result of the speed and the driving force.

  Since the position control apparatus according to an embodiment of the present invention partially updates the two-dimensional database for feedforward control during operation, the time required for updating the two-dimensional database is reduced. When the two-dimensional database is updated before the machining operation, it contributes to an improvement in the operating rate of the apparatus.

It is a block diagram which shows the outline of the position control apparatus which concerns on 1st Embodiment. It is a flowchart of the process in a drive calculating part. It is a block diagram which shows the outline of the position control apparatus at the time of database creation. It is a flowchart of a database creation procedure. It is a figure which shows the example of a sine wave-like command. It is a figure which shows the example of the measurement result of a driving force and a displacement. It is a figure which shows the example of the two-dimensional database of the driving force with respect to a displacement and speed. It is a flowchart concerning database creation according to a processing program. It is a figure which shows the example which selects a data point from the inversion operation | movement extracted. It is a figure which shows the example of the difference of the data point which can be updated by the difference of condition No. It is a figure which shows the example which selects condition No. from the data point to be used. It is a flowchart of the preparation procedure of a database.

[First Embodiment]
A first embodiment of the present invention will be described with reference to the drawings. The present embodiment relates to a position control device to which a method for updating a two-dimensional database of driving force with respect to displacement and speed from a reverse position is added.

  FIG. 1 is a configuration diagram illustrating an outline of a position control device 100 according to the present embodiment. First, the rolling stage 1 to be controlled will be described. The rolling stage 1 is divided into a fixed part and a movable part. The fixed part of the rolling stage 1 includes a base 2 and a rail 3 installed on the upper surface thereof. The movable part of the rolling stage 1 includes a carriage 4 and a table 5 installed on the upper surface thereof, and a linear motor 6 and a position sensor 7 are installed on the table 5.

  The surface of the rail 3 of the fixed part of the rolling stage 1 is the “rolling surface”, and the ball built in the carriage 4 of the movable part of the rolling stage 1 is the “rolling body”. When the rolling surface comes into contact with the rolling elements, a frictional force is generated between them.

  The thrust for moving the movable part of the rolling stage 1 is generated by the linear motor 6, and the amount of movement of the movable part is determined by measuring the relative position between the table 5 and the base 2 by the position sensor 7. I want.

  The command generation unit 16 exchanges information with the position control unit 8, the driving force calculation unit 10, the database creation unit 13, and the data measurement unit 14 according to various programs stored in the storage unit 15, and the position control device 100. Control the whole. The storage unit 15 stores a workpiece machining program and the like.

  Next, the control of the movable part of the rolling stage 1 by the position control device 100 will be described. Based on the difference between the current position of the movable part of the rolling stage 1 acquired by the position sensor 7 and the command value (position command) from the command generation unit 16, the position control unit 8 performs PID control, and the driver 9 The linear motor 6 generates a thrust of the movable part in response to a drive command sent via. In addition to such a feedback control configuration, the driving force calculation unit 10 performs feed forward control of the driving force. Then, the movable part of the rolling stage 1 that has undergone the feedback control and the feedforward control moves to the position specified by the command from the command generation unit 16 at the specified speed (and acceleration).

  Here, the feedforward control process by the driving force calculation unit 10 will be described with reference to the flowchart of FIG. The feedforward control process is performed for each command in the machining program related to workpiece machining.

In S <b> 101, the driving force calculation unit 10 acquires the current command value P from the command generation unit 16. The current command value P includes information (position command) indicating the position where the movable part of the rolling stage 1 is to be located. In S102, the driving force calculation unit 10 calculates the current speed V of the movable part of the rolling stage 1 from the current command value P and the past command value _Pold . Here, the driving force calculation unit 10 reads and uses the past command value P _old stored in the internal memory in S113 in the previous feedforward control process. Further, the current speed V is calculated based on the current position of the movable part of the rolling stage 1 based on the past command value P _old , the position to be located in the future designated by the current command value P, and the position to reach it. Calculate based on time.

In S103, the driving force calculation unit 10 stores the sign s (+ or-) of the current speed V in an internal memory (not shown). In S104, the driving force calculation unit 10 determines whether the code s of the current speed V matches the code s _{old of the} past speed. Here, reference numeral s _old past speed is used reads the value stored in the internal memory of the drive force computing section 10 in S114 in the previous feedforward control processing. If they do not match (No in S104), in S105, the driving force computing unit 10 is stored in the internal memory the current position of the movable portion of the rolling stage 1 (start moving before position) as reversal position _{P rev.} If they match (Yes in S104), the process proceeds to S107.

In S106, the driving force calculation unit 10 calculates a driving force (reversing driving force F _rev ) for reversing and moving the movable part of the rolling stage 1 and stores it in the internal memory. The driving force F is calculated based on a thrust force on the movable portion of the rolling stage 1 to be output by the linear motor 6 in accordance with the position command (or speed or acceleration command).

In S107, the driving force calculating section 10, the current command value P current position (or the reverse position _{P rev)} the current position based on (or reverse position _{P rev)} from the position specified by the current command value P (commanded position) The displacement X up to is calculated. In S108, the driving force calculation unit 10 passes the displacement X calculated in S107 and the value of the current speed V calculated in S102 to the interpolation calculation unit 11.

  In S109, the interpolation calculation unit 11 communicates with the database unit 12 and performs interpolation calculation of the driving force F corresponding to the received displacement X and speed V. Interpolation calculation is performed by reading out the values of the driving force F corresponding to the displacement X and the velocity V from a later-described two-dimensional database stored in the database unit 12. In S <b> 110, the driving force calculation unit 10 receives the driving force F interpolated from the interpolation calculation unit 11.

In S111, the driving force calculating section 10, the driving force _{F rev} during inversion stored in the driving force F and S106 received from the interpolation operation unit 11 calculates a drive command _{F total} by Equation (1). Note that when it is not during reversal, the driving force calculated by the driving force calculation unit 10 based on a command from the command generation unit 16 is used instead of F _rev .

In S <b> 112, the driving force calculation unit 10 adds the obtained driving command F _total to the command from the position control unit 8, and the added driving command is output to the driver 9. In this way, feedforward control of driving force is performed. In S113, the driving force calculation unit 10 stores the current command value P in the internal memory as the past command value _Pold . In S114, the driving force calculating unit 10 stores the code s of the current speed V as the code s _old of the past speed in the internal memory.

  Next, a method for creating a database stored in the database unit 12 by the database creating unit 13 will be described. FIG. 3 is a configuration diagram showing an outline of the position control device 100 at the time of database measurement. FIG. 4 is a flowchart of a procedure for creating a two-dimensional database of driving force with respect to displacement and speed by the database creation unit 13.

  In S201, the database creation unit 13 initializes a condition number (condition number = 0). In S202, the database creation unit 13 adds a condition No (condition No = condition No + 1). In S203, the database creation unit 13 creates a sinusoidal position command corresponding to the condition No.

  Here, considering a sinusoidal acceleration command as shown by the solid line (condition 1) in FIG. 5A, the speed command related to condition 1 is indicated by the solid line in FIG. Thus, the position command is as shown by the solid line in FIG. Note that sinusoidal commands relating to conditions 2 and 3 are also depicted in FIG.

In S204, the database creation unit 13 adds the position command created in S203 to the command value input to the position control unit 8, as shown in FIG. The linear motor 6 that has received the command value via the driver 9 generates thrust, and the movable part of the rolling stage 1 is driven. At this time, the command value from the command generator 16 and the driving force F _total from the driving force calculator 10 are not added. Feedback control is performed based on the command value from the database creation unit 13 and the past command value, and the database is created based on the measurement results of the displacement, speed, and acceleration of the movable part of the rolling stage 1.

  In step S <b> 205, the data measurement unit 14 measures the position (displacement), speed, and driving force when the movable unit of the rolling stage 1 is driven, and sends the measurement result to the database creation unit 13. The database creation unit 13 stores the measurement result in the internal memory. Here, in FIG. 6, the example of the measurement result of the driving force with respect to the displacement for every conditions 1-3 measured by the data measurement part 14 is shown.

  In S <b> 206, the database creation unit 13 picks up (samples) speed and driving force values for a plurality of predetermined displacements based on the measurement result sent from the data measurement unit 14. The method for determining the displacement is not limited. However, since the relationship between the displacement and the frictional force tends to be close to the logarithmic proportion, the values of the speed and the driving force may be picked up in logarithmic increments of the displacement. In addition, picking up speed and driving force intensively for locations where the driving force shows a sudden change (low displacement side in the example of FIG. 6) and increasing the number of data points is effective in reducing compensation errors. It is.

  In S207, the database creation unit 13 creates a database of driving force for displacement and speed based on the speed and driving force for the plurality of displacements picked up in S206, and stores the database in the database unit 12. In S208, the database creation unit 13 determines whether the condition number is smaller than the target condition number. The target condition number may be the number of all conditions (3 in the example of FIG. 5) or may be a number smaller than the number of all conditions. If the condition number is smaller than the total number of conditions (Yes in S208), the database creation unit 13 repeats the processes in S202 to 208, and adds data to the database created in S207. When the target condition number is reached (No in S208), the database creation procedure ends.

  Here, a sinusoidal command corresponding to the condition No in S203 is created in advance by changing several types of sine wave cycles as indicated by a broken line (conditions 2 and 3) in FIG. As a method of changing the cycle, the relationship between the speed and the frictional force tends to be close to the logarithmic proportion, so it is preferable to change the cycle in logarithmic increments. By creating a database in logarithmic increments for both displacement and speed, the number of data points can be reduced compared to creating a database in a linear fashion, which is effective in reducing the memory area used for the database and reducing the calculation time for interpolation calculations. is there. When the condition number reaches the target condition number, the creation of the database is completed. FIG. 7 shows an example of a two-dimensional database of the driving force with respect to the created displacement and speed.

  Next, the program operation will be described. The program operation is an operation based on a machining program and assumes an operation that requires precise positioning such as a workpiece machining operation. The machining program is a program that describes the position of the movable portion of the rolling stage 1 on which the workpiece is placed in the workpiece machining process.

  First, the command generation unit 16 reads the machining program stored in the storage unit 15 and generates an operation command for moving the stage to a position set in the machining program. At this time, the command generation unit 16 also generates a movement operation command before and after the machining operation, such as movement from the standby position to the start position of the machining program and movement from the end position of the machining program to the standby position. The command generation unit 16 gives the generated operation command to the position control unit 8 and the driving force calculation unit 10, and when the command is transmitted to the movable unit of the rolling stage 1 through the driver 9, the movable unit moves.

  When the operation based on the machining program is started, the movable part of the rolling stage 1 is moved to the start position of the machining operation, and the machining operation is started by a machining device (not shown) on the workpiece arranged on the movable part. The When all the machining operations are finished, the movable part moves to the standby position, and the machining operation is finished.

  Conventional position control devices for rolling stages measure and update all regions (total displacement and total velocity) of a two-dimensional database used for interpolation processing in feedforward control before the machining operation. However, the position control apparatus 100 according to the present embodiment reads the machining program in advance, checks in advance the data points of the two-dimensional database used in the machining operation, and specifies the update location in advance accordingly. And the position control apparatus 100 updates the database of the specified location before the start of the workpiece | work processing operation. Since the two-dimensional database is partially updated in this way, the time required for updating the two-dimensional database is reduced.

  Next, a method for specifying the update location of the two-dimensional database from the machining program will be described with reference to FIG. The update location is a portion relating to the displacement and speed from the position where the movable part of the rolling stage 1 is reversed in the two-dimensional database.

  In S301, the command generation unit 16 reads one line of the machining program stored in the storage unit 15. In the machining program, the position where the movable part of the rolling stage 1 should be positioned at every fixed period from the start of operation is set for each row.

  In S302, the command generation unit 16 detects whether there is a command to reverse the moving direction of the movable unit of the rolling stage 1 in the machining program read in S301. Whether or not to reverse is determined by whether or not the sign s of the speed command described in the machining program is reversed.

  When it is detected that the moving direction of the movable part of the rolling stage 1 is reversed (Yes in S302), in S303, the command generating unit 16 is a position where the moving direction of the movable part of the rolling stage 1 is reversed (reversed position). Is stored in the internal memory. If no inversion is detected (No in S302), the process proceeds to S308.

  In S304, the command generation unit 16 calculates the displacement after reversal from the current position of the movable part of the rolling stage 1 and the reversal position stored in S303, and confirms whether it is within the set value of the measurement range. If it is within the set value of the measurement range (Yes in S304), the process proceeds to S305, otherwise (No in S304), the process proceeds to S308.

  In S305, the command generation unit 16 calculates the displacement Xr from the reversal position to the next position to be positioned (read from the machining program), and is designated by the machining program and the position to be located next from the reversal position. The speed Vr is calculated based on the time. Then, the command generation unit 16 sends the displacement Xr and the velocity Vr to the database creation unit 13. In S306, the database creation unit 13 picks up data points related to the driving force on the database for the displacement Xr and the velocity Vr from the database stored in the database unit 12.

  Here, the data point F [i, j] related to the driving force with the closest values of the displacement Xr and the velocity Vr is selected for the pickup of the data point on the database. For example, when an operation of displacement x and speed v is extracted from the reversing operation, a data point F [i, j] related to the driving force closest to the displacement x and speed v is selected as shown in FIG. . When the data point to be selected is determined, in S307, the database creation unit 13 stores the array index [i, j] related to the selected data point in the internal memory.

  In S308, the command generation unit 16 checks whether the machining program has been read (in other words, whether the processing has been performed up to the last line of the machining program). If not completed, the command generation unit 16 returns to S301. S308 is repeated. When the completion of reading the program is detected in S308, in S309, the database creation unit 13 uses the array index [i, j] related to the data point to be updated from the array index [i, j] stored in the internal memory. The condition No to be specified is specified.

  Here, a method for specifying an operation for database update from the use location of the two-dimensional database will be described. FIG. 10 shows the difference in the data points that can be updated on the database due to the difference in the condition number. For example, when the movable part of the rolling stage 1 is operated with a sine wave-like position command of condition No1, the data point indicated by the triangle symbol in the figure can be updated. Similarly, in condition Nos. 2 and 3, data points indicated by corresponding symbols can be updated.

  When all the data points on the two-dimensional database are updated, the frictional characteristics are measured under all conditions by giving sine wave position commands corresponding to a plurality of condition Nos. However, when conditions are specified according to the program operation (displacement and speed from the reverse position) of the machining program as in this embodiment, the measurement operation is performed only under the condition No where the data point used during the machining operation can be updated. I do.

For example, the points on the line in FIG. 11 indicate the data points used during the operation of the machining program. In the example of FIG. 11, the condition No = 1 is specified for the data point of the array index [i, j] = [i ₁ , j ₁ ], and the array index [i, j] = [i ₂ , j ₂ ], [I ₃ , j ₃ ], [i ₄ , j ₄ ], [i ₅ , j ₅ ] are specified for condition No = 2. In this way, the condition No. for updating this data point is specified in S309. In step S310, the database creation unit 13 performs the process illustrated in the flowchart of FIG. 12, and updates the data value of the driving force F of the two-dimensional database related to the array index [i, j].

  Next, a method for updating only the data points used during the machining operation will be described.

  FIG. 12 shows an operation flow. This update method differs from the database creation method described above in part S403, but performs the same processing. In S401, the database creation unit 13 initializes a condition number (condition number = 0). In S402, the database creation unit 13 adds a condition No (condition No = condition No + 1).

  In S403, the database creation unit 13 confirms whether or not the current condition number is the condition number specified in S309. If the current condition No matches the condition No specified in S309 (Yes in S403), the processes of S404 to S408 are performed. If not (No in S403), the process proceeds to S409.

  In S404, the database creation unit 13 creates a sinusoidal position command corresponding to the condition No. In S405, the database creation unit 13 drives the movable part of the rolling stage 1 in addition to the position command created in S203 in addition to the command value input to the position control unit 8 in the configuration diagram shown in FIG. In S406, the data measuring unit 14 simultaneously measures the displacement, speed, and driving force during driving of the movable part of the rolling stage 1 and sends it to the database creating unit 13, which stores it in the internal memory. .

  In S407, the database creation unit 13 picks up (samples) values of speed and driving force with respect to a predetermined displacement. In S <b> 408, the database creation unit 13 stores the driving force for the displacement and speed in the database unit 12. In S409, the database creation unit 13 determines whether the condition number is smaller than the target condition number. If it is smaller (Yes in S409), the processing of S402 to 409 is repeated, and if it is not smaller (No in S409), the process is completed. The target condition number may be the number of all conditions (3 in the example of FIG. 5) or may be a number smaller than the number of all conditions.

  Next, the effect of this embodiment will be described. Usually, the database is updated by performing a stage operation with a plurality of sinusoidal acceleration commands. On the other hand, in this embodiment, a machining program is read in advance, the rolling stage is operated only with a sinusoidal acceleration command corresponding to the condition No., and only the data points used during the machining operation among the data points on the database are updated. I do. Thereby, the time required for database update can be reduced. An apparatus that updates the database every time before the machining operation can contribute to an improvement in the operating rate of the apparatus.

(Other embodiments)
As another embodiment of the present invention, the update of the database is not limited to the implementation before the actual machining operation. For example, by performing the database update process using idle time when the apparatus is not operating, it is possible to prevent a decrease in the operating rate of the apparatus. In addition, when the database can be calculated without external force during normal operation, such as a measuring instrument, it is possible to prevent a reduction in the operating rate of the apparatus by performing database update processing during the measurement operation.

Further, by calculating the optimum update time using the database update history and performing the minimum necessary database update processing, it is possible to prevent the operation rate of the apparatus from being lowered.
In addition, when the required accuracy is low, the operation rate of the apparatus can be prevented from being lowered by performing the processing operation without performing the database update process.

DESCRIPTION OF SYMBOLS 1 Rolling stage 2 Base 3 Rail 4 Carriage 5 Table 6 Linear motor 7 Position sensor 8 Position control part 9 Driver 10 Driving force calculation part 11 Interpolation calculation part 12 Data base part 13 Database preparation part 14 Data measurement part 15 Storage part 16 Command Generator

Claims (4)

A position control device that drives a movable part of a rolling stage by a driving force of a linear motor,
A database unit for storing a database relating to a driving force with respect to a displacement and a speed from a reversal position where the moving direction of the movable unit is reversed, which is used for feedforward control of the movable unit;
A command generation unit that identifies a reversal position of the movable part from a machining program that describes the position of the movable part in a workpiece processing process, and calculates a displacement and a speed of the movable part from the reversal position;
A driving force corresponding to the displacement and speed calculated by the command generation unit is extracted from the database, a condition corresponding to the extracted driving force is specified, and a position command from the reverse position corresponding to the condition is created. And a database creation unit that drives the movable part based on the created position command and updates the database based on the measurement results of the displacement, speed, and driving force of the movable part at that time. .   The position control apparatus according to claim 1, wherein the update of the database is performed before an actual operation of the movable part based on the machining program.   The position control device according to claim 1, wherein the position command is a sinusoidal position command, and a cycle of the sinusoidal position command changes according to the condition. A method for controlling the position of a movable part of a rolling stage driven by a driving force of a linear motor,
Identifying a reversal position at which the moving direction of the movable part is reversed from a machining program that describes the position of the movable part in a workpiece machining process;
Calculating the displacement and speed of the movable part from the reversal position;
A step of extracting a driving force in accordance with the calculated displacement and speed from a database, wherein the database is used for feedforward control of the movable part, and is driven with respect to the displacement and speed from the reverse position of the movable part. A database of power, steps,
Identifying a condition according to the extracted driving force;
Creating a position command from the reverse position corresponding to the condition;
A position control method comprising: driving the movable portion based on the created position command; and updating the database based on measurement results of displacement, speed, and driving force of the movable portion at that time.

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