JP6582814B2 - Numerical controller and lost motion compensation method for numerical controller - Google Patents

Description

  The present invention relates to a numerical controller and a lost motion compensation method for the numerical controller.

  The numerical controller feeds back a detection position detected by a motor that drives the drive shaft of the moving body, and controls the position of the moving body by driving the motor so that the detection position follows the command position. When the moving direction of the moving body is reversed, a deviation (delay) occurs due to elastic deformation of the drive mechanism of the drive shaft. The deviation is a lost motion. In particular, when performing high-precision machining of an arc shape, it is important to measure and compensate for the deviation generated in the drive mechanism. The correction parameter adjustment device disclosed in Patent Document 1 includes an accelerometer, a mechanical motion analysis unit, and a correction parameter calculation unit. The accelerometer measures the acceleration of the machine tool in the numerical control device. The machine motion analysis unit approximates the error waveform between the position obtained by integrating the acceleration measured by the accelerometer twice and the detected position with a predetermined approximate expression, and solves the approximate expression from the result of integrating the acceleration twice. The machine motion is analyzed by calculating the machine position by subtracting. The correction parameter calculation unit determines a correction parameter for improving the motion accuracy of the machine tool from the analysis result of the machine motion analysis unit.

JP 2011-221612 A

  Since the mechanical motion analysis unit integrates the acceleration measured by the accelerometer twice, there is a problem that a measurement error is likely to occur.

  An object of the present invention is to provide a numerical controller that can easily and highly accurately compensate for lost motion, and a lost motion compensation method for the numerical controller.

  A numerical control device according to a first aspect of the present invention includes a moving mechanism that has a ball screw and a nut that is screwed to the ball screw, moves a moving body fixed to the nut, and a motor that rotationally drives the ball screw. The machine controls the machine, generates a position command for designating the position of the moving body, and according to the position command, the motor control means for controlling the motor, and the frictional force after the moving direction of the moving body is reversed. Calculating means for calculating a compensation amount that compensates for lost motion that is an elastic deformation of the moving mechanism, and adding means for correcting the position command by adding the compensation amount calculated by the calculating means to the position command; In the numerical control apparatus, the arithmetic means linearly reciprocates the moving body with respect to a reference object fixed to the machine, and sets a relative position between the moving body and the reference object at a predetermined time. Measuring means for measuring every time, first information that is information of the relative position measured by the measuring means at the predetermined time, and the motor control at the time of measuring the relative position at the predetermined time by the measuring means. Based on the second information that is the information of the command position specified by the position command generated by the unit every predetermined time, based on the lost motion calculated by the calculation unit that calculates the lost motion, Compensation amount calculation means for calculating the compensation amount, wherein the calculation means is the moving direction of the moving body in each locus of the relative position in the first information and the command position in the second information. Correction means for correcting at least one of the first information and the second information so that the portions before the inversion match each other, and the correction by the correction means. After, and calculates the difference of the second information and the first information as the lost motion. Therefore, the numerical control apparatus can easily and accurately compensate for the lost motion that occurs when the moving direction of the moving body is reversed, so that the circular arc shape can be processed particularly accurately. The present invention can efficiently calculate the compensation amount of lost motion for all machines at the time of factory shipment.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the correction means includes the relative position when the moving direction of the moving body in the first information is reversed, and A first correction value of a distance in the moving direction with respect to the first information or the second information so that the command position when the moving direction of the moving body in the second information is reversed is matched. A first correction unit for adding a correction value; a first locus portion before the moving direction is reversed among the locus of the relative position indicated by the first information after correction by the first correction unit; Measurement of the first information or the second information at the predetermined time intervals by the measuring means so that the second locus portion before the moving direction is reversed of the locus of the command position indicated by two information. Against time Second correction means for adding a second correction value that is a positive value, and after the correction by the second correction means, the difference between the first information and the second information is calculated as the lost motion. And Therefore, the numerical control device can easily and accurately match the portions before reversal in the respective loci of the relative position and the command position.

  According to a third aspect of the present invention, in addition to the configuration of the first aspect of the invention, the correction means includes a third controller before the moving direction is reversed in the locus of the relative position indicated by the first information. By the measuring means for the first information or the second information so that the locus portion and the locus of the command position indicated by the second information coincide with the fourth locus portion before the moving direction is reversed. Third correction means for adding a third correction value, which is a time correction value, to the measurement time for each predetermined time, and after the correction by the third correction means, the movement of the moving body in the first information The relative position when the direction is reversed overlaps the locus of the command position, or the command position when the movement direction of the moving body in the second information is reversed is the locus of the relative position. Front to overlap Fourth correction means for adding a fourth correction value, which is a correction value of a distance in the moving direction, to the first information or the second information, and after the correction by the fourth correction means, the first information The difference between the second information and the second information is calculated as the lost motion. Therefore, the numerical control device can easily and accurately match the portions before reversal in the respective loci of the relative position and the command position.

According to a fourth aspect of the present invention, in addition to the configuration of the invention according to the second aspect , the calculating means includes the first correcting means and the first correcting means until the first locus portion and the second locus portion coincide with each other. The correction by the second correction unit is repeatedly executed. When the measurement interval between the relative position and the command position is different, the first trajectory portion and the second trajectory portion may not match in one correction performed by the correction means. In that case, the numerical controller repeatedly executes the correction by the correction means, so that the first locus portion and the second locus portion can be matched.
According to a fifth aspect of the present invention, in addition to the configuration of the invention according to the third aspect, the calculation means performs correction by the correction means until the third locus portion and the fourth locus portion coincide with each other. It is characterized by being repeatedly executed.

According to a sixth aspect of the present invention, in addition to the configuration of the invention according to any one of the first to fifth aspects, the measuring unit is configured to measure the relative position between the movable body and the reference object with a laser displacement meter. Is measured every predetermined time. Since the numerical controller uses a laser displacement meter, the relative position can be measured with high accuracy. For example, when a laser displacement meter is already used for other purposes such as measuring the accuracy of the machine in the machine inspection process, it is not necessary to prepare another measuring device or the like specially for the lost motion measurement. Therefore, it is possible to inspect the lost motion of all the machines and adjust the compensation amount.

The numerical control device according to claim 7, in addition to the configuration of the invention according to any one of claims 1 to 6, the mass of the moving body M [kg], the feed rate of the mobile v [m / s ], When the time constant until the moving body reaches the maximum speed is t1 [s] and the frictional force during the movement of the moving body is F [N], the measurement means On the other hand, it is caused by the frictional force by linearly reciprocating at a feed speed v such that F> M (v / t1), and measuring the relative position between the moving body and the reference object every predetermined time. Only elastic deformation is measured as lost motion. Therefore, the numerical controller can accurately measure only the elastic deformation caused by the frictional force as the lost motion.

A lost motion compensation method for a numerical control device according to claim 8 includes: a moving mechanism that has a ball screw and a nut screwed into the ball screw and moves a moving body fixed to the nut; and the ball screw is driven to rotate. And a motor having a motor for generating a position command for specifying the position of the moving body, and a motor control means for controlling the motor according to the position command. Calculating a compensation amount that compensates for lost motion that is elastic deformation of the moving mechanism caused by a frictional force after the moving direction of the moving body is reversed; and calculating the compensation amount calculated in the calculating step to the position command In the lost motion compensation method for a numerical control apparatus, comprising: an addition step of correcting the position command by adding to the position command. A measuring step of linearly reciprocating the moving body with respect to a reference object, and measuring a relative position between the moving body and the reference object at a predetermined time, and the relative position measured at the predetermined time in the measuring step. First information which is information and second information which is information on a command position designated by the position command generated by the motor control unit at the predetermined time when the relative position is measured at the predetermined time in the measurement step. A calculation step for calculating the lost motion based on the information, and a compensation amount calculation step for calculating the compensation amount based on the lost motion calculated in the calculation step, wherein the calculation step includes the first information. So that the moving direction of the moving body in each locus of the relative position in the second information and the command position in the second information coincide with each other before reversing, A correction step of correcting at least one of the relative position and the command position, and after correction in the correction step, the difference between the first information and the second information is calculated as the lost motion. . The numerical control device can obtain the effect of the first aspect by performing the above steps.

1 is a perspective view of a machine tool 1. The perspective view of the table moving mechanism 10. FIG. FIG. 3 is a block diagram showing an electrical configuration of the numerical control device 30 and the machine tool 1. Schematic which shows the relative position measuring method. The flowchart of a lost motion compensation amount calculation process (1st Example). The chart which shows the locus | trajectory of a relative position. The chart which shows the locus of relative position and command position. The table | surface which shows the state which correct | amended the locus | trajectory of the command position shown in FIG. 7 with the position correction value. The chart which shows the state which correct | amended the locus | trajectory of the command position shown in FIG. 8 with the time correction value. The chart which expanded the peak part of Drawing 9 (a). The chart which shows the time change of the amount of lost motion. The chart which shows the relationship with the relative position of a lost motion compensation amount. The flowchart of a lost motion compensation amount calculation process (2nd Example). The chart which shows the locus | trajectory of a relative position. The chart which shows the locus of relative position and command position. The chart which shows the state which correct | amended the locus | trajectory of the command position shown in FIG. 15 with the time correction value. The chart which expanded the peak part of Drawing 16 (a). The chart which shows the state which correct | amended the locus | trajectory of the command position shown in FIG. 15 with the position correction value. The chart which expanded the peak part of Drawing 18 (a). The chart which shows the state which correct | amended the locus | trajectory of the command position shown in FIG. 18 again with the time correction value. The chart which expanded the peak part of Drawing 20 (a). The flowchart of a compensation process. The chart which shows the simulation result of error after compensation. The chart which shows the actual value of the error after compensation.

  A first embodiment of the present invention will be described with reference to the drawings. In the following description, left, right, front, back, and top and bottom indicated by arrows in the figure are used. The left-right direction, the front-rear direction, and the vertical direction of the machine tool 1 are an X-axis direction, a Y-axis direction, and a Z-axis direction, respectively. A machine tool 1 shown in FIG. 1 rotates a tool 4 mounted on a spindle 9 to cut a workpiece (not shown) held on the upper surface of a table 13. The numerical control device 30 (see FIG. 3) controls the operation of the machine tool 1.

  The structure of the machine tool 1 will be described with reference to FIGS. As shown in FIG. 1, the machine tool 1 includes a base 2, a column 5, a spindle head 7, a spindle 9, a table moving mechanism 10, a tool changer 20, a control box 6, an operation panel 15 (see FIG. 3), and the like. . The base 2 is a substantially rectangular parallelepiped metal base. The column 5 is erected on the upper rear side of the base 2.

  The spindle head 7 moves up and down in the Z-axis direction by a Z-axis moving mechanism provided on the front surface of the column 5. The Z-axis moving mechanism includes a pair of Z-axis linear guides (not shown), a Z-axis ball screw (not shown), and a Z-axis motor 51 (see FIG. 3). The Z-axis linear guide extends along the Z-axis direction and guides the spindle head 7 in the Z-axis direction. The Z-axis ball screw is disposed between a pair of Z-axis linear guides. The spindle head 7 includes a nut (not shown) on the back surface. The nut is screwed onto the Z-axis ball screw. The Z-axis motor 51 rotates the Z-axis ball screw in the forward and reverse directions. Therefore, the spindle head 7 moves in the Z-axis direction together with the nut. The spindle head 7 includes a spindle motor 52 (see FIG. 3). The main shaft 9 is rotatably provided inside the main shaft head 7 (see FIG. 4). The main shaft 9 has a mounting hole (not shown) at its lower end (front end). The mounting hole is located below the spindle head 7. The spindle 9 is mounted with the tool 4 in the mounting hole, and is rotated by driving the spindle motor 52. The table moving mechanism 10 is provided at the upper center of the base 2 and drives the table 13 in the X-axis direction and the Y-axis direction. The structure of the table moving mechanism 10 will be described later.

  The tool changer 20 is provided on the front side of the spindle head 7 and includes a disk-shaped tool magazine 21. The tool magazine 21 is provided with a plurality of grip arms 90 radially on the outer periphery. The grip arm 90 holds a tool (not shown). The tool changer 20 drives the magazine motor 55 (see FIG. 3) to rotate the tool magazine 21, and positions the tool 4 indicated by the tool change command described in the NC program at the tool change position. The tool change position is the lowest position of the tool magazine 21. The tool changer 20 exchanges and exchanges the tool 4 that is currently mounted on the spindle 9 and the next tool at the tool change position by the raising / lowering operation of the spindle head 7 and the swinging action of the grip arm 90.

  The control box 6 is attached to the back side of the column 5 and stores the numerical control device 30 (see FIG. 3). The numerical control device 30 controls the operation of the machine tool 1 and relatively moves the work material held on the table 13 and the tool 4 mounted on the main shaft 9 to perform various processes on the work material. The various types of processing include, for example, drilling using a drill, a tap or the like, side processing using an end mill, a milling cutter, or the like.

  The operation panel 15 (see FIG. 3) is provided on the outer wall of a cover (not shown) that covers the machine tool 1, for example. The operation panel 15 includes an input unit 24 and a display unit 25. The input unit 24 accepts inputs such as various information and operation instructions, and outputs various input information to the numerical control device 30. The display unit 25 displays various screens based on commands from the numerical control device 30.

  The structure of the table moving mechanism 10 will be described with reference to FIG. The table moving mechanism 10 shown in FIG. 2 is an X-axis / Y-axis ball screw drive system mechanism. FIG. 2 shows a simplified main part of the table moving mechanism 10 shown in FIG.

  The table moving mechanism 10 includes a table 13, a Y-axis table 12, an X-axis motor 53, a Y-axis motor 54, and the like. The table 13 is a work table that holds a work material on the upper surface. The Y-axis table 12 supports the table 13 on the upper surface so as to be movable in the X-axis direction (left-right direction), and is movable in the Y-axis direction (front-rear direction) at the center of the upper surface of the base 2.

  The table moving mechanism 10 includes a pair of Y-axis linear guide 61, Y-axis ball screw 62, and Y-axis motor 54 at the center of the upper surface of the base 2. The Y-axis linear guide 61 extends in the Y-axis direction and guides the Y-axis table 12 in the Y-axis direction. The Y-axis ball screw 62 is disposed between the pair of Y-axis linear guides 61. The Y-axis table 12 includes a nut (not shown) on the lower surface. The nut is screwed into the Y-axis ball screw 62. The Y-axis motor 54 rotates the Y-axis ball screw 62 in the forward and reverse directions. Therefore, the Y-axis table 12 moves in the Y-axis direction together with the nut.

  The Y-axis table 12 includes a pair of X-axis linear guides 63, an X-axis ball screw 64, and an X-axis motor 53 on the upper surface. The X-axis linear guide 63 extends in the X-axis direction and guides the table 13 in the X-axis direction. The X-axis ball screw 64 is disposed between the pair of X-axis linear guides 63. The table 13 includes a nut (not shown) on the lower surface. The nut is screwed into the X-axis ball screw 64. The X-axis motor 53 rotates the X-axis ball screw 64 in the forward and reverse directions. Therefore, the table 13 moves in the X-axis direction together with the nut. Therefore, the table 13 also moves in the Y-axis direction via the Y-axis table 12. That is, the table 13 can move in the X-axis direction and the Y-axis direction.

  With reference to FIG. 3, the electrical configuration of the numerical controller 30 and the machine tool 1 will be described. The numerical control device 30 includes a CPU 31, a ROM 32, a RAM 33, a storage device 34, an input / output unit 35, drive circuits 51A to 55A, and the like. The CPU 31 performs overall control of the numerical control device 30. The ROM 32 stores a main program, a lost motion compensation amount calculation program, various programs including a compensation program, and the like. The main program executes main processing. The main process reads the NC program line by line and executes various operations. The NC program is composed of a plurality of lines including various control commands, and controls various operations including axis movement of the machine tool 1, tool change, etc. in line units. The lost motion compensation amount calculation program measures a lost motion amount generated in the table moving mechanism 10 and calculates a compensation parameter by executing a lost motion compensation amount calculation process (see FIGS. 5 and 13) described later. The compensation program compensates for an error in the position of the table 13 specified by the NC program based on the compensation parameter calculated by the lost motion compensation amount computation processing by executing compensation processing (see FIG. 22) described later. The RAM 33 temporarily stores various information. The storage device 34 is nonvolatile and stores various information such as an NC program and a reference error average value described later. The CPU 31 can store, in the storage device 34, an NC program read by an external input in addition to the NC program input by the operator through the input unit 24 of the operation panel 15.

  The drive circuit 51A is connected to the Z-axis motor 51 and the encoder 51B. The drive circuit 52A is connected to the spindle motor 52 and the encoder 52B. The drive circuit 53A is connected to the X-axis motor 53 and the encoder 53B. The drive circuit 54A is connected to the Y-axis motor 54 and the encoder 54B. The drive circuit 55A is connected to a magazine motor 55 that drives the tool magazine 21 and an encoder 55B. The Z-axis motor 51, the main shaft motor 52, the X-axis motor 53, the Y-axis motor 54, and the magazine motor 55 are all servo motors. The drive circuits 51A to 55A receive position commands from the CPU 31 and output position command signals to the corresponding motors 51 to 55, respectively. The position command signal is a pulse signal (drive current). The drive circuits 51A to 55A receive encoder information from the encoders 51B to 55B and perform feedback control of position and speed. The encoder information includes various information such as a torque monitor value, speed, position, and position deviation. The CPU 31 can read the encoder information via the input / output unit 35. The input / output unit 35 is connected to the input unit 24 and the display unit 25 of the operation panel 15, respectively.

  With reference to FIG. 4, the outline of the lost motion compensation amount calculation process using the laser displacement meter 80 will be described. When the moving direction of the table 13 of the table moving mechanism 10 is reversed, the table moving mechanism 10 has a deviation (delay) due to elastic deformation. The deviation is a lost motion. In the lost motion compensation amount calculation processing described later in the present embodiment, the measurement beam splitter 70 is supported and fixed on the table 13 and the table 13 is linearly reciprocated in the X-axis direction or the Y-axis direction. The laser displacement meter 80 continuously measures the relative position of the beam splitter 70 relative to the mirror 8 attached to the tip of the main shaft 9 at predetermined time intervals. The numerical control device 30 compares a path connecting a plurality of relative positions measured every predetermined time with the laser displacement meter 80 and a path connecting a plurality of command positions corresponding to respective measurement times of the relative positions. By doing so, the amount of lost motion is calculated with high accuracy.

  A first embodiment of lost motion compensation amount calculation processing will be described with reference to FIGS. In the first embodiment, in order to explain the features of the present invention in an easy-to-understand manner, the measurement time for the relative position and the command position is the same time, and the command position is assumed to be not interpolated with an acceleration / deceleration time constant. When the operation panel 15 receives an operation for executing the lost motion compensation amount calculation process, the CPU 31 reads the lost motion compensation amount calculation program (first embodiment) stored in the ROM 32 and executes this process.

  As shown in FIG. 5, the CPU 31 starts reciprocating movement of the measurement target axis of the machine tool 1 (S1). The measurement target axis is, for example, the X-axis direction. The conditions for the reciprocating movement are, for example, a feeding speed of 1 mm / min and a moving distance of 1 mm. The CPU 31 starts reciprocating the table 13 in the X-axis direction under the above conditions. The CPU 31 measures the relative position (coordinates) of the table 13 (beam splitter 70) with respect to the mirror 8 attached to the tip of the main spindle 9 at a predetermined time with a laser displacement meter 80 (see FIG. 4) (S2). The position is stored in the RAM 33 together with the measurement time (S3). In order to minimize the influence of disturbances other than lost motion during reciprocating movement, the feed speed is low.

The reason for lowering the feed rate will be described. There are two main reasons.
In high-speed movement, a large acceleration is generated when the moving direction of the table 13 is reversed, the table moving mechanism 10 is bent due to the acceleration, and the amount of lost motion due to the frictional force cannot be measured.
When a general-purpose laser displacement meter 80 or the like is used, the measurement interval may be long, and therefore the feed rate of the table 13 needs to be slowed down for accurate measurement.

In the present embodiment, the parameters for determining the feed rate of the table 13 are, for example, the rigidity of the moving mechanism of the measurement target axis is K [N / m], the maximum acceleration of the moving body is α [m / s ² ], The mass of the moving body is M [kg], and the feeding speed is v [m / s]. When the time constant until the table 13 reaches the maximum speed is t1 [s], α = v / t1. When the X axis is the measurement target axis, the stiffness K is the stiffness of the X axis table moving mechanism 10. At this time, M (2 × v / t1) / K [m] is elastic deformation caused by acceleration when the moving direction is reversed. The lost motion to be measured is the elastic deformation of the table moving mechanism 10 caused by the friction force when the moving direction is reversed. Therefore, when the magnitude of the friction force of the table moving mechanism 10 is F [N], 2 × F / K [m ]. The frictional force F of the table moving mechanism 10 can be obtained by a method such as measuring a motor current (torque) while moving the table 13 at a constant speed. At this time, it is possible to consider that M (2 × v / t1) / K + 2 × F / K≈2 × F / K by determining the feed speed v such that F >> M (v / t1). Ignoring the influence of elastic deformation due to acceleration, the lost motion can be measured accurately. Specifically, the feed of the table 13 is such that M (2 × v / t1) / K is sufficiently small with respect to the lost motion 2 × F / K [m] to be measured, for example, 0.1 μm or less. The speed v [mm / s] may be determined. Alternatively, the relative position interval obtained from the relationship between the measurement time interval t [s] of the general-purpose laser displacement meter 80 and the feed speed v [m / s] is vt, and vt corresponds to the magnitude of the lost motion to be measured. If it is large, the state of change in the lost motion cannot be captured. Therefore, v may be set so that vt is 0.5 μm or less, for example. However, even in this case, v needs to satisfy F> M (v / t1). There is no particular reference to the lower limit value of the feed speed v [m / s], but the time required for measurement increases as v is decreased, and the capacity of the RAM 33 required to store the measured position is also increased. Since it increases, it is desirable to use a value slightly smaller than the upper limit obtained above. The feed rate v may be a minimum unit that can be input as a parameter. For example, if the minimum unit that can be input as a parameter is 1 (mm / s), it is 1. Therefore, the numerical controller 30 can minimize the influence of the acceleration / deceleration torque in the reciprocating movement of the table 13.

  CPU31 memorize | stores the command position corresponding to each of the several relative position measured for every predetermined time in RAM33 (S4). The command position means a position specified by a position command generated by the CPU 31. The CPU 31 determines whether or not the reciprocation of the table 13 has been completed (S5). Until the reciprocating movement is completed (S5: NO), the CPU 31 returns to S2, and continuously measures and stores the relative position and the command position (S2 to S4). When the reciprocation of the table 13 is completed (S5: YES), the RAM 33 stores all data (corresponding to the first information of the present invention) for each relative position measurement time in the reciprocation of the table 13 and every measurement time of the command position. All data (corresponding to the second information of the present invention) are stored. The CPU 31 calculates a position correction value in order to make the reversal positions in the respective loci of the relative position and the command position coincide (S6). The position correction value is a value for correcting by adding to all data of the command position.

  The position correction value will be described. 6A shows the locus of the relative position during the reciprocating movement, and FIG. 6B shows all the data for each measurement time of the relative position during the reciprocating movement. As shown in FIG. 6A, the path from the movement start position to the reverse position is the forward path, and the path from the reverse position to the movement start position is the return path. The reverse position in the locus of the relative position is 0.950 [mm] at which the relative position becomes maximum 1.2 [s] after the start of measurement. The locus of the relative position has a mountain shape with an apex at 0.950 [mm]. FIG. 7 (a) is obtained by superimposing the locus of the command position during the reciprocating movement on the locus of the relative position shown in FIG. 6 (a). FIG. 7B shows all data for each measurement time of the command position during the reciprocating movement. The inversion position in the command position trajectory is 1.00 [mm] at which the command position becomes maximum 1.1 [s] after the start of measurement. The inversion position of the command position is larger than the inversion position of the relative position, and the difference is the distance P. The distance P is −0.05 [mm], which is a position correction value for matching the reverse position of the relative position with the reverse position of the command position. CPU31 adds -0.05 [mm] which is a position correction value with respect to all the data of a command position (S7). As a result, as shown in FIGS. 8A and 8B, the locus of the command position moves downward, and the reverse position of the relative position and the reverse position of the command position coincide with each other at 0.950 [mm].

  As shown in FIG. 8A, the reversal position of the relative position matches the reversal position of the command position, but the locus portions before each reversal position are shifted from each other. Subsequently, the CPU 31 calculates a time correction value in order to match the respective loci of the forward position before the reversal position of the command position with the relative position (S8). The time correction value is a value that minimizes the average value of the error between the relative position and the command position at the same time in a certain section in the forward path before the reverse position.

  The time correction value will be described. As shown in FIG. 8 (a), the average value of the error between the command position and the relative position at the same time is calculated in a section where the relative position is 0.250 mm to 0.900 mm, for example, and the error is minimized. Is obtained as a time correction value. The time correction value in the first embodiment is, for example, 0.1 [s]. The CPU 31 adds the time correction value to all the data at the command position to which the position correction value has been added in S7 (S9). As a result, as shown in FIGS. 9 (a) and 9 (b), the locus of the command position moves to the right and ranges from 0.250 mm to 0.900 mm before reaching the reverse position of 0.950 [mm]. Thus, the respective loci of the relative position and the command position substantially coincide with each other.

  As shown in FIGS. 9A and 10, the difference between the relative position and the command position at the same time after the reverse position has passed corresponds to the amount of lost motion generated on the X axis of the table moving mechanism 10. Therefore, the CPU 31 subtracts all data of the command position corrected for time and position from all data of the relative position, and calculates a lost motion amount for each measurement time (S10). As shown in FIGS. 10 and 11, the lost motion amount rapidly increases after 1.2 [s] after reaching the reverse position from the start of the reciprocating movement, and is constant after 1.4 [s] from the start of the reciprocating movement. Is shown.

  The CPU 31 calculates the lost motion compensation amount based on the calculated lost motion amount (S11). The CPU 31 calculates a compensation parameter based on the calculated lost motion compensation amount and stores it in the storage device 34 (S12). In the chart shown in FIG. 12, the change in the lost motion amount before and after the reversal position is indicated by a solid line, and the change in the lost motion compensation amount corresponding to the change is indicated by a dotted line. Since the lost motion amount increases in relation to the distance from the reversal position, for example, the lost motion amount can be approximated as a linear function, and the maximum amount and inclination of the lost motion amount can be approximated as a compensation parameter. At this time, the compensation parameter for the lost motion amount and the inclination can be obtained by optimization using the least square method so that the sum of squares of errors with the approximate function is minimized, for example. In addition, the lost motion amount may be approximated using, for example, an exponential function, a trigonometric function, a hyperbolic function, or the like. For the calculation of the compensation parameter, the maximum value or the average value of the error from when the moving direction of the table 13 is reversed to when traveling a certain distance may be used. As an optimization algorithm, the steepest descent method or Newton method may be used.

  The CPU 31 calculates the compensation parameter as described above and stores it in the storage device 34 (S11), and then ends this process. The CPU 31 can calculate the compensation parameter of the lost motion compensation amount in the Y axis direction by executing the lost motion compensation amount calculation process (first embodiment) using the Y axis as the measurement target axis in the same manner as the X axis. It can be stored in the storage device 34. Therefore, the CPU 31 can store the compensation parameter for each drive axis of the table moving mechanism 10 in the storage device 34.

  A second embodiment of the lost motion calculation process will be described with reference to FIGS. The second embodiment will be described assuming that the measurement times of the relative position and the command position are different from each other, and the command position is interpolated with an acceleration / deceleration time constant. When a general-purpose laser displacement meter 80 is used, the measurement interval of the laser displacement meter 80 may be longer than the measurement interval of the command position. Therefore, the trajectory of the relative position and the trajectory of the command position may be greatly shifted on the time axis. As in the first embodiment, with respect to the trajectory of the forward path portion before the reversal position of each of the relative position and the command position, the correction process for adjusting the time after matching each reversal position is performed only once. In some cases, the trajectories cannot be matched. When the command position is interpolated with an acceleration / deceleration time constant, the peak shape of the trajectory of the command position draws a gentle curve. Therefore, it is difficult to make the locus before the reversal position coincide with each other only by performing the correction process once. The second embodiment performs a correction process for adjusting the reversal position after correcting the trajectory of the command position in a certain section before the reversal position with time, and repeatedly until the relative position and the trajectory of the command position before the reversal position match. .

  When the operation panel 15 receives an operation to execute the lost motion compensation calculation process, the CPU 31 reads the lost motion calculation program (second embodiment) stored in the ROM 32 and executes the process shown in FIG. Since the process of S1-S5 is the same as the lost motion compensation calculation process (refer FIG. 5) of 1st Example, description is abbreviate | omitted. When the reciprocating movement of the table 13 is completed (S5: YES), the CPU 31 executes a time correction value calculation process (S31). The time correction value is a value for correction by adding to all data of the command position.

  FIG. 14A shows the locus of the relative position during the reciprocating movement, and FIG. 14B shows all the data for each measurement time of the relative position during the reciprocating movement. In the second embodiment, as described above, since the command position is interpolated with the acceleration / deceleration time constant, the peak shape of the trajectory of the command position is gently curved. Therefore, the maximum value in the locus of the command position is not always the reverse position. Therefore, in the second embodiment, in the respective trajectories of the relative position and the command position, the slope of the straight line connecting the point of interest and the point immediately before it is downward and the point of interest and the point after it are The first point in time at which the slope of the connecting line falls to the right is defined as the inversion position.

  The path from the movement start position to the reversal position is the forward path, and the path from the reversal position to the movement start position is the return path. The inversion position in the locus of the relative position is 0.880 [mm] after 1.4 [s] from the start of measurement. The trajectory of the relative position has a mountain shape with the apex at 0.908 [mm], which is the maximum value immediately before the reversal position. FIG. 15A is obtained by superimposing the locus of the command position during the reciprocating movement on the locus of the relative position shown in FIG. FIG. 15B shows all data for each measurement time of the command position during the reciprocating movement. The inversion position in the command position locus is 0.970 [mm] after 1.3 [s] from the start of measurement. The trajectory of the command position has a mountain shape with the peak at 1.000 [mm], which is the maximum value immediately before the reverse position. The inversion position of the command position is larger than the inversion position of the relative position.

  As shown in FIG. 15A, the trajectories before the relative position and the inversion position of the command position are shifted from each other. In order to make each locus part in the forward path before the reversal position of the relative position and the command position coincide with each other, the CPU 31 executes time correction value calculation processing (S31). The time correction value of the second embodiment is a value that minimizes the average value of the error between the relative position and the command position at the same time in a certain section before the reversal position. For example, the CPU 31 calculates the average value of the error between the command position and the relative position at the same time in the interval where the relative position is 0.250 mm to 0.800 mm, and obtains the time when the error is the minimum as the time correction value. The time correction value is 0.15 [s]. The CPU 31 adds the time correction value to all the data at the command position stored in the RAM 33 (S32). As a result, as shown in FIGS. 16 (a) and 16 (b), the trajectory of the command position moves to the right and reaches 0.280 mm to 0.800 mm before reaching 0.880 [mm], which is the reverse position of the relative position. In the sections up to this point, the loci of the relative position and the command position almost coincide with each other.

  Next, the CPU 31 executes position correction value calculation processing so that the reverse position of the relative position overlaps the path of the command position (S33). As shown in FIG. 17, the reverse position of the relative position is 0.880 [mm] (see FIG. 14). The command position at the same time (after 1.4 [s]) is 0.985 [mm]. Therefore, the position correction value is 0.880−0.985 = −0.105 [mm]. The CPU 31 adds the position correction value to all the data of the command position corrected with the time correction value (S34). As a result, as shown in FIGS. 18A, 18B, and 19, the reverse position of the relative position overlaps the path of the command position.

  As shown in FIG. 19, as a result of adding the position correction value to all the data of the command position, the trajectory portion in the forward path before the reverse position of the command position and the relative position is shifted again. The CPU 31 determines whether the average value of the error between the relative position and the command position at the same time in the fixed section before inversion is smaller than the reference error average value (S35). The reference error average value is stored in advance in the storage device 34 (see FIG. 3). For example, the CPU 31 determines whether the average value of the error between the relative position and the command position at the same time is smaller than the reference error average value in the interval where the relative position is 0.250 mm to 0.800 mm. When it is equal to or larger than the reference error average value (S35: NO), the trajectory before the inversion position of the command position and the relative position is greatly deviated. Then, the time correction value and the position correction value are calculated again, and the trajectory of the command position is corrected again (S31 to S34). The CPU 31 repeatedly executes the processes of S31 to S34 until the average value of the error between the relative position and the command position becomes smaller than the reference error average value.

  When the average value of the error between the relative position and the command position becomes smaller than the reference error average value (S35: YES), the command position and the locus before the reverse position of the relative position match. In this embodiment, as shown in FIGS. 20A, 20B and 21, when the time correction value is 0.08 [s] and the position correction value is -0.075 [mm], the relative position is reversed. The position overlaps the path of the command position, and the trajectory of the command position and the relative position before the reversal position substantially coincides. Therefore, as in the first embodiment, the CPU 31 subtracts all data at the command position corrected for time and position from all data at the relative position, and calculates a lost motion amount for each measurement time (S10). Since the processing of S10 to S12 is the same as that of the first embodiment, the description thereof is omitted. The CPU 31 can calculate the compensation parameter of the lost motion compensation amount in the Y axis direction by executing the lost motion compensation amount calculation process (second embodiment) using the Y axis as the measurement target axis in the same manner as the X axis. It can be stored in the storage device 34. Therefore, the CPU 31 can store the compensation parameter for each drive axis of the table moving mechanism 10 in the storage device 34.

  The compensation process will be described with reference to FIG. When the CPU 31 executes a position command for designating the position of the table 13 based on the NC program stored in the storage device 34, the CPU 31 reads the compensation processing program stored in the ROM 32 and executes this processing. For example, when executing a movement command of the table 13 in the X-axis direction, the CPU 31 generates a position command signal in the X-axis direction (S21). The CPU 31 specifies the relative position from the reversal position where the moving direction of the table 13 is reversed (S22). Based on the compensation parameters stored in the storage device 34, the CPU 31 calculates a lost motion compensation amount corresponding to the specified relative position as shown in FIG. 12 (S23). The CPU 31 generates a lost motion compensation signal based on the calculated lost motion compensation amount (S24). The CPU 31 adds the generated lost motion compensation signal to the position command signal generated in S21 (S25), inputs it to the drive circuit 53A (see FIG. 3) (S26), and ends this process. Therefore, since the CPU 31 can move the table 13 to a position where the amount of lost motion is compensated, the processing accuracy of the work material can be improved.

  23 and 24, the effect of the lost motion compensation calculation process will be verified. In this embodiment, two verification tests were performed. The first test is a simulation that compensates for an error in the position of the table 13 when the table 13 is reciprocated based on the compensation parameter calculated in the second embodiment. In FIG. 23, the thick line shows the simulation result of the error before compensation, and the thin line shows the simulation result of the error after compensation. The error before compensation occurs rapidly after the reversal position (position about 30000 [s] after the start of movement) where the moving direction of the table 13 is reversed, and increases to about -0.0020 [mm]. did. On the other hand, since the error after compensation is maintained in the vicinity of 0, it was confirmed that the error caused by the lost motion can be compensated.

  The second test is based on the result of the first test and measures the error in the position of the table 13 when the table 13 is actually reciprocated based on the compensation parameter calculated in the second embodiment. The conditions for reciprocal movement were a feed rate of 1 mm / min and a moving distance of 1 mm. As shown in FIG. 24, as in the simulation result of FIG. 23, since the error was maintained near 0, it was proved that the error caused by the lost motion can be almost eliminated.

  As described above, the numerical controller 30 of the above embodiment controls the operation of the machine tool 1. The machine tool 1 includes a table moving mechanism 10. The table moving mechanism 10 is an X-axis / Y-axis ball screw drive system mechanism, and can move the table 13 in the X-axis direction and the Y-axis direction. The CPU 31 generates a position command for designating the position of the table 13 based on the NC program, and controls the X-axis motor 53 and the Y-axis motor 54. The CPU 31 executes a lost motion compensation amount calculation process. The lost motion compensation amount calculation processing calculates a compensation parameter for compensating for lost motion caused by frictional force after the moving direction of the table 13 is reversed.

  In the lost motion compensation amount calculation processing, the CPU 31 measures the relative position of the table 13 with respect to the tip of the spindle 9 during the reciprocating movement every predetermined time using the laser displacement meter 80 and stores it in the RAM 33 together with the measurement time. The CPU 31 acquires the command position generated when measuring the relative position, and stores it in the RAM 33 together with the measurement time. The CPU 31 corrects the position and measurement time of all data of the command position with respect to the relative position in order to make the portions before the reversal position in the respective loci of the relative position and the command position coincide with each other. The difference between the relative position and the command position at the same time after passing the reversal position corresponds to the amount of lost motion generated on the drive shaft of the table moving mechanism 10. Therefore, the CPU 31 can easily calculate the lost motion amount for each measurement time by subtracting all the data for the command position corrected for the position and the measurement time from all the data for the relative position. The CPU 31 calculates a compensation parameter based on the calculated lost motion amount. The CPU 31 generates a compensation signal based on the calculated compensation parameter, and adds the generated compensation signal to the position command, thereby moving the table 13 to a position where the lost motion amount is compensated.

  In the lost motion compensation amount calculation processing, the relative positions measured when the table 13 is linearly reciprocated in the X-axis direction or the Y-axis direction are compared with the respective loci of the command position, so that the linear portions of the respective loci can be compared. Therefore, the portions before the reversal position in the respective loci of the relative position and the command position are made to coincide with each other, and the error generated after the reversal position can be calculated as the lost motion amount. In this embodiment, even if the laser displacement meter 80 with a long measurement interval is used, the lost motion can be measured with high reproducibility and high accuracy. Even if the measurement time of the command position and the measurement interval of the laser displacement meter 80 are different, the amount of lost motion can be measured with high accuracy. Since the distance for moving one drive shaft at the time of measuring the relative position may be short, even when a jig (not shown) or the like is mounted on the machine tool 1 at the time of measurement, it does not easily interfere with the table 13.

  In the lost motion compensation amount calculation processing, filter processing may be performed to remove noise caused by vibration of the floor or the machine itself, which is included in the relative position measured using the laser displacement meter 80. When performing the filter process, it is necessary to process not only the relative position but also the command position with the same filter in order to match the phase of the relative position and the command position. However, if the cutoff of the filter is lowered, the lost motion that is the measurement target is also attenuated, so it is necessary to use a filter with an appropriate cutoff. Since the measurement of the relative position by the laser displacement meter is easily affected by noise due to vibration, the amount of lost motion can be accurately measured by using a filter having an appropriate cut-off.

  In the first embodiment of the lost motion compensation amount calculation process, the CPU 31 calculates a position correction value and adds it to all data of the command position in order to make the portions of the relative position and the command position before the reverse position coincide with each other. To do. The position correction value is a value for matching the reverse position of the relative position with the reverse position of the command position. After correcting the command position with the position correction value, the CPU 31 calculates a time correction value and adds it to all data of the command position corrected with the position correction value. The time correction value is a time when the average value of the error between the command position and the relative position at the same time is calculated in a certain section before the relative position is reversed, and the error is minimized. Therefore, the CPU 31 can easily and quickly match the portions before the reversal positions in the respective loci of the relative position and the command position.

  In the second embodiment of the lost motion compensation amount calculation process, the CPU 31 calculates the time correction value, contrary to the first embodiment, in order to make the portions of the relative position and the command position before the reverse position coincide with each other. And added to all data at the command position. The time correction value is a value that minimizes the average value of the error between the relative position and the command position at the same time in a certain section before the reverse position. After correcting with the command position time correction value, the CPU 31 calculates the position correction value and adds it to all data of the command position. The position correction value is a value for causing the reversal position of the relative position to overlap the path of the command position. Therefore, the CPU 31 can easily and quickly match the portions before the reversal positions in the respective loci of the relative position and the command position.

  In the second embodiment, in one correction in which the time correction value and the position correction value are added to the command position, the relative position and the locus before the inversion position of the command position may not be matched. After correcting with the time correction value and the position correction value, the CPU 31 determines whether the average value of the error between the relative position and the command position in the same time in the fixed section before inversion is smaller than the reference error average value. When the average error value is equal to or greater than the reference error average value, the locus before the reversal position of the relative position and the command position is greatly shifted. The CPU 31 calculates the time correction value and the position correction value with respect to the command position corrected with the time correction value and the position correction value until the average error value becomes smaller than the reference error average value, and converts it into all data of the command position. Repeat the correction to be added. Therefore, the relative position and the locus before the inversion position of the command position can be matched as much as possible.

  In the embodiment, the amount of lost motion is measured using the laser displacement meter 80. Since the laser displacement meter 80 which is a general-purpose measuring device can be used, it is not necessary to set another measuring device specially for the lost motion measurement. Therefore, there is no problem that preparation takes time like a ball bar or a grid encoder. By using the laser displacement meter 80, there is no problem of accuracy compared to the case of using an acceleration pickup, and high-precision measurement can be performed.

  In the manufacture of the machine tool 1, the inspection process, and the like, the laser displacement meter 80 may already be used to measure the accuracy of the machine tool. Therefore, in the above embodiment, the inspection of all the lost motions of the machine tool 1 and the adjustment of the compensation parameters can be easily performed with almost no additional man-hours.

  In the above description, the machine tool 1 is an example of the machine of the present invention. The table moving mechanism 10 is an example of the moving mechanism of the present invention. The table 13 is an example of the moving body of the present invention. The X-axis motor 53 and the Y-axis motor 54 are examples of the motor of the present invention. The CPU 31 that executes the process of S21 in FIG. 22 is an example of the motor control means of the present invention. The CPU 31 that executes the lost motion compensation amount calculation processing of FIGS. 5 and 13 is an example of a calculation means. The CPU 31 that executes the process of S25 in FIG. 22 is an example of the adding means of the present invention. The mirror 8 provided at the tip of the main shaft 9 is an example of the reference object of the present invention. The CPU 31 that executes the processes of S1 to S3 in FIGS. 5 and 13 is an example of the measuring means of the present invention. The CPU 31 that executes the processes of S6 to S10 in FIG. 5 and the processes of S31 to S34 and S10 in FIG. 13 is an example of the calculating means of the present invention. The CPU 31 that executes the processes of S11 and S12 in FIGS. 5 and 13 is an example of the compensation amount calculating means of the present invention. In the first embodiment of the lost motion compensation amount calculation process, the CPU 31 that executes the processes of S6 and S7 in FIG. 5 is an example of the first correction means of the present invention. The CPU 31 that executes the processes of S8 and S9 is an example of the second correction means of the present invention. In the second embodiment of the lost motion compensation amount calculation process, the CPU 31 that executes the processes of S31 and S32 in FIG. 13 is an example of the third correction means of the present invention. The CPU 31 that executes the processes of S33 and S34 is an example of a fourth correction unit of the present invention. The lost motion compensation amount calculation process of FIGS. 5 and 13 is an example of a calculation process. The process of S25 in FIG. 22 is an example of the adding step of the present invention. The processing of S1 to S3 in FIGS. 5 and 13 is an example of the measurement process of the present invention. The processes in S6 to S10 in FIG. 5 and the processes in S31 to S34 and S10 in FIG. 13 are examples of the calculation process of the present invention. The processing of S11 and S12 in FIGS. 5 and 13 is an example of the compensation amount calculation step of the present invention. The processes in S6 to S9 in FIG. 5 and the processes in S31 to S34 in FIG. 13 are examples of the correction process of the present invention.

  Needless to say, the present invention is not limited to the above-described embodiment, and various modifications are possible. In the above embodiment, the laser displacement meter 80 is used to measure the relative position, but other general-purpose displacement meters, for example, image recognition, can be used as long as the device can accurately measure the single axis movement of the machine tool 1. The displacement meter used may be used.

  In the first embodiment of the lost motion compensation amount calculation process shown in FIG. 5, the position of the locus before the inversion position of the command position is corrected by adding the position correction value and the time correction value to the command position for correction. It is made to correspond to the locus part before the reversal position. In the above embodiment, by correcting the relative position by adding the position correction value and the time correction value, the locus portion before the reversal position of the relative position can be matched with the locus portion before the reversal position of the command position. Good. Similarly, in the second embodiment, by correcting the relative position by adding the position correction value and the time correction value, the locus portion before the reversal position of the relative position becomes the locus portion before the reversal position of the command position. You may match.

  When the time correction value is added to all the data of the command position in the process of S9 in FIG. 5, if the portions before the reverse position in the respective loci of the relative position and the command position do not match each other, until they match each other Alternatively, the processes of S6 to S9 may be repeatedly executed until the average value of the error between the relative position and the command position at the same time in a certain section before inversion becomes smaller than the reference error average value.

  In the above embodiment, the X axis and the Y axis, which are drive axes of the table moving mechanism 10, are the measurement target axes. Similarly, in the Z axis movement mechanism that lifts and lowers the spindle head 7, the Z axis is the measurement target axis. The amount of motion can be measured.

  Although the drive circuits 51A to 55A of the above embodiment are provided in the numerical controller 30, the drive circuits 51A to 55A may be provided in the machine tool 1.

DESCRIPTION OF SYMBOLS 1 Machine tool 4 Tool 9 Spindle 10 Table moving mechanism 13 Table 30 Numerical control apparatus 31 CPU
53 X-axis motor 54 Y-axis motor 62 Y-axis ball screw 64 X-axis ball screw 80 Laser displacement meter

Claims (8)

Controlling a machine having a ball screw and a moving mechanism for moving a moving body fixed to the ball screw and a motor for rotating the ball screw. A position command for designating the position of the body, and in accordance with the position command, motor control means for controlling the motor, and lost that is elastic deformation of the moving mechanism caused by frictional force after the moving direction of the moving body is reversed In a numerical control device comprising: a calculation unit that calculates a compensation amount that compensates for motion; and an addition unit that adds the compensation amount calculated by the calculation unit to the position command to correct the position command.
The computing means is
A measuring means for linearly reciprocating the moving body with respect to a reference object fixed to the machine, and measuring a relative position between the moving body and the reference object every predetermined time;
The motor control unit generates the first information, which is information on the relative position measured by the measuring unit every predetermined time, and the motor control unit at the predetermined time when the measuring unit measures the relative position every predetermined time. Calculation means for calculating the lost motion based on the second information which is information on the command position specified by the position command;
Compensation amount calculation means for calculating the compensation amount based on the lost motion calculated by the calculation means,
The calculating means includes
The first information and the first information and the first information and the first information and the second information so that portions before the moving direction of the moving body in the trajectory of the relative position of the first information and the command position of the second information are reversed. Correction means for correcting at least one of the second information,
A numerical control apparatus, wherein after the correction by the correction means, the difference between the first information and the second information is calculated as the lost motion. The correction means includes
The relative position when the moving direction of the moving body in the first information is reversed and the command position when the moving direction of the moving body in the second information is reversed are matched with each other. First correction means for adding a first correction value, which is a correction value of the distance in the moving direction, to the first information or the second information;
Of the locus of the relative position indicated by the first information after the correction by the first correction means, the first locus portion before the moving direction is reversed and the locus of the command position indicated by the second information The first correction value is a time correction value with respect to the measurement time for each predetermined time by the measurement means of the first information or the second information so that the second locus portion before the moving direction is reversed. Second correction means for adding two correction values,
The numerical control apparatus according to claim 1, wherein after the correction by the second correction unit, a difference between the first information and the second information is calculated as the lost motion. The correction means includes
Of the locus of the relative position indicated by the first information, a third locus portion before the moving direction is reversed and a fourth portion before the moving direction is reversed among the locus of the command position indicated by the second information. Third correction means for adding a third correction value, which is a correction value of time, to the measurement time of the predetermined time by the measurement means of the first information or the second information so that the locus portion matches. When,
After the correction by the third correction means, the relative position when the moving direction of the moving body in the first information is reversed overlaps the locus of the command position, or the second information The command position when the moving direction of the moving body is reversed is a correction value of a distance in the moving direction with respect to the first information or the second information so that the command position overlaps the locus of the relative position. A fourth correction means for adding the four correction values,
The numerical control apparatus according to claim 1, wherein after the correction by the fourth correction unit, the difference between the first information and the second information is calculated as the lost motion. The calculating means includes
The numerical control apparatus according to claim 2 , wherein the correction by the correction unit is repeatedly executed until the first locus portion and the second locus portion coincide with each other.   The calculating means includes
  Repeatedly performing the correction by the correcting means until the third locus portion and the fourth locus portion coincide with each other.
The numerical control device according to claim 3. The measuring means includes
Wherein the movable body and the laser displacement gauge the relative position of the reference object, the numerical control apparatus according to any one of claims 1 5, characterized in that the measuring for each of the predetermined time. The mass of the moving body is M [kg], the feed speed of the moving body is v [m / s], the time constant until the moving body reaches the maximum speed is t1 [s], When the frictional force is F [N],
The measuring means includes
The reference object is linearly reciprocated at a feed speed v such that F> M (v / t1), and the relative position between the moving body and the reference object is measured every predetermined time, numerical control apparatus according to any one of claims 1 to 6, characterized in that to measure only the elastic deformation caused by the frictional force as a lost motion. Controlling a machine having a ball screw and a moving mechanism for moving a moving body fixed to the ball screw and a motor for rotating the ball screw. A position command that specifies the position of the body is generated, and is generated by a frictional force after the moving direction of the moving body is reversed, which is performed by a numerical control device that includes a motor control unit that controls the motor according to the position command. A calculation step of calculating a compensation amount for compensating for lost motion that is elastic deformation of the moving mechanism; and an addition step of correcting the position command by adding the compensation amount calculated in the calculation step to the position command. In the lost motion compensation method of the numerical controller,
The calculation step includes
A measuring step of linearly reciprocating the movable body with respect to a reference object fixed to the machine, and measuring a relative position between the movable body and the reference object at predetermined time intervals;
The motor control unit generates the first information, which is information on the relative position measured at the predetermined time in the measuring step, and the relative position at the predetermined time in the measuring step at the predetermined time. A calculation step of calculating the lost motion based on the second information which is information on the command position specified by the position command;
A compensation amount calculating step of calculating the compensation amount based on the lost motion calculated in the calculating step,
The calculation step includes
The relative position and the command so as to coincide with each other in a portion before the moving direction of the moving body in the trajectory of the relative position in the first information and the command position in the second information is reversed. A correction step of correcting at least one of the positions,
A lost motion compensation method for a numerical controller, wherein the difference between the first information and the second information is calculated as the lost motion after correction in the correction step.

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