CN110875699A

CN110875699A - Interference observer, control device, machine tool, and interference estimation method

Info

Publication number: CN110875699A
Application number: CN201910720856.9A
Authority: CN
Inventors: 寺田弦
Original assignee: Brother Industries Ltd
Current assignee: Brother Industries Ltd
Priority date: 2018-08-31
Filing date: 2019-08-06
Publication date: 2020-03-10
Anticipated expiration: 2039-08-06
Also published as: JP2020035394A; JP7298119B2; CN110875699B

Abstract

The invention provides a disturbance observer, a control device, a machine tool, and a disturbance estimation method, wherein the disturbance observer performs feedback control on a motor based on a command, and acquires position information and current information of the motor to estimate a disturbance acting on the motor. The disturbance observer includes: a constant calculation unit that acquires temperature information of the motor and calculates a torque constant of the motor based on a temperature indicated by the acquired temperature information; a torque calculation unit that calculates a torque of the motor by multiplying the torque constant calculated by the constant calculation unit by the current indicated by the acquired current information; and a torque estimation unit that estimates a torque of the motor based on the position indicated by the acquired position information and a constant of the load machine driven by the motor, wherein the disturbance observer estimates the disturbance by subtracting the torque estimated by the torque estimation unit from the torque calculated by the torque calculation unit.

Description

Interference observer, control device, machine tool, and interference estimation method

Technical Field

Relates to a disturbance observer, a control device, a machine tool and a disturbance estimation method of a feedback control system.

Background

Conventionally, in a feedback control device for a motor, a disturbance that affects a system is estimated by a disturbance observer, and the estimated disturbance is used. When a disturbance observer is used in the feedback control device of the motor, the torque constant is regarded as a fixed value that does not depend on the temperature.

Japanese laid-open patent publication and japanese patent application laid-open No. 03-196313 disclose a collision detection method using a disturbance observer. When the magnitude of the estimated disturbance torque is equal to or greater than a set value, the disturbance observer detects a collision of the driven body and stops the motor.

In the technique disclosed in the above publication, the torque constant Kt that changes with temperature is set to a fixed value. Therefore, when the motor temperature rises, an error of the estimated disturbance torque increases, and even when the driven body does not collide, the collision may be erroneously detected.

Disclosure of Invention

The invention aims to provide a disturbance observer, a control device, a machine tool and a disturbance estimation method, which can reduce the error of estimated disturbance.

The disturbance observer according to claim 1 performs feedback control on a motor based on a command, acquires position information and current information of the motor, and estimates a disturbance acting on the motor, the disturbance observer including: a constant calculation unit that acquires temperature information of the motor and calculates a torque constant of the motor based on a temperature indicated by the acquired temperature information; a torque calculation unit that calculates a torque of the motor by multiplying the torque constant calculated by the constant calculation unit by a current indicated by the acquired current information; and a torque estimation unit that estimates a torque of the motor based on a position indicated by the acquired position information and a constant of a load machine driven by the motor, wherein the disturbance observer subtracts the torque estimated by the torque estimation unit from the torque calculated by the torque calculation unit to estimate the disturbance. The disturbance observer corrects the torque constant according to the temperature of the motor, and therefore can accurately calculate the actual torque of the motor including the torque that is resistant to disturbance, thereby improving the accuracy of calculation of the disturbance.

The command of the disturbance observer according to claim 2 is either one or both of a position command and a speed command.

The disturbance observer performs feedback control of a current of the motor generating a torque of the motor in accordance with the content of the command, and thus converges either or both of a position and a speed of the motor on a target.

The torque estimation unit of the disturbance observer according to claim 3 estimates the torque based on a sum of a product of a rotation speed obtained by first-order differentiating the position indicated by the acquired position information and the viscosity of the load machine, a product of an acceleration obtained by further first-order differentiating the rotation speed and the inertia moment of the load machine, and a coulomb friction force corresponding to the moving direction of the load machine.

The disturbance observer adds a viscous torque calculated by multiplying a rotational speed obtained by first-order differential of a position of the motor by a viscosity of the load machine, an inertia torque calculated by multiplying an acceleration obtained by further first-order differential of the rotational speed by an inertia moment of the load machine, and a coulomb friction force having a sign that is positive/negative depending on a movement direction change of the load machine, to estimate a torque. The disturbance observer estimates the torque of the motor by combining the inertia moment, viscosity, and coulomb friction of the load machine including the motor, and thus can estimate the torque of the motor from which the disturbance is removed with high accuracy.

The constant calculation unit of the disturbance observer according to claim 4 approximates the torque constant by using a polynomial or a piecewise polynomial of degree n (n is an integer of 1 or more) based on a relationship between the torque and the temperature of the motor actually measured in advance.

Therefore, the disturbance observer determines a polynomial to be applied to all or each of the sections in consideration of the curvature, inflection point, and number of actual measurement points of the curve indicated by the actual measurement result, and improves the approximation accuracy of the torque constant in accordance with the degree of the polynomial or the number of sections of the piecewise polynomial.

The disturbance observer according to claim 5 further comprises a table storing a correspondence relationship between the current and the rotational speed of the motor and a torque constant of the motor, wherein the constant calculation unit calculates the torque constant based on a content stored in the table in correspondence with the current indicated by the acquired current information and the rotational speed obtained by first-order differentiating the position indicated by the acquired position information, and the polynomial or piecewise polynomial.

In addition to the above-described polynomial or piecewise polynomial, the correspondence between the current and the rotational speed of the motor and the torque constant of the motor is actually measured in advance and stored in a table. When calculating the torque constant during execution, the torque constant calculated based on the contents stored in the table in association with the current of the motor and the rotation speed of the motor is corrected based on the polynomial or the piecewise polynomial, or the torque constant calculated by applying the detected temperature to the polynomial or the piecewise polynomial is corrected based on the contents stored in the table. Therefore, the disturbance observer can further improve the calculation accuracy of the torque constant and reduce the calculation load.

The disturbance observer according to claim 6 further comprises a table that stores a correspondence relationship between the current and temperature of the motor and a torque constant of the motor, and the constant calculation unit calculates the torque constant based on contents stored in the table in correspondence with the current indicated by the acquired current information and the temperature indicated by the acquired temperature information.

Therefore, the disturbance observer can improve the calculation accuracy of the torque constant and reduce the calculation load.

The disturbance observer according to claim 7 further comprises a table storing a correspondence relationship between the current, the temperature, and the rotation speed of the motor and a torque constant of the motor, and the constant calculation unit calculates the torque constant based on a content stored in the table in correspondence with the current indicated by the acquired current information, the temperature indicated by the acquired temperature information, and the rotation speed obtained by first-order differentiating the position indicated by the acquired position information.

The disturbance observer can further improve the calculation accuracy of the torque constant and reduce the calculation load.

The control device according to claim 8 includes the disturbance observer and a control unit that issues the command.

A disturbance observer that estimates disturbance with high accuracy can be applied to a control device that controls a load machine.

A machine tool according to claim 9 includes the control device, the motor, and the load machine, and further includes: a position detection unit that detects a position of the motor and feeds back position information indicating the detected position; a current detection unit that detects a current of the motor and feeds back current information indicating the detected current; and a temperature detection unit that detects a temperature of the motor and generates temperature information indicating the detected temperature, wherein the disturbance observer acquires the temperature information from the temperature detection unit.

The control unit of the control device issues a command to perform feedback control of the motor that drives the load machine. A disturbance observer of the control device acquires position information and current information of the motor, which are fed back by the position detection unit and the current detection unit, respectively, and temperature information from the temperature detection unit to estimate the disturbance. Therefore, the machine tool can estimate the disturbance acting on the motor via the load machine with high accuracy.

The interference estimation method according to claim 10, which performs feedback control of a motor based on an instruction, and acquires position information and current information of the motor to estimate interference acting on the motor, includes: acquiring temperature information of the motor, and calculating a torque constant of the motor based on a temperature indicated by the acquired temperature information; calculating a torque of the motor by multiplying the calculated torque constant by a current indicated by the acquired current information; estimating a torque of the motor based on a position indicated by the acquired position information and a constant of a load machine driven by the motor; and subtracting the estimated torque from the calculated torque to estimate the disturbance.

Drawings

Fig. 1 is a perspective view showing a machine tool according to embodiment 1.

Fig. 2 is a block diagram showing the control device.

Fig. 3 is a block diagram showing information exchanged between the control device and the X-axis motor.

Fig. 4 is a block diagram showing a functional configuration of the servo circuit.

Fig. 5 is a block diagram showing a functional structure of the disturbance observer.

Fig. 6 is a flowchart showing a processing procedure of the CPU for estimating the disturbance force by the disturbance observer according to embodiment 1.

Fig. 7 is a flowchart showing a processing procedure of the CPU that detects the rotational direction of the motor to calculate the rotational speed and the acceleration.

Fig. 8 is a table showing the contents of a table storing the correspondence relationship between the motor current, temperature, and rotation speed and the torque constant.

Fig. 9 is a flowchart showing a processing procedure of the CPU for estimating the disturbance force by the disturbance observer according to embodiment 2.

Fig. 10 is a table showing the contents of a table storing the correspondence relationship between the motor current and the rotational speed and the torque constant.

Fig. 11 is a flowchart showing a processing procedure of the CPU for calculating a torque constant by the disturbance observer of embodiment 3.

Fig. 12 is an explanatory diagram schematically showing a temperature model of the motor.

Fig. 13 is a graph showing simulation results of temperature changes of respective portions in the motor.

Detailed Description

The present invention will be described in detail below with reference to the drawings showing embodiments of the present invention.

(embodiment mode 1)

In the following description, the upper and lower, left and right, and front and rear directions indicated by arrows in the drawings are used. As shown in fig. 1, a machine tool 100 includes a rectangular base 1 extending in the front-rear direction. The work holding portion 3 is provided on the front side of the upper portion of the base 1. The workpiece holding portion 3 is rotatable about an a axis extending in the left-right direction and a C axis extending in the up-down direction. The support base 2 is provided on the rear side of the upper portion of the base 1 and supports the column 4.

The Y-axis direction moving mechanism 10 (corresponding to a loading machine) is provided above the support base 2 and moves the moving plate 16 in the front-rear direction. The Y-axis direction moving mechanism 10 includes two rails 11 extending in the front-rear direction, a Y-axis screw shaft 12, a Y-axis motor 13, and a bearing 14. Rails 11 are provided on the left and right sides of the upper portion of the support table 2. The Y-axis screw shaft 12 extends in the front-rear direction and is disposed between the two rails 11. The bearing 14 is provided at a tip end portion and a middle portion (not shown) of the Y-axis screw shaft 12. The Y-axis motor 13 is connected to the rear end of the Y-axis screw shaft 12. A nut (not shown) is screwed to the Y-axis screw shaft 12. The plurality of sliders 15 are slidably provided on the respective rails 11. The moving plate 16 extends in the horizontal direction and is coupled to the nut and the upper portion of the slider 15. The Y-axis screw shaft 12 is rotated by rotation of the Y-axis motor 13, the nut moves in the front-rear direction, and the moving plate 16 moves in the front-rear direction.

An X-axis direction moving mechanism 20 (corresponding to a loading mechanism) is provided on the upper surface of the moving plate 16 and moves the column 4 in the left-right direction. The X-axis direction moving mechanism 20 includes two rails 21 extending in the left-right direction, an X-axis screw shaft 22, an X-axis motor 23 (see fig. 2), and a bearing 24. The rails 21 are provided on the front and rear sides of the upper surface of the moving plate 16. The X-axis screw shaft 22 extends in the left-right direction and is disposed between the two rails 21. The bearing 24 is provided at a left end portion and a middle portion (not shown) of the X-axis screw shaft 22. The X-axis motor 23 is connected to the right end of the X-axis screw shaft 22. A nut (not shown) is screwed to the X-axis screw shaft 22. The plurality of sliders 26 are slidably provided on the respective rails 21. The column 4 is connected to the nut and the upper part of the slider 26. The X-axis screw shaft 22 is rotated by rotation of the X-axis motor 23, the nut moves in the left-right direction, and the column 4 moves in the left-right direction.

A Z-axis direction moving mechanism 30 (corresponding to a loading machine) is provided on the front surface of the column 4 and moves the spindle head 5 in the vertical direction. The Z-axis direction moving mechanism 30 includes two rails 31 extending in the vertical direction, a Z-axis screw shaft 32, a Z-axis motor 33, and a bearing 34. The rails 31 are provided on the left and right sides of the front surface of the pillar 4. The Z-axis screw shaft 32 extends in the up-down direction and is disposed between the two rails 31. The bearing 34 is provided at a lower end portion and a middle portion (not shown) of the Z-axis screw shaft 32. The Z-axis motor 33 is connected to an upper end portion of the Z-axis screw shaft 32. A nut (not shown) is screwed to the Z-axis screw shaft 32. The plurality of sliders 35 are slidably provided on the respective rails 31. The spindle head 5 is coupled to the nut and the front portion of the slider 35. The Z-axis screw shaft 32 is rotated by rotation of the Z-axis motor 33, the nut moves in the vertical direction, and the spindle head 5 moves in the vertical direction.

A spindle 51 (corresponding to a loading machine) extending in the vertical direction is provided in the spindle head 5. The main shaft 51 rotates around the shaft. The spindle motor 6 is provided at an upper end portion of the spindle head 5. A tool is attached to the lower end of the spindle 51. The spindle 51 is rotated by the rotation of the spindle motor 6, and the tool is rotated. The rotating tool machines the workpiece held by the workpiece holding portion 3.

As shown in fig. 2, the machine tool 100 includes a control device 60 that controls driving of the spindle motor 6, the Y-axis motor 13, the X-axis motor 23, the Z-axis motor 33, and the like. The control device 60 includes a CPU 61, a ROM 62, a RAM63, a nonvolatile storage device 64 such as an EEPROM, an input interface 65, an input/output interface 66, and the like. The storage device 64 stores machining processes for machining a workpiece. The process sequence includes a plurality of lines (commands). The CPU 61 sequentially reads the lines and issues an instruction for executing a command to drive each unit.

The machine tool 100 further includes a receiving unit 67 (setting unit), a Z-axis sensor 68, and a spindle sensor 69. The receiving unit 67 includes a keyboard, a touch panel, a display screen, and the like, and receives a user operation. The user sets execution of a specific process in the storage device 64 via the receiving unit 67. The Z-axis sensor 68 detects the position of the spindle 51 in the up-down direction (the axial position of the spindle 51). The spindle sensor 69 detects the position of the spindle 51 in the circumferential direction. The control device 60 receives settings from the receiving unit 67 via the input interface 65, receives an axial position from the Z-axis sensor 68, and receives a rotational speed from the spindle sensor 69. The control device 60 issues a position command or a speed command to the spindle motor 6, the X-axis motor 23, the Y-axis motor 13, and the Z-axis motor 33 via the input/output interface 66. The control device 60 also acquires position information and current information of each of the spindle motor 6, the X-axis motor 23, the Y-axis motor 13, and the Z-axis motor 33 via the input/output interface 66.

When the CPU 61 executes the machining process, the CPU 61 issues commands to the spindle motor 6, the X-axis motor 23, the Y-axis motor 13, and the Z-axis motor 33 to control the rotation of the spindle 51 and the movement of the X-axis direction moving mechanism 20, the Y-axis direction moving mechanism 10, and the Z-axis direction moving mechanism 30. The CPU 61 machines a workpiece using a tool attached to the spindle 51.

The flow of information between the X-axis motor 23 and the controller 60 will be described with reference to fig. 3. The Y-axis motor 13, the Z-axis motor 33, and the spindle motor 6 are the same as the X-axis motor 23, and therefore, description thereof is omitted. The control unit 600 and the disturbance observer 610 included in the control device 60 are one of the functional blocks realized by the control device 60. The X-axis motor 23 has a motor 23a that drives the X-axis screw shaft 22 and a servo circuit 230. The servo circuit 230 performs feedback control of the current flowing through the motor 23a based on either or both of the position command and the speed command output from the control unit 600. The current flowing through the motor 23a is detected by the current detection unit 237, and the current detection unit 237 feeds back current information indicating the detected current to the servo circuit 230.

The motor 23a is an AC servomotor having a magnet in a rotor, but is not limited thereto. The rotational position of the motor 23a is detected by an encoder 23b (corresponding to a position detecting unit), and the encoder 23b feeds back position information indicating the detected rotational position to the servo circuit 230 as a pulse signal. The temperature of the motor 23a is detected by the temperature detector 23c, and the temperature detector 23c supplies temperature information indicating the detected temperature to the disturbance observer 610. The temperature detection unit 23c preferably detects the temperature of the magnet of the rotor (hereinafter referred to as magnet temperature). When the magnet temperature cannot be directly detected, the current of the motor 23a and the outside air temperature of the motor 23a may be detected to estimate the magnet temperature (see a simulation described later). Instead of using the magnet temperature, the temperature of the outer wall of the motor 23a, the temperature of the encoder 23b, or the like may be used.

The disturbance observer 610 acquires position information and current information from the servo circuit 230, and acquires temperature information from the temperature detection unit 23c, and estimates a disturbance, that is, a disturbance torque (disturbance force), acting on the motor 23 a. The disturbance observer 610 may acquire the position information and the current information without via the servo circuit 230. When the disturbance force estimated by the disturbance observer 610 exceeds a predetermined threshold value, the control unit 600 can issue a predetermined alarm and issue a command to stop the motor 23 a.

The operation of servo circuit 230 that receives a position command from control unit 600 will be described with reference to fig. 4. The servo circuits of the Y-axis motor 13, the Z-axis motor 33, and the spindle motor 6 are also the same. The servo circuit 230 has an amplifier 231 (position proportional gain), and the amplifier 231 amplifies a position error, which is a difference between a target position included in the position command and a position indicated by the position information fed back from the encoder 23b, to generate a speed command. The servo circuit 230 further has: a differentiator 232 that generates the rotation speed of the motor 23a by first-order differentiating the position indicated by the position information; an amplifier 233 (speed proportional gain) for amplifying a speed error, which is a difference between the speed command generated by the amplifier 231 and the rotational speed generated by the differentiator 232; and an integrator 234 and an amplifier 235 (velocity integrating gain) that integrates and amplifies the velocity error.

The servo circuit 230 performs PI control by using, as a current command, a result obtained by adding an amount proportional to the velocity error amplified by the amplifier 233 and an amount proportional to the integral result of the velocity error amplified by the amplifier 235. The servo circuit 230 further has a current controller 236, and the current controller 236 performs feedback control of the current flowing through the motor 23a based on the current command described above. The current detection unit 237 feeds back current information indicating the detected current to the current controller 236, and the current controller 236 controls the current corresponding to the current command to flow to the motor 23 a.

The operation of the servo circuit 230 when the position command is issued by the control unit 600 has been described above, but the speed command from the control unit 600 may be used instead of the speed command generated by the amplifier 231 when the speed command is issued by the control unit 600. When the control unit 600 simultaneously issues the position command and the speed command, the operations when the respective commands are issued individually may be overlapped.

The operation of the disturbance observer 610 will be described with reference to fig. 5. The same applies to the disturbance observer of the Y-axis motor 13, the Z-axis motor 33, and the spindle motor 6. The disturbance observer 610 includes a constant calculation unit 611, and the constant calculation unit 611 acquires temperature information from the temperature detection unit 23c and calculates a torque constant based on the temperature indicated by the acquired temperature information. The disturbance observer 610 further includes a torque calculation unit 612, and the torque calculation unit 612 calculates the torque of the motor 23a by multiplying the torque constant calculated by the constant calculation unit 611 by the current indicated by the acquired current information. The torque calculated by the torque calculation unit 612 includes torque that is resistant to disturbance. The disturbance observer 610 further has a torque estimation unit 613, and the torque estimation unit 613 estimates the torque of the motor 23a based on the position indicated by the acquired position information and a constant relating to the X-axis direction moving mechanism 20.

The constant calculation unit 611 approximates the torque constant Kt by applying the temperature T indicated by the acquired temperature information to a polynomial or a piecewise polynomial of degree n (n is an integer equal to or greater than 1). The polynomial expression is one of a primary expression of the temperature T as shown in the following expression (1), a secondary expression of the temperature T as shown in the expression (2), and an nth expression of the temperature T as shown in the expression (3) which are determined in advance so as to actually measure the temperature of the motor 23a while changing the temperature. In general, the higher the temperature of the motor 23a, the higher the magnet temperature of the rotor of the motor 23a, and the lower the magnetic flux density of the magnet, so the smaller the torque constant. The relationship between the temperature and the torque of the motor 23a can be actually measured in advance, and an equation that optimally expresses the relationship between the temperature and the torque can be established in consideration of the curvature, the inflection point, and the number of actually measured points of the curve expressed by the actual measurement result.

Kt＝a-bT···(1)

Kt＝a-b(T-c)²···(2)

Kt＝a0+a1T+a2T²+···+anTⁿ···(3)

Wherein a, b, c, a0, a1, a2, · -an are fixed constants or coefficients.

Instead of the above-described equations (1) to (3), a function sj (t) such as the following equation (4) for spline interpolation using the interval [ Tj, Tj +1] (

j

0, 1, 2 · · may be actually measured and determined in advance. In this case, the constant calculation unit 611 defines the value of the function sj (T) defined by the section [ Tj, Tj +1] including the temperature T indicated by the acquired temperature information as the torque constant Kt at the temperature T.

Sj(T)＝aj(T-Tj)³+bj(T-Tj)²+cj(T-Tj)+dj···(4)

Wherein aj, bj, cj, dj are fixed coefficients or constants.

The torque estimating unit 613 includes: a direction detector 614 that detects the rotational direction of the motor 23a, that is, the moving direction of the X-axis direction moving mechanism 20, based on the acquired position information; a differentiator 615 that generates a rotational speed by first-order differentiating the position indicated by the acquired position information; and a differentiator 616 that first-order differentiates the rotational speed generated by the differentiator 615 to generate an acceleration. Further, 617 included in the torque estimating unit 613 in fig. 5 is an output unit that outputs positive or negative coulomb friction force acting on the X-axis direction moving mechanism 20 including the motor 23 a. The multiplier 618 multiplies the viscosity of the X-axis movement mechanism 20 including the motor 23a, and the multiplier 619 multiplies the inertia moment.

The direction detector 614 may calculate the difference between the previous value and the present value of the position information and output the sign of the difference. The direction detector 614 may detect the rotation direction of the motor 23a using a known hardware circuit. The output section 617 outputs positive and negative friction torques based on the detection result of the direction detector 614. The differentiator 615 calculates the difference between the previous value and the present value of the position information and divides the acquisition interval time of the position information, thereby calculating the rotation speed. The differentiator 616 calculates the acceleration by calculating the difference between the previous value and the present value of the rotation speed calculated by the differentiator 615 and dividing by the acquisition interval time of the position information. The multiplier 618 multiplies the rotational speed generated by the differentiator 615 by the viscosity to output a viscous torque. The multiplier 619 multiplies the acceleration generated by the differentiator 616 by the inertia moment to output an inertia torque. The result of adding the friction torque, the viscous torque, and the inertia torque is the torque estimated by the torque estimation unit 613. The disturbance observer 610 subtracts the torque estimated by the torque estimation unit 613 from the torque calculated by the torque calculation unit 612 (the torque calculated including the torque that is resistant to disturbance) to estimate the disturbance force. The speed of the motor 23a is fixed to a plurality of rotational speeds, and the torque value during rotation is measured, and the viscosity is calculated from the proportional relationship between the speed and the torque value. The acceleration of the motor 23a is fixed to a plurality of accelerations, the torque value during rotation is measured, and the inertia moment is calculated from the proportional relationship between the acceleration and the torque value. As for the inertia moment, a value calculated from a design drawing of the load machine may be used.

The operation of the disturbance observer 610 will be described with reference to fig. 6 and 7. The Y-axis motor 13, the Z-axis motor 33, and the spindle motor 6 are also the same. The process shown in fig. 6 starts at a fixed period (e.g., every 1 ms).

When the process of fig. 6 is started, the CPU 61 acquires temperature information of the motor 23a from the temperature detecting unit 23c (S11), and applies the temperature T indicated by the acquired temperature information to any one of the polynomials of expressions (1) to (3) or the piecewise polynomial of expression (4) to calculate the torque constant Kt (S12: equivalent to the constant calculating unit 611). The CPU 61 causes the torque estimating unit 613 to estimate the torque of the motor 23a based on the rotation direction, the rotation speed, and the acceleration of the motor 23a, which are the processing results of fig. 7 (S13: corresponding to the torque estimating unit 613). The CPU 61 acquires the current information from the current detection unit 237 directly or via the servo circuit 230 (S14), and calculates the torque of the motor 23a by multiplying the current indicated by the acquired current information by the torque constant calculated in step S12 (S15: equivalent to the torque calculation unit 612). The CPU 61 subtracts the torque estimated in step S13 from the calculated torque to estimate a disturbance force as a disturbance torque (S16), and ends the processing of fig. 6.

When the process of fig. 7 is started, the CPU 61 detects the rotational direction of the motor 23a based on the pulse signals of different phases from the encoder 23b (S21: corresponding to the direction detector 614). The output unit 617 shown in fig. 5 outputs a positive or negative frictional force in accordance with the rotation direction detected by the direction detector 614. The CPU 61 calculates the rotation speed of the motor 23a as a value proportional to the reciprocal of the acquisition interval of the position information (S22: equivalent to the differentiator 615). The CPU 61 calculates the acceleration of the motor 23a as a value proportional to the time rate of change of the rotation speed of the motor 23a (S23: corresponding to the differentiator 616), and ends the processing of fig. 7.

In embodiment 1, the torque constant is not dependent on the rotation speed of the motor 23a, but is smaller when the field-weakening control is performed than when the field-weakening control is not performed. In this case, any one of the plurality of equations (1) to (3) or the piecewise polynomial equation of the equation (4) may be determined based on a result of actual measurement so as to change the temperature and the current of the motor 23a in advance. The constant calculation unit 611 may calculate the torque constant using a polynomial or a piecewise polynomial corresponding to the detected current of the motor 23 a.

The torque constant differs depending on whether the motor 23a is in the power running state or the regenerative state. In the regeneration state, any one of the plurality of equations (1) to (3) or the piecewise polynomial of equation (4) may be determined based on a result actually measured in advance so as to change the temperature of the motor 23a and the powering/regeneration state. The constant calculation unit 611 may detect the power running state and the regeneration state of the motor 23a and calculate the torque constant using a polynomial or a piecewise polynomial corresponding to the detected state.

As described above, embodiment 1 calculates the torque constant of the motor 23a based on the temperature of the motor 23a, calculates the torque of the motor 23a by multiplying the calculated torque constant by the current of the motor 23a, estimates the torque of the motor 23a based on the position of the motor 23a and the constant of the X-axis direction movement mechanism 20 driven by the motor 23a, and estimates the disturbance force as the disturbance torque acting on the motor 23a by subtracting the estimated torque of the motor 23a from the calculated torque of the motor 23 a. Since the disturbance observer 610 corrects the torque constant in accordance with the temperature of the motor 23a, the actual torque of the motor 23a including the torque that is resistant to disturbance can be calculated with high accuracy, and the accuracy of calculating the disturbance is improved. Thus, the disturbance observer 610 can reduce the error of the estimated disturbance.

Embodiment 1 controls the current flowing through the motor 23a in accordance with either or both of the issued position command and speed command. Thus, the disturbance observer 610 feedback-controls the current of the motor that generates the torque of the motor 23a according to the content of the command, and hence either or both of the position and the speed of the motor 23a converge on the instructed target.

In embodiment 1, the torque is estimated by adding a viscous torque calculated by multiplying the rotational speed obtained by first-order differentiating the position of the motor 23a by the viscosity of the load machine, an inertial torque calculated by multiplying the acceleration obtained by further first-order differentiating the rotational speed by the inertial torque of the X-axis direction moving mechanism 20, and a coulomb friction force whose sign changes to positive/negative according to the moving direction of the X-axis direction moving mechanism 20. Therefore, the disturbance observer 610 estimates the torque of the motor 23a by combining the inertia moment, viscosity, and coulomb friction of the X-axis direction moving mechanism 20 including the motor 23a, and thus can estimate the torque of the motor 23a from which the disturbance is removed with high accuracy.

In embodiment 1, a polynomial expression or a piecewise polynomial expression is set up n times by actually measuring the relationship between the temperature and the torque of the motor 23a in advance, and the torque constant is approximated by applying the detected temperature of the motor 23a to the expression. Therefore, the disturbance observer 610 determines a polynomial to be applied to all or each of the intervals in consideration of the curvature, inflection point, and number of actual measurement points of the curve indicated by the actual measurement result, and the approximation accuracy of the torque constant is improved by the degree of the polynomial or the number of intervals of the piecewise polynomial.

Further, embodiment 1 can apply the disturbance observer 610 that estimates the disturbance with high accuracy to the control device 60 that controls the X-axis direction moving mechanism 20.

In embodiment 1, the control unit 600 of the control device 60 issues a position command to the servo circuit 230, and the servo circuit 230 that has received the position command performs feedback control on the motor 23a that drives the X-axis direction moving mechanism 20. The disturbance observer 610 of the control device 60 acquires position information and current information of the motor 23a, which are fed back to the servo circuit 230 by the encoder 23b and the current detection unit 237, respectively, and temperature information from the temperature detection unit 23c to estimate the disturbance. Therefore, the disturbance observer 610 can estimate the disturbance acting on the motor 23a with high accuracy via the X-axis direction movement mechanism 20.

(embodiment mode 2)

While in embodiment 1 the constant calculation unit 611 calculates the torque constant using a temperature polynomial or a piecewise polynomial, in embodiment 2 the constant calculation unit 611 reads the contents stored in the table and calculates the torque constant. Further, the relationship of more variables including temperature to the torque constant is stored in the table. In embodiment 2 and embodiment 3 described later, the motor 23a included in the X-axis motor 23 is described, but the other motors included in the Y-axis motor 13 and the Z-axis motor 33 are also the same.

The tables 641, 642, 643 shown in fig. 8 are recorded in the storage device 64, but may be recorded in the ROM 62. Tables 641, 642, 643 store relationships between the current and temperature of the motor 23a and the torque constant when the rotation speed of the motor 23a is 0rpm, 5000rpm, 10000rpm, respectively. The basic table of tables 641, 642, and 643 is a table 641 corresponding to the rotation speed of the motor 23a at 0 rpm. In each table, basically, when the temperature is 0 ℃ and the current is 50A, the torque constant becomes smaller as the temperature becomes higher or the current becomes higher than that.

Table 641 stores torque constants of 1, 0.99, 0.98, and 0.97 at a current of 50A and temperatures of 0 ℃, 10 ℃, 20 ℃, and 30 ℃. This corresponds to a magnetic flux density drop of about 0.1% for a temperature rise of 1 ℃ with a magnet generally used for an AC servomotor. Table 641 shows: when the current is greater than 50A at the same temperature, the torque constant of the motor decreases. The same applies to tables 642 and 643. In table 642, it is assumed that the rotation speed of motor 23a is increased, and therefore, the current of 10A is passed through the field weakening control, and the torque constant is lowered with respect to table 641. In table 643, it is assumed that the field weakening current of 20A flows, and the torque constant further decreases.

A method of calculating a torque constant based on the contents stored in the table shown in fig. 8 will be described with reference to fig. 9. The process shown in fig. 9 is started at a fixed cycle (for example, every 1 ms). The rotation speed and acceleration in the figure are the rotation speed and acceleration of the motor 23a calculated by the CPU 61 through the processing shown in fig. 7 of embodiment 1.

At the start of the process of fig. 9, the CPU 61 acquires the current information from the current detection section 237 directly or via the servo circuit 230 (S31), and acquires the temperature information of the motor 23a from the temperature detection section 23c (S32). The CPU 61 reads out the contents stored in any one of the tables 641, 642, and 643 in association with the current indicated by the acquired current information, the temperature indicated by the acquired temperature information, and the rotation speed of the motor 23a (S33). Specifically, the CPU 61 selects two tables close to the calculated rotation speed, and reads out the contents of four cells close to the acquired current and temperature from each table. More specifically, when the rotation speed is 500rpm, the obtained current is 35A, and the obtained temperature is 5 ℃, the CPU 61 reads 1, 0.99, 1, and 0.99 from the table 641, and reads 0.67, 0.66, 0.6, and 0.59 from the table 642.

Then, the CPU 61 calculates one torque constant by linear interpolation, for example, based on the eight torque constants read out in step S33 (S34: equivalent to the constant calculating unit 611). The CPU 61 causes the torque estimating unit 613 to estimate the torque of the motor 23a based on the rotational direction, rotational speed, and acceleration of the motor 23a (S35: corresponding to the torque estimating unit 613). CPU 61 also multiplies the current indicated by the current information acquired at step S31 by the torque constant calculated at step S34 to calculate the torque of motor 23a (S36: corresponding to torque calculating unit 612). The CPU 61 subtracts the torque estimated in step S35 from the calculated torque to estimate a disturbance force as a disturbance torque (S37), and ends the processing of fig. 9.

The torque constant differs depending on whether the motor 23a is in the power running state or the regenerative state. Therefore, the tables shown in fig. 8 may be prepared for the powering state and the regeneration state, respectively. The power running indicates a state in which the motor 23a performs work on the outside, specifically, a state in which the rotation speed of the motor 23a and the torque have the same sign. The regeneration indicates a state in which work is applied to the motor 23a from the outside, specifically, a state in which the rotation speed of the motor 23a and the torque have different signs.

In embodiment 2, tables 641, 642, and 643 subdivided according to the rotation speed of the motor 23a are used, but the present invention is not limited thereto, and a single table may be used by changing the description method of the tables. When the difference in the rotation speed of the motor 23a is not considered, only the table 641 may be prepared to calculate the torque constant.

As described above, in embodiment 2, the correspondence relationship between the current and temperature of the motor 23a and the torque constant of the motor 23a is actually measured in advance and stored in the table 641, and the torque constant is approximated by interpolating the contents stored in the table 641 in correspondence with the current and temperature of the motor 23a as necessary. Thus, the calculation accuracy of the torque constant of the disturbance observer 610 is improved, and the calculation load can be reduced.

In embodiment 2, the correspondence relationship between the current, temperature, and rotation speed of the motor 23a and the torque constant of the motor 23a is actually measured in advance and stored in the tables 641, 642, and 643, and the contents stored in the tables 641, 642, and 643 in correspondence with the current, temperature, and rotation speed of the motor 23a are read out and interpolated as necessary to approximate the torque constant. Thus, the calculation accuracy of the torque constant of the disturbance observer 610 is higher, and the calculation load can be reduced.

(embodiment mode 3)

In embodiment 1, the constant calculation unit 611 calculates the torque constant using a temperature polynomial or a piecewise polynomial. In embodiment 2, the constant calculation unit 611 reads the contents stored in the table to calculate the torque constant. In contrast, in embodiment 3, the constant calculation unit 611 corrects the torque constant calculated using the temperature polynomial or the piecewise polynomial based on the contents stored in the table, or corrects the torque constant calculated using the temperature polynomial or the piecewise polynomial based on the contents stored in the read table.

The table 644 of fig. 10 is recorded in the storage device 64, but may be recorded in the ROM 62. Table 644 stores torque constants obtained by combining the current of motor 23a at 100A, 75A, 50A, and 25A and the rotation speed of motor 23a at 0rpm, 5000rpm, and 10000 rpm. These torque constants are the same as those at 0 ℃. For example, the torque constant (0.81) at a current of 75A and a rotation speed of 5000rpm is the same as the torque constant at a current of 75A and a temperature of 0 ℃.

In embodiment 3, the relationship between the temperature and the torque constant of the motor 23a is shown in any of equations (1) to (4), and the relationship between the current and the rotation speed of the motor 23a and the torque constant is shown in table 644. When the provisional torque constant a is calculated using any one of the equations (1) to (4), the torque constant a is corrected using the table 644, and the target torque constant is calculated. When the temporary torque constant a is calculated using the table 644, the torque constant a is corrected using any one of the expressions (1) to (4), and the target torque constant is calculated. In order to calculate the temporary torque constant a, one of the expressions (1) to (4) or the table 644 may be used first, or may be determined to be fixed.

A method of calculating a torque constant using any one of equations (1) to (4) and table 644 will be described with reference to fig. 11. The processing shown in fig. 11 is executed by the CPU 61 as a part of the processing of estimating the disturbance force. The rotation speed in the figure is the rotation speed of the motor 23a calculated by the CPU 61 through the processing shown in fig. 7 of embodiment 1.

At the start of the process of fig. 11, the CPU 61 acquires temperature information of the motor 23a from the temperature detection section 23c (S41), and acquires current information from the current detection section 237 (S42). The CPU 61 determines whether any of the polynomials of expressions (1) to (3) or the piecewise polynomial of expression (4) is used first (S43). As described above, the determination may be omitted, and the process may be shifted to the next step S44 or S51.

When the polynomial or the piecewise polynomial is used first (yes in S43), the CPU 61 applies the temperature T indicated by the acquired temperature information to any one of the polynomials of equations (1) to (3) or the piecewise polynomial of equation (4) to calculate the temporary torque constant a (S44). The CPU 61 reads out the contents stored in the table 644 in association with the current indicated by the acquired current information and the rotation speed of the motor 23a (S45), and calculates a temporary torque constant B by linear interpolation (S46).

CPU 61 also reads out temporary torque constant C at a current of 4A and a rotation speed of 0rpm from table 644 (S47), and calculates ratio D of torque constant B to torque constant C (S48). The CPU 61 multiplies the provisional torque constant a by the ratio D to calculate a target torque constant (S49: equivalent to the constant calculation unit 611), and ends the processing in fig. 11.

When it is determined in step S43 that the polynomial expression or piecewise polynomial expression is not to be used first (S43: no), CPU 61 reads out the contents stored in table 644 in association with the current indicated by the acquired current information and the rotation speed of motor 23a (S51), and performs linear interpolation to calculate a temporary torque constant a (S52). The CPU 61 applies the temperature T indicated by the acquired temperature information to any one of the polynomials of equations (1) to (3) or the piecewise polynomial of equation (4), and calculates a temporary torque constant B (S53). The CPU 61 also calculates a provisional torque constant C at a temperature T of 0 ℃ using the above polynomial or piecewise polynomial (S54), and shifts the process to step S48 to calculate a target torque constant.

In embodiment 3, the torque constants at 0 ℃ among the torque constants stored in tables 641, 642, and 643 are stored in table 644, but the present invention is not limited to this. The same results were obtained even when the torque constants at any one of the temperatures of 10 ℃, 20 ℃ and 30 ℃ were stored in table 644.

As described above, in embodiment 3, in addition to the above polynomial expression or piecewise polynomial expression, the correspondence between the current and the rotational speed of the motor 23a and the torque constant of the motor 23a is actually measured in advance and stored in the table 644. When calculating the torque constant during execution, the temporary torque constant a calculated based on the contents stored in the table 644 in association with the current of the motor 23a and the rotational speed of the motor is corrected based on the polynomial or piecewise polynomial, or the temporary torque constant a calculated by applying the detected temperature to the polynomial or piecewise polynomial is corrected based on the stored contents of the table 644. Thus, the calculation accuracy of the torque constant of the disturbance observer 610 becomes higher, and the calculation load can be reduced.

(simulation)

The results of modeling and simulating the temperature change of each part of the motor 23a will be described with reference to fig. 12 and 13. In the temperature model of fig. 12, heat is transferred between the winding and the air inside the motor, between the winding and the outside air, between the air inside the motor and the magnet, and between the air inside the motor and the outside air. The heat quantity Qc [ J ] supplied to the winding can be expressed by the following formula (5) using the motor current Im [ A ] and the winding resistance Rc [ omega ].

Qc＝Rc×Im²···(5)

The heat quantity Qca transferred from the winding to the motor air can be expressed by the following formula (6) in terms of the winding temperature Tc [ ° c ], the motor air temperature Ta [ ° c ], and the thermal resistance Trca [ sK/J ]. The heat quantity Qcat transmitted from the winding to the outside air can be represented by the following formula (7) by the winding temperature Tc, the outside air temperature Tat, and the thermal resistance Trcat.

Qca＝(Tc-Ta)/Trca···(6)

Qcat＝(Tc-Tat)/Trcat···(7)

The heat Qam transferred from the air in the motor to the magnet can be expressed by the following equation (8) using the air temperature Ta in the motor, the magnet temperature Tm, and the thermal resistance Tram. The heat amount Qaat transferred from the motor internal air to the external air can be expressed by the following equation (9) using the motor internal air temperature Ta, the external air temperature Tat, and the thermal resistance Traat.

Qam＝(Ta/Tm)/Tram···(8)

Qaat＝(Ta-Tat)/Traat···(9)

When the heat capacity of the winding is Hc [ J/K ], the heat capacity of the air in the motor is Ha, and the heat capacity of the magnet is Hm, the temperature changes Δ Tc, Δ Ta, and Δ Tm per 1 second of the winding, the air in the motor, and the magnet can be expressed by the following expressions (10), (11), and (12).

ΔTc＝(Qc-Qca-Qcat)/Hc···(10)

ΔTa＝(Qca-Qam-Qaat)/Ha···(11)

ΔTm＝(Qam)/Hm···(12)

Using the above-based modeling of equations (10) to (12), simulations were performed under the following conditions.

Initial values of Tc, Ta, Tm, Tat: 20

Rc＝0.1

Trca＝Tram＝0.05

Traat＝Trcat＝0.1

Hc＝2000，Ha＝100，Hm＝2000

In fig. 13, the horizontal axis represents time (seconds) and the vertical axis represents temperature (deg.c). The solid line, the broken line, and the one-dot chain line in the figure indicate the magnet temperature Tm, the winding temperature Tc, and the air temperature Ta in the motor, respectively. The motor current Im is set to 100[ a ] only for a period of time from 0 second to 1500 seconds, and then set to 0.

From the above simulation results, it is known that: the air temperature Ta in the motor rises slightly later than the winding temperature Tc of the motor 23a, and the magnet temperature Tm rises slightly later. After 1500 seconds, the winding temperature Tc gradually approaches around 80 ℃, and the air temperature Ta inside the motor gradually approaches around 60 ℃ lower than that. The magnet temperature Tm is only in heat transfer with the air in the motor and thus gradually approaches the same temperature as the air temperature Ta in the motor. The same calculation as in the present simulation is performed in real time, and the magnet temperature Tm is obtained from the motor current Im and the outside air temperature Tat. As for the outside air temperature Tat, in addition to the temperature of the outside air being directly measured by the temperature sensor, values of the temperature sensor of the encoder 23b of the motor 23a and the temperature sensor in the control board may be used as substitute values of the outside air temperature, and an approximate value may be calculated from these values as the outside air temperature.

Claims

1. A disturbance observer (610) that performs feedback control on a motor (23a) based on a command, acquires position information and current information of the motor, and estimates a disturbance acting on the motor, the disturbance observer (610) comprising:

a constant calculation unit (611) that acquires temperature information of the motor and calculates a torque constant of the motor based on the temperature indicated by the acquired temperature information;

a torque calculation unit (612) that calculates the torque of the motor by multiplying the torque constant calculated by the constant calculation unit by the current indicated by the acquired current information; and

a torque estimation unit (613) that estimates the torque of the motor based on the position indicated by the acquired position information and a constant of a load machine (10, 20, 30, 51) driven by the motor,

wherein the disturbance observer (610) estimates the disturbance by subtracting the torque estimated by the torque estimation portion from the torque calculated by the torque calculation portion.

2. The disturbance observer according to claim 1,

the command is either or both of a position command and a velocity command.

3. The disturbance observer according to claim 1 or 2,

the torque estimation unit estimates the torque based on a sum of a product of a rotational speed obtained by first-order differentiating the position indicated by the acquired position information and the viscosity of the load machine, a product of an acceleration obtained by further first-order differentiating the rotational speed and the inertia of the load machine, and a coulomb friction force corresponding to the moving direction of the load machine.

4. The disturbance observer according to any of claims 1 to 3,

the constant calculation unit approximates a torque constant by using an n-th order polynomial or a piecewise polynomial obtained based on a relationship between a temperature and a torque of the motor actually measured in advance, where n is an integer of 1 or more.

5. The disturbance observer according to claim 4,

further provided with a table (644), wherein the table (644) stores a correspondence relationship between the current and the rotational speed of the motor and the torque constant of the motor,

the constant calculation unit calculates a torque constant based on the polynomial or piecewise polynomial and the content stored in the table in association with the current indicated by the acquired current information and the rotation speed obtained by first-order differentiating the position indicated by the acquired position information.

6. The disturbance observer according to any of claims 1 to 3,

further provided with a table (641), wherein the table (641) stores the corresponding relation between the current and the temperature of the motor and the torque constant of the motor,

the constant calculation unit calculates a torque constant based on contents stored in the table in association with the current indicated by the acquired current information and the temperature indicated by the acquired temperature information.

7. The disturbance observer according to any of claims 1 to 3,

further comprising tables (641, 642, 643) storing the correspondence between the current, temperature and rotational speed of the motor and the torque constant of the motor,

the constant calculation unit calculates a torque constant based on contents stored in the table in association with the current indicated by the acquired current information, the temperature indicated by the acquired temperature information, and the rotation speed obtained by first-order calculus on the position indicated by the acquired position information.

8. A control device is characterized in that a control unit,

the interference observer according to any one of claims 1 to 7, and a control unit (600) that issues the command are provided.

9. A machine tool (100) provided with the control device (60) according to claim 8, the motor, and the load machine, the machine tool (100) further comprising:

a position detection unit (23b) that detects the position of the motor and feeds back position information indicating the detected position;

a current detection unit (237) that detects the current of the motor and feeds back current information indicating the detected current; and

a temperature detection unit (23c) that detects the temperature of the motor and generates temperature information indicating the detected temperature,

wherein the disturbance observer acquires temperature information from the temperature detection section.

10. A disturbance estimation method for feedback-controlling a motor based on a command, acquiring position information and current information of the motor, and estimating a disturbance acting on the motor, the disturbance estimation method comprising:

acquiring temperature information of the motor, and calculating a torque constant of the motor based on a temperature indicated by the acquired temperature information;

calculating a torque of the motor by multiplying the calculated torque constant by a current indicated by the acquired current information;

estimating a torque of the motor based on a position indicated by the acquired position information and a constant of a load machine driven by the motor; and

the disturbance is estimated by subtracting the estimated torque from the calculated torque.