Servo motor position control device

Abstract

Device that performs position control of a servo motor, wherein the servo motor position control device comprises: a position control device (5) which derives and outputs a speed command signal corresponding to a target speed of the servomotor (1) from a position deviation by means of proportional control, for which a position signal corresponding to an actual position of the servomotor (1) is subtracted from a position command signal corresponding to a target position when driving the servomotor (1); a speed control device (6) that derives and outputs a current command signal corresponding to a current value to be applied to the servomotor (1) by means of proportional-integral control from a speed deviation, for which a speed signal corresponding to an actual speed of the servomotor (1) is subtracted from the speed command signal; and a q-axis current control device (7) which derives and outputs a q-axis voltage command signal corresponding to a voltage applied to a q-axis of the servo motor (1) from a current deviation by means of proportional-integral control, for which a q-axis current signal corresponding to a current value actually flowing with respect to the q-axis of the servo motor (1) is subtracted from the current command signal, wherein integral control in the q-axis current control device (7) is interrupted when the servo motor (1) reaches the target position in order to cancel the position deviation, wherein the proportional-integral control in the q-axis current control device (7) is switched to proportional control while the value of the current command signal is held at a value at the time when the position deviation is canceled.

Description

Technical field

[0001] The present invention relates to a position control device with which a drive position of a servo motor is controlled by means of control with feedback, i.e., regulation, in particular to regulate in such a way that oscillation is suppressed when the drive position of the servo motor reaches a target position and comes to a stop. Technical background

[0002] Servo motor position control is often implemented with a servo system that has a cascade configuration, where a position control loop forms a main control loop, while a secondary control loop is formed from a speed control loop and a current control loop in that order. For reasons of stability and convergence of the servo system, position control is carried out using proportional control, and speed control and current control are carried out using proportional-integral control.

[0003] In servo motor position control, the drive position (hereinafter also referred to simply as "position") of the servo motor is determined by counting the number of pulses output by a pulse generator attached to the servo motor. Generally, the drive speed (hereinafter also referred to simply as "speed") of the servo motor is determined by dividing the number of pulse generator pulses generated within a constant sampling time by the sampling time.

[0004] When the servo motor reaches the target position and comes to a stop, the encoder no longer outputs a pulse, and position control is not performed. Therefore, depending on the control method, the servo motor can oscillate within a range of minimum encoder resolution, thus causing vibrations.

[0005] This means that in the state where the servo motor is stopped, its position is within a predetermined accuracy range relative to a command position, and this state can also be described as a stop command state. Methods such as reducing the gain of a speed control loop and shifting the servo motor's electrical phase angle from 90° to 0° when the position deviation between the servo motor's actual position and a command position is zero or near zero are proposed as methods for controlling oscillation in the stop command state caused by the position and speed sensing system in which the encoder is used.

[0006] Further relevant state of the art is described in US 5,886,491 A. This document describes the control of the electric motor using a PID controller. Patent Document 1: JP S62-245312 A Patent Document 2: JP H07-123767 A Patent Document 3: JP H11-332278 A Disclosure of the invention

[0007] One object of the invention is to provide a method by which a more stable stopping state can be maintained by suppressing oscillations in a minimum resolution range of the pulse generator, which is a position sensor, when the servo motor reaches the target position and stops.

[0008] To solve the problem described above, a device that performs position control of a servomotor is specified. This device has the features of claim 1 and / or the features of claim 2. An advantageous embodiment is defined in claim 3.

[0009] In a servomotor position control device according to the invention, a cascade configuration is used, in which the position control loop forms the main control loop, while the secondary control loop is successively formed by a speed control loop and a current control loop. Position control is carried out by means of proportional control, and speed and current control are carried out by means of proportional-integral control. One of the characteristic features of the servomotor position control device is that integral control is interrupted in the current control when the servomotor reaches the target position and stops.

[0010] That is, in a device that performs position control of a servo motor, the servo motor position control device includes a position control unit that derives and outputs a speed command signal corresponding to a target speed of the servo motor by means of proportional control from a position deviation, for which a position signal corresponding to an actual position of the servo motor is subtracted from a position command signal corresponding to a target position when driving the servo motor; a speed control device that derives and outputs a current command signal corresponding to a current value to be applied to the servo motor from a speed deviation by means of proportional-integral control, for which a speed signal corresponding to an actual speed of the servo motor is subtracted from the speed command signal; and a q-axis current control device that derives and outputs a q-axis voltage command signal, corresponding to a voltage applied to a q-axis of the servo motor, from a current deviation by means of proportional-integral control, for which a q-axis current signal, corresponding to a current value actually flowing with respect to the q-axis of the servo motor, is subtracted from the current command signal. where integral control in the q-axis current control device is interrupted when the servo motor reaches the target position in order to cancel the position deviation.

[0011] When the servo motor reaches and stops at the target position, and the position deviation becomes zero, the speed command output by the position control unit also becomes zero. Since the speed deviation essentially becomes zero, the current command signal becomes a substantially constant value. Therefore, because the current deviation in the q-axis current control unit has a finite value at this point, the q-axis voltage command signal output by the q-axis current control unit increases over time.

[0012] The current applied to the servo motor gradually increases, the servo motor moves slightly, and the pulse generator outputs the next pulse due to this slight movement. Therefore, a position deviation is detected, and the q-axis voltage command signal is output, causing the servo motor to move in the opposite direction.

[0013] Due to this phenomenon, the servo motor repeats the slight iterative movement in a region of minimum resolution of the pulse generator, and this is one of the causes of the oscillation.

[0014] In contrast, in the invention, the integral control of the q-axis current control device is interrupted when the servo motor reaches the target position and stops in order to cancel the position deviation. Therefore, even if the current deviation in the q-axis current control device has the finite value, and the current command signal becomes the essentially constant value, the q-axis voltage command signal output by the q-axis current control device does not increase over time.

[0015] Accordingly, it can be prevented that the servo motor moves unintentionally in the stopped state, and the occurrence of oscillation can be prevented.

[0016] In the invention, when the position deviation is eliminated, the proportional-integral control in the q-axis current control device can be switched to proportional control, while the value of the current command signal is held at a value at the time when the position deviation is eliminated.

[0017] It is known that, with regard to the movement of the servo motor, it is understood that the servo motor must be moved and overcome a cogging torque. Due to the presence of this cogging torque, the servo motor has a position where it stops easily and a position where it stops with difficulty (the servo motor is affected by the cogging torque). When the servo motor stops, the current command signal is held at the value at the moment the position deviation is resolved, and the proportional-integral control of the q-axis current control device switches to proportional control. Therefore, a balance can be established between the torque generated in the servo motor by the q-axis voltage command signal and the cogging torque, and the positional stability of the servo motor can be improved when stopped. Consequently, oscillation can be more reliably prevented.

[0018] In these cases, because the q-axis current control device continues proportional control, if the value of the q-axis current—which is the current value actually applied to the q-axis of the servo motor—changes for any reason, the value of the q-axis voltage command signal changes to compensate for the change in the q-axis current value. This further improves the stability of the servo motor when it is stopped.

[0019] In the invention, the value of the q-axis voltage command signal can be held at a value at the time the position deviation is canceled, at which point the position deviation is canceled.

[0020] This means that when the servo motor reaches the target position and stops, the output (the value of the q-axis voltage command signal) of the q-axis current control unit is maintained at the value at the time the position deviation is corrected, regardless of the value of the current command signal and the result of the current control calculation in the q-axis current control unit. Therefore, the value of the q-axis voltage command signal can be stabilized more easily. The balance between the cogging torque and the torque generated in the servo motor by the q-axis voltage command signal can be established, and the positional stability in the servo motor's stopped state can be further improved.

[0021] In the invention, a linear servomotor can be used as the servomotor.

[0022] When servomotor position control is implemented, it's not just the position of the individual servomotor that's controlled. In most cases, the servomotor's position is controlled when it's integrated into a specific device, and the device itself is controlled as the output. Typically, with a rotary servomotor, the device often performs the output after a motion conversion mechanism, such as a gearbox, and the servomotor's output shaft is belt-driven.

[0023] Since numerous mechanisms underlie the oscillation of a low-amplitude rotary servomotor, the oscillation often does not directly affect the device's output. However, when a linear servomotor is used, the device's output is often directly connected to a rotor (moving element) of the linear servomotor, and the low-amplitude oscillation of the linear servomotor often directly affects the device's output.

[0024] Accordingly, the effect of suppressing vibration can be achieved more pronounced when the invention is used with the linear servomotor.

[0025] The methods described above can largely be combined.

[0026] In the invention, when the servo motor reaches the target position and stops, the oscillation in the minimum resolution range of the pulse generator, which is the position sensor, can be suppressed in order to maintain the stopping state more stably. Brief description of the drawings Fig. Figure 1 is a sectional view showing the structure of a drive guidance device according to embodiments of the invention. Fig. Figure 2 is a front view showing the structure of the drive guidance device of the embodiments. Fig. Figure 3 is a side view showing the structure of the drive guidance device of the embodiments. Fig. Figure 4 is a perspective view showing a guide mechanism of the drive guide device of the embodiments. Fig. Figure 5 is a block diagram of the position control of a servomotor of the embodiments. Fig. Figure 6 is a flowchart of conventional position control of the servo motor. Fig. Figure 7 is a flowchart that represents a position control routine of the first embodiment. Fig. Figure 8 is a flowchart representing a position control routine 2 according to a second embodiment of the invention. Description of reference symbols 1 Linear motor (servo motor) 2 pulse generators 2a linear scale 2b Scale Sensor 3 Position detection device 4 Speed ​​detection device 5 position control device 6 Speed ​​control device 7 q-axis current control device 8 current transformers 9 Three-phase / dq coordinate converters 10 Phase detector 11 d-axis current control device 12 dq / three-phase coordinate conversion device 13 power converters 14 Table 15 Guide mechanism 15a movable block 15b Last-Rollnut 15c Body of the movable block 15d End cap 16 base 17 Sliding table 18 rail 18a Ball rolling groove 19 Thermal insulator 21 End plate 22 attacks 23 scrapers 25 Magnetic pole sensor 26 carriers 27 Cable chain mounting plate 28 cable chain carriers 29 power cables 30 signal cables 31 Nylon tube 32 balls 50 Drive guide device Best implementations of the invention

[0027] A servomotor position control device according to an embodiment of the invention is described below with reference to the drawings. First embodiment

[0028] A first embodiment of the invention is described with reference to the drawings. In the present embodiment, the implementation of position control of a linear servomotor using a servomotor position control device according to the present invention is described as an example.

[0029] First, the construction of a linear servomotor 1 is described with reference to Fig. 1 to 4 described. As in Fig. As shown in Figure 1, the linear servomotor (hereinafter referred to as the linear motor) comprises a primary side 1a, which is a conductive side and contains an armature winding, and a secondary side 1b, which is a non-conductive side and contains a magnet. In the first embodiment, the linear motor 1 forms a drive guide device 50. The primary side 1a of the linear motor 1 is coupled to a movable block 15a in a guide mechanism 15, with a table 14 arranged between them. The secondary side 1b of the linear motor 1 is attached to a base 16, and the base 16 is attached to the top of a sliding table 17.

[0030] The base 16 contains two rails 18 parallel to each other. The movable block 15a is designed to receive a driving force from the linear motor 1 to move along the rails 18.

[0031] In the drive control device 50 of the first embodiment, a thermal insulator 19 is provided between the primary side 1a of the linear motor 1 and the table 14 to prevent the transfer of heat generated at the primary side 1a to the table 14. Because of the thermal insulator 19 between the primary side 1a of the linear motor 1 and the table 14, the heat generated by a drive current applied to an armature winding (not shown) at the primary side 1a is not transferred to the table 14 and the movable block 15a, thus preventing thermal expansion of the table 14 and the movable block 15a.Therefore, there is no fluctuation of a preload (contact pressure) acting on rolling elements, such as several balls, which are arranged on and contained in an endless recirculation path of the movable block 15a of the guide mechanism 15, and a rolling resistance can be kept constant in order to achieve a long service life of the drive guide device 50.

[0032] The thermal insulator 19 is not required; instead, an air cooling unit, such as a fin, may be present. The thermal insulator 19 is made, for example, of an epoxy resin material containing glass or a ceramic material. A recess (not shown), acting as a thermal insulation space, is located in a section enclosed by the underside of the table 14 and the thermal insulator 19, thus blocking radiant heat from the primary side 1a. The thermal insulator 19 extends along the longitudinal direction of the rail 18, i.e., the direction of movement of the table 14 and the movable block 15a, thereby increasing the rigidity along the longitudinal direction of the rail 18 to prevent oscillation. Specific example of the construction of the linear servomotor

[0033] A specific example of the construction of the drive guide device 50 of the first embodiment is described below. Fig. 2 and Fig. Figure 3 represents an example of the construction of the drive guidance device 15 of the first embodiment. Fig. 2 and Fig. 3 places that have the same reference symbol as in Fig. The components marked 1 are the same or equivalent components.

[0034] The primary side 1a of the linear motor 1 contains, as shown in Fig. 2 and Fig. Figure 3 shows an armature winding and an armature core, and the secondary side 1b contains a magnetic disk. The secondary side 1b is attached to the support 16. The rails 18 are located parallel to each other on both sides of the secondary side 1b of the linear motor 1, which contains the magnetic disk, at the base 16 (attached to it).

[0035] In each of the rails 18, several (two in the drawings) movable blocks 15a are present and movably arranged along the rail 18. The table 14 is supported by the several (four in the drawings) movable blocks 15a that are movably arranged along the rail 18.

[0036] A magnetic interaction is generated between the primary side 1a and the secondary side 1b by applying the drive current to the armature winding (not shown) on the primary side 1a of the linear motor 1, thus moving the primary side 1a along the secondary side 1b. The force of motion is transmitted via the table 14 to the movable block 15a, in order to move the movable block 15a along the rails 18.

[0037] End plates 21 are attached to both end sections of the base 16, and a stop 22 is attached to each of the end plates 21. Scrapers 23 are attached to both ends of the table 14.

[0038] An optical linear scale 2a, which outputs a pulse corresponding to a movement of the movable block 15a with respect to the base 16, is, as in Fig. Figure 3 shows a linear scale 2a located on one of the lateral sections of the base 16. A scale sensor 2b, containing an optical sensor, is attached to one of the lateral sections of the table 14, with a support 26 positioned between them. The scale sensor 2b reads the linear scale 2a to detect the position (distance) of movement of the table 14.

[0039] The linear scale 2a and the scale sensor 2b form a pulse generator 2. A magnetic pole sensor 25, which, for example, contains a Hall sensor, is located opposite the secondary side 1b of the table 14. The magnetic pole sensor 25 detects the type of magnetic pole of the magnet on the secondary side 1b. Depending on the type of magnetic pole, the magnetic pole sensor 25 outputs a signal "0" or "1".

[0040] A cable chain mounting plate 27 is attached to the other side section of the base 16, and a cable chain carrier 28 is attached to the other side section of the table 14. A power cable 29, a signal cable 30, and a nylon tube 31 are connected to the primary side 1a of the linear motor 1 via the cable chain carrier 28. The power cable 29 supplies drive current to the primary side 1a of the linear motor 1 and is attached to the cable chain mounting plate 27. The signal cable 30 sends and receives a signal. The nylon tube 31 supplies water for cooling the primary side 1a. Guidance mechanism

[0041] Fig. Figure 4 shows the detailed construction of the guide mechanism 15. The rail 18, which has a rectangular cross-section, contains, as shown in Fig. As shown in Figure 4, two ball-roll grooves 18a are formed longitudinally in each of the side surfaces, forming rolling surfaces for the rolling element, and a total of four ball-roll grooves 18a are formed in the side surfaces. The continuous recirculation path, which includes the load-roll groove 15b, is formed in the movable block 15a, and the load-roll groove 15b, which forms a rolling path for rolling elements under load, is arranged opposite the ball-roll groove 18a. Several balls 32, as the multiple rolling elements, are arranged and received in the continuous recirculation path. These balls roll during relative movement of the rail 18 and the movable block 15a and circulate between the ball-roll groove 18a and the load-roll groove 15b. The guide mechanism 15 is designed such that a load can be applied in any direction, for example, a load in a radial direction, a load in a horizontal direction, and a moment in any direction.

[0042] The movable block 15a includes a load-bearing roller groove 15b, a body 15c of the movable block, and an end cap 15d. A ball return path parallel to the load-bearing roller groove 15b is formed in the body 15c of the movable block. The end cap 15d includes a reversing path that connects the load-bearing roller groove 15b and the ball return path when the end caps are connected to both ends of the body 15c of the movable block. The movable block 15a is positioned so that it spans the rail 18. The table 14 is attached to the top of the movable block 15a. The load rolling groove 15b, which is formed in the movable block 15a, is formed opposite each of the ball rolling grooves 18a, which are formed in the rail 18, and several balls 32, which are the rolling elements, are enclosed between the load rolling groove 15b and the ball rolling groove 18a.The balls 32 are fed to the ball return path via the reversing path formed in the end cap 15d when the movable block 15a is moved, and the balls are guided back into the load rolling groove 15b so that the balls circulate on the endless circulation path.

[0043] The position control of the linear motor 1 is described below. Fig. Figure 5 is a block diagram of the control of the linear motor 1 by means of dq current control (vector current control) of the first embodiment. With the exception of the linear motor 1, a position control device of the linear motor 1 of the first embodiment corresponds to a setup in Fig. 5, and the position control of the linear motor 1 is carried out by means of the dq current control.

[0044] The position (i.e., the position of the movable block 15a with respect to the base 16) of the linear motor 1 is detected by the pulse generator 2, as described above. The pulse generator 2 is a pulse generator that produces a pulse signal corresponding to the position of the linear motor 1. The position signal (pulse signal) is input by the pulse generator 2 to a position detection device 3, a velocity detection device 4, and a phase detector 10.

[0045] The position sensing device 3 counts the number of pulses from the pulse generator 2 to generate the position signal, which corresponds to the absolute position of the linear motor 1. The position signal generated by the position sensing device 3 is input to a position control device 5. The speed sensing device 4 calculates a speed signal, corresponding to the speed of the linear motor 1, from the pulse signal of the pulse generator 2 and outputs it. The speed signal is calculated by dividing the number of pulses from the pulse generator 2 generated in a constant sampling time by the sampling time. The speed signal generated by the speed sensing device 4 is input to a speed control device 6.

[0046] A position command signal, corresponding to a target position of the linear motor 1, is input into the position control unit 5. The position control unit 5 calculates (derives) a speed command signal by multiplying a position proportional gain by a position deviation, which is determined by subtracting the position signal from the position command signal, and outputs this result. The speed command signal output by the position control unit 5 is input into the speed control unit 6.

[0047] The speed control unit 6 calculates a speed deviation by subtracting the speed signal output by the speed sensing unit 4 from the speed command signal, multiplying a speed proportional gain and a speed integral gain each by the speed deviation and an integral component in which the speed deviation is integrated, and adding the products to calculate and output a current command signal. The current command signal output by the speed control unit 6 is input into a q-axis current control unit 7.

[0048] Furthermore, as described above, the pulse signal output by the pulse generator 2 is also entered into the phase detector 10, and the phase detector 10 outputs position information about the linear motor 1 as an electrical angle.

[0049] Regarding the current applied to each three-phase winding of the linear motor 1, the current values ​​of two phases are recorded by a current transformer 8, and the remaining phase is determined by calculation. The current values ​​of three phases are inputted to a three-phase / dq AC coordinate converter 9. The three-phase / dq AC coordinate converter 9 calculates a q-axis current value and a d-axis current value from the current values ​​of the U-phase, V-phase, and W-phase of the three-phase winding of the linear motor 1 using three-phase-to-two-phase conversion and vector rotation calculations, and outputs the q-axis current value and the d-axis current value.

[0050] The q-axis current control device 7 multiplies a q-axis current deviation, for which the q-axis current signal output by the three-phase / dq AC coordinate converter 9 is subtracted from the current command signal output by the speed control device 6, by q-axis current proportional gain, multiplies an integrated value of the q-axis current deviation by a q-axis current integral gain, and adds the results of the multiplication to output a q-axis voltage command signal.

[0051] The current command signal (= 0) is input into a d-axis current control unit 11. The d-axis current control unit 11 multiplies a d-axis current deviation, for which the d-axis current signal output by the three-phase / dq AC coordinate converter 9 is subtracted from the current command signal (= 0), by a d-axis current proportional gain, multiplies an integrated value of the d-axis current deviation by a d-axis current integral gain, and adds the result of the multiplication to output a d-axis voltage command signal.

[0052] A dq / three-phase AC coordinate converter 12 converts the d-axis voltage command signal and the q-axis voltage command signal into voltage command signals with respect to the U-phase, the V-phase, and the W-phase of the three-phase winding of the linear motor 1. The voltage command signals are input to a power converter 13 and inverted to AC voltages.

[0053] The following describes a process for the position control of a conventional linear motor 1 in the control block. Fig. Figure 6 is a schematic flowchart that describes the position control of the conventional linear motor 1.

[0054] If the process in Fig. In S101, the position control unit 5 performs the calculation by proportional control (P) using the position command signal and the position signal of the linear motor 1, based on a program or user input, in order to calculate the velocity command signal. When the processing in S101 is complete, the process continues to S102.

[0055] Speed ​​control is performed in S102. Specifically, speed control unit 6 calculates the current command signal using proportional-integral (PI) control, based on the speed command signal calculated in S101 and the speed signal from speed sensing unit 4. Once processing in S102 is complete, the process continues to S103.

[0056] Current control is performed in S103. Specifically, the a-axis current control unit 7 performs the calculation using proportional-integral (PI) control, taking into account the current command signal calculated in S102 and the q-axis current signal from the three-phase / dq coordinate converter 9, to calculate the q-axis voltage command signal. The d-axis current control unit 11 performs the calculation using proportional-integral (PI) control, taking into account the current command (= 0) and the d-axis current signal from the three-phase / dq coordinate converter 9, to calculate the d-axis voltage command signal.

[0057] The dq / three-phase coordinate converter 12 calculates the voltage applied to each phase of the linear motor 1 according to the calculated q-axis voltage command signal and the d-axis voltage command signal. The current converter 13 converts the voltage into alternating current and supplies the alternating current to the linear motor 1. When processing in S103 is complete, the process continues to S104.

[0058] A determination as to whether the control of linear motor 1 has ended is made in S104. If the determination in S104 is positive, the routine of Fig. S6 terminates if, for example, the control of linear motor 1 is released for any reason. If, however, the determination is negative, the process returns to S101.

[0059] In the position control of the conventional linear motor, as long as the control is not finished, the proportional control in the position control unit 5, the proportional-integral control in the speed control unit 6 and the proportional-integral control in the q-axis current control unit 7 as well as the proportional-integral control in the d-axis current control unit 11 are repeatedly carried out in sequence in a predetermined control period.

[0060] This section considers the case where the linear motor 1 reaches the target position and comes to a stop. In this case, as long as the control of the linear motor 1 is not terminated, the proportional control in the position control unit 5, the proportional-integral control in the speed control unit 6, the proportional-integral control in the q-axis current control unit 7, and the proportional-integral control in the d-axis current control unit 11 are repeatedly executed.

[0061] However, in the state where the linear motor 1 reaches the target position and stops, since the position deviation between the position signal from the position detection device 3 and the position command signal becomes zero, the speed command signal output by the position control device 5 becomes essentially zero.

[0062] Since the speed signal output by the speed sensing device 4 also becomes essentially zero, the speed deviation during processing by the speed control device 6 becomes essentially zero. However, since the speed control device performs proportional-integral control, the current command signal is output with an essentially constant value.

[0063] When the current command signal with its essentially constant value is input into the q-axis current control unit 7, a finite q-axis current deviation is generated between the current command signal and the q-axis current signal output by the three-phase / dq coordinate converter 9. Since the q-axis current control unit 7 also performs proportional-integral control, the q-axis voltage command signal output by the q-axis current control unit 7 can increase in strength over time.

[0064] Therefore, the voltage applied to linear motor 1 also increases, creating the illusion that the linear motor 1 is moving slightly. When the pulse generator 2 outputs the next pulse due to this slight movement of the linear motor 1, it detects the position deviation, and the q-axis voltage command signal is output, causing the linear motor 1 to move in the opposite direction. The linear motor 1 repeats this slight iterative movement within a minimal resolution range of the pulse generator 2, and this can generate oscillations.

[0065] In the first embodiment, to suppress oscillation, the value of the current command signal output by the speed control unit 6 is held at the value at the moment the linear motor 1 reaches the target position and stops, and the position deviation between the position command signal and the actual position signal is eliminated. Simultaneously, the control in the q-axis current control unit 7 is switched from proportional-integral control to proportional control. Therefore, the q-axis voltage command signal, which is the output of the q-axis current control unit 7, is prevented from increasing in strength over time when the position deviation between the position command signal and the actual position signal is eliminated. This prevents the linear motor 1 from moving out of the stop position while in the stop state (stop command state).

[0066] Fig. Figure 7 represents a flowchart of a position control routine of the first embodiment. The routine in Fig. Figure 7 illustrates a control process in the control block in Fig. 5. When the routine in Fig. Since step 7 is performed, the processing elements in S101 and S102 are carried out. Because the content of the processing elements in S101 and S102 corresponds to that of the conventional position control process, the description is not repeated.

[0067] When processing in S102 is complete, the sequence proceeds to S201 to determine if a position deviation exists, i.e., to determine if there is a difference between the position signal input to the position control unit 5 and the position command signal. If the determination is positive, the sequence proceeds to S103. Conversely, if the determination is negative, the sequence proceeds to S202. When the sequence proceeds to S103, similar to the sequence of conventional position control, the q-axis current control unit 7 and the d-axis current control unit 11 perform proportional-integral (PI) control, and the sequence returns to processing in S101.

[0068] If, however, the process transitions to S202, the current command signal, which is the output signal of the speed control device 6, is held at a constant value. The held value is the current command signal value at the time the position deviation becomes zero. When processing in S202 is complete, the process transitions to S203.

[0069] In S203, the current transformer 8 continues to acquire and feed back the current value. This means that the control process continues based on the current command signal at the point when the position deviation becomes zero, and the three-phase / dq coordinate converter 9 outputs the q-axis current signal and the d-axis current signal. When processing in S203 is complete, the process continues to S204.

[0070] In S204, the control in the q-axis current control unit 7 and the control in the d-axis current control unit 8 are switched from proportional-integral control (PI) to proportional control (P). The q-axis current control unit 7 performs the current control (P) based on the current command signal maintained in S202 and the q-axis current signal. Furthermore, the d-axis current control unit 11 performs the current control (P) based on the current command signal (maintained at the value 0 from the beginning) and the d-axis current signal. When the processing in S204 is complete, the sequence continues to S104. Since the processing in S104 is identical to that of the described position control routine, the description is not repeated.

[0071] In the first embodiment, as described above, the current command signal, which is the output value of the speed control device 6, is held at the value at the time when the position deviation becomes zero, i.e., when the position deviation between the command position signal and the position signal of the linear motor 1 based on the pulse from the pulse generator 2 becomes zero. Simultaneously, the control performed by the q-axis current control device 7 and the control performed by the d-axis current control device 11 are switched from proportional-integral control (PI) to proportional control (P).

[0072] Therefore, the values ​​of the q-axis voltage command signal and the d-axis voltage command signal, which correspond to the voltage applied to the linear motor 1, can be prevented from increasing over time by the integral control in the q-axis current control unit 7 and the integral control in the d-axis current control unit 11, and the oscillation of the linear motor 1 can be suppressed. In the first embodiment, switching the control performed by the q-axis current control unit 7 from proportional-integral control (PI) to proportional control (P) also means the termination of the integral control (I) in the q-axis current control unit 7.

[0073] In the first embodiment, when the position deviation between the position signal of the linear motor 1 and the command position signal becomes zero, the current command signal, which is the output value of the speed control device 6, is held at the value at the time the position deviation becomes zero, and the control in the q-axis current control device 7 and the control in the d-axis current control device 11 are switched from proportional-integral control (PI) to proportional control (P). However, the content of the control for preventing oscillation is not limited to this embodiment.For example, when the position deviation becomes zero, only the control operation in which the control in the q-axis current control unit 7 and the control in the d-axis current control unit 11 are switched from proportional-integral control (PI) to proportional control (P) can be carried out (the integral control (I) in the q-axis current control unit 7 is interrupted), while the control for the current command signal, which is the output value of the speed control unit 6, continues. Therefore, the oscillation suppression effect is also achieved. Second embodiment

[0074] A second embodiment of the invention is described below. The control block diagram of the linear motor 1 of the second embodiment corresponds to that of the first embodiment. In the second embodiment, when the position of the linear motor 1 reaches the target position and it stops, i.e., when the position deviation between the position command signal and the position signal of the linear motor 1 based on the pulse from the pulse generator 2 becomes zero, the value of the q-axis voltage command signal, which is the output signal of the q-axis current control device 7, is held at a constant value.

[0075] Fig. Figure 8 represents a flowchart of a position control routine 2 of the second embodiment. Only one point of the routine in Fig. 8, which differs from that of the position control routine of the first embodiment, is described below. In the routine in Fig.8. The process continues to S301 when it is determined in S201 that the position deviation has been resolved.

[0076] In S301, the values ​​of the q-axis voltage command signal and the d-axis voltage command signal are held constant. These constant values ​​are the values ​​of the q-axis voltage command signal and the d-axis voltage command signal at the time when S201 determines that the position deviation has been eliminated. After processing in S301 is complete, the content of the processing is identical to that of the position control routine.

[0077] In the second embodiment, as described above, when the position of the linear motor 1 reaches the target position and stops, i.e., when the position deviation between the position command signal and the position signal of the linear motor 1 based on the pulse from the pulse generator 2 becomes zero, the value of the q-axis voltage command signal and the value of the d-axis voltage command signal are held at the values ​​at the time when the position deviation becomes zero.

[0078] Therefore, the voltage applied to the linear motor 1 in the stop (command) state can be stabilized more reliably, and the oscillation of the linear motor 1 can be suppressed more reliably.

[0079] In the embodiments, the servo motor is, for example, a linear servo motor. However, it is obvious that the invention can be used for the position control of a rotary servo motor. In the embodiments, the optical pulse generator 2 is used as an example. Alternatively, other pulse generators, such as a magnetic pulse generator 2, can be used.

Claims

[1] Device for performing position control of a servo motor, the servo motor position control device comprising: a position control device (5) which derives and outputs a speed command signal corresponding to a target speed of the servomotor (1) from a position deviation by means of proportional control, for which a position signal corresponding to an actual position of the servomotor (1) is subtracted from a position command signal corresponding to a target position when driving the servomotor (1); a speed control device (6) that derives and outputs a current command signal corresponding to a current value to be applied to the servomotor (1) by means of proportional-integral control from a speed deviation, for which a speed signal corresponding to an actual speed of the servomotor (1) is subtracted from the speed command signal; and a q-axis current control device (7) which derives and outputs a q-axis voltage command signal corresponding to a voltage applied to a q-axis of the servo motor (1) from a current deviation by means of proportional-integral control, for which a q-axis current signal corresponding to a current value actually flowing with respect to the q-axis of the servo motor (1) is subtracted from the current command signal, wherein integral control in the q-axis current control device (7) is interrupted when the servo motor (1) reaches the target position in order to cancel the position deviation, wherein the proportional-integral control in the q-axis current control device (7) is switched to proportional control while the value of the current command signal is held at a value at the time when the position deviation is canceled. [2] Device for performing position control of a servo motor, the servo motor position control device comprising: a position control device (5) which derives and outputs a speed command signal corresponding to a target speed of the servomotor (1) from a position deviation by means of proportional control, for which a position signal corresponding to an actual position of the servomotor (1) is subtracted from a position command signal corresponding to a target position when driving the servomotor (1); a speed control device (6) that derives and outputs a current command signal corresponding to a current value to be applied to the servomotor (1) by means of proportional-integral control from a speed deviation, for which a speed signal corresponding to an actual speed of the servomotor (1) is subtracted from the speed command signal; and a q-axis current control device (7) which derives and outputs a q-axis voltage command signal corresponding to a voltage applied to a q-axis of the servo motor (1) from a current deviation by means of proportional-integral control, for which a q-axis current signal corresponding to a current value actually flowing with respect to the q-axis of the servo motor (1) is subtracted from the current command signal, wherein integral control in the q-axis current control device (7) is interrupted when the servo motor (1) reaches the target position in order to cancel the position deviation, wherein the value of the q-axis voltage command signal is held at a value at the time when the position deviation is canceled. [3] Servomotor position control device according to one of claims 1 or 2, wherein the servomotor (1) is a linear servomotor.

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