Motor control device and assembling method for motor control system

Abstract

To provide a motor control device in which a plurality of motors drives the same drive body such that a positional error generated in each of the motors is suppressed.SOLUTION: A motor control device includes a master-side motor electric angle calculation unit 12 that obtains a master-side motor electric angle, an upper control unit 14 that obtains an electric angle command value for a slave-side motor 20 by adding an electric angle offset amount to the master-side motor electric angle, a slave-side motor electric angle calculation unit 22 that obtains a slave-side motor electric angle, and a slave-side motor control unit 18 that controls the slave-side motor on the basis of the difference between the slave-side motor electric angle and the electric angle command value. A master-side motor 10 and the slave-side motor 20 drive a drive body 40. The upper control unit 14 determines the electric angle offset amount in such a way that a ripple component of the drive force given by the master-side motor 10 to the drive body 40 and a ripple component of the drive force given by the slave-side motor 20 to the drive body 40 are mutually weakened.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric motor control device and an assembly method for an electric motor control system, and more particularly to a device that drives a driven body with a plurality of motors. [Background technology]

[0002] When driving a three-phase AC motor used in a machine tool, if the detection value of the current sensor contains an offset error, a periodic ripple is superimposed on the current obtained by converting the three-phase AC current into a two-phase rotating coordinate system using vector control.

[0003] The periodic current ripple generates a periodic position error in the motor position being controlled, and this position error can affect machining accuracy.

[0004] The following Patent Document 1 describes a technology for obtaining a detection value of a current sensor while no current is being applied to a motor and correcting the current as an offset correction amount. Patent Document 1 states that, due to the influence of noise and distortion, it is not sufficient to simply use such an offset correction value as a correction value for suppressing position errors, and proposes a technology for using the position error while the motor is being driven as an evaluation value to set the offset correction amount to an appropriate value.

[0005] In machine tools, for gravity axes and axes with large inertia of the driven body, a method of synchronous control using multiple motors is used to meet the required torque requirements.The multiple motors are each connected to a synchronous shaft, and each motor drives the driven body via the synchronous shaft.Even in such synchronous shafts, position errors similarly occur due to offset errors contained in the detection values ​​of the current sensors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-221105 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 discloses a method for suppressing position errors caused by offset errors contained in the detection value of a current sensor, focusing on the fact that position errors occur at current frequencies, and adjusting the amount of offset correction so that the power spectrum of the current frequency is reduced.

[0008] When applying the method of Patent Document 1 to the above-mentioned synchronous axes, it is possible to consider a method of repeatedly adjusting the offset correction amount for each motor. However, this method has problems such as difficulty in reducing the position error because the position errors generated by each motor interfere with each other, and the time required to adjust the offset correction amount is long.

[0009] An object of the present invention is to suppress position errors occurring in each motor in an electric motor control device in which a plurality of motors drive a common driving body. [Means for solving the problem]

[0010] An electric motor control device according to the present invention is an electric motor control device that controls a master motor and a slave motor, and includes: a master motor electrical angle calculation unit that determines a master motor electrical angle; a higher-level control unit that adds an electrical angle offset to the master motor electrical angle to determine an electrical angle command value for one or more of the slave motors; a slave motor electrical angle calculation unit that determines the slave motor electrical angle; and a slave motor control unit that controls the slave motor based on the difference between the slave motor electrical angle and the electrical angle command value, wherein the master motor and the slave motor drive a common driven body, and the higher-level control unit determines the electrical angle offset so that a ripple component of a driving force applied by the master motor to the driven body and a ripple component of a driving force applied by the slave motor to the driven body weaken each other.

[0011] Furthermore, an electric motor control device according to the present invention is an electric motor control device that controls a master motor and a slave motor, and includes: a master motor electrical angle calculation unit that calculates a master motor electrical angle; a higher-level control unit that adds an electrical angle offset to the master motor electrical angle to calculate an electrical angle command value for one or more of the slave motors; a slave motor electrical angle calculation unit that calculates the slave motor electrical angle; and a slave motor control unit that controls the slave motor based on a difference between the slave motor electrical angle and the electrical angle command value, wherein the master motor and the slave motor drive a common driven body, and the higher-level control unit sets the electrical angle offset for the slave motor to 180° when there is one slave motor, and sets the electrical angle offset for the k-th slave motor to k times 360° / (M+1), where k is an integer from 1 to M, when there are a plurality M of slave motors.

[0012] Preferably, each of the master-side motor and the slave-side motor is a linear motor including a linear stator having a plurality of magnetic poles arranged in a line, and a mover that moves along the direction in which the linear stator extends, the position of the mover relative to the linear stator being expressed by an electrical angle, and the mover included in the master-side motor and the mover included in the slave-side motor driving the driven body.

[0013] Preferably, the driving body is driven by a master-side synchronous shaft to which the master-side motor is coupled and a slave-side synchronous shaft to which the slave-side motor is coupled, and the motor control device includes a slave-side coupling that detachably connects the slave-side motor and the slave-side synchronous shaft.

[0014] The present invention also provides a method for assembling an electric motor control system including the electric motor control device, the master motor, and the slave motor, the method including controlling the electrical angle of the slave motor based on the difference between the slave motor electrical angle and the electrical angle command value, with the slave motor and the driver disengaged.

[0015] Preferably, the method includes finding a state in which a value indicating the difference between the slave-side motor electrical angle and the electrical angle command value is less than a predetermined threshold value, and coupling the slave-side motor and the driver in a state in which the value indicating the difference between the slave-side motor electrical angle and the electrical angle command value is less than the predetermined threshold value. [Effects of the Invention]

[0016] According to the present invention, in an electric motor control device in which a plurality of motors drive a common driving body, it is possible to suppress position errors occurring in each motor. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing an example of the configuration of an electric motor control system according to a first embodiment of the present invention; [Figure 2] FIG. 4 is a diagram showing an example of the configuration of an electric motor control system according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] As a basic matter related to the present invention, we will explain an electric motor control system in which one driven body is driven by two motors with the same characteristics. In such an electric motor control system, position errors may occur due to the operation of the inverter connected to the motor or due to offset errors in the current sensors. According to Patent Document 1, the torque ripple τrip [N·m] generated due to offset errors in the current sensors is expressed as follows, where Ke is the torque constant [N·m / A], du is the offset error [A] of the U-phase current sensor, dw is the offset error [A] of the W-phase current sensor, and θe is the electrical angle:

[0019] (Number 1) τrip=Ke / √6[du·cosθe-((2-√3)du+2√3dw)sinθe]…(1)

[0020] The position error caused by the offset error of the current sensor oscillates at the electrical angular frequency due to the torque ripple in equation (1). For example, in the case of an 8-pole motor, when the motor is rotated at 60 rpm, a position error of 4 Hz occurs.

[0021] In an electric motor control system in which one driving element is driven by two motors with the same characteristics, the motor that is the main control axis is called the master motor, and the other motor that acts as the slave axis is called the slave motor.

[0022] The torque ripple τripm of the master motor is calculated as follows from equation (1), where the torque constant of the master motor [N·m / A], the offset error of the U-phase current sensor [A], the offset error of the W-phase current sensor [A], and the electrical angle are Kem, dum, dwm, and θem, respectively.

[0023] (Number 2) τripm=Kem / √6[dum·cosθem-((2-√3)dum+2√3dwm)sinθem]…(2)

[0024] Similarly, the torque ripple τrips of the slave motor is calculated as follows from equation (1), where Kes, dus, dws, and θes are the torque constant of the slave motor [N m / A], the offset error of the U-phase current sensor [A], and the offset error of the W-phase current sensor, respectively.

[0025] (Number 3) τrips=Kes / √6[dus·cosθes-((2-√3)dus+2√3dws)sinθes]…(3)

[0026] In an electric motor control system in which one driven body is driven by two motors with the same characteristics, the torque ripple τrip generated in the driven body is considered to be the sum of the torque ripples of the master motor and the slave motor, and is therefore given as follows:

[0027] (Number 4) τrip=τripm+τrips…(4)

[0028] From equation (4), the position error caused by the offset error of the current sensor is determined by the electrical angle θem of the master motor and the electrical angle θes of the slave motor, and in addition to τripm=0 and τrips=0, the condition that the error is 0 also holds when τripm=-τrips.

[0029] When using motors with the same characteristics and the same current detection circuit, it can be assumed that the torque constant and the offset errors of the U-phase and W-phase current sensors will be roughly equivalent, so by setting θes = θem + 360° / 2, τripm = -τrips and the torque ripple τrip will be 0.

[0030] 1 shows an example of the configuration of an electric motor control system 100 according to a first embodiment of the present invention. The electric motor control system 100 includes a master motor 10, a master motor electrical angle calculation unit 12, a host control unit 14, a subtractor 16, a slave motor control unit 18, a slave motor 20, a slave motor electrical angle calculation unit 22, a master coupling 24, a master synchronous shaft 26, a slave coupling 28, a slave synchronous shaft 30, and a driver 40.

[0031] The master motor 10 is coupled to a master synchronous shaft 26 via a master coupling 24, and provides a driving force, i.e., torque, to the master synchronous shaft 26. The slave motor 20 is coupled to a slave synchronous shaft 30 via a slave coupling 28, and provides a driving force, i.e., torque, to the slave synchronous shaft 30. The driver 40 is driven by the torque provided to the master synchronous shaft 26 and the slave synchronous shaft 30.

[0032] In this embodiment, the master-side synchronous shaft 26 and the slave-side synchronous shaft 30 are configured with ball screws, and the driver 40 has a protrusion that engages with the screw groove. When the master-side synchronous shaft 26 and the slave-side synchronous shaft 30 rotate, the screw groove moves in the axial direction, and the driver 40 is transported by the screw groove.

[0033] The resolver 32 of the master motor 10 outputs a master motor detection value θmm to the master motor electrical angle calculation unit 12. The master motor detection value θmm is a value that indicates the rotational angle position of the master motor 10 by a mechanical angle.

[0034] Master-side motor electrical angle calculation unit 12 calculates master-side motor electrical angle θem by converting master-side motor detection value θmm into an electrical angle and outputs the calculated value to host control unit 14. Host control unit 14 calculates a value by adding an electrical angle offset amount θofs to the master-side motor electrical angle θem as electrical angle command value θ*=θem+θofs and outputs the value to subtractor 16. The electrical angle offset amount θofs will be described later.

[0035] The resolver 34 of the slave-side motor 20 outputs a slave-side motor detection value θms to the slave-side motor electrical angle calculation unit 22. The slave-side motor detection value θms is a value that indicates the rotational angle position of the slave-side motor 20 in terms of a mechanical angle. The slave-side motor electrical angle calculation unit 22 converts the slave-side motor detection value θms into an electrical angle to determine the slave-side motor electrical angle θes, and outputs the result to the subtractor 16.

[0036] The subtractor 16 subtracts the slave-side motor electrical angle θes from the electrical angle command value θ*=θem+θofs to obtain a control value d, and outputs the control value d to the slave-side motor control unit 18. The slave-side motor control unit 18 controls the rotation angle of the slave-side motor 20 so that the control value d approaches or coincides with 0. As a result, the slave-side motor electrical angle θes approaches or coincides with the electrical angle command value θ*=θem+θofs.

[0037] As described above, in the electric motor control system 100 according to this embodiment, the master motor electrical angle calculation unit 12, the higher-level control unit 14, the subtractor 16, the slave motor control unit 18, and the slave motor electrical angle calculation unit 22 constitute an electric motor control device that controls the master motor 10 and the slave motor 20. The master motor 10 and the slave motor 20 drive a common driving body 40.

[0038] The driver 40 is driven by a master-side synchronous shaft 26 to which the master-side motor 10 is coupled, and a slave-side synchronous shaft 30 to which the slave-side motor 20 is coupled. The motor control device further includes a slave-side coupling 28 that allows the slave-side motor 20 and the slave-side synchronous shaft 30 to be detachably connected to each other.

[0039] The master-side motor electrical angle calculation unit 12 calculates the master-side motor electrical angle θem from the master-side motor detection value θmm (mechanical angle) output from the resolver 32 of the master motor 10. The upper-level control unit 14 adds the electrical angle offset amount ofs to the master-side motor electrical angle θem to calculate the electrical angle command value θ* for the slave-side motor 20. The slave-side motor electrical angle calculation unit 22 calculates the slave-side motor electrical angle θes from the slave-side motor detection value θms (mechanical angle) output from the resolver 34 of the slave motor 20. The slave-side motor control unit 18 controls the slave-side motor 20 based on the difference between the slave-side motor electrical angle θes and the electrical angle command value θ*.

[0040] In the electric motor control system 100, a synchronous shaft assembly method is used in which the difference between the master motor electrical angle θem and the slave motor electrical angle θes is 180° (=360° / 2).

[0041] In this assembly method, the slave-side coupling 28 that connects the slave-side motor 20 and the ball screw serving as the slave-side synchronous shaft 30 is loosened, so that the slave-side motor 20 can be driven independently of the driver 40.

[0042] The master-side motor detection value θmm detected by the resolver 32 of the master-side motor 10 is input to the master-side motor electrical angle calculation unit 12, which then calculates the master-side motor electrical angle θem and outputs it to the upper control unit 14.

[0043] The upper control unit 14 outputs an electrical angle command value θem+180° to the subtractor 16 so that the slave motor electrical angle θes becomes an angle obtained by adding 180° to the electrical angle θem of the master motor 10.

[0044] For example, in an eight-pole motor, if the master motor detected value θmm of the master motor 10 is 120° and the slave motor detected value θms is 150°, the master motor electrical angle θem will be 120° and the slave motor electrical angle θes will be 240°. Therefore, the slave motor 20 is coupled to the slave synchronous shaft 30 via the slave coupling 28 and positioned so that the slave motor electrical angle θes is 300° (120° + 180°). (The slave motor detected value θms is positioned at 165°.)

[0045] While maintaining the rotational angle position of the slave motor 20, the slave coupling 28 is tightened, and the slave motor 20 is coupled to the slave synchronous shaft 30. In this state, control of the master motor 10 and the slave motor 20 begins.

[0046] In the above embodiment, the motor control system 100 is shown to include one master motor 10, one slave motor 20, one master synchronous shaft 26, and one slave synchronous shaft 30. In the present invention, a motor control system including two or more slave motors 20 and two or more slave synchronous shafts 30 may be configured.

[0047] Specifically, for a driven body driven by n synchronous shafts, an electric motor control system may be configured that includes one master motor 10 and M slave motors 20-1 to 20-M. Here, n is an integer of 3 or greater, M is an integer of 2 or greater, and n=M+1 holds. One of the n synchronous shafts is a master synchronous shaft 26, and the remaining M synchronous shafts are slave synchronous shafts 30-1 to 30-M. The slave motor 20-k is coupled to the slave synchronous shaft 30-k by a slave coupling 28-k. Here, k is an integer between 1 and M.

[0048] The upper control unit 14 calculates the electrical angle offset amount θofs for the k-th slave motor 20-k as θofs = 360° / n×k. With the slave coupling 28-k loosened for the k-th (k = 1, 2, 3, ..., M = n-1) slave motor 20-k, the upper control unit 14 outputs the electrical angle command value θ* = θem + θofs = θem + 360° / n×k to the subtractor 16. As a result, the electrical angle θes of the slave motor 20-k approaches or matches the electrical angle command value θ* = θem + 360° / n×k.

[0049] With this configuration and processing, the host control unit 14 determines the electrical angle offset amount so that the ripple component of the driving force applied by the master motor 10 to the driver 40 and the ripple component of the driving force applied by the slave motor 20 to the driver 40 cancel each other out, or weaken the ripple components applied to the driver 40. This corresponds to bringing the torque ripple τrip in (Equation 4) close to or equal to zero.

[0050] Specifically, when the number of slave motors 20 is one, the upper control unit 14 sets the electrical angle offset amount for the slave motor 20 to 180°. When the number of slave motors 20 is M, the upper control unit 14 sets the electrical angle offset amount for the k-th slave motor 20-k to k times 360° / (M+1), where k is an integer from 1 to M.

[0051] The method for assembling the motor control system 100 may include the following steps. (i) The coupling between the slave motor 20 and the driver 40 is released. (ii) When the slave motor 20 and the driver 40 are disengaged, the slave motor electrical angle θes is controlled based on the difference between the slave motor electrical angle θes and the electrical angle command value θ*. (iii) Finding a state in which the value indicating the difference between the slave motor electrical angle θes and the electrical angle command value θ* is less than a predetermined threshold value. (iv) The slave motor 20 and the driver 40 are coupled in a state where the value indicating the difference between the slave motor electrical angle θes and the electrical angle command value θ* is less than a predetermined threshold value.

[0052] In the above, an embodiment has been described in which ball screws are used as the master-side synchronous shaft 26 and the slave-side synchronous shaft 30. However, each synchronous shaft may be a shaft that drives a pinion gear that meshes with a rack gear. In this case, the rack gear is attached to a driver 40. Also, each synchronous shaft may include a rotating shaft that is coupled to a speed reduction mechanism.

[0053] The host control unit 14 shown in FIG. 1 may be implemented by a computer numerical control (CNC). The master motor electrical angle calculation unit 12, the slave motor electrical angle calculation unit 22, and the slave motor control unit 18 may be implemented by a CPU included in the CNC executing various programs stored in a storage device included in the CNC or in a storage device external to the CNC. The master motor electrical angle calculation unit 12, the slave motor electrical angle calculation unit 22, and the slave motor control unit 18 may also be implemented by a CPU (such as a microcomputer) included in an inverter unit that controls the current of the master motor 10 executing various firmware programs stored in the storage device. The programs that realize the functions of the master motor electrical angle calculation unit 12, the slave motor electrical angle calculation unit 22, and the slave motor control unit 18 may be recorded on various computer-readable recording media (e.g., semiconductor memory such as ROM, EEPROM, or flash memory, magnetic recording media, or optical disks such as CD-ROM or DVD-ROM). The host control unit 14 may perform a process to reduce position errors using the technique described in Patent Document 1.

[0054] 2 shows an example of the configuration of an electric motor control system 102 according to a second embodiment of the present invention. The electric motor control system 102 is a system that controls one driving body 80 in tandem using two independent linear motors. The master motor 50 and the slave motor 70 are linear motors, and each of the master motor 50 and the slave motor 70 includes a linear stator 52 and a mover 54. The linear stator 52 of the master motor 50 and the linear stator 52 of the slave motor 70 extend in parallel, and each linear stator 52 includes a plurality of magnetic poles 56 arranged linearly.

[0055] The mover 54 has magnetic poles 58 and moves along the extension direction of the linear stator 52. A common driver 80 is attached to each of the movers 54 of the master motor 50 and the slave motor 70. The position of the mover 54 relative to the linear stator 52 is expressed by an electrical angle. That is, the θe axis is defined as an electrical angle axis parallel to the linear stator 52, and the position of the mover 54 relative to the linear stator 52 for each of the master motor 50 and the slave motor 70 is expressed by a value on the θe axis.

[0056] Adjacent magnetic poles 56 in the linear stator 52 may have opposite polarities, represented by south poles or north poles. In this case, the mover 54 is moved by controlling the polarity of the magnetic poles 58 of the mover 54. Alternatively, the polarity of the magnetic poles of the mover 54 may be fixed, and the mover 54 may be moved by controlling the polarity of the magnetic poles 56 arranged in the linear stator 52.

[0057] In the electric motor control system 102, the currents flowing through the linear stators 52 of the master-side motor 50 and the slave-side motor 70 are synchronously controlled, thereby moving the movers 54 of the master-side motor 50 and the slave-side motor 70 in the θe-axis direction, and transporting the drivers 80 attached to each mover 54.

[0058] In this embodiment, the mover 54 of the slave-side motor 70 is positioned at a position where the electrical angle θes is θem+180°. In other words, the driver 80 is fixed to each of the movers 54 of the master-side motor 50 and the slave-side motor 70 in a state where the mover 54 of the slave-side motor 70 is positioned offset from the master-side motor 50 by half the combined length of the north and south poles of the linear stator 52.

[0059] In the above, the motor control system 102 is shown to be configured with one linear motor as the master motor 50 and another linear motor as the slave motor 70. The motor control system may also be configured with two or more linear motors as two or more slave motors.

[0060] Specifically, when the electrical angle of the master motor 50 is θem, for the kth (k=1, 2, 3, ..., n-1) slave motor, before the driver is attached to the mover, the host control unit 14 outputs the electrical angle command value θ*=θem+θofs=θem+360° / n×k to the subtractor 16. As a result, the slave motor electrical angle θes approaches or matches the electrical angle command value θ*=θem+360° / n×k. When the value indicating the difference between the slave motor electrical angle θes and the electrical angle command value θ* is less than a predetermined threshold, the mover 54 of the slave motor 70 and the driver are coupled.

[0061] As with the first embodiment, the motor control system 102 according to the second embodiment may also use an assembly method including the above steps (i) to (iv). [Explanation of symbols]

[0062] 10 master side motor, 12 master side motor electrical angle calculation unit, 14 upper control unit, 16 subtractor, 18 slave side motor control unit, 20 slave side motor, 22 slave side motor electrical angle calculation unit, 24 master side coupling, 26 master side synchronous axis, 28 slave side coupling, 30 slave side synchronous axis, 32, 34 resolver, 40 driver, 100, 102 electric motor control system.

Claims

1. An electric motor control device for controlling a master motor and a slave motor, a master-side motor electrical angle calculation unit for calculating a master-side motor electrical angle; an upper level control unit that adds an electrical angle offset amount to the master motor electrical angle to determine an electrical angle command value for one or more slave motors; a slave-side motor electrical angle calculation unit for calculating a slave-side motor electrical angle; a slave-side motor control unit that controls the slave-side motor based on a difference between the slave-side motor electrical angle and the electrical angle command value, the master motor and the slave motor drive a common driving body; The upper control unit an electric motor control device that determines the electrical angle offset amount so that a ripple component of a driving force applied to the driven body by the master motor and a ripple component of a driving force applied to the driven body by the slave motor weaken each other.

2. An electric motor control device for controlling a master motor and a slave motor, a master-side motor electrical angle calculation unit for calculating a master-side motor electrical angle; an upper level control unit that adds an electrical angle offset amount to the master motor electrical angle to determine an electrical angle command value for one or more slave motors; a slave-side motor electrical angle calculation unit for calculating a slave-side motor electrical angle; a slave-side motor control unit that controls the slave-side motor based on a difference between the slave-side motor electrical angle and the electrical angle command value, the master motor and the slave motor drive a common driving body; The upper control unit When the number of the slave motors is one, The electrical angle offset amount for the slave motor is set to 180°, When the number of the slave motors is M, 1. An electric motor control device, wherein k is an integer between 1 and M, and the electrical angle offset amount for the k-th slave motor is k times 360° / (M+1).

3. 3. The motor control device according to claim 1 or 2, each of the master motor and the slave motor is a linear motor, a linear stator in which a plurality of magnetic poles are linearly arranged; a mover that moves along the direction in which the linear stator extends, a linear motor in which the position of the mover relative to the linear stator is expressed by an electrical angle; The motor control device is characterized in that the mover included in the master motor and the mover included in the slave motor drive the driving body.

4. 3. The motor control device according to claim 1 or 2, The driver is a master-side synchronous shaft to which the master-side motor is coupled; a slave-side synchronous shaft to which the slave-side motor is coupled; The electric motor control device includes: a slave-side coupling that enables the slave-side motor and the slave-side synchronous shaft to be detachably connected to each other.

5. 3. A method for assembling an electric motor control system including the electric motor control device according to claim 1 or 2, the master motor, and the slave motor, comprising: controlling the electrical angle of the slave-side motor based on a difference between the slave-side motor electrical angle and the electrical angle command value, while the coupling between the slave-side motor and the driven body is released.

6. 6. A method for assembling an electric motor control system according to claim 5, comprising the steps of: Finding a state in which a value indicating a difference between the slave motor electrical angle and the electrical angle command value is less than a predetermined threshold value; and coupling the slave-side motor and the driven body in a state where a value indicating a difference between the slave-side motor electrical angle and the electrical angle command value is less than a predetermined threshold value.

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