Servo motor control device

Abstract

The present invention provides a servo motor control device that can set an offset more easily and with higher precision than before. The servo motor control device is used to control a servo motor of an industrial machine, and comprises: a position detection unit (2) that detects the position of the servo motor; a magnetic pole detection unit (3) that detects the magnetic pole phase of the servo motor; and a phase calculation unit (4) that calculates a calculated phase based on the position data of the servo motor and the magnetic pole spacing information of the servo motor, and obtains an offset relationship between the magnetic pole phase obtained by the magnetic pole detection unit (3) and the calculated phase obtained by the phase calculation unit (4) after passing through a reference position.

Description

Technical Field

[0001] The invention relates to a control device for a servo motor. Background Art

[0002] For example, the rotational speed, torque, and other parameters of servo motors in industrial machinery, such as those used to drive the spindles of machine tools, are controlled. Furthermore, servo motor control devices detect the motor's position and magnetic pole position (the phase (angle) of the motor's magnets) using detectors. Based on various feedback values ​​from the detectors, they determine voltage command values ​​and apply a pulse-width-modulated (PWM) voltage to control the motor's drive.

[0003] On the other hand, as detectors for detecting position information (movement information) such as rotation angles, incremental encoders, such as incremental encoders, are often used. Such encoders, for example, are configured to include multiple detection elements, and detect position information based on detection signals output from the multiple detection elements. These multiple detection elements are configured to output detection signals with different phases.

[0004] For example, when an incremental encoder is used as a detector, the relationship between the machine's absolute coordinates and the encoder's position signal is unclear when the power is turned on. Therefore, absolute position establishment is necessary to establish this relationship. This is achieved through a zero-point return operation based on the incremental encoder's Z-phase signal. This absolute position establishment involves performing a zero-point return, i.e., performing an offset correction to determine and store a reference position that serves as the reference for the industrial machine's operation.

[0005] Patent Document 1 discloses "a bias value calculation method for use in a position detection system of a camera optical system, for calculating a bias value of a sinusoidal wave signal output from a magnetoresistive element to determine the position of an object. The bias value calculation method is characterized by moving the object by more than one cycle of the sinusoidal wave signal, acquiring the sinusoidal wave signal at a predetermined sampling cycle, calculating a differential parameter corresponding to a second-order differential value of the sinusoidal wave signal based on the acquired sampling data, and using the differential parameter to calculate data corresponding to each acquired sampling data and averaging the data to thereby calculate the bias value."

[0006] Patent document 2 discloses "a position detection circuit characterized by comprising: a phase signal generating circuit which inputs a sine wave signal and a cosine wave signal whose phases are orthogonal to each other and which are output from a magnetoresistive sensor according to the position of a position detection object in a moving direction, calculates the arc tangent of the ratio of the sine wave signal to the cosine wave signal, and generates a phase signal representing the phase of the sine wave signal or the cosine wave signal; and a position calculation circuit which calculates the position of the position detection object in the moving direction by adding or subtracting a predetermined bias from the phase signal every 360°."

[0007] Patent document 3 discloses "an encoder characterized by comprising: n detection elements, which output output signals having mutually different phases according to position information of a driven body; a correction unit, which uses N phase signals (where N=n) obtained by equally dividing m periods (where m is an integer greater than 1) as reference signals, and corrects the n output signals based on respective phase differences between the N phase signals and the n output signals and the n output signals, so that the n output signals become the N phase signals, and generates corrected output information; and a detection unit, which detects the position information of the driven body according to the corrected output information generated by the correction unit."

[0008] Patent document 4 discloses "a position detection device comprising a magnetic recording medium having recorded magnetic signals and a magnetic sensor comprising a magnetoresistive element (MR element) as a sensor element, wherein the magnetic sensor detects the position of the magnetic recording medium when the magnetic recording medium and the magnetoresistive element are in relative motion, wherein the position detection device is characterized in that a continuous magnetic signal group having a length P (P=kλ, where k is an integer) and a non-magnetized portion having the same length P as the magnetic signal group are alternately arranged and stored in a minimum recording unit λ in one track in the magnetic recording medium, and the magnetic sensor is constructed such that a pair of MR elements arranged at an interval of λ / 2 in the storage direction of the magnetic signal group serve as a positioning sensor element group, and the magnetic sensor has at least one positioning sensor element group."

[0009] On the other hand, there is a strong demand for the development of a method for performing offset correction more easily and with high accuracy.

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-310925

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-117430

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 2013-205163

[0013] Patent Document 4: Japanese Patent Application Laid-Open No. 06-34390 Summary of the Invention

[0014] One embodiment of a servo motor control device disclosed herein is a device for controlling a servo motor of industrial machinery, comprising: a position detection unit that detects the position of the servo motor; a magnetic pole detection unit that detects the magnetic pole phase of the servo motor; and a phase calculation unit that calculates a calculated phase based on position data of the servo motor and magnetic pole spacing information of the servo motor, and obtains an offset relationship between the magnetic pole phase obtained by the magnetic pole detection unit and the calculated phase obtained by the phase calculation unit after passing a reference position.

[0015] In one embodiment of the servo motor control device disclosed herein, offset correction can be performed more easily and accurately than conventional devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a diagram showing a servo motor control device according to one embodiment of the present disclosure.

[0017] Figure 2 This is a diagram showing an example of a servo motor control device according to one embodiment of the present disclosure.

[0018] Figure 3 This is a diagram used in explaining how to set a magnetic pole phase bias (AMR bias) using the servo motor control device according to one embodiment of the present disclosure.

[0019] Figure 4 This is a diagram used in explaining how to set a magnetic pole phase bias (AMR bias) using the servo motor control device according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] The following reference Figures 1 to 4 A servo motor control device according to one embodiment will be described.

[0021] In this embodiment, the description will be made assuming that the industrial machine is a machine tool and that the drive control of a main shaft and the like of the machine tool is performed by a control device for a servo motor.

[0022] However, the control device of the servo motor disclosed in the present invention is not limited to the drive control of machine tools, but can also be used for the drive control of servo motors used in other industrial machinery such as robots, conveyors, measuring instruments, testing equipment, punching machines, presses, printing machines, die-casting machines, injection molding machines, food machinery, packaging machines, welding machines, cleaning machines, coating machines, assembly equipment, installation machines, woodworking machinery, sealing devices, cutting machines, etc.

[0023] The control system for a machine tool (industrial machinery) according to this embodiment includes, for example, a CNC (Computerized Numerical Control) command unit and a servo motor control device (control unit, servo amplifier) ​​1 that controls the driving of the servo motor (drive unit) of the machine tool based on the CNC command.

[0024] On the other hand, Figure 1 、 Figure 2 As shown, the servo motor control device 1 of this embodiment is configured to include: an incremental position detection unit (position detector / Figure 2 : linear encoder) 2, which detects the position of the shaft of the servo motor, etc.; a magnetic pole detection unit (magnetic pole detector) 3, which detects the magnetic pole position and magnetic pole phase of the servo motor; a phase calculation unit 4, which calculates the phase based on the magnetic pole phase detected by the position detection unit 2 and the magnetic pole spacing information of the motor magnet; and a bias relationship acquisition unit 5, which obtains the bias relationship between the magnetic pole phase obtained from the magnetic pole detection unit 3 and the calculated phase obtained from the phase calculation unit 4 after passing through a predetermined reference position, and the control device 1 of the servo motor sets the magnetic pole phase offset (also called AMR offset) between the motor electrical angle 0° (magnetic pole phase from the U phase) and the motor reference position (Z phase).

[0025] Here, the “absolute position establishment”, “magnetic pole position (magnetic pole phase)”, and “magnetic pole detection unit (magnetic pole detector) 3 ” are described below.

[0026] In incremental encoders, the relationship between the machine's absolute coordinates and the encoder's position signal is unknown when power is turned on. Therefore, "establishing absolute position" means determining this relationship. This is achieved by performing a zero-point return operation based on the encoder's Z-phase signal.

[0027] The so-called "magnetic pole position (magnetic pole phase)" refers to the phase (angle) of the motor magnet. N pole → S pole → N pole, a complete rotation of 360 degrees.

[0028] A "magnetic pole detector" is a device that generates an electrical signal that matches the phase of the motor magnet. For example, when using an encoder to detect both position and magnetic pole position, a signal corresponding to the magnetic pole position is generated at a certain angle based on the relationship between position and magnetic pole position. Alternatively, a Hall effect sensor or other device can be used to directly measure the magnetic field.

[0029] Furthermore, in the servo motor control device 1 of the present embodiment, first, current control is performed as follows after the absolute position is established (after the reference position signal is acquired).

[0030] like Figure 2As shown, in the servo motor control device 1 of this embodiment, the magnetic pole phase used for current control is obtained from the magnetic pole detection unit 3 before the absolute position is established, and the phase from the position detection unit 2 is used after the absolute position is established. That is, in the servo motor control device 1 of this embodiment, the resolution of the position detection unit (position detector) 2 is higher than the resolution of the magnetic pole detection unit (magnetic pole detector) 3. In order to perform current control with high precision, the phase from the position detection unit 2 is used after the absolute position is established (after the offset between the magnetic pole phase and the phase calculated based on the position / magnetic pole interval is established).

[0031] In addition, in the control device 1 of the servo motor of this embodiment, for example, the magnetic pole detection unit 3 is used to obtain (generate) the magnetic pole phase before the absolute position is established, in the case of a linear motor, a linear scale is used to obtain (generate) the magnetic pole phase after the absolute position is established, and in the case of a rotary motor, an incremental encoder is used to obtain (generate) the magnetic pole phase after the absolute position is established.

[0032] More specifically, for example, Figure 3 As shown, the magnetic pole phase before the absolute position is established is obtained from the magnetic pole detection unit 3. The magnetic pole phase before the absolute position is established is the accumulated position / magnetic pole interval after power is turned on and is offset from the actual magnetic pole phase (magnetic pole phase offset).

[0033] On the other hand, the magnetic pole phase after the absolute position is established is obtained from the position detection unit 2. This magnetic pole phase after the absolute position is established is the magnetic pole phase obtained from the position detection unit 2 and is calculated by dividing the absolute position by the magnetic pole spacing + the offset. That is, in the servo motor control device 1 of this embodiment, the magnetic pole phase after the absolute position is established is offset from the origin of the Z phase by the offset.

[0034] Conventionally, for example, incremental encoders typically provide feedback on relative position. Therefore, after power is turned on, the absolute position is unclear. The absolute position is established by operating the motor and obtaining the encoder's Z-phase signal. Furthermore, before the absolute position is established, the magnetic pole phase (electrical angle) is determined based on the magnetic pole position obtained from magnetic pole detector 3 to determine the magnetic pole phase (electrical angle) used for motor current control.

[0035] In contrast, the servo motor control device 1 of the present embodiment is configured so that, after the absolute position is established, the magnetic pole phase from the magnetic pole detection unit 3 is not used. Instead, the value obtained by dividing the absolute position by the magnetic pole interval is used. The magnetic pole phase is thus obtained using the result of an encoder having a resolution much higher than the resolution of the magnetic pole detection unit 3. At this time, a correction process is performed by adding an offset to resolve the problem of an offset between the phase calculated based on the absolute position / magnetic pole interval and the actual magnetic pole phase.

[0036] Therefore, according to the servo motor control device 1 of the present embodiment, the offset can be set more easily and accurately than before.

[0037] Here, if Figure 4 As shown, the servo motor control device 1 of the present embodiment can be configured to obtain an offset at a plurality of points and obtain an average or optimal value, thereby improving the accuracy of the offset.

[0038] For example, the offset relationship between the magnetic pole phase and the calculated phase may be obtained a plurality of times, and the offset relationship may be newly calculated based on at least one of the offset relationships.

[0039] In this way, by acquiring data multiple times after the absolute position is established and obtaining offsets at multiple points, it is possible to further improve the accuracy.

[0040] Furthermore, by averaging the offset values, the influence of variations in the acquisition timing can be eliminated, allowing the offset to be set appropriately and accurately. Furthermore, by selecting the minimum value as the offset when moving in the positive direction and the maximum value as the offset when moving in the negative direction, etc., optimal values ​​can be obtained, allowing the offset to be set appropriately and accurately.

[0041] An embodiment of the servo motor control device has been described above, but the present invention is not limited to the above embodiment and can be modified appropriately without departing from the spirit and scope of the invention.

[0042] Explanation of symbols

[0043] 1. Servo motor control device

[0044] 2. Position detection unit (position detector)

[0045] 3. Magnetic pole detection unit (magnetic pole detector)

[0046] 4Phase calculation unit

[0047] 5. Offset relationship acquisition unit.

Claims

1. A servo motor control device for controlling a servo motor of an industrial machine, characterized in that: have: a position detection unit for detecting the position of the servo motor and acquiring position data; a magnetic pole detecting unit that detects a magnetic pole phase of the servo motor; and a phase calculation unit for calculating a phase based on the position data and magnetic pole interval information of the servo motor; The phase resolution of the position detection unit is higher than the phase resolution of the magnetic pole detection unit. After passing through a reference position, a magnetic pole phase offset relationship between the magnetic pole phase obtained by the magnetic pole detection unit and the calculated phase obtained by the phase calculation unit is obtained. The magnetic pole phase used in current control uses a value obtained by dividing the accumulated position after power-on obtained from the magnetic pole detection unit before the absolute position is established by the magnetic pole interval, and the magnetic pole phase used in current control uses a value obtained by adding a magnetic pole phase offset to a value obtained by dividing the absolute position obtained from the position detection unit after the absolute position is established by the magnetic pole interval.

2. The servo motor control device according to claim 1, wherein: The magnetic pole phase offset relationship between the magnetic pole phase and the calculated phase is obtained multiple times, and the magnetic pole phase offset relationship is newly calculated based on at least one of the magnetic pole phase offset relationships.

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