Control device for a servo motor

Abstract

The present invention provides a control device for a servo motor, which can eliminate the problem of erroneously detecting and setting the position of the shaft of the servo motor due to the influence of noise or the like. A control device for a servo motor performs drive control by detecting the Z-phase signal of an incremental encoder for detecting the rotation of the servo motor. The control device for the servo motor includes: a position detection unit that detects a reference position of the rotation shaft of the servo motor based on the Z-phase signal of the encoder; a signal interval detection unit that measures the interval between a plurality of detected Z-phase signals; and an abnormality determination unit that determines that the Z-phase signal is abnormal when the interval measured by the signal interval detection unit is equal to or greater than a predetermined threshold value.

Description

Technical Field

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

[0002] For example, servo motors for industrial machinery such as servo motors for driving the spindle of a machine tool are subjected to drive control regarding the amount of rotation, speed, torque, etc. In addition, the control device of the servo motor detects the position of the motor and the magnetic pole position (phase (angle) of the motor magnet) by a detector, determines a voltage command value based on various feedback values from the detector, and applies a voltage modulated by a pulse width modulation (PWM) method, thereby performing drive control of the motor.

[0003] In addition, an incremental encoder (position detector) commonly used in an AC servo motor, for example, includes a light emitting element, a rotating slit plate, a light receiving element, a waveform shaping circuit, and a signal transmission circuit. In addition, as output signals, two-phase signals having a 90-degree phase difference from each other to be able to discriminate the rotation direction, a reference origin Z signal of one pulse per rotation, and a commutation signal for performing phase excitation switching of the AC servo motor are used.

[0004] Patent Document 1 discloses "a rotary encoder, comprising: a raw signal output unit that outputs A and B two-phase incremental signals having a 90-degree phase difference from each other, a reference signal Z indicating the origin during one rotation, and phase excitation switching signals (commutation signals) CS1, CS2, and CS3 of a three-phase AC servo motor; a power-on (ON) / off (OFF) detection circuit that detects the on and off states of the main power supply of the encoder; an A and B phase direction discrimination circuit that detects the change edges of the A and B two phases and outputs a forward count pulse and a reverse count pulse according to the phases of the A and B two phases; a reversible counter that pre-loads count initial data according to the output of the power-on / off detection circuit and counts the output pulses of the A and B phase direction discrimination circuit; an initial value detection circuit that outputs the initial data to be pre-loaded into the reversible counter according to the levels of the A and B two phases; an abnormality detection circuit that discriminates whether there is a malfunction of the encoder according to the output from the A and B phase direction discrimination circuit and the Z phase, CS1, CS2, and CS3 phases; a data latch circuit that latches the Z phase and CS1, CS2, and CS3 phases from the raw signal output unit, the data from the reversible counter, and the state from the abnormality detection circuit; a Z signal conversion circuit that samples the Z phase from the raw signal output unit and outputs the state of the Z phase; and a parallel-serial conversion circuit that converts the count data, CS1, CS2, and CS3 phases, the state, and the data output from the Z signal conversion circuit output from the data latch circuit into serial data and outputs it."

[0005] Prior art documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Laid-Open No. 09-280891 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] On the other hand, for example, as Figure 6 shown, when performing an operation of capturing a Z-phase signal to establish the position of the shaft of a servo motor or the like (an operation of establishing an absolute (reference) position) for position control of a servo motor using an incremental encoder as a position detector, depending on the speed at the time of Z-phase detection, the Z-phase signal may not be detected at the correct position due to the influence of noise or the like. As a result, in this case, there is a problem that the absolute position is shifted and position control cannot be performed with high precision.

[0010] Solutions for solving the problems

[0011] One aspect of the control device for a servo motor according to the present disclosure is a control device for a servo motor that performs drive control by detecting a Z-phase signal of an incremental encoder for detecting the rotation of the servo motor. The control device for the servo motor includes: a position detection unit that detects a reference position of a rotation shaft of the servo motor based on the Z-phase signal of the encoder; a signal interval detection unit that measures an interval between a plurality of detected Z-phase signals; and an abnormality determination unit that determines that the Z-phase signal is abnormal when the interval measured by the signal interval detection unit is equal to or greater than a predetermined threshold.

[0012] Effects of the invention

[0013] According to one aspect of the control device for a servo motor according to the present disclosure, in the detection operation of the Z-phase signal, the interval between a plurality of detected Z-phase signals is measured, and it is determined whether the interval exceeds a preset threshold (range of the threshold), whereby it is possible to determine whether the Z-phase signal is abnormal. As a result, it is possible to eliminate the problem of erroneously detecting and setting the position of the shaft of the servo motor or the like due to the influence of noise or the like, and as a result, it is possible to perform highly reliable position control with high precision. Brief Description of the Drawings

[0014] Figure 1 is a diagram showing a control system of a servo motor according to one aspect.

[0015] Figure 2 is a block diagram showing a control device of a servo motor according to one aspect.

[0016] Figure 3 It is a flowchart showing a method for determining the presence or absence of an abnormality in a Z-phase signal using a control device for a servo motor in one manner.

[0017] Figure 4 It is a flowchart showing a method for determining the presence or absence of an abnormality in a Z-phase signal using a control device for a servo motor in one manner.

[0018] Figure 5 It is a flowchart showing a method for determining the presence or absence of an abnormality in a Z-phase signal using a control device for a servo motor in one manner.

[0019] Figure 6 It is a diagram for explaining false detection caused by the influence of noise or the like.

[0020] Explanation of reference signs

[0021] 1: Control system of servo motor; 2: Upper control device (CNC); 3: Servo motor; 4: Control device of servo motor; 5: Encoder; 6: Position detection unit; 7: Signal interval detection unit; 8: Abnormality determination unit; 9: Speed change unit; 10: Abnormality notification unit. Detailed implementation mode

[0022] Next, with reference to Figures 1 to 5 a control device for a servo motor according to an embodiment will be described.

[0023] In the present embodiment, it is assumed that the industrial machine is a machine tool, and the control device of the servo motor drives and controls the spindle of the machine tool, etc. for explanation.

[0024] However, the control device for a servo motor according to the present invention is not limited to being applied to a machine tool, and of course, it can also be applied to the drive control of a servo motor used in other industrial machines such as robots, conveyors, measuring instruments, test devices, presses, press-fit machines, printing machines, die-casting machines, injection molding machines, food machines, packaging machines, welding machines, cleaning machines, coating machines, assembly devices, mounting machines, woodworking machines, sealing devices, cutting machines, etc.

[0025] For example, as Figure 1As shown, the control system 1 of the machine tool (industrial machine) of the present embodiment is configured to include: a CNC (Computerized Numerical Control) 2 as an upper control device; a control device (such as a servo amplifier, a motor control device) 4 of a servo motor, which controls the drive of the servo motor (drive unit) 3 of the machine tool based on the instruction of the CNC 2; and an incremental encoder (incremental encoder) 5, which detects the rotation of the servo motor 3.

[0026] As Figure 1 , Figure 2 shown, the control device 4 of the servo motor of the present embodiment includes: a position detection unit 6, which detects the reference position of the rotation axis of the servo motor 3 based on the Z-phase signal of the encoder 5; a signal interval detection unit 7, which measures the interval between the detected multiple Z-phase signals; and an abnormality determination unit 8, which determines that the Z-phase signal is abnormal when the interval measured by the signal interval detection unit 7 is equal to or greater than a predetermined threshold.

[0027] Moreover, in the control device 4 of the servo motor of the present embodiment, there is provided: a speed change unit 9, which changes the speed of the servo motor 3 when it is determined to be abnormal by the abnormality determination unit 8; and an abnormality notification unit 10, which notifies an abnormality to the CNC 2 or the like as an upper control device when: at the stage of changing the speed of the servo motor 3 to a predetermined speed, the latest detected value of the interval between the Z-phase signals is equal to or greater than a predetermined threshold, or the average value of the detected values of the interval between the Z-phase signals within a fixed period is equal to or greater than a predetermined threshold, so that the abnormality determination unit 8 determines it to be abnormal.

[0028] Furthermore, when performing position control using the control device 4 of the servo motor of the present embodiment configured as described above, as Figure 3 ( Figure 1 , Figure 2 ) shown, as the servo motor 3 is driven, the encoder 5 starts to detect the shaft rotation position of the servo motor 3 together, and the position detection unit 6 detects the reference position of the rotation axis of the servo motor 3 based on the Z-phase signal of the encoder 5.

[0029] At this time, in the control device 4 of the servo motor of the present embodiment, in the rotation state of the servo motor 3, the signal interval detection unit 7 receives multiple Z-phase signals and starts measuring the time from the detection of the previous Z-phase signal to the detection of the next Z-phase signal (the current Z-phase signal) (step 1).

[0030] When the Z-phase signal is detected (step 2) and the signal interval detection unit 7 measures the interval between the previous Z-phase signal and the next Z-phase signal, the abnormality determination unit 8 confirms whether the interval exceeds a threshold value (the range of the upper and lower limits of the threshold value) preset based on the normal value (step 3).

[0031] When the threshold value is not exceeded, the abnormality determination unit 8 determines that the current Z-phase signal is normal and establishes the reference position (absolute position establishment) (step 4).

[0032] When it is above the threshold value, the abnormality determination unit 8 determines that the current Z-phase signal is abnormal and does not establish the reference position (step 5).

[0033] Here, in the present embodiment, it is set to determine whether there is an abnormality by confirming whether the most recent detected value of the interval of the Z-phase signal is above a predetermined threshold value. However, it may also be set to determine whether there is an abnormality by confirming whether the average value of the detected values of a plurality of Z-phase signals detected within a fixed period is above a predetermined threshold value.

[0034] In addition, in the control device 4 of the servo motor in the present embodiment, preferably, as Figure 4 shown, when the abnormality determination unit 8 determines that it is abnormal, the abnormality notification unit 10 notifies an abnormality to the CNC 2 or the like, which is a higher-level control device (step 6).

[0035] And, in the control device 4 of the servo motor in the present embodiment, as Figure 5 ( Figure 1 ) shown, when the abnormality determination unit 8 determines that it is abnormal, the speed of the servo motor 3 is changed to increase or decrease within a preset range, and the interval of the Z-phase signal after the speed change is measured again (retry) (steps 7, 8, 1), and the abnormality determination is performed again. In addition, for the value of the speed change, a plurality of values are also preset within a preset range, and the intervals between the Z-phase signals at each set change speed are repeatedly measured again (retry).

[0036] Therefore, in the control device 4 of the servo motor in the present embodiment, in the detection operation of the Z-phase signal, the intervals between the detected plurality of Z-phase signals are measured, and it is determined whether the interval exceeds a preset threshold value (the range of the threshold value), thereby enabling the determination of whether there is an abnormality in the Z-phase signal. As a result, problems such as misdetection and mis-setting of the position of the shaft of the servo motor 3 due to the influence of noise or the like can be eliminated, and as a result, highly reliable position control can be performed with high precision.

[0037] In addition, when the abnormality determination unit 8 determines an abnormality, the speed of the servo motor 3 is changed, and the signal interval detection unit 7 measures the interval between Z-phase signals again (retry), whereby it is possible to capture the abnormality of the Z-phase signal with higher accuracy.

[0038] In addition, an abnormality notification unit 10 is provided. When the abnormality determination unit 8 determines an abnormality, the abnormality notification unit 10 notifies an abnormality to the CNC 2 or the like, which is a host control device. As a result, the operator can quickly recognize the abnormality, and further stop the servo motor 3 or generate an alarm, thereby preventing an unexpected dangerous operation of the machine tool (industrial machine).

[0039] As described above, one embodiment of the control device for a servo motor has been described. However, the present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist thereof.

[0040] For example, in the present embodiment, when the abnormality determination unit 8 determines an abnormality, the speed change unit 9 changes the speed of the servo motor 3, and the signal interval detection unit 7 measures the interval between Z-phase signals again at the stage where the speed of the servo motor 3 is changed to a predetermined speed. The abnormality determination unit 8 and the abnormality notification unit 10 perform abnormality determination and notification.

[0041] On the contrary, it may be configured to fix the speed, detect the time for detecting the Z-phase signal, and determine the presence or absence of an abnormality based on the detection times (intervals) of a plurality of Z-phase signals.

Claims

1. A control device for a servo motor performs drive control by detecting a Z-phase signal of an incremental encoder for detecting the rotation of the servo motor. The control device for the servo motor includes: a position detection unit that detects a reference position of a rotation shaft of the servo motor based on the Z-phase signal of the encoder; a signal interval detection unit that measures an interval between a plurality of detected Z-phase signals; and an abnormality determination unit that determines that the Z-phase signal is abnormal when the interval measured by the signal interval detection unit is equal to or greater than a predetermined threshold, Among them, and changes the speed of the servo motor when the abnormality determination unit determines an abnormality, and performs re-measurement by the signal interval detection unit.

2. The control device for a servo motor according to claim 1, wherein it is configured to change the speed of the servo motor within a preset range when the abnormality determination unit determines an abnormality, and perform re-measurement by the signal interval detection unit after the speed change of the servo motor is completed.

3. The control device for a servo motor according to claim 1 or 2, wherein it further includes an abnormality notification unit that notifies an upper control device of an abnormality when, at a stage where the speed of the servo motor is changed to a predetermined speed, a most recently detected value of an interval between the Z-phase signals is equal to or greater than a predetermined threshold, or an average value of detected values of the interval between the Z-phase signals within a fixed period is equal to or greater than a predetermined threshold, and thus the abnormality determination unit determines an abnormality.

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