Machine tool control device with diagnostic function for malfunctions of the sensor for detecting a 1-revolution signal

Abstract

Machine tool control device for driving a feed axis or a main axis by a motor, comprising: a feedback counter (1) for receiving A- and B-phase signals of square waves or sine waves and a 1-revolution signal generated each time the motor or main axis completes one revolution, wherein the A and B phase signals and the 1-revolution signal are provided by a sensor for detecting the position or speed of the driven axis or of the motor to calculate a feedback count, which is a count of the number of feedback pulses generated by the A and B phase signals; a feedback count storage unit (2) for storing an inter-1-revolution signal feedback count, which is the feedback count counted between two sequential 1-revolution signals; a reference value storage unit (3) for storing an abnormality determination reference value for determining the presence or absence of an abnormality according to the inter-1-revolution signal feedback count value; and an abnormality cause determination unit (4) for determining the cause of the abnormality by comparing the inter-1-revolution signal feedback count value with the abnormality determination reference value, wherein, when the inter-1-revolution signal feedback count is higher than the anomaly determination reference value and a difference between the inter-1-revolution signal feedback count and an inter-1-revolution signal feedback count in the normal case corresponds to an integer multiple of an error calculated from the number of pulses or waves of the A- and B-phase signals per revolution, the anomaly cause determination unit (4) determines that noise is disturbing the A- and B-phase signals; and if the difference is not an integer multiple of the error, the abnormality cause determination unit (4) determines that there is an abnormality in the 1-turn signal.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a machine tool control device, and more particularly to a machine tool control device having a function for diagnosing a malfunction of a sensor for detecting 1-revolution signals. 2. Description of related technology

[0002] When driving feed axes or main axes of machine tools, sensors are used to detect the rotational speeds or positions of the axes. If a sensor malfunction occurs, it is necessary to analyze the cause of the malfunction. Analyzing the cause of the sensor malfunction generally requires external measuring devices, such as an oscilloscope and a computer tool. These devices are used to measure the waveforms of the sensor signals and deduce the cause of the malfunction from the waveforms.

[0003] Possible causes of sensor malfunctions include faulty wiring, sensor installation errors, noise, and the like. However, determining the specific cause using the above-mentioned tools is time-consuming and expensive.

[0004] Accordingly, a device has been reported that counts the number of feedback pulses between the pulses of a Z-phase signal (1-turn signal) and detects a wire connection error when a count value differs from a predetermined value (for example, Japanese Utility Model Registration No. 2574740). According to this device, an anomaly in the feedback signal can be measured based on the count value of the number of feedback pulses between the 1-turn signals. However, since all anomalous count values ​​are determined as wire connection errors, there is a problem that it cannot be determined whether an anomaly in the count value is caused by noise or by a sensor itself. SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide a machine tool control device which can determine an abnormal part of a sensor when an abnormality is detected in a count value of the number of feedback pulses between 1-revolution signals.

[0006] A machine tool control device according to an embodiment of the present invention drives a feed axis or a master axis by a motor. The machine tool control device includes a feedback counter for receiving the A- and B-phase signals of square waves or sine waves and a 1-revolution signal generated each time the motor or master axis makes one revolution, which are output from a sensor for detecting the position or rotational speed of the driven axis or motor, to calculate the feedback count, which is a count of the number of feedback pulses generated by the A- and B-phase signals; a feedback count storage unit for storing an intermediate 1-revolution signal feedback count corresponding to the feedback count counted between the two sequential 1-revolution signals;a reference value storage unit for storing an abnormality determination reference value for determining the presence or absence of an abnormality in accordance with the inter-1-revolution signal feedback count value; and an abnormality cause determination unit for determining the cause of the abnormality by comparing the inter-1-revolution signal feedback count value and the abnormality determination reference value.

[0007] JP H11-264742 A discloses a displacement amount detection device that can further ensure encoder displacement detection. Each time a servo motor origin is detected by a counter data latch circuit, a CPU detects the individual displacement amount of an encoder based on a difference value from the last detected original data. The individual displacement amount is accumulated, and if the accumulated position displacement amount exceeds a preset allowable value of the accumulated displacement amount, it is judged to be abnormal.

[0008] DE 10 2012 011 722 A1 discloses an absolute position detector with an abnormality function. In the absolute position detector, a relative error calculation circuit calculates, at timings specified by a clock signal C1, a relative error E between an output θ2 from an absolute position detection sensor and a position output θ1 from a high-resolution position detection sensor. An abnormality judgment unit judges whether the relative error E exceeds a predetermined abnormality judgment value. A clock switching unit outputs, as the clock signal, a high-rate clock CH having a shorter period than a noise generation period when the relative error E is judged to exceed the predetermined abnormality judgment value, and outputs a low-rate clock CL in other cases.A counter measures a period of time in which the abnormality detection signal AF is maintained at HIGH based on the clock signal C1 and issues an alarm when the period of time exceeds the noise generation period. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The objects, features, and advantages of the present invention will become more apparent from the following detailed description of a preferred embodiment, together with the accompanying drawings. In the accompanying drawings: Fig. 1 is a block diagram of a machine tool control device according to the embodiment of the present invention; Fig. 2 is a flowchart of the schematic operation method of the machine tool control device according to the embodiment of the present invention; Fig. 3 is a flowchart of an abnormality determination process when an inter-1-revolution signal feedback count value is smaller than the abnormality determination reference value in the machine tool control device according to the present embodiment of the invention; Fig. 4 is a flowchart of an abnormality determination process when an inter-1-revolution signal feedback count value is greater than the abnormality determination reference value in the machine tool control device according to the present embodiment of the invention; and Fig. 5 is a flowchart of an abnormality determination process when an inter-1-revolution signal feedback count value is smaller or larger than the abnormality determination reference value in the machine tool control device according to the present embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] A machine tool control device according to the invention will be described below with reference to the accompanying drawings. Fig. 1 is a block diagram of a machine tool control device according to an embodiment of the present invention. A machine tool control device (hereinafter referred to simply as a "control device") 10 for driving a feed axis or main axis by a motor 30 includes a feedback counter 1, a feedback count value storage unit 2, a reference value storage unit 3, an abnormality cause determination unit 4, and a motor control unit 5.

[0011] A sensor 40 is provided near the motor 30. The sensor 40 detects the position or rotational speed of a driven axis (not shown) or the motor 30. An encoder, for example, can be used as the sensor 40. The sensor 40 outputs A- and B-phase signals and one-revolution signals. The A- and B-phase signals are two pulse signals with a phase difference of 90°. The B-phase signal has a phase difference of +90° or -90° with respect to the output A-phase signal, depending on the direction of rotation of the motor. Depending on the rotational speed of the motor, the number of pulses (feedback pulses) of each output A- and B-phase signal is increased or decreased. Depending on the rotational speed of the motor, the pulse interval of each output A- and B-phase signal is increased or decreased.The 1-revolution signal is a pulse signal that is generated every time the motor or main axis completes one revolution.

[0012] The motor control unit 5 controls the motor 30 with the 1-revolution signals and the A and B phase signals from sensor 40 as feedback signals.

[0013] Feedback counter 1 receives the A- and B-phase signals and the 1-turn signal output from sensor 40 to calculate an intermediate 1-turn signal feedback count. The intermediate 1-turn signal feedback count is a count of the number of feedback pulses generated by the A- and B-phase signals between the two sequential 1-turn signals. Feedback counter 1 outputs the calculated intermediate 1-turn signal feedback count to anomaly cause determination unit 4.

[0014] The anomaly cause determination unit 4 has the feedback count value storage unit 2 and the reference value storage unit 3. However, the feedback count value storage unit 2 and the reference value storage unit 3 may be provided outside the anomaly cause determination unit 4.

[0015] The feedback count storage unit 2 stores the inter-1-revolution signal feedback count.

[0016] The reference value storage unit 3 stores an abnormality determination reference value for determining the presence or absence of an abnormality in accordance with the inter-1-revolution signal feedback count value. For example, the abnormality determination reference value may be set to a standard count value (Ct1), which is an inter-1-revolution signal feedback count value assumed to be obtained when the sensor 40 is operating normally. The abnormality determination reference value may be set to an allowable error. However, these are only examples, and the present invention is not limited thereto.

[0017] The abnormality cause determination unit 4 determines the cause of an abnormality by comparing the inter-1-revolution signal feedback count value with the abnormality determination reference value. A method for determining the cause of an abnormality will be described in detail later. The abnormality cause determination unit 4 outputs a determination result regarding the cause of the abnormality to a numerical control device 20.

[0018] The numerical control device 20 includes a monitor 21. Upon receiving a signal (notification) that the inter-1-revolution signal feedback count output from the abnormality cause determination unit 4 differs from the abnormality cause determination value, the numerical control device 20 displays a notification for initiating an abnormality occurrence check on the monitor 21. The monitor 21 may also display a notification that the 1-revolution signals are detected or the feedback pulses between the 1-revolution signals.

[0019] Next, the schematic operation procedure of the machine tool control device according to the embodiment of the present invention will be described with reference to the flowchart Fig. 2. In step S101, sensor 40 detects 1-turn signals. Sensor 40 also detects A- and B-phase signals and outputs the detected 1-turn signals and A- and B-phase signals to feedback counter 1.

[0020] In step S102, feedback counter 1 calculates an inter-1-revolution signal feedback count (Ct2). Feedback counter 1 outputs the calculated inter-1-revolution signal feedback count to abnormality cause determination unit 4. Abnormality cause determination unit 4 stores the obtained inter-1-revolution signal feedback count in feedback count storage unit 2.

[0021] In step S103, the abnormality cause determination unit 4 determines the status of the sensor. In other words, the abnormality cause determination unit 4 determines the status of the sensor by comparing the inter-1-revolution signal feedback count stored in the feedback count storage unit 2 with the abnormality determination reference value stored in the reference value storage unit 3.

[0022] As described above, the machine tool control device according to the embodiment of the present invention can detect the presence or absence of an abnormality in the sensor based on the 1-revolution signals and the A and B phase signals output from the sensor.

[0023] Next, a method for determining the cause of an abnormality in the sensor is described. The machine tool control device 10 determines an abnormal part of the sensor in cases where an abnormality occurs in the 1-revolution signals and when an abnormality occurs in the A- and B-phase signals, taking into account how feedback pulses vary between the 1-revolution signals.

[0024] An abnormality determination process of the machine tool control device according to the embodiment of the present invention when an inter-1-revolution signal feedback count value is less than an abnormality determination reference value will first be described with reference to the flowchart in Fig. 3 described.

[0025] First, in step S201, it is determined whether an inter-1-revolution signal feedback count (count value (Ct2)) is less than an abnormality determination reference value A. When noise causes disturbance and abnormality in 1-revolution signals, the 1-revolution signals are likely to occur at multiple locations during one revolution. Therefore, the inter-1-revolution signal feedback count (count value) is likely to be much lower than in normal cases.

[0026] Likewise, if a sensor installation error prevents normal counting of pulses generated by A- and B-phase signals, the inter-1-revolution signal feedback count is likely to be much lower.

[0027] Therefore, if the inter-1-revolution signal feedback count is less than the abnormality determination reference value A, it is determined in step S202 that there is an abnormality in the 1-revolution signals or the sensor installation. As described above, if the inter-1-revolution signal feedback count is less than the abnormality determination reference value, it is determined that noise is interfering with the 1-revolution signals or that there is a problem with the sensor installation.

[0028] Next, an abnormality determination process of the machine tool control device according to the embodiment of the present invention when an inter-1-revolution signal feedback count value is higher than the abnormality determination reference value will be described.

[0029] When noise interferes with the A- and B-phase signals, an anomaly occurs in a circuit for detecting phase changes by comparing the A-phase signals with the B-phase signals. Therefore, compared with a value for normal cases, a count of feedback pulses has an error D in a period of one pulse width of each signal when the A- and B-phase signals are square waves, and in a period of one wavelength of each signal when the A- and B-phase signals are sine waves. However, the error due to a single anomaly is relatively small. Therefore, the inter-1-turn signal feedback count will not be much lower than in normal cases.Therefore, it is determined that the A- and B-phase signals are disturbed by noise when the inter-1-revolution signal feedback count value is higher than the abnormality determination reference value, and an error relative to a value in normal cases is an integer multiple of the error D. In other words, the abnormality cause determination unit 4 determines that noise interferes with the A- and B-phase signals when the inter-1-revolution signal feedback count value is higher than the abnormality determination reference value, and the error between the inter-1-revolution signal feedback count value and an inter-1-revolution signal feedback count value at which the sensor functions normally is an integer multiple of the error calculated from the number of pulses or waves of the A- and B-phase signals per revolution as an error likely to occur when noise interferes with the A- and B-phase signals.

[0030] On the other hand, if the inter-1-revolution signal feedback count value is higher than the abnormality determination reference value, and the error relative to the value in normal cases is not an integer multiple of the error D, it is determined that an abnormality in the 1-revolution signals is likely to cause variations at the generation points of the 1-revolution signals. In other words, the abnormality cause determination unit 4 determines that an abnormality in the 1-revolution signals exists if the error of the inter-1-revolution signal feedback count value is not an integer multiple of an error likely to occur when noise interferes with the A- and B-phase signals.

[0031] Next, the abnormality determination process of the machine tool control device according to the embodiment of the present invention when an inter-1-revolution signal feedback count value is higher than an abnormality determination reference value will be described with reference to the flowchart in Fig. 4. First, in step S301, it is determined whether an inter-1-revolution signal feedback count value (count value (Ct2)) is higher than an abnormality determination reference value A. If the count value is higher than the abnormality determination reference value A, it is determined in step S302 whether the following equation (1) holds, which indicates that the difference between an inter-1-revolution signal feedback count value (Ct1) at which the sensor functions normally and the calculated inter-1-revolution signal feedback count value (Ct2) is an integer multiple of the (n-times) error D. (Ct1−Ct2)=n×D

[0032] If equation (1) holds, it is determined in step S303 that an abnormality due to noise occurs in the A- and B-phase signals. On the other hand, if equation (1) does not hold, it is determined in step S304 that an abnormality occurs in the Z-phase signal (1-turn signals).

[0033] The above describes the methods for determining an abnormality in cases where the inter-1-revolution signal feedback count value (count value (Ct2)) is lower and higher than the abnormality determination reference value A, respectively. However, this is not limited to this, as both methods can also be performed sequentially. A method for determining the presence or absence of an abnormality, in which, after determining the presence or absence of an abnormality under the condition that an inter-1-revolution signal feedback count value (count value (Ct2)) is higher than the abnormality determination reference value A, the presence or absence of an abnormality is determined under the condition that the inter-1-revolution signal feedback count value (count value (Ct2)) is lower than the abnormality determination reference value A, is described with reference to a flowchart in Fig. 5 described.

[0034] First, in step S401, it is determined whether an inter-1-revolution signal feedback count value (count value (Ct2)) is higher than an abnormality determination reference value A. If the count value is higher than the abnormality determination reference value A, it is determined in step S402 whether the above equation (1), which indicates whether the difference between an inter-1-revolution signal feedback count value (Ct1) when the sensor is functioning normally and the calculated inter-1-revolution signal feedback count value (Ct2) is an integer multiple of the (n-times) error D, holds.

[0035] If equation (1) holds, it is determined in step S403 that an abnormality due to noise occurs in the A- and B-phase signals. On the other hand, if equation (1) does not hold, it is determined in step S404 that an abnormality occurs in the Z-phase signal (1-turn signals).

[0036] On the other hand, if the count value is lower than the abnormality determination reference value A, it is determined in step S405 whether the inter-1-revolution signal feedback count value (count value (Cts)) is lower than the abnormality determination reference value A. If the inter-1-revolution signal feedback count value is lower than the abnormality determination reference value A, it is determined in step S406 that an abnormality occurs in the 1-revolution signals or in the sensor installation.

[0037] On the other hand, when the inter-1-revolution signal feedback count value (count value (Ct2)) is equal to the abnormality determination reference value A, it is determined that the sensor has no abnormality.

[0038] The above describes the method in which, after determining the presence or absence of an abnormality under the condition that the inter-1-revolution signal feedback count value is higher than the abnormality determination reference value, the presence or absence of an abnormality is determined under the condition that the inter-1-revolution signal feedback count value is lower than the abnormality determination reference value, but the present invention is not limited to this. In other words, after determining the presence or absence of an abnormality under the condition that an inter-1-revolution signal feedback count value is lower than the abnormality determination reference value, the presence or absence of an abnormality can be determined under the condition that the inter-1-revolution signal feedback count value is higher than the abnormality determination reference value.

[0039] As described above, the machine tool control device according to the embodiment of the present invention can monitor the status of the sensor without using external measuring devices and determine an abnormal part of the sensor.

[0040] According to the machine tool control device of the embodiment of the present invention, it is possible to determine an abnormal part of the sensor when an abnormality is detected in a count value of the number of feedback pulses between the 1-revolution signals.

Claims

[1] Machine tool control device for driving a feed axis or a main axis by a motor, comprising: a feedback counter (1) for receiving A- and B-phase signals of square waves or sine waves and a 1-revolution signal generated each time the motor or main axis completes one revolution, wherein the A and B phase signals and the 1-revolution signal are provided by a sensor for detecting the position or speed of the driven axis or of the motor to calculate a feedback count, which is a count of the number of feedback pulses generated by the A and B phase signals; a feedback count storage unit (2) for storing an inter-1-revolution signal feedback count, which is the feedback count counted between two sequential 1-revolution signals; a reference value storage unit (3) for storing an abnormality determination reference value for determining the presence or absence of an abnormality according to the inter-1-revolution signal feedback count value; and an abnormality cause determination unit (4) for determining the cause of the abnormality by comparing the inter-1-revolution signal feedback count value with the abnormality determination reference value, wherein, when the inter-1-revolution signal feedback count is higher than the anomaly determination reference value and a difference between the inter-1-revolution signal feedback count and an inter-1-revolution signal feedback count in the normal case corresponds to an integer multiple of an error calculated from the number of pulses or waves of the A- and B-phase signals per revolution, the anomaly cause determination unit (4) determines that noise is disturbing the A- and B-phase signals; and if the difference is not an integer multiple of the error, the abnormality cause determination unit (4) determines that there is an abnormality in the 1-turn signal. [2] The machine tool control device according to claim 1, wherein, when the inter-1-revolution signal feedback count value is lower than the abnormality determination reference value, the abnormality cause determination unit (4) determines that there is an abnormality in the 1-revolution signal due to noise or an abnormality in sensor installation. [3] A machine tool control device according to any one of claims 1 to 2, wherein, when the inter-1-revolution signal feedback count value is different from the abnormality determination reference value, a signal is output to indicate a message for initiating an abnormality occurrence check.

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