Position detection device

Abstract

To provide a position detection device capable of diagnosing a bi-phase signal with a smaller positional change than a prior art.SOLUTION: A position detection device calculates a first radius AMP_D1 as a Lissajous radius in a first detection point P1 shown by a bi-phase signal detected at first timing and a second radius AMP_D2 as a Lissajous radius in a second detection point P2 detected at second timing, determines presence or absence of abnormality in the bi-phase signal on the basis of comparison of the first radius AMP_D1 and the second radius AMP_D2 and a prescribed initial radius AMP, and identifies a phase causing abnormality on the basis of a comparison result between the first radius AMP_D1 and the second radius AMP_D2, a quadrant in which the first detection point P1 and the second detection point P2 are positioned, and a displacement direction from the first detection point P1 to the second detection point P2.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This specification discloses a position detection device that converts an output signal from a position sensor that outputs two-phase signals with different 90-degree phases that change sinusoidally with respect to the measured displacement into position information.

Background Art

[0002] In a position detection device used in a machine tool, it is generally performed to diagnose the state of the position detection device by comparing the detected signal with a preset reference value.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The signal used for diagnosis often uses a value obtained by performing some arithmetic processing on the two-phase signal, such as the radius of the Lissajous waveform depicted by the two-phase signal, and does not diagnose the two-phase signal itself. Therefore, for example, when there is an abnormality in the radius of the Lissajous waveform, a detailed diagnosis such as which of the two-phase signals is abnormal cannot be made. Also, when diagnosing the radius of the Lissajous waveform, if the Lissajous waveform is not a perfect circle, the radius is not constant, so an accurate diagnosis cannot be made unless the Lissajous waveform is depicted for one period of the two-phase signal.

[0004] This specification is made in view of the above circumstances, and provides a position detection device capable of diagnosing two-phase signals with a small position change as compared with the prior art. [[ID=,27]]

Means for Solving the Problems

[0005] The position detection device disclosed herein is a position detection device that converts an output signal from a position sensor that outputs two phase signals with 90-degree phase differences that change sinusoidally with respect to a measured displacement into position information, and comprises a calculation unit that calculates the Lissajous radius from the two phase signals, and a diagnostic unit that diagnoses the quality of the two phase signals, wherein the calculation unit calculates a first radius, which is the Lissajous radius at a first detection point indicated by the two phase signals detected at an arbitrary first timing, and a second radius, which is the Lissajous radius at a second detection point indicated by the two phase signals detected at an arbitrary second timing and located in the same quadrant as the first detection point, and the diagnostic unit determines whether there is an abnormality in the two phase signals based on a comparison of the first radius and the second radius and a predetermined initial radius, and if it determines that there is an abnormality, it identifies the phase in which the abnormality is occurring based on the comparison result of the first radius and the second radius, the quadrant in which the first detection point and the second detection point are located, and the displacement direction from the first detection point to the second detection point. [Effects of the Invention]

[0006] The technology disclosed herein enables the diagnosis of two-phase signals from a position detection device with less positional change compared to the conventional technology. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of the position detection device. [Figure 2] This is a flowchart of the diagnostic method. [Figure 3] This is a flowchart showing the diagnostic process for Pattern 1. [Figure 4] This is a flowchart showing the diagnostic process for Pattern 2. [Figure 5] This is a Lissajous waveform corresponding to the judgment result. [Modes for carrying out the invention]

[0008] The configuration of the position detection device is described below. Hereafter, the two-phase signals will be referred to as the A-phase signal and the B-phase signal, respectively, with the A-phase signal being a cosine wave signal and the B-phase signal being a sine wave signal. Figure 1 shows a schematic diagram of the position detection device. The position detection device comprises a communication unit 1, a detection unit 2, a calculation unit 3, a storage unit 4, and a diagnostic unit 5. Physically, the position detection device is a computer comprising a processor 10, memory 12, and a communication interface 14. The various calculations described below are performed by the processor 10.

[0009] The communication unit 1 has the function of sending and receiving data with the higher-level system. The detection unit 2 has the function of transmitting an excitation signal to the position sensor 6 based on a command received from the communication unit 1 and detecting the A-phase signal and B-phase signal output from the position sensor 6. The position sensor 6 outputs the A-phase signal and B-phase signal, which change in response to the measured displacement, to the detection unit 2 based on the excitation signal received from the detection unit 2. The calculation unit 3 has the function of digitizing the A-phase signal and B-phase signal and converting them into position information, and creating data to be transmitted to the higher-level system. The storage unit 4 has the function of storing the signals detected by the detection unit 2 and the information calculated by the calculation unit 3. The diagnostic unit 5 has the function of diagnosing the status of the position detection device from the information from the storage unit 4 and the calculation unit 3 and notifying the calculation unit 3.

[0010] Next, the method for diagnosing the quality of the two-phase signals will be explained. The position detection device stores the radius of the initial Lissajous waveform as the initial radius AMP in the storage unit 4. This initial radius AMP is obtained by driving the machine to operate the position detection device for its full stroke when the machine is mounted or at a timing that is to be used as a reference for diagnosis, and calculating the radius of the Lissajous waveform obtained at that time (i.e., the Lissajous radius). Note that the Lissajous radius may be the Lissajous radius for each signal period of the A-phase signal and the B-phase signal. Next, the diagnostic operation will be explained. Diagnosis is performed only while the machine is running. First, the detection unit 2 acquires the A-phase signal A(t) and B-phase signal B(t) at the first timing t in which the diagnosis is performed. Next, the calculation unit 3 performs various corrections on these values, such as offset correction, amplitude ratio correction, and phase correction. The Lissajous radius at the first detection point P1 represented by the corrected A-phase signal Ac(t) and B-phase signal Bc(t), i.e., the first radius AMP_D1, is calculated using the following equation 1. AMP_D1=√(Ac(t) 2 +Bc(t) 2 ) Equation 1

[0011] Similarly, at the second timing (t+Δt) after a certain time Δt has elapsed, the detection unit 2 acquires the A-phase signal A(t+Δt) and the B-phase signal B(t+Δt). The calculation unit 3 performs various corrections on these values, such as offset correction, amplitude ratio correction, and phase correction. The Lissajous radius at the second detection point P2, i.e., the second radius AMP_D2, represented by the corrected A-phase signal Ac(t+Δt) and B-phase signal Bc(t+Δt), is calculated using the following equation 2. AMP_D2 = √(Ac(t+Δt)) 2 +Bc(t+Δt) 2 ) Equation 2

[0012] Here, the value of Δt is determined by the machine's driving speed and is set to a value that satisfies equations 3 to 5 below. sign(Ac(t))=sign(Ac(t+Δt)) Equation 3 sign(Bc(t))=sign(Bc(t+Δt)) Equation 4 |arctan(Bc(t) / Ac(t))-arctan(Bc(t+Δt) / Ac(t+Δt))|≧45° Equation 5

[0013] Note that sign(P) is a function that represents the sign of the variable P. Therefore, if both equations 3 and 4 are true, the first detection point P1 and the second detection point P2 are located in the same quadrant. Also, equation 5 means that the absolute value of the difference between the angle of the first detection point P1 and the angle of the second detection point P2 is 45 degrees or more. Note that the angle of a detection point is the angle of the line connecting the detection point and the origin with respect to the horizontal axis.

[0014] Based on these values, the diagnostic unit 5 performs a diagnosis according to the flowchart shown in Figure 2. Before the diagnosis, the initial radius AMP is read from the storage unit 4. Next, the initial radius AMP is compared with the first radius AMP_D1, and the initial radius AMP is compared with the second radius AMP_D2 (S10). If the absolute value of the difference between the first radius AMP_D1 and the initial radius AMP is less than the preset first reference value α, and the absolute value of the difference between the second radius AMP_D2 and the initial radius AMP is less than the preset first reference value α, then the two-phase signals are determined to be normal (S18). If the absolute value of the difference between either one is greater than or equal to the first reference value α, then the first radius AMP_D1 and the second radius AMP_D2 are compared (S12). If the absolute value of the difference between the two is less than the preset second reference value β, then the A-phase signal and the B-phase signal are similarly reduced, and it is determined that there is a Lissajous radius abnormality (S20). The second reference value β is a value smaller than the first reference value α. If the absolute value of the difference is greater than or equal to the second reference value β, then the quadrant in which the first detection point P1 is located and the direction of movement from the first detection point P1 to the second detection point P2 are determined (S14, S16, S22). The quadrant in which the first detection point P1 is located is determined based on the signs of the two-phase signals Ac(t) and Bc(t). Specifically, if sign(Ac(t))=sign(Bc(t)) is true (Yes in S14), then the first detection point P1 can be determined to be located in the first or third quadrant. On the other hand, if this is not true (No in S14), then the first detection point P1 can be determined to be located in the second or fourth quadrant. As mentioned above, the second detection point P2 is located in the same quadrant as the first detection point P1.

[0015] The direction of movement is defined as the direction in which the angle of the detection point (i.e., the angle of the line connecting the detection point and the origin with respect to the horizontal axis) increases, which is the position increase direction, and the opposite direction is the position decrease direction. The detection point is obtained by interpolating the A-phase signal and the B-phase signal.

[0016] If the first detection point P1 is located in the first quadrant or the third quadrant (Yes in S14), and the moving direction of the detection point is the position increasing direction (Yes in S16), then pattern 1 diagnosis (S24) is performed. Also, if the first detection point P1 is located in the second quadrant or the fourth quadrant (No in S14), and the moving direction of the detection point is not the position increasing direction (No in S22), then pattern 1 diagnosis (S24) is also performed.

[0017] On the other hand, if the first detection point P1 is located in the first quadrant or the third quadrant (Yes in S14), and the moving direction of the detection point is not the position increasing direction (No in S16), then pattern 2 diagnosis (S26) is performed. Also, if the first detection point P1 is located in the second quadrant or the fourth quadrant (No in S14), and the moving direction of the detection point is the position increasing direction (Yes in S22), then pattern 2 diagnosis (S26) is also performed.

[0018] Figure 3 is a diagram showing the flow of pattern 1 diagnosis, and Figure 4 is a diagram showing the flow of pattern 2 diagnosis. In the diagnosis pattern 1 diagnosis shown in Figure 3, the first radius AMP_D1 and the second radius AMP_D2 are compared (S30). As a result of the comparison, if the first radius AMP_D1 is greater than or equal to the second radius AMP_D2, it is determined that the B-phase signal is abnormal (S​​​​​​​The Lissajous waveforms corresponding to the respective determination results are shown in FIG. 5. In FIG. 5, the solid-line circle indicates the ideal Lissajous waveform C*. Also, the dashed circles Cmax and Cmin indicate the upper and lower allowable limits that can be judged as normal. Further, the thick dashed circle or ellipse indicates the Lissajous waveform obtained from the actually detected two-phase signal.

[0021] Example 1 in FIG. 5 shows the case where it is determined as normal. In Example 1, both the first detection point P1 and the second detection point P2 are located within the allowable range (that is, between the circle Cmax and the circle Cmin). In other words, the absolute value of the difference between the first radius AMP_D1 and the initial radius AMP, and the absolute value of the difference between the second radius AMP_D2 and the initial radius AMP are both less than the first reference value α. Therefore, in the case of Example 1, it becomes Yes in step S10, and the two-phase signal is judged as normal (S18).

[0022] Example 2 shows the case where it is determined that the Lissajous radius is abnormal. In Example 2, both the first detection point P1 and the second detection point P2 are located outside the allowable range (that is, inside the circle Cmin). Therefore, it becomes No in step S10. Also, the absolute value of the difference between the first radius AMP_D1 and the second radius AMP_D2 is less than the second reference value β. In this case, it becomes No in step S12, and it is determined that the Lissajous radius is abnormal where both of the two-phase signals have decreased (S20).

[0023] Example 3 shows a case where a B-phase signal abnormality is determined in Pattern 1 diagnosis. In Example 3, the second detection point P2 is located outside the acceptable range (i.e., inside the circle Cmin), so it can be determined that the 2-phase signal is abnormal (No in S10). Also, because the absolute value of the difference between the first radius AMP_D1 and the second radius AMP_D2 is large, step S12 is Yes. Furthermore, since the first detection point P1 is located in the first quadrant, step S14 is Yes, and since the direction of movement from the first detection point P1 to the second detection point P2 is in the direction of position increase, step S16 is also Yes, and the process proceeds to Pattern 1 diagnosis. Furthermore, in Example 3, the first radius AMP_D1 is larger than the second radius AMP_D2, so step 30 is Yes, and the B-phase signal is determined to be abnormal.

[0024] Example 4 shows a case where an abnormality in the A-phase signal is determined in the Pattern 2 diagnosis. In Example 4, since both the first detection point P1 and the second detection point P2 are located outside the acceptable range (i.e., inside the circle Cmin), it can be determined that the two-phase signal is abnormal (No in S10). Also, because the absolute value of the difference between the first radius AMP_D1 and the second radius AMP_D2 is large, step S12 is Yes. Furthermore, since the first detection point P1 is located in the first quadrant, step S14 is Yes, and since the direction of movement from the first detection point P1 to the second detection point P2 is in the direction of position decrease, step S16 is No, and the process proceeds to Pattern 2 diagnosis. Furthermore, in Example 4, since the first radius AMP_D1 is larger than the second radius AMP_D2, step 40 is Yes, and the A-phase signal is determined to be abnormal.

[0025] The diagnostic unit 5 notifies the calculation unit 3 of the judgment result obtained above. It is preferable to use 2-bit data as the notification method. For example, if bit 1 is phase A and bit 0 is phase B, then 00 indicates no abnormality, 10 indicates a phase A signal abnormality, 01 indicates a phase B signal abnormality, and 11 indicates that both phase A and phase B are abnormal, i.e., a Lissajous radius abnormality. In this way, it is possible to represent which phase is abnormal with 2-bit data. The calculation unit 3 transmits the data received from the diagnostic unit 5 to the communication unit 1. The communication unit 1 outputs the diagnostic result to an alarm device (not shown). The alarm device notifies the operator of the diagnostic result. Therefore, the alarm device may include a display that shows an image representing the diagnostic result, a speaker that outputs sound according to the diagnostic result, and a communication device that sends a message according to the diagnostic result to the operator in the form of email or SMS. The alarm device may also be provided outside the position detection device or may be incorporated into the position detection device.

[0026] The above embodiment makes it possible to diagnose which of the two phase signals of the position detection device is abnormal with less position change compared to conventional technology. Furthermore, since the signal in which the abnormality occurred can be identified, it is also useful for analyzing the cause of the malfunction. For example, if only the A-phase signal is abnormal, it can be estimated that the amplification circuit of the A-phase signal is the cause, and if both the A-phase and B-phase signals are abnormal, it can be estimated that the excitation circuit is the cause. [Explanation of Symbols]

[0027] 1 Communication unit, 2 Detection unit, 3 Calculation unit, 4 Storage unit, 5 Diagnostic unit, 6 Position sensor, 10 Processor, 12 Memory, 14 Communication interface, AMP Initial radius, AMP_D1 First radius, AMP_D2 Second radius, P1 First detection point, P2 Second detection point.

Claims

1. A position detection device that converts an output signal from a position sensor, which outputs a two-phase signal with a 90-degree phase difference that changes sinusoidally in response to the measured displacement, into position information, A calculation unit that calculates the Lissajous radius from the two-phase signals, A diagnostic unit for diagnosing the quality of the two-phase signals, The calculation unit comprises a first radius, which is the Lissajous radius at the first detection point indicated by the two-phase signal detected at an arbitrary first timing, and a second radius, which is the Lissajous radius at the second detection point indicated by the two-phase signal detected at an arbitrary second timing and located in the same quadrant as the first detection point. The aforementioned diagnostic unit, Based on a comparison of the first radius and the second radius with a predetermined initial radius, the presence or absence of an abnormality in the two-phase signal is determined. If an abnormality is determined, the phase in which the abnormality is occurring is identified based on the comparison result of the first radius and the second radius, the quadrant in which the first detection point and the second detection point are located, and the direction of displacement from the first detection point to the second detection point. A position detection device characterized by the following features.

2. A position detection device according to claim 1, A position detection device characterized in that the absolute value of the difference between the angle of the first detection point and the angle of the second detection point is 45 degrees or more.

3. A position detection device according to claim 1 or 2, The position detection device is characterized in that the diagnostic unit determines that the two-phase signal is abnormal if the absolute value of the difference between at least one of the first radius and the second radius and the initial radius is greater than or equal to a specified first reference value.

4. A position detection device according to claim 3, The position detection device is characterized in that, when the diagnostic unit determines that the two-phase signals are abnormal, if the absolute value of the difference between the first radius and the second radius is less than a specified second reference value, it determines that both the two-phase signals have decreased, resulting in a Lissajous radius abnormality.

5. A position detection device according to claim 3, When the diagnostic unit determines that the two-phase signals are abnormal, if the first or second condition is met, it determines that one of the two-phase signals is abnormal, and if the third or fourth condition is met, it determines that the other of the two-phase signals is abnormal. The first condition is that the first detection point and the second detection point are located in the first or third quadrant, and the angle increases and the radius increases or the angle decreases and the radius decreases as one moves from the first detection point to the second detection point. The second condition is that the first detection point and the second detection point are located in the second or fourth quadrant, and the angle increases and the radius decreases or the angle decreases and the radius increases as one moves from the first detection point to the second detection point. The third condition is that the first detection point and the second detection point are located in the first or third quadrant, and the angle increases and the radius decreases or the angle decreases and the radius increases as one moves from the first detection point to the second detection point. The fourth condition is that the first detection point and the second detection point are located in the second or fourth quadrant, and the angle increases and the radius increases or the angle decreases and the radius decreases as you move from the first detection point to the second detection point. A position detection device characterized by the following features.

6. A position detection device according to claim 1, The diagnostic unit is characterized by outputting the abnormal state of the two-phase signal as two-bit data.

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