Position detector

Abstract

To obtain an A-phase signal and a B-phase signal similar to a signal locus passing through a K point and a Q point on a Lissajous figure and allowing fault diagnosis of an abnormality detection circuit even when the A-phase signal and the B-phase signal output from a position detector do not change.SOLUTION: A position detector comprises a light-emitting element 12, a scale 10, an index scale 13a, and a light receiving element 14a converting light passing through the scale 10 and the index scale 13a into an electrical signal. The scale 10 is provided with main grid scale marks 16 and auxiliary grid scale marks 17. The A-phase signal and the B-phase signal are changed by individually turning on diagnosis light-emitting elements 20, 21 provided close to the light receiving element 14a one by one. This provides an effect similar to a signal locus moving on a Lissajous figure around 1 / 4 cycle. When fault occurs in an abnormality detection circuit, an internal determination circuit can determine the abnormality.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical position detector that can be used for position measurement in machine tools such as milling machines and semiconductor manufacturing apparatuses. Background Art

[0002] A position detector according to the prior art will be described with reference to FIG. 6. FIG. 6 is a perspective view showing an example of a signal detection unit of an optical position detector according to the prior art.

[0003] A position detector used as a position detection device for a moving shaft of a machine tool or the like includes a scale 10 and a slider 15 that linearly moves relatively to the scale 10.

[0004] Main grating graduations 16 and auxiliary grating graduations 17 with mutually different pitches are formed on the scale 10. The main grating graduations 16 and the auxiliary grating graduations 17 are each periodic graduations.

[0005] The slider 15 is provided with a light-transmissive index scale 13a, a light-emitting element 12, a collimator lens 11, and the like. The index scale 13a forms four periodic sub-gratings corresponding to the main grating graduations 16. The light-receiving unit includes four light-receiving elements 14a corresponding to the four sub-gratings. The collimator lens 11 collimates light emitted from the light-emitting element 12 into parallel light.

[0006] The relative movement of the slider 15 in the longitudinal direction of the scale 10 causes a change in light intensity. The light intensity change is photoelectrically converted by the light-receiving elements 14a, whereby four signals a1, a2, b1, b2 having the same period and different phases are obtained.

[0007] By applying the following differential operation to the above four signals (i.e., signals a1, a2, b1, b2), an A-phase signal with no offset and a B-phase signal that is 90° ahead in phase relative to the A-phase signal can be obtained. A-phase signal = a1 - a2 B-phase signal = b1 - b2

[0008] The A-phase and B-phase signals are analog signals with sine or cosine shapes. Figure 4a shows the trajectories of the A-phase and B-phase signals on a Lissajous figure. The horizontal axis represents the A-phase signal, and the vertical axis represents the B-phase signal. In Figures 4b and 4c, described later, the horizontal axis also represents the A-phase signal, and the vertical axis represents the B-phase signal. When the slider 15 moves one pitch on the main grid scale 16 of the scale 10, the signal trajectory completes one revolution on the Lissajous figure.

[0009] Referring to Figure 5, the anomaly detection circuit included in the position detector described above will be explained. Figure 5 is a block diagram of the anomaly detection circuit.

[0010] The sine signal output from the photodetector represents the A-phase signal. The cosine signal output from the photodetector represents the B-phase signal.

[0011] The method for detecting anomalies is as follows: When the machine operates and sine and cosine signals are obtained, these signals are pulsed, and a phase count is performed by a counter. Specifically, when the signal trajectory exceeds one quadrant on the Lissajous figure, a count value of "1" is obtained. When the signal trajectory completes one revolution and exceeds four quadrants, a count value of "4" is obtained. When the signal trajectory completes N revolutions, a count value of "N × 4" is obtained. The speed can be determined by calculating the difference between the count value obtained during the previous position detection and the count value obtained during the current position detection. By comparing this speed with the maximum speed threshold, anomalies can be detected.

[0012] Furthermore, by performing A / D conversion on the A-phase signal and the B-phase signal, calculating the sum of the squares of each value after A / D conversion to determine the Lissajous radius, and comparing this Lissajous radius with the lower and upper threshold limits to determine the amplitude, anomalies can be detected.

[0013] As described above, in conventional technology, abnormalities are detected by a dual abnormality detection system consisting of a speed determination function and an amplitude determination function. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2021-196279 [Overview of the project] [Problems that the invention aims to solve]

[0015] In conventional diagnostic methods, a failure mode may occur in which the A-phase signal is normal, but the amplitude of the B-phase signal decreases. Figure 4b shows a Lissajous figure of this failure mode. In the example of the failure mode shown in Figure 4b, the amplitude of the B-phase signal is reduced to approximately half.

[0016] Furthermore, Figure 4c shows the Lissajous figure when the amplitude of the A-phase signal is abnormal. In the example of the failure mode shown in Figure 4c, the amplitude of the A-phase signal is approximately 1 / 4, and a positive offset is superimposed on the signal trajectory. It is expected that the failure modes shown in Figures 4b and 4c will occur when the electronic circuitry included in the operational amplifier circuit that performs differential amplification of the A-phase and B-phase signals fails, etc.

[0017] When the machine stops immediately after power-on, one point is obtained on the Lissajous figure. For example, if the power is turned on at point Q in Figure 4b, the signal amplitude is smaller than the lower limit, so an abnormality can be detected before the machine starts operating. However, if the power is turned on at point K, the amplitudes of the A-phase signal and the B-phase signal are the same as the amplitudes under normal conditions, so it is determined to be normal and an abnormality cannot be detected. In Figures 4a, 4b, and 4c, the lower limit of the threshold for this amplitude determination is indicated by the dashed line ERLLVL, and the upper limit of the threshold is indicated by the dashed line ERHLVL.

[0018] Furthermore, in the example shown in Figure 4c, the amplitude analysis cannot detect an anomaly regardless of whether the power-on point is point K or point Q.

[0019] In the examples shown in Figures 4b and 4c, since the machine is stopped, it is not possible to detect an abnormality by determining the speed at which the A-phase signal and B-phase signal are pulsed.

[0020] As described above, conventional diagnostic methods cannot detect abnormalities if the machine is stopped immediately after power-on. As a result, abnormalities can only be detected when the machine starts operating, changes occur in the A-phase and B-phase signals, and sampling is performed at point Q on the Lissajous figure. This delay in abnormality detection can lead to dangerous situations.

[0021] The objective of the present invention is to enable fault diagnosis of the abnormality detection circuit by obtaining A-phase and B-phase signals that are similar to the signal trajectories passing through points K and Q on a Lissajous figure, even when there is no change in the A-phase and B-phase signals output from the optical section of the position detector, such as when the machine is stopped immediately after power-on. [Means for solving the problem]

[0022] One aspect of the present invention is a position detector that includes a speed determination circuit that outputs A-phase signals and B-phase signals having a sine or cosine shape and a phase difference of 90° from each other, pulses the A-phase signals and B-phase signals, determines the speed by phase counting, and detects abnormalities in the A-phase signals or B-phase signals and failures in the abnormality detection circuit by comparing the speed with a reference threshold, and further includes two diagnostic light-emitting elements provided near a light-receiving element, and by individually lighting up the two diagnostic light-emitting elements one by one, the individual A-phase signals and B-phase signals are positioned in adjacent quadrants on a Lissajous figure.

[0023] According to one aspect of the present invention, an A-phase signal and a B-phase signal that have a sine shape or a cosine shape and have a phase difference of 90° from each other are output, the A-phase signal and the B-phase signal are A / D converted, and the sum of squares of the A-phase signal and the B-phase signal after A / D conversion is calculated to obtain a radius value of amplitude on a Lissajous figure. By comparing the radius value with a reference threshold, the position detector includes an amplitude determination circuit that detects an abnormality in the A-phase signal or the B-phase signal and a failure of an abnormality detection circuit. The position detector comprises two diagnostic light-emitting elements provided near a light-receiving element, one of the two diagnostic light-emitting elements is disposed at a position where the A-phase signal is substantially zero, and the other of the two diagnostic light-emitting elements is disposed at a position where the B-phase signal is substantially zero, and the two diagnostic light-emitting elements are individually lit one by one.

[0024] In the above configuration, two diagnostic light-emitting elements are provided near the light-receiving element, and the A-phase signal and the B-phase signal are changed by individually lighting each diagnostic light-emitting element one by one. For example, the two diagnostic light-emitting elements are arranged such that when the first diagnostic light-emitting element is lit, the signal state at point K in FIG. 4a is obtained, and when the second diagnostic light-emitting element is lit, the signal state at point Q in FIG. 4a is obtained.

[0025] For example, even if there is no mechanical movement in the optical unit of the position detector, if there is no failure in each block of the A / D conversion circuit, the pulsing circuit, the counting function, the Lissajous radius calculation function, the speed determination function and the amplitude determination function included in the abnormality detection circuit shown in FIG. 2, signals at two points K and Q in FIG. 4a can be obtained.

[0026] In addition, if there is a failure in the abnormality detection circuit, signals at two points K and Q on the Lissajous figure shown in FIG. 4b can be obtained, and when the signal at point Q is obtained, the abnormality can be determined by amplitude determination.

[0027] Furthermore, if the failure mode is different and movement occurs on the Lissajous figure shown in Figure 4c, signals from two points within the same quadrant will be obtained. Therefore, the speed obtained by pulse-counting the A-phase signal and B-phase signal will be 0, and the abnormality can be detected by the speed determination function. [Effects of the Invention]

[0028] According to the present invention, even if there is no change in the A-phase signal and B-phase signal output from the optical section of the position detector, such as when the machine is stopped immediately after power-on, it is possible to obtain A-phase and B-phase signals that are similar to the signal trajectory passing through points K and Q on the Lissajous figure, and to diagnose a malfunction in the abnormality detection circuit. [Brief explanation of the drawing]

[0029] [Figure 1] This figure shows the configuration of the position detector according to the embodiment. [Figure 2] This figure shows an abnormality detection circuit and its diagnostic function according to an embodiment. [Figure 3] This figure shows the layout of the light-receiving element and the diagnostic light-emitting element according to the embodiment. [Figure 4a] This is a Lissajous diagram showing the A-phase and B-phase signals in a normal state. [Figure 4b] This is a Lissajous figure showing an abnormal state in the B-phase signal. [Figure 4c] This is a Lissajous diagram showing an abnormal state in the A-phase signal. [Figure 5] This is a functional block diagram of a conventional anomaly detection circuit. [Figure 6] This diagram shows the configuration of a position detector according to conventional technology. [Modes for carrying out the invention]

[0030] Referring to Figure 1, the position detector according to the embodiment will be described. The position detector according to the embodiment includes a scale 10 and a slider 15 that moves in a straight line relative to the scale 10.

[0031] Scale 10 has a main grid scale 16 and an auxiliary grid scale 17 with different pitches. The main grid scale 16 and the auxiliary grid scale 17 are periodic scales.

[0032] The slider 15 is equipped with a light-transmitting index scale 13a, a light-emitting element 12, and a collimator lens 11, etc. The index scale 13a forms four periodic sub-grids relative to the main grating scale 16. The light-receiving section includes four light-receiving elements 14a corresponding to the four sub-grids. The collimator lens 11 makes the light emitted from the light-emitting element 12 into parallel light.

[0033] A change in light intensity occurs due to the relative movement of the slider 15 in the longitudinal direction of the scale 10. This change in light intensity is converted photoelectrically by the photodetector 14a, yielding four signals a1, a2, b1, and b2 that have the same period but different phases.

[0034] By applying the following differential operation to the four signals above (i.e., signals a1, a2, b1, and b2), we can obtain an A-phase signal with no offset and a B-phase signal that is 90° ahead in phase of the A-phase signal. A phase signal = a1-a2 B phase signal=b1-b2

[0035] The scale 10, collimator lens 11, light-emitting element 12, index scale 13a, photodetector 14a, and slider 15 shown in Figure 1 are the same as the configurations shown in Figure 5.

[0036] The position detector according to this embodiment further includes diagnostic light-emitting elements 20 and 21. The diagnostic light-emitting element 21 is positioned near the light-receiving element 14a. Specifically, the diagnostic light-emitting element 20 is positioned so that the A-phase signal can be increased and the B-phase signal is close to zero.

[0037] A specific example of this arrangement is shown in the left diagram of Figure 3. When four light-receiving elements a2, a1, b1, and b2 are arranged on the light-receiving element 14a in that order, the diagnostic light-emitting element 20 is positioned closer to the light-receiving region of light-receiving element a1 than to the light-receiving region of light-receiving element a2, and between the light-receiving region of light-receiving element b1 and the light-receiving region of light-receiving element b2 (for example, an intermediate position). The diagnostic light-emitting element 21 is positioned closer to the light-receiving region of light-receiving element b1 than to the light-receiving region of light-receiving element b2, and between the light-receiving region of light-receiving element a1 and the light-receiving region of light-receiving element a2 (for example, an intermediate position).

[0038] The signals obtained from the photodetectors a2, a1, b1, and b2 are defined as signals a2, a1, b1, and b2, respectively.

[0039] By turning on the diagnostic light-emitting element 20 and turning off the diagnostic light-emitting element 21, signals b1 and b2 show the same magnitude, and the relationship between signals a1 and a2 is a1 > a2. Therefore, the A-phase signal shows a positive value, and the B-phase signal shows a value of approximately 0. This signal is located at point K on the Lissajous figure shown in Figure 4a.

[0040] By turning off the diagnostic light-emitting element 20 and turning on the diagnostic light-emitting element 21, the A-phase signal shows a value of approximately 0, and the B-phase signal shows a positive value. This signal is located at point Q on the Lissajous figure shown in Figure 4a.

[0041] If a fault occurs in the anomaly detection circuit shown in Figure 5, and that fault is such that the amplitude of the B-phase signal is halved, then the signals at points K and Q on the Lissajous figure shown in Figure 4b will be obtained. Therefore, when the signal at point Q is obtained, the amplitude determination function can be used to determine if an anomaly has occurred.

[0042] In the example shown in Figure 4b, the determination is made without changing the threshold for determining abnormalities. However, if the light emission intensity of the diagnostic light-emitting elements 20 and 21 is insufficient, the determination can be made by changing the lower or upper threshold to an appropriate value.

[0043] In the embodiment described above, we focused on points K and Q, but the same effect as the combination of points K and Q can be obtained by using the combinations of points Q and R, points R and M, and points M and K shown in Figure 4a.

[0044] In the left diagram of Figure 3, the light-receiving elements are arranged in the element layout 30 within the light-receiving element 14a in the order a2, a1, b1, and b2 from left to right. By changing this arrangement to a1, a2, b2, and b1 from left to right, the signals at point M and point R can be obtained.

[0045] Furthermore, if a fault occurs in the abnormality detection circuit shown in Figure 5 that results in the Lissajous figure shown in Figure 4c, the signals at point K and point Q on the Lissajous figure shown in Figure 4c will be obtained. In this case, since the quadrants of points K and Q remain unchanged (i.e., points K and Q are in the same quadrant), when the phase A and B signals are pulsed and phase counting is performed, the count value will be 0. Normally, the count value would be 1, but since the count value is 0, an abnormality can be detected by speed judgment. In this case, the judgment threshold for diagnosis is set to 0.5 and the diagnostic function is activated.

[0046] Figure 2 shows the configuration (anomaly detection circuit and diagnostic function) for realizing the diagnostic function according to this embodiment. The anomaly detection circuit according to this embodiment, similar to the anomaly detection circuit shown in Figure 5, includes a pulsation unit (e.g., a pulsation circuit), a counter, a speed determination unit (e.g., a speed determination circuit), an anomaly processing unit (e.g., an anomaly processing circuit), an A / D conversion unit (e.g., an A / D conversion circuit), a Lissajous radius calculation unit (e.g., a Lissajous radius calculation circuit), and an amplitude determination unit (e.g., an amplitude determination circuit). The anomaly detection circuit according to this embodiment further includes a diagnostic processing unit (e.g., a diagnostic processing circuit) and a diagnostic threshold setting unit (e.g., a diagnostic threshold setting circuit).

[0047] As explained with reference to Figure 5, the sine signal output from the photodetector represents the A-phase signal. The cosine signal output from the photodetector represents the B-phase signal.

[0048] When the machine operates and sine and cosine signals are obtained, these signals are pulsed, and a phase count is performed by a counter. Specifically, when the signal trajectory exceeds one quadrant on the Lissajous figure, a count value of "1" is obtained. When the signal trajectory completes one revolution and exceeds four quadrants, a count value of "4" is obtained. When the signal trajectory completes N revolutions, a count value of "N × 4" is obtained. The speed can be determined by calculating the difference between the count value obtained during the previous position detection and the count value obtained during the current position detection. By comparing this speed with the maximum speed threshold, anomalies can be detected.

[0049] Furthermore, by performing A / D conversion on the A-phase signal and the B-phase signal, calculating the sum of the squares of each value to obtain the Lissajous radius, and then comparing this Lissajous radius with the lower and upper threshold limits to determine the amplitude, anomalies can be detected.

[0050] The diagnostic processing unit controls the individual illumination and extinguishing of each diagnostic light-emitting element 20, 21. The diagnostic threshold setting unit pre-sets a dedicated threshold for the speed determination unit.

[0051] For example, immediately after power-on and before position detection begins, the diagnostic processing unit shown in Figure 2 is activated to diagnose any malfunctions in the abnormality detection circuit.

[0052] The diagnostic light-emitting elements 20 and 21 may be point light sources, as shown in the left diagram of Figure 3, or they may be linear light sources arranged with multiple light-emitting elements, as shown in the right diagram of Figure 3. When the diagnostic light-emitting elements 20 and 21 are composed of linear light sources, the diagnostic light-emitting element 20 is positioned at locations corresponding to the light-receiving areas of light-receiving elements a1, b1, and b2, and the diagnostic light-emitting element 21 is positioned at locations corresponding to the light-receiving areas of light-receiving elements a2, a1, and b1.

[0053] The two diagnostic light-emitting elements 20, 21 and the light-receiving element 14a may be composed of a single semiconductor chip. Of course, they may also be composed of separate elements.

[0054] In the embodiment described above, two diagnostic light-emitting elements 20 and 21 are used, but three or more diagnostic light-emitting elements may be used. Specifically, three or more diagnostic light-emitting elements are arranged so that the signal can be moved on the Lissajous figure, similar to the case where two diagnostic light-emitting elements 20 and 21 are used.

[0055] Each component shown in Figure 2 (i.e., the pulsing unit, counter, speed determination unit, abnormality processing unit, A / D conversion unit, Lissajous radius calculation unit, amplitude determination unit, diagnostic processing unit, and diagnostic threshold setting unit) can be implemented using hardware resources such as a processor or electronic circuits, and devices such as memory may be used as needed in their implementation. Alternatively, each component may be implemented by a computer. In other words, all or part of each component may be implemented through the cooperation of hardware resources such as the CPU (Central Processing Unit) and memory of a computer, and software (programs) that define the operation of the CPU, etc. This program is stored in the storage device of the position detector via a recording medium such as a CD or DVD, or via a communication path such as a network. As another example, each component may be implemented by a DSP (Digital Signal Processor) or FPGA (Field Programmable Gate Array), etc. [Explanation of symbols]

[0056] 10 Scale, 11 Collimator lens, 12 Light-emitting element, 13a Index scale, 14a Photodetector, 15 Slider, 16 Main grid scale, 17 Auxiliary grid scale, 20 Diagnostic light-emitting element, 21 Diagnostic light-emitting element.

Claims

1. A position detector that outputs A-phase signals and B-phase signals having a sine or cosine shape and a phase difference of 90° from each other, pulses the A-phase signals and B-phase signals, determines the speed by phase counting, and compares the speed with a reference threshold to detect abnormalities in the A-phase signal or B-phase signal and failures in the abnormality detection circuit, including a speed determination circuit, It includes two diagnostic light-emitting elements located near the light-receiving element, By individually illuminating each of the two diagnostic light-emitting elements, the individual A-phase signal and B-phase signal are generated in adjacent quadrants on the Lissajous figure. A position detector characterized by the following features.

2. In a position detector including an amplitude determination circuit that outputs A-phase signals and B-phase signals having a sine or cosine shape and a 90° phase difference from each other, performs A / D conversion on the A-phase and B-phase signals, calculates the radius value of the amplitude on a Lissajous figure by summing the squares of the A-phase and B-phase signals after A / D conversion, and compares this radius value with a reference threshold to detect abnormalities in the A-phase or B-phase signal and failures in the abnormality detection circuit, It includes two diagnostic light-emitting elements located near the light-receiving element, One of the two diagnostic light-emitting elements is positioned at a location where the A-phase signal is approximately zero, and the other diagnostic light-emitting element is positioned at a location where the B-phase signal is approximately zero. The two diagnostic light-emitting elements are illuminated individually, one by one. A position detector characterized by the following features.

3. In the position detector according to claim 1, By setting a new threshold for the aforementioned speed determination circuit, a fault is diagnosed. A position detector characterized by the following features.

4. In the position detector according to claim 2, By setting a new threshold for the amplitude determination circuit, a fault is diagnosed. A position detector characterized by the following features.

5. In the position detector according to any one of claims 1 to 4, The two diagnostic light-emitting elements and the light-receiving element are each composed of a single-chip semiconductor element. A position detector characterized by the following features.

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