JP4668396B2 - Origin signal generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a linear scale for measuring a relative movement amount between two objects. In particular, in such a scale, by outputting a reference position as an origin signal, for example, the movement amount of a machine tool or the like is an absolute value. It is related with the origin signal generator of the length measuring device which became possible to know by this.
[0002]
[Prior art]
In a machine tool or the like, it is extremely important to accurately measure the relative movement amount of a tool with respect to a workpiece, and various measuring apparatuses for this purpose have been commercialized.
As one of them, an optical scale using moire fringes obtained by superposing two optical gratings is conventionally known. As shown in FIG. 4, the optical scale includes a main scale 101 provided with a grid (engaged line) on one surface of a transparent glass scale 100 so that translucent portions and non-translucent portions are arranged at a predetermined pitch, and transparent The glass scale 102 has an index scale 103 provided with a lattice (scribing line) so that the translucent part and the non-translucent part are arranged at a predetermined pitch, as shown in FIG. The index scale 103 is opposed to the main scale 101 with a minute interval, and the grating of the index scale 103 is arranged so as to be inclined at a minute angle with respect to the grating of the main scale 101 as shown in FIG. .
[0003]
Note that the grids provided on the main scale 101 and the index scale 103 are formed of grids having the same pitch formed by vacuum-depositing and etching chromium on the glass scales 100 and 102.
When arranged in this manner, moire fringes shown in FIG. 5 are generated. The interval between the moire fringes is W, and a dark portion or a bright portion is generated for each interval W. The dark part or the bright part moves from the top to the bottom or from the bottom to the top according to the direction in which the index scale 103 moves relatively to the left and right relative to the main scale 101. In this case, if the grid pitch of the main scale 101 and the index scale 103 is P, and the mutual inclination angle is θ [rad], the interval W of the moire fringes is
W = P / θ
The interval W of the moire fringes is an optically expanded interval 1 / θ times the lattice interval P. For this reason, when the grating moves by one pitch P, the moire fringes are displaced by W, and the amount of movement in the pitch P can be accurately measured by reading the change in the vertical direction of W. .
[0004]
For example, as shown in FIG. 6, a photoelectric conversion element 110 that optically detects a change in moire fringes is provided on the index scale, and a light source is provided on the opposite side of the main scale so that the index scale (103 ) Is moved relatively, and a change in the current flowing through the photoelectric conversion element 110 is read.
That is, when the moire fringe pattern is in the A state, the amount of light applied to the photoelectric conversion element 110 is the largest, and the current flowing through the photoelectric conversion element 110 is the maximum value I ₁ . Next, when the light is relatively moved to the B state, the amount of light applied to the photoelectric conversion element 110 is slightly reduced, and the current becomes I _2. Further, when the light is moved to the C state, the photoelectric conversion element 110 Is irradiated with the least amount of light, and its current is the smallest I ₃ . Further, when the light is further moved to the D state, the amount of light applied to the photoelectric conversion element 110 is slightly increased, and the current becomes I ₂ . The current has a maximum value I ₁ .
As described above, the current flowing through the photoelectric conversion element 110 changes in a sine wave shape, and the main scale 101 and the index scale 103 are relatively moved by the lattice interval P when the change passes for one cycle.
[0005]
In FIG. 6, only one photoelectric conversion element 110 is provided. However, as shown in FIG. 7, when two photoelectric conversion elements 111 and 112 are provided with a 90 ° shift from one cycle (interval W). The current flowing in the B-phase photoelectric conversion element 112 with respect to the current flowing in the A-phase photoelectric conversion element 111 is a current shifted by 90 ° as shown in FIG. That is, if the current flowing through the A-phase photoelectric conversion element 111 is a sine wave (A-phase signal), the current flowing through the B-phase photoelectric conversion element 112 is a cosine wave (B-phase signal).
As described above, the phase of the B phase signal with respect to the A phase signal is advanced by 90 ° or delayed by 90 ° depending on the relative moving direction of the main scale 101 and the index scale 103. When two photoelectric conversion elements are provided, the relative movement direction of the scale can be detected by detecting the phase between them.
[0006]
FIG. 9 shows an outline of a perspective view of an optical scale using the principle described above. In this figure, one surface of an elongated main scale 101 is engraved with a lattice of the same pitch formed by vapor-deposited chromium, and an index scale 103 is formed on one surface of a U-shaped holder 104 that holds the main scale 101. Is fixed. The surface of the index scale 103 facing the main scale is engraved with a grid having the same pitch formed by vapor deposited chrome similarly to the main scale 101, and on the back side of the index scale 103 is a photoelectric conversion element. 113 is provided.
[0007]
Furthermore, as shown in FIG. 10, a light source 105 is disposed on the surface of the U-shaped holder 104 on the opposite side of the main scale 101, and light passing through the main scale 101 and the index scale 103 is transmitted by the photoelectric conversion element 113. It is configured to detect.
The main scale 101 and the index scale 103 are movable with respect to each other.
Note that, as described above, the lattice (engraved line) of the index scale 103 is opposed to the lattice (engraved line) of the main scale 101 with a minute interval, and is inclined at a minute angle.
[0008]
From the cross-sectional view 10 of the principle structure of the optical scale configured as described above, the light emitted from the light source 105 passes through the glass main scale 101 and further passes through the glass index scale 103, and then the photoelectric Light is received as moire fringes by the conversion element 113.
The photoelectric conversion element 113 outputs an A-phase signal and a B-phase signal having a phase difference of 90 ° as shown in FIG. 8, and the moving direction and moving distance are measured from the two signals as described above. can do.
The photoelectric conversion element 113 is usually provided with four photoelectric conversion elements, two of which are the A phase signal and the B phase signal, and the other two are an A phase signal and a B phase obtained by inverting these signals. By outputting a signal and inputting the A homology and B homology into the adder, an A phase signal and a B phase signal whose amplitude is doubled are obtained.
[0009]
By the way, the optical scale configured in this way is mounted on an NC machine tool and measures the relative movement amount of the workpiece and the tool. In general, when the numerical control is performed, the movement amount from the origin is used. Since it is programmed, this relative movement must be measured as the movement from the origin.
Therefore, the origin position is usually provided in the main scale in advance, and when the index scale passes through this origin position, the origin is detected, and this origin detection signal is supplied to the NC device to reset the NC device, thereby setting the origin position. I was trying to set up the NC unit.
Therefore, in the above-described photoelectric linear scale, as shown in FIG. 11A, a marking (grid) 109 indicating the origin Z serving as a reference point is located at a predetermined track position different from the marking position of the main scale 101. Alternatively, if a photoelectric conversion element that detects light that passes through or reflects the grating 109 or the reflection plate serving as the origin, or is detected as moire fringes, is provided, the main scale 101 and the index scale 103 are specified. Only when the positional relationship is established, it becomes possible to detect the signal as the origin.
[0010]
That is, as shown in FIG. 11 (b), a thick line signal Sz whose amplitude changes at the position of the origin Z within one pitch P of the main scale 101 as in FIG. 6 is detected as the origin position signal. Therefore, if the peak point of the waveform of the origin position detection signal Sz is clipped at a predetermined level TH to form the origin pulse signal Pz, for example, as shown in FIG. A point can be the origin Z of the main scale.
Depending on the detection method, the polarity of the origin signal can be a positive value.
[0011]
[Problems to be solved by the invention]
However, this origin position signal is generally detected by the relative movement of the main scale 101 and the index scale 103, but is detected by the direction passing through the origin Z and the relative movement speed of the scale at that time. There arises a problem that the signal level changes as indicated by a dotted line or a one-point difference line, and the position (Pz1, Pz2) of the origin pulse signal formed based on the origin signal waveform also changes.
[0012]
For this reason, when determining the origin, it is necessary to adjust the level of the origin signal by using, for example, a predetermined jig and an oscilloscope so as to obtain a predetermined pulse width.
However, when a scale is completed and an origin position is set, a skilled worker needs to make careful adjustments, resulting in a problem of poor work efficiency.
[0013]
[Means for Solving the Problems]
The present invention was made for the purpose of reducing such problems, and in the first invention, at least a first score line indicating the origin position and a second score scaled at equal intervals in the length direction. A main scale provided with a line, and an origin signal which is arranged to be movable with respect to the main scale and is output at a predetermined position from the first score line, and from the second score line Detection means for detecting the A phase and B phase signal waveforms indicating the relative amount of movement of the scale, and an interpolation pulse signal obtained by dividing one period of the A phase and B phase signal waveforms by a predetermined number An internal pulse generator, and an internal origin signal generator for generating an internal origin signal having a predetermined width from a reference point of the origin signal, and the timing of the reference point of the A phase or B phase signal waveform Which phase region (quadrant) belongs to A pattern detection unit for determination, and a timing for generating a reference origin signal based on the interpolated pulse signal at a predetermined position in a second phase region delayed from the first phase region determined by the pattern detection unit A data portion and a coincidence detecting portion for determining an origin position by coincidence of the reference origin signal and the internal origin signal are provided.
[0014]
Further, the reference point of the origin signal is configured such that the reference signal ZD is output when the peak detection unit drops a predetermined voltage ΔV from the time when the peak point of the origin signal Zin waveform is detected. The generation unit is configured by a circuit that obtains a signal having a predetermined pulse width from the falling point of the reference signal ZD waveform, and the timing data unit sets a region two points ahead from the phase region from which the origin signal is obtained. The timing period for outputting the reference origin signal is determined. The interpolation pulse signal generation unit is configured to output an A / B phase pulse signal indicating the amount of scale movement, which is output as a counting pulse indicating an absolute value obtained by dividing the engraving line of the main scale. .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an embodiment when the present invention is applied to an optical linear scale.
Hereinafter, the reference point setting operation will be described with reference to FIG. 1 and the timing waveform shown in FIG.
In these figures, analogs A and B indicate that sinusoidal A-phase signals and B-phase signals having a phase difference of 90 degrees are input as Lissajous waveforms as shown in FIG. For example, the waveform is divided into 20 by its phase and supplied to an interpolation pulse generator 11 which outputs an interpolation pulse signal.
[0016]
This interpolated pulse generator 11 can be constituted by an A / D converter, a sampling circuit, etc. as described in (Japanese Patent Application No. 2000-148330) previously proposed by the applicant. A binary signal that is sampled by a sampling clock that divides at least 20 phases of one phase of each input A-phase signal (B-phase signal), compares the sampling level with a predetermined value, and repeats 1 or 0 Is generated.
Therefore, when one pitch of the scale is 20 μm, the period of the interpolated pulse signal is 1 μm, and the B1 signal that is 90 degrees phase-shifted from the A1 signal is output.
[0017]
Reference numeral 12 denotes a phase division unit for dividing the input A / B signal into quadrants, for example, for example, an A5 signal obtained by dividing one period of the sine wave-like Lissajous waveform indicating the amount of movement of the scale into four, and B5 Output a signal.
Therefore, when the pitch of one pitch of the scale is 20 μm, the output of the phase dividing unit 12 has a waveform indicating a movement amount of 5 μm in one cycle as seen in A5 and B5 of FIG.
[0018]
Reference numeral 13 denotes a direction discriminating unit that detects the phase states of the A-phase signal and the B-phase signal in the linear scale and discriminates the direction in which the linear scale is moving. When the phase is advanced, the scale is moving in the forward direction, and when the phase B signal is advanced 90 degrees, the scale is moving in the reverse direction.
[0019]
Reference numeral 14 denotes a peak detector of the signal waveform of the origin signal Zin detected from a specific position of the scale as described above. From the time when the peak point of the waveform is detected as shown in the origin signal Zin of FIG. The reference signal ZD is output when the voltage drops by a predetermined voltage ΔV. Such a circuit can be constituted by a circuit as shown in FIG. 3 as described later.
The next internal origin signal generator 15 is triggered at the edge of the falling signal, and the internal origin signal SYNC1 having a predetermined pulse width is output.
[0020]
The internal origin signal generator 15 is constituted by a circuit for obtaining a signal having a predetermined pulse width from the falling point of the reference signal ZD waveform as seen in the SYNC1 signal in FIG.
Such a circuit can be configured by a phase-stable multivibrator that is set at the falling edge of the reference signal ZD and reset at the edge of the A5 signal that is two areas ahead.
[0021]
Reference numeral 16 denotes an ABS counter that counts the number of pulses of the A1 phase signal or B1 phase signal that is the output of the interpolated pulse signal generator 11, and the count value is supplied to the next sync generator 17.
Although not shown, the ABS counter 16 is configured to be reset at 0 degrees of the Lissajous waveform and repeat counting in one cycle.
For example, in this embodiment, the counting of 0 to 19 is repeated.
[0022]
Reference numeral 18 detects in which polarity pattern region of the reference signal ZD the A5 signal (B5 signal) is generated based on the polarities of the A5 signal and the B5 signal that are output signals of the phase division unit 12. 2 is a pattern detection unit that detects the relationship between the phase region of (1), (2), (3), and (4) and the generation phase of the reference signal ZD.
[0023]
The timing information supplied from the pattern detection unit 18 to the timing data unit 19 is configured to be stored in the non-volatile memory 19a at the same time. The set reference data can be saved.
[0024]
The timing data unit 19 sets a phase-shift region that is two ahead from the phase region (quadrant) of the A5 signal (B5 signal) when the origin signal is input, and inputs this timing to the sync generation unit 17. The sync generator 17 outputs a change in the count value of the ABS counter 16 within this timing period as a pulse signal. For example, in the case of FIG. 2, the phase region in which the origin signal is desired to be obtained is (2), and the region (4) two points ahead from this region is set to determine the timing period for outputting the origin signal. When the count value of the ABS counter 16 input during this timing period is 12, 13, and 14, the reference origin signal SYNC is formed during the period when the count value 13 is approximately the center.
[0025]
Therefore, the reference signal ZD of the origin signal detected by the scale is asynchronous with respect to the A / B phase signal, whereas this reference origin signal SYNC is detected by the scale as a relative movement amount. The signal is synchronized with the / B phase signal.
This indicates that the reference origin signal SYNC is always output at a fixed position in synchronization with the A / B phase signal even if the reference signal ZD is output in a range of the phase region (2).
[0026]
As described above, the reference origin signal SYNC is formed in the area ahead from the time when the origin signal is input, so that the reference origin signal may vary even when the moving speed of the scale when passing the origin is high. I am trying not to.
In peak detection, which is an embodiment of the present invention, since the origin position is different when the origin position is detected when the scale is in the reverse feed state, the origin position adjustment determines the moving direction of the scale. It is preferable to keep it.
[0027]
The phase regions (1), (2), (3), and (4) are set every 0 to 90 degrees, 90 to 180 degrees, 180 degrees to 270 degrees, and 270 degrees to 360 degrees of the Lissajous waveform. Therefore, as shown in FIG. 2, when the phase of the B5 signal is delayed by 90 degrees with respect to the A5 signal, a pattern of “10” is output in the phase region {circle around (1)}, and the phase region of 90 to 180 ° {circle around (2)}. In the range of ▼, the pattern “11” is output.
The current phase region of the Lissajous waveform input in this way can be detected by, for example, phase data (00 to 11) in four quadrants.
[0028]
Reference numeral 20 denotes a coincidence detector that detects a coincidence between the internal origin signal SYNC1 and the reference origin signal SYNC, and can be constituted by a circuit that takes the logical product of the two, for example.
Accordingly, the coincidence detection unit 17 can obtain a signal serving as a reference for the origin synchronized with the interpolation pulse signal interpolating between the marking pitches of the scale only when the origin signal Zin is detected. Yes.
An A1 phase signal and a B1 phase signal in which the amount of movement of the scale is highly accurately interpolated by the interpolated pulse signal are generated, and this signal is supplied to an NC machine or the like and can be processed by automatic control.
[0029]
FIG. 3A is a circuit diagram showing the principle of the peak detector 14. The output of the detector PD for detecting the origin signal is amplified with a predetermined gain by the amplifier A1.
The output of the amplifier A1 charges the capacitor C to the peak level via the diode D, and is supplied to the positive phase input terminal of the comparator A4 via the amplifier A3 to which the potential of ΔV is applied as the offset voltage.
The terminal voltage of the capacitor C is supplied to the negative phase input terminal of the comparator A4 through the buffer amplifier A2 set to unity gain.
[0030]
When the origin signal is generated in this circuit, the potential Vc of the capacitor C becomes a constant value at the peak point p as shown in FIG. 3B, but the positive phase terminal of the comparator A4 is a signal higher by Δv than the origin signal waveform. Is supplied, the output is at the H level. However, the voltage at the positive phase input terminal decreases from the peak point p, and when this voltage decreases by Δv, the output of the comparator A4 changes to L level so that the falling point of the reference signal ZD can be detected. . Then, when the level of the origin signal becomes 0 by a circuit not shown, the original level is restored.
[0031]
In the embodiment of the present invention, as described above, the reference origin signal SYNC indicating the origin position is shifted depending on the moving direction of the scale. Therefore, when displaying the origin position, the output of the direction discriminating unit 13 is used. Output when indicates forward.
However, since the reference origin signal in which the A / B phase signal is synchronized is obtained by the same signal processing even when the scale is reversely transmitted, the scale is reversely transmitted from the data of the pattern detection unit 18 and the direction detection unit 13. Even when the operation is performed, it is possible to perform control so that an origin signal at the time of reverse feeding provided separately can be converted into a reference origin signal at the time of forward feeding and output.
It should be noted that the origin position is preferably obtained at the point where the A phase signal is at the H level and the B phase level is at the H level, but depending on the scale model, other level positions of the A phase signal and the B phase signal may be obtained. It can also be set to be based on comrade.
[0032]
In the above embodiment, the data when dividing one pitch of the scale into 20 is read as A / B phase pattern data. However, by sampling at a higher clock period, the number of samples of the Lissajous waveform is increased. Furthermore, the length measurement unit of the scale can be determined with higher resolution, and the resolution of the origin position can be increased.
[0033]
In addition, the peak point is detected from the detected origin signal, and the point that is lower than the peak point by a predetermined level is used as the reference signal for the origin. It is also possible to apply an origin detection method such as
[0034]
【The invention's effect】
In the present invention, as described above, the origin position signal is determined in synchronization with the signal indicating the position obtained by dividing the lattice, so that the speed when the main scale passes through the origin greatly changes. However, there is an effect that a stable origin position can be output.
Especially when the origin position is detected by a reflective photoelectric conversion element, the width of the output waveform of the origin signal is widened, and the error of the origin position is enlarged, but in the peak detection method employed in such a case, Since a synchronized origin signal can be obtained with almost no adjustment, there is an advantage that workability is remarkably improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of an origin signal generator of the present invention.
FIG. 2 is a timing waveform diagram of signal processing in the origin signal generator.
FIG. 3 is a circuit diagram of an origin signal generation circuit that detects an origin based on a peak point of a detected waveform.
FIG. 4 is a principle diagram of an optical scale.
FIG. 5 is a diagram showing moire fringes.
FIG. 6 is a diagram illustrating movement of moire fringes.
FIG. 7 is a diagram illustrating a position where a photoelectric conversion element is installed.
FIG. 8 is a waveform diagram of an A phase signal and a B phase signal.
FIG. 9 is a perspective view of an optical scale.
FIG. 10 is a cross-sectional view of an optical scale.
FIG. 11 is an explanatory diagram showing a grid for detecting an origin position and a detected waveform thereof;
[Explanation of symbols]
11 interpolation pulse signal generation unit, 12 phase division unit, 13 direction discrimination unit,
14 peak detector, 15 internal origin signal generator, 16 ABS counter,
17 sync generation unit, 18 pattern detection unit, 19 timing data unit,
20 Match detection unit

Claims (4)

A main scale provided with at least a first score line indicating the origin position, a second score line graduated at equal intervals in the length direction, and arranged to be movable with respect to the main scale, Detecting means for detecting an origin signal output at a predetermined position from the first score line, and detecting A-phase and B-phase signal waveforms indicating a relative movement amount of the scale from the second score line; the a-phase, and a interpolation pulse generator for outputting a interpolation pulse signal of one period is divided by a predetermined number of B-phase signal waveform,
An internal origin signal generator for generating an internal origin signal having a predetermined width from a reference point of the origin signal;
A pattern detection unit for determining which phase region (quadrant) of the phase A or phase B signal waveform the timing of the reference point belongs to;
A timing data unit for generating a reference origin signal based on the interpolated pulse signal at a predetermined position in a second phase region delayed from the first phase region determined by the pattern detection unit;
An origin signal generator having a coincidence detection unit that determines an origin position based on a coincidence of the reference origin signal and the internal origin signal . The origin signal generator according to claim 1 , wherein the reference signal ZD is output when the reference point of the origin signal is lowered by a predetermined voltage ΔV from the time when the peak detector detects the peak point of the origin signal Zin waveform . The internal origin signal generator is configured by a circuit that obtains a signal having a predetermined pulse width from a falling point of the reference signal ZD waveform,
3. The origin signal generator according to claim 1, wherein the timing data section sets a timing period in which a reference origin signal is output by setting a second area from the phase area where the origin signal is obtained . The interpolation pulse signal generating unit is output as the count pulses indicating the absolute value obtained by dividing the between score line of the main scale, the claims are configured to form a A / B-phase pulse signal indicating the scale movement amount 1 to 3 origin signal generator.

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