JP2002071385A - Zero-point signal generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To synchronize a zero-point signal, outputted from the peak detection part of the zero-point signal with an A/B phase pulse signal for interpolating the travel amount (length) of a scale as a reference signal. SOLUTION: A- and B-phase signals are supplied to an interpolation pulse generating section 11 for forming the digitized A- and B-phase signals for interpolation within a single pitch of the scale; the phase relation between the phase region of the A-phase signal (B-phase signal) and a reference signal ZD outputted from a peak detection section 14 is detected by a pattern detection section 18; and a reference zero-point signal is outputted from a coincidence detection section 20. In this case, the reference zero-point signal is synchronized with the A- and B-phase signals that are digitized at a phase-shift region, for example, at two regions which are ahead of the phase region of the reference signal ZD.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field 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, a machine tool The present invention relates to an origin signal generation device of a length measuring device capable of knowing an amount of movement such as an absolute value.

[0002]

2. Description of the Related Art In a machine tool or the like, it is extremely important to accurately measure a relative movement amount of a tool with respect to a workpiece in performing precision machining, and various measuring devices have been commercialized. . As one of them, an optical scale using moire fringes obtained by superposing two optical gratings has been conventionally known. This optical scale is a transparent glass scale 100 as shown in FIG.
The main scale 101 is provided with a grid (marked line) so that the light-transmitting portion and the non-light-transmitting portion are arranged at a predetermined pitch on one surface, and the light-transmitting portion and the non-light-transmitting portion are provided on one surface of the transparent glass scale 102. And an index scale 103 provided with a lattice (notched line) so as to be arranged at a pitch of .times .. As shown in FIG. 3A, the index scale 103 is opposed to the main scale 101 at a small interval. As shown in FIG. 3B, the index scale 10 is tilted by a small angle with respect to the grid of the main scale 101.
3 grids are arranged.

The grating provided on the main scale 101 and the index scale 103 is a glass scale 1
Chromium is vacuum-deposited on 00 and 102, and is formed by a grid of the same pitch formed by etching. With this arrangement, moire fringes shown in FIG. 5 are generated. The interval between the moire fringes is W, and a dark portion or a bright portion occurs at each interval W. The dark part or the bright part moves from top to bottom or from bottom to top in accordance with the direction in which the index scale 103 moves left and right relative to the main scale 101. In this case, assuming that the pitch of the grids of the main scale 101 and the index scale 103 is P, and the mutual inclination angle is θ [rad], the interval W between the moire fringes is expressed as follows: W = P / θ Means that the lattice spacing P is optically enlarged to 1 / θ times. For this reason, when the grating moves by one pitch P, the moiré fringes are displaced by W, and by reading the change in the vertical direction of W, the amount of movement within the pitch P can be accurately measured. .

For example, as shown in FIG. 6, a photoelectric conversion element 110 for optically detecting a change in moire fringes is provided on an index scale, and a light source is provided on the opposite side of the main scale. The change in the current flowing through the photoelectric conversion element 110 is read while the scale (103) is relatively moved. That is, when the moire fringe pattern is in the state of A, 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 relatively moved to the state of B, the amount of light applied to the photoelectric conversion element 110 slightly decreases, and the current becomes I ₂ . Is irradiated with the least amount of light, and its current is also the smallest I ₃ . Then, when further moved to the state of D, the amount of light applied to the photoelectric conversion element 110 slightly increases, the current becomes I ₂ , and when the state moves to the state of E, it becomes the position where the amount of light is largest again. current becomes maximum I _1. As described above, the current flowing through the photoelectric conversion element 110 changes sinusoidally, and when one cycle of the change has elapsed, the main scale 101 is shifted by the lattice interval P.
And the index scale 103 have relatively moved.

In FIG. 6, only one photoelectric conversion element 110 is provided. However, as shown in FIG. 7, two photoelectric conversion elements 11 are shifted from one cycle (interval W) by 90 °.
1 and 112, the current flowing through the A-phase photoelectric conversion element 111 can be replaced by the B-phase photoelectric conversion element 112.
Is a current shifted by 90 ° as shown in FIG. That is, assuming that the current flowing in the A-phase photoelectric conversion element 111 is a sine wave (A-phase signal), the current flowing in the B-phase photoelectric conversion element 112 is a cosine wave (B-phase signal. As described above, the main scale 101. 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 movement direction of the A and the index scale 103. Therefore, if two photoelectric conversion elements arranged by being shifted by 90 ° are provided. The relative movement direction of the scale can be detected by detecting the phase between the two.

FIG. 9 schematically shows a perspective view of an optical scale utilizing the above-described principle. In this figure, a grid of the same pitch formed by evaporated chromium is engraved on one surface of an elongated main scale 101, and a U-shaped holder 10 holding the main scale 101 is provided.
The index scale 103 is fixed to one surface of the reference numeral 4. On the surface of the index scale 103 facing the main scale, a grid of the same pitch formed of chromium deposited in the same manner as the main scale 101 is engraved. 113 are provided.

Further, as shown in FIG. 10, a light source 105 is disposed on a surface of the U-shaped holder 104 opposite to the main scale 101 to photoelectrically convert light transmitted through the main scale 101 and the index scale 103. It is configured to detect by the element 113. And
The main scale 101 and the index scale 103 are movable with respect to each other. As described above, the grid (index line) of the index scale 103 is opposed to the grid (index line) of the main scale 101 at a small interval, and is tilted by a small angle.

From the cross-sectional view 10 of the principle structure of the optical scale thus constructed, the light emitted from the light source 105 passes through the glass main scale 101 and further passes through the glass index scale 103. rear,
The light is received as moire fringes by the photoelectric conversion element 113.
From the photoelectric conversion element 113, 9 shown in FIG.
An A-phase signal and a B-phase signal having a phase difference of 0 ° are output, and the moving direction and the moving distance can be measured from the two signals as described above. In addition, the photoelectric conversion element 1
13 is usually provided with four photoelectric conversion elements, two of which output the A-phase signal and B-phase signal, and the other two output A-phase and B-phase signals obtained by inverting these signals, The A-phase signal and the B-phase signal are input to the adder to obtain an A-phase signal and a B-phase signal whose amplitude is doubled.

The optical scale constructed as described above is mounted on an NC machine tool and measures the relative movement between the workpiece and the tool. In general, when performing numerical control, the optical scale from the origin is used. Since this is programmed as a movement amount, this relative movement amount needs to be measured as a movement amount from the origin. Therefore, an origin position is usually provided in advance on the main scale, and the origin is detected when the index scale passes through the origin position.
By resetting the NC device after being supplied to the C device, the origin position is set in the NC device. Therefore, in the photoelectric linear scale as described above, as shown in FIG.
A marking line (grating) 109 or a reflecting plate indicating the origin Z serving as a reference point is provided at a predetermined track position different from the marking line position of, and passes or reflects through the grating 109 or the reflecting plate serving as the origin. If a photoelectric conversion element that detects light as moiré fringes is arranged, only when the main scale 101 and the index scale 103 have a specific positional relationship can be detected as a signal of the origin.

That is, as shown in FIG. 11B, even at the position of the origin Z, a signal Sz of a thick line whose amplitude changes during one pitch P of the main scale 101 as in FIG. Since the signal is detected as a signal, the peak point of the waveform of the origin position detection signal Sz is clipped at a predetermined level TH, for example, as shown in FIG. P
The rising point of z can be set as the origin Z of the main scale. The polarity of the origin signal can be a positive value depending on the detection method.

[0011]

However, the signal of the origin position is generally detected by the relative movement of the main scale 101 and the index scale 103. The level of the detection signal changes as indicated by a dotted line or a dashed line in the figure according to the relative moving speed of the scale, and the position (Pz1, Pz1,
Pz2) also changes.

Therefore, when determining the origin, it is necessary to adjust the level of the origin signal so as to have a predetermined pulse width using, for example, a predetermined jig and an oscilloscope. However, when a scale is completed and the origin position is set, a skilled worker needs to make careful adjustments, which causes a problem that the working efficiency is poor.

[0013]

SUMMARY OF THE INVENTION The present invention has been made for the purpose of reducing such a problem. According to the first aspect of the present invention, at least a first inscribed line indicating an origin position is provided at least in a longitudinal direction. Detecting a main scale provided with second engraved lines graduated at intervals and an origin signal output at a predetermined position from the first engraved line movably disposed with respect to the main scale. And a detecting means for detecting A-phase and B-phase signal waveforms indicating the relative amount of movement of the scale from the second marking line, the linear scale having a predetermined distance from a reference point of the origin signal. An internal origin generating unit for generating an internal origin signal having a width;
And an interpolation pulse signal generating section that outputs an interpolation pulse signal obtained by dividing one cycle of the B-phase signal waveform by a predetermined number, and the phase region of the A-phase or B-phase signal waveform whose timing of the reference point is (Quadrant), and
A synchronization generation unit that sets a second phase region delayed from the first phase region determined by the determination unit, and generates a synchronization signal based on the interpolation pulse signal in the second phase region; And the origin position is determined from the synchronization signal.

The detecting means is configured to detect moiré fringes when the scale is moved by the photoelectric conversion element, so that an optical linear scale can be produced. It is configured to be output as a count pulse indicating an absolute value obtained by dividing the interval of the main scale, and to form an A / B phase pulse signal indicating the amount of scale movement. The reference point of the origin may employ a peak detection method formed based on a level lowered by a predetermined potential from the peak point of the origin signal.

[0015]

FIG. 1 is a block diagram showing an embodiment in which the present invention is applied to an optical linear kale. Hereinafter, the reference point setting operation will be described with reference to the timing waveforms shown in FIG. 1 and FIG. In these figures, analogs A and B indicate that a sine-wave A-phase signal and a B-phase signal having a phase difference of 90 degrees are input as Lissajous waveforms as shown in FIG. The waveform is, for example, 20
An interpolation pulse generator 1 that divides and outputs an interpolation pulse signal
1 is supplied.

The interpolation pulse generator 11 is constituted by an A / D converter, a sampling circuit, etc., as described in Japanese Patent Application No. 2000-148330 previously proposed by the present applicant. A phase signals (B
A phase signal) is sampled by a sampling clock that divides the phase of one cycle of the phase signal into at least 20 and the sampling level is compared with a predetermined value to generate a binary signal that repeats 1 or 0. Therefore, one pitch of the scale is 2
In the case of 0 μm, the interpolation pulse signal is configured to output an A1 signal having a period of 1 μm and a B1 signal that is 90 ° out of phase with the A1 signal.

A phase division unit 12 divides the input A / B signal into quadrants, for example.
An A5 signal and a B5 signal obtained by dividing one cycle of the sinusoidal Lissajous waveform indicating the amount of movement of the scale into four are output. Therefore, the score of one pitch of the scale is 20 μm.
In the case of m, the output of the phase dividing unit 12 has a waveform whose one cycle indicates a movement amount of 5 μm as shown in A5 and B5 in FIG.

Reference numeral 13 denotes a direction discriminator for detecting the phase state of the A-phase signal and the B-phase signal in the linear scale to determine the direction in which the linear scale is moving. When the 90-degree phase shift advances, the scale moves in the forward direction, and when the B-phase signal advances 90 degrees, the scale moves in the reverse direction.

Reference numeral 14 denotes a peak detector for the signal waveform of the origin signal Zin detected from a specific position on the scale as described above, and detects the peak point of the waveform as shown in the origin signal Zin of FIG. The reference signal ZD is output at a point in time when the voltage drops by a predetermined voltage ΔV from the point in time. Such a circuit can be constituted by a circuit as shown in FIG. 3, for example, as described later. Then, the edge of the falling signal triggers the next internal origin signal generation unit 15 to output the internal origin signal SYNC1 having a predetermined pulse width.

The internal origin signal generating unit 15 is a SYNC of FIG.
As seen from one signal, it is constituted by a circuit for obtaining a signal of a predetermined pulse width from the falling point of the waveform of the reference signal ZD. Such a circuit can be constituted by a phase-stable multivibrator which is set at the falling edge of the reference signal ZD and reset at the edge of the A5 signal two areas ahead.

Reference numeral 16 denotes an ABS counter which counts the number of pulses of the A1 phase signal or the B1 phase signal output from the interpolation pulse signal generator 11 and supplies the counted value to the next sync generator 17. Is done. ABS counter 16
Although not shown, is configured to be reset at 0 degrees of the Lissajous waveform and to repeat counting in one cycle. For example, in the case of the present embodiment, the counting of 0 to 19 is repeated.

Reference numeral 18 denotes an output signal A of the phase division unit 12.
Based on the polarities of the 5 signal and the B5 signal, it is detected in which region of the polarity pattern of the A5 signal (B5 signal) the reference signal ZD is generated, and the phase region and the reference signal ZD as shown in FIG. This is a pattern detection unit that detects the relationship between the occurrence phases of.

The timing information supplied from the pattern detecting section 18 to the timing data section 19 is simultaneously stored in the non-volatile memory 19a, so that the reference data initially set in the machine tool on which the scale is installed, Alternatively, the reference data set at the start can be stored.

When the origin signal is input, the timing data section 19 sets a phase shift area two ahead of the phase area (quadrant) of the A5 signal (B5 signal), and sets this timing to the sync generation section 17. To the sink generation unit 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, and a region two ahead of this region is set to determine the timing period for outputting the origin signal. Then, the count value of the ABS counter 16 input during this timing period is 12,1.
In the case of 3 and 14, the reference origin signal SYNC is formed in a period in which the count value 13 is substantially at the center.

Therefore, while the reference signal ZD of the origin signal detected by the scale is asynchronous with respect to the A / B phase signal, the reference origin signal SYNC is detected as a relative movement of the scale. The signal is synchronized with the A / 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 scattered within the range of the phase region.

As described above, by making the reference origin signal SYNC be formed in a region ahead of the time when the origin signal is inputted, even when the moving speed of the scale at the time of passing the origin is high, the reference origin signal is kept. I try not to vary. In the peak detection, which is an embodiment of the present invention, when the scale is in the reverse feed state and the origin position is detected, the origin position of the origin signal will be different. Preferably.

The above-mentioned phase region corresponds to 0 to 90 degrees, 90 to 180 degrees, and 180 to 27 degrees of the Lissajous waveform.
0 degrees, set every 270 degrees to 360 degrees. Therefore,
As shown in FIG. 2, the phase of the B5 signal is 9 with respect to the A5 signal.
When the phase is delayed by 0 degrees, a pattern of "10" is output in the phase region, and a pattern of "11" is output in the range of the phase region of 90 to 180 degrees. In this manner, the current phase region of the input Lissajous waveform can be detected by, for example, four-quadrant phase data (00 to 11).

Numeral 20 denotes a coincidence detecting section for detecting coincidence between the internal origin signal SYNC1 and the reference origin signal SYNC, and can be constituted by, for example, a circuit which takes a logical product of the two. Therefore, only when the origin signal Zin is detected, a signal serving as a reference of the origin synchronized with the interpolation pulse signal interpolating between the engraved pitches of the scale can be obtained from the coincidence detection unit 17. I have. An A1 phase signal and a B1 phase signal in which the amount of movement of the scale is interpolated with high precision by the interpolation pulse signal are generated, and these signals are supplied to an NC machine or the like, and processing can be performed by automatic control.

FIG. 3A is a circuit diagram showing a principle diagram of the peak detector 14, and a detector P for detecting an origin signal is provided.
The output of D is amplified by the amplifier A1 with a predetermined gain. 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 ΔV is applied as the offset voltage. The terminal voltage of the capacitor C is supplied to the opposite-phase input terminal of the comparator A4 via the buffer amplifier A2 set to unity gain.

When the origin signal is generated, the circuit shown in FIG.
As shown in (b), the potential Vc of the capacitor C becomes a constant value at the peak point p. However, since the signal at the positive phase terminal of the comparator A4 is higher than the origin signal waveform by Δv, the output is H. Level. However, the voltage of 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. . When the level of the origin signal becomes 0 by a circuit (not shown), the signal returns to the original level.

In the case of 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. 13 is output when the output indicates the forward direction. However, even when the scale is feeding backward, A / B
Since the reference origin signal synchronized with the phase signal is obtained, the data of the pattern detection unit 18 and the direction detection unit 13 can be used to determine whether or not the reference signal at the time of reverse transmission is provided separately even when the scale is reversely transmitted. It is possible to convert the signal so as to be a reference origin signal and control it so that it can be output. It is preferable that the origin position is obtained at the point where the H level of the A-phase signal and the H level of the B-phase signal are obtained. It can also be set to be based on comrades.

In the above embodiment, the data in the case where one pitch of the scale is divided into 20 is read out as the A / B phase pattern data. By sampling at a higher clock cycle, the number of samples of the Lissajous waveform can be reduced. As the number increases, the length measurement unit of the scale can be determined with a higher resolution, and the resolution of the origin position can be increased.

Further, a peak point is detected from the detected origin signal, and a point lower by a predetermined level from the peak point is used as a reference signal of the origin. An origin detection method in which is set as the origin position can be applied.

[0034]

As described above, according to the present invention, the position signal of the origin is determined in synchronization with the signal indicating the position where the grid is divided, so that the speed at which the main scale passes through the origin is increased. There is an effect that a stable origin position can be output even when it changes. In particular, when the origin position is detected by a reflection type photoelectric conversion element, the width of the output waveform of the origin signal is widened, and the error of the origin position is enlarged. Since the synchronized origin signal can be obtained almost without 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 generating device of the present invention.

FIG. 2 is a timing waveform chart of signal processing in an origin signal generation device.

FIG. 3 is a circuit diagram of an origin signal generation circuit that detects an origin based on a peak point of a detection waveform.

FIG. 4 is a principle diagram of an optical scale.

FIG. 5 is a diagram showing moire fringes.

FIG. 6 is a diagram showing movement of moiré fringes.

FIG. 7 is a diagram showing positions where photoelectric conversion elements are 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 sectional view of an optical scale.

FIG. 11 is an explanatory diagram showing a grid for detecting an origin position and a detection waveform thereof.

[Explanation of symbols]

11 interpolation pulse signal generation unit, 12 phase division unit, 13
Direction discriminator, 14 peak detector, 15 internal origin signal generator, 16 ABS counter, 17 sync generator, 18 pattern detector, 19 timing data section, 20 coincidence detector

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 2F065 AA02 DD19 FF16 FF18 QQ28 QQ51 2F077 AA38 CC02 NN05 NN30 PP19 QQ05 QQ10 QQ11 QQ13 TT06 TT21 TT42 TT52 TT62 2F103 BA32 CA02 CA05 CA06 DA02 EA20 EA18 EA18 FA12 FA15

Claims (4)

[Claims] 1. A main scale provided with at least a first marking line indicating an origin position, a second marking line graduated at equal intervals in a length direction, and movable with respect to the main scale. And detects an origin signal output at a predetermined position from the first engraved line, and converts the A-phase and B-phase signal waveforms indicating the relative movement amount of the scale from the second engraved line. A linear scale having a detecting means for detecting, wherein an internal origin generating unit for generating an internal origin signal having a predetermined width from a reference point of the origin signal; and one cycle of the A-phase and B-phase signal waveforms. An interpolation pulse signal generating unit for outputting an interpolation pulse signal divided by a predetermined number, and determining which phase region (quadrant) of the A-phase or B-phase signal waveform the timing of the reference point belongs to Means and the discriminator A second phase region that is delayed from the first phase region determined by the above, and generates a synchronization signal based on the interpolation pulse signal at a predetermined position in the second phase region. And an origin signal generator for determining an origin position from the synchronization signal. 2. The origin signal generating apparatus according to claim 1, wherein said detecting means is constituted by a photoelectric conversion element. 3. The interpolation pulse signal generating section is output as a counting pulse indicating an absolute value obtained by dividing the engraved line of the main scale, and A / B indicating an amount of scale movement.
The origin signal generating device according to claim 1, wherein the origin signal generating device is configured to form a phase pulse signal. 4. The origin signal generating apparatus according to claim 1, wherein the reference point of the origin signal is formed based on a level lowered by a predetermined potential from a peak point of the origin signal.