JPH08327401A - Displacement-information detection apparatus, drive control device and scale for detection of displacement information - Google Patents

Abstract

PURPOSE: To detect displacement information with high accuracy by a method wherein an irregularity in quantities of light between a plurality of pattern formation parts is monitored so as to be detected according to the difference between the quantities of light. CONSTITUTION: A luminous flux from a light source LGT is shone at a scale D which is moved relatively. Illumination light to an origin track TZ generates a light and shade pattern in a space, and transmitted light from an amplitude grating GTZ for the origin is received by a photodetector SZ. Then, whenever the light is transmitted through the origin, a pulse- shaped analog signal is outputted via a signal processing circuit, and the passage of the origin in the scale D is detected. From the illumination light onto absolute code pattern tracks Tu , Tv , Tw , the transmitted light is projected intermittently on photodetectors Su , Sv , Sw by a direct-acting part D, and an absolute position is specified by the signal processing circuit on the basis of their outputs. The illumination light is transmitted also through tracks Tref1 Tref2 for monitoring of a quantity of light, and photodetectors Sref1 , Sref2 output quantity-of-light signals. Then, the signal level of the photodetectors Sref1 (or Sref2 ) is subtracted from signal levels of the photodetectors Su , Sv (or Sw , Sz ) so as to be corrected by the processing circuit before the signals are processed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement information detecting device, a drive control device, and a displacement information detecting scale. The present invention irradiates a luminous flux on a grating and a code pattern of a scale attached to a relative (rotating) object, and detects modulated signal light obtained from the luminous flux to detect the position of the scale, the amount of positional deviation, and the positional deviation direction. Good for encoders that detect speed, acceleration, etc., and devices that rotate and move objects by controlling the current amount and direction of drive devices such as AC motors based on the above detection information (motors with encoders, etc.) It is applicable.

[0002]

2. Description of the Related Art Conventionally, an incremental encoder for relative displacement detection has been used for the purpose of highly accurately measuring position information (displacement amount, velocity, acceleration, etc.) of an object. On the other hand, for brushless motors typified by AC motors,
An absolute rotary encoder that detects the absolute rotation position of the rotor in the motor has been used to rotate the motor.

In order to control the rotational position of an object using an AC motor or the like, a composite rotary encoder that can obtain both signals has been used.

Here, a conventional high-precision incremental encoder illuminates a monochromatic luminous flux onto a micron-order fine grating recorded on a scale, as shown in Japanese Patent Publication No. 58-26002. A configuration in which at least two of the diffracted lights obtained there are taken out and caused to interfere with each other to create a periodic change in the amount of light accompanying the movement of the grating, and the photoelectric element detects it to output an incremental encoder signal. I was doing.

On the other hand, the absolute rotary encoder, as disclosed in, for example, US Pat. No. 3591841, has a plurality of transmission / non-transmission (or reflection / non-reflection) patterns ( For example, a gray code pattern) is formed so that there is only one code combination during one rotation, and the absolute light rotation position of the disk is detected by detecting transmitted light (or reflected light) at a specific position on each circumference. Was being output. Absolute encoders for motors in particular
Multiple transmissive / non-transmissive (or reflective / non-reflective) patterns (for example, gray code patterns) on different circumferences on the rotating disk, only M combinations depending on the motor structure (number of poles M) If it is formed like this, transmitted light (or reflected light) at a specific position on each circumference
Is detected, the position between the rotor and the stator of the motor is output.

[0006]

As a recent trend, there is a demand for miniaturization of rotary encoders (EX.Φ10 mm disc). To miniaturize composite encoders based on different principles as described above. It is desirable to record a pattern for generating a plurality of signals on the disc with a narrow track width and uniformly irradiate all the tracks with a light beam.

On the other hand, a small light source is desirable as a light source for such a small displacement information measuring device. LED as a small light source
Light emitting elements such as

FIG. 1 is an explanatory view of a light emitting state of such a light emitting element such as an LED. (A) is a diagram showing the distribution of the amount of light emitted in each direction of a light emitting element such as an LED, and (b) is a cross section of a parallel light flux when the light from the light emitting element such as an LED is collimated by a collimator lens. It is a figure which shows light amount distribution.

In the case of the composite encoder based on the different principle as described above, when the divergent light from the light source LGT such as an LED is converted into a parallel light flux by the collimator lens LNS, the innermost circumference of the track is illuminated in order to illuminate all the tracks. The diameter and focal length of the collimator lens are selected so that the luminous flux diameter covers the width up to the outermost circumference.

On the other hand, when miniaturizing the entire structure of the encoder, it is desirable to use a lens having a short focal length in order to miniaturize the optical system.

However, in order to shorten the focal length while keeping the luminous flux diameter of the parallel luminous flux to some extent, it is necessary to dispose a special lens having a large NA close to the light emitting position of the light source.

In general, the luminous flux emitted from a light emitting element such as an LED changes in amount depending on the emission direction as shown in FIG. 1 (a). Therefore, the parallel luminous flux obtained by the collimator lens is As shown in FIG. 1B, the center is strong and the periphery is weak. Therefore, in general, the unevenness of the light amount is corrected by an electric circuit in the subsequent stage to correct the amplitude offset. However, such unevenness of the light amount also varies depending on the optical system. For example, when the optical axis shifts, the light amount in the peripheral portion becomes large on one side and becomes small on the other side. Therefore, if such a light amount unevenness is corrected with a fixed constant, the correction becomes inaccurate and an error may occur.

In view of the above-mentioned conventional example, the present invention provides a small-sized composite displacement information detecting device capable of highly accurate displacement information detection in consideration of a light amount difference such as light amount unevenness according to the exit direction, and the same. The present invention relates to a drive control device used and a displacement information detection scale used therein.

[0014]

According to a first aspect of the present invention, a first pattern forming portion on a scale provided on an object whose relative displacement is to be detected is irradiated with a light beam to form the first pattern. First detection means for detecting light emitted from the section and outputting a signal corresponding to relative displacement information of the object,
A second unit provided at a position different from that of the first pattern forming unit on the scale provided on the object whose relative displacement is to be detected.
Second detecting means for irradiating the pattern forming part with a light beam to detect light emitted from the second pattern forming part and outputting a signal corresponding to relative displacement information of the object; and the first and second detecting means.
Light quantity monitor means for detecting light emitted from light quantity monitoring areas provided in the respective pattern forming portions or in the vicinity of the respective pattern forming portions, and performing light quantity monitoring in the vicinity of each of the first and second pattern forming portions. It is a displacement information detection device characterized by having.

Further, the second invention is characterized in that a plurality of absolute position detecting patterns and origin position detecting patterns are separately arranged in the first and second pattern forming portions. And

A third invention for achieving the above object is to provide a phase type diffraction grating provided on a scale, which is provided on an object whose relative displacement is to be detected by a light beam from a light source, and the phase type diffraction grating. The phase type diffraction grating, the absolute position detection pattern, and the origin position detection pattern are irradiated by irradiating the absolute position detection pattern and the origin position detection pattern, which are provided separately in the first and second pattern forming portions sandwiching The modulated light beams obtained from the above are projected onto the corresponding light receiving elements, and the periodic light / dark signal, the absolute position code signal, and the origin position signal associated with the relative displacement are output, respectively, and the first and second The light emitted from the light amount monitoring areas provided in the pattern forming portions or in the vicinity of the respective pattern forming portions is detected, and the first and second patterns are detected. A displacement information detecting apparatus characterized by having a light quantity monitoring means for the light quantity monitoring around each chromatography emissions forming unit.

Further, the fourth invention is characterized by further comprising a processing circuit for correcting the output signal on the basis of the monitoring result of the light quantity monitoring means.

Further, a fifth invention for attaining the above object is characterized in that the above displacement information detecting device is provided, and the driving of the object is controlled based on the signal corrected by the processing circuit. It is a control device.

A sixth invention for achieving the above object is to provide a phase type diffraction grating, an absolute position detection pattern and an origin position detection for forming relative displacement information detection from the modulated light obtained by irradiation with a light beam. And an absolute position detecting pattern and an origin position detecting pattern sandwiching the phase type diffraction grating.
The displacement information detecting scale is characterized in that it is provided separately in the pattern forming portion, and that a light amount monitoring area is provided in each of the first and second pattern forming portions or in the vicinity thereof.

The seventh aspect of the invention is further characterized in that the relative displacement is a relative rotational displacement.

[0021]

FIG. 2 is an optical layout diagram of a linear encoder according to the first embodiment of the present invention.

FIG. 3 is an optical layout diagram of a rotary encoder according to a second embodiment of the present invention.

In the first and second embodiments, it is detected whether the arrangement of the respective patterns on the scale D which moves relative to each other is linear or circumferential, and whether the displacement of the scale D is direct or rotational. There is a difference between linear displacement information and rotational displacement information,
The other points are the same as the outline, and will be described below collectively.

A light beam emitted from a light source LGT such as an LED is a collimator lens formed by a multiple annular diffraction grating.
It is collimated by the LNS and illuminated on the scale D that moves relative to it (moves straight or rotates). In FIG. 2, the scale D is not shown except for the vicinity of the light beam irradiation portion.

An incremental signal track GT1 having a concavo-convex transmission phase diffraction grating formed on the scale D by glass etching or a molding method, and a concavo-convex transmission phase diffraction grating partially arranged at the origin position. The origin track Tz in which the pattern is formed and the absolute code tracks Tu, Tv, Tw in which the irregularly arranged transmissive phase phase diffraction grating pattern is formed are recorded along the displacement detection direction.

In these embodiments, a set of absolute code tracks Tu and Tv and an absolute code track T are arranged on both sides of the incremental signal track GT1 as a center.
w, the tracks Tref1 and Tre for light quantity monitoring, which are light flux transmission tracks that are arranged separately for each set of the origin track Tz and no pattern is formed between the tracks of each set.
f2 is arranged.

The cross-sectional shape of the phase type diffraction grating is a lamella grating, the unevenness ratio is 1: 1 and the refractive index n of the constituent materials is
As the wavelength λ of the light source, the step h is set to satisfy h = λ / (2 × (n−1)). The amount of transmitted light due to the unevenness is the same.

First, transmitted diffracted light is generated by the luminous flux illuminated on the incremental track GT1 (lattice pitch P1 μm). As the transmitted diffracted light flux moves away from the grating GT1, due to the diffraction phenomenon, the phase discontinuities are connected smoothly, and the interference of the light fluxes from both irregularities increases, and the clear light quantity drops above the phase discontinuities. Parts occur regularly. The grating pitch of this light-dark pattern is the phase grating GT
It is half the grid pitch P1 of 1. That is, a light-dark pattern (light-dark cycle P2 = P1 /
2 μm) is generated.

The transmitted light is emitted as a light / dark signal by selecting a light / dark pattern by an amplitude grating (slit grating) GT2 (grating pitch P2 = P1 / 2 μm) arranged there.

When the phase grating is moved by one pitch due to the movement of the scale D, the light and dark patterns are displaced by two pitches,
The amount of transmitted light changes in a sinusoidal manner for two cycles.

Here, in this embodiment, the amplitude grating GT2 is
As shown in Figure 2, the areas are GT2-a, GT2-b, GT2-a bar, GT2.
-B bar is divided into four, and each region is formed by shifting the phase of the lattice arrangement of each other by 1/4 pitch.

The light and dark phases of the light emitted from the respective areas are deviated from each other by ¼ cycle.

Since the light emitted from each of these areas is incident on the corresponding light receiving elements SA, SB, SA bar, and SB bar, sinusoidal analog signal currents are mutually emitted from the light receiving elements SA, SB, SA bar, and SB bar. It occurs with a shift of 1/4 cycle. Using these four phase-shifted sinusoidal analog signals, a relative linear displacement amount (or rotation amount) and linear movement (or rotation) direction of the scale D are calculated by a signal processing circuit (not shown). It Since this calculation is well known, its explanation is omitted.

On the other hand, on the origin track Tz, the phase type diffraction grating is partially formed at the origin position with the pitch varied. The light flux illuminated on the origin track Tz generates diffracted light when a spot where this phase type diffraction grating is formed in the illuminated area, and produces a specific bright-dark pattern in a space slightly apart from the scale surface. . At this light / dark pattern generation position, an origin amplitude grating (slit grating) GTz formed in the same pattern as the light / dark pattern is formed on the same substrate as the amplitude grating GT2. With the configuration in which the origin amplitude grating GTz is transmitted, the minimum amount of transmitted light is obtained at the moment when the bright-dark pattern and the origin amplitude grating GTz completely match. Therefore, one pulse-shaped analog signal is generated every time the origin passes from the light receiving element Sz arranged at the position for receiving the transmitted light. Such a pulse signal is generated by a signal processing circuit (not shown) that receives the output of the light receiving element Sz. As a result, the passage of the scale D through the origin is detected.

On the other hand, the above-mentioned parallel luminous fluxes illuminating the absolute code pattern tracks Tu, Tv, Tw indicate whether or not the luminous flux part irradiating the part corresponding to the light receiving element is on the phase type diffraction grating, that is, the absolute code. The transmitted light is intermittently projected onto the light receiving elements Su, Sv, Sw by the linear movement or rotation of the scale D in accordance with the light transmission / non-transmission of the portion corresponding to the light receiving element of the pattern track. Here, when there is a pattern in the irradiation position, the light beam is diffracted and the optical path is shifted to a non-transmissive state.

From the light receiving elements Su, Sv, Sw, an absolute code signal group corresponding to the current linear or rotational position of the scale D is output, and the absolute position is determined by a signal processing circuit (not shown) by combining the binary information. Specified. Since the method of specifying the absolute position is well known, the description thereof will be omitted.

The light beams illuminated on the light amount monitor tracks Tref1 and Tref2 are transmitted as they are, and the light receiving elements Sref1 and Sref2 are transmitted.
The light quantity signal is output.

With this structure, Sv and Sz which receive the modulated light beam near the center of the light beam receive the outer modulated light beam.
The light level output is larger than that of Su and Sw, and the average value of both light levels and the output from the light receiving elements Sref1 and Sref2 become almost the same (however, the light level is the phase grating non-formation part luminous flux It is the light receiving element signal output level during transmission).

FIG. 4 is a circuit explanatory diagram showing a processing circuit for signal correction, which is arranged between each of the above-mentioned light receiving elements and a signal processing circuit (not shown).

The outputs of the light receiving elements SA and SA bar are subtracted to obtain A
It is output as a phase signal. Similarly, the outputs of the light receiving elements SB and SB bar are subtracted and output as a B-phase signal.

On the other hand, the analog signal output from each of the light receiving elements Su, Sv, Sw, and Sz is multiplied by an appropriate coefficient for each analog signal level so that the average value of the brightness level of each output becomes equal, and the amplitude is standardized. Further, each analog signal level is multiplied by an appropriate coefficient so that the analog signal output from each of the light amount monitor light receiving elements Sref1 and Sref2 becomes the same value as the above-mentioned average value of the brightness level. From the analog signal level obtained by multiplying the signals from the photo detectors Su, Sv, Sw, and Sz by this appropriate coefficient, the light intensity monitor photo detectors Sref1 and Sre
The offset is normalized by subtracting the analog signal level multiplied by this appropriate factor of the signal from the near side of f2. That is, the analog signal level obtained by multiplying the signals from the light receiving elements Sv and Su by an appropriate coefficient is subtracted from the analog signal level obtained by multiplying the signal from the light amount monitor light receiving element Sref1 by an appropriate coefficient, and the appropriate signal levels from the light receiving elements Sw and Sz are obtained. The analog signal level multiplied by the appropriate coefficient subtracts the analog signal level multiplied by an appropriate coefficient of the signal from the light amount monitor light receiving element Sref2.
In this way, the signals U, V, W, and Z having standardized offsets and amplitudes are obtained. The signals U, V, W, Z are binarized by a signal processing circuit (not shown), and then various processes are performed.

The coefficient value multiplied by the coefficient in these electronic circuits is fixed by the resistance in the circuit whose resistance value is properly designed based on the general light intensity distribution measured in advance.

With such a configuration, the amplitude and offset can be accurately corrected even if the light amount from the light source fluctuates. In addition, in such a configuration, the optical axis of the light receiving element Sr
If it is deviated to the ef1 side, the output amplitude and offset of the light receiving elements Sv, Sref1, Su become large, and the light receiving elements Sz, Sref
2. The output amplitude and offset of Sw become small. Light receiving elements Sv, Sref1, Su are close to each other, and light receiving elements Sz, Sre
Since f2 and Sw are also close to each other, the directions of increase and decrease of the light amount are the same in each group, and the ratio of the light level output does not change so much. Therefore, even if the amplitude is corrected by the coefficient multiple fixed by the resistance as described above, the influence of the error is small, and particularly at the stage of the offset correction by subtracting the amplitude-corrected analog signal levels, the correction error can be extremely small.

Consider, for example, a case where a light quantity monitor track is provided at only one position on the scale and the amplitude and offset are corrected based on the output obtained from that track. However, in the case of light amount fluctuation due to optical axis deviation, etc., the necessary correction direction differs depending on the measurement location, but it can only be corrected uniformly, so the correction is partially over- or under-correction. The situation is likely to occur.

On the other hand, in the present apparatus, as described above, the light quantity monitor tracks are provided close to the respective tracks for each group, and the correction is performed based on the signals obtained from the respective tracks. Stable analog signal U,
V, W and Z can be obtained.

Based on this analog signal, it is converted into a digital signal by a known binarization circuit in a signal processing circuit (not shown) to obtain various encoder signals.

By the recording method of the encoder pattern and the signal processing circuit as described above, even if an unexpected light amount unevenness occurs in each position information signal light due to an attachment error of an optical system component or a deviation of a radiation characteristic of a light emitting element. It is possible to realize an encoder that is small in size, small in diameter, and thin, and can stably output a position information signal without having to readjust the circuit configuration again.

FIG. 5 is a schematic configuration diagram of a motor driver system according to a third embodiment of the present invention. In the figure, DH is a detection head in which the all-optical configuration except the scale D from the light source LGT to each light receiving element and the circuit configuration shown in FIG. 4 are arranged in the above-described second embodiment, and PU is from the circuit shown in FIG. Signal processing of each output to perform incremental rotation amount and rotation direction measurement, discrete rotation position measurement, and origin detection, and a signal processing circuit that generates a control signal.IM inputs a rotation command input to the signal processing circuit PU. Input part for doing, MD
Is a motor driver that receives a control signal from the signal processing circuit PU to control the drive of the motor, MT is a motor, and SF is a shaft that is rotationally driven by the motor and that transmits the driving force to a driven part (not shown).

The signal processing circuit PU generates a control signal based on the output from the circuit configuration shown in FIG. 4 and the command input information from the input section, and thereby the rotational drive of the shaft SF by the motor MT is controlled.

With the above-mentioned configuration, the circuit configuration should be readjusted even if an unexpected light amount unevenness occurs in each position information signal light due to an error in mounting an optical system component or a deviation of the radiation characteristic of the light emitting element. However, a motor driver system that can stably output a position information signal while being small, small in diameter, and thin has been realized.

In addition, the following changes are possible. (1) Absolute code pattern track Tu, Tv, Tw
The pattern inside may be changed to normal pure binary code, gray code, etc., not for motor control. (2) Absolute code pattern track Tu, Tv, Tw
The pattern in the center track Tz may be changed to one recorded with a transparent, non-transmissive or reflective, non-reflective film. (3) Amplitude grating GT2 for incremental phase difference signal generation
The number of divisions and the amount of phase shift may be changed (two divisions, 90 degrees shift, six divisions, 60 degrees shift, etc.). (4) Light intensity monitor tracks Tref1, Tref2 are absolute code pattern tracks Tu, Tv, Tw, origin tracks
It may be arranged not near the Tz but in the vicinity of the portion where these tracks are formed or the like.

[0052]

As described above, according to the first aspect of the present invention, it is possible to monitor the light amount unevenness between a plurality of pattern forming portions, and it is possible to appropriately detect the light amount difference.
As a result, a small-sized composite displacement information detection device capable of highly accurately detecting displacement information is realized.

Further, according to the second invention, the absolute position detection and the origin detection can be appropriately performed according to the light amount difference due to the light amount unevenness, and as a result, the displacement information can be detected with high accuracy and is small in size. A composite displacement information detection device is realized.

Further, according to the third aspect of the invention, it is possible to appropriately perform absolute position detection and origin detection depending on the light amount difference due to the light amount unevenness, with the periodic light / dark detection associated with the relative displacement therebetween. As a result, a small-sized composite displacement information detection device capable of highly accurately detecting displacement information is realized.

Further, according to the fourth aspect of the present invention, it is possible to perform an appropriate correction according to the light amount unevenness among a plurality of pattern forming portions, and as a result, it is possible to perform highly accurate displacement information detection, which is small in size. A composite displacement information detection device is realized.

Further, according to the fifth aspect of the invention, highly accurate drive control is realized by the small-sized composite displacement information detection device which enables such highly accurate displacement information detection.

Further, according to the sixth aspect of the invention, a scale for detecting displacement information is realized which can easily monitor the light amount unevenness between a plurality of pattern forming portions.

The seventh aspect of the invention can realize such highly accurate displacement measurement, drive control and the like in the rotational displacement.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a light amount distribution of light emitted from a light source.

FIG. 2 is a diagram showing a first embodiment of the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a processing circuit of this embodiment.

FIG. 5 is a diagram showing a third embodiment of the present invention.

[Explanation of symbols]

LGT light source LNS collimator lens D scale GT2 amplitude grating GT1 phase type diffraction grating GTz origin amplitude grating SA, SA bar, SB, SB bar periodic light-dark detection light receiving element SZ origin light receiving element Su, Sv, Sw absolute light receiving Element Sref1, Sref2 Light intensity monitor light receiving element Tz Origin track Tu, Tv, Tw Absolute code pattern track Tref1, Tref2 Light intensity monitor track

Claims (7)

[Claims] 1. Relative displacement information of the object by irradiating a first pattern forming unit on a scale provided on an object whose relative displacement is to be detected with light flux and detecting light emitted from the first pattern forming unit. To the second pattern forming portion provided at a position different from the first pattern forming portion on the scale provided on the object whose relative displacement is to be detected, and the second detecting means for outputting a signal corresponding to Second detecting means for detecting light emitted from the second pattern forming portion and outputting a signal corresponding to relative displacement information of the object;
A light amount monitor for detecting light emitted from light amount monitoring areas provided in each of the second pattern forming portions or in the vicinity of each of the second pattern forming portions to monitor the light amount in the vicinity of each of the first and second pattern forming portions. Displacement information detecting device having means. 2. A plurality of absolute position detection patterns and a plurality of origin position detection patterns are separately arranged in the first and second pattern forming sections, respectively. The displacement information detection device described. 3. A phase type diffraction grating provided on a scale, which is provided on an object whose relative displacement is to be detected, and first and second pattern forming portions sandwiching the phase type diffraction grating. The absolute position detection pattern and the origin position detection pattern provided separately are irradiated, and the modulated light obtained from the phase type diffraction grating, the absolute position detection pattern and the origin position detection pattern are respectively received. It is configured so as to project on the above and output a periodic light / dark signal accompanying the relative displacement, an absolute position code signal, and an origin position signal, respectively.
A light amount monitor for detecting light emitted from light amount monitoring areas provided in each of the second pattern forming portions or in the vicinity of each of the second pattern forming portions to monitor the light amount in the vicinity of each of the first and second pattern forming portions. Displacement information detecting device having means. 4. The displacement information detecting device according to claim 1, further comprising a processing circuit that corrects the output signal based on a monitor result of the light amount monitor means. 5. A drive control device comprising the displacement information detection device according to claim 4, and controlling the drive of the object based on a signal corrected by the processing circuit. 6. A phase type diffraction grating, an absolute position detecting pattern, and an origin position detecting pattern for forming relative displacement information detection from the modulated light obtained by irradiating a luminous flux, and for detecting the absolute position. The pattern and the origin position detection pattern sandwich the phase type diffraction grating
And a second pattern forming portion, which are provided separately, and a light amount monitor area is provided in each of the first and second pattern forming portions or in the vicinity of each of the first and second pattern forming portions. 7. The displacement information detecting device, the drive control device, or the displacement information detecting scale according to claim 1, wherein the relative displacement is a relative rotational displacement.