JP2003161645A - Optical encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical encoder capable of detecting movement information of an object to be measured with high precision. <P>SOLUTION: The optical encoder has a scale in which optical gratings are formed at a predetermined pitch, a light detecting means which is arranged relatively movable with respect to the scale and includes a plurality of light receiving elements arranged in relation to the pitch of the optical gratings, a light source means for illuminating the light receiving elements through the scale, and a signal processing circuit for detecting relative displacement information between the scale and the light detecting means. An electric dividing circuit for electrically increasing resolving power using an analog signal obtained from the light detecting means is integrated with the signal processing circuit. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder for detecting movement information such as a movement amount, a movement direction and an angle change of an object to be measured.

[0002]

2. Description of the Related Art An optical encoder is basically a first type in which a grating that transmits light and a grating that does not transmit light are arranged at a constant period.
The main scale on which the optical grating is formed, the index scale on which the second optical grating of the same grating is formed facing the main scale, the light source for irradiating the main scale with light, and the optical grating on the main scale are transmitted. Alternatively, it is configured to include a light receiving element that receives the light that is reflected and that is further transmitted through the index scale optical grating. In this type of optical encoder, various methods have already been proposed in which a light receiving element array is used also as an index scale optical grating.

FIG. 9 is a schematic view of a main part of a conventional optical encoder of this type.

In FIG. 9, a plurality of light receiving elements 13 are formed on the index scale 10 directly on the substrate 11 in accordance with the pitch of the two scales of the optical grating 3 of the main scale 1 which are light transmitting and light non-transmitting. It was done. That is,
After the oxide film 12 is formed on the n-type semiconductor substrate 11, the oxide film 12 is selectively removed according to the pitch of the optical grating 3, and the oxide film 12 is used as a mask for the n-type semiconductor substrate 11
By diffusing p-type impurities into the p-type semiconductor layer 13
To form. As a result, a photodiode is formed at the pn junction between the n-type semiconductor substrate 11 and the p-type semiconductor layer 13. The index scale 10 is formed by forming the transparent current collecting layer 14 on the entire surface of the substrate 11.

In the figure, the optical grating 3 of the main scale 1 is shown.
The diffracted light from the openings 3a1, 3a2 ... Interferes with each other to form a bright-dark pattern on the index scale 10. Then, the light-dark pattern formed on the index scale 10 is detected by the photodiode.

According to this, the light from the light source 5 is reflected by the lens 6
After passing through one optical grating 3, the light receiving efficiency is improved, the influence of noise due to diffracted light is eliminated, and the optical grating of the index scale 10 constitutes a light receiving element. It has the feature that it can be downsized.

FIG. 10 shows the relationship between the pattern examples of the photodiode arrays A and B used in the optical encoder shown in FIG. 9 and the light-dark pattern Pa of the light formed on the photodiodes and detected by the photodiodes. Show. FIG. 11 shows an IV conversion circuit that converts the optical input given to the photodiodes A and B of FIG. 10 into a voltage (converts the current value from the photodiodes A and B into a voltage). Figure 1
In 0, the photodiode group A is arranged at 0 ° and the photodiode group B is arranged at 90 ° out of phase with respect to the light / dark pattern Pa of light. Signals SA and SB from the photodiodes A and B are I- in FIG.
It is input to the IV conversion amplifiers 41 and 42 of the V conversion circuit.

The photocurrent generated by such a structure is converted into a voltage by the IV conversion circuit when the light-dark pattern of light crosses over the photodiode groups A and B, and the analog sine voltage is out of phase with 0 ° and 90 °. Signals Asinθ, Acosθ
Is obtained.

FIG. 12 shows an example of a conventional resistance division circuit (electric division circuit) capable of dividing the pitch of the primary signal into 16 parts.

In the figure, reference numeral 15 is an electric division circuit.
20A is a buffer amplifier for the Asin θ signal output from the IV conversion amplifier 41, 20B is a buffer amplifier for the Acos θ signal output from the IV conversion amplifier 42, and 22 is an inverted signal of the output of the buffer amplifier 20A. -Inverting amplifier for applying Asin? To the nodes of the resistance chain 16, 24A to 24H are eight comparators respectively provided corresponding to each node of the resistance chain 16, and 26 is each comparator 24A to 24H. A reference voltage setter for supplying a reference voltage Vr for comparison, 28
A to 28F are exclusive OR gates for combining the outputs from the comparators 24A to 24H, 30 is a direction discriminating circuit, and 32 is an oscillator.

In the electric division circuit 15, the resistance R
The value of 1, R2, R3, and R4 is 1: 0.70, respectively.
The ratio is set to 7: 0.707: 1, and 180 ° is divided into 8 parts, so 16 decomposition is performed at 360 °.

Since this resistance division circuit is disclosed in detail in Swiss Patent No. 407569, detailed description thereof will be omitted. The light-dark pattern of the light thus obtained in the light-receiving element group can obtain a pulse signal having a higher resolution than that optically obtained through the IV conversion amplifier and the electric division circuit, and a highly accurate position, The rotation information is obtained.

[0013]

The analog output signal Asin from the light receiving element of the encoder as shown in the conventional example.
In order to electrically divide θ and Acos θ by the resistance division method, the amplitude and offset voltage on the input side of the electric division circuit 15 greatly affect the accuracy. Moreover, since the analog output signal from the light receiving element of the encoder fluctuates greatly due to fluctuations in the light amount of the light source, fluctuations in the distance between the main scale 1 and the index scale 10, etc. I couldn't.

An object of the present invention is to provide an optical encoder capable of detecting movement information of an object to be measured with high accuracy.

In addition, the present invention can stabilize the DC component and AC component fluctuations of the signal input to the electric division circuit, electrically divide the output signal from the photodetector with high accuracy, and obtain high resolution. The purpose is to provide an optical encoder.

[0016]

An optical encoder according to a first aspect of the present invention is provided with a scale in which an optical grating is formed at a predetermined pitch, a scale movable relative to the scale, and a pitch of the optical grating. A light detecting means including a plurality of light receiving elements arranged in association with each other, a light source means for irradiating the light receiving element with light through the scale, and a scale obtained by using a signal obtained by the light detecting means. In an optical encoder having a signal processing circuit for detecting relative displacement information with respect to the light detecting means, an electric division circuit for electrically increasing resolution by using an analog signal obtained from the light detecting means. Can be integrated with the signal processing circuit.

According to a second aspect of the present invention, in order to integrally provide the electric division circuit according to the first aspect of the present invention, there is provided a stabilizing means for stabilizing DC and AC component fluctuations of a signal input to the electric division circuit. It is characterized by being.

The invention of claim 3 is characterized in that, in the invention of claim 2, the stabilizing means has a push-pull circuit.

The invention of claim 4 is characterized in that, in the invention of claim 2, the stabilizing means has a light quantity feedback function.

The invention of claim 5 is characterized in that, in the invention of claim 2, the stabilizing means has a function of obtaining a difference signal between certain light receiving elements by a differential amplifier.

According to a sixth aspect of the present invention, in the first aspect of the present invention, a signal from each differential amplifier for signal-processing the I / V amplifier output is input from the signal processing circuit to the input terminal of the resistance chain of the electric division circuit. It is characterized by having entered.

According to a seventh aspect of the present invention, in the first aspect of the present invention, an addition means for adding a constant voltage to the differential amplifier is provided so that the signal processing circuit and the electric division circuit can be driven by a single power source. It has a feature.

The invention of claim 8 is characterized in that, in the invention of claim 1, the electric division circuit is formed on the same semiconductor substrate together with the signal processing circuit.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a main part of a photoelectric encoder according to a first embodiment of the present invention.

In the figure, 1 is a main scale (first scale), which is a light transmitting portion 3a (3a1, 3a2 ...
.) And the light shielding portion 3b are arranged at a constant pitch along the relative displacement direction (arrow direction) to form the optical grating 3. Reference numeral 2 denotes a light detecting means (second scale), which is (1/4) × n (n is 1 or more and 4 of 4 in the period (SF) in the displacement direction (arrow direction) of the pitch of the optical grating 3. Three or more light receiving elements (photodiodes) A, B, C having a width WS of an integer excluding multiples are arranged.

In this embodiment, three light receiving elements (photo diode) of n = 3 are arranged.

The light receiving elements A, B and C form one light receiving element group (photodiode array).

Reference numeral 5 is a light source. A lens system 6 guides the light flux from the light source 5 to the main scale 1 as parallel light.

Light transmission parts 3a1, 3a of the main scale 1
The diffracted lights from 2 ... Interfere with each other to form a bright / dark pattern Pa on the light receiving element surface of the light detecting means 2.

The main scale 1 and the light detecting means 2
Is relatively moved in the direction of the arrow, the light flux from the light source 5 that has passed through the lens 6 is incident on the main scale 1, is diffracted by the light transmitting portion 3a of the optical grating 3, and interferes with the light-dark pattern Pa. It is incident on the light receiving elements A, B, and C.

From the light receiving elements A, B and C, a signal based on the relative movement of the main scale 1 and the light detecting means 2 is detected.

At this time, the output signals from the light receiving elements A, B and C are processed by the signal processing circuit Y1 to detect the relative movement information between the main scale 1 and the light detecting means 2.

Next, a method of processing the signals obtained by the light receiving elements A, B and C of this embodiment will be described.

In the optical encoder of this embodiment, when the main scale on which the optical grating is formed and the light detecting means (index scale) provided with the photodiode array are relatively moved in one direction, the light receiving element ( A signal corresponding to the light-dark pattern of light is obtained by the photodiode, and this signal is obtained to obtain relative displacement information of both.

FIG. 2 is an explanatory diagram of the first embodiment showing the relationship between the pattern example of the photodiode used in the optical encoder and the light / dark pattern of light detected by the photodiode. In FIG. 2, the light-dark pattern Pa is 1
Three photodiodes A, B, and C each having a width WS of ¼ of the period SF are arranged in order with their phases shifted by 90 °.

Further, the photodiode has a plurality of light receiving elements (A, A1, A2) having a common spatial phase with respect to the optical grating 3 (light transmitting portion 3a and light non-transmitting portion 3b) of the scale 1.
It includes (B, B1, B2) and (C, C1, C2).

FIG. 3 is an explanatory diagram of the signal processing circuit Y1 which processes the signals SA, SB and SC from the photodiodes A, B and C which constitute the photodetector of FIG. Reference numerals 41 to 43 are amplifiers (IV conversion circuits) for amplifying (IV converting) the signals of the photodiodes A, B, and C. Reference numeral 45 denotes an inverting adder (adding means) that adds the amplified voltages of the signals from the photodiodes A and C and inverts the output voltage,
Reference numeral 46 denotes an LED (light emitting diode) whose light emission amount changes according to the result of the signals added by the adder 45. FIG. 4 shows an example of an output signal waveform from the IV conversion circuit 41 when the light / dark pattern of light moves from the left side to the right side of the photodiode shown in FIG. (In FIG. 4, the output signal from the IV conversion circuit 41 is taken as an example, but the output signals from the IV conversion circuits 42 to 43 also have similar signal waveforms with different phases.) 15 is electric This is a division circuit, and the resolution is electrically increased by using the analog signals from the photodiodes A and B.

The signal processing of this embodiment will be described with reference to FIGS. The detection signal A1 in FIG. 4 is the light amount from the light source 5 in the optical encoder, the encoder head (light detection means).
2 is a signal waveform when the distance between 2 and the main scale 1 is within a specified range. Normally, the output signal from the IV conversion circuit 41 has a waveform in which an AC signal with a certain amplitude is superimposed on a certain DC voltage. (In Fig. 4, DC: 3V, AC: ±
It is 1V. The electric division circuit 15 is adjusted so as to obtain an accurate division result with this input signal.
The detection signal A2 is, for example, a waveform generated when the interval between the encoder head 2 and the main scale 1 becomes narrow, and the DC component and the AC amplitude are large. Further, the detection signal A3 is a waveform generated when, for example, the amount of light from the light source 5 is reduced or the distance between the encoder head 2 and the main scale 1 is widened, and the DC component and AC The amplitude is getting smaller. In this way, the output component of the light source 5 and the mounting error of each scale change the DC component and AC amplitude of the detection signal. Then, the accuracy of the electric division also deteriorates.

Therefore, the photodiode C is provided as shown in FIGS. 2 and 3, and the total of the photodiode C and the photodiode A is the adder 4
5 is input to the minus side of the adder 45, and the set voltage Vref is input to the plus side of the adder 45.

Since the signal SA from the photodiode A and the signal SC from the photodiode C have a phase of 180 °, the sum of them is a DC voltage signal VAC proportional to the amount of light from the light source 5. By comparing this DC voltage signal VAC with the set voltage Vref, the LED
The light emission amount of 46 is determined. That is, by using such stabilizing means, the amount of light emitted from the light source 5 is hood-back controlled so that the amount of light emitted from the light source 5 reaches a certain target value.

Then, the obtained detection signal becomes the detection signal A1 shown in FIG. 4, and variations in DC and AC are eliminated. As described above, in the circuit configuration having the stabilizing means shown in FIG. 3, a stable signal is always output, so that the electric division circuit 15 can be adjusted without adjustment.
Can be an input signal to. Here, the light detecting means 2 may be a light receiving sensor arranged in a certain phase relationship, but since the photodiode has a plurality of light receiving elements having the same phase relationship, there is an effect that variations are averaged and DC
There is an advantageous effect that the fluctuation of AC and AC can be reduced.

(Second Embodiment) FIG. 5 shows a second embodiment of the present invention.
FIG. 6 is an explanatory diagram of the arrangement of photodiodes according to the present invention. The difference from the first embodiment is that the number of photodiodes for 1/4 of one cycle of the light and dark pattern is 3 to 4, and the photodiodes are 0 ° and 9 respectively.
That is, they are arranged so as to have a relationship of 0 °, 180 °, and 270 °. In addition, those photodiode groups are S
1, S2, S3, S4.

FIG. 6 is an explanatory diagram of a circuit configuration according to the second embodiment. Since the width of the photodiode is 1/4 of one cycle of the bright / dark pattern Pa, the photodiodes S1 and S3 are
Since the signals are out of phase with each other by 180 °, a reference signal for feeding back the light emission amount of the light source 5 can be obtained from the results S1 and 3 of the addition of the photodiodes S1 and S3, as in the first embodiment. In FIG. 6, the output signal SA is obtained from the result of the differential amplification of the differential amplifier photodiodes S1 and S3, and the output signal SB is obtained from the result of the differential amplification of the photodiodes S2 and S4. There is. When the difference between the photodiodes S1 and S3 and the photodiodes S2 and S4 is taken, only the signal component necessary for the encoder remains in order to remove the DC voltage component and noise component due to the fluctuation of the light amount of the light source 5 and the mounting error of each member. In this way, the differential amplifiers 47 and 48 allow unnecessary DC
In order to remove the signal component, the obtained signal is a clean signal with no noise, and becomes a signal that is kept constant by the light amount feedback as in the first embodiment. As described above, in the present embodiment, a so-called push-pull circuit is configured which can always obtain a stable signal and which is used as an input signal to the electric division circuit 15 without adjustment. can do.

(Third Embodiment) FIG. 7 shows a third embodiment of the present invention.
3 is a circuit configuration diagram in FIG.

In this embodiment, a signal (0 °, 90 °) from each of the differential amplifiers T3 for processing the output signal from the I / V amplifier T2 is applied to each of the input terminals T1 of the resistance chains of the electric division circuit.
Signals having a phase difference of 180 ° and 180 °) are input.

In this embodiment, the photodiode group S3-
Differential amplifiers 47 to 49 are provided for S1, S4-S2, and S1-S3, respectively.

In the second embodiment, there are two differential amplifiers for the photodiode groups S3-S1 and S4-S2, but in the present embodiment the number is three.

In the first and second embodiments, the signals SA and SB having a phase relationship of 0 ° and 90 ° are input to the electric division circuit 15. Actually, 0 °, 90 °, 180 ° for electrical division
Since a signal having a phase relationship of 1 is required, a 180 ° signal is conventionally generated by using the inverting circuit 22 from the 0 ° signal in the electric division circuit. In the circuit configuration of the first embodiment, when a signal of 0 ° is used to generate a signal of 180 ° by using the inverting circuit 22, the signal of 0 ° also includes a DC voltage component, so that simply inverting the DC voltage The components have opposite polarities, and the DC voltages of the 0 °, 90 °, and 180 ° signals differ. Therefore, the inverting circuit 22 is required to have a circuit configuration in which the DC voltages are uniform and only the AC voltage is inverted.

In the second embodiment, the DC voltage is cut off, but the AC voltage fluctuates around zero, so that the electric division circuit 15 needs ± power supplies. Moreover, the inversion circuit 2
A delay will occur in the signal by the amount of passing 2.

FIG. 7 is constructed so that it can operate even with a single power source. That is, addition means T5 for adding a constant voltage to the differential amplifier T3 is provided.

In FIG. 7, a constant voltage (Vref2) is superimposed on the differential amplification result of the photodiode groups S3-S1 to obtain the output signal SA. Similarly, the output signal SB is obtained from the photodiode group S4-S2, and the output signal SC is obtained from the photodiode group S1-S3. At this time, output signals SA and S
B and SC have a phase relationship of 0 °, 90 °, 180 ° and D
The C voltage is the same (Vref2). Since the AC voltage is also the detection voltage from the photodiodes located at substantially the same position, the respective levels are equal and the light amount feedback control is performed, so that a constant amplitude with less influence of light amount fluctuation and mounting error can be obtained. Center voltage from zero to V
Since it is set to ref2, it can operate even with a circuit of one power supply. Reference numeral 15 is an electric dividing circuit, which has the same structure as the conventional example shown in FIG. However, compared to the conventional case, there is no input circuit 20A, 20B, 22 and the differential amplifier 47
The ~ 49 signals are directly input to the resistance chain. Also,
This electric division circuit is configured to operate even with a single power supply.

As described above, even with a circuit configuration of one power supply, an encoder signal including an accurate electric division circuit can be easily obtained.

(Embodiment 4) FIG. 8 is an explanatory view of a reflection type optical encoder.

FIG. 8 is a schematic view of a circuit board 51 on which a semiconductor substrate 53 on which a photodiode array PAL, a signal processing circuit Y1, and an electric division circuit 15 according to the present invention are mounted and a semiconductor substrate 52 for a light source are mounted. The light source of FIG. 8 (for example, L
The light generated from the semiconductor substrate 52 for ED) is incident on the object to be measured OB through an optical system, and the reflected light from the object to be measured OB is connected to a photodiode array, which is a light receiving sensor, a signal processing circuit, and an electric division circuit. The semiconductor substrate 53 mounted is reached. An optical grating as shown in FIG. 1 is formed on the object to be measured OB, and a pattern Pa is formed on the photodiode array. Then, the sine-shaped light amount distribution moves on the photodiode array as shown in FIG.

A signal obtained by the photodiode is processed and electrically divided according to the light amount distribution, and the result is output. The circuit board 51 has a structure in which the output of the semiconductor substrate 53 is taken out by, for example, a wire or the like and further taken out.

In the present invention, by integrating the photodiode array, the signal processing circuit and the electric division circuit, a high resolution output signal can be obtained even with such a small size substrate.

[0057]

According to the present invention, it is possible to achieve an optical encoder capable of detecting movement information of an object to be measured with high accuracy.

In addition, according to the present invention, it is possible to stabilize the fluctuations of the DC component and AC component of the signal input to the electric division circuit, and to electrically divide the output signal from the photodetector with high accuracy, resulting in high resolution. The resulting optical encoder can be achieved.

In addition, according to the present invention, a stable DC voltage and AC voltage can be obtained, so that it is possible to achieve an encoder that can be electrically divided without adjusting the signal from the encoder head (light detecting means). .

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an optical encoder of the present invention.

FIG. 2 is an explanatory diagram of a relationship between a pattern of the photodiode array according to the first embodiment of the present invention and a light-dark pattern of detected light.

FIG. 3 is an explanatory diagram of a signal processing circuit and an electric division circuit for processing a signal from the photodiode array of FIG.

4 is an explanatory diagram of a signal waveform when a condition of a part of the IV amplifier of the signal processing circuit of FIG. 3 is changed.

FIG. 5 is an explanatory diagram of a relationship between a pattern of a photodiode array and a light / dark pattern of light detected on the photodiode array according to the second embodiment of the present invention.

6 is an explanatory diagram of a signal processing circuit and an electric division circuit for processing a signal from the photodiode array of FIG.

FIG. 7 is an explanatory diagram of a signal processing circuit and an electric division circuit for processing a signal from the photodiode array according to the third embodiment of the present invention.

FIG. 8 is an explanatory diagram of a circuit board on which a semiconductor substrate on which a photodiode array, a signal processing circuit, and an electric division circuit of the present invention are mounted and a semiconductor substrate for a light source are mounted.

FIG. 9 is an explanatory diagram of a configuration of a conventional optical encoder.

FIG. 10 is an explanatory diagram of a relationship between a pattern example of a conventional photodiode array and a detected light / dark pattern of light.

FIG. 11 is an explanatory diagram of a signal processing circuit that processes a signal from a photodiode array of a conventional example.

FIG. 12 is an explanatory diagram of a conventional electric division circuit.

[Explanation of symbols]

1 Main Scale 3 Optical Lattice 5 Light Source 6 Lens 10 Index Scale 11 Substrate 12 Oxide Film 13 p-Type Semiconductor Layer 14 Current Collection Layer 15 Electrical Dividing Circuit 16 Resistor Chain 20 Buffer Amplifier 22 Inverting Amplifier 24 Comparator 26 Voltage Setting Device 28 Exclusive OR Gate 30 Directional discrimination circuit 32 Oscillator 41-44 IV converter 45 Adder circuit 47-49 Differential amplifier 46 LED 50 Electric division circuit 51 Circuit board 52 Semiconductor substrate 53 for light source Photodiode array, signal processing circuit, electric division circuit Semiconductor substrate with and

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Keizo Miyazaki             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2F103 BA37 CA01 CA02 CA03 DA01                       DA12 EA15 EA17 EB06 EB12                       EB15 EB16 EB17 EB32 EB33                       ED02 ED03 ED30

Claims (8)

[Claims] 1. An optical grating includes a scale formed at a predetermined pitch, and a plurality of light-receiving elements provided so as to be movable relative to the scale and arranged in relation to the pitch of the optical grating. Using the light detection means, the light source means for irradiating the light receiving element with light through the scale, and the signal obtained by the light detection means, the relative displacement information between the scale and the light detection means is detected. In the optical encoder having the signal processing circuit for performing the above, it is possible to integrally provide an electric division circuit for electrically increasing the resolution by using the analog signal obtained from the photodetection means. Optical encoder 2. A stabilizing means for stabilizing the DC and AC component fluctuations of a signal input to the electric division circuit in order to integrally provide the electric division circuit. The optical encoder described. 3. The optical encoder according to claim 2, wherein the stabilizing means includes a push-pull circuit. 4. The optical encoder according to claim 2, wherein the stabilizing means has a light quantity feedback function. 5. The optical encoder according to claim 2, wherein the stabilizing means has a function of obtaining a difference signal between certain light receiving elements by a differential amplifier. 6. The signal from each differential amplifier for signal-processing the output of the I / V amplifier is input to each of the input terminals of the resistance chain of the electric division circuit from the signal processing circuit. The optical encoder described in. 7. The optical apparatus according to claim 1, further comprising adding means for adding a constant voltage to the differential amplifier so that the signal processing circuit and the electric division circuit can be driven by a single power source. Expression encoder. 8. The optical encoder according to claim 1, wherein the electric division circuit is formed on the same semiconductor substrate together with the signal processing circuit.