JPH01417A - optical encoder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention provides a main grating plate and a scanning grating plate that are relatively movably disposed between a light source and a receiving element. The present invention relates to an optical encoder that adds IJ4 to the amount of relative movement of a grating plate by detecting a change in transmitted light due to the relative displacement of each grating of a grating plate and a scanning grating plate. [Prior art] Transmitted 4'1 light, 7E (encoder has light source, light receiving, H
It is constructed by arranging a mi-gase r-plate and a scanning path f-plate in f rows with a relative movement of r+1. The light emitted from the light source is modulated by the relative displacement of the gratings formed on the L grating plate and the scanning grating plate, and enters the light receiving element. The relative change of the lattice! Accordingly, an electrical signal of an approximate sine wave whose period coincides with the case f-pitch is output. Then, by counting the period of this electric signal, the amount of relative movement of the case r in units of grating pitch is measured. For example, in an optical rotary encoder, a rotary path f plate (the above-mentioned one-tooth plate) with a predetermined thermal grid formed radially between a fixed light source and a light receiver is used. The light source, the light receiving element, and a scanning grating plate capable of relative movement are arranged in close proximity and parallel to each other.6 When the rotating grating plate rotates, the grating and the scanning grating plate are arranged in parallel. Due to the relative position change with f-, the light beam that passes through both gratings and reaches the photodetector changes with the grating pitch as a period, and from the photodetector, the grating beam 5 is transmitted in response to this change in grating pitch.
- An electrical signal that changes in an IE sinusoidal waveform with a period of 1 is output, and this sinusoidal change ', IE Qin V) is processed by a signal processing circuit to become a pulse signal, and this pulse signal is counted. , the rotation angle of the rotation path F plate is measured with lattice beach I as the middle position. In such an optical encoder, the main grating plate and the scanning path
The higher the precision of the pulse signal outputted with respect to the relative movement amount between f & As a result, the amount of relative movement between the main grating plate and the scanning path can be measured with high precision.In addition, the phase of the sinusoidal signal detected by the light receiving element is divided into pulse signals that are subdivided by the grating pitch. It is also possible to measure the amount of relative movement between the main grating plate and the scanning grating plate with higher accuracy than the grating pitch.For this purpose, it is necessary to measure the change in the electrical signal detected by the light receiving element (i.e. The change in the light beam reaching the photodetector due to relative movement) must be a 1F accurate +E sinusoidal wave with a period equal to the grating pitch, and if the waveform deviates from the sine wave shape, accurate phase division will not be possible. figure,
Therefore, the accuracy of measuring the movement is reduced. [Another point between the prior art] However, if the lattice p and chi of each case F board are coarse, it is safe to assume that the rays travel straight, especially when it comes to I.
However, if the grating pitch is made finer in order to improve measurement accuracy, the grating -f becomes a so-called diffraction grating, and the light that passes through it will undergo a diffraction phenomenon. In order to avoid the influence of this diffraction phenomenon and maintain measurement accuracy, the interval between the =E plate and the scanning grating plate (interval interval) must be made extremely narrow.
This means that it must be placed within a narrow tolerance range. In other words, the light beam transmitted through the main grating plate (case f) is based on optical theory 1.
: A diffraction phenomenon called Fresnel diffraction occurs, resulting in diffracted light that has multiple peaks depending on the distance from the l2 grating plate (
The peak position is defined by the grating pitch and the wavelength of the transmitted light, and the peak position is determined by the grating pitch and the wavelength of the transmitted light. It is desirable that the position of the scanning grating plate (the distance between the main grating plate and the scanning grating plate) match the peak position of the F-Nell diffracted light formed by the gratings of the L grating plate. Set at the first peak position of the diffracted light. If the scanning grating is placed at the first peak position in this way and an error occurs in the set position, the above-mentioned problem will occur. As the inter-grid spacing increases, the DC component of detection disease 1) increases, the signal contrast decreases, and the SZN ratio worsens.
The accuracy when converting this signal into a pulse signal is faithful,
Therefore, measurement accuracy decreases. Furthermore, as the inter-lattice spacing decreases, the harmonic distortion of the detection signal increases (the waveform of the detection signal becomes closer to a rectangular wave than a sine wave), which impairs the division accuracy when dividing one phase, resulting in poor measurement accuracy. decreases. Therefore, to obtain a complete IT sinusoidal signal. The spacing between the gratings must be set within an extremely narrow tolerance range, and the layer surface accuracy of the grating plate and the scanning path f must be kept within an extremely narrow tolerance range.
- Changes in the pitch interval when moving relative to the root cause a difference of 5 in the measurement, so high accuracy is required for the cutter and assembly t11 adjustment of the component parts, and as a result. There is a problem in that it requires a large manufacturing cost. In a rotary encoder, measurement errors may occur due to eccentricity of the rotary path f or the plate, so it is necessary to perform the adjustment of the ρ1 turning point with high viscosity. . Furthermore, as the lattice pitch becomes smaller, the case f-spacing must also become narrower (for example, the case f-bench 28pm,
Light wavelength input: 0.95#Lm, case spacing d=
60 am), if dust or the like gets into these narrow gaps, it will damage the grid and deteriorate the signal, so dust-proofing measures are also required, further increasing the manufacturing cost. Furthermore, since Fresnel diffraction images are formed periodically for each grating pitch, if there is an error in the side line width or pitch of each grating, the period of the sine wave signal changes depending on the position n of the main grating plate, and - It also has the disadvantage that a certain level of measurement accuracy cannot be obtained. [Objective of 5e Akira] In view of the circumstances as described above, the present invention is relatively unaffected by the installation accuracy of the grid spacing and the accuracy of the relative movement of the grid plates,
Therefore, it is an object of the present invention to provide an optical encoder that is capable of highly accurate measurement even if the installation accuracy of the grid spacing and the movement accuracy of the grating plate are relaxed, and that can also be easily dust-proofed due to the wide spacing between the grids. That purpose. [Means for Solving the Problems] For this reason, the optical encoder according to the present invention includes a seven-line light generating means, a light receiving stage disposed opposite to the parallel light generating stage F, and a light receiving stage parallel to the light receiving means. A measuring section is constituted by a converging means installed between the light beam generator and the main grating means installed between the converging means and the light receiving means, and the main grating means of the measuring section and the light receiving means are arranged in a stage. The scanning path f[stage is installed at n(movement) with respect to the measuring section.Then, the scanning path f[stage is set at n(movement) with respect to the measuring section. ff, the diffracted light by the stage, the light rs (transmitted through the scanning grating r and the stage) is received and converted into an hypochondria signal by the stage, and each case f- of the 1mm case f- means and the scanning grating r; By counting the changes in the signal 1 corresponding to the relative displacement of the scanning gratings f and f2, the relative moving ends of the scanning gratings and r-stages are measured. [Example 1 Fig. 1 1 is a conceptual diagram of a rotary encoder using the principle of an optical encoder according to the present invention, and FIGS. 2 and 3 show the details of the measuring section and the measurement principle. First, the explanation will be given in FIG. 6 is an F grating plate, 8 is a scanning plate installed in relative rotation with the grating plate 6, and 10-10 is a light source fixed to the L grating plate 6. is provided with diffraction gratings F6a having 1 u case f r = steps at three locations with the axis 11 fixed to the nominative f-plate 6 as the center of symmetry.The light source section to-10 has a main grating It is fixed at a position corresponding to the diffraction grating f-6a of the plate 6 so as to emit 1B of light toward the diffraction grating 6a.
At the position corresponding to O.10, there are light receiving elements f'-5-5 with light receiving elements f'-5-5, respectively, and arm 7 fixed to nominative f&6.
-7. Between the main grating plate 6 and the light receiving element 5, a scanning path F4 as a scanning grating step formed on the scanning plate 8 is moved relative (relative rotation) τ in a direction orthogonal to the grating line direction. "f
Intervened by Noh. The scanning plate 8 is a disc-shaped transmission diffraction grating plate on which transmission scanning gratings 4 are formed radially from the center at a predetermined pitch.
It is rotatably fitted onto the shaft 11 with the direction of the lattice markings parallel to the direction of the lattice markings of the main lattice plate 6, and is capable of relative rotation to the -E lattice plate 6. That is, the light [parts 10 and 10, the diffraction grating 6a and the light receiving element f5
The measuring section 20 is constructed by the following, and the scanning path f4 is rotated n between the diffraction grating 6a and the light receiving element 5 of the measuring section 20.
(The light beam emitted from the light source section 10-10 is 1:
The light is diffracted by the diffraction grating 6a of the grating plate 6 and becomes diffracted light, which passes through the scanning grating 4 and enters the light receiving element 5, where it is converted into an electric zero beam according to the human illumination. The electric signal obtained by 2Yi/-5 is inputted to the signal processing circuit 9, and the signal processing circuit 9 converts it into a diffraction grating.
The incident light j- caused by the relative position change between the scanning grating 6a and the scanning grating 4
The device is configured to detect and count the changes in the lattice &6, thereby detecting and measuring the relative position change, that is, the rotation angle, between the king lattice &6 and the scanning path T-4 (1!II, ie, the scanning plate 8). Next, based on FIGS. 2 and 3, the measurement unit 20 and the scanning path f4 are
I will explain the measurement principle based on this. The light source section 10 is an LED (light emitting diode) that is a light source.
! , a collimator lens 2, a condensing lens 3, etc., arranged in one direction of the light beam emission direction I, and the light beam emitted from the LED 1 is converted into a beam of light by the collimator lens 2. Then, four condensing lenses 3 with the same focal length...(3
a, 3b, 3c, and 3d) are arranged in parallel within the moving light beam formed by the collimator lens 2, and are configured to focus on the deplane 1- at the same distance. The LED 1 and collimator lens 2 constitute a beam generating means, and the condensing lens 3 serves as a converging element. Focal position 2?F... (F%F, FC
-Fa), the scanning grating plate 4 is installed with the grating direction matching these focal positions tF... as described above.Here, the optical axis of each condenser lens 3... are arranged so as to be shifted by 711 1/4 pitches from the case f-pitch of the scanning grating 4. That is, if the condenser lenses 3 are arranged in parallel in the case-E scanning direction (direction perpendicular to the grid lines), the distance between the optical axes of each condenser lens 3 is the third As shown in the figure, by pressing the case f-bin of scan path /4 with P, we get n P + 1 /
It is arranged so that it becomes 4P. (n is an integer) Or, as shown in Fig. 16, condense the light onto a straight line that is in line with the case line of the scanning path F4, line up the lenses 3, and set the scanning grid at the focus position of the person. However, in FIG. 16, two condenser lenses are used. In general, it would be possible to combine the configurations of 121,114 persons into 11, but in this example, as mentioned above, the optical axis of the condenser lens 3... On the other hand, LI: is configured to shift by 1/4 pitch. On the side opposite to the light incident side of each scanning grating 4, the light receiving elements 1'5...-(5a*5b*5c, 5d) are held by the arm 7 whose subject is fixed to the plate 6 as described above. They are staffed with people. Condensing lens 3... and its focal position (i.e. scanning path f4
There is a main lattice plate 6 between the case (face position). It is arranged at a predetermined distance d from the scanning path 4, that is,
Above LED l・Collimator lens 21 Condensing lens 3・
...'E grade r board 6 and receiving X, elementary e5... are. The 71+17 section 20 is fixed so as not to be relatively movable, and the scanning grating 4 is configured to rotate relative to the measuring section 20 in a direction perpendicular to the direction of the grating lines. The light emitted from the LED 1 is made into parallel light by the collimator lens 2, and is formed in several lines in the grating direction of the scanning grating 4 by the condensing lens 3. is diffracted by the diffraction grating 6a, and due to the diffraction phenomenon, a 7 round hole γ diffraction image is generated in the direction of the scanning grating 4 in the grating pitch of the diffraction grating 1"-6a, which does not correspond to the grating pitch of the diffraction grating 1"-6a. In the present invention, the scanning grating 4 configured as described above is installed at a predetermined distance (d) Ml from the main grating plate 6 of the Fraunhofer diffraction image formed by the L-rated fk6 diffraction grating 6a. The amount of light is converted into an electric signal by the light receiving element 5..., and the light entering Q1 ((light of Fraunhofer diffraction image: ti: ), one piece of the relative pt1 rotation angle is measured.Next, 1: The measurement method described above is

[Relative (q) relation of component parts in order to function 11 p (=4a): Case f・Pitch m+1: Number of gratings in the illumination vision differential d: Inter-lattice spacing From the optical theory of Fraunhofer diffraction, ]:
The multiple large peaks of the Fraunhof diffraction image generated at the focal point of the condensing lens 3 due to the case t6 are
appears every distance XI=input d/p. These are 0.±1 with F a as the center.
・±2-±3・±g-order diffracted light spot. (4th
(A schematic diagram is shown in the figure) Between the diffracted light spots, m small peaks appear every Xvr=input d/(mal)p. Using the case f of the scanning grating 4, the O-th order diffraction spot at the center of this diffraction image is scanned (nearby). In order to obtain a sine wave as a scanning waveform, the intervals of 1111 (d
). That is, the inter-lattice spacing (d) may be set to d=(mal)pa/in. here. Input: 0.95 (JLm) 2a: 5 (ILrn) polo (end m) mal: 401 (book) Calculated by setting d = 10, 8 (mm), and simulated with a computer to obtain 1. The diffraction analysis/IJ/travel waveform and its resun wave are reduced to 5th and 7j4. In No. 514, in the range of Ixl>3a, the minimum peak 11 of the diffraction image is 2% or more t- of the central peak value, and it can be considered that it does not contribute γ to the scanning signal. Therefore, the light receiving element The number of lA lines (marked lines a used for scanning) of scanning path 1'4 corresponding to the light receiving range of 5 is set to 3 to 5. When scanning conventional Fresnel diffraction light, the scanning area of the rotation path r- covers the entire illumination field of view.
Compared to the fact that it detects changes in darkness,
This point is a big difference. In FIG. 6, at the focal point F□ in FIG. 3, the light receiving element f5...
The rE sinusoidal scanning signal detected by the rE waveform is omitted. On the other hand, from the focal point Fb of the condenser lens 3b, whose optical axis is shifted by L/4 of the scanning grating 4, a cosine wave-like scanning signal with a 90 degree phase difference is detected, although not shown. It is something that will be done. By applying these two signals to the X-axis and Y-axis, a Lissajous figure shown by the solid line in Fig. 7 is created. In Fig. 6, the scanning signal has a lot of harmonic distortion. , it is not 6 yen but close to a square (z
4 is small, the serge figure will be close to a perfect circle), at this time, the distortion rate・as=t i, 5 (%), and the visibility・V=(19g. Therefore, by changing the interlattice spacing・d As a result of calculating d to obtain the optimal diffraction image distribution, scanning waveform, and Lissajous figure, we found that the distortion rate was small and the Lissajous figure was close to a perfect circle, as shown in Figures 8 and 10, which is a very satisfactory image. In this case, d=15.55 (mm), V=08:1.
DS = 0, 22 (%). 1114th
is a graph showing the relationship between the visibility φV and the distortion rate D with respect to the inter-grid spacing dK. From this graph, the allowable range of d can be determined from the angle measurement allowable range of V and . Now, if V > 0.7, I), < L (%) are the angle measurement tolerance ranges, then d = 16.55 ± 2 (mm) and this case f-
The spacing and its tolerance range are significantly larger than those for conventional scanning Fresnel diffraction images. In the above case, it is assumed that the case f-plane of the scanning path f and the plate 4 is exactly +1- exactly at the focal position of the coming lens 3, but next we will consider the influence of an error from the focal position. Figure 12 is a graph showing the relationship between visibility V and distortion rate D5 with respect to error Δd (ILm). From this graph, the allowable range of Δd can be determined from the angle measurement allowable ranges of ■ and . . Here, if D<0.2% is the allowable limit, then the installation error of the scanning path f: Δdl≦30 (final m). Note that ■ is parabolically low, but as long as the distortion factor D is small and the Lissajous figure is close to a perfect circle. It has already been confirmed by electronic circuit technology that the low V value does not have a large effect on angle measurement accuracy. The scanning signals obtained from each of the light receiving elements 5... The signal correcting unit 30 of the signal processing circuit 9 generates a pair of scanning signals of a sine wave and a cosine wave with DC components contained therein, and further subdivides their phase to detect an intermediate angle. ing. In a normal encoder, the scanning signal is configured to obtain a sine wave signal and a cosine wave signal with a phase difference of 90 degrees, and these phases are subdivided to detect intermediate angles.
'rfffi thing. Therefore, basically even in this configuration, the pair of condenser lens 3 and light receiving element 5 (7) is arranged so that the optical axis of the condenser lens 3 is 1/1/2 with respect to the pitch of the scanning grating 4.
Two sets shifted by 4 pitches are fine, but in this embodiment, one set is 1/4 for the grating pitch of one scan case -f4.
It is constructed by arranging four sets of condensing lenses 3 (and light-receiving elements 5 at corresponding positions) that are shifted by a pitch, each detects a 90-degree phase signal, and calculates the signal as follows. It is configured to correct the DC component. Now, through the scanning path f4... of people, the light receiving element 5...
Scanning detected by
Then, Shinshi>S+ is, Sl = a+blsin [c*x+ (i-1)
/lr], (a, b, c are constants) From this formula, S++S:=(tz+b7) sin (c@x)S;
+Sa == (b2+bi) cos (c @
X), the DC component is eliminated, and the pair of scanning signals of 1F sinusoidal wave and cosine wave becomes 1! It is something that can be done. The phase is subdivided from the pair of scanning signals 7) of the sine wave and cosine wave obtained in this manner, and minute angle measurement is performed. At this time, the interpolation technique for subdividing the phase from a pair of travel signals has been considered to include optical interpolation or electrical interpolation. These are already known techniques. The method of phase subdivision using the resistance division method will be explained within the cylinder. :jrJ13 as shown in the diagram]・Correction unit 30 to 77)
Two signals, a sine wave and a cosine wave with a phase difference of 90 degrees, are connected to both ends of the bleeder resistor via buffer amplifiers 3I and 32, and one of the sine wave nails 7) is phase-inverted by an inverter 32. Connect the signal and the output of the other buffer amplifier 32 to another bleeder resistor. Here, from the midpoint P of the breeder resistance? ! The phase difference signal t is Vn in the vector diagram of Fig. 14, and by changing the ratio kn of the 1-divided resistor, the phase difference (No. , as shown in Figure 15, a large number of signals (A - B - c - D) with a phase difference of α are converted into waveforms A'e.
B'*C'・Do), by converting the rise and fall into pulses and counting them, the case r pitch is further subdivided (in this example, subdivided into 1/8) with high resolution. It is something that can be measured. Here, the reason why the measurement units 12u and 20 are installed at two symmetrical positions with the center of rotation of the scanning plate 8 as the center of symmetry is as follows.
This is to cancel out a sinusoidal measurement difference S having a period of rotation (360') of the scanning plate 8, which occurs when the scanning plate 8 rotates eccentrically with respect to the triangular f-plate 6. In addition, in the wood example, the measurement parts 20 and 20 are fixed, and the scanning &8 is rotated n [function (scanning scale -1'4
Although the scanning plate 8 is fixed, the measurement i! The part 20 (1! II F grating - plate 6) may be configured as a rotating I function. Furthermore, although this embodiment is constructed as a rotary encoder, the scanning plate (scanning path) is made linear, and the δl11 fixed part moves along the scanning plate (the first part is 1!). It goes without saying that it may be applied to a so-called linear encoder. [Effects of the Invention] According to the optical encoder according to the first embodiment of the invention, the lattice formed by the t' grating and reaching the light receiving element r- By configuring the Nhofer diffraction image to be scanned by a scanning grating, it is possible to widen the distance between the grating and the scanning grating, and the permissible width of the setting can also be increased. By maintaining the measurement accuracy even if the precision is relaxed, it is possible to significantly reduce the molding cost. Also, because the lattice spacing is wide, there is less influence from dust. ,
Dust-proofing measures are also 6 easy, and durability is also high. Furthermore, it is also possible to construct an optical encoder with high constant accuracy, which has not been possible in the past due to constraints on the mechanical precision of addition and assembly.

[Brief explanation of the drawing]

FIG. 1 is a conceptual M/4 diagram of the optical goniometer according to the present invention.
Figure 2 is a conceptual diagram of the measuring section, and Figure 3 is the ■-■ of Figure 2.
4 is a liquefaction distribution diagram of the Fraunhofer diffraction image at the focal point of the condenser lens, 5 and 8 are light lance distribution diagrams of the diffraction image, 6 and 9 are scanning waveform diagrams, Figures 7 and 10 are the Lissajous figure, Figure 11 is a curve diagram of visibility and Φ factor with respect to grid spacing, Figure 12 is a curve diagram of visibility and distortion rate with respect to error in the scanning path F position, and Figure 13 is the scanning signal phase. Figure 14 is a vector composite diagram of the resistance division, Figure 15 is a waveform diagram of the signal divided by 1, Figure 16 is the diagram of the optical axis of the condensing lens and the scanning grating. It is a figure showing a relationship. 3... Condensing lens (converging [stage)] 4... Scanning grating (scanning path fTJ11>5... Light receiving element -r- (light receiving [stage)] 6a...1: Case f ('E grating Means) 9...Signal processing circuit lO...Light source unit 20...Measurement unit Patent applicant Asahi Kori Gyo Co., Ltd. Figure 1 Figure 3:, +b) -b 3CFC No. 5
Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 d=10.55 +aCJLmrn) - Figure 12 d ()J) Figure 14 VC V5-vnlcos nd Figure 15 Break 1

Claims (9)

[Claims] (1) A parallel ray generating means, a light receiving means arranged opposite to the parallel ray generating means, a converging means installed between the light receiving means and the parallel ray generating means, and the converging means and the light receiving means a main grating means installed between the main grating means and the light receiving means; an optical encoder comprising: a scanning grating means movable at the same time; (2) Claim (2) characterized in that the measuring section is fixedly installed and the scanning grating means is configured to be movable.
1) The optical encoder described above. (3) The scanning grating means is fixedly installed, and the measuring section is configured to be movable.
1) The optical encoder described above. (4) At least two of the converging means are arranged in parallel in the parallel light beam from the parallel light generating section with their optical axes shifted by 1/4 pitch with respect to the grating of the scanning grating means. 4. The optical encoder according to claim 1, wherein the optical encoder comprises a lens, and the light receiving means comprises a plurality of light receiving elements corresponding to the condenser lens. (5) The converging means includes at least two condensing lenses arranged in parallel in the parallel light beam from the parallel light generating section, and the scanning grating means is configured to adjust the focal position of each of the condensing lenses. Claims (1) to (1), characterized in that the light receiving means is comprised of a plurality of light receiving elements corresponding to the condenser lens. 3) The optical encoder described. (6) the converging means consists of four condensing lenses;
The optical encoder according to claim 4 or 5, characterized in that: (7) Claim (1) characterized in that the scanning grating means comprises a disc-shaped grating plate forming a radial grating, and the relative movement of the grating means with respect to the measuring section is rotational movement.
) to (6). (8) The optical encoder according to any one of claims (1) to (7), characterized in that a plurality of the measurement units are provided for the scanning grating means. (9) The optical encoder according to claim 7, characterized in that two of the measuring sections are provided at symmetrical positions with respect to a center of relative rotation between the measuring section and the scanning grating means.