JPH01212316A - Optical encoder - Google Patents

Abstract

PURPOSE:To render the distance of a fixed slit plate and a moving slit plate relatively wide, by setting said distance by nP<2>/lambda (n=1,2,...). CONSTITUTION:An optical encoder of this invention is provided with a light projecting element of point light source type which emits light of the wavelength lambda, a light receiving element placed opposite to the light projecting element and a fixed slit plate 18 having a plurality of slits formed a predetermined slit pitch P each other. Moreover, a moving slit plate 13 is provided which moves relatively to the fixed slit plate 18 fixed between the light projecting and light receiving elements, with a plurality of slits formed the same slit pitch P each other as in the fixed slit plate 18. The distance between the moving and fixed slit plates 13 and 18 is set to be nP<2>/lambda (n=1,2,...). Therefore, the amplitude of a false sinusoidal wave signal obtained at the light receiving element through the two slit plates when the moving slit plate 13 is moved can be at a high level approximately equal to that obtained when the fixed and moving slit plates 18 and 13 are brought in close contact.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an optical encoder that converts the amount of mechanical rotation or linear movement into an electrical signal.

[Prior art]

As shown in FIG. 5, the conventional optical encoder rotates in conjunction with a fixed slit plate 4 and a rotating shaft 5 between a light emitting element 2 and a light receiving element 3 provided in a case 1, and the circular It has a movable slit plate 6 with a large number of slits provided on its circumference. And in this rotary encoder, the rotation axis 5
By rotating the light emitting element 2, a pseudo sine wave signal as shown by the solid line A in FIG. 6 is obtained from the light projecting element 2 via the fixed slit plate 4 and the movable slit plate 6. Therefore, this signal is discriminated by a predetermined darkness value and converted into a square wave signal, and the rotational speed signal of the rotating shaft 5 is obtained based on the differential signal.

[Problem to be solved by the invention]

However, in such a conventional optical encoder t, it is necessary to narrow the slit interval in order to increase the level of the received light signal obtained from the light receiving element. By keeping the amplitude constant, a pseudo sine wave signal with a constant amplitude is obtained. If this interval changes, curve B in Figure 6
Or, as shown in C, the peak value of the pseudo sine wave signal obtained by the light receiving element 3 fluctuates. Particularly in a separate encoder where the movable slit plate 6 is separated from the encoder body, it is difficult to maintain a constant slit interval. Also, even a slight change in the slit interval causes a large change in the amplitude of the output signal.Therefore, when obtaining a speed signal by differentiating this pseudo sine wave signal, there is a problem that the amplitude change directly appears as an error in the speed signal. there were.

The present invention has been made in view of the problems of conventional optical encoders, and it is possible to maintain a relatively wide interval between the fixed slit plate and the movable slit plate, and even when the interval changes. The technical problem is to suppress the amplitude change of a pseudo sine wave signal to a small level.

[Structure and effects of the invention]

(Means for Solving the Problems) The present invention is an optical encoder that converts mechanical rotation amounts and linear movement amounts into electrical signals, and includes a point light source type light projecting element that emits light with a wavelength λ; A light-receiving element disposed opposite to the light-emitting element, a fixed slit plate fixed between the light-emitting element and the light-receiving element, and having a plurality of slits separated by a certain slit pinch P; A movable slit plate that moves relatively and has a plurality of slits formed at the same slit pitch P as the fixed slit plate, and the interval between the movable slit plate and the fixed slit plate is set to n.
pg/λ (n=1.2...--).

(Function) According to the present invention having such characteristics, a point light source light projecting element with wavelength λ is used as a light source, and the distance between the fixed slit plate and the movable slit plate is set to nP! /λ. In this way, when the movable slit plate moves, the amplitude value of the pseudo sine wave signal obtained through the two slit plates to the light receiving element will be at almost the same large level as when the fixed slit plate and the movable slit plate are brought into close contact. .

(Effects of the Invention) Therefore, according to the present invention, the interval between the slit plates can be maintained at an arbitrary interval that satisfies a specific relationship during assembly.

Therefore, it is not necessary to set the interval between the slit plates to be extremely narrow as in the conventional optical encoder, and it is possible to eliminate the possibility of contact between the slit plates. Also, when moving the movable slit plate, 2
An output signal of the same level as when two slit plates are brought into close contact is obtained, and the amplitude value is increased, making signal processing easier. Furthermore, even if the spacing between the slit plates varies slightly from a predetermined value, the effect on the amplitude of the output signal can be made relatively small, making it possible to obtain accurate position and velocity signals.

[Explanation of Examples]

FIG. 1 is a side view showing one side of a separate linear encoder according to an embodiment of the present invention. In the figure, the rotary encoder main body has a light projecting section 11 and a light receiving section 12 fixed at a constant interval in a case IO. A movable slit plate 13 is configured to move freely left and right between the light emitting and receiving parts 11 and 12. The movable slit plate 13 has a large number of slits arranged in parallel at a constant slit pitch P, and is separated from the linear encoder main body at a constant interval and moves left and right. is obtained as a position signal from a linear encoder. Now, as shown in the figure, the light projecting section 11 of the encoder body is provided with a point light source type light projecting element, such as a laser diode 14, having a constant wavelength λ, for example, a wavelength of 780 nm. A cylindrical light guide 15 is provided, which is tilted at a predetermined angle by the optical axis of the laser beam and has an axis perpendicular to the moving triple plate 13. A reflecting mirror 16 that reflects the laser beam is provided inside the light guide 15, and a collimating lens 17 that expands the diameter of the laser beam in parallel is provided on the surface facing the light receiving section 12. The laser beam emitted from the laser diode 14 passes through the reflecting mirror 16
．． Parallel light is applied to the light receiving section 12 side via the collimating lens 17 .

The light receiving section 12 is provided with a fixed slit plate 18 in which a large number of minute slits are formed at a predetermined slit pitch P in a position facing the collimating lens 17, and behind the fixed slit plate 18, a light receiving element, for example, a photodiode 19 is provided. . Further, a printed circuit board 20 is mounted on the light receiving section 12, and a signal processing section is provided above the printed circuit board 20. Photodiode 19
The output of is fed to the signal processing section like a normal linear encoder, amplified, and output as a pseudo sine wave signal.
Alternatively, the speed signal is obtained by further differentiating the output.

Now, the distance between the movable slit plate 13 and the fixed slit plate 18, the wavelength λ of the laser diode 14, and the slit of the slit plate and the distance P are set so as to maintain the relationship defined by the following equation.

λ (n-1, 2, . . . -) In this embodiment, for example, n is set to 1 and the interval L1=P2/λ.

Here, the amplitude value of the pseudo sine wave signal obtained at the light receiving element 19 with respect to the slit plate interval has a relationship as shown in FIG. As is clear from this figure, the output signal obtained when the distance between the two slit plates 13 and 18 is zero, that is, when they are in close contact with each other, has the maximum peak value,
It is extremely small at the position of mP”/2λ (m is an odd number),
The amplitude value is maximum at the position of nPf/λ, and a curve changes sinusoidally between them. This is a phenomenon caused by a Fourier image obtained as a result of diffraction from a slit pattern, and the present invention utilizes this phenomenon. That is, in the present invention, this diffraction phenomenon is utilized by using a light projecting element as a point light source and applying the light to the light receiving element side as a parallel light beam through a collimating lens.

On the other hand, FIG. 3 is a diagram showing the distance between two slit plates and the change in amplitude value of a pseudo sine wave signal obtained at a light receiving element in a conventional optical encoder.

In the conventional optical encoder, as shown in Figure 3,
A large amplitude value is obtained by narrowing the distance between the two slit plates. However, in the present invention, it is not necessary to reduce these intervals, and by setting them to P2/λ, the intervals can be reduced to zero, that is, the moving slit plate 13
The same output amplitude as in the case where the fixed slit plate 18 and the fixed slit plate 18 are brought into close contact can be obtained. Furthermore, as shown in FIG. 2, almost the same signal level can be obtained even if this interval is set to 2P''/π or 3P''/π, . . . -1111.

Furthermore, as shown in FIG. 2, when the distance is set to pt/π, it is possible to reduce the change in signal amplitude with respect to the change in distance. That is, in the conventional linear encoder, for example, the slit pitch P is 40μ, and the slit interval L
2 is 100 μm, the displacement of slit interval Δl=±
In the case of 50/JIm, the amplitude changes by about 30% as shown. However, in this embodiment, the same slit pitch P=
If a laser diode with λ=780 nm is used for 40 μι, and the slit interval Ll is 2050 μm, the amplitude change will be less than 1% for the same slit interval displacement Δl=±50 μι. Also, slit pinch P = 16μm
, when the slit interval L3 is 330 μm, the amplitude change is approximately 13% for the same slit displacement Δl = ±50 μm.
Therefore, the value can be much smaller than that of the conventional example.

Although this embodiment uses a laser diode as a light projecting element to obtain a point light source with a single wavelength, it is also possible to use a point light source type light emitting diode with an extremely small light emitting area as a light projecting element. Figure 4 shows the use of this point light source type light emitting diode as a light emitting element, with a slit pitch P of 40.
12 is a graph showing the relationship between the amplitude value of the output voltage obtained from the light receiving element and the inter-slit gap when μm and wavelength λ are 957n11. As shown in this figure, even if a light emitting diode having a certain spread in wavelength is used, a graph almost the same as that in FIG. 2 can be obtained. Therefore, the distance between the slit plates can be set to any value that satisfies the above-mentioned formula, and it is possible to obtain accurate position signals without causing the slit plates to contact each other.

Further, although this embodiment describes a separate linear encoder, the present invention can be applied to all optical encoders such as ordinary linear encoders and rotary encoders.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a linear encoder according to an embodiment of the present invention, FIG. 2 is a graph showing the relationship between slit spacing and output amplitude of this embodiment, and FIG. 3 is a slit spacing of a conventional optical encoder. Figure 4 is a graph showing the change in slit spacing and output voltage when a light emitting diode is used as a light source. Figure 5 is an example of a conventional optical rotary encoder. FIG. 6 is a graph showing changes in the output voltage. 10--Case 11--Light emitter 12
--------・Light receiving section 13...Moving slit plate 14...Laser diode 1
7--Collimating lens 18...Fixed slit plate 19...Photodiode 13-----1 Bone movement S°), To root 14-- --- Ray size °゛Diode 18---
-Ichitsuta Matamata゛], 7 tosaka 19----- Photodiode Figure 2 Figure 3 Figure 5 Figure 6

Claims (1)

[Claims] (1) A point light source type light projecting element that emits light with a wavelength λ, a light receiving element disposed opposite to the light projecting element, and a slit pitch P fixed between the light projecting element and the light receiving element. a fixed slit plate with a plurality of slits formed therebetween, and a movable slit plate that moves relative to the fixed slit plate and has a plurality of slits formed with the same slit pitch P as the fixed slit plate. and, the distance between the movable slit plate and the fixed slit plate is nP^
2/λ (n=1, 2, . . . ).