JP4672894B2 - Photoelectric linear encoder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectric linear encoder, and in particular, when a plurality of main scales are connected to detect a long measurement range, a single detection unit also detects a discontinuous lattice. The present invention relates to a photoelectric linear encoder that can be used.
[0002]
[Prior art]
As a conventional photoelectric linear encoder, a transmission type having a two-grating structure as shown in FIG. 1 and a reflection type having a three-grating structure as shown in FIG. 2 are well known. In the figure, reference numeral 10 denotes a main disposed in the displacement direction, in which a large number of optical gratings (referred to as main gratings) 12 extending in a direction substantially perpendicular to the displacement direction (horizontal direction in the figure) (up and down direction in the figure) are formed. The scale 20 is provided with, for example, four optical gratings (referred to as sub-lattices) 24A, 24B, 24C, and 24D, each of which has a phase difference of 90 ° to identify the moving direction, corresponding to the main grating 12. The index scale 30 is connected to the linear scale 10 and the index scale 20 via a collimator lens 32 (in the case of FIG. 1) or an optical grating (referred to as a sub-grating) 22 on the index scale 20 (in the case of FIG. 2). Light sources 34A, 34B, 34C, and 34D for irradiating parallel light or diffused light involve the main lattice 12 and the sub-lattices 24A, 24B, 24C, and 24D. It is a light receiving element for detecting the scattered light, and the light source 30 other than the main scale 10, the collimating lens 32, the index scale 20, and the like are disposed on a slider (not shown) that can be relatively moved in the longitudinal direction of the main scale 10. Is referred to as a detector.
[0003]
Such a photoelectric linear encoder has a measurement range of either the transmission type as shown in FIG. 1 or the reflection type as shown in FIG. Limited. On the other hand, the length of the main scale is limited by the processing length of the lapping machine, the length of the vacuum furnace of the vapor deposition machine for surface treatment, and the like. Therefore, in order to connect a plurality of scales to widen the measurement range, the following method has been proposed.
[0004]
That is, in Japanese Patent Laid-Open No. 2-64405, as shown in FIG. 3, a plurality of main scales 10A and 10B are arranged in a displacement direction at a predetermined interval, and these are arranged on the moving table 40 in a displacement direction at a predetermined interval. In addition, it is described that detection is performed by a plurality of sliders 42A and 42B including a detection unit.
[0005]
In Japanese Patent Laid-Open No. 6-137899, as shown in FIG. 4, a plurality of main scales 10A and 10B are arranged in a displacement direction at a predetermined narrow interval, and the slider 42 is used for detection at the connecting portion without any trouble. It is described that the two detection units 44A and 44B arranged close to each other perform detection across the connecting portion.
[0006]
[Problems to be solved by the invention]
However, in any of the methods, a plurality of main scales 10A and 10B are arranged at predetermined intervals, and a plurality of detection units are required, which not only complicates the configuration but also increases the cost. Had.
[0007]
Therefore, it is preferable that the connecting portion can be detected by a single detection unit because the configuration is simplified. However, in the connecting portion 10C, the continuity of the left and right main lattices 12A and 12B must be maintained, and there should be no phase shift δP as shown in FIG. For example, when the grating pitch P is 20 μm and the phase shift δP is 10 μm, when the detection unit comes to the connecting part 10C, the interference fringes obtained from the left and right main gratings are in opposite phases, so that there is no signal. In particular, in an incremental encoder that integrates count values, if there is even one such place, the integration is interrupted at that point, and measurement after passing therethrough becomes impossible.
[0008]
Therefore, since it is necessary to connect a plurality of main scales while ensuring that the phase shift δP is not 10 μm, which is half of the grating pitch P, a complicated mechanism for connecting main scales with a length of several meters with accuracy of several μm An assembly method is required. Furthermore, when the temperature changes, there is a problem that the scale pitch accuracy at the joint portion changes due to the difference in thermal expansion coefficient between the scale and the main body base.
[0009]
The present invention has been made to solve the above-mentioned conventional problems. In particular, the main scale that is connected without managing the shift of the left and right scales is combined with a single detection unit so that the signal is not lost. It is an object to detect in the following.
[0010]
[Means for Solving the Problems]
The present invention includes a plurality of main scales formed in a plurality of main lattices extending in a direction substantially perpendicular to the displacement direction, and arranged in a substantially straight line along the displacement direction, and an index scale that moves along the main scale. A photoelectric linear encoder having a detection unit that reads a change in received light amount due to an interaction between a main lattice formed on the main scale and a sub-lattice formed on the index scale and converts the change into an electric signal. against formed main grid, slightly tilt the sub-grating formed in the index scale, the displacement of the displacement direction of the sublattice due to inclination, by Rukoto provided within the valid range of the sub lattice, single detector Therefore, the above-mentioned problem is solved by obtaining an output signal with little decrease in signal intensity at the joint of the main scale.
[0011]
Further, deviation in the displacement direction of the grating by said inclination is obtained by a so larger than the phase shift in the main scale joint.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
In the first embodiment of the present invention, as shown in FIG. 1, the light generated from the light source 30 passes through the main lattice 12 formed on the main scale 10 and the sub lattice 24 formed on the index scale 20. The present invention is applied to a transmission type photoelectric linear encoder having a two-grating structure that reaches the light-receiving element 34. As shown in FIG. By tilting the formed sub-lattice 24 a little by the angle θ, the drop in the detection signal at the joint 10C between the adjacent main scales 10A and 10B is reduced.
[0014]
The displacement in the displacement direction of the sub-grating 24 due to the inclination is provided within the effective range of the sub-grating 24, and is larger than the phase deviation δP in the connecting portion 10C of the main scale and disappears in the opposite phase. prevent.
[0015]
FIG. 7 shows an actual measurement example of the relationship between the output amplitude voltage near the joint and the inclination angle θ when the pitch deviation is about 3 μm. As the inclination angle θ is increased from 0 ° to 0.15 °, 0.24 °, 0.34 °, and 0.40 °, it is clear that the drop in the output signal at the joint portion becomes smaller. It is. In this actual measurement example, since the height of the effective range of the sub-lattice 24 is 1000 μm, the displacement in the displacement direction when setting the tilt angle is 0, 2.6 μm, 4.2 μm, 5.9 μm, and 7 respectively. 0.0 μm.
[0016]
As is apparent from FIG. 8, if a displacement in the displacement direction (3 to 4 μm) is set to the same extent as the pitch deviation of about 3 μm, a signal about twice as much as that obtained when the tilt is not obtained is obtained. If the displacement in the displacement direction is set to 6 μm (about twice as large as the pitch displacement (3 μm)), an output of 50% or more of the output obtained at a place other than the connecting portion can be obtained.
[0017]
Next, FIG. 9 shows a second embodiment of the present invention applied to a three-grating configuration transmission type photoelectric linear encoder in which two sub-gratings 24 and 26 are disposed on the light receiving element 34 side of the main scale 12. .
[0018]
In the present embodiment, the two sub-lattices 24 and 26 formed on the index scale 20 are both inclined with respect to the main lattice 12 formed on the main scale 10. The displacement in the displacement direction due to the inclination is defined by the deviation between the upper end and the lower end of the effective range of the two sub-lattices 24 and 26 having the wider effective range (the sub-lattice 26 in the case of diffusion). It is larger than the phase shift δP in the part 10C.
[0019]
Next, FIG. 10 shows a third embodiment of the present invention applied to a transmissive photoelectric linear encoder having a three-grating structure in which two sub-gratings 22 and 24 are arranged on both sides of the main scale 10.
[0020]
Also in the present embodiment, the two sub-lattices 22 and 24 formed on the index scale 20 are inclined with respect to the main lattice 12 formed on the main scale 10. The displacement in the displacement direction due to the inclination is defined by the displacement between the upper end and the lower end of the effective range of the two sub-lattices 22 and 24, which has the wider effective range, and is larger than the phase shift δP in the joint portion 10C. To do.
[0021]
Next, FIG. 11 shows a fourth embodiment of the present invention applied to a reflective photoelectric linear encoder having a three-grid configuration in which the main scale 10 is a reflective type as shown in FIG.
[0022]
Also in the present embodiment, the two sub-lattices 22 and 24 formed on the index scale 20 are inclined with respect to the main lattice 12 formed on the main scale 10. The other points are the same as in the third embodiment, and thus the description thereof is omitted.
[0023]
Next, FIG. 12 shows a fifth embodiment of the present invention applied to a three-grating transmissive photoelectric linear encoder in which two sub-gratings 22 and 24 are arranged on the light source 30 side of the main scale 10.
[0024]
Also in the present embodiment, the two sub-lattices 22 and 24 formed on the index scale 20 are inclined with respect to the main lattice 12 formed on the main scale 10. The other points are the same as in the third embodiment, and thus the description thereof is omitted.
[0025]
【The invention's effect】
According to the present invention, it is possible to reduce the signal fluctuation in the connecting portion even if the single connected detecting portion detects the scale that is easily connected without precisely adjusting. Therefore, a photoelectric linear encoder having a long measurement range can be provided at low cost.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of a conventional transmissive photoelectric linear encoder having a two-grid configuration. FIG. 2 is a perspective view showing a configuration of a conventional reflective photoelectric linear encoder having a three-grid configuration. FIG. 4 is a cross-sectional view showing a configuration of a connecting portion of a plurality of main scales of a photoelectric linear encoder proposed in Japanese Patent No. 2-64405. FIG. 5 is a front view for explaining a problem in detecting a connecting portion with a single detection unit. FIG. 6 is a cross-sectional view showing the configuration of the first embodiment of the present invention. FIG. 7 is a diagram showing an example of the relationship between the position in the vicinity of the connecting portion and the output signal amplitude for explaining the principle of the present invention. FIG. Diagram showing examples of relationships [Fig. 9 Sectional view and front view showing the configuration of the second embodiment of the present invention FIG. 10 is a sectional view and front view showing the configuration of the third embodiment of the present invention. FIG. 11 shows the configuration of the fourth embodiment of the present invention. FIG. 12 is a sectional view and a front view showing the configuration of the fifth embodiment of the present invention.
DESCRIPTION OF SYMBOLS 10, 10A, 10B ... Main scale 10C ... Joint 12, 12A, 12B ... Main lattice 20 ... Index scale 22, 24, 26 ... Sub lattice 30 ... Light source 32 ... Collimating lens 34 ... Light receiving element

Claims (2)

A plurality of main grids are formed that extend in a direction substantially perpendicular to the displacement direction, and are arranged in a substantially straight line along the displacement direction;
An index scale that moves along the main scale;
In a photoelectric linear encoder having a detection unit that reads a change in received light amount due to an interaction between a main lattice formed on the main scale and a sub-lattice formed on the index scale and converts it into an electric signal,
The main grating formed on the main scale, slight angle sublattice formed in the index scale, the displacement of the displacement direction of the sublattice due to inclination, by Rukoto provided within the valid range of the sub lattice, A photoelectric linear encoder characterized in that an output signal with little decrease in signal strength at the joint of the main scale is obtained by a single detection unit.   2. The photoelectric linear encoder according to claim 1, wherein a deviation in a displacement direction of the sub-lattice due to the inclination is larger than a phase deviation at a joint of the main scale.

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