JPH0638049B2 - Photoelectric displacement detector - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a photoelectric displacement detector, and in particular, it is suitable for use in a reflection type displacement detector, and cancels a DC component of a light-receiving element output that fluctuates in the longitudinal direction of the main lattice to reflect the reflectance of the main lattice. The present invention relates to a high-resolution, high-precision photoelectric displacement detector capable of generating a stable detection signal even if the transmittance, the line width, etc. vary to some extent in the longitudinal direction of the main grating.

[Prior art]

A light-transmissive reference scale in which a main scale having a periodic main grating is fixed to one of the facing members, and a corresponding periodic sub-grating is formed in the other member, and an illumination system including a light source. , A photoelectric type that fixes a light receiving element that photoelectrically converts light from the illumination system modulated by the main grating and the sub grating, and generates a detection signal that periodically changes according to relative displacement of both members. Displacement detectors are widely used in the field of measuring the tool feed amount of machine tools. FIG. 10 shows an example of a conventional reflection type photoelectric displacement detector, which includes a light emitting diode 10 as a light source, and a collimator lens 12 which makes light emitted from the light emitting diode 10 into parallel illumination light rays. A main scale 14 as a first member on which a periodic main grating 16 is formed, and a light-transmissive first on which a corresponding periodic sub-lattice 20 is formed, which is arranged so as to be movable relative to the main scale 14. Reference scale 18 as two members, and the main scale 14
Of the parallel illumination system reflected by the main grating 16 and passing through the sub-grating 20 of the reference scale 18.
And a light receiving element 22 for photoelectrically converting the light. The periodic detection signal is generated according to the relative displacement of the main scale 14 and the reference scale 18. In such a photoelectric displacement detector, the sub-lattice 20
As shown in FIG. 11, two light-receiving elements 22 are usually provided on the reference scale 18 in a direction parallel to the grid scale (vertical direction in the figure) and two in the longitudinal direction of the main grid (horizontal direction in the figure). and a total of four arranged in, for example, the phase of the sub-gratings 20A ₁ and the reference value 0 °, the phase of the sub-grating 20A ₂ -90 °, the phase of the sub-grating 20B ₁ and +180 °, sublattice 20B ₂
Is + 90 °, the difference (A ₁ −) between the detection signals of the light receiving elements arranged diagonally with respect to the longitudinal direction of the main grating.
B ₁ ) and (A ₂ −B ₂ ) are used to generate two-phase detection signals. In the figure, 24 and 26 are differential amplifiers. In this way, two-phase detection signals whose phases are different from each other by 90 ° can be obtained, and the reference scale 1
It is possible to absorb a measurement error due to a disturbance due to mechanical factors such as rotation and inclination with respect to the center of 8. However, the main scale 14 is, for example, 30 in length.
When it becomes a long product of 0 mm or more, it is generally manufactured by exposing it while transferring it by using a short product as an original plate while positioning with a stepper. Therefore, the thickness (shade) of the chrome that composes the grid scale varies depending on the position in the longitudinal direction.
Since the reflectance and the transmittance vary, and the line width also varies slightly, it is extremely difficult to manufacture them uniformly. For example, in the case of the main scale main lattice of 8 μm pitch,
The line width has a variation of about 0.2 μm, that is, about 2.5%, and in consideration of other factors, the variation of the detection signal may be about 10%. If there is such a variation in the longitudinal direction, the DC component of the received light output changes, and this greatly affects the interpolation accuracy when the pitch is interpolated.Therefore, as the resolution improves, it becomes a problem. It was That is, the parameters of the detection signal adjustment error include the DC component (level) and the phase difference between the two-phase signals, but normally the phase error of the two-phase signal is, for example, 3
Adjusted to within%, and there are few problems with interpolation error, but with respect to DC component error, it is 10% at maximum.
It could be a degree. Such a problem may be a problem particularly in a long main scale, but even if it is short, there are variations due to temperature distribution. Therefore, conventionally, scales having small variations in the longitudinal direction have been selected and used from among the scales that have been completed, so that there is a problem that the yield is poor and the inspection man-hours are increased.

[Problems to be achieved by the invention]

The present invention has been made to solve the above-mentioned conventional problems, such as the reflectance of the main grating, the transmittance, the variation of the line width, and the like,
Even if there is a twist (inclination) in the grid arrangement in the grid width direction, it is possible to obtain a stable detection signal with a small error, and thus a photoelectric displacement detector that can achieve high resolution and high accuracy. The purpose is to provide.

[Means for achieving the object]

The present invention provides an illumination system, a first member having a periodic main grating, a light-transmissive second member having a corresponding periodic sub-grating, and modulation by the main grating and the sub-grating. In a photoelectric displacement detector that includes a light receiving element that photoelectrically converts light from the illumination system, and that generates a periodic detection signal according to the relative displacement of the both members, substantially the same position in the longitudinal direction of the main grating. A plurality of sets of sub-lattices, each of which is composed of three or more sub-lattices, are arranged at different positions in the longitudinal direction of the main lattice, and each light-receiving element corresponds to the sub-lattice located at substantially the same position in the longitudinal direction of the main lattice. A primary detection signal is generated according to the difference in output between the two, and the difference in the primary detection signal between the pair of light receiving elements corresponding to the pair of sub-gratings arranged at different positions in the longitudinal direction of the main grating is used. Therefore, by generating the detection signal, the light receiving element output that varies in the longitudinal direction of the main grating is generated. DC component offset the one in which to achieve the above object. Further, four sub-lattices at substantially the same position in the longitudinal direction of the main lattice are arranged in a grid pattern.

[Action and effect]

In the present invention, it is extremely difficult to prevent variations in the reflectance and transmittance of the main grating, and further variations in the line width and the like depending on the position in the longitudinal direction, but on the other hand, in the direction parallel to the scale, This was done focusing on the fact that there is almost no variation. That is, for example, as shown in FIG. ₁ , sublattices 20A ₁ , 20A ₂ , 20A ₃ , 20B ₁ , 20 on the reference scale 18 are shown.
B ₂ , 20B ₃ and the light-receiving element 2 corresponding to each sub-lattice
2A ₁ , 22A ₂ , 22A ₃ , 22B ₁ , 22B ₂ , 2
_Three 2B ₃ are arranged at the same position in the longitudinal direction of the main lattice, that is, in the direction parallel to the lattice scale. Here, the phase of the sub-grating 20A ₁ is set to a reference value of 0 °, and the sub-grating 2
The phase of 0A ₂ is + 90 °, and the phase of sub-grating 20A ₃ is -9.
0 °, the phase of the sub-grating 20B ₁ is + 180 °, the sub-grating 20
The phase of B ₂ is + 90 ° and the phase of the sub-lattice 20B ₃ is +27.
Assuming 0 °, as shown in Fig. 2, the main scale 14
Each of the light receiving elements 22A _{1 to} 22B _{3 at} an arbitrary point P above
Output signals A _{1 to} A ₃ and B _{1 to} B ₃ are as shown in the following equation. A ₁ = a ₁ + m ₁ sin θ ………… (1) A ₂ = a ₂ + m ₂ sin {θ + (π / 2)} ………
(2) A ₃ = a ₃ + m ₃ sin {θ + (π / 2)} ………
(3) B ₁ = b ₁ + n ₁ sin (θ + π) ……… (4) B ₂ = b ₂ + n ₂ sin {θ + (π / 2)} ………
(5) B ₃ = b ₃ + n ₃ sin {θ + (3/2)} ………
(6) Here, m ₁ to m ₃ , n ₁ to n ₃ are amplitude (PP) components of each output signal, and a ₁ to a ₃ and b ₁ to b ₃ are direct current (DC) components. The zero point of the received light signal is adjusted at point P, and as shown in the following equation, a ₁ = a ₂ = a ₃ = a, b ₁ = b ₂ = b ₃ = b
It is possible to A ₁ = a + m ₁ ′ sin θ ………… (1 ′) A ₂ = a + m ₂ ′ sin {θ + (π + 2)} …………
(2 ′) A ₃ = a + m ₃ ′ sin {θ + (π / 2)} ………
(3 ′) B ₁ = b + n ₁ ′ sin (θ + π) ……… (4 ′) B ₂ = b + n ₂ ′ sin {θ + (π / 2)} ………
(5 ′) B ₃ = b + n ₃ ′ sin {θ + (3 / 2π)} ………
(6 ') Here, in the direction parallel to the scale, there is no variation in reflectance, transmittance, line width, etc., and since it is almost uniform, m ₁ ′ ≈ m ₂ ′ ≈ m ₃ ′ ≈ mn ₁ ′ ≈n ₂ ′ ≈n ₃ ′ ≈n can be set. Therefore, the output difference between the light-receiving elements corresponding to the sub-gratings at the same position in the longitudinal direction of the main grating, for example, the output difference between the light-receiving elements 22A ₂ and 22A ₁ , that is, 1
Next the detection signal _(A 2 -A ₁₎ is expressed by the following equation. Similarly, the difference in output between the main grating longitudinal position with the same other light receiving elements, i.e., the other primary detection signal (B 3 _{-B 1),}
The following equations (8) to (10) hold for (A ₁ -A ₃ ) and (B ₁ -B ₂ ). Further, when the difference of the primary detection signal between the set of light receiving elements corresponding to the set of sub-gratings arranged at different positions in the longitudinal direction of the main grating is calculated, the following expression is obtained. Therefore, a two-phase signal with a phase difference of 90 ° can be obtained as in the conventional case. The two-layer signal obtained at the point P does not include the direct current component a or b. Next, consider a case where the reference scale 18 is moved relative to the main scale 14 and is moved to the point Q in FIG.
Since there are variations in the longitudinal direction, variations of the DC component are represented by Δa and Δb, and variations of the amplitude component are represented by Δm and Δn, the signal at this Q point is as shown in the following equation. A ₁ ≈ (a + Δa) + (m + Δm) sin θ ………… (13) A ₂ ≈ (a + Δa) + (m + Δm) sin {θ + (π / 2)} ……… (14) A ₃ ≈ (a + Δa) + ( m + Δm) sin {θ− (π / 2)} ……… (15) B ₁ ≈ (b + Δb) + (n + Δn) sin (θ + π) ……… (16) B ₂ ≈ (b + Δb) + (n + Δn) sin { θ + (π / 2)} ………… (17) B ₃ ≈ (b + Δb) + (n + Δn) sin {θ + (3 / 2π)} ………… (18) Even at this Q point, it is the same as the case of the P point. Similarly, when the difference of the primary detection signals between the sets of light receiving elements having different positions in the longitudinal direction of the main grating is taken, the following expression is obtained. This equation (19) and equation (20) also include the amplitude component (a + Δ
a) and (b + Δb) are not included, and like point P,
At this point Q, no DC component is included. Although the amplitude component fluctuates slightly, the fluctuation of the amplitude component is
Since the influence on the interpolation accuracy is extremely small when the pitch is interpolated and divided, an extremely stable signal can be obtained under this condition. On the other hand, when the case of the conventional example shown in FIG. 11 is examined under the same conditions, the output signal A of each of the light receiving elements 20A ₁ , 20A ₂ , 20B ₁ , 20B ₂ when adjusted at point P
₁ , A ₂ , B ₁ and B ₂ are as shown in the following equation. A ₁ = a + m sin θ ... (21) A ₂ = a + m sin {θ− (π / 2)} (22) B ₁ = a + n sin (θ + π)… (23) B ₂ = a + n sin {θ + (π / 2)} (24) Therefore, the difference between the output signals of the light-receiving elements arranged diagonally, that is, the detection signals (A ₁ -B ₁ ), (A ₂ -B ₂₎
Is as shown in the following equation. A ₁ −B ₁ = a + m sin θ−a · n sin (θ + π) = (m + n) sin θ (25) A ₂ −B ₂ = a + m sin {θ− (π / 2)} − a −n sin {θ + (π / 2)} = (m + n) sin {θ− (π / 2)} (26) At this P point, as is clear from the equations (21) to (24), Since a = b (= a), it is not included in the DC component. However, when moving to point Q, the dispersion of the DC component is Δa and Δb, and the dispersion of the amplitude component is Δm and Δn,
The received light signal is as shown in the following equation. _{A 1 = a + Δa + (} m + Δm) sinθ ... (27) A 2 = a + Δa + (m + Δm) × sin {θ- (π / 2)} ...... (28) B 1 = a + Δb + (n + Δn ) × sin (θ + π) (29) B ₂ = a + Δb + (n + Δn) × sin {θ + (π / 2)} (30) Therefore, the detection signals (A ₁ -B ₁ ) and (30) A ₂ −B ₂ ) is as shown in the following equation. A ₁ −B ₁ = a + Δa + (m + Δm) sin θ−a−Δb− (n + Δn) sin (θ
+ Π) = (Δa + Δb) + (m + n + Δm + Δn) sin θ ... (31) A ₂ −B ₂ = a + Δa + (m + Δm) × sin {θ− (π / 2)} − a−Δb−
(N + Δn) × sin {θ + (π / 2)} = (Δa−Δb) + (m + n + Δm + Δn) × sin {θ− (π / 2)} ………
(32) As is apparent from the equations (31) and (32), in the conventional case, the DC component (Δa −Δ
b) remains without being removed. Therefore, the condition becomes extremely bad especially when the sign of Δb is opposite to that of Δa. For example, in the case of an 8 μm pitch main lattice, when the sign of Δa or Δb is opposite, it may be up to about 10%. This DC component has a great influence on the interpolation accuracy when the pitch is interpolated and divided. According to an experiment conducted by the inventor, it was possible to reduce the DC component to 1/4 or less by applying the present invention in an example in which the variation of the DC component was about 5% in the related art. In the above description, three sub-gratings are provided in the direction parallel to the grid scale, but the number of sub-gratings and light-receiving elements provided is not limited to this. Further, in the above description, since two sets of the sub-grating and the light-receiving element are arranged in different positions in the longitudinal direction of the main grating, they are disposed due to mechanical disturbances such as rotation and inclination with respect to the center of the reference scale. There are few errors that occur. Note that the present invention is particularly effective for a reflection type photoelectric displacement detector, but also has a similar effect for a transmission type.

【Example】

An embodiment of the present invention applied to a reflection type detector of a diffuse illumination system will be described in detail below with reference to the drawings. The first embodiment of the present invention is constructed as shown in FIGS. In this embodiment, the illumination system is composed of a diffused light source 30 including a laser diode (LD) chip 34 (see FIG. 4) housed in a housing 32. As shown in detail in FIG. 4, the diffused light source 30 serves as the LD chip 34 as a primary point light source and a condenser lens for converging divergent light from the LD chip 34 to generate a secondary point light source. , A cylindrical distributed index lens 40, and the secondary point light source is focused on the sub-lattice forming surface (chrome vapor deposition surface) 42 of the reference scale 18. Main scale 14 made of glass plate
The main grating 16 is formed on the surface of the opposite side of the diffused light source 30. This is for downsizing the detector by the thickness of the main scale 14. The light transmissive reference scale 18 includes six sub-gratings 20A ₁ corresponding to the main grating 16 as shown in detail in FIG.
~20A is _{3, 20B} 1 _{~20B 3, 3} pieces in a grid scale parallel direction, are two sets of a total of six formed in the main grating longitudinal direction. The sub-lattices 20A _{1 to} 20B ₃ have the same pitch and a phase of 0 ° and +90 in the chrome vapor deposition surface 42.
It is divided into 6 sections corresponding to °, -90 °, +180 °, +90 °, and +270 °, and an opening 52 through which the secondary point light source is focused and passes is also formed in the center. . The opening 52 has a height of 0.4 mm and a width of 0.
The size of the LD chip 34 is 1 mm, and the divergent light of the LD chip 34 is focused by the distributed index lens 40 (for example, Selfoc lens, a trade name of Nippon Sheet Glass Co., Ltd.) in the secondary point light source 54. Are formed (see FIG. 4). _On the back side of each sub-grating 20A _{1 to} 20B ₃ , the main grating 1
Six light receiving elements _22A 1 _{~22B 3} that the light is photoelectrically converted from the diffuse source 30 that has passed through is reflected each sublattice _20A 1 _{~20B 3} are provided at 6. These light receiving elements 22A ₁ ~22B _3, as shown in FIG. 4, is disposed on the light-receiving substrate 56, they are in a positional relationship as shown by the broken line in FIG. 5. In the center of the light receiving substrate 56,
The distributed index lens 40 is also inserted. As shown in FIG. 6, the signal generating circuit 60 that forms a two-phase detection signal from the outputs of the light receiving elements 22A _{1 to} 22B ₃ has a variable resistor for amplifying the output signal A ₁ of the light receiving element 22A _1. Operational amplifier (operational amplifier) OP1 whose amplification factor is variable by the device VR1 and the light receiving element 22.
For amplifying an output signal _{A 2} of A _2, the variable resistor VR
An operational amplifier OP2 whose amplification factor is variable by 2;
Wherein for amplifying an output signal A ₃ of the light receiving element 22A _3, an operational amplifier OP3 to by the variable resistor VR3 connexion amplification factor is variable, for amplifying the output of the light receiving element 22B _1, the variable resistor an operational amplifier OP4 to by connexion amplification factor is variable in VR4, for amplifying the output of the light receiving element 22B _2, a variable resistor operational amplifier OP5 to VR5 by the connexion amplification factor is variable, the light receiving element 22
For amplifying the output of the B _3, the variable resistor VR6 operational amplifier OP6 to by connexion amplification factor is variable, the differential signal of the output of the operational amplifier OP2 and OP1 _(A 2 _-A 1)
Operational amplifier OP7 for outputting
When an operational amplifier OP8 the output OP3 differential signal of the output of the _(A 1 -A _3), an operational amplifier OP for outputting a differential signal of the output of the operational amplifier OP4 and OP5 _(B 1 -B ₂₎
9, an operational amplifier OP10 outputs a differential signal of the output of the operational amplifier OP6 and OP4 _(B 3 -B _1), the differential signal of the output of the operational amplifier OP8 and OP9 _(A 1 -A
₃ )-(B ₁ -B ₂ ) is output as one of the two-phase detection signals, and the operational amplifiers OP7 and O7.
P10 differential signal output _{(A 2 -A 1) - (} B 3 -
And a B ₁₎ and outputs as a local 2-phase detection signal operational amplifier OP12 Prefecture. The operation of the embodiment will be described below. First, at any point (P) on the main scale 14, the variable resistors VR1 to VR6 are adjusted to obtain the DC component a at the point P as shown in the above equations (1 ') to (6'). ₁ , a ₂ and a ₃ all have the same value a, and DC components b ₁ , b ₂ and b ₃ have the same value b. Then, the two-phase detection signals obtained by the operational amplifiers OP11 and OP12 of the signal generation circuit 60 are the same as the above (11) and (1
It becomes as shown in the equation (2). In this state, when the reference scale 18 is moved relative to the main scale 14 and is moved to another arbitrary point (Q), the two-phase detection signals at that time are (19) and (20).
As shown in the equation, the amplitude component fluctuates slightly, but
DC components are not included. Therefore, an extremely stable detection signal can be obtained, and highly accurate interpolation division can be performed to obtain a highly accurate measurement signal. In the first embodiment, the sub-lattice _20A 1 through 20a ₃
Alternatively, _three sets of 20B _{1 to} 20B 3 are arranged in a direction parallel to the lattice scale, respectively, and a set of partially overlapping light receiving elements (2
_{2A 2 -22A 1), (22A} 1 -22A 3) or (2
_{2B 3 -22B 1), (22B} 1 -22B 2) 1 primary detection signal based on the difference between the output of the _{(A 2 -A 1), (} A 1 -A
₃ ) or (B ₃ −B ₁ ), (B ₁ −B ₂ ) are generated, the minimum number of three sub-lattices may be provided at the same position in the main lattice longitudinal direction. Variations in the longitudinal direction can be reliably absorbed, and the configuration is simple. Further, in the first embodiment, since the secondary point light source 54 is formed by using the distributed index lens 40 as the condenser lens, a substantially ideal small diffused light source can be obtained. The method for forming the diffused light source is not limited to this, and a laser diode can be used as a direct diffused light source, or a tungsten lamp or a light emitting diode other than the laser diode can be used. Further, instead of the diffused light source, a parallel light source using, for example, a collimator lens can be used. Further, in this first embodiment, the secondary point light source 54 is
Since the sub-lattices 20A _{1 to} 20B ₃ are formed in the central portion, each sub-lattice can be illuminated substantially uniformly, and the detector can be downsized. The formation position of the secondary point light source 54 is not limited to this. Further, in the first embodiment, the secondary point light source 54 is formed by focusing on the small square opening 52 on the sub-lattice forming surface (42), so that the extra scattered light irradiates the main lattice 16. It is possible to obtain a detection signal with a good S / N ratio. The shape and size of the opening 52 for passing the illumination light beam is not limited to this. Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the same photoelectric displacement detector and the first embodiment, as shown in FIG. 7, the sublattice 20A ₁ ~
20A _{4, 20B} 1 ~20B ₄ to those provided four each in a grid scale parallel direction. Here, for example, when the reference value of the sub-grating 20A ₁ is 0 °, the phase of the sub-grating 20A ₂ is + 90 ° and the phase of the sub-grating 20A ₃ is +.
180 °, subgrating 20A ₄ phase is + 270 °, subgrating 2
The phase of 0B ₁ is + 180 ° and the phase of sub-grating 20B ₂ is +
270 °, phase of sub-grating 20B ₃ is 0 °, sub-grating 20B
The phase of ₄ is + 90 °. In this second embodiment, the sub-gratings _20A 1 to 20
From the output signals A _{1 to} A ₄ and B _{1 to} B _{4 of} the light receiving elements (not shown) corresponding to A ₄ and 20B _{1 to} 20B ₄ , respectively, (A ₁ −A ₃ ) − (B ₁ −B ₃ ) ( _{a 2 -A 4) - (B} 2 -B 4) that Yotsute to obtaining a difference signal, second 90 degree phase difference
A phase signal can be obtained. In the second embodiment, the sub-lattice _20A 1 through 20a ₄
Or _20B 1 _{~20B 4,} respectively arranged four by four grid scale parallel directions, mutually independent sets of output difference between the light receiving elements _{(A 1 -A 3), (} A 2 -A 4) or ( B ₁ -B
_3), (since so as to generate a primary detection signal based on B 2 _{-B 4),} the number of light receiving elements as compared with the first embodiment is increased two, output signals, first Compared to the example growing. Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, four sub-gratings 20A ₁ , 20A ₂ and 20 having the same phase difference as each other by 90 ° are used.
In the photoelectric type displacement detector with B _1, 20B _2, as shown in FIG. 8, between the sub-gratings 20A ₁ and 20A _2,
Further, between the sub-lattices 20B ₁ and 20B ₂ , sub-lattices 20A ₀ and 20B ₀ containing only a DC component are provided, respectively. That is, the sub-lattices 20A ₀ and 20B ₀ are provided with stripes in the direction perpendicular to the grid in order to adjust the level of the DC component, but are not provided with stripes in the direction parallel to the scale and the DC component A Only ₀ = a and _B0 = b. In this third embodiment, the sublattices 20A _{0 to} 20
From output signals A _{0 to} A ₂ and B _{0 to} B _{2 of} light receiving elements (not shown) corresponding to A ₂ and 20B _{0 to} 20B ₂ , respectively, (A ₁ −A ₀ ) − (B ₁ −B ₀ ) ( By taking a differential signal of A ₂ −A ₀ ) − (B ₂ −B ₀ ), a 90 ° phase difference of 2
A phase signal can be obtained. In the third embodiment, the sub-lattice _20A 0 through 20a ₂
Alternatively, three 20B _{0 to} 20B ₂ are arranged in a direction parallel to the grid graduations, respectively, and the output difference (A _{1 -A 0), (A 2 -A} 0) or _(B 1 _-B 0),
Since so as to generate a primary detection signal based on (B 2 _{-B 0),} construction is extremely simplified. In the third embodiment, the number of light receiving elements is the first.
As with the first embodiment, only six signals are required, but the amplitude value of the output signal is smaller than that of the first embodiment. Becomes smaller. Next, a fourth embodiment of the present invention will be described with reference to FIG. The fourth embodiment is a photoelectric displacement detector having four sub-lattices arranged in a T-shaped pattern, the phases of which are different by 90 ° from each other, as shown in FIG. Two sets of grids (20A ₁ ~
20A ₄ ), (20B _{1 to} 20B ₄ ) are arranged, the differential signal obtained by each of them is used as a primary detection signal, and the differential of the primary detection signal is further taken to obtain a two-phase detection signal. Is to get. Here, the sub-lattice 20A ₁ , 2
0B ₃ has a reference value of 0 °, and sub-lattices 20A ₂ and 20B ₄
Is + 90 °, the sublattices 20A ₃ and 20B ₁ are + 180 ° in phase, and the sublattices 20A ₄ and 20B ₂ are +27 in phase.
It is said to be 0 °. In the fourth embodiment, the sub-gratings _20A 1 to 20
From the output signals A _{1 to} A ₄ and B _{1 to} B _{4 of} the light receiving elements (not shown) corresponding to A ₄ and 20B _{1 to} 20B ₄ , respectively, (A ₁ −A ₃ ) − (B ₁ −B ₃ ) ( _{a 2 -A 4) - (B} 2 -B 4) that Yotsute to obtaining a difference signal, the phase difference can be obtained a detection signal of 90 ° two different phases. In the fourth embodiment, the set of sub-lattices arranged at substantially the same position in the longitudinal direction of the main lattice is four sub-lattices arranged in the same T-shape as the conventional one. The sub-grid can be manufactured with the same manufacturing equipment as before, and the cost is low. or,
Since two sub-lattices may be arranged in the grid scale direction, the size in the grid scale direction does not increase. In each of the above-described embodiments, two sets of three or four sub-lattices are arranged by changing the position of the main lattice in the longitudinal direction, and between the light-receiving elements corresponding to the sub-lattices at substantially the same position in the longitudinal direction of the main lattice. To generate a primary detection signal based on the difference between the outputs of the sub-lattices, and then between the groups of light-receiving elements corresponding to the sub-lattice groups arranged at different positions in the longitudinal direction of the main grating, the first detection signal is formed on a substantially diagonal line. Since the detection signal is generated by taking the difference between the next detection signals,
This is effective not only for fluctuations in the longitudinal direction of the main lattice but also for disturbances due to rotation, inclination, etc. with respect to the center of the reference scale. Further, in each of the above embodiments, since the corresponding light receiving element is arranged immediately after the sub-lattice, the structure is simple and the size is small. The arrangement position of the light receiving element is not limited to this, and it is also possible to arrange the light receiving element at a position apart from the corresponding sub-lattice by using an optical fiber or the like. Further, in the above-mentioned embodiment, the present invention was applied to a reflection type linear displacement detector including a reflection scale made of glass, but the application range of the present invention is not verified by this, and a reflection scale made of metal is used. It is similarly applicable to a device including, a transmission type detector, and a rotational displacement detector.

[Brief description of drawings]

FIG. 1 is a front view showing an arrangement example of a sub-lattice and a light receiving element on a reference scale for explaining the principle of the present invention, FIG.
Similarly, FIG. 3 is a front view showing an example of a main grid on the main scale, FIG. 3 is a perspective view showing the overall configuration of the first embodiment of the photoelectric displacement detector according to the present invention, and FIG. IV- in Figure 3
Fig. 5 is a cross sectional view taken along line IV, Fig. 5 is a cross sectional view taken along line VV in Fig. 4, and Fig. 6 is a block diagram showing the configuration of the signal generation circuit of the first embodiment. The figure is a front view showing the arrangement of the sub-lattice on the reference scale in the second embodiment of the present invention,
FIG. 8 is a front view showing the arrangement of the sub-lattice on the reference scale in the third embodiment of the present invention, and FIG. 9 is a fourth view of the present invention.
FIG. 10 is a front view showing the arrangement of the sub-gratings on the reference scale in the embodiment, and FIG. 10 is a cross-sectional view showing the configuration of an example of a reflection type photoelectric displacement detector using a conventional parallel illumination light beam.
FIG. 1 is a front view showing a reference scale in the conventional example. 14 ... Main scale, 16 ... Main lattice, 18 ... Reference scale, 20A _{1 to} 20B ₄ ... Sub lattice, 22A _{1 to} 22B ₃ ... Photodetector, A _{1 to} B ₄ ... Photodetection signal, 60 ... ... Signal generation circuit.

Claims (2)

[Claims] 1. A first system in which an illumination system and a periodic main grating are formed.
A member, a light-transmissive second member forming a corresponding periodic sub-grating, and a light-receiving element for photoelectrically converting light from the illumination system modulated by the main grating and the sub-grating,
In a photoelectric displacement detector that generates a periodic detection signal according to the relative displacement of both members, a sub-lattice set consisting of three or more sub-lattices arranged at substantially the same position in the longitudinal direction of the main lattice is used. A plurality of sets are arranged by changing the position of the main grating in the longitudinal direction, and a primary detection signal is generated by the difference in output between the light receiving elements corresponding to the sub-gratings at substantially the same position in the longitudinal direction of the main grating. The detection signal is generated according to the difference in the primary detection signal between the set of light receiving elements corresponding to the set of sub-gratings arranged at different positions in the longitudinal direction of the grating, thereby varying in the longitudinal direction of the main grating. A photoelectric displacement detector characterized in that the direct current component of the light receiving element output is canceled. 2. A photoelectric displacement detector according to claim 1, wherein four sub-lattices are arranged in a grid pattern at substantially the same position in the longitudinal direction of the main lattice.