JPH0791983A - Encoder - Google Patents

Abstract

PURPOSE:To provide an encoder by which a reliable signal without any signal quality deterioration is obtained. CONSTITUTION:A mark line where marks are laid out periodically with fine pitches are formed on a medium 5, a light beam from a semiconductor laser 1 is turned into a parallel beam by a collimator lens 2, the parallel beam is reflected by a beam splitter 3, and then the reflected light is focused on the mark of the medium by an objective lens 4 as a focusing spot. Further, the beam which is reflected by the medium 5 is passed through the beam splitter after the light is turned into parallel beam by the objective lens 4 and then is focused on a photodetector 7 by a focusing lens 6. When the medium 5 moves in the direction parallel to the mark line, a sinusoidal wave signal is obtained by the photodetector 7, thus measuring the movement of the medium 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoder (linear encoder, rotary encoder).

[0002]

2. Description of the Related Art FIG. 24 shows an example of a conventional encoder known for its small size and high resolution. Further, a partially enlarged view thereof is shown in FIG. The operating principle of this encoder will be described below. The light from the light source 101 is collimated by the lens 102. The collimated light is incident on the two diffraction gratings. The first diffraction grating 103 is fixed, and the second diffraction grating 104 is for moving. Therefore, it suffices for the fixing diffraction grating 103 to have at least the size of the incident diameter of light,
The length of the moving diffraction grating 104 is the measurement range. The pitches of the two diffraction gratings 103 and 104 are the same. The fixed diffraction grating 103 and the movable diffraction grating 104 generate at least ± first-order diffracted light. If the pitch is sufficiently larger than the wavelength, higher order diffracted light is generated.

Taking the ± 1st order diffracted light as an example, the + 1st order light generated by the fixed diffraction grating 103 and the 0th order light of the moving diffraction grating 104, that is, the transmitted light (A ) And 0th-order light generated by the fixed diffraction grating 103, that is, transmitted light that is the first-order light (B) of the movable diffraction grating 104 is condensed by the lens 105 and is incident on the photodetector 107. Two diffraction gratings 103, 1
Since 04 has the same pitch, the diffraction angle is the same, so (A)
And (B) are perfectly parallel. As the moving diffraction grating 104 moves, the phase of the diffracted light generated by this diffraction grating changes, so the phase of (B) changes, and the phase of the interference light between (A) and (B) on the photodetector 107 changes. Changes. The interference fringes do not appear if the collimated lights that are parallel to each other interfere with each other, but the interference fringes are generated because they are converged by the lens 105, and when the size of the photodetector 107 is smaller than the interval of the interference fringes, the moving diffraction grating 104. The output of the photodetector 107 changes in a sine wave shape in accordance with the movement of. Therefore, the amount of movement can be detected. In addition,
The sine wave signal becomes 1 as the diffraction grating moves 1 pitch.
It is output for a period.

The -1st order light generated by the fixed diffraction grating 103 and the 0th order light of the moving diffraction grating 104, that is, the transmitted light (D), and the 0th order light generated by the fixed diffraction grating 103, that is, In the case of transmitted light which is the −1st order light (C) of the moving diffraction grating 104, the same principle operates. In FIGS. 24 and 25, reference numeral 108 is a photodetector.

[0005]

However, in the above-mentioned conventional example, when used in a rotary encoder, the moving diffraction grating forms a radial diffraction grating on a disk. Also,
Since the collimated light is incident on the diffraction grating in the conventional example, there is a problem that the pitch of the diffraction grating is different within the diameter of the incident light, an ideal diffracted light cannot be obtained, and the signal quality is deteriorated.

It is an object of the present invention to provide an encoder which solves the above-mentioned problem of signal quality deterioration.

[0007]

According to another aspect of the present invention, an encoder is provided with a mark row having a fine pitch on a medium, and light from a light source is condensed as a condensed spot on the mark row by a condenser lens. The amount of movement of the optical system including the condenser lens or the medium is detected by detecting the reflected light from the medium or the transmitted light transmitted through the medium.

The encoder according to claim 2 is the encoder according to claim 1.
In, the two converging spots by the condensing lens are arranged on the mark row of the medium in parallel with the mark row direction and at appropriate intervals, and reflected light from the medium or transmitted through the medium. It is characterized in that two signals having different phases are obtained by detecting the transmitted light.

The encoder according to claim 3 is the encoder according to claim 1.
In the above-mentioned medium, two rows of fine pitch marks having mutually different phases are provided on the medium, and an elliptical focused spot is focused on the mark rows with its major axis perpendicular to the mark row direction. It is characterized in that two signals having different phases are obtained by detecting the reflected light from or the transmitted light transmitted through the medium.

The encoder according to claim 4 is the encoder according to claim 1.
In the above-mentioned medium, two rows of marks having fine pitches different in phase from each other are provided on the medium, one focused spot is provided on each of the marked rows, and these two focused spots are perpendicular to the mark row direction. Two signals having different phases are obtained by arranging them and detecting reflected light from the medium or transmitted light transmitted through the medium.

The encoder according to claim 5 is the encoder according to claim 1.
In the above-mentioned medium, two rows of fine pitch marks are provided on the medium, one focused spot is provided on each of the marked rows, and these two focused spots are arranged at an appropriate angle with respect to the mark row direction. Then, the reflected light from the medium or the transmitted light transmitted through the medium is detected to obtain two signals having different phases.

The encoder according to claim 6 is the encoder according to claim 2.
In any one of the items 5 to 5, the two light sources are provided,
The light from the light source is condensed by the condenser lens to form two condensed spots.

The encoder according to claim 7 is the encoder according to claim 2.
1 to 5, the light from the light source is processed by an appropriate mechanism to form two light fluxes having a partial phase difference, and these light fluxes are formed on the mark row by the condenser lens. It is characterized by forming two condensing spots by condensing the light on the.

The encoder according to claim 8 is the encoder according to claim 1.
1 to 7, the medium is formed into a cylindrical shape, and the mark rows with the fine pitch are provided on the outer peripheral surface of the medium.

The encoder according to claim 9 is the encoder according to claim 1.
1 to 7, the medium is formed into a disk shape, and the mark row with the fine pitch is provided on the disk surface.

[0016]

In the encoder according to the first aspect of the invention, since a minute focused spot is formed on the mark row, a highly reliable signal without quality deterioration can be obtained.

In the encoder according to claim 2,
Since it is configured to obtain two signals having different phases, it is possible to obtain the direction determination signal.

In the encoder according to claim 3,
Since it is configured to obtain two signals having different phases, it is possible to obtain the direction determination signal. Further, since the elliptical focused spot is used, the beam shaping optical system is unnecessary, and the elliptical emitted light from the semiconductor laser can be focused as it is to obtain two signals having different phases.

In the encoder according to claim 4,
Since it is configured to obtain two signals having different phases, it is possible to obtain the direction determination signal. Also, since each focused spot is irradiated on each mark row,
The utilization efficiency of the light from the light source is higher than that in the case of irradiating an elliptical focused spot.

In the encoder according to claim 5,
Since the focused spots are arranged on the two mark rows at an appropriate angle with respect to the mark row direction and the signal of the phase difference is detected, the mark row is perpendicular to the moving direction of the optical system or the medium. A straight line may be used, which simplifies its production.

In the encoder according to claim 6,
Since two focused spots are formed using two light sources, the intensity of the focused spot can be increased.

In the encoder according to claim 7,
Since the light flux from the light source is partially given a phase difference to form two focused spots, one light source is sufficient. Further, it is possible to obtain two converging spots that are close to each other.

In the encoder according to claim 8,
Since the mark row is provided on the outer peripheral surface of the cylindrical medium, the rotary encoder can be configured.

In the encoder according to claim 9,
Since the mark row is provided on the surface of the disk-shaped medium, the rotary encoder can be configured. In addition, such a medium can be easily manufactured by an optical disk manufacturing technique.

[0025]

The present invention will be described in more detail below with reference to the embodiments shown in the drawings. Example 1 FIG. 1 is an explanatory diagram of an optical system of an encoder according to the present invention. The light from the semiconductor laser 1 which is the light source is collimated by the collimator lens 2, is reflected by the beam splitter 3, and is condensed on the medium 5 by the objective lens 4. In this case, as shown in FIG. 3, on the medium 5, there are formed mark rows 11 in which marks 21 are periodically arranged at a fine pitch, and light from the objective lens 4 is placed on the mark rows 11. It is focused as a focused spot 31. The light reflected by the medium 5 is collimated again by the objective lens 4, passes through the beam splitter 3, and is condensed by the condenser lens 6 on the photodetector 7. When the medium 5 moves in the mark row 11 direction, a sine wave signal is obtained by the photodetector 7, and the moving distance of the medium 5 can be measured. This sine wave signal is output for one cycle as the mark 21 on the medium 5 moves by one pitch.

In this embodiment, the photodetector 7 detects the intensity of the reflected light from the medium 5 as a signal.
The intensity is not necessarily required, and for example, the mark 21 of the medium 5 may be formed by a magnetization signal to detect the polarization direction of light. Further, although the optical system in FIG. 1 detects the reflected light from the medium 5, as shown in FIG.
Can be used to detect the transmitted light of the medium 15.

The fine pitch marks 21 on the medium 5 may have a fine pitch in the moving direction of the medium 5, for example, as shown in FIG.
A linear shape as shown in FIG. Although FIG. 1 shows an example in which the medium 5 is moved, it can also be used for measuring the moving distance of the optical system by moving the optical system with respect to the medium 5.

Embodiment 2 Next, a method of detecting two sine wave signals having a phase difference in the present invention will be described. The moving direction of the medium 5 (or 15) can be determined by the sine wave signal having the phase difference. As shown in FIG. 5, the two focused spots 31,
32, one mark row 11 with an appropriate gap between them.
Focus on top (see below for how to give two focus spots). Each focused spot 31, 32
By detecting the reflected light of 2 by dividing the photodetector 7 of FIG. 1 into two, two sine wave signals having a phase difference can be obtained. The mark 21 shown in FIG. 5 may be a linear mark perpendicular to the moving direction of the medium 5 as shown in FIG.

A general encoder detects two sine wave signals (called A phase and B phase) having a 90 ° phase difference. In order to obtain two sine wave signals having a 90 ° phase difference in the encoder of the present invention, the interval between the two converging spots 31 and 32 should be 1/4 of the period of the mark row 11.
And it is sufficient. The interval between the two focused spots 31 and 32 may be a quarter of the mark row 11 cycle plus an integral multiple of the mark row 11 cycle. In this case, it is possible to increase the distance between the focused spots 31 and 32.

Embodiment 3 Another embodiment for detecting two sinusoidal signals having a phase difference will be described. As shown in FIG. 7, two mark rows on the medium 5, that is, a mark row 11 having a minute pitch by the marks 21,
The mark rows 12 having a minute pitch formed by the marks 22 are formed with their phases shifted from each other. The elliptical condensing spot 31 is focused on these mark rows so that its major axis is perpendicular to the mark row direction. Since the light emitted from the semiconductor laser 1 has an elliptical shape, the focused spot 31 also has an elliptical shape when condensed without beam shaping. Then, by detecting the reflected light from each of the mark rows 11 and 12 with two photodetectors (not shown), two sine wave signals having a phase difference can be obtained. in this case,
If the two minute pitch mark rows 11 and 12 are formed so as to have a 90 ° phase difference, two sine wave signals (A phase and B phase) having a 90 ° phase difference can be obtained.

Embodiment 4 In the embodiment shown in FIG. 8, two mark rows 1 having a phase difference are used.
Focusing spots 31 and 32 are focused on 1 and 12, respectively, and are arranged perpendicularly to the directions of these mark rows 11 and 12. In this embodiment, the same mark row as that shown in FIG. 7 is used, but since two converging spots are formed instead of the elliptical condensing spot, the mark row can be efficiently irradiated. Each mark 2
The light reflected by 1 and 22 is detected by two photo detectors. Similar to the third embodiment, if the mark rows 11 and 12 are formed so as to have a 90 ° phase difference, signals of A phase and B phase can be obtained from the two photodetectors. Also, FIG.
It is also possible to modify the mark rows 11 and 12 shown in FIG. 9 to form a mark row 11 composed of linear marks 21 having an appropriate inclination with respect to the moving direction of the medium 5, as shown in FIG.

Example 5 In this example, as shown in FIG. 10, focused spots 31 and 3 are respectively formed on two mark rows 11 and 12 having the same phase.
2 are tilted at an appropriate angle with respect to the mark row direction and arranged so as to have a phase difference. In this case, the signal detection is the same as in the above embodiment. The mark row 11 shown in FIG. 10 may be modified to form the mark row 11 with linear marks 21 perpendicular to the moving direction of the medium 5 as shown in FIG. Further, by combining the embodiments shown in FIG. 8 and FIG. 10, as shown in FIG. 12, the focused spots 31 and 32 are respectively formed on the two mark rows 11 and 12 having the phase shifts.
It is also possible to arrange them so as to have an arbitrary phase difference by inclining them at an appropriate angle with respect to the moving direction of the medium 5.

Embodiment 6 Next, a method of forming two converging spots will be described. FIG.
As shown in, the two light sources are arranged side by side. For that purpose, for example, a semiconductor laser array is used. Semiconductor laser 1
When the light beams emitted from a and 1b are collimated by the collimator lens 2 and condensed by the objective lens 4, two converging spots 3 corresponding to the respective light sources are formed on the medium 5.
1, 32 are formed. In this embodiment, since one light source is used for one focused spot, the intensity of the focused spot becomes large. In FIG. 13, 7a and 7b are photodetectors.

Embodiment 7 Next, another method for forming two focused spots will be described. As shown in FIG. 14, the light from the semiconductor laser 1 is converted into parallel light by the collimator lens 2, and a relative phase difference π is given between the light beam a and the light beam b through the wavefront conversion element 8. The specific structure of the wavefront conversion element 8 will be described later. When the light beam a and the light beam b having a relative phase difference π are condensed by the objective lens 4, the central intensity on the medium 5 becomes zero, and two condensed spots 31 and 32 are formed. The distance 1 between the two focused spots 31 and 32 is given by [Equation 1].

[0035]

[Equation 1] Here, λ: wavelength of light source f: focal length of objective lens r: radius of aperture of objective lens NA: numerical aperture of objective lens

For example, when the wavelength λ of the light source is 0.78 μm and the NA of the objective lens 4 is 0.5, the distance l between the two converging spots 31 and 32 is 1.1 μm.

Embodiment 8 Next, a concrete configuration of the wavefront conversion element 8 which gives a relative phase difference π between the light beam a and the light beam b shown in FIG. 14 is shown. As shown in FIG. 15, when the transparent flat plate 10 having the refractive index n ₁ is inserted in the light beam a, the relative phase difference expressed by [Equation 2] and [Equation 3] is obtained between the light beam a and the light beam b. Δφ occurs.

[0038]

[Formula 2] Δφ = k · Δn · d

[0039]

[Formula 3] Δn = n ₁ −n _{0 In} [Formula 1] and [Formula 2], k is the wave number and is equal to 2π / λ d: Thickness of transparent plate n ₁ : Refractive index of transparent plate n ₀ : Refractive index of air

A transparent flat plate 1 having a thickness d satisfying the following [Equation 4]
When 0 is inserted in the light flux a, the number of focused spots becomes two.

[0041]

## EQU4 ## Δφ = (2m + 1) π (m is an integer)

Embodiments 9 and 10 Further, the structure shown in FIGS. 16 and 17 can be adopted according to the same principle. That is, in the configuration shown in FIG. 16, assuming that the size of the step in the figure is d ₁ , the phase difference Δφ is represented by [Equation 5] and [Equation 6].

[0043]

[Equation 5] Δφ = k · Δn · d ₁

[0044]

(6) Δn = n ₁ −n ₀

In the configuration shown in FIG. 17, the refractive index of the transparent flat plate 10a through which the light beam a is transmitted is different from the refractive index of the transparent flat plate 10b through which the light beam b is transmitted, and the respective refractive indices are n ₁ and n.
Assuming ₂ , the phase difference Δφ is given by the following [Equation 7] and [Equation 8].
It is represented by.

[0046]

[Formula 7] Δφ = k · Δn · d

[0047]

[Formula 8] Δn = n ₂ −n ₁

Embodiment 11 FIG. 18 shows another structure of the wavefront conversion element 8. This is because the parallel light flux is reflected by the reflecting surface 8a having a step, and the light flux a
This is an example in which a relative phase difference Δφ is given between the light beam and the light beam b. The relative phase difference Δφ between the light beam a reflected on the upper surface of the step and the light beam b reflected on the lower surface of the step is represented by [Equation 9],
The parameters may be selected so that this Δφ satisfies [Equation 4].

[0049]

[Formula 9] Δφ = 2πkne · cos θ where k: wave number and equal to 2π / λ n: refractive index of medium in optical path e: step size θ: incident angle

Embodiments 12 and 13 The present invention can be applied not only as a linear encoder but also as a rotary encoder. 19 and 20 show marks 21 with a fine pitch formed on the outer peripheral surface of the cylindrical medium 5. In this encoder, the mark row 11 moves as the medium 5 rotates, and a signal is detected.

Embodiments 14 and 15 The encoder shown in FIGS. 21 and 22 is one in which marks 21 having a fine pitch are formed on a disk-shaped medium 5. FIG. 22
When the linear mark 21 is formed as shown in FIG. 3, the mark becomes radial and the pitch width is different between the inside and the outside of the medium 5, but since the light is a minute condensed spot on the medium 5, it has almost no influence. Absent.

Embodiment 16 In order to make the encoder of the present invention high resolution,
It is necessary to reduce the mark length and the focused spot. When the mark length and the focused spot are reduced, it is necessary to adjust focusing and tracking in the focal plane of the objective lens.

FIG. 23 shows an optical system when the knife edge method is used for focusing error detection and the push-pull method is used for tracking error detection. Focusing error can be detected by detecting the movement of the spot on the two-divided photodetector 7c for detecting focusing error, and tracking error signal can be detected by detecting the light reflected by the knife edge 41 by the photodetector 7d. . Actuator 42
The objective lens 4 is moved by to adjust focusing and tracking. Further, the mark signal can be detected by the sum signal of the four photodetectors (7c and 7d). Here, the knife edge method is used for the focusing error signal detection and the push-pull method is used for the tracking error signal detection, but the error detection may be performed by another method, for example, the astigmatism method may be applied. .

In recent years, pickups of optical discs such as CDs have been mass-produced, and the optical system of the encoder of the present invention is almost the same as the pickup optical system of the optical discs, and cost reduction can be expected. Further, with respect to the light source, research on shortening the wavelength is in progress, and realization of a short wavelength light source and an objective lens with a high NA will enable an encoder with a higher resolution.

Optical tapes have also been recently researched, and if a tape-shaped medium is used as the encoder medium of the present invention, a linear encoder with a large measurement moving distance and high resolution can be realized.

[0056]

As is apparent from the above description, according to the encoder of the first aspect, since the minute focused spot is formed on the mark row, the conventional radial pattern formed on the disk is used. Unlike an encoder in which a parallel light flux is incident on the diffraction grating, there is no influence of the difference in pitch width due to the radial diffraction grating, so that a highly reliable signal without quality deterioration can be obtained. Further, since the encoder of the present invention is almost the same as the optical pickup system of the optical disc, it can be manufactured at low cost. According to the encoder of the second aspect, since the two signals having different phases are obtained, the direction determination signal can be obtained. According to the encoder of claim 3,
Since it is configured to obtain two signals having different phases, it is possible to obtain the direction determination signal. Further, since the elliptical focused spot is used, the beam shaping optical system is unnecessary, and the elliptical emitted light from the semiconductor laser can be focused as it is to obtain two signals having different phases. According to the encoder of the fourth aspect, since the two signals having different phases are obtained, the direction determination signal can be obtained. Further, since each mark row is irradiated as each converging spot, the utilization efficiency of the light from the light source is higher than that in the case of irradiating an elliptical condensing spot. According to the encoder of claim 5, the focus spots are arranged on the two mark rows at an appropriate angle with respect to the mark row direction, and the phase difference signal is detected. May be a straight line perpendicular to the moving direction of the optical system or medium, which simplifies its manufacture. According to the encoder of claim 6, since two converging spots are formed by using two light sources,
The intensity of the focused spot can be increased. According to the encoder of the seventh aspect, since the light flux from the light source is partially given a phase difference to form two converging spots, one light source is sufficient. Further, it is possible to obtain two converging spots that are close to each other. According to the encoder of the eighth aspect, since the mark row is provided on the outer peripheral surface of the cylindrical medium, the rotary encoder can be configured. According to the encoder of the ninth aspect, since the mark row is provided on the surface of the disk-shaped medium, the rotary encoder can be configured. In addition, such a medium can be easily manufactured by an optical disk manufacturing technique.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an optical system of an encoder according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an optical system of an encoder according to another embodiment.

FIG. 3 is an explanatory diagram showing an example of a mark row on a medium and a relationship between the mark row and a focused spot.

FIG. 4 is an explanatory diagram showing another example of the mark row and the relationship between the mark row and the focused spot.

FIG. 5 is an explanatory diagram showing another example of the mark row and the relationship between the mark row and the focused spot.

FIG. 6 is an explanatory diagram showing another example of the mark row and the relationship between the mark row and the focused spot.

FIG. 7 is an explanatory diagram showing another example of the mark row and the relationship between the mark row and the focused spot.

FIG. 8 is an explanatory diagram showing another example of the mark row and the relationship between the mark row and the focused spot.

FIG. 9 is an explanatory diagram showing another example of the mark row and the relationship between the mark row and the focused spot.

FIG. 10 is an explanatory diagram showing an example of a mark row and a relationship between the mark row and a focused spot.

FIG. 11 is an explanatory diagram showing another example of the mark row and the relationship between the mark row and the focused spot.

FIG. 12 is an explanatory diagram showing another example of the mark row and the relationship between the mark row and the focused spot.

FIG. 13 is an explanatory diagram showing an optical system of an encoder that forms two focused spots.

FIG. 14 is an explanatory diagram showing another example of the optical system of the encoder that forms two focused spots.

FIG. 15 is an explanatory diagram showing another example of the optical system of the encoder that forms two focused spots.

FIG. 16 is an explanatory diagram showing another example of the optical system of the encoder that forms two focused spots.

FIG. 17 is an explanatory diagram showing another example of the optical system of the encoder that forms two focused spots.

FIG. 18 is an explanatory diagram showing another example of the optical system of the encoder that forms two focused spots.

FIG. 19 is a schematic perspective view showing an embodiment of a rotary encoder using a cylindrical medium.

FIG. 20 is a schematic perspective view showing another embodiment of a rotary encoder using a cylindrical medium.

FIG. 21 is a schematic perspective view showing an embodiment of a rotary encoder using a disk-shaped medium.

FIG. 22 is a schematic perspective view showing another embodiment of a rotary encoder using a disk-shaped medium.

FIG. 23 is an explanatory diagram showing an optical system of an encoder using a knife edge method for detecting a focusing error and a push-pull method for detecting a tracking error.

FIG. 24 is an explanatory diagram showing an optical system of a conventional encoder.

25 is a partially enlarged view of an optical system of the encoder shown in FIG.

[Explanation of symbols]

1, 1a, 1b Semiconductor laser 2 Collimator lens 3 Beam splitter 4 Objective lens 5,15 Medium 6 Condenser lens 7, 7a to 7d, 106, 107, 108 Photodetector 8 Wavefront conversion element 8a Reflective surface 10, 10a, 10b Transparent flat plate 11, 12 Mark row 21, 22 Mark 31, 32 Focus spot 41 Knife edge 42 Actuator 101 Light source 102, 105 Lens 103 Fixing diffraction grating 104 Moving diffraction grating

Claims (9)

[Claims] 1. A mark row having a fine pitch is provided on a medium, light from a light source is condensed as a condensed spot on the mark row by a condenser lens, and reflected light from the medium or
An encoder that detects the amount of movement of an optical system including the condenser lens or the medium by detecting transmitted light that has passed through the medium. 2. The two converging spots formed by the condensing lens are arranged on the mark row of the medium in parallel with the mark row direction.
The two signals having different phases are obtained by arranging the light beams at appropriate intervals and detecting the reflected light from the medium or the transmitted light transmitted through the medium. Encoder. 3. The medium is provided with two rows of fine pitch marks having phases different from each other, and an elliptical focused spot is focused on the marks with the major axis thereof being perpendicular to the mark row direction. The encoder according to claim 1, wherein two signals having different phases are obtained by detecting reflected light from the medium or transmitted light transmitted through the medium. 4. The medium is provided with two mark rows having fine pitches having mutually different phases, one focused spot on each of the mark rows, and these two focused spots in the mark row direction. 2. The encoder according to claim 1, wherein two signals having different phases are obtained by vertically arranging them and detecting reflected light from the medium or transmitted light transmitted through the medium. 5. The medium is provided with two fine pitch mark rows, one focused spot is provided on each of the mark rows, and these two focused spots are formed at appropriate angles with respect to the mark row direction. The encoder according to claim 1, wherein two signals having different phases are obtained by arranging them in a tilted manner and detecting reflected light from the medium or transmitted light transmitted through the medium. 6. The two light sources are provided, and the light from the light source is condensed by the condenser lens to form two converging spots. The encoder according to item. 7. The light from the light source is processed by an appropriate mechanism to form two light fluxes having a partial phase difference, and these light fluxes are condensed on the mark row by the condenser lens. The encoder according to claim 2, wherein two encoder spots are formed. 8. The encoder according to claim 1, wherein the medium has a cylindrical shape, and the mark rows having the fine pitch are provided on an outer peripheral surface of the medium. 9. The encoder according to claim 1, wherein the medium has a disk shape, and the mark rows with the fine pitch are provided on the disk surface.