JPH05126604A - Optical position detector and manufacture of scale - Google Patents

Abstract

PURPOSE:To detect the position with high precision by squeezing at least two or more laser beams on a scale formed with periodic diffraction grooves, receiving the reflected rays with two ray detection sections, and processing the sine- wave reception signal having the same cycle as the cycle of the diffraction grooves. CONSTITUTION:The beam from a semiconductor laser 11 is divided into mainly three diffraction beams by a diffraction grating 12, they are made parallel beams by a collimator lens 14 via a half-mirror 13, and they are squeezed on a scale 1 by an objective lens 15. Three laser beams divided by the diffraction grating 12 are squeezed as three laser spots. Reflected beams from the scale 1 are reflected by the half-mirror 13, astigmatism is applied by a cylindrical lens 16, and they are radiated onto a light detection section 17. The radiated reflected beams are focally controlled by the astigmatism method of an optical disk, and the most squeezed portions of the laser spots are automatically radiated on the scale 1. The position signal is detected with the reception quantity of the reflected beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical position detecting device and a manufacturing method thereof.

[0002]

2. Description of the Related Art An optical scale or a laser length measuring device is used for position detection.

In a conventional optical scale, a lamp is used as a light source, a periodic grating is formed on a scale such as glass, the light of the lamp is applied to the scale, and the amount of transmitted light is received by a photodetector. When the relative position between the scale and the light source is changed, the amount of received light changes according to the period of the grating, but the position is detected using the periodic detection signal. The period of the detection signal is about 10 μm like the period of the grating, and the signal can be electrically divided to detect the position with a resolution of about 0.1 μm. However, since the scale is light-transmissive, it is necessary to dispose the scale between the lamp and the photodetector, and the place of use is limited. Further, the positional relationship between the scale and the read head to which the photodetector is attached requires high accuracy.

The laser length measuring device has a reflecting mirror attached to a moving object, interferes the light from the laser with the light reflected from the reflecting mirror, and detects the position from the received light signal. A HeNe laser with a wavelength of 0.633 μm can be used to detect position with a resolution of about 0.01 μm using electrical signal processing, but a complicated interference optical system is required, and a wavelength-stabilized laser is also used for the light source. There must be.

Therefore, in order to enable simple and accurate position detection, a laser is focused on a scale having periodic diffraction grooves, and the position is detected using a signal received by the photodetector of the reflected light. The concept of an optical position detector has been proposed (Tadaoki Yamashita; “Reflection Diffraction Group Position Encoder Using Semiconductor Laser”, Precision Engineering Society, Chugoku / Shikoku area, Kyushu area, Joint lecture, November 1991). 1.6μm pitch, 0.07μm depth, 0.06 width on scale
A reflection diffraction groove of 5 μm is formed, a semiconductor laser having a wavelength of 0.78 μm is stopped by an objective lens, and the reflected light is received by a photodetector. When the scale is moved, the cycle is 1.6μ
Although a received light signal of a sine wave of m is obtained, the signal can be electrically decomposed to detect the position with a smaller resolution. If a focus control method similar to that of an optical head of an optical disk is used, the laser spot can be automatically focused on the scale.
Therefore, the positional relationship between the scale and the photodetector need not be so accurate. Further, since the position can be detected by reflected light, there are various methods for attaching the scale to a moving object, and the range of use is wide.

[0006]

The change in the intensity of the reflected light received by the photodetector when the relative position between the scale and the laser spot changes is due to the effect of diffraction and interference so that the spot center irradiates the center of the diffraction groove of the scale. It is a sine wave having the same period as the period of the diffractive groove, which becomes the minimum when irradiated and the maximum when irradiated in the middle of the groove. When the center of the spot, which is the intermediate position between them, irradiates the vicinity of the end of the diffraction groove, the reflected light intensity changes greatly with a slight change in the relative position, and the received light signal of the sine wave has a steep slope and the electrical High resolution can be obtained by decomposing into. However, at the maximum or minimum value of the sine wave, the change in the amount of received light is small with respect to the change in relative position, and high resolution cannot be obtained. Ie 1
Only by electrically decomposing two periodic sine wave received signals, the resolution differs depending on the relative position. It is necessary to devise to keep the resolution high.

[0007]

At least two or more laser beams are narrowed on a scale having periodic diffraction grooves, and reflected light is received by at least two photodetection sections. Each received light signal is a sine wave having the same period as the period of the diffraction groove of the scale.

Two or more spots are arranged in a direction perpendicular to the groove with a slight offset from each other. For example, the interval of each spot in the direction perpendicular to the groove is set to 1/4 of the groove pitch.

[0009]

[Operation] The received light signals from two or more photodetectors are sine waves. If the arrangement of each spot is such that the interval in the direction perpendicular to the groove is 1/4 of the groove pitch, the received light signals from each spot have different quarter cycle phases, and one sine wave has a steep slope. When you have it, the others are maximum or minimum. In the vicinity of a steep sine wave gradient, a small change in relative position causes a large change in the detection signal. That is, at least one sine wave of two or more detection signals has a steep slope and changes greatly even with a small relative position change. It becomes possible to construct a high position detector.

[0010]

1 is a sectional view of a scale 1 of the present invention.
An uneven groove 2 is formed, and a reflective film 3 of aluminum or gold is formed on the groove 2 and is further protected by a transparent resin layer 4. When the wavelength of the laser used for the measurement is λ, the groove pitch p is about twice the laser wavelength λ. If the refractive index of the transparent resin layer 3 is n, the depth of the groove is about λ / 8.
set to n.

A method of manufacturing this scale is shown in FIG. The groove 1 is formed on the disk 5 in a concentric circle or spiral shape. Since this disk 5 is manufactured in the same manner as the optical disk master, it will be briefly described. Irradiation is performed while rotating the glass plate coated with the photoresist and moving the spot where the argon laser is focused in the radial direction of the glass plate. When developed, the groove 2 having an uneven shape is formed on the glass plate.
After the aluminum or gold reflection film 3 is provided on the master by a sputtering method or the like, a transparent plate such as acrylic or glass is attached with an ultraviolet curable resin sandwiched between them and irradiated with ultraviolet rays to be solidified to form the protective film 4. .. In this method, since the glass master is rotated, a spiral groove is formed. However, if this master is cut into a strip shape elongated in the radial direction as shown in FIG. 2, it can be used as a scale with little influence that the groove is curved with a narrow width.

For example, a measuring laser having a wavelength λ of 0.6
If a semiconductor laser of 8 μm is used, the groove pitch p is 1.36 μm. The refractive index n of the protective layer material such as an ultraviolet curable resin, acryl, or glass is about 1.5, and the depth of the concave-convex groove is 0.057 μm. The width of the groove is about 0.05 μm.

Next, the optical system of the optical head for signal detection will be described with reference to FIG. Since one laser beam can be easily transmitted through the diffraction grating and divided into three beams, the case of using three laser beams will be described in this embodiment as well. Reference numeral 11 denotes a semiconductor laser, the light of which is mainly divided into three diffracted lights by a diffraction grating 12, passes through a half mirror 13, and becomes collimated by a collimator lens 14, respectively, and then focused on a scale by an objective lens 15. .. The beam divided by the diffraction grating is not shown separately in FIG. 3 in order to avoid complication of the drawing. The three laser beams divided by the diffraction grating are 3 as shown in Fig. 4.
The two laser spots 21, 22 and 23 are focused on the scale. The diffraction grating 12 is rotated and adjusted so that the spot distance d across the groove becomes 1/4 of the groove period p.

The reflected light from the scale is reflected by the half mirror 1.
The light is reflected by 3 and is given astigmatism by the cylindrical lens 16 to illuminate it onto the photodetector 17. The state of the reflected light with which the photodetector 17 is irradiated is shown in FIG. 21 ', 2
2'and 23 'are the reflected lights of 21, 22, and 23, respectively. Focus control can be performed using the astigmatism method of the optical disc. That is, the central photodetector is divided into four parts, and if the sum of the received light amounts of 31 and 33 and the sum of the received light amounts of 32 and 34 are controlled to be equal to each other, each laser spot is most narrowed. The part is automatically illuminated on the scale.
The position signal is detected by using the received light amount of each reflected light. The received light signal of 21 'is the sum of 31, 32, 33 and 34, and the received light signals of 22' and 23 'are obtained from 35 and 36 respectively. Be done.

FIG. 6A shows changes in the three received light signals when the three laser spots cross the groove on the scale. FIG. 6B shows a cross section of the groove on the scale. When the center of the laser spot 21 irradiates each position of FIG. 6B, the spot 21,
The light reception signals of 22 and 23 are made to correspond to 41 and 4 respectively.
What is shown as 2, 43 is FIG. Each received light signal is a sine wave, and when the center of the spot 21 is irradiated to the center of the groove, the sum signal 41 of the photodetectors 31, 32, 33, 34 is minimum. At that time, the center of the spot 22 is deviated from the center of the spot 21 in a direction perpendicular to the groove of the scale by a quarter of the pitch of the groove.
The light receiving signal 42 of is a signal having the steepest sine wave.
Similarly, the reflected light of the spot 23 is on the side opposite to the spot 22 and is shifted from the center of the spot 21 in the direction perpendicular to the groove of the scale by a quarter of the groove pitch.
The light reception signal 43 of 1 is a signal having the steepest sine wave whose phase is 180 degrees different from that of the light reception signal 42. A change in the relative position between the scale and the spot is detected by electrically detecting the change in the size of these sine waves. Even if the relative position of the spot 21 changes near the center of the groove, the received light signal 41 does not change so much, but the detection signals 42 and 43 have a large change gradient and accurate position detection is possible. Thus, regardless of the position of the spot on the scale, any of the three detection signals 41, 42, and 43 has a steep slope, and accurate position detection can always be performed.

The positions where the three sine waves have the steepest slope are shifted by a quarter period. Cycle 1.36
If the distance is μm, the distance is 0.34 μm. If the distance is divided into tenths, the position can be detected with a resolution of 0.04 μm or less, and if it can be divided into one-twentieth, the position can be detected with a resolution of 0.02 μm or less. ..

[0017]

In the position detector of the present invention, the laser for measurement has only to have a coherence so that it can be narrowed to the diffraction limit, and a subtle change in wavelength does not affect the measurement. Therefore, the light source may be a general semiconductor laser, and it is not necessary to stabilize the wavelength. Moreover, signals can be detected by a simple optical system similar to the optical head of an optical disc. Further, since the position can be detected by using the reflected light, the method of attaching the scale is diverse and the application range is wide.

As described above, the position detector of the present invention can provide a highly accurate resolution comparable to that of a laser length measuring device with a simple device at low cost and in a wide range of applications.

[Brief description of drawings]

FIG. 1 is a sectional view of a scale of the present invention.

FIG. 2 is an explanatory diagram of a method of manufacturing a scale.

FIG. 3 is an explanatory diagram of a configuration of an optical system for detecting a position signal.

[Fig. 4] Layout of laser spots on the scale

FIG. 5 is a layout diagram of reflected light on a photodetector for position detection.

FIG. 6 is an explanatory diagram of a waveform for position detection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diffraction groove 2 Reflective film 3 Protective film 4 Disc 11 Semiconductor laser 12 Diffraction grating 17 Photodetector 21-23 Laser spot 21'-23 'Reflected light 31-36 Photodetector 41-43 Detection signal

Claims (2)

[Claims] 1. A means for arranging a scale in which periodic reflection diffraction grooves are formed, for squeezing at least two laser beams on the scale, and at least two means for receiving the light reflected by the laser beams from the scale. An optical position detector having a photodetection unit, wherein a laser spot and a scale are moved relative to each other, and a light reception signal of the photodetection unit is used for position detection. 2. A step of forming a concentric or spiral reflection diffraction groove on a disk, a step of forming a transparent protective layer on the groove, and a step of cutting out an elongated shape from the disk in the radial direction of the disk. Characteristic scale manufacturing method.