JPH05215574A - Optical position detector - Google Patents

Abstract

PURPOSE:To obtain an optical position detector which can be reduced in size in an entire device and can be reduced in cost. CONSTITUTION:A light detecting part 11, a buffer layer 12 and a waveguide layer 13 are integrally formed on an upper face of a semiconductor substrate 10. A collimator lens 14, a chirp grating 15 and a beam splitter 16 are formed on the waveguide layer 13. A laser diode 17 is attached to an end face of the substrate 10 and thus a reading head 18 is constituted. A scale (reference scale) 20 provided relatively movable with respect to the reading head 18 is formed with a highly reflective mask in a pattern of a plurality of parallel lines on a substrate with low reflectance, is attached to a moving body, and is movable in a lengthwise direction according to movement of the moving body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical position detector used in various precision measuring instruments and machine tools which require precise position reading and positioning.

[0002]

2. Description of the Related Art Generally, a conventional optical position detecting device is
As shown in FIG. 11, a scale (reference scale) 3 formed by forming a large number of opaque striped marks 2 at the same pitch on a transparent substrate 1 made of glass or plastic, and this scale 3
A light emitting element 4 for irradiating the light of the light spot S through a lens and a light receiving element 5 for detecting the transmitted light from the scale 3.
And a read head 6 constituted by
In such a device, each time the scale 3 moves in the direction of one pitch arrow (D1, D2 direction) relative to the read head 6, the light receiving element 5 detects a change in the amount of transmitted light from the scale 3. The amount of movement of the scale 3 is detected by converting it into an electric signal.

In the transmission type optical position detecting device as described above, as shown in FIG. 11A, two sets of light emitting elements 4 and two sets of light receiving elements 5 are arranged so as to face each other with the scale 3 interposed therebetween. Has been done. And these two sets of elements 4 and 5 are
As shown in FIG. 11 (B), the two light spots S are set so as to be shifted by a quarter pitch on the scale 3, and the phase relationship between these two light spots S relates to the moving direction of the scale 3. I try to get information.

[0004]

In the above-mentioned transmission type conventional optical position detecting device, two sets of the light emitting element 4 and the light receiving element 5 must be arranged with the scale 3 sandwiched therebetween. There is a physical limit to the miniaturization of the read head 3 and the read head 6, which is an obstacle to the miniaturization of the entire apparatus in which these are incorporated and used.

In order to overcome the drawbacks of the transmission type, a reflection type optical position detecting device in which a light emitting element and a light receiving element are arranged only on one side of the scale is disclosed in, for example, Japanese Utility Model Publication No. 60-279.
Known as No. 26. However, this conventional example is also unsatisfactory because there is a limit to miniaturization due to the distance between the scale and the element, the thickness of the element, and the like. Further, both types of devices require accurate alignment between the two sets of light emitting element and light receiving element. Generally, the position adjustment of the optical members forming the optical system requires a dedicated adjusting machine and a complicated procedure. The cost of the device is increased because of the need for and. Therefore, it is an object of the present invention to provide an optical position detecting device that can be downsized and inexpensive.

[0006]

An optical position detecting device according to the present invention comprises a read head and a scale movable relative to the read head and having a reflective pattern, the read head comprising: A semiconductor laser, a waveguide layer that guides light emitted from the semiconductor laser, a thin-film diffraction grating that focuses the light guided by the waveguide layer on the scale, and reflected light according to a reflection pattern from the scale. Is integrated with a semiconductor light receiving element that receives the light and outputs an electric signal indicating the relative movement of the scale on the same semiconductor substrate.

[0007]

The radiation emitted from the semiconductor laser is guided by the waveguiding layer to the thin film diffraction grating, where it is focused on a scale that moves relative to the read head.
The condensed light is reflected according to the reflection pattern formed on the scale, is received by the semiconductor light receiving element, and is converted into an electric signal indicating relative movement of the scale. By processing this electric signal, it is possible to know the moving distance and / or the moving direction of the scale.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical position detecting device according to an embodiment of the present invention will be described below with reference to the accompanying drawings together with an example of its manufacturing method.

1 to 3 are a perspective view of a completed optical position detecting device, a top view and a sectional view of a read head. In the figure, reference numeral 10 indicates an N-conductivity type semiconductor substrate, for example, a silicon substrate. By selectively diffusing P-conductivity type impurities in a part of the upper surface of the substrate to form a PN junction in the substrate, In the upper surface, a photodetecting section 11 including two semiconductor light receiving elements 11a and 11b adjacent to each other is integrally formed. A buffer layer 12 made of a silicon oxide film is formed on the entire upper surface of the substrate 10 by thermally oxidizing the surface of the substrate. The buffer layer 12 is formed such that the upper surface of the photodetection unit 11 is thinner than the other parts so that the reflected light from the scale propagating in the waveguide layer described later is efficiently incident on the photodetection unit 11. (Fig. 3). A waveguide layer 13 such as a glass layer or a zinc oxide layer is formed on the entire upper surface of the buffer layer 12 by a thin film technique such as sputtering. On the upper surface of the waveguide layer 13, a collimator lens 14 that converts divergent light from a laser diode described later into parallel light, that is, a rectangular beam, and the parallel light is focused on a scale described later located above. The chirp grating 15 and the beam splitter 1 located between the collimator lens 14 and the chirp grating 15.
6 and 6 are formed at a predetermined interval. These collimator lens 14 and chirp grating 15
The beam splitter 16 and the beam splitter 16 apply a resist to the upper surface of the waveguide layer 13, pattern the chirp grating with a predetermined shape by an electron beam, and etch the waveguide layer 13 by reactive ion etching or the like to form a pattern. It is composed of a thin film diffraction element formed by transferring to the waveguide layer 13. A laser diode 17 is attached to one end surface of the semiconductor substrate 10 by an adhesive or the like so as to be aligned with the waveguide layer 13, and thus a read head 18 is constituted. In this case, as shown in FIG.
Two parallel alignment marks 10a are formed at 0 at the same time when the collimator lens 14, the chirp grating 15 and the beam splitter 16 are formed, and the laser diode 17 is attached in accordance with these. , To prevent misalignment between the optical elements.

The chirp grating 15 is shown in FIG.
As shown in FIG. 5, the two pattern portions 15a and 15b are arranged adjacent to each other and in parallel. These pattern portions 15a and 15b are linear patterns having a pitch that gradually becomes finer in the traveling direction of guided light, and are formed so as to deviate from each other in the waveguide direction with the center at Sakai. This pattern is calculated by the following calculation.

When the phase of the wave emitted from the collimator lens 14 is Φc and the phase of the wave emitted from the chirp grating 15 is Φdf, Φc = kNy (1) Φdf = -k [(y −f sin θ) ² + (Fcos θ) ² ] ^1/2 …………… (2). M-th line shape of the chirp grating 15, when the phase shift amount generated when the light wave passes through the chirped grating and Φ _FG, Φ _FG -Φc = 2
Determined by mπ + Const (constant), x = 0, y
If a constant is determined so that m = 0 at = 0,

Ny + [(y−fsin θ) ² + (Fcos θ) ² ] ^1/2 = −mλ + f (3) By arranging the linear patterns at the intervals of y that satisfy the expression (3), a linear light-collecting pattern having a pitch as shown in FIG. 5 is obtained. In the above equation, N is the effective refractive index of the waveguide, k is the wave number (2π / λ), f is the focal length, θ is the exit angle, and m is an integer.

A scale (standard scale) 20 is provided so as to be movable relative to the read head 18 having the above structure.
As shown in FIG. 6, a low-reflectance substrate, that is, a transparent substrate 21 on which a high-reflectance mask 22 is formed as a plurality of parallel straight lines, is attached to a moving object (not shown). , With the movement of this moving object, arrow D in the figure
It is movable in the longitudinal direction indicated by 1 and D2. Such a scale 20 and the read head 18 are shown in FIG.
As shown in, the light is emitted at a predetermined emission angle in the moving direction of the scale 20 so that the light is vertically incident on the scale 20. The scale 20 is not parallel but has an angle corresponding to the emission angle. ing. In this example, the semiconductor substrate 10 of the read head 18 is arranged on the inclined upper surface of the triangular pedestal 29 to obtain an angle corresponding to the emission angle.

In the read head 18 and the scale 20 arranged as shown in FIG. 7, there is a relationship between the scale 20 as shown in FIG. 6 and the two light spots As and Bs from the chirp grating 15. That is, the light beams emitted from the pattern portions 15a and 15b respectively extend on the scale 20 in the width direction of the scale 20 and are displaced from each other in the length direction of the scale 20 by ¼ of the pitch of the mask pattern. The light enters as linear spots As and Bs. Thus, when the scale 20 is moved, the light beam incident on the scale 20 is not reflected toward the chirp grating 15 at the low reflectance region (low reflectance substrate) 21 and is highly reflected. Rate mask 2
Only the reflected light reflected at the position 2 is incident on the chirp grating 15. This incident light is transmitted to the beam splitter 1
The light corresponding to the spot light As is guided to the photodetector 11 via 6 and the light corresponding to the spot light Bs is converted into an electric signal corresponding to each of the semiconductor light receiving element 11a and the light corresponding to the spot light Bs. To be converted. Next, an example of a method of processing the output signal from the photodetection unit 11 will be described with reference to FIGS. 8 and 9.

As shown in FIG. 8, the semiconductor light receiving element 1
1a and 11b respectively include semiconductor light receiving elements 11a and 11b.
The comparators 30a and 30b for shaping the output signal from the digital signal into digital signals as shown in FIG. 9 are connected. The output of one comparator 30a is supplied to the clock terminal of the D-type flip-flop circuit 31, and the output of the other comparator 3a.
The outputs of 0b are connected to the data terminals of the same circuit 31, respectively. As a result, this D-type flip-flop circuit 31
Outputs the lead and lag of the phases of both input signals from the output terminal as a direction determination signal. The output of the other comparator 30b is connected to a counter 32 which counts the number of pulses of the input signal and outputs a product of the counted number and the scale pitch of the scale 20 as a movement amount signal of the scale 20. .

Now, when the scale 20 moves in one direction indicated by the arrow D1, the output signal a1 from one semiconductor light receiving element 11a is output from the other semiconductor light receiving element 11b as shown in FIG. 9 (A). The output signal b1 is input to the D-type flip-flop circuit 31 in a phase advanced by 90 degrees, and the D-type flip-flop circuit 31 outputs a signal indicating one direction indicated by D1. On the other hand, when the scale 20 moves in the other direction indicated by the arrow D2, the semiconductor light receiving element 11a
The output signal a1 is input to the D-type flip-flop circuit 31 with a phase delay of 90 degrees with respect to the output signal b1 from the other semiconductor light receiving element 11b. This flip-flop circuit 31 is indicated by D2. Outputs the signal that detected the other direction. Thus, whether the scale 20 has moved in one direction or the other direction is determined by the output signal of the D-type flip-flop circuit 31. Further, the movement amount of the scale 20 is recognized by the output signal from the counter 32.

The light spot A on the scale 20 is
The widths of s and Bs (distance in the length direction of the scale) depend on the wavelength of the laser beam emitted from the laser diode 17 by λ, and the length of the chirp grating 15 by Ly and the focal length f, respectively. If the half-width is Lw,
Lw is approximately 2λf / Ly, and for example, λ is 0.79
When μm, f is 1 mm, and Ly is 1 mm, Lw is about 1.6 μm, and a sufficiently high resolution can be obtained even when the scale 20 is formed with a very small scale pitch such as 2 μm. It is possible to perform optical position detection with extremely high accuracy.

In the optical position detector of the above embodiment, the collimator lens 14 and the chirp grating 1 are used.
Since the beam splitter 5 and the beam splitter 16 are formed in the same process such as electron beam drawing, mutual positional error is extremely small and can be suppressed to, for example, a submicron order. The alignment of the laser diode 17 with the diffractive element forming these optical elements is performed by using the alignment mark 10a as shown in FIG. 4, which can be simultaneously drawn when the diffractive element is drawn. So get
The alignment between them can be similarly precise. Next, another embodiment will be described with reference to FIG.

The parts that are substantially the same as or similar to those in the above embodiment are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, the chirp grating 15 is provided between the photodetector 11 and the waveguide layer 13 in parallel with the photodetector 11, and the beam splitter is omitted. Then, the scale 20 is arranged parallel to the read head 18 and is moved relatively. Therefore, the reflected light on the scale 20 of the light obliquely emitted from the chirp grating 15 toward the scale 20 is directly received by the photodetection unit 11. In this embodiment, since the light from the chirp grating 15 is obliquely incident on the scale 20, the width of the light spot becomes larger than that in the above embodiment, and the resolution is slightly lowered, but the read head 18 and the scale are reduced. Since 20 can be arranged in parallel, a triangular pedestal 29 or the like for tilting the read head is not required, the overall size can be further reduced, and a beam splitter is not required, so that manufacturing and structure are simplified. Have an effect.

[0020]

In the optical position detecting device according to the present invention, the read head has a waveguide layer for guiding the light emitted from the semiconductor laser and a thin film for focusing the light guided by the waveguide layer on a scale. Since the diffraction grating and the semiconductor light receiving element that receives the reflected light from the scale and outputs the electric signal indicating the relative movement of the scale are arranged and integrated on the same semiconductor substrate, this head is compared to the conventional technology. Therefore, the size can be greatly reduced, and the device can be installed in a device that does not have enough space. Further, since the semiconductor laser, which is a light source, is also integrated on this semiconductor substrate, the position adjustment between the optical elements can be performed accurately at the time of forming these. Therefore, these position adjustments can be performed after the formation. There is no need to do it. For example, these optical elements can be formed with a precision error of submicron order by using a semiconductor device manufacturing technique. Further, since a semiconductor device manufacturing technique such as film formation can be used, there is also an effect that, in the case of mass production, the manufacturing cost can be made much lower than the conventional one.

[Brief description of drawings]

FIG. 1 is a perspective view showing an optical position detection device according to an embodiment of the present invention.

2 is a top view of the read head of the device shown in FIG. 1. FIG.

3 is a cross-sectional view of the read head shown in FIG.

FIG. 4 is a diagram for explaining the mounting of the laser diode on the substrate of the read head. FIG.

FIG. 5 is a plan view of the read grating of the read head.

FIG. 6 is a plan view showing a scale of the optical position detecting device together with an incident light spot.

FIG. 7 is a perspective view showing a state in which the read head is inclined and positioned with respect to the scale.

FIG. 8 is an electric circuit diagram for processing an output signal from the photodetector.

9 is a waveform chart showing an output signal from the comparator of the electric circuit shown in FIG. 8 in correspondence with the moving direction of the scale.

FIG. 10 is a perspective view of an optical position detecting device according to another embodiment, (B) is a top view of a read head, and (C) is a side view.

FIG. 11 shows a conventional optical position detecting device, (A) is a perspective view of the whole, and (B) is a diagram showing a relation between a scale and a light spot.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate, 11 ... Photodetection part, 12 ... Buffer layer, 13 ... Waveguide layer, 14 ... Collimator lens, 15 ... Chirp grating, 16 ... Beam splitter, 17
... laser diode, 18 ... read head, 20 ... scale, 22 ... mask with high reflectance.

Claims (1)

[Claims] 1. An optical position detecting device comprising a read head and a scale movable relative to the head and having a reflection pattern, wherein the read head includes a semiconductor laser and a semiconductor laser. Relative movement of the scale by receiving a waveguiding layer that guides radiated light, a thin film diffraction grating that collects the light guided by the waveguiding layer on the scale, and reflected light according to the reflection pattern from the scale An optical position detecting device characterized in that it is integrated by disposing a semiconductor light receiving element for outputting an electric signal indicating the same on the same semiconductor substrate.