GB2094974A

GB2094974A - Photoelectric encoder device

Info

Publication number: GB2094974A
Application number: GB8207294A
Authority: GB
Original assignee: Mitutoyo Manufacturing Co Ltd
Current assignee: Mitutoyo Manufacturing Co Ltd
Priority date: 1981-03-12
Filing date: 1982-03-12
Publication date: 1982-09-22
Also published as: GB2094974B; DE3209043A1; DE3209043C2

Abstract

A photoelectric encoder device includes a first optical lattice (10) comprising an array of narrow light- transmitting zones (14a) or light- reflecting zones, and a second optical lattice (12) comprising a semiconductor bed (28), and semiconductor zones (34) having a photoelectric converting function with light-shielding zones (30) therebetween. The photoelectric converting zones (34) and the light- shielding zones (30) are arranged at equally-spaced intervals, and the second lattice (12) is arranged in face- to-face relationship to the first lattice (10). The second optical lattice (12) has a current-collecting layer (36) over substantially all the semiconductor zones (34). The photoelectric converting elements may be photodiodes as shown, phototransistors, or photo-FETs, converting the intensity of the light to electric current. An amorphous semiconductor layer may be used as the bed (28) on the base plate (26). <IMAGE>

Description

SPECIFICATION Photoelectric encoder device This invention relates to photoelectric encoder devices, and more particularly to a photoelectric encoder device which converts the light intensity variation generated by relative movement of a pair of optical lattices to an electric current.

A photoelectric encoder is a device which once converts physical quantity changes into light intensity variations, converts the light intensity variations to an electric current photoelectrically, and outputs the electric current corresponding to such physical quantity changes. Since this device provides an electric current with a contactless action and with little noise, it has widespread application in various fields of measurement.

In the photoelectric encoder there is a device which detects physical quantity changes through relative movement of a pair of optical lattices, and the device of this type is widely utilised for length measuring instruments, photoelectric vernier calipers, dial gauges, and micrometers for example, and for co-ordinate measuring apparatus.

Among the photoelectric encoders, there is the rotary type in which the optical lattices move rotationally and the linear type in which the lattices move rectinlinearly. In this specification reference will be made to the photoelectric encoder devices of the linear type.

In Figure 1 there is shown a known linear-type photoelectric encoder device which can be used to measure the length of an object.

In Figure 1 the optical lattices are formed from base plates 14 and 16 made of glass on which are laid layers of metal by vapour deposition, these layers being etched to produce lighttransmitting zones 1 4a and 1 6a. The first base plate 14 and the second base plate 16 are arranged facing each other. A light emitter 18 is installed on one side of one plate, and a light receiver 20 is installed on the far side of the other plate. In order to obtain parallel rays and converging rays, collimating lenses 22 and 24 are provided and comprise a main portion of the measuring instruments. The light-shielding zones are marked as 1 4b and 1 6b.

According to the conventional length measuring instruments, the light from the light emitter 18 reaches the light receiver 20 through the lens 22, the first base plate 14, the second base plate 16 and the lens 24.

Accordingly, the size of the device, from the light emitted 18 to the light received 20, which directly affects the size of the length measuring instrument, is physically determined by the six elements of the device, i.e. light emitter 18, lens 22, first base plate 14, second base plate 16, lens 24 and light receiver 20, and by the distances between the six elements. In order to miniaturise the instrument, some elements must be omitted, and/or the relative distances between the elements must be reduced, or the six elements must themselves be made smaller.

The light from the emitter 18 must nevertheless go through two optical lattices.

Because of this the light reaching the light receiver 20 includes complex diffracted light which gets mixed on the way and is attenuated by reflection and refraction at the surfaces of the glass and by absorption within the glass.

Therefore, the measured electric current includes noise, and the amount of light received becomes small in comparison with the amount of light emitted. Although the electric circuits, not illustrated, following the light receiver 20 widely use CMOS and their electric current consumption is remarkably low, the electric current consumption of the instruments is so large in the light-emitting section that the total electric current consumption is not reduced much, and a large power supply is still required. Actually, in the conventional device, the electric power source is used for emitting light to about 70 to 80 percent.

As mentioned above, the prior art device shows low efficiency in its light receiving capability. In order to compensate for such low efficiency, the amount of light emitted must be increased, with the result that the electric current consumption becomes higher.

Furthermore, the large built-in power source needed to support the high electric current consumption makes the length measuring instrument large in size.

Accordingly, it is a general object of the present invention to provide a photoelectric encoder device which can solve these problems of the prior art devices and which can be operated with low electric current consumption.

Specifically, it is an object of the present invention to omit some elements, improve the light receiving efficiency and further improve the accuracy.

In accordance with the present invention, this is accomplished with a photoelectric encoder device having a pair of optical lattices which are capable of relative movement and which provide a measure of the amount of relative movement by detecting variations in the light which penetrates through or is reflected from one optical lattice and reaches the other optical lattice, wherein the first optical lattice has an array of narrow lighttransmitting zones or light-reflecting zones, and the second optical lattice includes semiconductor zones having a photoelectric converting function, in which said photoelectric conversion zones are arranged at a fixed pitch with optically opaque areas therebetween, and with said second optical lattice in face-to-face relationship to said first optical lattice.

These and otherfeatures of the present invention will become more apparent by reference to the following description taken in conjuction with the accompanying drawings, wherein like reference numerals denote like elements, and in which: Figure 1 is an illustration of a prior art photoelectric encoder device; Figure 2 is an illustration showing a first embodiment of photoelectric encoder device in accordance with the present invention:: Figure 3 is a partially schematic plan view of the second optical lattice of the encoder device in accordance with the present invention; Figure 4 is a sectional view taken on line IV IV of the second optical lattice in Figure 2; Figure 5 is a waveform chart of the output current of the first embodiment of encoder device; Figure 6 is an illustration showing another example of the second optical lattice; Figure 7 is an equivalent circuit diagram for the second optical lattice of Figure 6; Figure 8 is an illustration showing a manufacturing process for the second optical lattice in the first embodiment of encoder device; Figure 9 is an illustration showing a second embodiment of the present invention Figure 10 is an illustration showing a third embodiment of the present invention;; Figure 11 is an illustration showing a fourth embodiment of photoelectric encoder device in accordance with the present invention; Figure 12 is a partially schematic plan view of the second optical lattice of the fourth embodiment of encoder device; Figure 13 is a sectional view taken on line Xlll-Xlll of the second optical lattice of Figure 12; Figure 14 is an illustration showing a manufacturing process for the second optical lattice of the fourth embodiment of encoder device; Figure 15 is an illustration showing a fifth embodiment in accordance with the present invention; Figure 16 is an illustration showing a sixth embodiment in accordance with the present invention; Figure 17 is a partially schematic plan view of the second optical lattice of the sixth embodiment of encoder device;; Figure 18 is a sectional view taken on line XVlll-XVlll of the second optical lattice of Figure 17; Figure 19 is an illustration showing one example of a manufacturing method for the second optical lattice of the sixth embodiment of encoder device; and, Figure 20 is an illustration showing one example of a manufacturing method for the second optical lattice having an amorphous semiconductor layer.

Referring more particularly to the drawings, Figure 2 shows the first embodiment of encoder device in accordance with the present invention.

This embodiment does not require the collimating lens 24 or the light receiver 20 of the prior art device of Figure 1, and the optical lattice itself is characterised by having a photoelectric conversion function.

Figure 3 shows the upper surface of the second optical lattice 12 in Figure 2 and Figure 4 shows a section taken on line lV-lV in Figure 3.

The second optical lattice 12 arranged facing the first optical lattice 10 fixed to the base plate of the measuring instrument is arranged to move in conjuction with a probe which can move in accordance with the quantity to be measured. In the present invention, the light intensity variation resulting from the relative movement of the two optical lattices is converted into an electric current by an array of photodiodes formed on the second optical lattice 12 itself, so that the current can be detected without reduction of the amount of light and with extremely high efficiency. The photodiode array in this embodiment can be manufactured by the process described hereinafter.

An oxidized film 30 (SiO2) is formed on the upper surface of an N-type semiconductor bed 28, and an array of narrow rectangular slots 32 is made in the film 30 with the slots side by side along the length of the second optical lattice 12 and with the longer sides of the slots 32 at rightangles to the longer sides of the second optical lattice 12. Beneath the slots 32 P-type semiconductor zones 34 are diffusingly formed in the upper surface of the semiconductor bed 28.

Accordingly, the P-N junctions between the Ptype semiconductor zones 34 and the N-type semiconductor bed 28 constitute a photodiode group of narrow rectangular light-receiving zones arranged in a parallel array along the length of the optical lattice 12 at a predetermined pitch as shown in Figure 3. Furthermore, the semiconductor bed 28 is glued and fixed to the base plate 26 which is made of glass, stainless steel, etc., in order to increase the mechanical strength.

As mentioned above, in this embodiment the photo-electric conversion is performed by the photodiodes spaced along the semiconductor bed 28 at a predetermined pitch, and the collimating lens 24 and the light receiver 20 are not required and can be omitted. In this embodiment, the semiconductor bed 28 and the narrow zonal slots 32 prepared in the oxidized film 30 correspond to the light shielding portion 16b and the lighttransmitting portion 16a shown in Figure 1.

At the respective P-N junctions of the second optical lattice 12, each of the P-N junctions has a long, narrow shape with its longer axis across the width of the second optical lattice 12 to enlarge the light-receiving area so that the light through the first optical lattice 10 can be converted into electric current with high efficiency.

Furthermore, in order to increase the accuracy of the measured values each of the P-N junctions is only a few microns in width.

In this embodiment, the electric current obtained from each P-N junction of the second optical lattice 12 as described above is led out as described hereinafter.

In Figures 3 and 4, a current collecting layer 36 is formed so as to cover the oxidized film 30 and the P-type semiconductor zones 34, in other words, to cover all over the upper side of the optical lattice 12. The electric charge appears between the current collecting layer 36 and the semiconductor bed 28.

The current collecting layer 36 consists of a conductive material such as oxidized iridium, oxidized tin or the like through which infra-red rays penetrate. The electric current led out from the current collecting layer 36 is supplied to the following circuits by way of an electrode prepared at the end portion of the current collecting layer 36. Similarly, one side of the semi-conductor bed 28 has the other electrode attached thereto and connected to the following circuits.

The infra-red rays which reach the current collecting layer 36 and the infra-red rays which reach the oxidized film 30 are prevented from reflection at these two surface areas since the materials of the current collecting layer 36 and the oxidized film 30 have large refractive indexes.

Because of this, penetration of the infra-red rays is increased at these two surface areas and the photo-electric conversion efficiency rises. The infra-red rays which reach the current collecting layer 36 are thus introduced into the P-N junctions with high efficiency through the semiconductor zones 34.

Furthermore, the current collecting layer 36 also acts as a protective film protecting the P-N junctions from the influence of the open air by isolating the P-type semiconductor zones 34 from the open air.

The preferred embodiment of the present invention is composed as described above, and its manner of functioning will be described hereinafter.

The infra-red rays from the light emitter 18 irradiate the optical lattice 12 after the infra-red rays have been made parallel by the collimating lens 22. At this time, the infra-red rays irradiate the optical lattice 12 with little decrease in light intensity since the infra-red rays do not go through the second collimating lens 24 and the second optical lattice 12 as in the prior art device shown in Figure 1.

The infra-red rays which reach the optical lattice 12 pass through the current collecting layer 36 without reflection to reach each of the P-N junctions, and the generation of electronelectron hole pairs at each of the P-N junctions creates a photoelectric e.m.f. between the semiconductor bed 28 and the semiconductor zones 34. This photoelectric e.m.f. produces a net voltage corresponding to the amount of light received at the P-N junctions and a photoelectric current flows from the electrode of the P-type semiconductor zones 34 to the electrode of the N-type semiconductor bed 28 in proportion to the intensity of the infra-red rays.

When the probe moves and the second optical lattice 12 likewise moves relative to the first optical lattice, the amount of light passing through the light-transmitting portion 14a of the first optical lattice and entering each of the P-N junctions in the second optical lattice 12 changes, and the electric current output from the electrode of the current collecting layer 36 to the following circuits is in proportion to the amount of light received by the P-N junctions. The electric current obtained as mentioned above is shown in Figure 5. It will be seen that the electric current is a sinusoidal waveform in accordance with the amount of movement of the slots.

As described above, according to the present invention, since the light passes through only one optical lattice, the light-receiving efficiency is increased and the current consumption for light emission is decreased. Furthermore, the light refraction is decreased, and measured signals with little noise can be obtained. Consequently, according to the present invention, a photoelectric encoder device with low electrical consumption and substantially without error in the measured values can be obtained. The device can also be very small in size since the second light-receiving collimating lens and the light receiver of the prior art devices are not required.

Furthermore, according to this embodiment, there is little phase difference between the two electrodes respectively connected to the semiconductor bed and to the current collecting layer, or among the photoelectric e.m.f.s distributed within each of the photodiodes since the current collecting layer is formed in order to connect almost all of the semiconductor zones of the second optical lattice.

For example, if the second optical lattice was to have an electrode structure as shown in Figure 6, then the phase difference becomes large among the photoelectric e.m.f.s of the respective photodiodes which appear at the output end of the second optical lattice.

In other words, in the second lattice 12 shown in Figure 6 the semiconductor layer 34 formed on the semiconductor bed 28 has the configuration of a comb with a top layer and projecting teeth.

On the top of the semiconductor layer 34 the current collecting plate 38 is formed along the lenght of the second optical lattice 12 by means of vapour deposition, etc. The output of the second optical lattice 12 can be obtained between an electrode connected to the current collecting plate 38 and an electrode prepared at the side of the semiconductor bed 28. The output current is led out through terminals 40 and 42.

In Figure 6 the width of the tooth-shaped semi conductor zones 34a, 34b, - - - is denoted by W and their length by L. The width W must be extremely small, i.e. a few microns, in order to achieve accuracy of measurement, and the length L must be extremely long in comparison with the width W in order to achieve sensitivity of measurement. Accordingly, when the electric current flows along the resistors having a large LAW ratio towards the longer side, the resistance values of the semiconductor zones 34a, 34b, 34e - - - become large, reaching a few kilohms in the actual device.

In Figure 7 there is shown an equivalent circuit for the second optical lattice 12 of Figure 6. This circuit is a CR ladder network consisting of R1, - - - Rk, -- - Rn, andC1,---Ck,---Cn. R1,---Rk, - - - Rn represent the resistances of the respective semiconductor zones 34a, 34b, 34c - - - while C1, - - - Ck, - - - Cn show the capacitances existing between the respective semiconductor zones 34a, 34b, - - - and the semiconductor bed 28.

As mentioned above, the frequency of the electric current output from the terminals 40 and 42 becomes high and it becomes impossible to measure due to the RC filter effect at the respective P-N junctions, in the case of an electrode structure as shown in Figure 6, since each of the resistors R1, - - - Rk, - - - Rn in Figure 7 has a large resistance value and the relative speed between the first optical lattice 10 and the second optical lattice 12 becomes higher.

On the other hand, as distinct from the second optical lattice 12 shown in Figure 6, in the second optical lattice in accordance with the present invention the value of the respective resistors R1, - - - Rk, - - - Rn in Figure 7 is disregarded since the current collecting layer is formed over almost all of the respective semiconductor zones.

Accordingly, the photoelectric encoder device in accordance with the present invention has the advantage that the relative speed of movement of the two optical lattices can be increased and prompt measurement can be performed.

Furthermore, already developed semiconductor manufacturing techniques make it easy to manufacture the second optical lattice of the present invention, and to increase the accuracy of the device.

In Figure 8 there is illustrated a manufacturing process for the optical lattice 12 of Figures 2, 3 and 4. As shown in Figure 8 (A), the thin oxidized film 30 (SiO2) is first formed on the N-type semiconductor bed 28, and the slots 32 are then formed by a photo-etching method as shown in Figure 8(B). When diffusion of the P-type impurities is performed at high ternperature, the diffusion advances to the portions of the N-type semiconductor bed 28 just below the slots 32, and the selective diffusion is performed as shown in Figure 8 (C) to form the semiconductor zones 34. The depth of the semiconductor zones 34 is a few microns. Then, as shown in Figure 8 (D), the light-transmitting conductive material is formed all over the upper surface to produce the current collecting layer 36.On one side of the N-type semiconductor bed 28 one electrode is attached, and the end portion of the current collecting layer 36 is fitted with the other electrode.

As mentioned above, the optical lattice 12 can be manufactured easily, and, since the respective semiconductor zones 34 can be formed at predetermined positions, with predetermined shape and size, measured values can be obtained with a high accuracy.

In the following, a second preferred embodiment will be described with reference to Figure 9.

Figure 9 shows the second optical lattice in which elements corresponding to those in the previous Figures are denoted by like reference numerals. In this embodiment, N-type semiconductor zones 44 are formed on the P-type semiconductor zones 34 to create phototransistors, as compared to the embodiment of Figure 1 which shows photodiodes. The N-type semiconductor zones 44 can easily be formed by the selective diffusion technique mentioned with reference to Figure 8.

In this embodiment, the second optical lattice 12 comprises transistors having an amplifying action and highly sensitive light reception can be achieved.

A third preferred embodiment will now be described with reference to Figure 10. Elements corresponding to those in previous Figures are denoted by like reference numerals.

In this embodiment, the light emitted Dy tne emitter 18 towards the semiconductor zones 34 reaches the second optical lattice 12 after reflection from the first optical lattice 10. In this embodiment the light emitter 18 and the collimating lens 22 are held at a predetermined angle relative to the first optical lattice 10, and the base 14 of the first control optical lattice 10 must be made of a material which will reflect the light, i.e. stainless steel for example. On the base 14 there are narrow light-absorbing zones 46.

In this third embodiment the light-reflecting portions and the light-opaque portions are formed by the base 14 and by the light absorbers 46 respectively, and light emitted by the emitter reaches the second optical lattice 12 by passing through the collimating lens 22 and being reflected from the reflecting regions of the first optical lattice 10.

This embodiment of device has the same characteristics as the first embodiment described previously.

In Figures 11,12 and 13 there is shown a fourth embodiment. In this embodiment, the Ntype semiconductor bed 28 is attached to the base plate 26, and a P-type semiconductor layer 50 is formed on the semiconductor bed 28. A P-N junction is formed over almost all the base plate 26 by the semiconductor layer 50 and the semiconductor bed 28, and this P-N junction is used to form photodiodes which convert the light passing through the first optical lattice 10 into electrical signals. The output from the photodiodes is led out by way of electrodes attached to the end portion of the semi conductor bed 28 and to the semiconductor layer 50 respectively.

On the semiconductor layer 50 is deposited a light transmitting insulating layer 52 made of oxidized silicon, so as to cover the upper surface of the semiconductor layer 50 and prevent the P-N junctions from the deterior tion due to ageing.

In this embodiment, on the upper surface of the insulating layer 52 are formed opaque films 54 arranged as narrow zones in such a way that the width of the film extends parallel to the longer side of the optical lattice 12 and the longer sides of each film zone extend parallel to the width direction of the optical lattice 12.These narrow opaque film zones 54 correspond to the light shielding portions 16b of the prior art device shown in Figure 1, and are of a material which does not permit passage of the light from the first optical lattice 10, in other words, any of or a combination of the following materials, namely Cr, Al, Ti, Mo, W, Ni, Ta, Au, etc. Over. the opaque film zones 54 and the insulating layer 52, or on the extreme outside of the second optical lattice, in order to provide a flat surface, there is laid a light-transmitting film 56 made of silicon which permits passage of the light from the first optical lattice 10 with high refractive index.

The light emitter 18 is an infra-red radiation emitting diode. This is because the light emitting diode is the most efficient in the near-infra-red region and is therefore preferable to reduce the current consumption. The infra-red radiation from the emitter 18 reaches the P-N junctions without reflection with high efficiency by way of the lighttransmitting film 56, the insulating layer 52 and the semiconductor layer 50.

As mentioned above, with this second optical lattice 12, measurement can be performed with high efficiency and with high accuracy, since the P-N junctions are formed almost all over the base plate 26 to convert the light from the first optical lattice 10 into electrical signals, and the narrow opaque film zones 54 are arranged in an array over the P-N junctions so that the relative movement of the two optical lattices 10 and 12 will provide light intensity variations.

In order to enable the light from the first optical lattice 10 to pass to the P-N junctions it is preferable to make the semiconductor layer 50 extremely thin, normally a few microns in thickness.

The width W of each opaque film zone 54 is required to be small in order to increase the measuring accuracy of the device. The length L is determined in comparison with the width W in order to obtain adequate sensitivity by increasing the amount of light received at the P-N junctions.

In ordinary cases, the width W is a few microns and the length L is a few millimetres.

The manner of operation of this embodiment will now be described.

The infra-red rays from the light emitter 18 are produced as parallel rays by the collimating lens 22 and are directed to the optical lattice 12. Since the infra-red rays do not pass through the collimating lens 24 and the second optical lattice 12 as in the prior art device shown in Figure 1, the infra-red rays reach the optical lattice 12 in a less attenuated and a less diffracted state. Since the light-permeable film 56 is flat on its surface and has a high refractive index, the infra-red rays pass to the second optical lattice 12 without reflection and with high efficiency.

The infra-red rays reaching the second optical lattice 12 are partly shielded by the opaque film zones 54. The infra-red rays which do reach the P-N junctions of the second lattice 12 generate a photoelectric e.m.f. This photoelectric e.m.f.

produces a voltage in accordance with the amount of light received at the P-N junctions, and an electric current in proportion to the intensity of the infra-red rays flows from the electrode of the P-type semiconductor 50 to the electrode of the N-type semiconductor bed 28.

When the probe is moved through the distance to be measured, the two optical lattices 10 and 12 are relatively moved, and the light shielding portions 1 4b of the first optical lattice 10 and the opaque film zones 54 of the second optical lattice 12 change the amount of light reaching the P-N junctions of the second optical lattice 12 so that the light intensity various in dependence on the amount of relative movement of the optical lattices 10 and 12. The light intensity variation is converted into the electric current corresponding to the measured value of the P-N junctions of the second lattice 12 and is led out to the outside by way of the electrodes.

According to this embodiment, the electric current obtained at the P-N junctions is led out to the outside without any problem and with high efficiency since the P-N junctions are formed over almost all the base plate 26.

In other words, with the second optical lattice of this embodiment, the resistors corresponding to the respective resistors R1, - - - Rk,---Rn shown in Fiugre 7 can be disregarded, since the P-N junctions are formed over almost all the base plate 26, and the photoelectric encoder of this embodiment has the advantage that the speed of relative movement can be considerably increased and a prompt measurement can be performed.

Furthermore, already developed semiconductor manufacturing techniques make is easy to create the second optical lattice and to increase the accuracy of the device.

Figure 14 illustrates the manufacturing process for the optical lattice 12 of the fourth embodiment. On the N-type semiconductor bed 28 shown in Figure 14(A) the P-type semiconductor layer 50 (a few microns thick) is formed by diffusion of the P-type impurities at high temperature, as shown in Figure 14 (B).

Consequently, P-N junctions are formed almost all over the base plate 26 by the semiconductor bed 28 and the semiconductor layer 50.

Next, the oxidized film protecting the P-N junctions against ageing is formed on the semiconductor layer 50 as the insulating layer 52, as shown in Figure 14 (C). Then, the opaque film 58 of Al, Ti, Mo, W, Ni, Ta, etc., is laid down as shown in Figure 14 (D). Next, as shown in Figure 14 (E), the narrow opaque film zones 54 are formed by a vapoour deposition method, a photoetching method, or the like. Consequently, the opaque film zones 54 corresponding to the lightshielding portions 16b of Figure 1 are arranged in an array above the P-N junctions. Lastly, the lightpermeable film 56 is formed by a vapour deposition method or the like. The electrodes are placed on the semiconductor bed 28 and on the semiconductor layer 50, and the second optical lattice is completed by being attached on to the glass base plate 26 as shown in Figures 12 and 13.

As mentioned above, the optical lattice 12 can be manufactured easily. Since the opaque film zones 54 are formed at predetermined positions, and with an accurately defined shape and size, measurements can be performed with high accuracy.

A fifth preferred embodiment will now be described with reference to Figure 15. In this embodiment an N-type semiconductor layer 60 is formed on the P-type semiconductor layer 50 and phototransistors are created, as compared with the fourth embodiment which comprises photodiodes. This N-type semiconductor layer 60 is easily formed by the selective diffusion techniques described with reference to Figure 14.

The insulating layer is omitted.

In this embodiment, the second optical lattice 12 can receive the light with high sensitivity since it comprises transistors having an amplifying action.

Figures 16, 17 and 18 illustrate a sixth preferred embodiment. In this embodiment a plurality of photo-FETs are created in the second lattice to convert the light from the first optical lattice into electrical signals and the electric current is led out with extreme sensitivity.

In Figures 17 and 18, on the base plate 26, which is made of glass for mechanical strength of the second optical lattice 12, the N-type semiconductor bed 28 is glued to form the basis for the photo-FETs mentioned above. On the Ntype semiconductor bed 28 is formed an oxidized film 64 of SiO2. This has narrow rectangular slots 62 arranged with their longer sides parallel to the width direction of the second optical lattice 12 and arranged at a predetermined pitch along the length of the second optical lattice 12. P-type semiconductor zones 66 are diffusingly formed in the N-type semiconductor bed 28 below the slots 62 in the oxidized film 64.In the respective photo-FETs of this embodiment a channel portion 68 is formed in that portion of the N-type semiconductor bed 28 in the vicinity of the interface between the adjacent P-type semiconductor zones 66 and the oxidized film 64, and the upper surface of the second optical lattice 12 over the channel portion 68 forms the lighttransmitting gate portion 70. In other words, in this embodiment, enhancement type photo-FETs of P-channel are arranged in an array along the length of the second optical lattice 12 at a predetermined pitch.

In Figure 17, above the respective P-type semiconductor layers 66, are shown alternately formed drain electrode zones 72 and source electrode zones 74 which are made of lightpermeable material so that the drain current can be supplied to the subsequent circuits. Each of the drain electrode zones 72 and source electrode zones 74 is respectively connected to a drain lead plate 76 and a source lead plate 78, each consisting of a metal plate, with the two plates arranged on opposite sides of the the surface of the oxidized film 64 along its length dimension. The drail lead plate 76 and the source lead plate 78 are connected to the external circuitry. The output currents of the respective photo-FETs are connected in parallel to the external circuitry.

The surface of the second optical lattice 12 is formed by a second oxidized film 80 of SiO2 and of high refractive index. This oxidized film 80 protects the photo-FETs from the influence of the ambient air by isolating the photo-FETs from the air, as well as preventing reflection at the surface of the second optical lattice 1 2.

The light emitter 18 is an infra-red light emitting diode, and can reduce the electric current consumption at the light emitter 18 since it emits with low electric current with high efficiency.

The manner of operation of this sixth preferred embodiment of the present invention will now be described.

The infra-red rays emitted by the emitter 18 are made parallel by the collimating lens 22 and reach the second optical lattice 12 by way of the first optical lattice 10. The infra-red rays reach the second optical lattice 12 in a less attenuated and less diffracted state, since the rays do not have to pass through the collimated lens 24 and the second optical lattice 12 as described in the prior art device shown in Figure 1.

In this embodiment, the light which reaches the second lattice 12 is converted into electric current by the photo-FET group with high sensitivity. The channel portion 68 of the second optical lattice 12 is an extremely thin channel layer when the light is not irradiating it and is put in such a state that the drain current does not flow. When the light is present at the light gate portion 70, the drain current starts flowing. In other words, when the light irradiates the light gate portion 70, since the channel layer increases its depth in accordance with the amount of light, the carrier conductivity is increased between the gate and the source, and the drain current flows in the channel portion 68 in accordance with the amount of light irradiating the light receiving gate 70.In this embodiment, the photo-FETs having an amplifying action can perform the photoelectric conversion and produce electric current with high sensitivity.

The electric current obtained from the respective photo-FETs is supplied to the external circuitry by way of the drain electrode zones 72 and the source electrode zones 74.

The light passing through the first optical lattice 10 irradiates the N-type semiconductor bed 28, the semiconductor zones 66, the oxidized films 64 and 80, and the electrode zones 72 and 74 with little loss and the photo-electric converting action can be maintained with high efficiency When the first optical lattice 10 and the second cptical lattice 12 move relatively and the amount of light varies at the light receiving gate portion 70, the drain current changes in accordance with such variations to supply the electric current to the external circuitry in accordance with the amount of relative movement of the two optical lattices 10 and 12, whereby the length is measured.

Furthermore, in this embodiment, the photoelectric conversion by means of the photo FET group having an amplifying action and present in the second optical lattice 12 produces electric current with high sensitivity.

The manufacturing process for the second optical lattice 12 in the sixth embodiment will now be described.

Figure 19 shows the manufacturing process for the second optical lattice 12. On the N-type semiconductor bed 28 shown in Figure 19 (A) the oxidized film 64 is laid by vapour deposition as shown in Figure 19 (B), and the narrow slots 62 are formed through the oxidized film so that the slots are arranged with their longer sides parallel to the width direction of the second optical lattice 12 as shown in Figure 19 (C). Then, as shown in Figure 1 9#(D), the selective diffusion is performed to form the P-type semiconductor zones 66., and the light-permeable conductive material is formed on the respective semiconductor zones 66 as the drain electrode zones 72 and the source electrode zones 74 as shown in Figure 19 (E).Then, the semiconductor bed 28 is glued on to the base plate 26 which is made of glass, and on the upper surface of the second optical lattice 12 are formed the lead plates 76 and 78 (not illustrated) for the drain and the source. Lastly, the oxidized film 80 is formed over the surface of the second optical lattice 12.

The description given above applied for the case where the enhancement type photo-FET group is created in the second optical lattice 12, but it is sufficient in the present invention that the photo-FETs having the narrow photoelectric conversion area are provided in the second optical lattice 12. For example, a depression type photo FET can be formed by changing the semiconductor bed 28 corresponding to the channel portion 68 in Figure 18 to a P-type bed.

In the previously described embodiments the semiconductor zones in the second optical lattice are formed by crystalloid semiconductor material, but it is possible that the semiconductor bed of the photodiode group arranged as an array in the second optical lattice could be formed by an amorphous semiconductor material, in which case the second optical lattice can be obtained with ease and accuracy in a length suitable for long length measurement. It is impossible to obtain such a size and shape for the second optical lattice from the wafer of the conventional crystalloid semiconductor material.

For example, in the first embodiment of Figure 2, on the upper surface of the base plate 26 which maintains the mechanical strength of the second optical lattice 12 the amorphous N-type semiconductor layer 28 is formed continuously over almost all the surface of the base plate 26 without connection to constitute the semiconductor bed of the photodiode group mentioned above.

An amorphous semiconductor is a semiconductor in which two or three kinds of elements are combined in a proper mixing ratio in the amorphous state, and is distinguished from the general crystalloid semiconductor.

In Figure 20 there is shown one example of a manufacturing method for the semiconductor layer 128 in the above-mentioned embodiment.

The amorphous semiconductor layer 128 is formed on the surface of the base plate 126 by means of plasma deposition. In other words, the base plate 126 of glass, stainless steel, etc., is introduced into a high frequency induction reactor, and the N-type amorphous semiconductor layer 128 of about one micron thick silicon is continuously and solidly formed on and with the base plate 126 by SiH4+H2 including an extremely small amount of boron in the plasma state at very high temperature.

Furthermore, the acceptor of boron ion (B+), etc., is selectively instilled into the semiconductor layer 128 at a comparatively low temperature, and the semiconductor zones of N-type and Ptype mentioned above can be formed after laser annealing.

As described above, the P-N junctions performing the photoelectric conversion can be formed at predetermined positions, with given sizes and shapes, by the well known semiconductor manufacturing methods.

It is a characteristic that the amorphous semiconductor can be utilised as the semiconductor bed of the P-N junctions in this embodiment. Since the semiconductor bed can be continuously and solidly formed on and with the baseplate without connection, the device can be operated with high accuracy, and manufactured with ease when the device required a long light-receiving portion. Also, the device can be produced with less expense.

Contrary to the above-mentioned, when a long light-receiving portion for the second optical lattice must be manufactured, and a crystalloid semiconductor is utilised for the photoelectric conversion semiconductor bed, the wafter is cut out of semiconductor crystal, the semiconductor bed is produced after the wafer is cut to a predetermined size, the narrow P-N junctions for the photoelectric conversion are formed in an array on the semiconductor bed, and glued on the base plate of the second optical lattice to make the second optical lattice. In this case, since the crystalloid semiconductor itself is not only expensive but also the manufacturing process increases and it is difficult accurately to determined the pitch of the P-N junctions at the connecting portion of the respective semiconductor bed, there are such drawbacks that it is hard for the device to be produced and the device cannot be obtained with high accuracy.

In this embodment, since the semiconductor bed is made of the amorphous semiconductor,and can be continuously and solidly obtained on and with the base plate without connection, the second optical lattice can not only be manufactured with ease but also the measuring accuracy can be increased and the device can be manufactured at relatively low cost.

Claims

1. A photoelectric encoder device comprising a pair of optical lattices which are capable of relative movement and which provide a measure of the amount of relative movement by detecting variations in the light which penetrates through or is reflected from one optical lattice and reaches the other optical lattice, wherein the first optical lattice has an array of narrow light-transmitting zones or light-reflecting zones, and the second optical lattice includes semiconductor zones having a photoelectric converting function, in which said photoelectric conversion zones are arranged at a fixed pitch with optically opaque areas therebetween, and with said second optical lattice in face-to-face relationship to said first optical lattice.

2. A photoelectric encoder device according to claim 1, wherein said second optical lattice comprises a semiconductor bed provided with narrow semiconductor zones of conductive type opposite to that of said semiconductor bed and arranged in an array at a fixed pitch spacing.

3. A photoelectric encoder device according to claim 1 or 2, wherein a current collecting layer of light-permeable conductive material is formed over substantially all the semiconductor zones of said second optical lattice.

4. A photoelectric encoder device according to claim 1, wherein the second optical lattice comprises P-N junctions over substantially all of a base plate, said junctions converting the light passing through said first optical lattice into electric current, and narrow opaque film zones arranged in an array over the P-N junctions.

5. A photoelectric encoder device according to claim 1, wherein said second optical lattice comprises a semiconductor bed, a plurality of narrow semiconductor zones on said bed and of conductive type opposite to that of said semiconductor bed and arranged at a predetermined spacing, the portions of the semiconductor bed surface between the respective semiconductor zones constituting channel portions, the surface of said channel portions serving as light-receiving gates for photo-FETs, and the photo-FETs converting the intensity variations of the light from said first optical lattice into electric current.

6. A photoelectric encoder device according to claim 1, wherein said second optical lattice comprises an amorphous semiconductor layer formed on a base plate, and narrow P-N junction zones to convert the light passing through said first optical lattice into electric current formed a fixed pitch on the amorphous semiconductor layer.

7. A photoelectric encoder device substantially as hereinbefore described with reference to Figs 2 to 5 and 8, Fig. 9, Fig. 10, Figs. 11 to 14, Fig. 15, Figs. 1 6 to 19 or Fig. 20, of the accompanying drawings.