JPH03115920A - Zero-point position detector - Google Patents

Abstract

PURPOSE:To constitute the device of a simple optical system and to reduce the size by splitting luminous flux into 1st and 2nd parts through the ridge line of a prism means, and directing the 1st luminous flux and 2nd luminous flux to a 1st and a 2nd photoelectric converting means through the prism means. CONSTITUTION:An irradiating means is equipped with the prism means 4 which has 1st and 2nd refracting surfaces 42 and 43 separated along the specific ridge line 41. The irradiating means splits the luminous flux from ja light source 1 into the 1st and 2nd parts by the ridge line 41 of the prism means 4, the 1st part is refracted by the 1st refracting surface 42 and made incident slantingly on a scale as the 1st luminous flux R1, and the 2nd part is refracted by the 2nd refracting surface 43 and made incident slantingly on the scale as the 2nd luminous flux R2; and the 1st luminous flux R1 and 2nd luminous flux R2 which are reflected by a pattern for zero-point detection are directed to the 1st and 2nd photoelectric converting means through the prism means 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for detecting the zero point position of an encoder installed in the field of industrial machine tools, measuring machines, etc. to measure the movement and rotation of objects.

[Prior Art] Encoders have conventionally been used in NO machine tools and the like as displacement sensors for detecting positions and angles. There is a growing demand for higher resolution and higher accuracy for this type of encoder.

The applicant set the recording density of the diffraction grating used as a scale to several microns/pitch, extracted a pair of diffracted lights generated by this diffraction grating, caused them to interfere, and photoelectrically converted the interference light, thereby responding to the displacement of the diffraction grating. obtain a periodic signal,
We have devised several high-resolution and high-precision displacement measurement devices. On the other hand, the detection resolution and accuracy of the zero point position detection device of the scale incorporated in this device is also required to be the same as that of the displacement measurement device of the diffraction grating. In line with this request,
The applicant has devised a zero point position detection device shown in FIG. In the apparatus shown in FIG. 4, a parallel beam from a semiconductor laser 1 is partially reflected and extracted by a beam splitter 3, and a cylindrical lens 6 reduces the cross-sectional shape of the beam only in the moving direction of a scale 7 shown by an arrow to form a linear beam. Then, a linear beam is irradiated onto the planned passage point P of the linear pattern 8 for zero point position detection on the scale 7. When the linear pattern 8, which is a reflector, enters there, the linear beam is reflected by the pattern 8, a reflected light is generated, and as the pattern 8 moves in the direction of the arrow, the reflected light advances. The area changes continuously. Therefore, if the reflected light is transmitted through the cylindrical lens 6 again to return the beam cross-sectional shape to almost its original state, and then transmitted through the beam splitter 3, it is incident on the light receiving elements S, , S2, and then the light receiving elements S1, . The balance of the amount of light incident on each of S2 changes continuously as the pattern 8 moves.

Here, two light receiving elements S1. When the output levels of S2 match, a signal indicating the zero point position of the scale 7 is generated.

However, in this device, the relationship between the line width dg of the beam irradiation area (beam spot) and the line width dP of the linear pattern for zero point detection must satisfy 2dP≧dB≧dP, and the beam is directed in the direction of the arrow. Since the scale 7 is convergent with respect to the cylindrical lens 6, it is sensitive to changes in the distance from the cylindrical lens 6 to the scale 7.

Therefore, when the reading head and scale 7 for measuring the displacement of the diffraction grating 70 are separated and used by being incorporated into the object to be measured (embedded type device),
Installation is not easy to adjust. Therefore, the applicant
Prepare two beams in advance, and each
We are proposing a device that irradiates slightly shifted positions on the scale.

[Summary of the Invention] The present invention relates to an improvement of the above-mentioned zero point position detecting device using a plurality of beams, and aims to provide a zero point position detecting device having a simple optical system.

In order to achieve this object, the apparatus according to the first aspect of the present invention includes an irradiation means for irradiating first and second light beams onto a scale on which a pattern for detecting the zero point position is formed, and a light beam reflected by the pattern. A first unit that photoelectrically converts one luminous flux and outputs a first signal.
a photoelectric conversion means, a second photoelectric conversion means that photoelectrically converts a second light flux reflected by the pattern and outputs a second signal, and levels of the first and second signals output from the first and second photoelectric conversion means. and zero point detection means for outputting a signal indicating the zero point position of the scale in response to coincidence of the zero point position, wherein the irradiation means includes a light source and first and second refractive surfaces separated by a predetermined ridge line. and a prism means comprising a prism means, wherein the irradiation means divides the luminous flux from the light source into first and second parts via the ridge line of the prism means, and divides the first part into a first part.
A first beam that is refracted by a refracting surface and obliquely incident on the scale as the first beam, a second portion of which is refracted by a second refracting surface and obliquely incident on the scale as the second beam, and reflected by the pattern. The light beam and the second light beam are configured to be directed to the first and second photoelectric conversion means via the prism means.

Similarly, the device according to the second aspect of the present invention includes an irradiation means for irradiating the first and second light beams onto a scale on which a pattern for detecting the zero point position is formed, and a first light beam reflected by the pattern. A first photoelectric conversion means that photoelectrically converts and outputs a first signal, a second photoelectric conversion means that photoelectrically converts a second light beam reflected by the pattern and outputs a second signal, and first and second photoelectric conversion means. and zero point detection means for outputting a signal indicating the zero point position of the scale in response to matching of the levels of the first and second signals output from the scale, wherein the irradiation means includes a light source and a diffraction means. The irradiation means diffracts the light beam from the light source by the diffraction means, and causes the diffracted light of the same positive and negative orders to be obliquely incident on the scale as the first and second light beams, and is reflected by the pattern. The first and second light beams are configured to be directed to the first and second photoelectric conversion means via the diffraction means.

In the present invention, since the illumination means is configured as described above, the apparatus can be configured with a simple optical system even though a plurality of beams are used to detect a pattern. Therefore,
It also becomes possible to provide a small, inexpensive, built-in displacement measuring device. Furthermore, the device of the present invention can be applied to various types of displacement measuring devices, such as magnetic and optical linear or rotary type encoders, and can measure the displacement of a diffraction grating using interference light as described above. It is not limited to the type of reading.

Some features and specific forms of the present invention will be made clear in the Examples described below.

[Example] FIG. 1 is a schematic diagram showing an embodiment of the present invention.

In the figure, ] is a laser diode, 2 is a collimator lens, 3 is a half mirror, 14 is a prism, 41 is a ridgeline of the prism 40, 42.43 is a refractive surface of the prism 40 divided by the ridgeline 41, and 6 is a cylindrical lens. ,
7 is a linear scale on which a diffraction grating (not shown) is formed;
8 is a pattern for detecting the zero point position, 81° and 82 are first and second reflective marks constituting the pattern 8, SL and S2 are light receiving elements, 9 is an optical system for reading the diffraction grating formed on the scale, 100 is a light receiving element s.

This is a zero point detection means that outputs a signal indicating the zero point position of the scale 7 based on the signal from S2. The light beam emitted from the laser l is converted into a parallel light beam by the collimator lens 2 and directed toward the half mirror 3. This light beam is partially reflected by the half mirror 3, heads toward the ridgeline 41 of the prism 4, which is set to intersect with the optical axis of the collimator lens 2, and is divided into two parts by two refractive surfaces around the ridgeline 41. A luminous flux R traveling in two different directions,
, R2. Further, the direction in which the ridge line 41 extends is made to coincide with the moving direction of the scale 7 (arrow A). Next, the luminous fluxes R, , R2 are each contracted and condensed by the cylindrical lens 6 in the direction of the arrow A, and the reflective mark 81
．． 82 are obliquely incident on the expected passing positions PI and P2 (almost at the same position with respect to the arrow A direction), and linear beam spots extending in the direction perpendicular to the arrow A are formed at the positions P, P2, respectively. Form. [In order to form such a bead spot, the generatrix of the cylindrical lens 6 is oriented in a direction perpendicular to the direction of arrow A.

Now, the reflective marks 81 and 82 are formed with their positions shifted from each other in the direction of arrow A, and each mark has a rectangular shape with its longitudinal direction perpendicular to the direction of arrow A. . ” When such reflective marks 81 and 82 reach the position PI+P2, the reflective mark 81 reaches the position P1 first, so the luminous flux R3 reaches the reflective mark 8 first.
1 to produce a reflected light beam R, I. Subsequently, the reflection mark 82 reaches position P2, and the light beam R2 is reflected by the reflection mark 82, producing a reflected light beam R2. Then, the light beams R1 and R2' pass through the cylindrical lens 6 again, are returned to approximately the original cross-sectional shape, and further enter the prism 4 again.

At this time, the light beam R1 that passed through the refraction surface 41 on the outward path is transmitted through the refraction surface 42 and refracted on the return path, and the light beam R2 that passed through the refraction surface 42 on the outbound path is transmitted through the refraction surface 41 and refracted on the return path. It will be done. At this time, both luminous fluxes R,
, R2 pass through a position away from the ridgeline 41 of the prism 4. Both light beams R1R2 are reflected by the two refractive surfaces 4 of the prism 4.
．． 1.42 (parallel to the light that first entered the prism 4), the light passes through the half mirror 3 and enters the light receiving elements S, , S2, respectively. Light receiving element S,,S2
photoelectrically converts the incident light beams R, , R2, and outputs a signal corresponding to the intensity thereof. These signals are out of phase with each other, and are input to the detection means 100 via signal lines at their respective zero points. The zero point detection means 100 determines whether the levels of these signals match, and generates a zero point signal indicating the zero point position of the scale 7 at the moment when these signal levels match.

This means that the zero point position of the scale 7 has been detected.

In this embodiment, two luminous fluxes R,,R are generated using the method described above.
Since the prism 4 was used to irradiate the light beam 2 onto the scale 7, the configuration of the optical system could be made extremely simple. still,
In Fig. 1, the luminous flux R1゜R29 reflected luminous flux R,,R
In order to facilitate the explanation of the optical path No. 2, only half of the prism 4 and the cylindrical lens 6 in the direction of arrow A are illustrated.

To briefly explain the diffraction grating reading optical system 9 shown in FIG. 1, this optical system 9 includes a beam splitter 3
A parallel beam of light from the collimator lens 2 is received and directed to a diffraction grating (not shown) formed on a scale 7. Then, the diffracted lights of the same positive and negative orders generated by the diffraction grating are caused to interfere with each other to form interference light, and this interference light is detected by a photodetector and converted into an electrical signal corresponding to the displacement of the scale 7.

The amount of movement of the scale 7 is measured based on this signal, and this signal and the zero point signal output from the detection means 00 are input to a control device (not shown), so that the position of the scale 7 can be detected.

FIG. 2 is a schematic diagram showing another embodiment of the present invention;
A diffraction grating is used instead of a prism as a means for generating a beam of light.

In FIG. 2, 1 is a laser diode, 2 is a collimator lens, 3 is a half mirror, 15 is a diffraction grating, and 6
is a cylindrical lens whose generating line is orthogonal to the grating lines of the diffraction grating 5 and the direction of arrow A; 7 is a linear scale; 8 is a pattern for zero point position detection; 81.2 is a reflective mark forming pattern 8; SI+82 is a light receiving element,
9 is a diffraction grating reading optical system. In addition, the light receiving element S
, , the output signals from S2 are input to the zero point detection means 100 shown in FIG. Then, the diffraction grating 5 of this embodiment
The arrangement and functions of all other parts are the same as in the apparatus shown in FIG.

The light beam emitted from the laser l passes through the collimator lens 2
The beam is converted into a parallel beam by a half-mirror.
3 and enters the diffraction grating 5. The diffraction grating 5 diffracts the incident light beam to generate diffracted lights R1 and R-. At this time, diffracted lights of orders other than R+ and R- are also generated from the diffraction grating 5, but these unnecessary diffracted lights of other orders are blocked by a light shielding means such as a mask.

The diffracted lights R+ and R- are transmitted by the cylindrical lens 6.
Each line is contracted (condensed) in the direction of arrow A, made incident on the expected passing position PI + P2 of the reflective mark 81, 82, and each extends in a direction perpendicular to the direction of arrow A at positions P, , P2. A shaped beam spot is formed. Reflective marks 81 and 82 are at position P1. When you reach R2,
Since the reflective mark 81 reaches the position PI first, the diffracted light R- is reflected by the reflective mark 81 first to generate a reflected light flux R-, and then the reflective mark 82 reaches the position P2 and the diffracted photons are generated. The light is reflected by the reflective mark 82 to generate a reflected light beam R'. Luminous flux R+' and R- are cylindrical lens 6
The beam is transmitted again and returned to approximately the original beam cross-sectional shape, and then enters the diffraction grating 5 again. At this time, the light beam R+' that has been diffracted to the +1st order on the outward path is diffracted to the -1st order by the diffraction grating 5 on the return path, and the light beam R that has been diffracted to the 11th order on the forward path is diffracted to the +1st order by the diffraction grating on the return path. Then, both luminous fluxes R+', R-
are emitted from the diffraction grating 5 substantially parallel to the light beam that first entered the diffraction grating 5, transmit through the half mirror 3, and enter the light receiving elements S, , S2.

Therefore, similarly to the embodiment shown in FIG.
Based on the output signal from 2, the zero point detection means 100 outputs a zero point signal.

FIG. 3 is a schematic diagram showing a further embodiment of the invention.

In this embodiment, the diffraction grating used as a means for generating two beams in FIG. 2 is also used as a beam splitter for taking out a beam for the reading optical system 9, for example. In Fig. 3, 1 is a laser diode, 2 is a collimator lens, 5 is a diffraction grating consisting of alternating light reflecting parts and transparent parts, 6 is a cylindrical lens, 7 is a linear scale, and 8 is a zero point position detection pattern. , 81.82 are reflective marks constituting pattern 8, S, , S2 are light receiving elements,
9 is a diffraction grating reading optical system. In addition, the light receiving element S
l.

The output signal from S2 is transmitted to the zero point detection means 1 shown in FIG.
00 is input. Then, the diffraction grating 5 of this embodiment is
The arrangement and function of the other parts are exactly the same as the apparatus shown in FIG.

The light beam emitted from the laser 1 passes through the collimator lens 2
is converted into a parallel light beam, and this light beam is partially reflected and diffracted by the diffraction grating 5, and the diffraction grating 5 generates the diffracted light R+,
generate R-. At this time, from the diffraction grating 5, R+, R-
Although diffracted lights of other orders are also generated, these unnecessary diffracted lights of other orders are blocked by a light shielding means such as a mask.

The diffracted lights R1 and R- are respectively contracted (condensed) by the cylindrical lens 6 in the direction of the arrow, and reach the expected passing positions P of the reflective marks 81 and 82.

are made incident on P2, and at positions p, , p2, respectively,
A linear beam spot extending in a direction perpendicular to the direction of arrow A is formed. Reflective marks 81 and 82 are at position P1. R2
When reaching the position, the reflective mark 81 reaches the position PI first, so the diffracted light R- is reflected by the reflective mark 81 first to generate a reflected luminous flux R-, and then the reflective mark 82 reaches the position P2. The diffracted light R0 is reflected by the reflective mark 82 to generate a reflected light beam R1'. The light beams R1' and R- are transmitted through the cylindrical lens 6 again, are returned to substantially the original cross-sectional shape, and are further incident on the diffraction grating 5 again. At this time, the light beam R+' that was reflected and diffracted in the +1st order on the outward path is subjected to the 11th order transmission diffraction by the diffraction grating 5 on the return path, and the light beam R- that was reflected and diffracted in the -1st order on the outgoing path is subjected to the +1st order transmission diffraction by the diffraction grating 5 on the return path. do. Then, both luminous fluxes R+' and R- are reflected by the diffraction grating 5
, each of the light beams is emitted substantially parallel to the light beam initially emitted from the diffraction grating 5, and enters the light receiving element S I +S2.

Therefore, similarly to the embodiments shown in FIGS. 1 and 2, the zero point detection means 1
A zero point signal is output from 00.

In FIG. 3, among the parallel light beams from the collimator lens 2, the light beams that pass through the diffraction grating 5 are transmitted through the reading optical system 9.
At this time, multiple transmitted diffracted lights are generated.

In this embodiment, in order to selectively allow the zero-order transmitted diffracted light (light traveling in a straight line) from the diffraction grating 5 to enter the optical system 9, a light-shielding mask 10 blocks higher-order diffracted light. This prevents unnecessary light (ghost light) from entering the optical system 9, thereby improving the accuracy of reading the diffraction grating by the optical system 9.

In the embodiments shown in FIGS. 2 and 3 described above, the configuration of the optical system is extremely simple because the diffraction grating 5 that irradiates the two luminous fluxes R+ and R- onto the scale 7 in the manner described above is used. I was able to do it.

Incidentally, also in FIGS. 2 and 3, the luminous flux R+.

To make it easier to explain the optical path of the R-1 reflected light beams R1' and R-, the diffraction grating 5 and the cylindrical lens 6 are shown in FIG.
In FIG. 3, only half of the cylindrical lens 6 in the direction of arrow A is shown.

In each of the embodiments described above, the light receiving element Sl+32 is provided on an optical path different from the optical path reaching the laser 1 via the half mirror 3 or the diffraction grating 5. Since the irradiation means (1 to 6) are configured to be shifted from the optical path of . At this time, if the laser l is used only for zero point position detection and the reading optical system 9 is equipped with a separately capable light source (laser), the half mirror 3 can be made into a total reflection mirror, for example, and the light can be used effectively.

Regarding pattern 8, for example, only the mark 81 is formed on the scale 7 without using the two marks 81 and 82, and this mark is projected onto the scale to form two lines aligned in the moving direction of the scale. The irradiation means may be configured to detect with a shaped beam.

In addition, instead of the cylindrical lens 6, a plate-shaped Fresnel lens or a plate-shaped hologram lens using a diffraction grating whose grating pitch is gradually changed can also be used. In this case, this lens can be used as a prism for generating two beams. 4 or the diffraction grating 5 (for example, by adhering them), the optical system can be made compact. Also, the ridgeline of prism 4 is on scale 5
You can also turn to the side.

In addition, although each of the above embodiments is directed to an optical scale, the present invention can be applied to various types of encoders as described above, and therefore, the present invention is directed to a magnetic scale in which a magnetization pattern is recorded as a scale. It's good as well. In this case, the zero point position of the magnetic scale will be detected optically.

[Effects of the Invention] As described above, according to the present invention, although a plurality of beams are used to detect a pattern, the apparatus can be configured with a simple optical system. Therefore, it is also possible to provide a compact, inexpensive, built-in displacement measuring device.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention. FIGS. 2 and 3 are schematic diagrams showing other embodiments of the present invention. FIG. 4 is an explanatory diagram showing a conventional zero point position detection device.

Claims (2)

[Claims] (1) An irradiation unit that irradiates a scale on which a pattern for detecting the zero point position is formed with first and second light beams, and a first photoelectric device that photoelectrically converts the first light beam reflected by the pattern and outputs a first signal. a conversion means, a second photoelectric conversion means for photoelectrically converting the second light beam reflected by the pattern and outputting a second signal;
and zero point detection means for outputting a signal indicating the zero point position of the scale in response to matching of the levels of the first and second signals output from the second photoelectric conversion means, wherein the irradiation means has a light source and a prism means having first and second refractive surfaces separated by a predetermined ridge line, and the irradiation means directs the light beam from the light source to the first and second refractive surfaces through the ridge line of the prism means. A first part is refracted by a first refracting surface to be obliquely incident on the scale as the first beam, and a second part is refracted by a second refracting surface to be obliquely incident on the scale as the second beam. The zero point position detection device is characterized in that it is configured to direct the first and second light beams reflected by the pattern to the first and second photoelectric conversion means via a prism means. (2) An irradiation unit that irradiates a scale on which a pattern for detecting the zero point position is formed with first and second light beams, and a first photoelectric device that photoelectrically converts the first light beam reflected by the pattern and outputs a first signal. a conversion means, a second photoelectric conversion means for photoelectrically converting the second light beam reflected by the pattern and outputting a second signal;
and zero point detection means for outputting a signal indicating the zero point position of the scale in response to matching of the levels of the first and second signals output from the second photoelectric conversion means, wherein the irradiation means has a light source and a diffraction means,
The irradiation means diffracts the light beam from the light source by the diffraction means, and causes the diffracted light of the same positive and negative orders to be obliquely incident on the scale as the first and second light beams, and the first and second beams reflected by the pattern. The two beams are passed through the diffraction means to the first
and a zero point position detection device configured to direct toward the second photoelectric conversion means.