JPH0228518A - Displacement measuring instrument - Google Patents

Abstract

PURPOSE:To prevent a leakage of a laser beam from a read-out head by controlling an irradiation of the laser beam in the manner of providing detection means to detect the relation of a position between an entering position of the laser beam to a movable substrate and an optical scale. CONSTITUTION:The laser beam from a semiconductor laser 1 is divided to a transmitting luminous flux and a reflecting luminous flux through a collimator lens 2 and a polarizing BS(beam splitter) 9. The reflected flux and the transmitted flux from the BS9 are entered to a reflection film 12 respectively through plates 51, 52 with 1/4 wavelength, reflection mirrors 101, 102, diffraction grating 3 and optical component 11. Next, the diffracted light beams reflected on the film 12 are turned back on the previous optical path, and two diffracted light beams are overlapped on the BS9 then entered to photodetectors 81, 82 through the BS31, plane 53 with 1/4 wavelength, BS6 and polarizing plates 71, 72. At this time, whether the grating 3 is irradiated with the laser beam or not, is detected by a detection system consisting of a light emitting element 33 and a photodetector 34. Therefore when a signal intensity of the element 34 is less than the threshold, a driving to the laser 1 is stopped, thereby the leakage of the laser beam to the outside from the read-out head can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a displacement measuring device such as an optical linear encoder or an optical rotary encoder.

[Prior art]

Conventionally, for example, U, S, Pat, No. 4,629,88
6 and U, S, Pat, No. 4,676.645, the linear scale is installed by irradiating the linear scale with laser light and detecting the light from the linear scale with a photodetector. A device for measuring the displacement of a test object is known.

The displacement measuring device indicated by the above U, S, Patents is:
The scale is formed of a diffraction grating, and the diffracted light emitted from the scale by laser beam irradiation forms interference fringes, and the displacement of the object or scale is measured based on the signal obtained by photoelectrically converting the interference fringes. It is possible to perform measurements with extremely high resolution. However, if the linear scale moves beyond its effective length due to the movement of the object to be tested, or if the linear scale is tilted more than a certain degree with respect to the direction of displacement, or if it is deviated in a direction perpendicular to the direction of displacement. , there was a risk that the laser light would leak out from the read head.

[Summary of the invention]

The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide a displacement measuring device capable of preventing leakage of laser light from a reading head.

In order to achieve the above object, the displacement measuring device of the present invention irradiates a movable substrate on which an optical scale is formed with a laser beam,
In a displacement measuring device that measures displacement of the movable substrate by detecting light from the optical scale with a photodetector, detecting a positional relationship between the incident position of the laser beam on the movable substrate and the optical scale. has a detection means to
It is characterized in that the irradiation of the laser beam is controlled based on the output signal from the detection means.

Further, in a displacement measuring device according to another aspect of the present invention, a movable substrate on which an optical scale is formed is irradiated with a laser beam, and the light from the optical scale is detected by a photodetector, thereby measuring the displacement of the movable substrate. The displacement measuring device for measuring the displacement of the movable substrate includes a detection means for detecting the positional relationship between the irradiation position of the laser beam on the movable substrate and the optical scale, The present invention is characterized in that the positional relationship between the movable substrate and a reading head including a light source to be supplied and the photodetector is adjusted.

Further features and specific embodiments of the present invention are described in the Examples below.

〔Example〕

FIG. 1 shows a schematic diagram of an optical system showing an embodiment of the displacement measuring device of the present invention.

In FIG. 1, a coherent laser beam from a semiconductor laser 1 is made into a substantially parallel beam by a collimator lens 2, and is incident on a polarizing beam splitter 9. It is divided into two light beams: a transmitted light beam of polarized light and a reflected light beam of S-polarized light. At this time, the mounting position of the laser l is adjusted so that the polarization direction of the emitted light beam of the laser l is 45 degrees with respect to the polarization direction of the polarization plane of the polarizing beam splitter 9. As a result, the intensity ratio between the transmitted light beam and the reflected light beam from the polarizing beam splitter 9 is approximately 1:1.

The reflected light beam and the transmitted light beam from the polarizing beam splitter 9 are made into circularly polarized light through quarter-wave plates 51 and 5□, respectively, and the reflection mirror 10. , 102 and incident on the diffraction grating 3 forming an optical scale, the m-th order tongue tip from the target diffraction grating 3 is reflected from the diffraction grating 3 substantially perpendicularly.

That is, when the grating pitch of the diffraction grating 3 is P1, the wavelength of the coherent light beam is λ, m is an integer, and the angle of incidence of the coherent light beam on the diffraction grating 3 is θ□, 0 m 5in-' (mλ/
P) (1).

The diffraction grating 3 is a member serving as an optical scale of this measuring device, and is formed on the movable substrate 100 as an amplitude type or phase type grating. And the board 10
0 moves in the X direction, the diffraction grating 3 is also displaced in the X direction.

The two m-th order tongue tips emitted substantially perpendicularly from the diffraction grating 3 enter the optical member ll. Since a reflective film 12 is provided near the focal plane of the optical member 11, the incident light beam is reflected by the reflective film 12, returns to the original optical path, exits from the optical member 11, and enters the diffraction grating 3 again. do.

Then, the m-th order reflected diffracted light that is diffracted again by the diffraction grating 3 returns to the original optical path and returns to the reflecting mirror 10. ．． Reflected at 102, 1/
The polarizing beam splitter 9 passes through the 4-wavelength plates 51 and 5□.
to be re-injected.

At this time, the re-diffracted light goes back and forth between the quarter-wave plates 5I and 5□, so when the light beam first reflected by the polarizing beam splitter 9 enters again, the polarization direction is 90 with respect to the polarizing beam splitter 9. The polarizing beam splitter 9 is transmitted through the polarizing beam splitter 9 at different degrees. Conversely, the light beam that first passes through the polarizing beam splitter 9 is reflected when it enters the polarizing beam splitter 9 again.

In this way, the two diffracted lights are overlapped by the polarizing beam splitter 9, and the beam splitter 31 and the l/4 wavelength plate 5
After passing through the beam splitter 6, it becomes circularly polarized light, and the beam splitter 6
After splitting into two light beams and passing through a polarizing plate 71°7□,
The light is linearly polarized and incident on the light receiving elements 8□ and 8°, respectively.

Note that the angle θ□ in equation (1) indicates that it is sufficient if it is within a range that allows the diffracted light to enter the condensing system 2o and then enter the diffraction grating 3 again.

In this embodiment, the phase of the m-th order diffracted light changes by 2mπ when the diffraction grating moves one pitch. Therefore, since the light receiving elements 88, 8□ receive the interference of the light beams that have undergone positive and negative m-order diffraction twice, when the diffraction grating moves one pitch of the grating, 4m sine wave signals are generated. can get.

For example, the pitch of the diffraction grating 3 is 3.2 μm, and 1 diffracted light is 1
If we use the order (m = 1), the diffraction grating 3 becomes 3
．． When moving by 2 μm, four sine wave signals are obtained from the light receiving elements 81, 8□. In other words, the resolution per sine wave is 1/4 of the pitch of the diffraction grating 3, that is, 3.2/4 =
0.8 μm is obtained.

Also, quarter wavelength plates 58, 5□, 53 and polarizing plates 7□, 7
The combination of □ creates a phase difference of 90 degrees between the output signals from the light receiving elements 81e8□, so that the moving direction of the diffraction grating 3 can also be determined.

In addition, if only the amount of movement is to be measured, the number of light receiving elements is 1.
(Also, the quarter-wave plate 53 and beam splitter 6 are not necessary.

In FIG. 1, a reading head for measuring the displacement of the diffraction grating 3 is designated by the symbol R.

In this embodiment, a predetermined reflective portion is formed on the substrate 100 together with the diffraction grating 3. This situation is shown in FIG.

In FIG. 2, the part indicated by reference numeral 35 is a reflective part, and a linear pattern extending in the grating arrangement direction (X direction) of the diffraction grating 3 is formed adjacent to the diffraction grating 3. The reflecting section 35 is provided to detect the positional relationship between the incident position of the laser beam on the substrate 100 and the diffraction grating 3, and is composed of a set of a light emitting element 33 and a light receiving element 34 shown in FIG. In cooperation with the detection system M, it is monitored whether or not the substrate lOO is located at the position where the laser beam is incident on the diffraction grating 3.

The light emitting element 33 in FIG. 1 is an element that emits light that does not affect the human body, unlike a laser, and in this embodiment, it is an LED.
are using. The light from the light emitting element 33 illuminates the reflecting section 35, and the reflected light from the reflecting section 35 is received by the light receiving element 34.

Further, the reflecting portion detection system M consisting of the light emitting element 33 and the light receiving element 34 and the displacement measuring optical system shown in FIG. 1 described above are housed in the same reading head R.

Here, the irradiation position of the laser beam and the light emitting element are set so that the intensity of the reflected light received by the light receiving element 34 becomes below a predetermined threshold when or before the irradiation position of the laser beam deviates from the diffraction grating 3. The irradiation position of the light from 33 and the arrangement of the diffraction grating 3 and the reflection section 35 are determined.

Therefore, whether or not the laser beam is irradiating the diffraction grating 3 can be detected based on the output signal of the detection system consisting of the light emitting element 33 and the light receiving element 34, that is, the photoelectric conversion signal by the light receiving element 34. For this reason, the change in the intensity of the signal from the light receiving element 34 is monitored, and if this intensity becomes below the threshold, for example, the drive of the laser 1 is stopped to prevent external laser light from leaking from the reading head. be able to.

Returning to FIG. 1, the beam splitter 31 reflects a part of the light beam from the polarizing beam splitter 9 and directs this part of the light to the light receiving element 32. Since the light beam from the polarizing beam splitter 9 is a combination of overlapping diffracted lights whose polarization directions are orthogonal to each other, no change in intensity occurs even if the diffraction grating 3 moves. Therefore, the light receiving element 32 can simply monitor the intensity of the diffracted light, regardless of the movement of the diffraction grating 3, and it is possible to simply monitor the intensity of the diffracted light, which is dependent on the output fluctuation of the laser l and the relative positional relationship between the diffraction grating 3 and the incident laser light. Changes in the intensity of the diffracted light can be detected.

The output signals from this light receiving element 32 and the above-mentioned light receiving element 34 are processed by, for example, a circuit shown in FIG. In FIG. 3, 41 and 42 are amplifiers, 43 and 44 are comparators,
45, 46, 49, and 50 are resistors, 47 and 48 are reference voltage power supplies, and 51 and 52 are display light emitting elements such as LEDs. Also, 53. 54 is " from the comparators 43 and 44.
This is a terminal for inputting a "HIGH" or "LOW" signal to a subsequent control circuit (not shown). For example, as shown in the figure, the signal from the comparator 44 is used to control the drive circuit of the laser 1. used.

The current generated in the light receiving elements 32 and 34 according to the light intensity is
It is converted into a voltage according to the light intensity by amplifiers 41, 42 and resistors 45, 46. Each of these is set to a predetermined reference voltage (
Threshold value) 47.48 is compared with the comparator 43.44, and when the intensity is greater than a predetermined value, the output terminal 53.54 is set to LO.
The voltage is set to W, and LEDs 51 and 52 are turned on. When the intensity is less than a predetermined value, the output terminals 53 and 54 are HIGH.
voltage and the LED turns off. This allows the intensity of the light received by each light receiving element 32, 34 to be known. Since the luminous flux from the light emitting element 33 has a large diameter and has no directivity, the change in the intensity of the light incident on the light receiving element 34 becomes small even if the substrate 100 is slightly displaced from its original position in the Y direction. On the other hand, the intensity of the laser light incident on the light receiving element 32 changes greatly with respect to the displacement of the substrate 100 in the Y direction because the beam diameter is small, the beam is almost parallel, and the optical path is long. Therefore, the optimum range of the laser beam incident position on the substrate 100 is narrowed. Therefore, first, while monitoring the intensity of the light incident on the light receiving element 34, the position of the substrate 100, that is, the diffraction grating 3, is roughly adjusted. Next, by making fine adjustments to the position of the diffraction grating 3 while monitoring the intensity of the light incident on the light receiving element 32, the adjustment is very easy and the substrate 1OO1, that is, the diffraction grating 3 can be easily positioned at the optimum position. It is possible to make the laser beam incident on the diffraction grating 3.

Further, as mentioned earlier, when the intensity of the light incident on the light receiving element 34 does not reach a certain predetermined value, the operation of the laser 1 is stopped, and when the intensity of the light incident on the light receiving element 34 reaches a certain predetermined value, the operation of the laser 1 is started. By doing so, even if the power is inadvertently turned on while the diffraction grating 3 is not at the laser beam incident position, or if the diffraction grating 3 moves beyond its effective length during displacement measurement, the laser beam will not be transmitted. Not ejected. Therefore, it is safe.

This control causes the output of the terminal 54 to act on the drive circuit of the laser 1, so that when the output of the terminal 54 is a HIGH voltage, the emission of the laser I is stopped, and when the output of the terminal 54 is a LOW voltage, the laser 1 is driven. do. As a result, the diffraction grating 3
This prevents the laser l from inadvertently emitting laser light when the laser l is not at the laser light incident position.

It goes without saying that the output voltages of the amplifiers 41 and 42 may be directly monitored for changes in each light intensity.

The operations described above can be summarized as shown in Table 1 below.

The angle of incidence of the light beam irradiated from the front light emitting element 33 to the reflecting portion 35 of the substrate 100 is not particularly limited, and the light beam may be incident from a substantially perpendicular direction as shown in FIG. 4(A). In addition, the detection system is the fourth
As shown in Figure (B), a pair of light-emitting and light-receiving elements may be packaged. Further, the light emitting element 33 is
In addition to LEDs, anything can be used as long as it is highly safe, and the light receiving element 34 is not particularly limited, such as a photodiode or a phototransistor.

The representation of the two signals obtained by the circuit shown in Figure 3 can also be displayed in the read head of the encoder or in an interface unit that processes the signals obtained from the read head. However, it does not depart from the spirit of the present invention no matter where it is displayed.

Furthermore, in FIG. 1, the arrangement of the beam splitter 31 is not limited to this position, and may be placed, for example, between the 1/4 wavelength plate 53 and the beam splitter 6.

〔Effect of the invention〕

As described above, according to the present invention, a detection means is provided for detecting the positional relationship between the incident position of the laser beam on the movable substrate and an optical scale such as a diffraction grating formed on the movable substrate, and the output from the detection means is provided. By controlling the irradiation of laser light based on the signal, a highly safe displacement measuring device can be obtained in which the laser light does not leak from the reading head.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical system showing an embodiment of the displacement measuring device of the present invention. FIG. 2 is a top view showing the diffraction grating and reflection section on the substrate. FIG. 3 is a circuit diagram showing a processing circuit that processes output signals from two light receiving elements. FIGS. 4(A) and 4(B) are diagrams showing a modification of the reflective portion detection system.

Claims (1)

[Claims] A displacement measuring device that measures the displacement of the movable substrate by irradiating a movable substrate on which an optical scale is formed with a laser beam and detecting the light from the optical scale with a photodetector. A displacement measuring device comprising: a detection means for detecting a positional relationship between an incident position on a substrate and the optical scale; and controlling irradiation of the laser beam based on an output signal from the detection means.