JPH076811B2 - Displacement measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a displacement measuring device such as an optical linear encoder or an optical rotary encoder.

[Conventional technology]

Conventionally, for example, US Pat.No.4,629,886 or US Pat.No.4,67
As shown in 6,645, there is known a device that measures the displacement of an object to be inspected with a linear scale by irradiating the linear scale with laser light and detecting the light from the linear scale with a photodetector. There is.

The displacement measuring device indicated by the above US Patents forms a scale with a diffraction grating, forms interference fringes with diffracted light emitted from the scale by irradiation of laser light, and based on a signal obtained by photoelectrically converting this interference fringe. It measures the displacement of the object to be inspected or the scale, and can perform measurement with extremely high resolution. However, when the linear scale moves more than the effective length due to the movement of the object to be inspected, or the linear scale is tilted to some extent or more with respect to the displacement direction, or is displaced in the direction orthogonal to the displacement direction. , It was necessary to adjust the positional relationship between the reading head and the movable substrate.

[Outline of Invention]

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a displacement measuring apparatus capable of easily and accurately moving a read head and a movable substrate to an optimum position.

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 the displacement of the movable substrate by detecting interference light of diffracted light from the optical scale with a photodetector, in the vicinity of the incident position of the laser light on the movable substrate, A light-emitting element that inputs light having a large luminous flux diameter, a first light-receiving element that receives the light reflected from the movable substrate from the light-emitting element, and a part of the diffracted light that enters the photodetector. A second light receiving element, and performs coarse adjustment based on an output signal of the first light receiving element for position adjustment of the laser beam and the movable substrate, and based on an output signal of the second light receiving element It is characterized by fine adjustment.

Further features and specific forms of the present invention will be described in the embodiments described later.

〔Example〕

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

In FIG. 1, a laser beam having coherence from a semiconductor laser 1 is converted into a substantially parallel light flux by a collimator lens 2 and is incident on a polarization beam splitter 9, and the polarization beam splitter 9 causes P-polarized light beams whose polarization directions are orthogonal to each other. Is divided into two light beams, a transmitted light beam of S and a reflected light beam of S-polarized light. At this time, the mounting position of the laser 1 is adjusted so that the polarization direction of the emitted light beam of the laser 1 becomes 45 degrees with respect to the polarization direction of the polarization plane of the polarization beam splitter 9. As a result, the intensity ratio of the transmitted light flux and the reflected light flux from the polarized beam splitter 9 is set to be approximately 1: 1.

Then, the reflected light beam and the transmitted light beam from the polarized beam splitter 9 are circularly polarized through the 1/4 wavelength plates 5 ₁ and 5 ₂ , respectively, and
When reflected by the reflecting mirrors 10 ₁ and 10 ₂ and incident on the diffraction grating 3 forming an optical scale, the m-th order diffracted light from the target diffraction grating 3 is incident so as to be reflected substantially vertically from the diffraction grating 3. I am letting you.

That is, when the grating pitch of the diffraction grating 3 is P, the wavelength of the coherent light beam is λ, m is an integer, and the incident angle of the coherent light beam to the diffraction grating 3 is θ _m , θ _m sin ⁻¹ (mλ / P) ... It is incident so that it becomes (1).

The diffraction grating 3 is a member that serves as an optical scale of the measurement apparatus, and the diffraction grating 3 is formed on the movable substrate 100 as an amplitude type or phase type grating. And the substrate 100 is X
The diffraction grating 3 is also displaced in the X direction by moving in the X direction.

The two m-th order diffracted lights emitted from the diffraction grating 3 substantially vertically enter the optical member 11. Since the reflection film 12 is provided in the vicinity of the focal plane of the optical member 11, the incident light flux returns from the original optical path after being reflected by the reflection film 12 and exits from the optical member 11 to enter the diffraction grating 3 again. To do.

Then, the m-th order diffracted diffracted light diffracted again by the diffraction grating 3 returns to the original optical path, is reflected by the reflecting mirrors 10 ₁ and 10 ₂ , and is reflected by the quarter wavelength plate 5
_The light passes through ₁ , 5 ₂ and is re-incident on the polarized beam splitter 9.

At this time, since the re-diffracted light reciprocates through the quarter-wave plates 5 ₁ and 5 ₂ , when the light beam first reflected by the polarization beam splitter 9 is re-incident, the polarization direction with respect to the polarization beam splitter 9 is changed. It is different by 90 degrees and is transmitted through the polarized beam splitter 9. On the contrary, the light beam first transmitted by the polarized beam splitter 9 is reflected when it re-enters the polarized beam splitter 9.

Thus after passing through the polarizing beam splitter -9 in beam splitter over 31 not overlapping the two diffracted light and the quarter-wave plate 5 _3, and a circularly polarized light, is divided into two beams by beam splitter -6, each polarizer After passing through 7 ₁ and 7 ₂ , linearly polarized light is made incident on the light receiving elements 8 ₁ and 8 ₂ , respectively.

In addition, at the angle θ _m in the equation (1), the diffracted light enters the focusing system 20,
It is shown that it may be within a range in which it can be incident on the diffraction grating 3 again.

In this embodiment, the phase of the m-th order diffracted light changes by 2 mπ when the diffraction grating moves by one pitch. Therefore, the light receiving element 8 ₁ ,
Since 8 ₂ receives the interference of the light flux that has received positive and negative m-th order diffraction twice, 4 m sine wave signals can be obtained when the diffraction grating moves by one pitch of the grating.

For example, if the pitch of the diffraction grating 3 is 3.2 μm and the first order (m = 1) is used as the diffracted light, when the diffraction grating 3 moves 3.2 μm, four sine wave signals are output from the light receiving elements 8 ₁ and 8 _2. can get. That is, the diffraction grating 3 is used as the resolution per sine wave.
That is, 1/4 of the pitch of 3.2, that is, 3.2 / 4 = 0.8 μm is obtained.

Further, a 90 degree phase difference is provided between the output signals from the light receiving elements 8 ₁ and 8 ₂ by the combination of the 1/4 wavelength plates 5 ₁ , 5 ₂ and 5 ₃ and the polarizing plates 7 ₁ and 7 ₂ , and the diffraction grating 3 It is also possible to determine the moving direction of. If only the amount of movement is measured, the number of light receiving elements may be one, and the 1/4 wavelength plate 5 ₃ and the beam splitter 6 are unnecessary.

In FIG. 1, the read head for measuring the displacement of the diffraction grating 3 is indicated by the symbol R.

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

In FIG. 2, a portion indicated by reference numeral 35 is a reflection portion, and a linear pattern elongated in the grating arrangement direction (X direction) of the diffraction grating 3 is formed adjacent to the diffraction grating 3. This reflector 35
Is the incident position of the laser light on the substrate 100 and the diffraction grating 3
The position where the laser light is incident on the diffraction grating 3 is provided in order to detect the positional relationship between the laser beam and the diffraction grating 3 in cooperation with the reflection part detection system M including the set of the light emitting element 33 and the light receiving element 34 shown in FIG. Monitor for board 100 in the.

Unlike the laser, the light emitting element 33 in FIG. 1 is an element that emits light that does not affect the human body, and an LED is used in this embodiment. The light from the light emitting element 33 illuminates the reflecting portion 35, and the reflected light from the reflecting portion 35 is received by the light receiving element 34.

In addition, a reflector detection system M including a light emitting element 33 and a light receiving element 34
And the displacement measuring optical system shown in FIG. 1 are stored in the same reading head R.

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

Therefore, whether or not the laser beam irradiates the diffraction grating 3 can be detected based on the output signal of the detection system including the set of the light emitting element 33 and the light receiving element 34, that is, the photoelectric conversion signal by the light receiving element 34. Therefore, the intensity change of the signal from the light receiving element 34 is monitored, and when this intensity becomes equal to or less than the threshold value,
For example, by stopping the driving of the laser 1, it is possible to prevent the laser light from leaking from the reading head to the outside.

Returning to FIG. 1, the beam splitter 31 reflects a part of the light beam from the polarized beam splitter 9 and directs this part of the light to the light receiving element 32. Since the light beam from the polarized beam splitter 9 is light in which diffracted lights whose polarization directions are orthogonal to each other are overlapped with each other, the intensity does not change 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 depends on the output fluctuation of the laser 1 and the relative positional relationship between the diffraction grating 3 and the incident laser light. The change in the intensity of the diffracted light can be detected.

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

The current corresponding to the light intensity generated in the light receiving elements 32 and 34 is converted into a voltage according to the light intensity by the amplifiers 41 and 42 and the resistors 45 and 46. This is the specified reference voltage (threshold) 47,4
8 is compared with the comparators 43 and 44, and when the intensity is larger than a predetermined value, the output terminals 53 and 54 are set to LOW voltage and the LEDs 51 and 52 are turned on. When the intensity is less than the specified value, the output terminals 53 and 54 are H
It becomes the IGH voltage and the LED goes off. As a result, each light receiving element
The intensity of the light received by 32 and 34 can 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 is small even if the substrate 100 is displaced in the Y direction from the original position to some extent.
On the other hand, the intensity of the laser light incident on the light receiving element 32 is
Since the beam diameter is small, the light is substantially parallel, and the optical path is long, it largely changes with respect to the displacement of the substrate 100 in the Y direction, so that the optimum range of the laser light incident position on the substrate 100 becomes narrow. Therefore, first, the position of the substrate 100, that is, the diffraction grating 3 is roughly adjusted while monitoring the intensity of light incident on the light receiving element 34, and then the diffraction grating 3 is monitored while monitoring the intensity of light incident on the light receiving element 32. If the position is finely adjusted, the adjustment can be performed very easily, and the substrate 100, that is, the diffraction grating 3 can be easily driven to the optimum position and the laser light can be incident on the diffraction grating 3.

As described above, the operation of the laser 1 is stopped when the intensity of the light incident on the light receiving element 34 does not reach a predetermined value, and the laser 1 is driven when the intensity reaches a predetermined value. If this is done, even if the diffraction grating 3 is inadvertently turned on while the laser beam is not at the incident position, or if the diffraction grating 3 moves for more than its effective length during displacement measurement, the laser beam will not be emitted. 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, the emission of the laser 1 is stopped when the output of the terminal 54 is HIGH voltage, and the laser 1 is driven when the output of the terminal 54 is LOW voltage. To do. This prevents the laser beam from being accidentally emitted from the laser 1 when the diffraction grating 3 is not at the laser beam incident position.

Further, it goes without saying that the output voltage of the amplifiers 41 and 42 may be directly monitored for the change of each light intensity.

The operations described above are summarized in Table 1 below.

The incident angle of the light flux emitted from the light emitting element 33 to the reflecting portion 35 of the substrate 100 is not particularly limited, and may be incident from a substantially vertical direction as shown in FIG. 4 (A). Further, the detection system may be one in which light emitting and light receiving elements are paired in a package as shown in FIG. 4 (B). The light emitting element 33 is an LED.
In addition to this, any device having high safety may be used, and the light receiving element 34 is not particularly limited to a photo diode, a photo transistor, or the like.

Also, the display of the two signals obtained with the circuit shown in FIG. 3 can be displayed at the read head of the encoder or in the interface unit which processes the signal obtained from the read head. However, no matter where it is displayed, it does not deviate from the gist of the present invention.

Further, in FIG. 1, the arrangement of the beam splitter 31 is not limited to this position, for example may be between the 1/4 wavelength plate 5 ₃ and beam splitter 6.

〔The invention's effect〕

As described above, according to the present invention, a light-emitting element that causes light having a larger luminous flux diameter than the laser light to enter near the incident position of the laser light on the movable substrate, and light that is reflected from the movable substrate by the light from the light-emitting element is received. And a second light receiving element for receiving a part of the diffracted light incident on the photodetector, and the first light receiving element for adjusting the positions of the laser beam and the movable substrate. Displacement measurement that allows the read head and the movable substrate to be easily and accurately driven to the optimum position by performing fine adjustment based on the output signal of the element and fine adjustment based on the output signal of the second light receiving element. It can be a device.

[Brief description of drawings]

FIG. 1 is a schematic view 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 the reflection portion on the substrate. FIG. 3 is a circuit diagram showing a processing circuit for processing output signals from two light receiving elements. 4 (A) and 4 (B) are views showing a modified example of the reflection part detection system. R …… Reading head M …… Reflector detection system 1 …… Semiconductor laser 3 …… Diffraction grating 32,34 …… Light receiving element 43,44 …… Comparator 51,52 …… Light emitting element for display 100 …… Movable substrate

Front Page Continuation (72) Inventor Ko Ishizuka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yoichi Kubota 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP 61-59632 (JP, A) JP 61-262597 (JP, A)

Claims (1)

[Claims] 1. Displacement measurement for measuring the displacement of the movable substrate by irradiating a movable substrate on which an optical scale is formed with laser light and detecting interference light of diffracted light from the optical scale with a photodetector. In the device, a light-emitting element that allows light having a larger light flux diameter than the laser light to enter near the incident position of the laser light on the movable substrate, and light that is emitted from the light-emitting element and reflected by the movable substrate is received. Of the first light receiving element for adjusting the positions of the laser light and the movable substrate. A displacement measuring device characterized in that rough adjustment is performed based on an output signal and fine adjustment is performed based on an output signal of the second light receiving element.