JPH08105710A - Optical sensor - Google Patents

Abstract

PURPOSE: To measure the thickness of a sheet, etc., during conveying without error without providing a mechanism for moving a contact part by providing a diffraction grating which is movable so that an incident direction is varied with respect to a beam direction and detecting the change of the angle of the grating due to the insertion of an object to be detected. CONSTITUTION: A collimated laser light from a light source 1 is diffracted by a diffraction grating 4 which is rotatable at a support 3 as a center, received by a photodetector 2, and the angle of the incident light is detected to detect the angle of the grating 4. The lower end of the grating 4 is brought into weak contact with a reference surface 5, lifted by the insertion of an object (sheet) 6 to be detected, and the angle of the grating 4 is varied. The variation of the angle of the grating 4 is detected as the angle change of the incident light at the photodetector 2, thereby measuring the thickness of the object 6 to be detected. In this case, as the photodetector 2, a photodiode PD is used, and the angle change of the incident light from the change of the light intensity is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor for detecting a displacement or an angle of an object, and more particularly to an optical sensor used for a paper thickness sensor or a precision measuring device.

[0002]

2. Description of the Related Art As a conventional optical sensor, a contact type position detecting sensor is provided with a scale consisting of a large number of slits between a light source and a light receiving portion as shown in Japanese Patent Laid-Open No. 56-76009. Is common. This position detection sensor has a structure that obtains the amount of movement of the scale or the light source and the light receiving unit by detecting that the light from the light source is blocked by the slit.

As a non-contact type, an optical displacement sensor using an optical position detector is disclosed in, for example, Japanese Patent Laid-Open No. 5-2.
There is one as seen in Japanese Patent No. 40611. The operation of this optical displacement sensor will be described with reference to FIG. Light emitting element 1
The detection light L1 emitted from the projection surface 60 is projected onto the projection surface 60 of the detection target object 6. Reflected light L2 reflected by the projection surface 60 of the detection target
Through the pinhole 10 through the light receiving surface 20 of the optical position detector 2.
Incident on. At this time, the light receiving position on the optical position detector is determined by the distance between the displacement sensor and the detection target, and therefore the position of the target can be detected from the output voltage of the optical position detector.

[0004]

However, in the above-mentioned sensor, in the case of the contact type, the scale is located between the light source and the light receiving part, and is movable only in the vertical direction, and the thickness of the object to be detected. When measuring, there is a drawback that another power and mechanism for sandwiching the object to be detected by the reference surface and the scale or the light receiving unit are required.

In the case of the non-contact type, the ATM of the bank
When used for detecting paper money or paper double feed of a copying machine, there is a risk of malfunction due to paper turbulence in the conveyed state.

The present invention has been made in view of the above points, and does not require a separate mechanism for moving the contact portion and power, and when detecting the thickness of paper or the like, detection can be performed without error even during transportation. The aim is to provide a possible optical sensor.

[0007]

In order to achieve the above object, the present invention provides a diffraction grating arranged so as to rotate about a central axis, a light source for projecting light on the diffraction grating, and a light source from the light source. Of a displacement / angle sensor having a light receiving portion for receiving the diffracted light diffracted by the diffraction grating, provided with the diffraction grating movable so that the incident angle changes with respect to the beam direction. Is.

Further, the diffraction grating is arranged at an angle with respect to the reference surface, and the diffraction grating is fixed to a supporting portion which is movable about a central axis and is in contact with the reference surface. The thickness of the detection target is measured by detecting the projection light from the light source by the light receiving unit that the angle of the diffraction grating is changed by inserting the detection target between the grating and the detection target. It is a thing.

Further, the diffraction grating has an incident angle selectivity,
A photodiode may be provided as the light receiving unit, and the change in the angle of the diffraction grating may be detected by detecting the amount of transmitted light or the change in diffracted light.

[0010]

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention. The light emitted from the light projecting unit 1 is incident on the diffraction grating 4 to generate diffracted light. Therefore, the irradiation light is preferably monochromatic parallel light, and a light source in which a semiconductor laser is used as a light source and collimated by a lens is preferable. Needless to say, the generality of the present invention is not lost even if an LED is used as a light source or if it is not a perfect collimated light. The light incident on the diffraction grating 4 generates diffracted light at an angle θ2 according to the following equation. sin θ1 + sin θ2 = m λ / Λ where θ1 is the incident angle, m is the diffraction order, λ is the wavelength of light, and Λ is the pitch of the diffraction grating. The light emitted at the angle θ2 is applied to the light receiving unit 2. At this time, the diffraction grating 4 is detected by detecting the angle of the light emitted by the light receiving unit 2.
The angle of can be detected. As a means for detecting the angle of the light applied to the light receiving section 2, there is a method of using a PD as the light receiving section and detecting a change in light intensity. This is a method of detecting a change in beam area with which the PD is irradiated by the change in the irradiation angle of the diffracted light, as a change in the light amount. It is preferable to select the PD that is slightly smaller than the beam diameter of the diffracted light. Further, it is possible to widen the detection range by forming an array structure in which a large number of PDs are arranged. By configuring the diffraction grating 4 such that the angle changes depending on the information to be detected, such as the rotation angle and the displacement, the desired information can be obtained by the light receiving unit 2. In this embodiment, the support portion is provided so as to rotate about the central axis, and the rotation angle and displacement of the axial center of the diffraction grating can be measured.

FIG. 2 shows a second embodiment of the present invention. The present embodiment is an example in which the invention of the above-described embodiment is applied to a displacement sensor that measures the thickness of paper or the like. The difference from the invention of the above-described embodiment is that it has a reference surface 5 that is fixed to the sensor body, and one end of the support portion 3 that fixes the diffraction grating 4 is in weak contact with the reference surface 5, 3 is a structure in which the object to be detected is pushed up around the central axis. The contact pressure between the support portion 3 and the reference surface 5 is applied by the weight of the support portion or an elastic body such as a spring. No matter how the contact pressure is applied, the generality of the present invention is not lost. With such a structure, when the object to be detected is inserted into the sensor, the support portion 3 is pushed up and the angle of the diffraction grating 4 changes. The thickness of the detection target 6 can be measured by detecting this by the method as described in claim 1.

Further, the diffraction grating 4 described above may be a grating having an angle selective transmission property, and the light receiving section 2 may be used as a PD to measure the angle and displacement of the support section 3 from the change in the amount of diffracted light. In general, the diffraction efficiency of the diffraction grating is determined by the incident angle, the depth of the grating, etc., so that the change in the angle of the diffraction grating appears as the change in the light intensity of the diffracted light. When the PD detects a change in the amount of diffracted light, the output of the PD changes depending on the angle of the diffraction grating, and the angle of the diffraction grating can be measured. Since the strength of the angle selectivity changes by changing the depth of the diffraction grating 4, a deep diffraction grating can be used to increase the sensitivity of the sensor, and a shallow diffraction grating can be used when detection sensitivity is not so required. The detection range can be expanded. P used at this time
Since D needs to have a size capable of always detecting the entire beam of diffracted light, it is preferable to use transmitted light whose diffraction angle does not change. Further, when using high-order diffracted light, it is preferable to fix the PD to the support portion.

FIG. 3 shows another embodiment of the present invention. The feature here is that the diffraction grating 4 is of a reflective type.
As a reflection type diffraction grating, a relief type diffraction grating and a metal,
Generally, it can be created by vapor deposition of aluminum or chrome. In FIG. 3, the light emitted from the light source to the diffraction grating is diffracted at the diffraction angle θ2. The diffraction angle at this time is an angle rotated by 180 degrees with respect to the transmission type diffraction grating. The diffracted light of FIG. 1 corresponds to the diffracted light of FIG. 3 in the reflection type. Since the diffracted light from the reflection type diffraction grating can be made into an acute angle by the reflection angle of the reflection from the mirror surface, the projector 1 and the light receiving unit 2 can be brought close to each other, and the size can be further reduced. Needless to say, the function does not change even if the diffraction grating is of a reflective type in the light from claim 3.

A PSD may be used as the light receiving section.
By using PSD, continuous detection is possible in a wide range. When the detection range is to be expanded using PD, there is a method of detecting using PD array as shown in FIG. However, according to this method, only a signal in which the peak of each PD element changes as shown in the graph, and continuous signals cannot be acquired. Since the PSD can detect the beam position as a voltage change, continuous detection without interruption is possible. Further, since it is an element for detecting the position of light, it has an advantage that errors due to changes in the light intensity of the light projecting portion are small. The configuration can be realized by replacing the light receiving unit 2 with PDS in the above-described embodiments. The irradiated beam is preferably a thin beam in order to improve resolution. The angle and displacement of the diffraction grating can be detected by detecting the light position of the diffracted light scanned by the change in the angle of the diffraction grating 4.

[0016]

As described above, in the optical sensor according to the present invention, the diffraction grating arranged so as to rotate about the central axis, the light source for projecting light on the diffraction grating, and the light source In the displacement and angle sensor having a light receiving portion for receiving the diffracted light diffracted by the diffraction grating, is the diffraction grating movable so that the incident angle changes with respect to the beam direction? Further, the diffraction grating is arranged at an angle with respect to the reference plane, and the diffraction grating is fixed to a support portion arranged so as to be movable around a central axis and to be in contact with the reference plane. Since the thickness of the detection target is measured by detecting the projection light from the light source by the light receiving unit that the angle of the diffraction grating is changed by inserting the detection target between contact Another mechanism for moving the, power is unnecessary, when detecting the thickness of such paper, it is possible to error-free detection even during transport.

Further, the diffraction grating has an incident angle selectivity,
The detection sensitivity can be improved by providing a photodiode as the light receiving unit and detecting the change in the transmitted light amount or the change in the diffracted light amount to detect the change in the angle of the diffraction grating.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing another embodiment of the present invention.

FIG. 5 is a diagram showing a conventional displacement sensor.

[Explanation of symbols]

 1 Light source 2 Light receiving part 3 Support part 4 Diffraction grating 5 Reference plane 7 PD array 8 PDS 9 Irradiated diffracted light

Claims (3)

[Claims] 1. A diffraction grating arranged so as to rotate about a central axis, a light source for projecting light on the diffraction grating, and light from the light source receives diffracted light diffracted by the diffraction grating. In a displacement / angle sensor having a light receiving portion for moving, an optical sensor including the diffraction grating movable so that an incident angle changes with respect to a beam direction. 2. The diffraction grating is arranged at an angle with respect to a reference plane, and the diffraction grating is fixed to a support part arranged so as to be movable about a central axis and in contact with the reference plane. The thickness of the detection target is measured by detecting the projection light from the light source by the light receiving unit that the angle of the diffraction grating changes when the detection target is inserted between the grating and the detection target. The optical sensor according to claim 1. 3. The diffraction grating has an incident angle selectivity, is provided with a photodiode as a light receiving portion, and detects an angle change of the diffraction grating by detecting a transmitted light amount or a diffracted light amount change. The optical sensor according to claim 1 or 2.