JPS6140506A - Angle sensor - Google Patents

Abstract

PURPOSE:To enable the measurement of a minute angle with high accuracy, by utilizing the change in transmissivity. CONSTITUTION:Light receiving elements 20, 21 are provided to the oblique sides 12, 13 of a critical angle prism 8 so as to provide a thin gap therebetween and perform the photoelectric conversion of the quantities of transmitted lights. The light receiving signals being the outputs of said light receiving elements 20, 21 are respectively inputted to current-voltage converters 22, 23. The respective outputs (a), (b) of the current-voltage converts 22, 23 are propertional to the quantities of transmitted lights changing in a parabolic shape. These outputs (a), (b) are respectively shaped to pulses (c), (d) and further outputted as a pulse (e) with a narrow width interposing a critical angle thetac by a NAND circuit 26. The trigger levels of Schmidt circuits 24, 25 can be set sothat the width of the pulse (e) corresponds to desired angle measuring sensitivity. Therefore, if this pulse (e) is generated, the incident or emitting light of the liquid level 7 of mercury is cleared to become vertical in the range of the width of the pulse (e).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an angle sensor used in an electronic goniometer or the like, which automatically and highly sensitively measures and displays the components of the inclination angle of a horizontal plane in two orthogonal axes directions.

Many devices have been proposed and put into practical use as angle sensors. For example, there are mechanical or electromagnetic angle sensors that use the movement of a weight hanging from a rotating shaft and read the rotation angle with an encoder, or convert it into the amount of excitation current of an electromagnetic rotor. However, all of these angle sensors involve friction in the rotating bearing, and there are many causes of coupling errors with sensors such as encoders, making it difficult to improve accuracy. Therefore, in recent years, the mercury liquid level has been used as a horizontal reference, and by using this as an optical mirror surface to project concentric ring patterns etc. onto the mercury liquid surface, the reflected image and the diffraction image generated by the original pattern have been So-called optical angle sensors have been proposed that photoelectrically detect deviations from the center. Using an optical image in this way allows the x and y2 components of the tilt angle to be automatically measured without contact, which has many advantages over the mechanical and electromagnetic angle sensors mentioned above. However, conventional optical angle sensors require large devices and have problems in terms of sensitivity.

The present invention has been made in view of the above-mentioned points, and eliminates the drawbacks of mechanical or electromagnetic angle sensors.
The present invention aims to provide a highly sensitive angle sensor having a compact mechanism capable of simultaneously and non-contactly automatically measuring angular components in the , y and two axis directions.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a schematic diagram of an embodiment of an angle sensor according to the present invention.

Light source 1 such as a quasi-monochromatic LED or semiconductor laser
The luminous flux from the condenser lens 2 becomes parallel light, which is deflected by 90' by the semi-transparent mirror 3 and directed vertically downward. A mercury tank 5 is fixed to a base 4 which can be leveled horizontally, and mercury is sealed therein.

The upper lid of the mercury tank 5 is made of a transparent flat glass 6, which encloses mercury and allows parallel incident light from the semi-transparent mirror 3 to pass therethrough. The mercury liquid level 7 serves as a horizontal reference and at the same time forms an optically high-quality reflective surface. The reflected light from the mercury liquid surface 7 passes through the semi-transparent mirror 3 and then enters the critical angle prism 8. Incidentally, these series of optical systems are attached to a housing (not shown) that is integrated with the base 4, and when the horizontal plane of the base 4 tilts, the optical axis 9 also tilts in the same way, which was originally set perpendicular to the mercury liquid level 7. The incoming light and the outgoing light are also deflected from the vertical direction.

Here, the critical angle prism 8 will be explained according to FIG.

The critical angle prism 8 is manufactured so that when the vertical reflected light beams 10.1] are incident on the slope 12.13, the respective incident angles θC form a critical angle with respect to these incident rays. That is, the ray 10 (or 11) incident on the hypotenuse 12 (or 13) at the critical angle θC is
) is not transmitted at all and is totally reflected back into this prism. Assuming that the refractive index of this critical angle prism 8 is 1.52, the critical angle θC is 41.146. As shown in the second diagram, the incident light beam is inclined with respect to the vertical optical axis 9, and the light beam 14.
15, the slope 1 of the optical axis 14
Since the angle of incidence on 2 is smaller than the critical angle oc, a part of it passes through the slope 12 and becomes transmitted light 16, and the other part is reflected and then enters the slope 13, but its angle of incidence is equal to the critical angle θC The total reflected light is 17 because it is larger than . On the other hand, since the incident angles of the light ray 15 with respect to the slopes 13 and 12 are both larger than the critical angle θC, the light ray 15 becomes totally reflected light 18. Even if the inclination directions of the light rays 14, 15 are both reversed from those shown, the behavior of these light rays will simply be reversed.

FIG. 3 shows the transmittance of transmitted light 16 near the critical angle.

The horizontal axis shows the incident angle range from the critical angle θC to /JX, and the vertical axis shows the transmittance TP + of P-polarized light and S-polarized light.
It shows T s.

These transmittances decrease rapidly as the critical angle is approached;
It is completely zero for angles of incidence above the critical angle. Also,
The transmittance Tp (or Ts) changes parabolically with respect to the incident angle θ and can be approximated as 2×102 θ in 'rp. Therefore, dT near the critical angle θC
p/dθ shows a steep change in transmittance of −3.3% per 5″.In other words, a minute angular change is amplified through the transmittance.

The angle sensor of the present invention makes it possible to measure small angles with high precision by utilizing this sharp change in transmittance.

Here, referring back to FIG. 1 and further referring to FIG. 4, the photoelectric conversion and signal processing of these transmitted lights will be explained.

Light receiving elements 20 and 21 are provided on the oblique sides 12 and 13 of the critical angle prism 8 with a thin gap in between, and photoelectrically convert the amount of transmitted light. The light reception signals output from the light receiving elements 20 and 21 are input to current voltage converters 22 and 23, respectively.

The respective outputs a and b of the current-voltage converters 22 and 23 are
As explained using FIG. 3, it is proportional to the amount of transmitted light, which changes parabolically. These outputs a and b are shaped into pulses c and d, respectively, by Schmitt circuits 24 and 25, and further outputted by a NAND circuit 26 as a narrow pulse e sandwiching the critical angle Oc. The trigger level γ0 of the Schmitt circuit 24, 25 can be set in advance so that the width Δ0 of the pulse e corresponds to a desired angle measurement sensitivity, for example Δθ=5#. Therefore, it can be seen that when this pulse e is generated, it is perpendicular to the incident or output light beam on the mercury liquid surface 7 within a range of 80 degrees. Such an angle measurement mode can be employed, for example, as a compensator of an electronic angle measurement instrument.

FIG. 5 shows an electronic circuit system that can provide other angle measurement modes.

Reference numeral 27 is an angle conversion circuit for converting the amount of transmitted light received into a corresponding angle value, and has a built-in conversion memory. The outputs of the current-voltage converters 22 and 23 are converted by the angle conversion circuit 27 into actual measurement values having desired units, and the Φ values are displayed on the display 28. Incidentally, since such an angle conversion circuit 27 can be easily constructed using existing electronic circuit technology, a description thereof will be omitted.

Further, the outputs of the current-voltage converters 22 and 23 are connected in turn to an inverter 29, 30 and an AND circuit 31, 32, respectively, and output a pulse indicating the direction of the tilt angle. For example, if the inclination angle at which the amount of transmitted light is incident on the light receiving element 21 is 0, then
The output pulses of the AND circuit 32 indicate a positive inclination angle, and these discrimination pulses in the inclination direction are also displayed on the display 32 in the same way as the actually measured angle values. The two discrimination pulses can be easily obtained by the inverters 29, 30 and AND circuits 31, 32 using level signals such as c and d in FIG. 4, so their explanation will be omitted.

In the above explanation, the direction of the inclination angle of the parallel rays was limited to the plane of the paper, but in reality, the direction of the inclination angle within the plane perpendicular to the plane of the paper must also be considered. In order to detect such a two-dimensional inclination angle, the critical angle prism 8 is a two-dimensional critical angle prism having four slopes that also form a pair of critical angles in a direction perpendicular to the plane of the paper. It would be better if one J photodetector was added to the slope in the direction perpendicular to , and an electronic circuit system for angle measurement signal processing as shown in Fig. 1 or 5 was added.
) e In the above embodiment, the reflective surface was a mercury liquid surface with the compensator of an electronic goniometer in mind, but 1
This reflective surface may be a reflector fixed to the object and having an arbitrary posture. In addition, it is desirable that the parallelism of the light rays incident on the critical angle prism be as good as possible, so the light source must be one with sharp directivity, such as a semiconductor laser. Even if it is used, there is no problem because the behavior of the critical transmitted light at the outer line of the divergence angle is still sharp. However, it is unavoidable that there is a limit to the angle measurement accuracy corresponding to this opening angle.

As described above, the angle sensor of the present invention only needs to be large enough to measure one parallel beam, and can be constructed compactly and relatively inexpensively using minute optical members. This has the advantage that even changes can be measured with high precision.

It is expected that the angle sensor of the present invention will be incorporated into all types of measurement and control equipment to perform a wide variety of functions.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIG. 2 is a surface measurement diagram showing an example of a critical angle prism used in the present invention, and FIG. 3 is a transmission of transmitted light near the critical angle A2--18= FIG. 4 is a diagram showing output waveforms of various parts in the electronic circuit system used in the present invention. ■ = Light source 2: Condenser lens 3: Semi-transparent mirror 7: Mercury liquid surface (reflecting surface) 8: Critical angle prism 20, 21: Light receiving element Patent applicant Asahi Optical Industry Co., Ltd. (Format) September 4, 1985/Display of the case 1985 Patent Application No. 77808 10 Name of the invention Angle sensor 3, person making the amendment Relationship to the case Patent applicant address Maeno-cho, Itabashi-ku, Tokyo 2-36-9 Name (
052) Asahi Optical Industry Co., Ltd. Representative: Toru Matsumoto Address: 174 Telephone: 03-960-5162 9 Address: 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Date of dispatch
August 27, 1985 Party B, "Brief explanation of drawings" column 7 of the specification subject to amendment, vegetation in "Brief explanation of drawings" of the statement of contents of amendment, page 10, line 2 5 is a block diagram showing an electronic circuit system that can provide other angle measurement modes. ζ = 2 −

Claims (1)

[Claims] a light source, a condenser lens that converts the light beam from the light source into parallel light, a semi-transparent mirror provided on the parallel optical path of the condenser lens, and a semi-transparent mirror that is fixed to the object to be measured and converts the parallel light flux reflected by the semi-transparent mirror into substantially perpendicular light. An angle sensor comprising: an incident reflecting surface; a critical angle prism provided on a path of reflected light from the reflecting surface; and a light receiving element provided close to a slope of the critical angle prism.