JPH0142014Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a photodetector used in a position detection device, a speed detection device, etc. in an electric motor, and improves the S/N ratio of the detection signal of the photodetector.
The purpose is to make the photodetector compact.

As shown in Fig. 1, a conventional position or speed detection device using a light reflection method consists of forming slit-shaped holes 1' by pressing or etching on a stainless steel reflector plate 1 with a smooth surface. , this reflecting plate 1 is attached to a rotor 2 whose surface is painted matte black, and a light projecting device 3 and a light receiving device 4 are attached.
The mounting angle is adjusted so that the light from the light projecting device 3 is reflected on a slit portion formed on the reflecting plate and enters the light receiving device 4. In this photodetector, the light incident on the light receiving device 4 is divided into two cases: when the light from the light projecting device 3 is reflected by the slit-shaped hole 1' which becomes the light absorbing section, and when the light is reflected by the slit-like hole 1'' which becomes the light reflecting section. The rotational position and rotational speed are detected by utilizing the fact that the amount of light differs depending on the case, and the light output of the light receiving device 4 changes.

However, in the conventional system, the rotor 2
The disadvantage is that the black-painted part provided on the sensor cannot completely absorb the light, and some amount of light is reflected, which reduces the sensitivity of the detection signal of the photodetector. In order to increase the amount of reflected light from the light reflecting section, the gap length between the light reflecting plate 1, the light projecting device 3, and the light receiving device 4 can be shortened. The amount also increases, which does not meet the purpose of improving photodetection sensitivity. There is usually an optimal gap length. In general, electric motors are required to have a compact shape, but when such a photodetection device is housed within the motor, the conventional method is to combine a light projector 3, a light receiver 4, and a light reflector 1. The disadvantage is that it cannot be made compact because the gap cannot be shortened.

In addition, to improve the photodetection sensitivity, a light blocking type photodetector as shown in Fig. 2 can be considered.
The configuration shown in FIG. 2a has the disadvantage that the light projecting device 3 and the light receiving device 4 must be arranged so as to sandwich the light blocking plate 5, which complicates the assembly method and structure. In addition, in the configuration shown in FIG. 2b, the toothed portion 7 of the light blocking plate 6 must be extended so that it is in the space between the light projecting device and the light receiving device 4.
A space is required over the entire circumferential direction by the length of the toothed portion 7 from the light shielding plate mounting surface, making it impossible to sandwich the light projecting device 3 and the light receiving device 4 in the stator coil of the motor, etc. The disadvantage is that space is limited.

The present invention solves the above-mentioned conventional drawbacks, and an embodiment thereof will be described below with reference to FIGS. 3 and 4. FIG. 3 shows the structure of a light reflecting plate 8 made of a stainless steel plate, etc. The light reflecting plate 8 has thin slits 9 formed at equal intervals by pressing or etching. The tooth-shaped light blocking portion 10 is formed by folding the cut and raised pieces that are produced in the axial direction. Figure 4 shows the positional relationship between the light reflecting plate 8, the light projecting device 3, and the light receiving device 4. A light blocking section 10 is located.

In the above configuration, the projected light from the light projecting device 3 is directly reflected by the light reflecting plate 8 in the portion where the tooth-shaped light blocking portion 10 is not provided, so that the reflected light enters the light receiving device 4 and the light is reflected from the light receiving device 4. A signal output is output according to the amount of reflected light. Moreover, when the tooth-shaped light blocking section 10 comes to the light reflection path, the light from the light projecting device 3 is blocked by the tooth-shaped light blocking section 10, and the light does not reach the light receiving side. There isn't. Of course, the light blocking effect can be improved if a slit-shaped mask having the same tooth width as the tooth-shaped light blocking section 10 is installed in either or both of the light projecting device 3 and the light receiving device 4.

In this case, the length of the tooth-shaped light blocking portion 10 of the light reflecting plate 8 is determined from the mounting surface of the light reflecting plate 8 to the projecting device 3,
The length may be up to the shortest distance of the light receiving device 4, and can be configured to be shorter than the length of the tooth-shaped portion of the light blocking type photodetector.

As is clear from the above description, the present invention provides the following effects.

(1) Since the light entering the light receiving device is blocked by the tooth-shaped light blocking section, a signal with a high S/N ratio can be obtained.

(2) Since it is possible to shorten the gap length between the light projecting device, the light receiving device, and the light reflecting plate, it is possible to obtain a signal with an even higher S/N ratio by shortening the gap.

(3) Since the gap can be reduced, the photodetector can be configured compactly.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the schematic structure of a conventional light reflection type photodetector, Figs. 2a and b are perspective views showing the schematic structure of a conventional light blocking type detector, and Fig. 3 is an implementation of the present invention. FIG. 4 is a plan view of a light reflecting plate showing an example, and a sectional view of a photodetector using the same light reflecting plate. 3... Light projecting device, 4... Light receiving device, 8... Light reflecting plate, 10... Light blocking section.

Claims (1)

[Scope of utility model registration request] A photodetector that reflects light from a light projector on a light reflecting plate and supplies an optical signal to a light receiver includes a light reflecting section that reflects the light from the light projector and guides it to the light receiver, and a light reflector that reflects the light from the light projector and guides it to the light receiver; The light reflecting plate is equipped with a light projecting device and a light receiving device, and the light projecting device and the light receiving device are connected to the light reflecting plate. A photodetector characterized in that the light beams and the cut-off portions, which are opposed to each other and constituted by tooth-like protrusions, are located on the incident path or reflection path of the light.