JP3542226B2 - Optical potentiometer - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical potentiometer including a fixed light source, a fixed light receiving element, and a slit disk interposed between the fixed light source and the fixed light receiving element. More specifically, the present invention relates to a slit disk structure for preventing a fixed light source from being electrically damaged.
[0002]
[Prior art]
Conventionally, various types of optical potentiometers are known. For example, JP-A-60-140117, JP-A-60-225024, and JP-A-7-43176 disclose a structure using a slit disk in which spiral slits are formed. As shown in FIG. 8, a slit disc 1 made of a light-shielding material such as a thin metal plate is fixed to a rotating shaft 2 and can be rotationally displaced. The rotating shaft 2 is connected to a measurement object (not shown). A spiral signal slit 3 whose distance from the center gradually increases along the circumferential direction is formed on the surface of the slit disk 1 by etching. Above the slit board 1, a light source 4 composed of, for example, an LED is fixedly arranged. The light source 4 irradiates the surface of the slit disk 1 with substantially parallel light via a light projecting lens 5 fixed to the surface. On the other hand, a light receiving element 6 is fixedly arranged below the slit board 1 in alignment with the light source 4. The light receiving surface 7 provided on the surface has a longitudinal shape along the radial direction of the slit disc 1. The light 8 passing through the signal slit 3 moves radially with the rotation displacement of the slit board 1 and is received by the light receiving surface 7. The light receiving element 6 is composed of, for example, a PSD, and outputs detection signals IA and IB to a pair of output terminals. The detection signals IA and IB change according to the light receiving position 9 of the passing light 8. The pair of detection signals IA and IB are subjected to difference processing by the processing circuit 10 to generate an output signal Vout representing the rotational displacement of the slit disk 1. In addition, an automatic light amount control circuit (APC) 15 is connected to the processing circuit 10 and controls a drive circuit 16 of the light source 4. That is, the APC 15 operates based on a signal obtained by adding the pair of detection signals IA and IB to each other, and controls the light emission amount of the light source 4 so as to keep the light reception amount of the light receiving element 6 constant.
[0003]
[Problems to be solved by the invention]
Generally, the slit board 1 is formed with a signal slit 3 partially in the circumferential direction. Therefore, depending on the rotational position of the slit disc 1, the light from the light source 4 may be completely shut off and the light receiving element 6 may not receive any light. If no countermeasures are taken, the drive current supplied from the drive circuit 16 to the light source 4 by the action of the APC 15 will increase extremely. Therefore, the APC 15 is provided with a current limit so that the light source 4 is not destroyed even when the light from the light source 4 is cut off by the slit board 1. By the way, the amount of the limiting current is set so as not to exceed the rated current of the light source over the entire operating temperature range. If the current exceeds the rated current, the light source may be damaged. Generally, the rated current of a light source decreases as the ambient temperature increases. For this reason, the limiting current is set so as to match the rated current of the light source at the maximum operating temperature. However, if the light source is used below the maximum operating temperature, even if the current consumption of the light source reaches the current limit and the product reaches the end of its product life, the light source will actually break down or deteriorate as long as it is used below the maximum operating temperature. If the current limit is newly set higher, for example, it can be used as it is. However, in reality, the life of the light source is considered to have expired in design, so that the light source cannot be used because it has not been destroyed. As described above, the provision of the current limitation has a disadvantage that the product life is shortened. It should be noted that a mechanical measure can be considered instead of the electric measure of providing a current limit. For example, a stopper is provided to prevent the rotation shaft 2 from mechanically rotating beyond the angle range where the signal slit 3 exists. However, in this case, a new rotation stop mechanism including a stopper is required, which leads to an increase in manufacturing cost.
[0004]
Here, in order to facilitate understanding of the above drawbacks, a brief description will be given of the product life of the optical potentiometer. In the optical potentiometer, the life of the light source is shortest among the components, and it is best that the life of the light source = the product life. However, this only holds true at maximum operating temperatures. The lifetime of a light emitting element used as a light source is generally when the current required to obtain the same light emission is 1.5 times the initial value or when the light emission is 67% at the same current. is there. Since the light source deteriorates with time, a larger current is required to obtain the same light amount. In an optical potentiometer, a change in the amount of light received by a light receiving element such as a PSD is output, so that the light emission amount of the light source must be APC-controlled so that the amount of light received by the PSD is constant. Therefore, when the deterioration of the light source progresses and the required current reaches the limit current, the amount of light received by the PSD cannot be maintained at the previous level. This time is defined as the product life. In the conventional optical potentiometer, the product life is artificially determined by providing the limiting current in this way. It is determined that the product has reached the end of its service life, even though it can actually be used if the deterioration has progressed by a predetermined amount, rather than until the component actually breaks down and no longer functions. Note that the setting formula of the limiting current is described below for reference.
Limited current = (light source current (at 25 ° C.)) / (Relative light quantity (at maximum operating temperature)) × (light source life setting coefficient) + (current consumption of circuit)
The relative light quantity (at the maximum operating temperature) depends on the characteristics of the light source. The life setting coefficient of the light source is generally 1.5. The current consumption of the circuit is determined by the circuit configuration.
[0005]
[Means for Solving the Problems]
The following measures were taken in order to solve the above-mentioned problems of the conventional technology. That is, the optical potentiometer according to the present invention includes, as basic components, a slit disk, a fixed light source, a fixed light receiving element, a processing circuit, and an automatic light amount control circuit. The slit disc is rotationally displaced about a rotation axis and has a signal slit formed along a circumferential direction. A fixed light source irradiates the slit disc with light. The fixed light receiving element has a long light receiving surface arranged along the radial direction of the slit disk, receives light passing through the signal slit that moves in the radial direction with rotational displacement, and detects a detection signal corresponding to the position. Is output. A processing circuit processes the detection signal to generate an output signal representing the rotational displacement. The automatic light amount control circuit operates based on the detection signal and controls the light emission amount of the fixed light source so as to keep the light reception amount of the fixed light receiving element constant. In such a configuration, the slit disc is divided into an effective angle region where rotation displacement can be detected and an invalid angle region where rotation displacement cannot be detected. The effective angle region is provided with the signal slit whose radial distance from the rotation axis changes linearly with respect to rotational displacement. As a characteristic feature, a protection slit for simply passing light is provided in the invalid angle region, and the automatic light amount control circuit operates in a steady state over the entire angle of the slit disk. Originally, the automatic light quantity control circuit is designed to always operate. However, if the light is blocked by the slit disc, the signal path of the feedback control system is cut off, so that the amount of received light cannot be controlled. Therefore, a slit is provided over the entire angle of the slit disc to maintain a steady operation of the automatic light amount control circuit. Preferably, the protection slit is divided into a plurality of pieces along the circumferential direction of the slit disc. Also preferably, the protective slit and the signal slit are partially overlapped with each other along the circumferential direction of the slit disk. More preferably, the protective slit has a larger radial width than the signal slit. From a different point of view, widening the slit width has the same effect as partially arranging the protection slit and the signal slit partially depending on the conditions. This is the same even when an opening is provided at the joint of the protective slit divided in the circumferential direction.
[0006]
The basic concept of the present invention is to make the light receiving element always receive the light from the light source regardless of the rotational position of the slit disc. For this reason, the protection slit is provided in an invalid angle area outside the effective angle area where the signal slit exists. In this manner, by providing slits over the entire 360-degree angle of the slit disk, the automatic light amount control circuit is always operated in a steady state, so that an excessive drive current is not supplied to the light source. As described above, in the present invention, since light is not blocked, there is no need to provide a current limit, the limiting resistor can be omitted, and the life of the light source is equal to the product life. The current limit is provided so that the light source is not destroyed when the light is blocked, and is not necessary if the light is not blocked. Further, a plurality of protective slits are divided along the circumferential direction of the slit disc. The seam is left between the protective slits, so that the mechanical strength of the slit disc can be maintained. Further, the protection slit and the signal slit are partially overlapped with each other along the circumferential direction of the slit disc and interfere with each other. This makes it possible to completely transmit the light from the light source over the full 360 degrees. In addition, the radial width of the protective slit is made wider than the radial width of the signal slit. Thereby, the drive current of the light source in the invalid angle region can be suppressed.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram showing a basic configuration of an optical potentiometer according to the present invention. As shown in the figure, the optical potentiometer includes a slit disk 1, a fixed light source 4, a light receiving element 6 also fixed, a processing circuit 10, and an automatic light amount control circuit (APC) 15. The slit disc 1 is rotationally displaced about a rotation shaft 2 and has a signal slit 3 partially formed along the circumferential direction. The slit disc 1 is made of a light-shielding material such as a thin metal plate, and the signal slit 3 can be formed by etching. The light source 4 is composed of, for example, an LED or the like, and receives a drive current from the drive circuit 16 to emit light and irradiates the slit disc 1 with light. The light source 4 irradiates the surface of the slit disk 1 with substantially parallel light through a light projecting lens 5 fixed to the surface thereof. The light receiving element 6 is arranged to face the light source 4 via the slit board 1 and has a long light receiving surface 7 arranged along the radial direction of the slit board 1 and moves in the radial direction with rotational displacement. It receives the passing light 8 from the signal slit 3 and outputs detection signals IA and IB corresponding to the position 9 thereof. The light receiving element 6 is composed of, for example, a PSD, and outputs detection signals IA and IB to a pair of output terminals. The detection signals IA and IB change according to the light receiving position 9 of the passing light 8. The processing circuit 10 processes the detection signals IA and IB to generate an output signal Vout representing the rotational displacement. Specifically, a difference process is performed on the pair of detection signals IA and IB to generate an output signal Vout representing rotation displacement information of the slit disc 1. The APC 15 is connected to the processing circuit 10 and operates based on a signal obtained by adding the pair of detection signals IA and IB to each other, and controls the light emission amount of the light source 4 so as to keep the light reception amount of the light receiving element 6 constant. . That is, when the total amount of the detection signals IA and IB increases, the APC 15 controls the drive circuit 16 to suppress the drive current supplied to the light source 4. When the total amount of the detection signals IA and IB decreases, the APC 15 controls the drive circuit 16 to increase the drive current supplied to the light source 4. Thus, the detection system including the combination of the light source 4 and the light receiving element 6 can be stably operated by the feedback control.
[0008]
The slit disc 1 is divided into an effective angle region where rotation displacement can be detected and an invalid angle region where rotation displacement cannot be detected. In the effective angle region, there is provided a signal slit 3 whose radial distance from the rotation shaft 2 changes linearly with respect to rotational displacement. The signal slit 3 has, for example, a spiral shape whose distance from the center gradually increases along the circumferential direction. On the other hand, in the invalid angle area, a protective slit 3a for merely passing light is provided. The protective slit 3a has, for example, a simple arc shape. In this manner, by providing the slits 3 and 3a over the entire 360-degree angle of the slit board 1, the automatic light amount control circuit 15 always operates steadily regardless of the rotational position of the slit board 1, and the light source 4 and the light receiving element 6 The stable operation of the detection system composed of the combination can be completely maintained.
[0009]
FIG. 2 is an embodiment showing the shape of the slit formed in the slit disc 1, and shows the simplest example. The signal slit 3 has a spiral shape and is formed in the effective angle area 31. On the other hand, the protective slit 3a has an arc shape and is formed in the invalid angle area 32. The shapes of the signal slit 3 and the protection slit 3a are not limited to these. In this example, the effective angle area 31 is about 120 degrees, the invalid angle area 32 is about 240 degrees, and the slits 3 and 3a are provided over the full 360 degrees of the slit disk 1. Thus, light from the light source is not blocked regardless of the rotational position of the slit board 1, and there is no danger of limiting the current of the APC.
[0010]
FIG. 3 shows another embodiment of the slit shape. In the simplest embodiment shown in FIG. 2, only two joints are left between the signal slit 3 and the protection slit 3a. For this reason, the mechanical strength of the slit disc 1 may be reduced. Therefore, in the embodiment shown in FIG. 3, the protective slit 3a is divided into a plurality of pieces along the circumferential direction of the slit board 1, and the number of joints is increased. In this example, by dividing the protective slit 3a into three, a total of four seams 33 are left on the slit disc 1, and the mechanical strength is increased.
[0011]
FIG. 4 shows another embodiment of the slit shape. In the example shown in FIG. 3, the edge of one slit and the edge of another slit adjacent thereto do not always completely match due to a manufacturing error such as etching. When the ends of the slit are separated from each other, part of the light from the light source is blocked, so that the driving current supplied to the light source becomes larger than when the light is completely passing. For this reason, the rated current may be exceeded. Therefore, in this embodiment, the ends of the slits are partially overlapped with each other along the circumferential direction so that even part of the light is not blocked. At this time, in order to prevent the effective electrical angle corresponding to the effective angle area 31 from decreasing, the cutting angle of the signal slit 3 is set large enough to overlap.
[0012]
FIG. 5 shows still another embodiment of the slit shape. In the embodiment shown in FIG. 4, since the amount of light passing through the portion where the adjacent slits overlap is larger than usual, the driving current supplied to the light source is smaller than usual. In order to suppress such a variation, in the embodiment shown in FIG. 5, the divided protective slits 3a are separated from each other to eliminate the overlapping portion, and a pair of openings 34 are provided instead. Here, the radial width of the protective slit 3a is d, the circumferential distance between the protective slit 3a adjacent to t, and the diameter of one opening 34 and 2r _1, 2r diameter of the other opening 34 ₂ Then, if the relationship of π (square of r ₁ + square of r ₂ )> dt is satisfied, the output at the boundary of the protective slit 3 a can be made substantially constant.
[0013]
FIG. 6 shows yet another embodiment of the slit. In general, the light source has a longer life as the drive current is smaller. In view of this point, in this embodiment, the radial width D of the protection slit 3a is set to be wider than the radial width d of the signal slit 3. With this configuration, when the optical potentiometer is in the invalid angle region, the driving current of the light source is suppressed by the APC as compared with the effective angle region, so that the deterioration can be delayed accordingly.
[0014]
Finally, FIG. 7 is a block diagram showing a specific configuration example of the processing circuit 10, the APC 15, and the driving circuit 16 shown in FIG. One detection signal IA output from the light receiving element 6 such as a PSD is converted into a corresponding voltage signal VA by the amplifier 11 and then applied to the positive input terminal of the differentiator 12. Similarly, the other detection signal IB is converted to a corresponding voltage signal VB by the amplifier 13 and then applied to the negative input terminal of the differentiator 12. The pair of voltage signals VA and VB are subjected to differential processing by the differentiator 12 to output a signal Vout corresponding to the light receiving position of the light passing through the slit 3. Further, the pair of voltage signals VA and VB are added to each other by the adder 14. A drive transistor 16a included in the drive circuit 16 is connected to the output terminal of the adder 14, and controls the drive current of the light source 4 including an LED or the like so that the addition result is constant.
[0015]
【The invention's effect】
As described above, according to the present invention, the signal slit is provided in the effective angle area of the slit disk, while the protection slit is provided in the invalid angle area of the slit disk, and the automatic light amount control circuit operates over the entire angle of the slit disk. Let me. Thereby, even when the optical potentiometer deviates from the effective angle region and enters the invalid angle region, it is possible to prevent the light source from being destroyed. Further, by dividing the protective slit into a plurality of pieces along the circumferential direction of the slit disc, a seam is left, and the mechanical strength of the slit disc can be maintained. Furthermore, by partially arranging the protection slit and the signal slit along the circumferential direction of the slit disc, light from the light source is prevented from being interrupted even for a moment, and there is no possibility of destruction of the light source. And In addition, by setting the width of the protection slit in the radial direction to be larger than that of the signal slit, deterioration over time of the light source can be delayed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of an optical potentiometer according to the present invention.
FIG. 2 is a schematic plan view showing one embodiment of a protective slit formed on a slit board.
FIG. 3 is a plan view showing another embodiment of the protective slit.
FIG. 4 is a plan view showing another embodiment of the protective slit.
FIG. 5 is a plan view showing still another embodiment of the protective slit.
FIG. 6 is a plan view showing still another embodiment of the protective slit.
FIG. 7 is a block diagram showing a specific configuration example of a processing circuit incorporated in the optical encoder shown in FIG.
FIG. 8 is a block diagram showing an example of a conventional optical potentiometer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Slit board, 2 ... Rotation axis, 3 ... Signal slit, 3a ... Protection slit, 4 ... Light source, 6 ... Light receiving element, 7 ... Light receiving surface, 8: transmitted light, 9: light receiving position, 10: processing circuit, 15: automatic light amount control circuit, 16: drive circuit

Claims (4)

A slit disc having a signal slit formed along the circumferential direction while being rotationally displaced about the rotation axis, a fixed light source for irradiating the slit disc with light, and a longitudinally arranged along the radial direction of the slit disc A fixed light receiving element having a light receiving surface having a shape, receiving light passing through a signal slit that moves in a radial direction with rotational displacement, and outputting a detection signal according to the position; An optical potentiometer comprising: a processing circuit for generating an output signal representing the following equation; and an automatic light amount control circuit that operates based on the detection signal and controls the light emission amount of the fixed light source so as to keep the light reception amount of the fixed light receiving element constant. At
The slit disc is divided into an effective angle area where rotational displacement can be detected and an invalid angle area where rotational displacement cannot be detected.In the effective angle area, the radial distance from the rotation axis is relative to the rotational displacement. While the signal slit which changes linearly is provided, a protection slit for merely passing light is provided in the invalid angle area, and an automatic light amount control circuit is provided over the entire angle of the slit disk. An optical potentiometer that operates steadily. The optical potentiometer according to claim 1, wherein the protective slit is divided into a plurality of pieces along a circumferential direction of the slit board. The optical potentiometer according to claim 1, wherein the protection slit and the signal slit are partially overlapped with each other along a circumferential direction of the slit disk. The optical potentiometer according to claim 1, wherein the protective slit has a larger radial width than the signal slit.

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