JPH0146039B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light emitter, a light receiver placed close to the light emitter, and a reflector placed at a certain distance from the light emitter and the light receiver. The present invention relates to a V-type light barrier with a retroreflector having lobes.

Conventional V-type light barriers have limited applications because the signal changes are highly dependent on the displacement of the reflector from its housing. This signal dependence is most likely due to the fact that the reflector used in this type of light barrier (reflective foil or molded plastic reflector) does not reflect the light rays exactly in the opposite direction, and the scattering angle is much larger than the angle of incidence. or at a scattering angle that is extremely smaller than the incident angle. In other words, retroreflectors commonly used to accurately retroreflect light rays do not have ideal reflective properties. Conversely, the retroreflector often has a significant reflective scattering lobe such that the incident light is reflected at an angle within the angular range of the reflective scattering lobe. The existence of the above-mentioned reflection scattering lobe in the retroreflector used in the V-type light barrier as above means that
Increasing the distance from this retroreflector to the V-shaped light barrier means that the proportion of the scattered reflected light beam incident on the receiver decreases.

If the V-type light barrier described above must be used with a relatively large reflector displacement, even if the light flux reflected from the reflector located at a large distance is small, it will not affect the function of the system. , the sensitivity of the system must be increased. However, the high sensitivity of this system means that at short distances from the light barrier, reflective objects that are much smaller than the reflector (objects that should originally be recognized as obstacles)
, which means not recognizing it. In other words, the V-type light barrier does not perform its function for light-reflecting objects located at a short distance from the V-type light barrier.

Therefore, an object of the present invention is to provide a V-type light barrier belonging to the above-mentioned type, in which the signal outputted from the receiver into which the light beam is incident without interruption is lower than that of the conventional V-type light barrier. The object of the present invention is to provide a reflector that is almost unaffected by the displacement of the reflector. As a result, in relation to the conventional V-type light barrier,
The range of displacements over which the reflector can produce, on average, a stable received signal can be greatly expanded.

In order to solve the above-mentioned problems, the present invention provides that the light emitter and the light receiver are several (for example, two) optical imaging elements that are close to each other (in particular, adjacent to each other), and that the light emitter and the light receiver are arranged in parallel. It is configured to include one having an axis. The technical idea of the present invention is that a plurality of light barrier beams are output from the same light source or input to the same receiving element in parallel so that the intersection areas of the beams are aligned on the axis of the light barrier. It means being done. A retroreflector with a well-defined scattering angle has a much larger displacement range in the area of intersection of the two light barrier beams than before, so
Despite relatively large variations in the displacement of the retroreflector, the output signal of the receiver remains constant over a wide range unless the light barrier beam is disturbed. By providing a large number of optical imaging elements, the range of displacement over which the retroreflector can be moved without causing a significant change in the output signal of the receiver can be practically freely increased. To put it simply, it is as described above, but it is desirable to provide only two adjacent optical imaging elements for each of the light emitter and the light receiver. This is because a stable output signal can be obtained for many practical applications without being affected by the position of the retroreflector.

In particular, the intersection area of each light barrier beam is
It is desirable that the optical axes of the optical imaging elements are arranged in parallel so that they are at least adjacent to each other and more preferably overlap on the axis of the optical barrier. With this parallel configuration, from one intersection area to the next intersection area,
Signal fluctuations due to axial movement of the retroreflector are minimized.

In particular, when the light barrier beam is uninterrupted and the reflector is moving axially through the intersection region, the output signal of the receiver is constant over a wide range;
In addition, it is desirable that the crossing regions overlap so that they vary by no more than 30% at most with respect to the center output signal.

The optical imaging element is in fact a lens, in particular an objective lens. A preferred embodiment of the invention has the following features. That is, two perfect lenses having a circular, elliptical or square planar shape are provided adjacent to the axis of the light barrier, the optical axes of these lenses are parallel to the central axis, and two perfect lenses are provided adjacent to the axis of the light barrier. A perfect lens is juxtaposed in close proximity to each of the perfect lenses, and the optical axes of these imperfect lenses are eccentric with respect to the central axis of the light barrier and further apart from the optical axis of the perfect lenses. parallel to its central axis.
In this case, the optical axis of the imperfect lens approximately coincides with the outer edge of the adjacent perfect lens. That is,
The imperfect lens is a semi-perfect lens (on which half a complete figure is mounted).

In the preferred embodiment, the optical axes of adjacent perfect lenses and imperfect lenses are closer to each other than the centers of the two lenses, so that the output signal of the optical receiver can spread over a wide range. remains constant over

In order to most effectively implement the V-shaped light barrier according to the invention, both the perfect lens and the imperfect lens are spherical lenses that are modified as necessary. Further, all the lenses have a rectangular planar shape and are arranged in a long and narrow manner so as to be adjacent to each other so as to border each other.

Prior to describing preferred embodiments according to the invention,
In order to highlight the functions and effects of the present invention in comparison with the conventional example, the structure, functions, effects, and drawbacks of this conventional V-type light barrier will be explained based on FIG.

As shown in FIG. 1, a light source 23 and a light receiver 24 are arranged within the light barrier housing 22 with a constant distance R between them. Light source 23 may be an incandescent lamp or other light source.

The light emitted from the light source 23 is focused by a convex objective lens 13 disposed in the front wall of the light barrier housing 22 into a parallel emitted light beam 18 .
This emitted light beam 18 is directed towards the central axis 2 of the V-shaped light barrier.
is projected from the light barrier housing 22 at an angle α/2 relative to zero. The central axis 20 coincides with a perpendicular bisector of a line connecting the light source 23 and the light receiver 24.

A retroreflector 21, indicated by a dashed line, is disposed on the central axis 20 of the V-shaped light barrier. This retroreflector 21 directs the reflected light beam 19 to an objective lens 14 provided in the front wall of the light barrier housing 22.
It has sufficient scattering properties to the extent that it returns to the direction of the object. The light beams 18 and 19 are determined by the area through which the objective lens 13 and the light source 23 constituting the light emitter 11 can emit light, and through which area the objective lens 14 and the light receiving element 24 constituting the light receiver 12 can emit light. In order to clearly show which area the light is received from,
In the figure, it is depicted as passing through the retroreflector 21. Optical axes 15 and 16 passing through the centers of objective lenses 13 and 14 are parallel to and equidistant from central axis 20 of the V-shaped light barrier. The distance between the optical axes 15 and 16 is the reference length B of the V-shaped light barrier.

The emitted light beam 18 and the reflected light beam 19 overlap in the intersection region 17 . The retroreflector 21 is
As shown in FIG.
When located at the center of the photoreceptor element 24
receives the greatest amount of luminous flux, thereby producing the greatest output signal. Considering this point, it is important that the retroreflector 21 substantially corresponds to the cross section of the emitted light beam 18. If the retroreflector 21 is moved back and forth on the central axis 20 (that is, in the direction of arrow F at both ends) and the optical path is not obstructed, the output signal of the photoreceptor element 24 will change as the retroreflector 21 moves. do.

The reference length B and the angle α between the light beams 18 and 19
By adjusting the size of the intersection area 17, the position and length of the intersection area 17 can be adjusted.

According to the conventional V-type light barrier, generally both the reference length B and the angle α are constant. Of course, V-type light barriers that can adjust these parameters have also been proposed. However, in order to ensure that this parameter adjustment does not have a detrimental effect on the accuracy of the V-type light barrier, it is unavoidable that the cost is considerably higher. If the V-shaped light barrier described above must be used in a range where the displacement of the reflector is both large and small, the values of the reference length B and angle α must be selected to be extremely small. .
However, if the values of the reference length B and the angle α are selected in this way, the retroreflector 21 can be attached to the light barrier housing 22.
When placed in close proximity to the photoreceptor element 24
The maximum value of the output signal from the output signal will be undesirably high. On the other hand, if the retroreflector 21 were placed a relatively large distance from the light barrier housing 22, a relatively small and unstable output signal would result from the light receiving element 24;
Moreover, the signal value is also relatively low.

In contrast to the conventional V-type light barrier which has the above-mentioned drawbacks, the V-type light barrier according to the present invention eliminates these drawbacks.
Examples of the molded light barrier will be described in detail with reference to FIGS. 2 to 5. In this description, the same numbers will be used when parts in the embodiment of FIG. 1 and parts of the V-type light barrier according to the invention correspond.

In FIG. 2, the conventional V-type light barrier objectives 13 and 14 shown in FIG.
These objective lenses 13a, 13
Optical axes 15a, 15b, 15c, 16a, 16 of b, 13c, 14a, 14b and 14c, respectively
b and 16c are arranged in parallel. Therefore, each of the emitted light beams 18a, 18b and 18c and each of the reflected light beams 19a, 19b and 19c intersect each other at different points on the central axis 20 of the V-shaped light barrier. The closer the light beam intersects the light barrier housing, the larger the angle α will be. Therefore, the light beams 18a and 19
The angle α ₁ between a is the angle α ₂ between the light beams 18b and 19b
, and this angle α ₂ is larger than the light beams 18c and 1
The angle α between 9c is greater than ₃ . In this way, the V-type light barrier in FIG. 2 has the shortest first reference length B1, the slightly longer second reference length B2, and the longest third reference length B3.
These standard lengths B1, B2 and B
3 each provide a different optimal reflector displacement.

According to the V-type light barrier system of the present invention, the retroreflector 21 is arranged so that the light beams 18a and 19a or the light beams 18b and 19b or the light beams 18c and 19
As long as it lies within the intersection region of c, the photoreceptor element 24 produces a virtually constant output signal. If the retroreflector 21 is placed between the intersection areas, the output signal of the photoreceptor element 24 will be invalid.
By carefully selecting the reference lengths B1, B2 and B3 and the angles α ₁ , α ₂ and α ₃ , the degree to which the output signal becomes invalid can be kept within a predetermined value.

In the embodiment shown in FIGS. 3 and 4,
The two spherical objective lenses 13a and 14a are disposed in contact with either side of the central axis 20 of the V-shaped light barrier, and have a rectangular planar shape as shown in FIG. have. Hemispherical objective lenses 13b and 14b have rectangular contours on both outer edges of the objective lenses 13a and 14a.
is adjacent. Since the two outer objective lenses 13b and 14b are hemispherical, their respective optical axes 15b and 16b are located on the outer edges of the inner completely spherical objective lenses 13a and 14a. In this way, the second reference length B2
corresponds to the distance between the centers of the objective lenses 13a and 13b and the objective lenses 14a and 14b, so it is only slightly longer than the first reference length B1. Therefore, the light beam 18
The respective intersection areas of a and 19a and light beams 18b and 19b will be closer to each other, so that the output signal of photoreceptor element 24 will be more constant.

FIG. 5 shows the relative output signal E of the photoreceptor element 24.
and the displacement X of the retroreflector 21 from the front of the light barrier housing 22, measured on the scale of FIG.

According to FIG. 5, the relative output signal E of the photoreceptor element 24 first increases as the displacement X of the retroreflector 21 increases, and reaches a maximum at the displacement _X1 . The position of this displacement _X1 is the position of the light beams 18a and 19a
coincides with the intersection of Then, as the retroreflector 21 moves further away from the light barrier housing 22 on the central axis 20, the relative output signal E of the photoreceptor element 24 becomes slightly smaller, reaching a minimum at displacement _X3 . The position of this _displacement
b coincides with the midpoint of each intersection. Finally, the relative output signal E of the photoreceptor element 24 is again
increases as the displacement X of the retroreflector 21 increases,
It reaches a maximum at displacement X ₂ . At this position of displacement _X2 , the light beams 18b and 19b intersect. Thereafter, the relative output signal E uniformly decreases.

The half-wave high value width H of the above relative output signal E is the displacement
It extends over a very long range, starting in front of the position X ₁ and ending well behind the displacement X ₂ . By adjusting the threshold of the V-type light barrier mentioned above to the relative output signal (0.5) corresponding to the half-wave peak width H, it is possible to achieve a constant response of the V-type light barrier over a displacement width equal to the half-wave peak width H. Become. In this specification, the term "constant" is to be understood to include the small discernible signal taper required to reach the V-type light barrier threshold.

It is of particular importance in the invention that the values of the surface areas F ₁ and F ₂ occupied by the front objective lenses 13a and 14a and the objectives 13b and 14b, respectively, can be varied. The reason is that by carefully selecting the surface area ratio F ₁ /F ₂ ,
This is because the amplitude of the signal at the positions of the displacements X ₁ and X ₂ (intersection) can be set to approximately the same magnitude with respect to the reflector and the light barrier as given conditions. For example, the value of surface area F ₂ can be greater than the value of surface area F ₁ if the measurement range is exposed to significant light absorption conditions. Surface area F ₁ and F ₂
The main reason why we can but do not need to change the value of is that fewer rays will be reflected by a reflector located at a point of larger displacement due to the scattering lobes of this reflector. be.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a V-type light barrier according to the prior art. FIG. 2 is a schematic diagram of a V-type light barrier according to the present invention, in which the emitter and receiver each have three
The case is shown in which the lens is equipped with several lenses. Figure 3 shows
FIG. 3 is a schematic diagram showing another embodiment of a V-type light barrier according to the present invention. FIG. 4 is a view taken along the - line in FIG. 3, and shows the front side of the V-shaped light barrier shown in FIG. 3. FIG. FIG. 5 is a graph showing the relationship between the output signal of the receiver of the V-type light barrier shown in FIGS. 3 and 4 and the displacement of the reflector. 11... Emitter, 12... Light receiver, 13, 13
a, 13b, 13c, 14, 14a, 14b and 14c...objective lens, 15, 15a, 15b,
15c, 16, 16a, 16b and 16c... Optical axis, 17... Intersection area, 18, 18a, 18b and 18c... Emitted light beam, 19, 19a, 19
b and 19c...Reflected light beam, 20... Central axis of light barrier, 21... Retroreflector.

Claims (1)

[Scope of Claims] 1. A light emitter formed from a light source and a photoimaging element; a light receiver disposed in close proximity to the emitter and formed from a photoreceptor element and a photoimaging element; a retroreflector for reflecting the irradiated light from the device to the light receiver, and the V-shaped light barrier has a central axis substantially equal to the perpendicular bisector of the line connecting the light source and the light receiving element. In this method, each optical imaging element forming a light emitter and a light receiver is formed from a lens set consisting of a plurality of adjacent or adjacent lenses, and the optical axes of each of the plurality of lenses forming the pair of lens sets are juxtaposed. A V-type light barrier, characterized in that each lens set is arranged substantially symmetrically and perpendicularly to the central axis of the V-type light barrier. 2. It is formed from the irradiation light that is irradiated onto the retroreflector through each lens of the lens set on the light emitter side, and the reflected light that is projected from the retroreflector onto each lens of the lens set on the light receiver side. The V-type according to claim 1, wherein the optical axes of the plurality of lenses forming each lens set are arranged in parallel so that the plurality of light intersection regions are adjacent to each other or overlap each other on the central axis of the V-type light barrier. light barrier. 3. Claim 1 in which the plurality of lenses forming each lens set are formed from circular, elliptical, or square perfect lenses and/or imperfect lenses.
V-type light barrier according to item or item 2. 4 Each lens set is formed from one complete lens and one incomplete lens, and the complete lens is disposed as close as possible to the central axis of the V-shaped light barrier, and the complete lens The V-type light barrier according to claim 3, characterized in that an imperfect lens is arranged adjacent to the V-shaped light barrier. 5. The V-type light barrier according to claim 3 or 4, wherein the imperfect lens is a semi-perfect lens, and the perfect lens and the imperfect lens are spherical lenses. 6. The V-shaped light barrier according to claim 5, wherein all the lenses forming each lens set have rectangular planar contours, are arranged adjacent to each other, and are arranged in a long and narrow strip.