JPH0520989A - Photoelectric sensor - Google Patents

Abstract

PURPOSE:To detect a substance position with high accuracy, without any need to enlarge a device by providing a multiple reflection mirror between the components of a two-piece detector working as a light receiving lens and a light receiving element, and moving one of constitutional mirrors for keeping the differential output of the detector at zero level. CONSTITUTION:A beam 6 from a luminous element 1 is projected to a substance 5 via a projection lens 2. Diffused reflection light 7 from the substance 5 is caused to be incident upon a multiple reflection mirror 12 via a light receiving lens 3. The light is thereby subjected to multiple reflection, and then introduced to a two-piece PD 11. In this case, a mirror 16 is moved highly accurately with a piezoelectric element 17, thereby keeping the differential output of the PD 11 at zero level. According to this construction, a distance L from the lens 2 to the substance 5 can be detected. Also, the use of a mirror 12 becomes equivalent to the case where a distance from the lens 3 to the PD 11 is made considerably longer than conventional. Consequently, distance resolution for substance detection, or detection accuracy can be improved without enlarging a device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring photoelectric sensor based on the triangulation method.

[0002]

2. Description of the Related Art As a conventional distance measuring photoelectric sensor,
As shown in FIG. 3, a light emitting element 1, a light projecting lens 2, a light receiving lens 3 and a position sensor (PSD) 4 are used as basic elements to detect an object 5 by a triangulation method.

In this case, the light beam 6 emitted from the light emitting element 1 is focused by the light projecting lens 2 into a minute spot on the object surface 5a, and the diffuse reflected light 7 is passed through the light receiving lens 3 to the position sensor 4 Focused on top. And position sensor
According to the principle of the triangulation method, the distance L from the projection lens 2 to the detection object 5 depends on the position of the spot focused on the surface 4.
Is detected. That is, from the projection lens 2 to the detected object
The distance L up to 5 is 1, the distance between the light emitting element 1 and the light projecting lens 2 is l, the distance between the light axis of the light projecting lens 2 and the light receiving lens 3 is D, and the light emitting element is When the distance between 1 and the position of the spot focused on the position sensor 4 is x, it is given by L = Dl / (x−D). Therefore, since x at the position of the spot focused on the position sensor 4 is detected by the position sensor 4, L can be detected.

The object 5 is displaced by ΔL and the object surface 5a
Is at the position of the chain line, the diffuse reflection light 7 on the object surface 5a is focused on the position sensor 4 via the light receiving lens 3 as shown by the chain line in the figure.

[0005]

However, in the above-mentioned conventional photoelectric sensor, when the light emitting diode (LED) is used as the light emitting element 1, the distance resolution is only 10% of the measured distance L, and There is a problem that the detection accuracy for the position is poor.

Further, the position of the position sensor 4 is set to the light receiving lens.
If the distance is more than 3, the distance resolution is improved and the detection accuracy for the object position is increased, but there is a problem that the device becomes large.

In view of such conventional problems, an object of the present invention is to provide a photoelectric sensor capable of improving the distance resolution and improving the detection accuracy for an object position without increasing the size of the entire apparatus. It is in.

[0008]

The photoelectric sensor of the present invention comprises:
A triangle having a light source, a light projecting lens for projecting light from the light source onto an object, a light receiving lens for collecting reflected light or diffused light from the object, and a light receiving element for receiving light from the light receiving lens. A distance-measuring photoelectric sensor based on a survey method, which is used as the light-receiving element and which outputs a differential output corresponding to the position of a light spot, a two-division photodetector, the light-receiving lens, and the two-division light. A multi-reflection mirror formed of a pair of mirrors, arranged between the detector and the detector, for reflecting the reflected light or diffused light from the object and guiding it to the two-division photo detector, and the two-division light detection. And a piezoelectric element for moving one of the multiple reflection mirrors so that the differential output of the container becomes zero.

[0009]

In the photoelectric sensor having the above structure, the light from the light source is projected onto the object through the light projecting lens, and the reflected light or the diffused light from the object is incident on the multiple reflection mirror through the light receiving lens. The reflected light or diffused light from the object is multiply reflected by the multiple reflection mirror and then guided to the two-division photodetector. In this case, one of the multiple reflection mirrors is controlled (moved) by the piezoelectric element so that the differential output of the two-division photodetector becomes zero. Thereby, the distance from the projection lens to the object can be detected. Moreover, by using the multiple reflection mirror, the optical path length between the light receiving lens and the two-divided photodetector can be made larger than that of the conventional one, and the distance between the light receiving lens and the two-divided photodetector can be substantially reduced. It is equivalent to a large separation compared to. Therefore, the distance resolution of the object position detection by the photoelectric sensor can be improved as compared with the related art without increasing the size of the entire photoelectric sensor as compared with the related art, and the detection accuracy for the object position can be improved.

[0010]

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

FIG. 1 is a simplified block diagram showing an embodiment of a photoelectric sensor according to the present invention. In the figure, the same reference numerals are used for the same or corresponding parts in FIG. In FIG. 1, 1
Reference numeral 1 is a two-division photodetector (two-division PD) configured by using a photodiode, and the two-division PD 11 is
When the light spot strikes both of the two divided portions formed by the photodiodes equally, the differential output thereof becomes zero. When the differential output of the two-division PD 11 is zero, the distance L from the light projecting lens 2 to the object can be detected. How to detect the distance L will be described later.

Reference numeral 12 denotes a multiple reflection mirror composed of a pair of reflection mirror 15 and reflection mirror 16 disposed between the light receiving lens 3 and the two-divided PD 11 as a light receiving element. Reference numeral 12 is a mirror in which reflecting mirrors 15 and 16 are attached so that multiple reflection can be performed inside two transparent plates 13 and 14 arranged in parallel and facing each other. In the multiple reflection mirror 12, the diffuse reflected light (diffused light or reflected light) 7 on the object surface 5 a is received by the light receiving lens 3
It is input to the multiple reflection mirror 12 via the, and after multiple reflection, it is output to the two-division PD 11 so that the reflection mirror 15
The reflection mirror 16 is displaced in position.

Reference numeral 17 denotes a piezoelectric element attached to either one of the two transparent plates 13 and 14, here, for example, outside the transparent plate 14. This piezoelectric element is divided into two
The transparent plate 14 is controlled with high accuracy so that the differential output of D11 becomes zero, and the transparent plate 14, and thus the reflection mirror 16 can be moved with high accuracy in the direction of the arrow 18.

Next, a method of detecting the distance L from the projection lens 2 of the photoelectric sensor to the detection object 5 will be described. When a certain voltage is applied to the piezoelectric element 17 by the voltage source 19, the piezoelectric element 17 straddles the two-divided portion of the two-divided PD 11 equally.
The differential output of the divided PD 11 becomes zero. At this time, the distance L from the projection lens 2 to the detection object 5 is obtained. When the detection object 5 moves with respect to the photoelectric sensor, the applied voltage V to the piezoelectric element 17 and the detection object 5 from the light projecting lens 2 when the differential output of the two-divided PD 11 becomes zero.
The relationship with the distance L up to is prepared in advance as described above. Therefore, in order to detect the position of the detected object 5 when the detected object 5 is moving, that is, the distance L from the projection lens 2 to the detected object 5, the voltage source 19 is applied to the piezoelectric element 17.
Voltage is applied to the transparent plate 14 by the arrow 18
Move in the direction. Then, if the applied voltage V to the piezoelectric element 17 when the differential output of the two-division PD 11 becomes zero is obtained,
From the relationship between the voltage V applied to the piezoelectric element 17 and the distance L from the projection lens 2 to the detection object 5 described above, the distance L is obtained.
Can be detected.

Under such a structure, the light beam 6 emitted from the light emitting element 1 is projected by the light projecting lens 2 onto the object plane 5a.
Focuses on a small spot with. Diffuse reflected light 7 on the object surface 5a is condensed by the light receiving lens 3 and is reflected by the multiple reflection mirror 12
Incident on. The diffuse reflection light 7 transmitted through the transparent plate 13 of the multiple reflection mirror 12 is reflected by the reflection mirror 16 and further reflected by the opposing reflection mirror 15. In this way, the diffuse reflection light 7 is repeatedly reflected between the reflection mirror 16 and the reflection mirror 15 (multiple reflection), and is emitted from the transparent plate 14 in the portion where the reflection mirror 16 is absent, as shown in the figure, and is divided into two PDs 11. Be led to.

In this case, the focused light spot is striking equally over the two-divided portion of the two-divided PD 11.
Therefore, so that the differential output of the two-division PD 11 becomes zero,
A voltage source 19 applies a voltage to the piezoelectric element 17, and the piezoelectric element 17 controls the transparent plate 14 in the direction of arrow 18 with high accuracy. The voltage applied to the piezoelectric element 17 at this time is read by a voltmeter (not shown), so that the projection lens 2
The distance L from to the detection object 5 can be detected.

Further, by using the multiple reflection mirror 12, the optical path length between the light-receiving lens 3 and the two-divided PD 11 can be made larger than that of the conventional one, and substantially between the light-receiving lens 3 and the two-divided PD 11. This is equivalent to making the distance larger than in the past. Therefore, the distance resolution of the object position detection by the photoelectric sensor can be improved as compared with the related art without increasing the size of the entire device (photoelectric sensor) as compared with the related art, and the detection accuracy for the object position can be increased.

FIG. 2 is a simplified block diagram showing another embodiment of the present invention. In the figure, the same reference numerals are used for the same or corresponding parts as in FIGS. In FIG. 2, a prism 21 for bending an optical path is arranged between the light-receiving lens 3 and the transparent plate 13 of the multiple reflection mirror 12 in FIG. 1, and other configurations are the same as in FIG. When detecting a short-distance object 5 with a photoelectric sensor, in order to prevent the incident angle of the diffuse reflection light 7 from the object surface 5a on the transparent plate 13 of the multiple reflection mirror 12 from increasing, 21
Is inserted (interposed) between the light receiving lens 3 and the transparent plate 13 of the multiple reflection mirror 12, and the optical path is bent to reduce the incident angle to the transparent plate 13. Thereby, the reflection mirror 15,
It is possible to perform the multiple reflection necessary to secure a large optical path length by the multiple reflection mirror 12 without increasing the length in the lateral direction shown in FIG.
Since it can be arranged near the lower side of 14 as shown in the figure, the size of the device is not increased.

2 is the same as that of FIG. 1 except that the prism 21 is used to bend the optical path, and therefore the description thereof is omitted. The present invention is not limited to this embodiment, and various applications can be considered without departing from the gist of the present invention. For example, in the embodiment of FIGS. 1 and 2, the piezoelectric element 17 is provided on the transparent plate 14 side, but the present invention is not limited to this, and the other transparent plate is used.
It may be provided on the 13 side.

[0020]

As described above, according to the present invention, a multiple reflection mirror is disposed between the light receiving lens and the two-divided photodetector as a light receiving element, and one reflection mirror constituting the multiple reflection mirror is piezoelectric. The position of the object, that is, the distance from the light projecting lens of the photoelectric sensor to the object can be detected by moving the element with high accuracy to make the differential output of the two-division photodetector zero. Moreover, since the multiple reflection mirror is used, the optical path length between the light-receiving lens and the two-divided photodetector can be made larger than in the conventional case, so that the object position can be detected by the photoelectric sensor without increasing the size of the entire device. The range resolution can be improved as compared with the conventional one, and the detection accuracy for the object position can be improved.

[Brief description of drawings]

FIG. 1 is a simplified configuration diagram showing an embodiment of a photoelectric sensor according to the present invention.

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

FIG. 3 is a simplified configuration diagram showing an example of a conventional photoelectric sensor.

[Description of Reference Signs] 1 light emitting element 2 light emitting lens 3 light receiving lens 5 object 6 light beam 7 diffuse reflected light 11 two-split PD 12 multiple reflection mirror 13, 14 transparent plate 15, 16 reflection mirror 17 piezoelectric element 19 voltage source 21 prism

Claims (1)

Claim: What is claimed is: 1. A light source, a light projecting lens for projecting light from the light source onto an object, a light receiving lens for collecting reflected light or diffused light from the object, and the light receiving. In a distance-measuring photoelectric sensor based on a triangulation method, which has a light receiving element for receiving light from a lens for use, and which is used as the light receiving element and which outputs a differential output corresponding to the position of a light spot A pair of a photodetector, which is arranged between the light-receiving lens and the two-division photodetector, and which multiple-reflects reflected light or diffused light from the object and guides it to the two-division photodetector. And a piezoelectric element for moving one of the multiple reflection mirrors so that the differential output of the two-divided photodetector becomes zero.