Optical distance sensor

Details Optical distance sensor Optical distance sensor

2002-06-18

2003-11-18

Buczinski, Stephen C. (Department: 3662)

Optics: measuring and testing

Range or remote distance finding

Triangulation ranging to a point with one projected beam

C250S201600, C250S559310, C396S089000, C396S106000, C396S111000

Reexamination Certificate

active

06650401

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical distance sensor that applies a light beam emitted from a light emitting element placed at a reference point to an object, detects a light beam reflected by the object at a distance to be measured by using a light detecting element, and measures the distance from the reference point to the object, or a location or displacement of the object using a triangulation technique.
2. Description of the Prior Art
FIG. 19
is a perspective view showing a prior art optical distance sensor that measures a distance to an object, or a location or the like of the object using a triangulation technique as disclosed in international patent application No. PCT/JP98/04144. In
FIG. 19
, reference numeral
101
denotes an input optical fiber, reference numeral
102
a
and
102
b
denote output optical fibers, reference numeral
103
denotes a three-layer waveguide in which a core layer
103
a
having a high refractive index is sandwiched by a cladding layer
103
b
having a low refractive index, reference numerals
104
a
and
104
b
denote plane mirrors on side walls of the three-layer waveguide
103
, each plane mirror being covered with a reflection coating, reference numerals
105
a
and
105
b
denote curved minors on side walls of the three-layer waveguide
103
, each curved mirror being covered with a reflection coating, reference numeral
106
a
and
106
b
denotes end faces of the three-layer waveguide
103
, reference numerals
107
a
and
107
b
denote cylindrical lenses, reference numeral
108
a
denotes a light beam emerging from the cylindrical lens
107
a
, reference numeral
108
b
denotes a light beam that is reflected by an object to be measured (not shown in the figure) and is incident upon the other cylindrical lens
107
b
, and reference numeral
109
denotes a Y-branch waveguide.
In operation, a light beam used for detection is introduced into the three-layer waveguide
103
by way of the input optical fiber
101
. The incident light beam is confined in the direction of the thickness of the three-layer waveguide and is brought to a focus at a predetermined position in a parallel direction parallel to a substrate by the curved mirror
105
a
after it is reflected by the plane mirror
104
a
. The light, which has been reflected by the curved mirror
105
a
, emerges from the edge surface
106
a
and is then incident upon the cylindrical lens
107
a
. The light beam is brought to a focus at a predetermined position while its optical axis is deflected by the cylindrical lens
107
a
. This light beam is then reflected by an object (not shown in the figure) placed forward of the outgoing light beam from the cylindrical lens
107
a
, and is incident upon the other cylindrical lens
107
b
and is introduced, by way of the edge surface
106
b
, into the three-layer waveguide
103
again. The introduced light beam is confined in the direction of the thickness of the three-layer waveguide and is reflected by the plane mirror
104
b
while it is converged in the parallel direction to a surface of the substrate by the curved mirror
105
b
, so that the light beam comes into a focus at a branching point of the Y-branch waveguide
109
. The light beam at the branching point is introduced into both the output optical fibers
102
a
and
102
b
after it is separated into two parts with a light power ratio corresponding to a position where the light beam is focused to the branching point of the Y-branch waveguide
109
. The two separated light lays are therefore output to outside the optical distance sensor.
The position of a light spot that is imaged at the branch point of the Y-branch waveguide
109
changes according to the location of the object to be measured by using a triangulation technique. In other words, the ratio between the powers of the two light beams respectively introduced into the output optical fibers
102
a
and
102
b
changes according to the location of the object to be measured. By measuring this change by using two photo detectors (not shown in the figure) respectively connected to the two output optical fibers
102
a
and
102
b
, the location of the object to be measured can be determined.
Japanese patent application publication (TOKKAIHEI) No. 3-102727 discloses an optoelectronic switch intended for factory automation, in which a lens block having a lenticular entrance surface and a lenticular exit surface coupled to each other via a prism is arranged on a substrate on which a light emitting element, a position detector, and a signal processing unit are mounted, the optoelectronic switch applying a light beam to an object to be detected which is placed in a detection area and detecting light reflected by the object to detect the presence of the object.
A problem with the prior art optical distance sensor constructed as above is that when the waveguide having a function of converging light beams in a direction parallel to a substrate is formed, since the core layer
103
a
and the two cladding layers
103
b
are laminated alternately so that the core layer is sandwiched between the two cladding layers, it is impossible to form the optical distance sensor in one process and therefore the manufacturing cost increases. Another problem is that since optical fibers are used for optical I/O, the handleability is bad. In addition, since the cylindrical lenses
107
a
and
107
b
are coupled to the thee-layer waveguide
103
, the cost of assembling the optical distance sensor increases. Coupling loss occurs because air or a bonding adhesive enters a gap between each of the cylindrical lenses
107
a
and
107
b
and the three-layer waveguide
103
. Additionally, since a reflection coating is adhered to the surface of each of the plane mirrors
104
a
and
104
b
and the curved mirrors
105
a
and
105
b
, light is absorbed by the reflection coating and performances, such as a signal to noise ratio, are deteriorated. In addition, to unite downsizing and high precision measurement, it is necessary to lengthen the optical path length in the sensor so as to enlarge the magnification of image formation of the optical system. So, since the direction in which the object to be measured can be moved, i.e., the measurement direction along which measurements are carried out is parallel to the substrate, as in the case of the optoelectronic switch disclosed in Japanese patent application publication No. 3-102727, there is no alternative but to lengthen the optical path length of the optical distance sensor in the measurement direction. As a result, it is impossible to make the optical distance sensor compact with respect to the measurement direction. In addition, since the diameter of the cylindrical lenses cannot be enlarged according to a size limitation, the prior art optical distance sensor cannot make long-distance measurements.
SUMMARY OF THE INVENTION
The present invention is proposed to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a small-size, low-cost, and easy-to-handle optical distance sensor.
In accordance with the present invention, there is provide an optical distance sensor that applies a light beam emitted out of a light emitting element placed at a reference point to an object to be measured, detects a light beam reflected by the object to be measured by using a light receiving element, and measures a distance from the reference point to the object to be measured, or the location or displacement of the object to be measured by using a triangulation technique, the sensor including: a substrate on which the light emitting element and the light receiving element are disposed; and an optical structure body in which a first converging mechanism for converging the light beam emitted out of the light emitting element, a second converging mechanism for converging the light beam reflected by the object to be measured, and a reflecting mechanism for deflecting the light beam reflected by the object to be measured twice are form

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