Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
1999-08-05
2001-10-09
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C180S169000, C356S005010, C356S141100
Reexamination Certificate
active
06301003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an optical distance measuring apparatus designed to transmit a laser beam in a cycle and to receive a return of the laser beam from an object to determine the distance to the object, and more particularly to such a distance measuring apparatus having a matrix of light sensitive cells which are selectively activated in each scan cycle for minimizing optical interference with incoming light other than a return of a laser beam in determining data on the distance to an object.
2. Background Art
Automotive distance measuring systems are known in the art which are designed to transmit laser beams intermittently over an angular range embracing an automobile and receive a return of the laser beam to determine the amount of time required by the laser beam to travel to and return from a reflective object. It is advisable for such distance measuring systems to broaden an area scanned by laser beams in order to increase a detectable range.
The broadening of the scan area, however, requires increase in light sensitive area covered by light sensitive cells installed in a receiver, which may cause a laser beam outputted from a distance measuring system installed in an oncoming vehicle or another vehicle traveling on an adjacent lane to be received undesirably, thus resulting in errors in measuring the distance to a target object.
In order to avoid the above problem, Japanese Patent First Publication No. 7-98381 teaches a radar system which has an array of light sensitive cells in a receiver and activates some of the light sensitive cells selected as a function of a direction of emission of a laser beam, thereby decreasing an area receiving a return of the laser beam to minimize unwanted optical disturbances.
The determination of two-dimensional position of a target object, however, requires changing the direction of emission of laser beams two-dimensionally as well as arraying light sensitive cells in a matrix arrangement. The former requires a horizontal scan mechanism for scanning a laser beam in a width-wise direction of the vehicle and a vertical scan mechanism for scanning a laser beam in a height-wise direction of the vehicle, thus resulting in complexity of a structure of the radar system. For example, a scan system designed to emit laser beams over a given angular range through reflections on a mirror requires a mechanism for turning the mirror in two directions: vertical and horizontal directions, which also results in complexity of control for the movement of the mirror.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a distance measuring system designed to minimize interference with optical disturbances such as incoming light other than a return of emitted light from a target to obtain data on a two-dimensional position of the target using a one-dimensional beam scan accurately.
According to one aspect of the invention, there is provided a distance measuring apparatus. The distance measuring apparatus comprises: (a) a laser scanner emitting a laser beam to scan a given object detection zone, in a cycle, defined by a first angular range and a second angular range substantially perpendicular to the first angular range, the laser beam having a cross section extending in a first angular direction so as to cover the first angular range of the object detection zone and being moved in a second angular direction so as to scan the second angular range in each scan cycle of the laser beam; (b) a light receiving unit receiving a return of the laser beam from a reflective object present in the object detection zone, the light receiving unit including a matrix of light sensitive cells defined by first arrays each of which extends in the second angular direction and which are disposed adjacent each other in the first angular direction for optically covering the first angular range of the object detection zone and second arrays each of which extends in the first angular direction and which are disposed adjacent each other in the second angular direction for optically covering the second angular range of the object detection zone, each of the light sensitive cells, when activated, converting the return of the laser beam falling thereon into an electric signal; (c) a time difference determining circuit responsive to the electric signal from the light receiving unit to determine a time difference between emission of the laser beam and reception of the return of the laser beam; (d) a distance determining circuit determining data on a distance to the reflective object based on the time difference determined by the time difference determining circuit; and (e) a cell activation selector selecting the light sensitive cells of the light receiving unit to be activated, the cell activation selector selectively activating the light sensitive cells of each of the second arrays in each scan cycle of the laser beam and also activating the light sensitive cells of each of the first arrays, in sequence, in the second angular direction in synchronism with scanning of the laser beam over the second angular range of the object detection zone in each scan cycle of the laser beam.
In the preferred mode of the invention, the cell activation selector activates the light sensitive cells of each of the second arrays, at least one in each scan cycle of the laser beam.
The cell activation selector selectively may activate the light sensitive cells of the light receiving unit in first and second cell selecting operation modes. In the first cell selecting operation mode, the light sensitive cells of each of the second arrays of the matrix are set operable selectively in each scan cycle of the laser beam. In the second cell selecting operation mode, the light sensitive cells of each of the first arrays of the matrix are switched to be operable, in sequence, in the second angular direction in synchronism with the scanning of the laser beam over the horizontal angular range of the object detection zone in each of the scan cycle of the laser beam. Each of the light sensitive elements is activated when operable simultaneously in the first and second cell selecting modes.
The cell activation selector may include switches each switching between an active condition and an inactive condition of one of the light sensitive cells of the light receiving unit.
A lens is further provided which converges incoming light at a light sensitive surface of the light sensitive unit defined by the matrix of the light sensitive cells. The cell activation selector selectively activates the light sensitive cells so that an area of the light sensitive surface optically covered by the light sensitive cells when activated is increased from a central portion toward a peripheral portion of the light sensitive surface.
The light sensitive cells of the light receiving unit have different sizes so that an area of the light sensitive surface of the light receiving unit optically covered by the light sensitive cells being activated is increased from the central portion toward the peripheral portion of the light sensitive surface.
The cell activation selector may selectively activate the light sensitive cells so that the number of the light sensitive cells activated is increased from the central portion toward the peripheral portion of the light sensitive surface of the light receiving unit.
The lens may be located so that a first distance between the lens and the central portion of the light sensitive surface of the light receiving unit may be shorter than a focal length of said lens, while a second distance between the lens and the peripheral portion of the light sensitive surface may be longer than the focal length.
An absolute value of a difference between the first distance and the focal length is equal to an absolute value of a difference between the second distance and the focal length.
When the distance measurin
Hoashi Yoshiaki
Matsui Takeshi
Shirai Noriaki
Buczinski Stephen C.
Denso Corporation
Pillsbury & Winthrop LLP
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