Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2002-06-20
2003-12-02
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S141100, C180S167000
Reexamination Certificate
active
06657705
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a distance measuring apparatus which implements the steps of (1) emitting a forward laser beam into a detection area, (2) controlling the forward laser beam to scan the detection area, (3) receiving an echo laser beam caused by reflection of the forward laser beam at an object in the detection area, and (4) measuring the time interval between the moment of emission of the forward laser beam and the moment of reception of the corresponding echo laser beam as an indication of the distance to the object. In addition, this invention relates to a radar apparatus.
2. Description of the Related Art
A known distance measuring apparatus mounted on an automotive vehicle intermittently emits a forward laser beam into a detection area in front of the subject vehicle, and controls the forward laser beam to scan the detection area. The known apparatus receives an echo laser beam caused by reflection of the forward laser beam at an object in the detection area. The known apparatus measures the time interval between the moment of emission of the forward laser beam and the moment of reception of the corresponding echo laser beam as an indication of the distance to the object.
A receiver in the known apparatus has a light sensitive area for receiving echo laser beams. The light sensitive area is covered by an array of light sensitive cells. The broadening of the detection area requires an increase in the light sensitive area. A large light sensitive area tends to receive noise laser beams such as a laser beam emitted from a distance measuring apparatus mounted on an oncoming vehicle with respect to the subject vehicle, and an echo laser beam related to a distance measuring apparatus mounted on a vehicle traveling along a lane adjacent to the lane of the subject vehicle. The noise laser beams cause errors in the distance measurement.
U.S. Pat. No. 5,760,886 corresponding to Japanese patent application publication number 7-98381 discloses a scanning-type distance measuring device responsive to selected signals to reduce interference due to stray light or noise light. The device of U.S. Pat. No. 5,760,886 emits a beam of light. The emitted beam of light is reflected from an object and returns to one among photodetectors in a linear array or a two-dimensional array. Selection is made as to the outputs of the photodetectors on the basis of the position of the emitted beam of light. Therefore, photodetectors which should not contribute to the reflected beam are ignored according to the geometry of the emitted beam and the reflecting object. This approach in U.S. Pat. No. 5,760,886 reduces the effects of stray noise from other light sources. The selection of the photodetectors is synchronized with generation of the beam of light by a scanning light emitter in response to a position signal and an angular signal so as to minimize the stray-light-caused noise components of the selection-resultant final output signal.
U.S. Pat. No. 6,301,003 B1 corresponding to Japanese patent application publication number P2000-56018A discloses an optical distance measuring apparatus which transmits a laser beam in a cycle and scans a two-dimensional detection zone by the laser beam. The apparatus of U.S. Pat. No. 6,301,003 B1 includes a light sensitive unit for receiving a return of the laser beam from a target object in the detection zone. Data on the distance to the target object are generated on the basis of the reception of the return of the laser beam. The light sensitive unit is made of a two-dimensional matrix of cells which are selectively activated in each scan cycle for minimizing optical interference with the return of the laser beam from the target object. In each column of the matrix, cells are selectively and sequentially activated. Accordingly, information about the two-dimensional position of the target object is generated.
Japanese patent application publication number 7-280557 discloses a triangulation-based distance measuring apparatus which includes a pair of photosensor arrays. Each photosensor array has a plurality of photodiodes arranged in a line. One or more windows can be provided on each photosensor array. The size of every window is determined by the number of photodiodes composing the window. The number and size of windows on each photosensor array are changed depending on a target distance measurement range. Object images are projected onto the photosensor arrays. Regarding every object, two images are projected onto the photosensor arrays, respectively. The output signals from the photodiodes composing the windows are processed to calculate a phase difference between the object images on the respective photosensor arrays. The distance to an object is computed from the calculated phase difference according to triangulation. The change in the number and size of windows makes it possible to accurately measure both the distance to a near object and the distance to a far object.
Japanese patent application publication number 7-218632 discloses a distance measuring apparatus which includes a laser unit and a photodetector unit. The laser unit has three laser diodes for emitting forward laser beams into three divided regions (transmission-side regions) respectively. The photodetector unit has four photodiodes for receiving echo laser beams from four divided regions (reception-side regions) respectively. The direction along which the reception-side regions are arranged is the same as the direction of the arrangement of the transmission-side regions. The boundaries among the reception-side regions are offset from the boundaries among the transmission-side regions. The laser diodes are sequentially activated in a prescribed order. Thus, a forward laser beam is outputted sequentially from one of the laser diodes. Calculation is carried out about the time interval between the moment of emission of a forward laser beam and the moment of reception of a corresponding echo laser beam. The distance to an object reflecting the forward laser beam and hence causing the echo laser beam is detected on the basis of the calculated time interval. A decision is made as to which of the transmission-side regions corresponds to the forward laser beam. In addition, a decision is made as to which of the reception-side regions corresponds to the echo laser beam. Information about the decided transmission-side region and the decided reception-side region is used in detecting the direction toward the object.
U.S. Pat. No. 5,949,365 corresponding to Japanese patent application publication number 10-288664 discloses a multi-beam radar system in which more transmission elements than reception elements are present. The transmission elements present can be activated both individually and also in any desired simultaneous combination. An observable angular region can thereby be widened. An example of the system in U.S. Pat. No. 5,949,365 includes a first number of transmission elements for transmitting radar waves, and a second number of reception elements for receiving reflected radar waves. The second number is less than the first number. An effective antenna characteristic of the system results from a superimposition of a transmission characteristic of at least one of the transmission elements and a reception characteristic of at least one of the reception elements. The effective antenna characteristic can be modified for at least one measurement cycle by switching between the transmission and reception elements. The transmission elements can be activated individually or simultaneously in a selectable combination.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide an improved distance measuring apparatus.
It is a second object of this invention to provide an improved radar apparatus.
A first aspect of this invention provides a distance measuring apparatus comprising scanning and applying means for applying a forward laser beam to a prescribed detection area, and controlling the forward laser beam to scan the detection area
Isogai Emiko
Sano Naoki
Sugawara Ryoichi
Buczinski Stephen C.
Denso Corporation
Posz & Bethards, PLC
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