Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
1998-07-07
2001-06-26
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S005010
Reexamination Certificate
active
06252655
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a distance measuring apparatus which emits pulse light toward a target and computes the distance to the target by measuring a period of time from the emission of pulse light until the detection of reflected pulse light.
1) Related Background Art
Conventionally known as an apparatus which emits a laser pulse toward a target, receives the light reflected by the target, and computes the distance to the target is, for example, that disclosed in Japanese Patent Application Laid-Open No. 53-1553.
This conventional distance measuring apparatus comprises a single measuring system which emits a laser pulse into a measurement optical path between the apparatus and a target and receives the reflected pulse light propagated through the measurement optical path; and computes the distance to the target according to the difference in time between the timing at which the laser pulse is emitted by the single measuring system and the timing at which the reflected pulse light is received by the same system.
In particular, in order to eliminate reflected signals from a reflective object located farther than the target, the conventional distance measuring apparatus adjusts the beam expansion of the laser light emitted therefrom such that the laser light does not reach anywhere other than the target. Also, the conventional distance measuring apparatus sequentially records temporal information of the reflected signal being received each time a laser pulse is emitted toward the target, and computes information about the distance to the target on the basis of the finally recorded temporal information of the reflected signal.
SUMMARY OF THE INVENTION
As a result of studies of the above-mentioned conventional distance measuring apparatus, the inventor has found the following problems.
Namely, the conventional distance measuring apparatus is based on a technique in which the angle of divergence of emitted laser light is restricted so that the laser light correctly impinges on the target. When the target has a very high reflectivity as in the case of a prism, however, there is a possibility of the light reflected by the prism being reflected by an emission optical system for adjusting the angle of divergence of the laser light and the like or a light receiving optical system for receiving the reflected light, thereby occurring multiple reflection directed toward the prism again. In this case, a plurality of reflected light beams caused by the multiple reflection are received, thus making it difficult to measure the distance with a high accuracy.
Also, unless the angle of divergence of emitted laser light can be controlled correctly; of the emitted laser light, the light reflected by reflective objects other than the target may be received as well.
Therefore, it is an object of the present invention to provide a distance measuring apparatus having a structure which allows the distance to be measured with a high accuracy without being influenced by its environment of measurement even when a reflective object exists behind the target or when multiple reflection occurs.
The distance measuring apparatus according to the present invention comprises a first measuring system for detecting, of measurement pulse light emitted into a measurement optical path toward a target, information concerning a reflected component from the target; a second measuring system for detecting information concerning reference pulse light emitted into a reference optical path; and a structure which enables highly accurate distance measurement by comparing results of measurement obtained from these measuring systems.
Specifically, the distance measuring apparatus according to the present invention comprises an emission system for emitting measurement pulse light into a measurement optical path between the apparatus and a target, and emitting reference pulse light into a reference optical path different from the measurement optical path; a light receiving system for receiving a reflected component of the measurement pulse light that propagates through the measurement optical path and receiving the reference pulse light that propagates through the reference optical path; a time measuring system for measuring, at least, a period of time from when the measurement pulse light is emitted from the emission system until the reflected component of the measurement pulse light reaches the light receiving system; a light quantity adjusting mechanism for adjusting a light quantity of the reflected component of the measurement pulse light that propagates through the measurement optical path; and a light quantity control system for controlling the light quantity adjusting mechanism.
Here, the time measuring system measures a period of time from when the measurement pulse light is emitted from the emission system until the reflected component of the measurement pulse light initially reaches the light receiving system, and a period of time from when the reference pulse light is emitted from the emission system until the reference pulse light reaches the light receiving system.
In particular, the light quantity control system controls the light quantity adjusting mechanism on the basis of the difference between the light quantity of the reflected component initially reaching the light receiving system after the measurement pulse light is emitted from the emission system into the measurement optical path and the light quantity of the reference pulse light reaching the light receiving system. More specifically, the light quantity control system comprises a detecting section for detecting the reflected component of the measurement pulse light initially reaching the light receiving system after the measurement pulse light is emitted from the emission system into the measurement optical path; a signal level changing section for blocking or attenuating an electric signal fed from the light receiving system after the initially reaching reflected component is detected by the detecting section; and a control section for controlling the light quantity adjusting mechanism on the basis of the electric signal from the signal level changing section.
Preferably, the light quantity control system controls the light quantity adjusting mechanism such that a peak light quantity level of the reflected component of the measurement pulse light initially reaching the light receiving system after the measurement pulse light is emitted from the emission system into the measurement optical path equals a peak light quantity level of the reference pulse light reaching the light receiving system. Thus, the light quantity control system equilibrates light quantity such that the light quantity of the reflected component from the target becomes a predetermined standard level, thereby, even in the case where a reflected component having a large light quantity reaches the light receiving system from an object located behind the target, the distance to the target can be measured correctly.
Also, the light quantity control system blocks or attenuates, of control signals for controlling the light quantity adjusting mechanism, electric signals corresponding to reflected components of the measurement pulse light reaching the light receiving system in the second place and later. As a consequence, even in the case where the light receiving system receives a plurality of reflected components propagating through the measurement optical path, light quantity is always equilibrated for the light quantity of the initially received reflected component, whereas no light quantity equilibration is carried out for undesirable reflected components received in the second place and later. Accordingly, in the distance measuring apparatus according to the present invention, the light quantity of the reflected component of the measurement pulse light initially reaching the light receiving system is set to the above-mentioned standard level, and information concerning the initially reaching reflected component is fed into a r
Buczinski Stephen C.
Foley & Lardner
Nikon Corporation
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