Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2000-03-03
2001-05-01
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S005010
Reexamination Certificate
active
06226076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distance measuring apparatus for measuring a distance to a target by using pulse light.
2. Related Background Art
It has been known that optical systems for distance measuring apparatus using light are roughly classified into two kinds, i.e., biaxial and coaxial types, depending on the arrangement of their light-transmitting optical path through which measurement pulse light is propagated and light-receiving optical path through which a reflected beam of the measurement pulse light is propagated. The light-transmitting optical path and the light-receiving optical path constitute a measurement optical path. Of these two types of optical systems, the coaxial optical system is advantageous from the viewpoints of reducing the size of apparatus, eliminating parallax, and making the light-transmitting optical path coincide with a collimation optical system for focusing onto a target. It is due to the fact that the coaxial optical system has a configuration in which the light-transmitting axis for transmitting light to the target and the light-receiving axis for receiving the reflected beam from the target coincide with each other.
Also, this kind of distance measuring apparatus includes those employing a continuous modulation system in which a light source such as LED, semiconductor laser, or the like is continuously modulated, thereby the distance to the target is determined from the phase difference between the transmitted light and the received light; and those employing a pulse system in which a semiconductor laser is used as a light source, thereby the distance to the target is determined from the period of time between the time at which pulse light is transmitted and the time at which part of thus transmitted light is returned after being reflected by the target.
In order to respond to the demand for enhancing the range capable of distance measurement and the demand for the ability of non-prism measurement in which reflectors such as corner cube reflector are not used at the measuring point for saving labor and attaining efficient operation, the pulse system adapted to employ a large peak power is quite advantageous.
Meanwhile, in the distance measuring apparatus using a coaxial optical system, when the output of the light source is intensified in view of the demand for enhancing the range capable of distance measurement and the demand for the ability of non-prism measurement, reflections within the apparatus such as those at the inner side face of an objective lens and the inner face of a lens barrel may be received by a light-receiving device as flare, thereby yielding a large error in measured values. Though the pulse system is quite advantageous for the demand for enhancing the range capable of distance measurement and the like, the pulse light has a greater peak, thus increasing the magnitude of flare, thereby yielding a larger error in measured values in the pulse system.
Methods for eliminating the error in measured values caused by flare are disclosed, for example, in U.S. Pat. No. 4,113,381 and Japanese Utility Model Publication No.
3-21502
. These methods employ a configuration in which the emission optical system and the light-receiving optical system are optically separated from each other, so as to eliminate flare.
SUMMARY OF THE INVENTION
Having studied the foregoing prior art, the inventor has found the following problems. Namely, the optical systems of the prior art are configured such that a smaller-diameter lens barrel accommodating the emission optical system is disposed in front of a larger-diameter lens barrel accommodating the light-receiving optical system so as to be coaxially supported. Therefore, a collimation optical system for collimating the target cannot be disposed on the same axis as the optical axis of the measurement optical system (including the light-receiving optical system and emission optical system), since the collimation optical system is blocked by the smaller-diameter lens barrel disposed in front thereof. As a consequence, in the case of non-prism measurement in particular, it becomes difficult for a measurer to recognize the measuring point, thus yielding a large drawback in the distance measurement. Also, since the light source is disposed in front of a large-diameter lens which functions as a light-receiving lens, the wiring of the power supply to the light source and the like may obstruct the light-receiving lens, thus clearly indicating a structural problem which causes the quantity of received light to decrease.
In view of such conventional problems, it is an object of the present invention to provide a highly accurate distance measuring apparatus and method which enhance the range capable of distance measurement, improve the non-prism distance measuring ability, and are free from influences of flare.
The distance measuring apparatus according to the present invention comprises two measurement systems, i.e., one for detecting, of measurement pulse light emitted into a measurement optical path toward a target, information concerning a component reflected from the target, and the other for detecting information concerning reference pulse light emitted into a reference optical path; and a structure enabling highly accurate distance measurement by comparing the results of measurement obtained from these measurement systems.
Specifically, the distance measuring apparatus according to the present invention comprises an emitter for emitting measurement pulse light into a measurement optical path between the apparatus and a target; a receiver for receiving a reflected beam (reflected component) of the measurement pulse light emitted into the measurement optical path; a detector for specifying a receiving time at which the reflected beam of the measurement pulse light is received; and a controller for measuring the period of time between an emitting time at which the measurement pulse light is emitted and the receiving time of the reflected beam of the measurement pulse light and calculating an optical path length of the measurement optical path on the basis of thus obtained time information. In this configuration, in particular, when the calculated value obtained in the initial measurement operation (pre-measurement operation) for the measurement optical path is not greater than a predetermined value, the controller inhibits the detector from effecting the specifying operation for a predetermined period of time from the emitting time of the measurement pulse light in the next measurement operation (main measurement operation) for the measurement optical path.
The distance measuring apparatus according to the present invention can further comprise therein a reference optical path which is different from the measurement optical path, and a switching mechanism for causing the receiver to selectively receive one of the reflected beam of the measurement pulse light propagated through the measurement optical path and reference pulse light propagated through the reference optical path so as to selectively measure the respective optical path lengths of the measurement optical path and the optical path length of the reference optical path.
It is presumed that, of the unnecessary reflected beam (flare) generated within the apparatus, the part having a strong power (pulse light having a power greater than a threshold which is set for eliminating noise) propagates by a shorter distance than the reflected beam from the target does, thereby reaching a pulse receiving element faster than the latter component does. The distance measuring apparatus according to the present invention inhibits flare, which may be mistaken as the reflected beam from the target, from being received, and securely receives the reflected beam from the target.
The distance measuring method realized by the measurement distance measuring apparatus having the above-mentioned configuration thus carries out the pre-measurement operation for confirming occurrence of flare, and the main measure
Buczinski Stephen C.
Foley & Lardner
Nikon Corporation
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