Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2000-01-20
2001-05-08
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S005030
Reexamination Certificate
active
06229598
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electro-optic distance measuring apparatus and method for measuring a distance to a measured object by use of pulse light and, more particularly, to an electro-optic distance measuring apparatus and method that can eliminate a measurement error due to flare produced upon sending the pulse light.
2. Related Background Art
Examples of the conventional distance measuring apparatus using light are disclosed in Japanese Patent Publication No. Sho 59-24397 and Japanese Utility Model Publication No. Hei 3-21502. Such a distance measuring apparatus is used as a surveying equipment in the fields of civil engineering and architecture and the details thereof are described in Japanese Laid-open Patent Application No. Sho 53-64056.
SUMMARY OF THE INVENTION
The biaxial and coaxial structures are known as to optical systems of the distance measuring apparatus from the viewpoint of relative locations of sending optical path and receiving optical path. Among them, the coaxial optical systems are advantageous in decreasing the scale of apparatus, avoiding the parallax, and installing a collimation optical path for collimating the sending optical path to the measured object. Namely, they are optical systems of the sending and receiving light coaxial type in which the sending optic axis of the light wave used in distance measurement coincides with the receiving optic axis for receiving reflected light from the measured object.
Meanwhile, the distance measuring methods of the distance measuring apparatus using the light wave are classified roughly into a continuous modulated wave method using an LED or a semiconductor laser as a light source and a pulse method using the light source of a pulse-drivable semiconductor laser capable of outputting a pulsa beam with high peak power. With these distance measuring apparatus, there have been and are desires for increase in the maximum measurement range and increasing desires for measurement performance in a non-prism state without using a reflector such as a corner cube prism at a measuring point in order to save labor and increase efficiency of work. For meeting such demands, the pulse method that can use the high peak power is definitely advantageous.
However, when the pulse light with high peak power is projected into the sending optical path by use of the coaxial optical systems, light reflected by the inside surface of an objective lens and the internal surface of a lens barrel is received as flare in the receiving optical path to cause a large error in measured values.
These optical systems are of the coaxial support structure in which a small-diameter lens barrel housing a light emission system is disposed coaxially in front of a large-aperture lens barrel housing a light receiving system. First, it is thus impossible to dispose the collimation optical system for sighting the measured object coaxially with the optic axis of a ranging optical system, because the collimation optical path is interrupted by the small-diameter lens barrel disposed ahead. This makes it difficult for a measuring person to see the measuring point, particularly, in the case of the non-prism measurement. Second, since the small-diameter lens barrel of the light emission system is disposed in front of the large-aperture lens being a receiving lens, the small-diameter lens barrel itself and wires, etc., from the power supply for supplying the power to the light source of the light emission system also interrupt the receiving lens, causing decrease in the quantity of received light and in turn narrowing the maximum measurement range.
A first distance measuring apparatus has light sending means for sending pulsed light, light receiving means for receiving reflected pulsed light, and a signal processing section for measuring a period from the light sending time to the light receiving time, wherein the signal processing section is arranged to make a decision on either a first state in which the reflected pulsed light from a measured object is detected without reflected pulsed light due to flare in response to sending of the pulsed light or a second state in which the reflected pulsed light from the measured object is detected with the reflected pulsed light due to the flare, to measure a period from the sending time to reception of the reflected pulsed light from the measured object in the first state, and to measure a period from the sending time to reception of the reflected pulsed light from the measured object while ignoring the reflected pulsed light due to the flare, in the second state.
This apparatus is arranged to make the decision on whether the reflected pulsed light due to the flare is detected or not when the pulsed light is sent into the ranging optical path; according to the decision, when the reflected pulsed light due to the flare is detected, the apparatus measures a delay time of the reflected pulsed light from the measured object while ignoring the reflected pulsed light due to the flare. Therefore, this apparatus is free of the measurement error due to the flare.
A second distance measuring apparatus has light sending means for sending pulsed light, light receiving means for receiving reflected pulsed light, and a signal processing section for measuring a period from the sending time to the receiving time, wherein the signal processing section is arranged to make a decision on either a first state in which a reflected pulsed beam is detected in response to the sending of the pulsed light or a second state in which two reflected pulsed beams are detected in response to the sending of the pulsed light, to measure a period from the sending time to reception of the first reflected pulsed beam in the first state, and to measure a period from the sending time to reception of the second reflected pulsed beam in the second state.
This apparatus is arranged to eliminate the measurement error caused by the reflected pulsed light due to the flare after discriminating the case wherein two pulsed are detected of the reflected pulsed light due to the flare and the reflected pulsed light from the measured object, from the case wherein one pulsed is detected of the reflected pulsed light from the measured object.
A third distance measuring apparatus is an electro-optic distance measuring apparatus having light sending means for sending pulsed light, light receiving means for receiving reflected pulsed light, and a signal processing section for measuring a period from the sending time to the receiving time, wherein the signal processing section comprises a first pulse detecting circuit for detecting a received pulse signal after photoelectric conversion of received pulsed light to generate a first detection signal, a received timing detecting circuit activated by a setpoint signal or the first pulse detection signal to detect the received pulse signal, to generate a second detection signal, and to detect timing of the received pulse signal, and a control section for setting the setpoint signal in a non-active level to monitor presence or absence of the second detection signal generated with sending of the pulsed light, setting the setpoint signal in an active level upon absence of the second detection signal to carry out a distance measuring step, and setting the setpoint signal in the non-active level upon presence of the second detection signal to carry out the distance measuring step.
According to the present invention, presence or absence of the reflected pulsed light due to the flare is determined by simply switching the setpoint signal and the delay time can be measured while ignoring the reflected pulsed light due to the flare, depending upon the determination result.
A first distance measuring method is an electro-optic distance measuring method comprising steps of sending pulsed light into a ranging optical path, receiving pulsed light reflected by a measured object, and measuring a distance, based on a period from the sending of light to the receiving of light, wherein when ref
Buczinski Stephen C.
Foley & Lardner
Nikon Corporation
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