Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
1999-05-12
2001-09-11
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C342S135000, C356S005080, C367S097000
Reexamination Certificate
active
06288775
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lightwave distance measuring apparatus which measures the distance to an object to be measured by using pulsed light; and, in particular, to a lightwave distance measuring apparatus which prevents erroneous measurement from occurring due to stray light or the like generated along with transmission of pulsed light.
2. Related Background Art
As the configuration of distance measuring apparatus using lightwaves, biaxial type and coaxial type have conventionally been known from the viewpoint of relative arrangement between the light-transmitting optical path and light-receiving optical path. Of these types, the coaxial type optical system has an advantage in its capabilities of making the apparatus smaller, avoiding parallax, and installing a collimation optical system for targeting the light-transmitting optical path at the object to be measured. Namely, it is a coaxial light-transmitting/receiving type optical system in which the light-transmitting axis of the lightwave used for distance measurement and the light-receiving axis for receiving the reflected light from the object to be measured coincide with each other.
On the other hand, the distance measuring system of the distance measuring apparatus using lightwaves is broadly divided into a continuously modulated wave type in which an LED or semiconductor laser is used as its light source; and a pulse type in which a semiconductor laser, adapted to be pulse-driven, outputting pulsed light with a large peak power is used as its light source. For these distance measuring apparatus, there has conventionally been a demand for enhancing their maximum distance measuring range, and there has been an increasing demand for their measuring capacity in a non-prism configuration which does not employ a reflector such as cube corner prism at the measuring point in order to save the labor and improve the efficiency of operations. For responding to these demands, the pulse type, which can use a large peak power, is definitely advantageous.
SUMMARY OF THE INVENTION
When a coaxial optical system is employed for projecting pulsed light having a large peak power into a light-transmitting optical path, there is a possibility of the light reflected from the inner side face of an objective lens, inner face of a lens barrel, or the like, i.e., so-called stray light, being received by the light-receiving optical path, which may cause a large error in measured values.
Therefore, it is an object of the present invention to provide a lightwave distance measuring apparatus which can determine, in a coaxial light-transmitting/receiving type optical system, whether stray light is made incident thereon or not.
In order to achieve the above-mentioned object, the lightwave distance measuring apparatus in accordance with the present invention is a lightwave distance measuring apparatus having a coaxial light-transmitting/receiving type optical system; the apparatus further comprising light-transmitting means for transmitting pulsed light toward an object, light-receiving means for receiving reflected pulsed light reflected by the object, a time measuring section for measuring a period of time from when the pulsed light is transmitted until the light is received, a distance measuring section for determining a distance to the object from the measured period of time, and a pulse number detecting section for detecting whether the number of pulses of light received by the light-receiving means in response to one transmitting pulsed light is one or more.
When so-called stray light is generated, the receiving means detects the reflected pulsed light caused by the stray light, in addition to the reflected pulsed light from the aimed object, whereby a plurality of pulses of reflected light are measured in response to one pulse of transmitted light. As a consequence, counting the number of pulses of reflected light can detect the occurrence of stray light.
Preferably, when a plurality of pulses of received light are counted by the pulse number detecting section, the distance measuring section is kept from carrying out distance measurement based on the received pulsed light. As a consequence, the values measured when stray light occurs are eliminated. When a plurality of measurement operations are carried out and their mean measured value is outputted, the values measured with stray light occurring can be eliminated, so that the values measured without stray light being generated can be used as a basis, whereby more correct distance measurement can be performed.
Preferably, the lightwave distance measuring apparatus of the present invention further comprises signal selecting means which outputs, when the light-receiving means yields an output signal strength at a predetermined value A or higher, a time measurement termination signal for detecting the time when the light is received, whereas the pulse number detecting section counts the number of pulses of received light by which the output signal strength of the light-receiving means becomes a predetermined value B or higher, the predetermined value B being set slightly lower than the predetermined value A.
As a consequence, when a plurality of time measurement termination signals are outputted to the time measuring section due to stray light, the pulse number detecting section reliably carries out counting so as to indicate that a plurality of pulses of light are received, whereby errors in measurement can more securely be prevented from occurring due to stray light or the like.
On the other hand, the lightwave distance measuring method in accordance with the present invention comprises: a preliminary light-transmitting step of transmitting pulsed light toward an object; a preliminary light-receiving step of receiving by a light-receiving apparatus the pulsed light reflected by the object; a step of detecting a reflected light quantity level of the received pulsed light and adjusting, in response thereto, an amount of transmission through a filter for regulating the quantity of pulsed light incident on the light-receiving apparatus; and a main measurement step, after termination of the adjustment, of repeatedly transmitting pulsed light toward the object and receiving the reflected light therefrom at a predetermined interval, measuring a period of time from when each pulse of light is transmitted until the reflected light corresponding thereto is received, determining a distance to the object from the measured period of time, counting the number of pulses received in response to each pulse of the transmitted light, making thus measured value effective only when the number of pulses of received light is one, and outputting a mean value of effective measured values as a measured result when at least a predetermined number of effective measured values are obtained.
As a consequence, reliable distance measurement can be carried out by use of lightwaves while eliminating influences of stray light.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
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patent: 3983557 (1976-09-01), Powell et al.
patent: 4040054 (1977-08-01), Overman
patent: 4113381 (1978-09-01), Epst
Buczinski Stephen C.
Foley & Lardner
Nikon Corporation
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