Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2000-06-14
2002-11-19
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S2140RC
Reexamination Certificate
active
06483121
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a distance measuring apparatus for measuring distance with light waves, in particular it relates to a distance measuring apparatus with which a distance can be measured effectively even in an environment containing noise light which may disturb the measurement.
In the case of a conventional distance measuring apparatus with light waves of a pulse system, distance is measured by the emission of a pulse light for a target and by the reception of the reflected pulse light. A semiconductor laser diode is utilized as the light source, the diode suitable for the emission of a pulse light.
The measurement is performed in two ways, a rough measurement and a precise measurement. In the rough measurement, the difference in time between the emission of a pulse and the reception of the reflected pulse is counted based on reference clock pulses. In the precise measurement, a beat sine wave is formed based on the emission and the reception timings of a light pulse, and from the beat frequency the distance is measured.
The distance to the target from the measuring position can be accurately measured from the results of the precise measurement and the rough measurement.
FIG. 7
shows an illustrative drawing for explaining the formation of a timing signal being the foundation of a distance measurement. A point corresponding to the center of gravity of a received pulse pattern is found and the point is utilized to form a reception timing signal. In other words, when a reflected pulse light from the target (a) is received, a damping oscillation waveform (b) is generated with a tuned antenna, etc. From the damping oscillation waveform (b) a reception timing signal is formed, which corresponds to the center of gravity position of the received pulse light (a). It is so arranged that the reception timing signal can be formed only in a case where a received light quantity is larger than a predetermined light quantity.
The reception of pulse light is confirmed with the catch of a point b
0
on the damping oscillation waveform (b) by a first threshold level V
S1
. After the confirmation of the reception of pulse light, an output signal ‘High’ (c) is output to make the circuit active for a certain period of time.
A second threshold level V
S2
which forms the timing signal is set in the vicinity of 0 V, and it catches a point b
1
on the damping oscillation signal (b) and a signal (d) is output. The reception timing signal utilizes the leading edge or the trailing edge of the output signal (d).
FIG.
8
(
a
) to FIG.
8
(
c
) show the reception states of pulses and the damping oscillation signal. The axis of ordinates expresses the voltage of the received light signal and the axis of abscissas expresses time.
FIG.
8
(
a
) shows a normal reception state. It shows a reception state where the damping oscillation signal J
2
is larger than the threshold level.
A small damping oscillation signal J
1
at the heading part expresses an internal noise at the time of emission of a light pulse. A small continuous signal shows external noise N. The received pulse is shown to be larger than the threshold level.
In the receiving system, an optical filter and an electrical filter, which are designed to pass only the pulse light, are provided. However, there are also incident lights from the sunlight, fluorescent lamps, etc., which are the causes of the noise light.
FIG.
8
(
b
) shows the case of a long distance measurement where the input pulse signal is small. In this case, the magnitudes of both external noise and internal noise which is generated at the time of emission of light pulses are kept unchanged, and when the input signal is smaller than the threshold level, even if the input signal is larger than the noise voltage, the case may be regarded to be a receiving limit and judged to be a measuring limit.
FIG.
8
(
c
) shows the case where the external noise is large, for example, the case where measurement is performed under the summer sunlight. Under the summer sunlight, the light intensity can be more than 100,000 lux. The noise level N in this case is able to reach the threshold level.
In this case, there is a problem that even if the reception signal level is larger than the threshold level, measurement becomes impossible influenced by the reception of external noise.
SUMMARY OF THE INVENTION
The present invention is invented to offer a distance measuring apparatus which is able to perform distance measurement effectively even in an environment in which the noise level is so high as to disturb the distance measurement with light waves. In the distance measuring apparatus, a projection system irradiates a target to be measured with measuring light beams; a reception means in a reception system receives the reflected beams; and a processing means calculates the distance from the measuring position to the target to be measured based on the received reflected beams. The threshold level of the reception system for judging the incidence of reflected beams can be made variable.
REFERENCES:
patent: 4518253 (1985-05-01), Takahashi
patent: 5579102 (1996-11-01), Pratt et al.
patent: 5850370 (1998-12-01), Stringer et al.
patent: 5867522 (1999-02-01), Green et al.
Kanokogi Mitsuru
Ohishi Masahiro
Yabe Masaaki
Baker & Botts LLP
Kabushiki Kaisha Topcon
Pyo Kevin
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