Optical position detection device and distance measurement...

Details Optical position detection device and distance measurement... Optical position detection device and distance measurement...

2001-12-07

2003-07-22

Fulton, Christopher W. (Department: 2859)

Radiant energy

Photocells; circuits and apparatus

With circuit for evaluating a web, strand, strip, or sheet

C250S559390, C356S622000, C356S221000

Reexamination Certificate

active

06597007

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical position detection device employing a semiconductor position detection element and to a distance measurement device wherein object distance is measured by using an optical position detection device to detect the reflected light of a spot beam or slit beam illuminating this object.
2. Related Background Art
In a semiconductor position detection element, incident light is subjected to photoelectric conversion to generate a photoelectric current (carriers) and, dependent on the position of incidence of the beam, a first signal current I
1
is output from a first output terminal and a second signal current I
2
is output from a second output terminal. The sum (I
1
+I
2
) of the first signal current and second signal current depends on the incident light beam intensity. If the sum (I
1
+I
2
) of the first signal current and second signal current is fixed, the difference (I
1
−I
2
) of the first signal current and second signal current corresponds to the position of incidence of the beam. An optical position detection device detects the position of beam incidence using such a semiconductor position detection element. Also, a distance measurement device comprises a light-emitting unit in addition to this optical position detection device and the distance to the object is detected by photodetection by the semiconductor position detection element in the optical position detection device of the reflected light of a spot beam illuminating the object by the light-emitting unit.
In a conventional optical position detection device the ratio (V
1
/V
2
) of a first signal voltage V
1
derived from the first signal current I
1
output from the semiconductor position detection element and a second signal voltage V
2
derived from the second signal current I
2
, is found and is used as an output indicating the position of beam incidence. Alternatively, in a conventional optical position detection device, the sum of the first signal voltage V
1
and the second signal voltage V
2
(V
1
+V
2
) and the difference (V
1
−V
2
) are found, the difference is divided by the sum, and the result of this division ((V
1
−V
2
)/(V
1
+V
2
)) is used as an output indicating the position of beam incidence (see for example Laid-open Japanese Patent Publication No. H.2-247504). Thus, in a conventional optical position detection device, in whichever case, division means were considered to be necessary for obtaining an output indicating the position of beam incidence on the semiconductor position detection element. In addition, the foregoing publication discloses a technique for improving resolution of the position of beam incidence wherein the signal voltages that are respectively to constitute the divisor and dividend are multiplied by a suitable multiplication factor before being subjected to A/D conversion, after which division is performed in order to output the result of this division as a digital value in a suitable range.
SUMMARY OF THE INVENTION
The division means in a conventional optical position detection device as described above may be realized by either analogue circuitry or digital circuitry but hardware costs are high owing to the difficulty of miniaturization due to the size of this circuitry, or the time required for division processing is long due to the large amount of calculation. Also, miniaturization of the division means disclosed in the above publication is difficult and hardware costs are high owing to the need to provide a large number of amplification circuits and A/D conversion circuits.
Furthermore, if a plurality of semiconductor position detection elements are provided, if only a single set of the processing circuits (including the current/voltage conversion circuit, division circuit, amplification circuit and A/D conversion circuit etc) that find the position of beam incidence from the signal current output from the semiconductor position detection elements is provided, the time required for finding the position of beam incidence is further lengthened. On the other hand, if the same number of the aforesaid processing circuits are provided as the number of semiconductor position detection elements, the size of the circuitry is further increased and hardware costs are further raised.
Conventional distance measurement devices including such optical position detection devices are likewise subject to the problems of large circuit size and long processing time.
The present invention was made in order to solve the problems mentioned above, its object being to provide an optical position detection device wherein the size of the circuitry is small, processing time short, and excellent resolution of the position of beam incidence output as a digital signal is obtained and a distance measurement device employing such an optical position detection device. A first optical position detecting device according to the present invention comprises: (1) a semiconductor position detection element whereby an incident beam is subjected to photoelectric conversion, and that outputs a first signal current from a first output terminal and outputs a second signal current from a second output terminal in response to the position of incidence of this beam; (2) a first current/voltage conversion unit that inputs the first signal current that is output from the first output terminal of the semiconductor position detecting element and outputs a first signal voltage in accordance with this first signal current; (3) a second current/voltage conversion unit that inputs the second signal current that is output from the second output terminal of the semiconductor position detecting element and outputs a second signal voltage in accordance with this second signal current; (4) a selection circuit that compares the magnitude of the respective values of the first signal voltage output from the first current/voltage conversion unit and the second signal voltage output from the second current/voltage conversion unit and that outputs a comparison signal indicating the result of this comparison and, of the first and the second signal voltages, respectively selects and outputs a maximum signal (maximum signal voltage) whose voltage is the larger and a minimum signal (minimum signal voltage) whose voltage is the smaller; (5) an A/D conversion circuit wherein an A/D conversion range is set in accordance with the maximum signal output from the selection circuit and that converts the minimum signal output from the selection circuit into a digital signal and outputs this digital value; and (6) an incidence position calculating unit that finds the incidence position of the beam on the semiconductor position detecting element, using the comparison signal output from the selection circuit and the digital output which is output from the A/D conversion circuit.
With the first optical position detection device according to the present invention, when a beam of light is incident on the semiconductor position detection element, this beam is subjected to photoelectric conversion and, depending on the position of incidence of this beam, a first signal current I
1
is output from the first output terminal and a second signal current I
2
is output from the second output terminal. The first signal current I
1
is input to the first current/voltage conversion unit so that a first signal voltage V
1
is output based on this first signal current I
1
. In the same way, the second signal current I
2
is input to the second current/voltage conversion unit so that a second signal voltage V
2
is output based on this second signal current I
2
. The first and second signal voltages V
1
and V
2
are respectively input to the selection circuit where the magnitudes of their respective values are compared and a comparison signal indicating the comparison result is output and, of the first and second of signal voltages V
1
and V
2
, that of larger voltage is designated as maximum signal Vmax and that of smaller voltage is

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