Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-10-15
2002-02-05
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C235S2010FS, C347S250000
Reexamination Certificate
active
06344644
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning device for a laser beam printer or the like. In particular, the present invention relates to an optical scanning device utilizing an SOS (Start Of Scan) signal as a synchronizing signal for adjusting a timing of a scanning beam.
Conventionally, in an optical scanning device such as an LSU (Laser Scanning Unit), the SOS signal is obtained as follows.
In the conventional LSU, the scanning laser beam is received by a photo diode, which outputs a light detection signal. Based on the light detection signal, the SOS signal is generated. Specifically, in the LSU, a laser beam LB is emitted by a laser diode. The laser beam is deflected by a polygon mirror which rotates at a relatively high speed to deflect the laser beam to scan within a predetermined angular range. The scanning beam is directed onto a photoconductive drum via an f&thgr; lens and scans the circumferential surface of the photoconductive drum in a direction of an axis thereof from one side to another (i.e., in a main scanning direction). While the beam scans in the main scanning direction, the photoconductive drum rotates about the axis thereof (i.e., an auxiliary scanning is performed). Within a scanning range of the laser beam, but out of an image forming area of the photoconductive drum, a photo diode is arranged. The photo diode receives the scanning beam and outputs a light detection signal, which is transmitted to the SOS signal processing circuit. Based on the SOS signal output by the SOS signal processing circuit, a controller controls an LD drive circuit. If the image formation is executed a predetermined period after the SOS signal has been output (i.e., the image formation is executed synchronously with the SOS signal), the image is always formed in the imaging area on the photoconductive drum.
In the photo diode for obtaining the SOS signal, received amount of light may vary due to variation of output power of the laser beam, oscillation of surfaces of the polygon mirror or the like. Therefore, the level of the light detection signal output by the photo diode may not-be constant. Further, the level of the light detection signal may also vary due to noise introduced at the photo diode and/or the signal processing circuit, a deviation of DC component of the light detection signal due to the dark current, and while the signal is transmitted from the photo diode to the signal processing circuit.
If the SOS signal is generated based on such an unstable light detection signal including noises, the timing of the SOS signal may vary, and it is difficult to obtain a reliable SOS signal.
In particular, if the conventional SOS signal generating circuit generates the SOS signal by comparing the light receiving signal value with a predetermined threshold value, the variation of the signal level directly affects the timing of the SOS signal.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an SOS signal generating circuit which is capable of suppressing noises in the light receiving signal and generating a reliable SOS signal.
According to an aspect of the invention, there is provided an optical scanning device, provided with:
a light source;
a scanning system which deflect the beam emitted by the light source to scan;
a light receiving unit having a plurality of light receiving elements arranged in a direction in which the scanning beams scans, a light receiving signal being output by each of the light receiving element upon incident of the scanning beam, the plurality of light receiving elements being divided into two groups such that every other light receiving element is fallen in the same group and adjoining light receiving elements are fallen in different groups;
a resonance amplifying system that amplifies the light receiving signals of the light receiving elements of the two groups, respectively;
a clock signal generating unit that generates a clock signal in accordance with the resonance amplified signals;
a delay signal generating circuit that generates a delay signal for generating a synchronizing signal in accordance with the light receiving signals output by at least part of the plurality of light receiving elements; and
a logic circuit which generates the synchronizing signal based on the clock signal output by the clock signal generating unit and the delay signal output by the delay signal generating unit.
The light receiving signals corresponding to each group are synthesized and resonance-amplified, and the clock signal is generated therefrom. Further, the delay signal which defines the start of the synchronizing signal is generated based on the light receiving signals. Then, the synchronizing signal is generated using the stabilized portion of the clock signal. Accordingly, a reliable SOS signal can be obtained.
Optionally, the scanning optical system may include:
a first adder that synthesizes the light receiving signals output by the light receiving elements fallen in one of the pair of groups; and
a second adder that synthesizes the light receiving signals output by the light receiving elements fallen in the other one of the pair of groups.
In this case, the resonance amplifying system may include:
a pair of narrow-band amplifiers that resonance amplify signals respectively output by the first and second adders; and
a first comparator for comparing the resonance amplified signals output by the pair of narrow-band amplifiers, output signal of the first comparator being utilized as the clock signal.
Further optionally, the resonance frequencies of the pair of narrow-band amplifiers are substantially coincide with the frequency of the sum of the light receiving signals output from the first and second adders, respectively.
Still optionally, the delay signal generating unit may include:
a second comparator that compares the sum of the light receiving signals output from all of the plurality of light receiving elements with a predetermined reference level; and
a first timer circuit that is triggered in response to an output signal of the second comparator to output a delay signal for a predetermined period.
Further, the delay signal generating unit may include:
a third comparator that compares the light receiving signals output by first two of the plurality of light receiving elements;
a fourth comparator that compares the sum of the output signals of the first two of the plurality of light receiving elements with a predetermined reference level;
an AND gate that applies AND operation to the outputs of the third and fourth comparators;
a third timer circuit that is triggered in response to an output signal of the AND gate to output a delay signal for a predetermined period.
Further optionally, the logic circuit unit may be provided with;
an enabling signal output system that outputs an enabling signal upon end of the delay signal output by the delay signal generating unit;
a second timer that outputs, in accordance with the enabling signal and the clock signal output by the clock signal generating unit, a gate signal which is kept for a predetermined period; and
a logic gate that outputs the synchronizing signal when the clock signal and the gate signal are input.
Optionally, the delay signal output by the delay signal generating unit is kept output at least when the light receiving signals are output by the plurality of light receiving elements.
In particular, the delay signal is terminated by a point of time at which an amplitude of the output signal of each narrow-band amplifier is a half of the maximum value thereof.
Further, the delay signal output by the delay signal generating unit is terminated within a rage from one period before to one period after with respect to a point of time where the output of the resonance amplifier has a maximum value.
According to another aspect of the invention, there is provided an optical scanning device, provided with:
a light source;
a scanning system which deflect the beam emitted by the light source to scan;
a light receiving unit having a plurality of l
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
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