Detector circuit for electrophotographic copier

Claim 2

In an electrophotographic copying apparatus comprising a photoconductive belt having on one side thereof regularly spaced markings the reflectivity of which differs from the average reflectivity of the said belt side, detector means including a light source and a photoelement located adjacent to said belt side for generating a signal pulse each time a marking passes the detector means and a copying control circuit to receive the signal pulses, the improvement which comprises said detector means including means for emitting a detector signal proportional to the amount of light sensed by said photoelement, a signal modifying circuit separated from said copying control circuit and including means for maintaining an output signal at a level corresponding to the average value of said detector signal and a detector light control circuit including means responsive to said output signal for controlling the intensity of said light source.

Claim 3

Apparatus according to claim 1, said means for maintaining said output signal level comprising a low-pass filter on a lead connecting said signal emitting means with said light control circuit.

Claim 4

Apparatus according to claim 2, said low-pass filter comprising a resistor and a capacitor connected in parallel between said lead and a terminal of a source of a control voltage for said light control circuit.

Claim 5

Apparatus according to claim 1, said signal-modifying circuit comprising a circuit separating element connected with said signal emitting means and from which element a lead extends to said light control circuit and a resistor and a capacitor connected in parallel between said lead and a voltage source.

Claim 6

Apparatus according to claim 1, said light control circuit comprising a voltage differential amplifier and an impedance converter.

Claim 7

Apparatus according to claim 5, said impedance converter comprising a transistor having its base connected with the output of said amplifier, its collector connected with a voltage source and its emitter connected with said light source.

Claim 8

Apparatus according to claim 1, said signal emitting means comprising a plurality of transistors connected together in Darlington configuration, said photoelement being a photo-transistor and constituting the first of the said transistors.

Claim 9

In an electrophotographic copying apparatus comprising a photoconductive belt having on one side thereof regularly spaced markings the reflectivity of which differs from the average reflectivity of the said belt side, detector means including a light source and a photoelement located adjacent to said belt side for generating a signal pulse each time a marking passes the detector means and a copying control circuit to receive the signal pulses, the improvement which comprises said detector means including means for emitting a detector signal proportional to the amount of light sensed by said photoelement, said signal emitting means comprising a plurality of transistors connected together in Darlington configuration, said photoelement being a phototransistor and constituting the first of said transistors, a signal modifying circuit separated from said copying control circuit and including means for maintaining an output signal at a level corresponding to the average value of said detector signal and a detector light control circuit including means responsive to said output signal for controlling the intensity of said light source, said signal-modifying circuit comprising a diode connected to the emitter of the last of said transistors and from which diode a lead extends to said light control circuit and a resistor and a capacitor connected in parallel between said lead and a voltage source, said light control circuit comprising a voltage differential amplifier and an impedance converter.

Claim 10

In an electrophotographic copying apparatus comprising a photoconductive belt having on one side thereof regularly spaced markings the reflectivity of which differs from the average reflectivity of the said belt side, detector means including a light source and a photoelement located adjacent to said belt side for generating a signal pulse each time a marking passes the detector means and a copying control circuit to receive the signal pulses, the improvement which comprises said detector means including means for emitting a detector signal proportional to the amount of light sensed by said photoelement, said signal emitting means comprising a plurality of transistors connected together in Darlington configuration, said photoelement being a phototransistor and constituting the first of said transistors, a signal modifying circuit separated from said copying control circuit and including means for maintaining an output signal at a level corresponding to the average value of said detector signal and a detector light control circuit including means responsive to said output signal for controlling the intensity of said light source, said signal-modifying circuit comprising a diode connected to the emitter of the last of said transistors and from which diode a lead extends to said light control circuit and a resistor and a capacitor connected in parallel between said lead and a voltage source, said light control circuit comprising a voltage differential amplifier and an impedance converter.

Claim 11

Apparatus according to claim 8, said impedance converter comprising a transistor having its base connected with the output of said amplifier, it collector connected with a voltage source and its emitter connected with said light source.