Thermally insensitive particle concentration controller

Claim 3

An apparatus as recited in claim 1, further including: comparator circuit means, in electrical communication with said amplifying circuit means, for comparing the amplified electrical output signal with a preselected reference to produce a control signal corresponding to the deviation between the measured density of particles deposited on said electrode means and the desired density thereof; and circuit means, in electrical communication with said comparator circuit means, for holding the control signal from said comparator circuit means.

Claim 4

An apparatus as recited in claim 2, further including: means, actuated by the control signal from said hold circuit, for dispensing particles into the mix to achieve the requisite concentration therein.

Claim 5

An apparatus as recited in claim 3, wherein said illuminating means includes a light source.

Claim 6

An apparatus as recited in claim 4, wherein said amplifying circuit means includes: a first operational amplifier connected electrically to said photodiode; and a first resistance circuit connected in parallel with said first operational amplifier to provide resistive feedback operating in an inverting mode.

Claim 7

An apparatus as recited in claim 5, wherein said comparator circuit means includes: a second operational amplifier in electrical communication with said first operational amplifier; and a second resistance circuit connected in parallel with said second operational amplifier so that said second operational amplifier functions as a level detector with positive feedback about the switch point to provide a hysteresis cycle thereabout.

Claim 8

An apparatus as recited in claim 6, wherein said hold circuit means includes: a silicon controlled switch in electrical communication with said second operational amplifier; a relay connected electrically in series with said silicon controlled switch; and a voltage source connected electrically in series with said relay.

Claim 9

An electrophotographic printing machine of the type having a photoconductive member and a development system employing a developer mix of carrier granules and toner particles to form a toner powder image on an electrostatic latent image recorded on the photoconductive member, including: electrode means mounted on the photoconductive member and biased electrically to attract toner particles thereto as said electrode means passes through the developer mix; means for illuminating said electrode means having the toner particles deposited thereon with light rays; a thermally insensitive photodiode for detecting the intensity of the light rays transmitted from said electrode means, said photodiode being adapted to generate a substantially thermally insensitive electrical output signal indicative of the density of toner particles deposited on said electrode means; and amplifying circuit means, in elEctrical communication with said photodiode, for stably amplifying the thermally insensitive electrical output signal from said photodiode to at least a preselected level.

Claim 10

An electrophotographic printing machine of the type having a photoconductive member and a development system employing a developer mix of carrier granules and toner particles to form a toner powder image on an electrostatic latent image recorded on the photoconductive member, including: electrode means mounted on the photoconductive member and biased electrically to attract toner particles thereto as said electrode means passes through the developer mix; means for illuminating said electrode means having the toner particles deposited thereon with light rays; a thermally insensitive photodiode for detecting the intensity of the light rays transmitted from said electrode means, said photodiode being adapted to generate a substantially thermally insensitive electrical output signal indicative of the density of toner particles deposited on said electrode means; and amplifying circuit means, in elEctrical communication with said photodiode, for stably amplifying the thermally insensitive electrical output signal from said photodiode to at least a preselected level.

Claim 11

A printing machine as recited in claim 8, further including: comparator circuit means, in electrical communication with said amplifying circuit means, for comparing the amplified electrical output with a preselected reference to produce a control signal corresponding to the deviation between the measured density of toner particles deposited on said electrode means and the desired density thereof; and circuit means, in electrical communication with said comparator circuit means, for holding the control signal from said comparator circuit means.

Claim 12

A printing machine as recited in claim 9, further including means, actuated by the control signal from said hold circuit, for dispensing toner particles into the developer mix to achieve the requisite concentration therein.

Claim 13

A printing machine as recited in claim 10, wherein said illuminating means includes a light source.

Claim 14

A printing machine as recited in claim 11, wherein said amplifying circuit means includes: a first operational amplifier connected electrically to said photodiode; and a first resistance circuit connected in parallel with said first operational amplifier to provide resistive feedback operating in an inverting mode.

Claim 15

A printing machine as recited in claim 12, wherein said comparator circuit means includes: a second operational amplifier in electrical communication with said first operational amplifier; and a second resistance circuit connected in parallel with said second operational amplifier so that said second operational amplifier functions as a level detector with positive feedback about the switch point to provide a hysteresis cycle thereabout.

Claim 16

A printing machine as recited in claim 13, wherein said hold circuit means includes: a silicon controlled switch in electrical communication with said second operational amplifier; a relay connected in series with said silicon controlled switch; and a voltage source connected electrically in series with said relay.