Abstract: In one example, an electrostatic printer includes: a photoconductor member; a charging unit to charge the photoconductor member to a charged voltage; an imaging unit to generate a latent electrostatic image on the photoconductor member by discharging areas of the charged photoconductor member; a developer unit to develop a toner image on the photoconductor member using a developer voltage; and a controller to change the developer voltage and to change the charged voltage dependent on the change of the developer voltage to keep the difference between the developer voltage and the charged voltage constant.

Abstract: In an example implementation, a method of cleaning a silicon photoconductor includes contacting the silicon photoconductor with a base-peroxide solution, rinsing the silicon photoconductor with a liquid, and heating the silicon photoconductor to evaporate the liquid.

Abstract: A cleaning solution is used to at least substantially remove colorant from the photoconductive drum as the photoconductive drum rotates. A wiper wipes the cleaning solution from the photoconductive drum while purposefully maintaining a layer of the cleaning solution on the drum. The wiper has an edge that is purposefully rounded.

Abstract: According to some examples, an apparatus includes a monitoring module to determine a length of a portion of an imaging member as the imaging member rotates; and indicate a fault condition in response to the determined length being different from a reference length.

Abstract: In an example implementation, a method of cleaning a silicon photoconductor includes contacting the silicon photoconductor with a base-peroxide solution, rinsing the silicon photoconductor with a liquid, and heating the silicon photoconductor to evaporate the liquid.

Abstract: An apparatus to calibrate a printer. The apparatus comprises a controller to: control deposition of white printing material on media, the white printing material having an opacity of at least 55%; control deposition of non-white printing material on the white printing material; receive data for at least one sensed characteristic of the non-white printing material; and calibrate the printer using the received data for the at least one sensed characteristic of the non-white printing material.

Abstract: According to one example, there is provided apparatus for detecting a fault in a printing system. The apparatus includes a monitoring module to determine the length of a portion of an imaging member as the imaging member rotates; and indicate a fault condition when the determined length is different to a reference length.

Abstract: An apparatus to calibrate a printer. The apparatus comprises a controller to: control deposition of white printing material on media, the white printing material having an opacity of at least 55%; control deposition of non-white printing material on the white printing material; receive data for at least one sensed characteristic of the non-white printing material; and calibrate the printer using the received data for the at least one sensed characteristic of the non-white printing material.

Abstract: In an example of a method for reducing contamination, a purified imaging oil is formed by filtering an imaging oil through an imaging oil filter, and then filtering the imaging oil through a polar absorbent filter. A surface of an amorphous silicon photoconductor of a liquid electrophotographic printing apparatus is maintained by periodically applying the purified imaging oil to the amorphous silicon photoconductor.

Abstract: In one example, a method is described that includes a processor detecting a voltage of a photoconductor layer (103) of a printing device, comparing the voltage of the photoconductor layer (103) to a threshold voltage, and applying a corrective voltage to a charging unit (110) or to a transfer member (104) when the voltage of the photoconductor layer (103) exceeds the threshold voltage.

Abstract: An electrostatic printer comprises a charging unit, a photoconductor member, an imaging unit, a developer unit and a controller. The charging unit is to charge the photoconductor member to a charged voltage. The imaging unit is to generate a latent electrostatic image on the photoconductor member by discharging areas of the charged photoconductor member. The developer unit is to develop a toner image on the photoconductor member using a developer voltage. The controller is to change the developer voltage, and to change the charged voltage dependent on the change of the developer voltage.

Abstract: In an example implementation, a method of cleaning a silicon photoconductor includes contacting the silicon photoconductor with a base-peroxide solution, rinsing the silicon photoconductor with a liquid, and heating the silicon photoconductor to evaporate the liquid.

Abstract: A method is described in which a spectrum of a surface of a photoconductor member is obtained using optical spectroscopy; and an extent of oxidation of the surface is determined based on the obtained spectrum.

Abstract: There is provided a method of cleaning an amorphous silicon electrophotographic printing drum. the method comprises contacting the amorphous silicon of the drum with a base and an oxidising agent; and then rinsing the amorphous silicon with a liquid.

Abstract: In one implementation, an image forming apparatus may include a photoconductive unit and a refresh unit. The photoconductive unit may include a photoconductive layer. The photoconductive layer may have a first polarity during a print routine. The refresh unit may apply a voltage to the photoconductive layer to electrically bias the photoconductive layer to have a second polarity during a refresh routine.

Abstract: An apparatus to calibrate a printer. The apparatus comprises a controller to: control deposition of white printing material on media, the white printing material having an opacity of at least 55%; control deposition of non-white printing material on the white printing material; receive data for at least one sensed characteristic of the non-white printing material; and calibrate the printer using the received data for the at least one sensed characteristic of the non-white printing material.

Abstract: According to one example, there is provided apparatus for detecting a fault in a printing system. The apparatus comprises a monitoring module to determine the length of a portion of an imaging member as the imaging member rotates; and indicate a fault condition when the determined length is different to a reference length.

Abstract: In one implementation, an image forming apparatus may include a photoconductive unit and a refresh unit. The photoconductive unit may include a photoconductive layer. The photoconductive layer may have a first polarity during a print routine. The refresh unit may apply a voltage to the photoconductive layer to electrically bias the photoconductive layer to have a second polarity during a refresh routine.

Abstract: A method for monitoring development parameters of a liquid toner electrophotographic (LEP) printer, the method comprising defining an operational window for a current utilized by the printer and monitoring the current to determine a deviation of the current outside the operational window.

Abstract: A charge director injection system includes a charge director tank, a liquid toner tank, a charge director pump to pump charge director from the charge director tank into the liquid toner tank, and a control system configured to measure a change in charge density per amount of charge director injected into the liquid toner tank, and create a charge profile indicating a relationship between amount of charge director injected into the liquid toner and change in charge density of the liquid toner within the liquid toner tank.