Example aspects described herein relate to an apparatus for adjusting control parameters of a printing substance for a printing system. Such adjustments may occur in conjunction with a color calibration process of the printing system.

An example system includes a power supply. The power supply is electrically coupled to an electrode, a developer roller, and a cleaner roller. The system also includes a controller. The controller is to instruct the power supply to reduce, at a first time, a magnitude of an electrode voltage supplied to the electrode. The controller also is to instruct the power supply to set, at a second time, a developer roller voltage and a cleaner roller voltage each to about a wet null voltage.

In one example of the disclosure, it is determined that an amount of print agent remaining in a print agent container of a print apparatus is below a threshold level. An amount of print solution is transferred from a print solution reservoir of the print apparatus, or an amount of print solution solvent is transferred from a solvent reservoir of the print apparatus, into the print agent container. At least some of the remaining print agent is caused to dissolve into the amount of print solution or print solution solvent to forma rinse solution. The rinse solution is transferred from the print agent reservoir to the print solution reservoir.

A print agent transfer assembly (200) comprising a print agent transfer member ((202) to receive a first layer and second layer of print agent, and an energy source (208) to provide energy at a first predetermined intensity level to the first layer and to provide energy at a second, different, predetermined intensity level to the second layer.

A developing roller is rotatable while carrying a liquid developer containing toner and a carrier liquid and contains an electroconductive agent, and includes a squeeze roller provided in contact with the developing roller through at least the carrier liquid, a voltage source capable of generating a potential difference between the developing roller and a squeeze roller, and a current detecting sensor for detecting a current passed between the developing roller and the squeeze roller. In addition, a controller controls the voltage source, and a display device outputs information on a lifetime of the developing roller. The controller outputs the information on the lifetime from the display device on the basis of a detection result by the current detecting sensor when a predetermined potential difference is generated between the developing roller and the squeeze roller by the voltage source.

An example method of performing a null cycle in a liquid electrographic printer is described. The method involves collecting, at a photo imaging plate cleaning station, imaging oil deposited on a photo imaging plate during a print cycle. During a null cycle, the photo imaging plate cleaning station is controlled to apply the collected imaging oil to the photo imaging plate.

Measures for controlling an engagement force between a photo imaging plate and a developer roller in a printing device are described. A motor is operated to generate rotational motion. The rotational motion is translated into linear motion. The linear motion causes an adjustment to the engagement force between the developer roller and the photo imaging plate. A characteristic of the motor is monitored. The motor is controlled on the basis of the monitored characteristic in order to maintain a desired engagement force between the developer roller and the photo imaging plate.

Described herein is a liquid electrostatic ink developer assembly comprising a developer roller having a surface coating, the surface coating comprising a polyurethane resin formed from a polyol; a hydroxyl-terminated polysiloxane; and a polyisocyanate. Also, described herein is a liquid electrostatic printing apparatus comprising the liquid electrostatic ink developer assembly.

An example method of performing a null cycle in a liquid electrographic printer is described. The method involves collecting, at a photo imaging plate cleaning station, imaging oil deposited on a photo imaging plate during a print cycle. During a null cycle, the photo imaging plate cleaning station is controlled to apply the collected imaging oil to the photo imaging plate.

A developer container 53 is capable of supplying a liquid developer to a portion, of a surface of a cleaning roller 58, between a cleaning position X and a contact position Y with respect to a rotational direction of the cleaning roller 58. A free end of a cleaning blade 56 is positioned in a range of 65 or more and less than 95 as a positive angle of the rotational direction of the cleaning roller 58 when a line passing through a center of the cleaning roller 58 and an upper end portion of the cleaning roller 58 with respect to a direction of gravitation is at 0 (reference line G). In this case, the cleaning blade 56 is disposed so that an angle between a line F perpendicular to a line E connecting the center of the cleaning roller 58 and the free end of the cleaning blade 56, and the cleaning blade 56 is in a range of 35 or more and less than 60.