Drop on demand inkjet printing systems eject ink drops from printhead nozzles in response to pressure pulses generated within the printhead by either piezoelectric devices or thermal transducers, such as resistors. The printheads have a plurality of inkjet ejectors that are fluidly connected at one end to an ink supplying manifold through an ink channel and at another end to an aperture in an aperture plate. The ink drops are ejected through the apertures, which are sometimes called nozzles.
In a typical piezoelectric inkjet printing system, application of an electrical signal to a piezoelectric transducer causes the transducer to expand. This expansion pushes a diaphragm, which is positioned adjacent the transducer, into a pressure chamber filled with ink received from the manifold. The diaphragm movement urges ink out of the pressure chamber and through the aperture to eject liquid ink drops. The ejected drops, referred to as pixels, land on an image receiving member opposite the printhead to form an ink image. The respective channels from which the ink drops were ejected are refilled through the ink channel from an ink manifold.
In some phase change or solid ink printers, which use an indirect printing process, the image receiving member is a rotating drum or belt coated with a release agent and the ink is a phase change material that is normally solid at room temperature. In these solid ink printers, the ink image is transferred from the rotating image receiving member to a recording medium, such as paper. The transfer is generally conducted in a nip formed by the rotating image receiving member and a rotating pressure roller, which is also called a transfix roller. One or both of the transfix roller and the recording medium may be heated prior to the recording medium entry in the transfixing nip. As a sheet of paper is transported through the nip, the fully formed image is transferred from the image receiving member and fixed on the sheet of paper. This technique of using heat and pressure at a nip to transfer and fix an image to a recording medium passing through the nip is typically known as “transfixing,” a well-known term in the art, particularly with solid ink technology.
During printing operations, phase change inks are heated to melt a solid ink into a liquid form for ejection by the inkjet ejectors. The phase change inks melt when heated above a predetermined melting temperature that is determined by the chemical formulation of the solid ink. One or more heaters in the printer heat the surface of the image receiving member so that ink drops on the imaging drum remain in a visoelastic state prior to being transfixed onto the media sheet. A typical embodiment of a heater is an electric heater that heats the surface of the image receiving member in response to an electrical current being passed through the heater. The image receiving member is configured as a rotating drum that is heated to an average temperature of approximately 60° C. prior to receiving ink drops that form latent ink images for printing.
At various times, the image receiving members in indirect solid ink printers may cool to a temperature that is below the operating temperature that enables the image receiving member to facilitate transfer of ink images from the receiving member to a media sheet. For example, if the printer is turned off, the heater is deactivated and the temperature of the image receiving member drops to the ambient temperature of the environment surrounding the printer. Modern printers also include power saving modes that deactivate heaters and other components when the printer is not in use to reduce the consumption of electrical power.
When a printer with a “cold” image receiving member receives a print job, a controller activates the heater to enable the temperature of the image receiving member to rise to a predetermined operating temperature before the ink ejectors eject in drops onto the image receiving member to form ink images. The amount of time taken to heat the image receiving member to the operating temperature results in a delay from the time that the printer receives a print job to the time that the printer produces the first printed page. In one common scenario, a printer with a “cold” image receiving member receives a print job that includes a small number of printed pages (e.g. one or two pages). The amount of time required to heat the image receiving member to the operating temperature represents a substantial portion of the total time taken to execute print jobs with a small number of pages. Consequently, improvements to the operation of indirect inkjet printers that reduce the amount of time that is needed to commence printing when the printer has a “cold” image receiving member would be beneficial.
USPTO Backgrounds
USPTO Backgrounds