An image printing device and method for printing an image to an information carrier. The image printing device includes apertures which can be selectively opened or closed to permit or restrict the transport of pigment particles during print sequences, a predetermined number of which print sequences are included in a print cycle, to thereby enable the formation of a pigment image. Further, deflection electrodes are included for, by means of predetermined deflection voltages related to each one of the predetermined number of print sequences, controlling the deflection of pigment particles in transport to thereby be able to deflect pigment particles against predetermined locations in view of the image which is to be printed. To enable a faster print speed, according to the invention, the change of the predetermined deflection voltages of a previous print sequence to the predetermined deflection voltages of a current print sequence is time displaced relative to the beginning of the current print sequence.

Direct electrostatic printing method and apparatus with increased print speed

The present invention relates to a direct electrostatic printing method, in which a stream of computer generated signals, defining an image information, are converted to a pattern of electrostatic fields which selectively permit or restrict the transport of charged toner particles from a particle source toward a back electrode and control the deposition of those charged toner particles in an image configuration onto an image receiving medium. Particularly, the present invention refers to a direct electrostatic printing method performed in consecutive print cycles, each of which includes at least one development period (tb) and at least one recovering period (tw) subsequent to each development period (tb), wherein the pattern of electrostatic fields is produced during at least a part of each development period (tb) to selectively permit or restrict the transport of charged toner particles from a particle source toward a back electrode, and wherein a supplemental voltage source is applied at the beginning of each development period to enhance the transport of the particle source at the beginning of each development period. Advantageously, an additional electric field is produced during at least a part of each recovering period (tw) to repel a part of the transported charged toner particles back toward the particle source. Preferably, the supplemental voltage source is supplied to a guard electrode so as to control the amount of toner attracted from the particle source by each aperture. By controlling the amount of toner attracted by each aperture, the boner may be distributed equally among the apertures thereby preventing toner starvation.

Direct printing method with improved control function

A direct electrostatic printing device and method for printing an image to an information carrier with increased density harmonization. This is attained by measuring the behaviour of the apertures and subsequently adjusting the control parameters of at least the diverging apertures. The measurement of the behaviour of the apertures is suitably performed by scanning a known print sample with a predetermined density. The scanned values are inverted around a predetermined value for which no compensation is done to create a compensation function. At least the apertures which have a behaviour which diverges from a predetermined behaviour are compensated according to the compensation function, thereby enabling an increased density harmonization. The compensation function can preferably be signal processed by, for example, a low pass filtering.

Direct electrostatic printing method and apparatus

A printing apparatus includes heat treatment means, a rotatable feeder roll chargeable to a predetermined first potential, a support roll chargeable to a predetermined second potential, and a matrix in the form of a flexible printing circuit. The matrix has supply apertures, each supply aperture having a first inner diameter and being surrounded by an electrically conducting control ring configured to be charged to a predetermined third potential and having a second inner diameter. The third potential is selected to control corresponding supply apertures between an open state and a closed state. The first inner diameter of the control ring is at least equal to the second inner diameter of the supply aperture. The matrix and the electrically conducting control rings are covered on upper surfaces and aperture edges with an electrically insulating layer. The feeder roll, the support roll and the matrix are configured to transfer a dry powder from the feeder roll through the supply apertures of the matrix to an object to be printed which is conveyed over the support roll. The powder deposited on the object is fixed by the heat treatment means.

Printing apparatus of toner-jet type

Printing apparatus of the type named 'toner jet' printing apparatus, and in which a dry print powder, generally named 'toner' is, by a direct process, transferred from a rotating toner feeder roll (1) which is charged with a certain predetermined, relatively low positive potential (for instance +50 V), through toner feeder bores (8) of a fixed toner matrix (3) in the form of a flexible printing circuit and down to an object (5) to be printed, for instance a paper which is conveyed over a support roll (4) which is charged with a certain predetermined, relatively high potential (for instance +1500 V), and in which the toner which has deposited on the paper (5) is finally fixed on the paper by a heating means (12), and in which each individual toner feeder bore (8) of the matrix (3) is surrounded by an electrically conducting control ring (9) which can alternatively be given a certain positive potential (for instance +300 V) which is higher than the potential of the toner feeder roll (1) but which is lower than the potential of the support roll (4), or a potential which is lower than the potential of the toner feeder roll (1), and in which the matrix (3), at the upper surface thereof has a protective layer (15) of an unmagnetic metal and is formed with through bores (16) having a diameter which is substantially the same as the outer diameter of the control rings (9) of the matrix, and in which the inner diameter of each toner control ring (9) is substantially the same as the diameter of the toner feeder bore (8) of the toner matrix base (13).

Printing apparatus of toner jet type having an electrically screened matrix unit

An image preprocessor is disclosed for a DEP device, wherein the image preprocessor corrects digital image data before printing. 
The image pre-processor preferably performs at least one the following steps :
 1. correcting the image input density according to a first look up table (LUT) for obtaining a desired grey scale value, 2. correcting grey scale values by a second LUT for varying toner fluxes 111 through different printing apertures 107, said second LUT being desirable for adjusting the toner flux 111 to the differing distance of printing apertures 107 belonging to different rows of apertures 107, and for adjusting the toner flux 111 through various printing apertures 107 having varying aperture diameter or shape. This is referred to as a shading correction in a direction orthogonal to the print direction), 3. correcting grey scale value for the grey scale values of neighbouring pixels, that influence the toner flux 111 for forming the actual image pixel, referred to as neighbour compensation, 4. correcting grey scale values for the image density that has been printed through the individual printing aperture 107 prior to the actual printing the required pixel, called previous compensation, 5. correcting grey scale values for the hardware design of the printhead structure 106, i.e. assignment of image pixels to controlling IC number and output channel number per IC, 6. expressing grey scale values as a time modulated or voltage modulated output signal, 7. transferring image output signals in a serial data stream to a FIFO memory from which the output signals are preferably converted to a parallel data stream that is fed to driving IC's, that are used to put a voltage to the individual control electrodes 106a of the printhead structure 106 in the DEP device 100.

o Agfa-Gevaert N.V. De Broeck

Papers

An image pre-processor in a device for direct electrostatic printing