There are numerous practical applications for moving charged particles suspended in a fluid. For example, in the field of ionography it is desirable to move ions suspended in an air fluid in a controlled manner so as to transport them past an array of modulation electrodes and onto a charge receptor surface for being made visible by a development system. In another example, a liquid development fluid containing charged marking particles suspended in a solvent fluid is moved past a charge image for making it visible.
Ionography, as presently practiced, is described in U.S. Pat. No. 4,644,373 to Sheridon et al. It requires the generation of air ions in the generation chamber of a marking head, and their subsequent movement out of the chamber, through a modulation region and their final collection upon the surface of an external charge receptor. Movement of the ions through the head is effected by moving the fluid, i.e. air, by means of a blower. The ions ejected from the head are collected upon the receptor in a desired image pattern are then developed by attracting a suitable marking material, either a powder or a liquid, to the charge image. In order to be able to attract the marking material, the ion current or ion throughput must be high enough to build up charge images of sufficient magnitude upon the receptor surface. This relies heavily on the air flow rate through the marking head.
While air flow transport of ions has been found to be quite effective, it has several drawbacks. Relatively large blowers are required to supply the needed air flow, because of large pressure losses through the system, and complex filtering arrangements are required to prevent various sorts of airborne contaminants from reaching the corona environment. Also, in order to increase the printing speed, it would be necessary to provide higher ion current output (ion throughput), requiring more air flow, which will exacerbate any nascent problems. For example, larger, noisier, more expensive air pumps may generate turbulence in the modulation tunnel which may produce difficulties in the operation of the marking head. Similarly, when moving a liquid developer through a development system great care must be taken to avoid fluid flow speeds and other conditions which will create turbulence.
It would be highly desirable to move charged particles suspended in a fluid, through the fluid, due to their electrical mobility, without requiring movement of the fluid. As used herein, electrical mobility, which will be referred to simply as mobility, describes the macroscopic motion of the charged particle in the fluid, in the presence of an external electrical field. The charged particle, such as an ion or other small particle moves with microscopic near-random motion in the suspension fluid, which is made up of particles virtually the same size as the charged particle. The macroscopic motion of the charged particle in the fluid, as will be discussed below, is associated with that particle's mobility.
Therefore, it is the primary object of this invention to provide a stable transport system wherein particle movement through a fluid is based on the particle's electrical mobility, and wherein a traveling electrostatic wave causes a drift movement of the particles through the fluid in the direction of propagation of the electrostatic traveling wave.