Printing system for applying a mixed combination of colorants for one separation to a photoreceptor

In a xerographic printer, the use of traveling wave toner transport devices to deliver toner from the individual single color toner sumps to an intermediate traveling wave belt by utilizing traveling wave roll-type devices, and the traveling wave belt to carry the combination of toners to the photoreceptor. The toner could be composed of two or more toner color particles which are used as a custom color. The traveling wave transport belt mixes the two or more colors while transporting them, so that pre-mixing a custom color, and delivering it separately to the photoreceptor, is not necessary, thus enabling the use of an ordinary CMYK color printer to be used to print custom colors.

BACKGROUND OF THE INVENTION
 Apparatus for mixing custom color toner for a color copier or printer using
 a traveling wave toner transport device, hereinafter referred to as a
 "device", which mixes the colorants while transporting them to the
 photoreceptor.
 In a typical color copier or printer, three color separations, cyan,
 magenta and yellow (CMY), can be used to create all colors in a final
 color print. However, while black can be generated by the use of these
 three colors, a better print will result if black toner is also used
 (CMYK) to produce the darker tones, resulting in four separations.
 A further refinement is to use a custom color for special areas. For
 example, skin tones are difficult to reproduce in standard CMYK systems
 because, in any combination of toners, the separate colors are applied one
 on top of the other, and so a smooth blend of toner is difficult to
 produce. If a custom color is required it is typical to load pre-mixed
 toner into the printer and use it as an additional separation. However,
 this can be inconvenient since the custom color toner must be loaded into
 the printer before printing and removed after the run is complete.
 What is needed is a system that can mix a custom color from the original
 CMYK toners and apply that to the photoreceptor.
 SUMMARY OF THE INVENTION
 This invention uses traveling wave toner transport devices to transport and
 mix toner. In its simplest form, a device is a belt made from insulating
 material on which is formed a lattice of conducting lines. Most of the
 lines are grounded but at regular intervals there are some that are held
 at a voltage. Further, each voltage is switched over time to adjacent
 lines, so that the overall effect is a voltage field that travels down the
 belt. Since the toner particles are themselves charged, they will be
 transported down the stationary belt as the voltage wave carries them.
 Such a device is described in U.S. Pat. No. 5,717,986 which is
 incorporated by reference herein.
 A number of devices, one for each toner, are generally cylindrical in
 shape, round, oval or the like, and transport toner from each toner supply
 to an intermediate device in the form of a belt. The belt device carrying
 all of the colorants then transports the toner to the photoreceptor. A
 property of the traveling wave transportation process is that the various
 toners deposited on it are mixed as they are being transported. Thus,
 although the colorants are applied separately to the belt, they are fully
 mixed when they arrive at the photoreceptor, and so can be used as a
 custom color at that point. The result is that custom colors need not be
 pre-mixed and separately loaded into the printer for the additional
 separation.

DETAILED DESCRIPTION OF THE INVENTION
 The system shown in FIG. 1 overcomes the difficulties of the prior systems.
 There are four single color travelling wave devices 10 for the four
 primary colors. Each color toner will be loaded onto its device by the
 traveling wave on the grid from a toner source of any kind such as a sump
 11. The toner will travel around the device 10 and return the excess back
 to the sump 11.
 At the top of the device 10, the dry toner cloud will be partially taken up
 by the intermediate traveling wave device belt 13 and carried in the
 direction of the arrow. Since the toner is carried in the form of a cloud
 of particles that are in constant motion, the several toners will be
 thoroughly mixed by the time they are deposited onto intermediate device
 belt 13. Finally, the belt will deliver the cloud to the photoreceptor 14
 which has been exposed to the image of the current separation, resulting
 in the partial depositing of the toner onto the photoreceptor 14.
 The development system 34 comprising the sump 11 and device 10 of FIG. 1,
 shown in more detail in FIG. 5, includes a chamber 76 for storing a supply
 of developer material which is mixed by two augers 86, 88. Device 10 is
 mounted on a stationary fixture 41, and together with the magnetic roller
 46, are located above the chamber 76. A magnetic roller 46 can be rotated
 in either the "with" or "against" direction relative to the direction of
 motion of the toner on the device 10 and is used to deposit toner onto the
 device 10. Similarly, toner on device 10 can be traveling in either the
 "with" or "against" direction relative to the direction of toner on the
 intermediate traveling wave device belt 13.
 The single color devices 10 and the intermediate device 13 comprise a
 flexible circuit board having a finely spaced electrode array thereon as
 shown in FIG. 2. The grid is composed of several sets of electrodes 20
 deposited on a flexible substrate, and applied voltages with the
 appropriate amplitude and phase such as to move the toner cloud forward
 above the surface of the grid are applied. This flexible substrate and
 grid can be formed into any shape, either flat for the belt or circular or
 oval for a roll. The grid used in this embodiment has 100 micrometer wide
 electrodes, separated by 100 micrometers. Toner can be moved on this grid
 with or without an electrically relaxable polymer overcoat layer.
 The amount of toner loaded is determined by the pulse width and amplitude,
 and the transport speed can be controlled by the frequency of the
 electrical signals applied to the traveling wave grid, resulting in speeds
 of approximately one meter per second.
 Four phases of driving signal, Phi 1-4, are generated in the clock
 generator and logic section 21, which has inputs of an optional clock,
 five volts, ground, and plus and minus high voltage. These phases, shown
 in FIG. 3, are applied to the grid of FIG. 2, to result in the toner
 movement shown in FIG. 4. Typical voltages are zero and four hundred
 volts, and there is some overlap of the phase waveshapes, as shown.
 The single colorant devices 10 and the intermediate device 13 transport the
 toner by the same process to a development zone where the toner is
 attracted to the photoreceptor 14. After development the residual toner on
 the intermediate device 13 is moved to a toner dump container. Complete
 removal of residual toner from the photoreceptor is accomplished by a
 combination of electrical forces from the grid and mechanical forces from
 a cleaning brush for removing a remaining toner on the intermediate
 travelling wave device.
 Combining toner transport and mixing in the intermediate device in the
 manner described has many other advantages. Color mixing is in-situ by
 electronic controls that regulate precisely the amount of toners or
 colorants there are on the grids, to eliminate expensive pre-mixed custom
 color toner and therefore offers versatility in the color process. In this
 embodiment grid voltages are either fully ON or OFF, and the amount of
 toner is determined by pulse width modulation. Jumping development enables
 superior image quality to in-contact magnetic brush development systems
 and allows an improved throughput in a one-pass color system. The conveyor
 grids are fabricated on flexible substrates, allowing them to be mounted
 on holding fixtures of any shape, which enables long and stable
 development zones, important for high efficiency development at high
 process speeds.
 Also, the use of electrical forces to move toner minimizes the number of
 moving parts in the development system and eliminates some mechanical
 disturbances in the development nip due to run-out, for example.
 Similarly, the development system width can be increased without added
 mechanical instability. Finally, since sections of the conveyer can be
 separated electrically, different electrical signals can be applied to
 grid areas in each of the different zones (loading, development and
 unloading) to optimize each of the steps in the toner cycle.
 While the invention has been described with reference to a specific
 embodiment, it will be understood by those skilled in the art that various
 changes may be made and equivalents may be substituted for elements
 thereof without departing from the true spirit and scope of the invention.
 In addition, many modifications may be made without departing from the
 essential teachings of the invention.