Ballistic aerosol marking apparatus with stacked electrode structure

This is a CIP application of U.S. Ser. No. 09,163,893 filed of Sep. 30, 1998.

The present invention is related to U.S. patent application Ser. Nos. 09/163,893, 09/164,124, 09/164,250, 09/163,808, 09/163,765, 09/163,839, 09/163,954, 09/163,924, 09/163,904, 09/163,799, 09/163,664, 09/163,518, 09/164,104, 09/163,825, all filed Sep. 30, 1998 Ser. No. 08/128,160, filed Sep. 29, 1993 Ser. No. 08/670,734, Jun. 24, 1996 Ser. No. 08/950,300, Oct. 14, 1997 Ser. No. 08/950,303, Oct. 16, 1997 issued U.S. Pat. No. 5,717,986, U.S. patent application Ser. No. 09/407,332, filed on Sep. 25, 1999, each of the above being incorporated herein by reference.

The present invention relates generally to the field of marking devices, and more particularly to a device capable of applying a marking material to a substrate by introducing the marking material into a high-velocity propellant stream.

Ink jet is currently a common printing technology. There are a variety of types of ink jet printing, including thermal ink jet (TIJ), piezo-electric ink jet, etc. In general, liquid ink droplets are ejected from an orifice located at a one terminus of a channel. In a TIJ printer, for example, a droplet is ejected by the explosive formation of a vapor bubble within an ink-bearing channel. The vapor bubble is formed by means of a heater, in the form of a resistor, located on one surface of the channel.

We have identified several disadvantages with TIJ (and other ink jet) systems known in the art. For a 300 spot-per-inch (spi) TIJ system, the exit orifice from which an ink droplet is ejected is typically on the order of about 64 μm in width, with a channel-to-channel spacing (pitch) of about 84 μm, and for a 600 dpi system width is about 35 μm and pitch of about 42 μm. A limit on the size of the exit orifice is imposed by the viscosity of the fluid ink used by these systems. It is possible to lower the viscosity of the ink by diluting it in increasing amounts of liquid (e.g., water) with an aim to reducing the exit orifice width. However, the increased liquid content of the ink results in increased wicking, paper wrinkle, and slower drying time of the ejected ink droplet, which negatively affects resolution, image quality (e.g., minimum spot size, inter-color mixing, spot shape), etc. The effect of this orifice width limitation is to limit resolution of TIJ printing, for example to well below 900 spi, because spot size is a function of the width of the exit orifice, and resolution is a function of spot size.

Another disadvantage of known ink jet technologies is the difficulty of producing greyscale printing. That is, it is very difficult for an ink jet system to produce varying size spots on a printed substrate. If one lowers the propulsive force (heat in a TIJ system) so as to eject less ink in an attempt to produce a smaller dot, or likewise increases the propulsive force to eject more ink and thereby to produce a larger dot, the trajectory of the ejected droplet is affected. This in turn renders precise dot placement difficult or impossible, and not only makes monochrome greyscale printing problematic, it makes multiple color greyscale ink jet printing impracticable. In addition, preferred greyscale printing is obtained not by varying the dot size, as is the case for TIJ, but by varying the dot density while keeping a constant dot size.

Still another disadvantage of common ink jet systems is rate of marking obtained. Approximately 80% of the time required to print a spot is taken by waiting for the ink jet channel to refill with ink by capillary action. To a certain degree, a more dilute ink flows faster, but raises the problem of wicking, substrate wrinkle, drying time, etc. discussed above.

One problem common to ejection printing systems is that the channels may become clogged. Systems such as TIJ which employ aqueous ink colorants are often sensitive to this problem, and routinely employ non-printing cycles for channel cleaning during operation. This is required since ink typically sits in an ejector waiting to be ejected during operation, and while sitting may begin to dry and lead to clogging.

Other technologies which may be relevant as background to the present invention include electrostatic grids, electrostatic ejection (so-called tone jet), acoustic ink printing, and certain aerosol and atomizing systems such as dye sublimation.

The present invention is a novel system for delivering marking material to a channel of a device for applying a marking material to a substrate, directly or indirectly, which overcomes the disadvantages referred to above, as well as others discussed further herein. In particular, the present invention relates to a system of the type including a propellant which travels through a channel, and a marking material which is controllably (i.e., modifiable in use) introduced, or metered, into the channel such that energy from the propellant propels the marking material to the substrate. The propellant is usually a dry gas which may continuously flow through the channel while the marking apparatus is in an operative configuration (i.e., in a power-on or similar state ready to mark). The system is referred to as “ballistic aerosol marking” in the sense that marking is achieved by in essence launching a non-colloidal, solid or semi-solid particulate, or alternatively a liquid, marking material at a substrate. The shape of the channel may result in a collimated (or focused) flight of the propellant and marking material onto the substrate.

In our system, the propellant may be introduced at a propellant port into the channel to form a propellant stream. A marking material may then be introduced into the propellant stream from one or more marking material inlet ports. The propellant may enter the channel at a high velocity. Alternatively, the propellant may be introduced into the channel at a high pressure, and the channel may include a constriction (e.g., de Laval or similar converging/diverging type nozzle) for converting the high pressure of the propellant to high velocity. In such a case, the propellant is introduced at a port located at a proximal end of the channel (defined as the converging region), and the marking material ports are provided near the distal end of the channel (at or further down-stream of a region defined as the diverging region), allowing for introduction of marking material into the propellant stream.

In the case where multiple ports are provided, each port may provide for a different color (e.g., cyan, magenta, yellow, and black), pre-marking treatment material (such as a marking material adherent), post-marking treatment material (such as a substrate surface finish material, e.g., matte or gloss coating, etc.), marking material not otherwise visible to the unaided eye (e.g., magnetic particle-bearing material, ultra violet-fluorescent material, etc.) or other marking material to be applied to the substrate. The marking material is imparted with kinetic energy from the propellant stream, and ejected from the channel at an exit orifice located at the distal end of the channel in a direction toward a substrate.

One or more such channels may be provided in a structure which, in one embodiment, is referred to herein as a print head. The width of the exit (or ejection) orifice of a channel is generally on the order of 250 μm or smaller, preferably in the range of 100 μm or smaller. Where more than one channel is provided, the pitch, or spacing from edge to edge (or center to center) between adjacent channels may also be on the order of 250 μm or smaller, preferably in the range of 100 μm or smaller. Alternatively, the channels may be staggered, allowing reduced edge-to-edge spacing.

The material to be applied to the substrate may be transported to, or metered out of the port into the propellant stream electrostatic control. The structure for accomplishing this electrostatic control comprises a plurality of electrodes arranged in a ladder fashion between a marking material reservoir and channel through which propellant flows and into which the marking material may be introduced. The electrodes are arranged in a phase relationship such that marking material (either particulate or otherwise) may be transported from electrode to electrode by way of electric fields generated by the electrodes.

The material to be applied to the substrate may be a solid or semi-solid particulate material such as a toner or variety of toners in different colors, a suspension of such a marking material in a carrier, a suspension of such a marking material in a carrier with a charge director, a phase change material, etc., both visible and non-visible One preferred embodiment employs a marking material which is particulate, solid or semi-solid, and dry or suspended in a liquid carrier. Such a marking material is referred to herein as a particulate marking material. This is to be distinguished from a liquid marking material, dissolved marking material, atomized marking material, or similar non-particulate material, which is generally referred to herein as a liquid marking material. However, the present invention is able to utilize such a liquid marking material in certain applications, as otherwise described herein. Indeed, the present invention may also be employed in the use of non-marking materials, such as marking pre- and post-treatments, finishes, curing or sealing materials, etc., and accordingly the present disclosure and claims should be read to broadly encompass the transport and marking of wide variety of materials.

Thus, the present invention and its various embodiments provide numerous advantages discussed above, as well as additional advantages which will be described in further detail below.

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained and understood by referring to the following detailed description and the accompanying drawings in which like reference numerals denote like elements as between the various drawings. The drawings, briefly described below, are not to scale.

FIG. 1 is a schematic illustration of a system for marking a substrate according to the present invention.

FIG. 2 is cross sectional illustration of a marking apparatus according to one embodiment of the present invention.

FIG. 3 is another cross sectional illustration of a marking apparatus according to one embodiment of the present invention.

FIG. 4 is a plan view of one channel, with nozzle, of the marking apparatus shown in FIG. 3 .

FIGS. 5A and 5B are end views of non-staggered and two-dimensionally staggered arrays of channels according to the present invention.

FIG. 6 is a plan view of an array of channels of an apparatus according to one embodiment of the present invention.

FIGS. 7A and 7B are plan views of a portion of the array of channels shown in FIG. 6, illustrating two embodiments of ports according to the present invention.

FIG. 8 is a process flow diagram for the marking of a substrate according to the present invention.

FIG. 9A is cross-sectional side view, and

FIG. 9B is a top view, of a marking material metering device according to one embodiment of the present invention, employing an electrode structure.

FIG. 10 is a perspective view of an electrode structure of a type employed in the device of FIGS. 9A and 9B.

FIG. 11 is a perspective view of an array of electrode structures.

FIG. 12 is an alternate embodiment of an electrode structure according to the present invention.

FIG. 13 is a plan view of the embodiment of an electrode structure of FIG. 12 .

In the following detailed description, numeric ranges are provided for various aspects of the embodiments described, such as pressures, velocities, widths, lengths, etc. These recited ranges are to be treated as examples only, and are not intended to limit the scope of the claims hereof. In addition, a number of materials are identified as suitable for various facets of the embodiments, such as for marking materials, propellants, body structures, etc. These recited materials are also to be treated as exemplary, and are not intended to limit the scope of the claims hereof.

With reference now to FIG. 1, shown therein is a schematic illustration of a ballistic aerosol marking device 10 according to one embodiment of the present invention. As shown therein, device 10 consists of one or more ejectors 12 to which a propellant 14 is fed. A marking material 16 , which may be transported by a transport 18 under the control of control 20 is introduced into ejector 12 . (Optional elements are indicated by dashed lines.) The marking material is metered (that is controllably introduced) into the ejector by metering means 21 , under control of control 22 . The marking material ejected by ejector 12 may be subject to post ejection modification 23 , optionally also part of device 10 . It will be appreciated that device 10 may form a part of a printer, for example of the type commonly attached to a computer network, personal computer or the like, part of a facsimile machine, part of a document duplicator, part of a labeling apparatus, or part of any other of a wide variety of marking devices.

The embodiment illustrated in FIG. 1 may be realized by a ballistic aerosol marking device 24 of the type shown in the cut-away side view of FIG. 2 . According to this embodiment, the materials to be deposited will be 4 colored toners, for example cyan (C), magenta (M), yellow (Y), and black (K), of a type described further herein, which may be deposited concomitantly, either mixed or unmixed, successively, or otherwise. While the illustration of FIG. 2 and the associated description contemplates a device for marking with four colors (either one color at a time or in mixtures thereof), a device for marking with a fewer or a greater number of colors, or other or additional materials such as materials creating a surface for adhering marking material particles (or other substrate surface pre-treatment), a desired substrate finish quality (such as a matte, satin or gloss finish or other substrate surface post-treatment), material not visible to the unaided eye (such as magnetic particles, ultra violet-fluorescent particles, etc.) or other material associated with a marked substrate, is clearly contemplated herein.

Device 24 consists of a body 26 within which is formed a plurality of cavities 28 C, 28 M, 28 Y, and 28 K (collectively referred to as cavities 28 ) for receiving materials to be deposited. Also formed in body 26 may be a propellant cavity 30 . A fitting 32 may be provided for connecting propellant cavity 30 to a propellant source 33 such as a compressor, a propellant reservoir, or the like. Body 26 may be connected to a print head 34 , comprised of among other layers, substrate 36 and channel layer 37 that will be discussed later.

With reference now to FIG. 3, shown therein is a cut-away cross section of a portion of device 24 . Each of cavities 28 include a port 42 C, 42 M, 42 Y, and 42 K (collectively referred to as ports 42 ) respectively, of circular, oval, rectangular or other cross-section, providing communication between said cavities and a channel 46 which adjoins body 26 . Ports 42 are shown having a longitudinal axis roughly perpendicular to the longitudinal axis of channel 46 . However, the angle between the longitudinal axes of ports 42 and channel 46 may be other than 90 degrees, as appropriate for the particular application of the present invention.

Likewise, propellant cavity 30 includes a port 44 , of circular, oval, rectangular or other cross-section, between said cavity and channel 46 through which propellant may travel. Alternatively, print head 34 may be provided with a port 44 ′ in substrate 36 or port 44 ″ in channel layer 37 , or combinations thereof, for the introduction of propellant into channel 46 . As will be described further below, marking material is caused to flow out from cavities 28 through ports 42 and into a stream of propellant flowing through channel 46 . The marking material and propellant are directed in the direction of arrow A toward a substrate 38 , for example paper, supported by a platen 40 , as shown in FIG. 2 . We have experimentally demonstrated a propellant marking material flow pattern from a print head employing a number of the features described herein which remains relatively collimated for a distance of up to 10 millimeters, with an optimal printing spacing on the order of between one and several millimeters. For example, the print head produces a marking material stream which does not deviate by more than between 20 percent, and preferably by not more than 10 percent, from the width of the exit orifice for a distance of at least 4 times the exit orifice width. However, the appropriate spacing between the print head and the substrate is a function of many parameters, and does not itself form a part of the present invention.

Referring again to FIG. 3, according to one embodiment of the present invention, print head 34 consists of a substrate 36 and channel layer 37 in which is formed channel 46 . Additional layers, such as an insulating layer, capping layer, etc. (not shown) may also form a part of print head 34 . Substrate 36 is formed of a suitable material such as glass, ceramic, etc., on which (directly or indirectly) is formed a relatively thick material, such as a thick permanent photoresist (e.g., a liquid photosensitive epoxy such as SU-8, from Microlithography Chemicals, Inc; see also U.S. Pat. No. 4,882,245) and/or a dry film-based photoresist such as the Riston photopolymer resist series, available from DuPont Printed Circuit Materials, Research Triangle Park, N.C. (see, www.dupont.com/pcm/) which may be etched, machined, or otherwise in which may be formed a channel with features described below.

Referring now to FIG. 4, which is a cut-away plan view of print head 34 , in one embodiment channel 46 is formed to have at a first, proximal end a propellant receiving region 47 , an adjacent converging region 48 , a diverging region 50 , and a marking material injection region 52 . The point of transition between the converging region 48 and diverging region 50 is referred to as throat 53 , and the converging region 48 , diverging region 50 , and throat 53 are collectively referred to as a nozzle. The general shape of such a channel is sometimes referred to as a de Laval expansion pipe. An exit orifice 56 is located at the distal end of channel 46 .

Referring again to FIG. 3, propellant enters channel 46 through port 44 , from propellant cavity 30 , roughly perpendicular to the long axis of channel 46 . According to another embodiment, the propellant enters the channel parallel (or at some other angle) to the long axis of channel 46 by, for example, ports 44 ′ or 44 ″ or other manner not shown. The propellant may continuously flow through the channel while the marking apparatus is in an operative configuration (e.g., a “power on” or similar state ready to mark), or may be modulated such that propellant passes through the channel only when marking material is to be ejected, as dictated by the particular application of the present invention. Such propellant modulation may be accomplished by a valve 31 interposed between the propellant source 33 and the channel 46 , by modulating the generation of the propellant for example by turning on and off a compressor or selectively initiating a chemical reaction designed to generate propellant, or by other means not shown.

Marking material may controllably enter the channel through one or more ports 42 located in the marking material injection region 52 . That is, during use, the amount of marking material introduced into the propellant stream may be controlled from zero to maximum per spot. The propellant and marking material travel from the proximal end to a distal end of channel 46 at which is located exit orifice 56 .

While FIG. 4 illustrates a print head 34 having one channel therein, it will be appreciated that a print head according to the present invention may have an arbitrary number of channels, and range from several hundred micrometers across with one or several channels, to a page-width (e.g., 8.5 or more inches across) with thousands of channels. The width W of each exit orifice 56 may be on the order of 250 μm or smaller, preferably in the range of 100 μm or smaller. The pitch P, or spacing from edge to edge (or center to center) between adjacent exit orifices 56 may also be on the order of 250 μm or smaller, preferably in the range of 100 μm or smaller in non-staggered array, illustrated in end view in FIG. 5 A. In a two-dimensionally staggered array, of the type shown in FIG. 5B, the pitch may be further reduced. For example, Table 1 illustrates typical pitch and width dimensions for different resolutions of a non-staggered array.

As illustrated in FIG. 6, a wide array of channels in a print head may be provided with marking material by continuous cavities 28 , with ports 42 associated with each channel 46 . Likewise, a continuous propellant cavity 30 may service each channel 46 through an associated port 44 . Ports 42 may be discrete openings in the cavities, as illustrated in FIG. 7A, or may be formed by a continuous opening 43 (illustrated by one such opening 43 C) extending across the entire array, as illustrated in FIG. 7 B.

Device Operation

The process 70 involved in the marking of a substrate with marking material according to the present invention is illustrated by the steps shown in FIG. 8 . According to step 72 , a propellant is provided to a channel. A marking material is next metered into the channel at step 74 . In the event that the channel is to provide multiple marking materials to the substrate, the marking materials may be mixed in the channel at step 76 so as to provide a marking material mixture to the substrate. By this process, one-pass color marking, without the need for color registration, may be obtained. An alternative for one-pass color marking is the sequential introduction of multiple marking materials while maintaining a constant registration between print head 34 and substrate 38 . Since, not every marking will be composed of multiple marking materials, this step is optional as represented by the dashed arrow 78 . At step 80 , the marking material is ejected from an exit orifice at a distal end of the channel, in a direction toward, and with sufficient energy to reach a substrate. The process may be repeated with reregistering the print head, as indicated by arrow 83 . Appropriate post ejection treatment, such as fusing, drying, etc. of the marking material is performed at step 82 , again optional as indicated by the dashed arrow 84 .

Marking Material

According to one embodiment of the present invention a solid, particulate marking material is employed for marking a substrate. The marking material particles may be on the order of 0.5 to 10.0 μm, preferably in the range of 1 to 5 μm, although sizes outside of these ranges may function in specific applications (e.g., larger or smaller ports and channels through which the particles must travel).

There are several advantages provided by the use of solid, particulate marking material. First, clogging of the channel is minimized as compared, for example, to liquid inks. Second, wicking and running of the marking material (or its carrier) upon the substrate, as well as marking material/substrate interaction may be reduced or eliminated. Third, spot position problems encountered with liquid marking material caused by surface tension effects at the exit orifice are eliminated. Fourth, channels blocked by gas bubbles retained by surface tension are eliminated. Fifth, multiple marking materials (e.g., multiple colored toners) can be mixed upon introduction into a channel for single pass multiple material (e.g., multiple color) marking, without the risk of contaminating the channel for subsequent markings (e.g., pixels). Registration overhead (equipment, time, related print artifacts, etc.) is thereby eliminated. Sixth, the channel refill portion of the duty cycle (up to 80% of a TIJ duty cycle) is eliminated. Seventh, there is no need to limit the substrate throughput rate based on the need to allow a liquid marking material to dry.

However, despite any advantage of a dry, particulate marking material, there may be some applications where the use of a liquid marking material, or a combination of liquid and dry marking materials, may be beneficial. In such instances, the present invention may be employed, with simply a substitution of the liquid marking material for the solid marking material and appropriate process and device changes apparent to one skilled in the art or described herein, for example substitution of metering devices, etc.

In certain applications of the present invention, it may be desirable to apply a substrate surface pre-marking treatment. For example, in order to assist with the fusing of particulate marking material in the desired spot locations, it may be beneficial to first coat the substrate surface with an adherent layer tailored to retain the particulate marking material. Examples of such material include clear and/or colorless polymeric materials such as homopolymers, random copolymers or block copolymers that are applied to the substrate as a polymeric solution where the polymer is dissolved in a low boiling point solvent. The adherent layer is applied to the substrate ranging from 1 to 10 microns in thickness or preferably from about 5 to 10 microns thick. Examples of such materials are polyester resins either linear or branched, poly(styrenic) homopolymers, poly(acrylate) and poly(methacrylate) homopolymers and mixtures thereof, or random copolymers of styrenic monomers with acrylate, methacrylate or butadiene monomers and mixtures thereof, polyvinyl acetals, poly(vinyl alcohol), vinyl alcohol-vinyl acetal copolymers, polycarbonates and mixtures thereof and the like. This surface pre-treatment may be applied from channels of the type described herein located at the leading edge of a print head, and may thereby apply both the pre-treatment and the marking material in a single pass. Alternatively, the entire substrate may be coated with the pre-treatment material, then marked as otherwise described herein. See U.S. patent application Ser. No. 08/041,353, incorporated herein by reference. Furthermore, in certain applications it may be desirable to apply marking material and pre-treatment material simultaneously, such as by mixing the materials in flight, as described further herein.

Likewise, in certain applications of the present invention, it may be desirable to apply a substrate surface post-marking treatment. For example, it may be desirable to provide some or all of the marked substrate with a gloss finish. In one example, a substrate is provided with marking comprising both text and illustration, as otherwise described herein, and it is desired to selectively apply a gloss finish to the illustration region of the marked substrate, but not the text region. This may be accomplished by applying the post-marking treatment from channels at the trailing edge of the print head, to thereby allow for one-pass marking and post-marking treatment. Alternatively, the entire substrate may be marked as appropriate, then passed through a marking device according to the present invention for applying the post-marking treatment. Furthermore, in certain applications it may be desirable to apply marking material and post-treatment material simultaneously, such as by mixing the materials in flight, as described further herein. Examples of materials for obtaining a desired surface finish include polyester resins either linear or branched, poly(styrenic) homopolymers, poly(acrylate) and poly(methacrylate) homopolymers and mixtures thereof, or random copolymers of styrenic monomers with acrylate, methacrylate or butadiene monomers and mixtures thereof, polyvinyl acetals, poly(vinyl alcohol), vinyl alcohol-vinyl acetal copolymers, polycarbonates, and mixtures thereof and the like.

Other pre- and post-marking treatments include the underwriting/overwriting of markings with marking material not visible to the unaided eye, document tamper protection coatings, security encoding, for example with wavelength specific dyes or pigments that can only be detected at a specific wavelength (e.g., in the infrared or ultraviolet range) by a special decoder, and the like. See U.S. Pat. Nos. 5,208,630, 5,385,803, and 5,554,480, each incorporated herein by reference. Still other pre- and post-marking treatments include substrate or surface texture coatings (e.g. to create embossing effects, to simulate an arbitrarily rough or smooth substrate), materials designed to have a physical or chemical reaction at the substrate (e.g., two materials which, when combined at the substrate, cure or otherwise cause a reaction to affix the marking material to the substrate), etc. It should be noted, however, that references herein to apparatus and methods for transporting, metering, containing, etc. marking material should be equally applicable to pre- and post-marking treatment material (and in general, to other non-marking material) unless otherwise noted or as may be apparent to one skilled in the art.

Metering (and Transport) of Marking Material

A critical step in the marking process is metering the marking material into the propellant stream. Transport of the marking material is also important, and the following discussion, while focussing on metering, necessarily also applies to transport. While the following specifically discusses the metering of marking material, it will be appreciated that the metering of other material such as the aforementioned pre- and post-marking treatment materials is also contemplated by this discussion, and references following which exclusively discuss marking material do so for simplicity of discussion only. Metering, then, may be accomplished by one of a variety of embodiments of the present invention.

According to a first embodiment for metering the marking material, the marking material includes material which may be imparted with an electrostatic charge. For example, the marking material may be comprised of a pigment suspended in a binder together with charge capture or control additives. The charge capture additives may be charged, for example by way of a corona 66 C, 66 M, 66 Y, and 66 K (collectively referred to as coronas 66 ), located in cavities 28 , shown in FIG. 3 . Another alternative is to initially charge the propellant gas, e.g., by way of a corona 45 in cavity 30 (or some other appropriate location such as port 44 , etc.) The charged propellant may be made to enter into cavities 28 through ports 42 , for the dual purposes of creating a fluidized bed 86 C, 86 M, 86 Y, and 86 K (collectively referred to as fluidized bed 86 , and discussed further below), and imparting a charge to the marking material. Other alternatives include tribocharging, by other means external to cavities 28 , or other mechanism.

With reference now to FIGS. 9A and 9B, there is illustrated therein one embodiment of the present invention. The marking material transport and metering structure 100 shown in a cut-away side view in FIG. 9A comprises a stacked electrode structure 102 which includes a minimum of three electrodes. Electrode structure 102 is disposed between cavity 28 containing marking material particles 24 (however, cavity 28 may contain material other than a marking material, although cavity 28 is generically referred to in this description as a marking material reservoir, for simplicity and clarity of explanation). Electrode structure 102 terminates at an injection port 104 in channel 46 , for example in the diverging region 52 . Connected to electrode structure 102 is driving circuitry 106 , also illustrated and described further below. FIG. 9B shows this structure in plan view.

The particulate marking material employed by the present invention may or may not be charged, depending on the desired application. In the event that a charged particulate marking material is employed, the charge on the marking material may be imparted by way of a corona 66 .

In operation, a traveling electrostatic wave is established by driving circuitry 106 across electrode structure 102 in a direction from cavity 28 toward injection port 104 . Marking material particles in the cavity 28 which are positioned proximate the electrode structure 102 , for example by gravity feed, are transported by the traveling electrostatic wave in the direction of injection port 104 . Once the marking material particles reach the injection port 104 , they are introduced into a propellant stream (not shown) and carried thereby in the direction of arrow A toward a substrate (not shown)

FIG. 10 is a perspective illustration of a portion of an electrode structure 102 according to one embodiment of the present invention. Electrode structure 102 consists of a plurality of electrodes 108 a, 108 b, 108 c, each defining an annular opening 110 a, 110 b, 110 c, respectively. These electrodes are grouped into sets, each set containing at least three such electrodes (although a greater number of electrodes per set is clearly contemplated by this description). Each electrode 108 a, 108 b, 108 c is connected to a driver circuit, such as an inverting amplifier or other driver circuit, as appropriate (not shown). Each driver is connected to clock generator and logic circuitry (not shown). More details on the driver and clock circuitry are provided in applicant's incorporated U.S. patent application Ser. No. 09/163,839.

Referring again to FIG. 9A, shown therein is a cross section of a device 100 . In one embodiment, electrodes 108 a, 108 b, 108 c are formed in layers 90 a, 90 b, 90 c, respectively, on top of insulating substrate 112 , with insulating layers 91 a and 91 b formed therebetween. Alternatively, electrodes 90 a, 90 b, and 90 c may be photolithographically patterned, with appropriate insulation therebetween, and electrical interconnection as further discussed below.

In operation, control signals from the clock generator and logic circuitry are applied to the electrode drivers which sequentially provide a phased voltage for example, 25-250 volts preferably in the range of 125 volts, to the electrodes 108 a, 108 b, 108 c to which they are connected. It will be noted that in order to establish a sufficient traveling wave at least three groups of electrodes are required, meaning that a voltage source of at least three phase is required. However, a greater number of groups and a great number of voltage phases may be employed as determined by the desired application of the present invention.

A typical operating frequency for the voltage source is between a few hundred Hertz and 5 kHz depending on the charge and the type of marking material in use. The traveling wave may be d.c. phase or a.c. phase, with d.c. phase preferred.

The force F required to move a marking material particle from one electrode to an adjacent electrode is given by F=Q.E t , where Q is the charge on the marking material particle, and E t is the tangential field established by the electrodes, given by E t =[1/d][V φ1 (t)−V φ2 (t)]. In the later equation, d is the spacing between electrodes, and V φ1 (t) and V φ2 (t) are the voltages of the two adjacent electrodes, typically varying as a function of time. For peak a.c. voltage v p from a sinusoidal waveform of the type shown in FIG. 4 (three-phase), the resulting field E t is given by E t (v p )=[1/d][v p sin(ω t )+v p sin(ω t +φ)], where φ is the phase difference between the two voltage waveforms. The maximum field thus depends on the phase of the waveform. The largest filed is obtained when the phase difference between the two waveforms is 180 degrees. In this case, the field equation reduces to E t =2v p /d.

However, a sinusoidal system can never achieve this maximum value since with a 180 degree phase shift in the waveform, the traveling wave looses directionality. Thus, the phase shift must always be something less (or more) than 180 degrees.

However, a phased d.c. waveform is able to achieve the E t =2v p /d maximum field without loosing directionality of the traveling wave. The maximum E t =2v p /d is obtained during the time that all but one of the waveforms have a zero voltage. At this time, the waveforms have sufficient overlap to impart directionality to the traveling wave established by the electrodes.

In either the case of an a.c. or d.c. waveform, a traveling wave is established along the electrode structure 102 in the direction of arrows B of FIG. 10 . Particles 114 of marking material travel from electrode to electrode, for example due to their attraction to an oppositely charge electrode.

Fabrication of electrodes 36 and required interconnections may be done in conjunction with the fabrication of associated circuitry such as drivers and clock and logic circuitry. Alternatively, the control circuitry may be off-board.

A coating layer may overlay the electrode structure for physical protection, electrical isolation, and other functions discussed in the aforementioned and incorporated U.S. patent applications Ser. Nos. 09/163,518, 09/163,664, and 09/163,825.

Ideally, electrode structure 102 will be one of an array of such structures in a complete marking device. An example of such an array is illustrated in FIG. 11 . One problem posed by such an array is the number of interconnections required to individually address each electrode. We have devised a scheme to simplify this interconnection. FIG. 11 illustrates a matrix array technique which dramatically reduces the number of interconnections to an array of electrodes. Each material transport and metering structure 100 includes an associate electrode structure 102 comprised of at least three electrodes 108 a, 108 b, and 108 c (referred to as a set of electrodes). The electrodes 108 b of each set is electrically connected to the electrodes 108 b of each of the other sets in the array. Likewise, the electrodes 108 c of each set is electrically connected to each electrode 108 c of each of the other sets in the array. Each of the electrodes 108 a of each set is separately addressed. Thus, if n is the number of material transport and metering structures 100 in the marking device, then the total connections required may be as small as n+2. This should be compared to the number 3n which would be required to individually address each electrode. In operation, the electrodes 108 b and 108 c are operated collectively in a phase relationship, and metering of marking material into a desired channel is accomplished by selectively activating electrode 108 a corresponding to the desired channel.

In a preferred embodiment, each material transport and metering structures 100 will consist of multiple sets stacked end-to-end, with the various electrodes interconnected as described above (i.e., all electrodes 108 b electrically connected together, all electrodes 108 c electrically connected, and all electrodes 108 a from each material transport and metering structure 100 electrically connected, but electrically isolated from the electrodes 108 a of other material transport and metering structures 100 ). In so doing, it is desirable to provide a region through which the marking material may travel, preferably a concentrically aligned annular region 110 a, 110 b, 110 c, as illustrated in FIG. 10 .

An alternate embodiment 120 of a material transport and metering structure is shown in FIG. 12 . According to this embodiment, a planar structure 122 is provided between cavity 28 and channel 46 . Sets 124 a, 124 b of at least three stacked electrodes 126 a, 126 b, 126 c are provided on a surface of planar structure 122 . These may be formed photolithographically by process well known in the art, and may be connected to driver and clock circuitry as described for example in applicant's incorporated U.S. patent application Ser. No. 09/163,839. The thickness of the electrodes 126 a, 126 b, 126 c, and insulation (not shown) required to electrically insulate the electrodes may be on the order of 5 μm to 15 μm depending on the size of the marking material particles (e.g. 3 μm, 5 μm, etc.). Planar structure 122 may be located with the assembly of the marking device for example by way of an alignment key 128 (for example on the order of 100 microns or more) or by other technique known in the art. An auxiliary electrode 130 may be positioned inside the channel 46 , and operated in phase with an electrode of the sets 124 , such as with electrode 126 a, to assist in “pulling” marking material into the channel 46 . Individual columns of electrodes which may, for example, supply marking material to a single channel, may be isolated from one another by means of lateral barriers 132 as illustrated in FIG. 13 . Lateral barriers 132 may be formed of this photoresist and defined by well known photolithographic techniques.

Again, the driving and clock circuitry may be on-or off-chip to provide phased input waveforms in a number equal to the number of electrodes per set (three-phase for three electrodes per set, four-phase for four electrodes per set, and so on). Drivers may switch from ground to a high (e.g. 75 volts) to generate the electrostatic field that moves the toner from electrode to electrode. The operating voltage for the drivers may be in the range of 15 volts to 125 volts depending on the electrode line width and electrode-to-electrode spacing. Typically, a field strength of 5-6 volts/μm should be maintained for desirable marking material motion. Incorporated U.S. patent application Ser. No. 09/163,839 describes further details about driving and clock circuitry.

It will now be appreciated that various embodiments of a particulate marking material transport device have been disclosed herein. The embodiments described and alluded to herein are capable of transporting marking material both intentionally charged and uncharged. Driving electronics may be integrally formed with an array of interdigitated electrodes. A plurality of such transports may be used in conjunction to provide multiple colors of marking material to a full color printer, to transport marking material not otherwise visible to the unaided eye (e.g., magnetic marking material), surface finish or texture material, etc. Thus, it should be appreciated that the description herein is merely illustrative, and should not be read to limit the scope of the invention nor the claims hereof.