Particulate marking material transport apparatus utilizing traveling electrostatic waves

[0002] 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, 09/163,954, 09/163,924, 09/163,799, 09/163,664, 09/163,518, and 09/164,104, issued U.S. patent Ser. Nos. 5,422,698, 5,717,986, 5,853,906, 5,893,015, 5,893,015, 5,968,674, 6,116,442, and 6,136,442, each of the above being incorporated herein by reference.

[0003] The present invention relates generally to the field of printing apparatus, and more particularly to devices and methods for moving and metering marking material in such devices.

[0004] There are a variety of marking systems currently known which utilize ejection of liquid inks for marking a substrate. Ink jet and acoustic ink ejection are two common examples. Systems ejecting liquid inks present several problems as the spot size is decreased, such as when designing to increase the resolution of a printer. For example, to produce a smaller spot on a substrate, the cross-sectional area of the channel and/or orifice through which the ink must be ejected is decreased. Below a certain cross-sectional area, viscosity inhibits proper flow of the ink, adversely affecting spot position control, spot size control, etc. Thus, there has been proposed apparatus for marking by ejecting a dry or solid, particulate marking material (hereafter particulate marking material), for example the ballistic aerosol marking apparatus of the aforementioned U.S. patent application Ser. No. 09/163,893.

[0005] One problem encountered with the use of particulate marking material is in the transport of that material from a reservoir holding such material to the point of delivery. With liquid inks, the material may flow through a channel or the like. However, particulate material tends not to flow, tends to clog, and otherwise may require transport augmentation.

[0006] Another problem encountered with the use of particulate marking material is in the metering of the material for delivery to a substrate. In order to enable proper spot size control, grey scale marking, and the like, it is necessary to introduce a precisely controlled, or metered amount of marking material, at a precisely controlled rate, and at a precisely controlled time for delivery to the substrate.

[0007] In U.S. Pat. 5,717,986, it is suggested that a grid of interdigitated electrodes may be employed, in conjunction with external driving circuitry, to generate an electrostatic traveling wave, which wave may transport toner particles from a sump to a latent image retention surface (e.g., a photoreceptor) for development. The system is relatively large, and as described, applies to a flexible donor belt used in ionographic or electrophotographic imaging and printing apparatus. As described, it is not suited to application in a particle ejection-type printing apparatus, as will be further described.

[0008] Traveling waves have been employed for transporting toner particles in a development system, for example as taught in U.S. patent Ser. No. 4,647,179, which is hereby incorporated by reference. According to said patent, the traveling wave is generated by alternating voltages of three or more phases applied to a linear array of conductors placed about the periphery of a conveyor. The force F for moving the toner about the conveyor is given by F=Q·E_t, where Q is the charge on the toner particles, and E_tis the tangential field supplied by a multi-phase a.c. voltage applied to the array of conductors. Toner is presented to the conveyor by means of a magnetic brush, which is rotated in the same direction as the traveling wave. This gives an initial velocity to the toner particles which enables toner having a relatively lower charge to be propelled by the wave. Again, as described, this approach is not suited to application in a particle ejection-type printing apparatus, as will be further described.

[0009] The present invention is a novel design and application of a grid of interdigitated electrodes to produce a traveling electrostatic wave capable of transporting and metering particulate marking material which overcomes the disadvantages referred to above. In particular, the grid of electrodes is sized to be employable within a print head, for example having a channel to channel spacing (pitch) of 50 to 250 μm. At the sizes of interest, it becomes possible to photolithographically form the grid of electrodes on a print head substrate. In certain embodiments, it may be possible to form the electrostatic grid using known complementary metal oxide semiconductor (CMOS) fabrication techniques. In such embodiments, the required driving circuitry may be formed simultaneously with the electrode grid, simplifying manufacture, reducing cost, and reducing the size of the completed print head.

[0010] According to another embodiment, electrical connection is made between the electrodes and the driving circuitry by interconnection lines oriented generally perpendicular to the long axis of the electrodes. The interconnection lines pass under or over the electrodes. As the spacing between the electrodes and the perpendicular interconnection lines decreases to accommodate a reduction in size of the electrode grid, cross talk is avoided by staggering the electrode and interconnection line order.

[0011] Transport of particulate marking material is accomplished by positioning one end of the electrode grid in proximity to a marking material delivery station (e.g., within a sump containing marking material, at a point of delivery of an electrostatic donor roll, etc.) and establishing an electrostatic traveling wave in the direction of desired marking material motion. The opposite end of the electrode grid is placed proximate a point of discharge, such as a port in a channel through which a propellant flows in the aforementioned ballistic aerosol marking apparatus. The traveling wave may be modulated to meter the transport as desired.

[0012] Thus, the present invention and its various embodiments provide numerous advantages including, but not limited to, a compact particulate marking material transport and metering device, which in one embodiment may include integrated driving electronics, and in another embodiment may have staggered electrodes, etc., as will be described in further detail below.

[0013] 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.

[0014] FIG. 1 is an illustration of a ballistic aerosol marking apparatus of the type employing a marking material transport and metering device according to one embodiment of the present invention.

[0015] FIG. 2 is a schematic illustration of a portion of a marking material transport and metering device according to one embodiment of the present invention.

[0016] FIG. 3 is a cross-sectional view of a substrate having formed thereon electrodes according to one embodiment of the present invention.

[0017] FIG. 4 is a sample waveform (sinusoidal) of a type employed in one embodiment of the present invention.

[0018] FIG. 5 is sample waveform (trapezoidal) of a type employed in another embodiment of the present invention.

[0019] FIG. 6 is a perspective view of a portion of a marking material transport and metering device according to one embodiment of the present invention, in operation.

[0020] FIG. 7 is a schematic illustration of one embodiment of clock and logic circuitry used to generate a phased voltage waveform according to one embodiment of the present invention.

[0021] FIG. 8 is an illustration of the input waveforms for clock and logic circuitry according to one embodiment of the present invention.

[0022] FIG. 9 is a cross-sectional illustration of a marking material transport and metering device, with an integrated electrode and thin film transistor structure, according to one embodiment of the present invention.

[0023] FIG. 10 is a perspective view of two electrodes and interconnection in electrical communication according to one embodiment of the present invention.

[0024] FIG. 11 is plan view of a prior art arrangement of electrodes and interconnections.

[0025] FIG. 12 is an illustration of one embodiment of an electrode and interconnection arrangement according to the present invention.

[0026] FIG. 13 is an illustration of another embodiment of an electrode and interconnection arrangement according to the present invention.

[0027] In the following detailed description, numeric ranges are provided for various aspects of the embodiments described, such as electrode width, height, pitch, 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 the substrate, electrodes, etc. These recited materials are also to be treated as exemplary, and are not intended to limit the scope of the claims hereof.

[0028] FIG. 1 illustrates a ballistic aerosol marking apparatus 10 employing a particulate marking material transport and metering device 12 according to one embodiment of the present invention. Apparatus 10 consists of a channel 14 having a converging region 16, a diverging region 18, and a throat 20 disposed therebetween.

[0029] Marking material transport and metering device 12 consists of a marking material reservoir 22 containing marking material particles 24. Connected to reservoir 22 is electrode grid 26, illustrated and described further below. Electrode grid 26 terminates at an injection port 28 in channel 14, for example in the diverging region 18. Connected to electrode grid 26 is driving circuitry 30, also illustrated and described further below.

[0030] 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 (not shown) located either internal or external to the marking material reservoir 22.

[0031] In operation, a traveling electrostatic wave is established by driving circuitry 30 cross electrode grid 26 in a direction from reservoir 22 toward injection port 28. Marking material particles in the reservoir 22 which are positioned proximate the electrode grid 26, for example by gravity feed, are transported by the traveling electrostatic wave in the direction of injection port 28. Once the marking material particles reach the injection port 28, they are introduced into a propellant stream (not shown) and carried thereby in the direction of arrow A toward a substrate 32 (for example sheet paper, etc.)

[0032] FIG. 2 is a schematic illustration of a portion of a particulate marking material transport device 34 according to one embodiment of the present invention. Device 34 consists of a plurality of interdigitated electrodes 36, organized into at least three, preferably four groupings 38a, 38b, 38c, and 38d. Each group 38a, 38b, 38c, and 38dis connected to an associated driver 40a, 40b, 40c, and 40d, respectively. Each of drivers 40a, 40b, 40c, and 40d, respectively, may be an inverting amplifier or other driver circuit, as appropriate. Each driver 40a, 40b, 40c, and 40dis connected to clock generator and logic circuitry 42, illustrated and described further below.

[0033] With reference to FIG. 3, shown therein is a cross section of a substrate 44 on which are formed electrodes 36. In one embodiment, electrodes 36 have a height between 0.2 μm and 1.0 μm, preferably 0.6 μm for CMOS process compatibility described further below. Electrodes 36 have a width w of between 5 μm and 50 μm, preferably 25 μm, and a pitch of between 5 μm and 50 μm, preferably 25 μm. The width and pitch of electrodes 36 will in part be determined by the size of the marking material particles to be employed.

[0034] Returning to FIG. 2, in operation, control signals from the clock generator and logic circuitry 42 are applied to drivers 40a, 40b, 40c, 40dand these drivers sequentially provide a phased voltage for example, 25-250 volts preferably in the range of 125 volts, to the electrodes 36 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 phases 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.

[0035] 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.

[0036] The force F required to move a marking material particle from one electrode 36 to an adjacent electrode 36 is given by F=Q·E_t, where Q is the charge on the marking material particle, and E_tis the tangential field established by the electrodes, given by E_t=[1/d][V_φ(t)−V_φ(t)]. In the later equation, d is the spacing between electrodes, and V_φ(t) and V_φ(t) are the voltages of the two adjacent electrodes, typically varying as a function of time. For peak a.c. voltage v_pfrom a sinusoidal waveform of the type shown in FIG. 4 (three-phase), the resulting field E_tis given by E_t(v_p)=[1/d][v_psin({overscore (ω)}_t)+v_psin({overscore (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.

[0037] 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.

[0038] 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. FIG. 5 illustrates a three-phase trapezoidal d.c. waveform preferably employed in the present invention. 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.

[0039] Again returning to FIG. 2, in either the case of an a.c. or d.c. waveform, a traveling wave is established across the electrode grid in the direction of arrow B. Particles 24 of marking material travel from electrode to electrode, for example due to their attraction to an oppositely charge electrode, as shown in FIG. 6.

[0040] FIG. 7 is a schematic illustration of one embodiment of a portion 46 of clock and logic circuitry 42 used to generate the phased voltage waveform referred to above. A portion 46 is required for each group 38a, 38b, 38c, and 38dof electrodes. Portion 46 consists of a first high voltage transistor 48, a second high voltage transistor 50, and a diode 52 connected as a push-pull output driver of a type known in the art. The input to portion 46 is a digital input φ_1-in. This input would be generated by convention low voltage logic, and would have a waveform relative to the inputs φ_2-in, φ_3-in, and φ_4-inof the other groups shown by FIG. 8. Portion 46 converts the digital input φ_1-ininto the high voltage waveform v_1-out, which is applied to the electrodes 36. Clocking of the circuit is thus handled by the low voltage logic.

[0041] Fabrication of electrodes 36 and required interconnections may be done in conjunction with the fabrication of associated circuitry such as drivers 40a, 40b, 40c, and 40d, and clock and logic circuitry 42. According to one embodiment, a conventional CMOS process is used to form these elements. A portion 54 of a marking material transport device with integrated circuitry (e.g., transistor 56) may be manufactured by a process described with reference to FIG. 9. The process begins with the provision of an appropriate conventional substrate 58, such as silicon, glass, etc. Over substrate 58 is deposited a field oxide 60. A transistor region 62 is formed in field oxide 60 in the form of a depression therein. Aluminum or similar metal is next deposited and patterned to form interconnection 64 (connecting electrodes 36) and simultaneously gate 66. n+ doped regions (or n− regions) 68 are next provided in the transistor region, using gate 66 as a mask, to provide source and drains for transistor 56. A passivation layer 70, such as glass, is next deposited over the structure, and a via 72 is formed therein to permit electrical connection to interconnect 64. A metal electrode layer 74 is next formed over the structure, and patterned to form electrodes 36. Finally, a coating layer 76 overlays the 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 U.S. Pat. No. 6,136,442.

[0042] As will be appreciated, the marking material transport device of the present invention includes a plurality of electrodes 36 and interconnections 64, arranged in overlapping fashion as illustrated in FIG. 10 (inverted for illustration purposes only). As the size of the marking material transport device is reduced, the spacings between the electrodes 36 and the interconnections 64 is reduced commensurately. We have discovered that in such a case, cross talk between the various interconnections and electrodes 36 increases. Thus, we have designed an interconnection scheme which reduces or eliminates this cross-talk. Shown in FIG. 11 is an interconnection scheme of the type contemplated by the aforementioned U.S. Pat. No. 5,717,986, and U.S. Pat. No. 5,893,015. According to this interconnection scheme, each electrode 36 is connected to an interconnection 64 in a stair-step fashion. That is, the first, left-most interconnection is connected to the first, lowest electrode 36, the second from the left interconnection 64 connected to the second from the lowest electrode 36, etc. Accordingly, each interconnection underlies each electrode. At each point that an interconnection underlies an electrode, other than the electrode to which it is directly connected by way of via 72, the signal carried by the interconnection may undesirably cause a signal through the passivation to other electrodes-hence cross-talk.

[0043] Accordingly, we have developed the interconnection scheme illustrated in FIG. 12 with the goal of eliminating this cross-talk. For purpose of this explanation, we refer to the interconnections as φ₁, φ₂, φ₃, and φ₄, and the electrodes as e₁, e₂, e₃, and e₄, and assume that the electrodes overly the interconnections. As shown in FIG. 12, a via 72 connects φ₁and e₁, with e₁overlying only φ₃. Likewise, a via 72 connects φ₂and e₂, with e₂overlying only φ₄. Similarly, a via 72 connects φ₃and e₃, with no interconnection overlaid by e₃. And finally, a via 72 connects φ₄and e₄, with no interconnection overlaid by e₄. In this way, each electrode overlays the fewest number of interconnections, while at the same time minimizing the size of the complete structure (for a given electrode and interconnection size). As no overlaid interconnection is adjacent in phase to the electrode which overlays it, the effects of cross talk are minimized or eliminated.

[0044] Of course, other electrode and interconnection arrangements are possible which serve the purpose of eliminating cross talk. For example, the positions of φ₂and φ₄in the scheme shown in FIG. 12 may be switched, as shown in FIG. 13. In general, no two adjacent interconnections are overlaid by adjacent electrodes. The important point is the recognition of the problem, and the provision of an architecture to address it.

[0045] 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. The electrodes may be staggered so as to minimize or eliminate cross talk. 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.