Thermal ink jet printing apparatus and driving method

Abstract: Thermal ink jet apparatus includes an ink jet pen with a plurality of ink ejection nozzles (20). Associated with each nozzle (20) is a first resistor (26) and second resistor (28). A feed channel (14) introduces a quantum of ink into thermal communication with each first resistor (26) and second resistor (28). The quantum of ink requires a level of applied thermal energy of E min to be caused to be ejected from the associated nozzle (20). An X-Y matrix drive circuit selectively applies a half-select address current to a first resistor (26) and a half-select address current to a second resistor (28), both resistors (26,28) located at a common nozzle (20). Each half-select current is insufficient to cause a resistor to emit E min thermal energy, but both half-select currents cause the first and second resistors (26,28) to couple at least E min of thermal energy to the co-located quantum of ink so as to enable an ejection thereof.

Description: This invention relates generally to thermal ink jet printing, for example to a system for providing part-select thermal addressing of each ink jet ejection nozzle. Thermal ink jet pens commonly utilize heater resistors that are placed on a common substrate and are aligned with individual ink reservoirs and corresponding ink ejection nozzles. The heater resistors are electrically driven by conductive traces which are photolithographically formed on the surface of a suitable resistor material, such as tantalum-aluminum. The heater resistors are isolated from the overlying ink reservoir by an inert dielectric material. To reduce the number of conductors required to drive the heater resistors, the prior art has combined the resistors with diodes to enable the resistors to be formed into an X-Y matrix which is, in turn, driven by a multiplexing circuit. Such an arrangement is shown in U.S. Patent 4,695,853 to Hackleman et al., assigned the same Assignee as this patent application. U.S. Patent 5,103,246 to Dunn, assigned to the same Assignee as this patent application, describes a technique for configuring such an X-Y electrical multiplexing arrangement so as to enable highly dense packing of the heater resistors. In each reference, a single resistor is employed per ink jet ejection nozzle. U.S. Patent 5,134,425 to Yeung, assigned to the same Assignee as this patent application, shows a further X-Y addressing matrix for plural ink jet heater resistors. Yeung describes a circuit which addresses the problem of parasitic voltages which appear across non-addressed heater resistors when plural addressed heater resistors are subjected to drive voltages. The parasitic voltages result from current flowing through non-addressed resistors along alternate paths between a drive voltage source and electrical ground. The preferred embodiment disclosed by Yeung drives each heating element in the matrix with a specified voltage and applies constant voltages across non-addressed heating elements, thus limiting the variations in total power dissipation of all heating elements. The power dissipated by each non-addressed heating element is less than or equal to 1/4 of the power that is dissipated by an addressed heating element, thus reducing the danger of misfiring in any particular print head design. US-A-5,479,196 discloses a thermal ink jet apparatus including an ink jet pen comprising, a plurality of ink ejection nozzles and underlying ink chambers; first and second resistors located at each chamber; means for introducing a quantum of ink into thermal communication with each first resistor and second resistor, the quantum of ink requiring at least Emin of applied thermal energy to be caused to be emitted from a chamber and through a nozzle; and drive circuit means for selectively applying a partial-select address current to a first resistor and a partial-select address current to a second resistor, both resistors being located at a common chamber, each partial-select current being insufficient to cause a resistor to couple Emin thermal energy into said quantum of ink, but both partial-select currents causing at least Emin of thermal energy to be coupled to said quantum of ink at said common chamber. Notwithstanding the success of prior art ink jet driving apparatus and circuitry, there is a continuing demand to achieve both simplification of the driving circuitry and reduced cost. Further, there is a need to assure that whatever driving technique is utilized enables reliable operation of the ink jet pen. The present invention seeks to provide improved ink jet printing. According to an aspect of the present invention, there is provided thermal ink jet apparatus as specified in claim 1. The preferred embodiment can provide a simple structure that enables an X-Y multiplexed drive circuitry to address ink nozzles electively. It can also control the addressing of individual ink jet nozzles. The preferred thermal ink jet apparatus includes an ink jet pen with a plurality of ink ejection nozzles. Associated with each nozzle is a first resistor and second resistor. A feed channel introduces a quantum of ink into thermal communication with each first resistor and second resistor. The quantum of ink requires a level of applied thermal energy of E min to be caused to be ejected from the associated nozzle. An X-Y matrix drive circuit selectively applies a half-select address current to a first resistor and a half-select address current to a second resistor, both resistors located at a common nozzle. Each half-select current is insufficient to cause a resistor to emit E min thermal energy, but both half-select currents cause the first and second resistors to couple at least E min of thermal energy to the co-located quantum of ink so as to enable an ejection thereof. An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a portion of a prior art ink jet pen. Fig. 2 is a circuit diagram of a first embodiment of ink jet pen in which an X-Y matrix selectively drives heater resistor pairs located at each ink jet ejection nozzle. Fig. 3 is a waveform diagram illustrating signal levels applied to the X-Y lines of Fig. 2. Fig. 4 is a planar view of multiple circuit levels of a pair of heater resistors that are off-set from each other when viewed from the ink jet ejection nozzle. Fig. 5 is a planar view of multiple circuit levels of a pair of heater resistors that are overlaid upon each other when viewed from the ink jet ejection nozzle. Fig. 6 is a circuit diagram of a second embodiment of ink jet pen in which an X-Y matrix selectively drives heater resistor pairs located at each ink jet ejection nozzle, without requiring electrical connection between a plurality of circuit layers. Fig. 1 illustrates a portion of a prior art ink jet pen and shows a representative ink jet nozzle and its underlying structure. A substrate 10 supports a barrier plate 12 which isolates an ink chamber 13 from adjacent ink chambers. Barrier plate 12 further provides an input channel 14 which enables a quantum of ink to be fed into ink chamber 13 and to overlay a heater resistor 16. A nozzle plate 18 forms the ink jet emitting surface and includes a nozzle 20 directly aligned over chamber 13 and heater resistor 16. When an appropriate current is applied to heater resistor 16, an amount of energy equal to or greater than E min is applied to the ink within chamber 13, causing the ink to be ejected through nozzle 20 towards a media sheet. In lieu of employing a single heater resistor 16 at each ink jet chamber location, the preferred embodiment provides a pair of resistors at each chamber which are driven in a half-select manner to enable sufficient power to be coupled to the ink in the chamber to enable that ink to be ejected through nozzle 20. Those skilled in the art will realize that the term "half-select" does not necessarily mean that exactly 1/2 the power is supplied by each resistor of the pair, but rather that each resistor provides a proportion of the applied power, with the proportion being less than that required to cause a level of thermal energy E min to be coupled to the ink within chamber 13. Thus, only when both resistors of the pair are supplied with current simultaneously (or substantially simultaneously) is sufficient energy coupled into the ink positioned in chamber 13 to cause it to be ejected from nozzle 20. Referring to Fig. 2, an X-Y matrix drive circuit 24 is shown which enables ink jet ejection nozzles in a multicolor ink jet pen to be selectively addressed, using the preferred dual resistor addressing arrangement. Each nozzle/chamber has a pair of resistors 26 and 28 positioned beneath the chamber and connected so as to the simultaneously driven by row and column drive circuits. Thus, each of resistors 26 in a first row 30 is connected between a row select conductor 32 and a ground conductor 34. When a half select drive voltage is applied to row select conductor 32, a half-select current is driven through each of resistors 26 to cause a heating thereof. However, as described above, the thermal energy imparted by each of resistors 26 to their associated ink reservoir chambers 13 is less than E min . Column selection is achieved by applying one or more strobe pulses to column lines 36. Each column line 36 connects to a plurality of resistors 28 whose other terminals are connected to an associated ground conductor (e.g. 34). By selectively energizing one or more of strobe lines 36, each resistor 28 associated with the energized strobe line has a voltage applied thereacross which causes a half-select current to flow therein. That current causes a heating of a resistor 28 which, in combination with the heat energy dissipated by resistor 26 at a fully selected chamber 13, causes the thermal energy coupled to the ink in chamber 13 to equal or exceed the value E min . Under such circumstances, an ink droplet is ejected from nozzle 20 towards the media sheet. The circuit shown in Fig. 2 enables half select addressing of a full-color (black, cyan, magenta, and yellow) ink jet pen using dual resistor addressing. The waveforms shown in Fig. 3 illustrate the signals which implement the half-select addressing action. In Fig. 4, a plan view shows a substrate structure which configures the dual resistor drive arrangement. In the structure of Fig. 4, dual resistors 26, 28 are offset, but adjacent, as viewed from nozzle plate 18. The composite view at the left of Fig. 4 illustrates the plural, superposed circuit layers which achieve the dual resistor, half-select operation. A contact 50 enables connection of a ground conductor to each of heater resistors 26, 28. Each heater resistor 28 is connected via a conductor 56 to a strobe line 58. In similar fashion, each heater resistor 26 is connected by a conductor 60 to a row drive conductor 62. Note that heater resistors 26 and 28 are on different levels of metallization, but are placed adjacent each other and directly beneath an ink chamber. To the right of the composite plan view of Fig. 4, is a view of "Layer 1" metallization showing how the row drive conductors 62 connect to heater resistors 26 and to ground contact 50. The illustration of the "Layer 2" metallization shows how heater resistors 28 connect to column strobe lines 58 for column selection. In Fig. 5, a similar structure to Fig. 4 is shown, however, heater resistors 26 and 28 are superposed over one another at each chamber and are separated by a dielectric layer (not shown). Thus, as can be seen in Layer 1 and Layer 2 in Fig. 5, the structure of row conductors 62 and strobe conductors 58 is somewhat altered to enable the achievement of the sandwich resistor structure. In Fig. 6, another embodiment is illustrated in which inter-circuit layer connections are not required. While heater resistors 70 are connected in parallel between parallel arranged strobe and ground conductors, heater resistors 72 are connected in series along each row of the matrix. Thus, no heater resistor needs to be connected between intersecting row and column conductors. The serial resistor connection may dictate a shorter string of heater resistors 72 connected to a row select driver to assure sufficient thermal emission at each heater resistor 72. In each of the above embodiments, only when voltage is applied to both heater resistors located at a selected ink chamber, will the combined energy coupled into the ink at the selected nozzle equal or exceed E min . The signals applied to the row select lines and the strobe lines do not have to be the same magnitude or duration and, thus, the term "half-select" is meant to incorporate any appropriate drive scheme which enables the above described addressing operation. The thermal multiplexing arrangement described above enables a reduction of total signal lines and further enables the ink jet cells to be produced on relatively inexpensive substrates (e.g. ceramics or glass).

Claims: Thermal ink jet apparatus including an ink jet pen with a plurality of ink ejection nozzles (20) and underlying ink chambers (13); first and second resistors (26, 28) located at each chamber (13); means (14) for introducing a quantum of ink into thermal communication with each said first resistor (26) and second resistor (28), said quantum of ink requiring at least E min of applied thermal energy to be caused to be emitted from a chamber (13) and through a nozzle (20); and X-Y matrix drive circuit means for selectively applying a partial-select address current to a first resistor (26) and a partial-select address current to a second resistor (28), both resistors (26, 28) being located at a common chamber (13), each partial-select current being insufficient to cause a resistor to couple E min thermal energy into said quantum of ink, but both partial-select currents causing at least E min of thermal energy to be coupled to said quantum of ink at said common chamber (13); said first and second resistors (26, 28) at each chamber (13) being offset from each other when viewed from an ink emitting surface of said thermal ink jet apparatus and being disposed on different superposed circuitry layers. Thermal ink jet apparatus as recited in claim 1, wherein said first and second resistors (26, 28) at each chamber (13) are disposed in a stack when viewed from an ink emitting surface of said thermal ink jet apparatus. Thermal ink jet apparatus as recited in claim 2, wherein said first and second resistors (26, 28) are separated by an insulating layer. Thermal ink jet apparatus as recited in any preceding claim, wherein for a X-Y matrix drive circuit including a plurality of rows and columns, the apparatus comprises a row select conductor for each row connected to one side of a first resistor (26) located at each chamber (13) associated with said row; a column select conductor for each column connected to one side of a second resistor (28) located at each chamber (13) associated with said column; and a common potential conductor connected to a second end of each first resistor (26) and each second resistor (28). Thermal ink jet apparatus as recited in any one of claims 1 to 3, wherein for a X-Y matrix drive circuit including a plurality of rows and columns, said apparatus comprises: a row select conductor for each row, each row select conductor comprising a series connection of first resistors (26), each first resistor (26) located at a chamber (13) associated with said row; a column select conductor for each column, each column select conductor for a column connected to one side of a second resistor (28) located at each chamber (13) associated with said column; and a common potential conductor connected to a second end of each said second resistor (28). Thermal ink jet apparatus as recited in any preceding claim, wherein each said partial select address current applied to a resistor causes said resistor to emit approximately a same value of thermal energy.

Inventors: ERNI ERNST R, ERNI, ERNST R.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1997
Main classification: B41J2
IPC codes: B41J2