Apparatus for Driving Multiple Ink Jet Printheads With a Single Set of Drive Outputs

The invention relates to ink jet printing apparatus, and more particularly, to ink jet printing apparatus for driving a plurality of ink jet printheads.

Ink jet printing systems are available which have either a single printhead, or multiple printheads. In systems having multiple printheads, a separate printhead controller/driver circuit is provided for each printhead. Although providing a separate printhead controller/driver for each printhead simplifies the design implementation, such duplication typically results in an increase in cost for each printhead controller/driver added to the system.

The invention is related to an ink jet printing apparatus which includes a single printhead controller capable of controlling a plurality of printheads. The printhead controller of the invention includes a printhead driver circuit having a set of ink jet nozzle control outputs and a printhead select circuit having a plurality of printhead select outputs. Each printhead of the invention includes a plurality of ink jet nozzles, a plurality of individually controllable ink jet nozzle firing circuits, and a printhead enable circuit. The printhead enable circuit of each printhead is electrically coupled between the plurality of individually controllable ink jet nozzle firing circuits of the printhead and the set of ink jet nozzle control outputs of the printhead driver circuit. The set of ink jet nozzle control outputs is common to each of the plurality of printheads. The printhead enable circuit is electrically coupled to one of the plurality of printhead select outputs and enables the electrical conduction of the plurality of controllable ink jet nozzle firing circuits of that printhead upon receipt of a printhead select signal from one of the printhead select outputs of the printhead select circuit.

The printhead select circuit supplies a printhead select signal to the enable circuit of one of the plurality of printheads via one of the printhead select outputs to select that printhead for printing. The printhead driver circuit then supplies control signals via the set of ink jet nozzle control outputs to control the plurality of individually controllable ink jet nozzle firing circuits of the selected printhead for controlling the output of ink from the ink jet nozzle corresponding to each ink jet nozzle firing circuit.

Other features and advantages of the invention may be determined from the drawings and the detailed description of the invention that follows.

FIG. 1 schematically shows a printing apparatus embodying the invention.

FIG. 2 shows a schematic diagram of a printhead of the invention.

FIG. 3 shows a more detailed schematic diagram of the printing apparatus of FIG. 1.

FIG. 1 shows in schematic form an ink jet printer 10 embodying the invention. Ink jet printer 10 includes printhead controller 12 and printing mechanism (not shown) which cooperate to generate an image on a print medium. The invention provides for the control of multiple printheads using a single set of drive electronics. This is accomplished by providing printhead controller 12 which includes a printhead driver circuit 14 having a set of ink jet nozzle control outputs 16 for controlling the ink output of printheads 18, individually identified as 18a and 18b, and a printhead select circuit 20 providing a plurality of printhead select outputs 22 for individually selecting one of the printheads 18 for printing. Printheads 18 further include enable circuitry to allow their individual selection.

Printheads 18a and 18b are functionally equivalent. Accordingly, elements common to each of the printheads 18a and 18b will share the same numerical indicator, but will have different alphabetic suffixes. At times, common elements of the printheads and their function may be described with reference only to the numerical indicator of the element. For example, the printheads 18a and 18b each include an enable circuit 24, individually identified as 24a and 24b.

Printhead driver circuit 14 of printer controller 12 is electrically coupled to printheads 18a and 18b via a control bus 26 having a plurality of conductors 26a-26d. Conductors 26a-26d are individually connected at a first end of control bus 26 to control outputs 16a-16d, respectively, of printhead driver circuit 14. Conductors 26a-26d are individually connected at a second end of control bus 26 to ink jet nozzle control inputs 28a, 30a, 32a and 34a, respectively, of printhead 18a, and to ink jet nozzle control inputs 28b, 30b, 32b and 34b, respectively, of printhead 18b. Accordingly, ink jet nozzle control signals present at control outputs 16a-16d are available for use by either printhead 18a or printhead 18b, but only the selected printhead will be able to act on these control signals at any given time.

Printhead select circuit 20 of printer controller 12 is electrically coupled to printheads 18a and 18b via a select bus 36 having individual conductors 36a and 36b. Conductor 36a is connected at a first end to select output 22a of printhead select circuit 20. Conductor 36a is connected at a second end to ink jet nozzle select input 38a of printhead 18a. Likewise, conductor 36b is connected at a first end to select output 22b of printhead select circuit 20, and conductor 36b is connected at a second end to ink jet nozzle select input 38b of printhead 18b. Accordingly, an ink jet printhead select signal present at select output 22a is used to select the operation of printhead 18a, and an ink jet printhead select signal present at select output 22b is used to select the operation of printhead 18b, but only the selected printhead will be able to act on the control signals supplied from control outputs 16a-16d at any given time.

The printheads 18 are functionally equivalent, and each includes a plurality of ink jet nozzles 40, a plurality of individually controllable ink jet nozzle firing circuits 42, 44, 46, 48, and a printhead enable circuit 24. Each ink jet firing circuit includes an electrically responsive element (not shown), such as a thermal element or a piezoelectric element, located near one of the individual ink jet nozzles which, when electrically excited, causes an output of ink from the nozzle. The printhead enable circuit 24 of each of the printheads 18a, 18b is electrically coupled to respective ink jet nozzle firing circuits 42, 44, 46, 48 via conductors 50, 52, 54, and 56, and to control inputs 28, 30, 32, and 34, wherein each control input is associated with one nozzle firing circuit. Accordingly, when installed in printer 10, the printhead enable circuit 24 of each of the printheads 18a, 18b is electrically coupled between the ink jet nozzle firing circuits 42, 44, 46, 48 of the respective printhead and the set of common ink jet nozzle control outputs 16a-16d of printhead driver circuit 14.

Each printhead enable circuit 24 includes a dedicated select input 38 for receiving a select signal from printhead select circuit 20 of printhead controller 12. Thus, a select signal received at select input 38 is effective in enabling all the ink jet nozzle firing circuits 42, 44, 46, 48 for electrical conduction in the selected printhead, thereby allowing control signals present at control outputs 16a-16d to effect the operation of ink jet nozzle firing circuits 42, 44, 46, 48, respectively, of the selected printhead. Likewise, in the absence of a select signal at select input 38, ink jet nozzle firing circuits 42, 44, 46, 48 are disabled from electrical conduction, thereby preventing control signals present at control outputs 16a-16d from effecting the operation of ink jet nozzle firing circuits 42, 44, 46, 48, respectively, of a non-selected printhead.

Accordingly, during operation of printer 10, for example, printhead select circuit 20 supplies a printhead select signal to printhead 18a via conductor 36a, or supplies a printhead select signal to printhead 18b via conductor 36b. If, for example, printhead 18a receives a printhead select signal at select input 38a, then enable circuit 24a will permit control signals from the control outputs 16a-16d of printhead driver circuit 14 to effect the operation of ink jet nozzle firing circuits 42a, 44a, 46a, and 48a. The preferred operation of printhead controller 12 is such that only one of the printhead select inputs 38a, 38b will receive a select signal at any given time. Thus, in this preferred example of operation, no select signal will be supplied to select input 18b of printhead 38b until the select signal is no longer applied to select input 38a of printhead 18a. It is contemplated, however, that in some situations it may be desirable to concurrently apply select signals to multiple printhead select inputs to concurrently enable multiple printheads for simultaneous operation.

FIG. 2 shows a preferred embodiment of the printhead 18 of the invention. Although FIG. 2 is specifically directed to printhead 18a, it should be understood that all components, connections and operations of components attributable to printhead 18a are equally applicable to printhead 18b. FIG. 2 shows a preferred embodiment of the enable circuit 24a of printhead 18a previously discussed with respect to FIG. 1. Enable circuit 24a includes a plurality of switch elements 58a, 60a, 62a, and 64a, such as the field effect transistors (FETs) as shown, each having a command input (gate) electrically connected to select input 38a. The common inputs connected to select input 38a are also coupled to ground G via resistor Ra. A current input (drain) of each of the switch elements 58a, 60a, 62a, and 64a is individually connected to control inputs 28a, 30a, 32a, and 34a, respectively. A current output (source) of each of the switch elements 58a, 60a, 62a, and 64a is individually connected to ink jet nozzle firing circuits 42a, 44a, 46a, and 48a, respectively.

Although enable circuit 24a is shown preferably constructed with switch elements 58a, 60a, 62a, and 64a as being FETs, those skilled in the art will recognize that the FETs could be replaced by any device capable of performing substantially the same function, such as for example, by replacing the FETs with bipolar transistors.

FIG. 3 is a more detailed representation of the printer of FIG. 1, and includes the enable circuit as described above with respect to FIG. 2. As shown in FIG. 3, all command inputs (gates) of switch elements 58a, 60a, 62a, and 64a of printhead 18a are commonly connected via select input 38a and conductor 36a to select output 22a of printhead controller 12 and to ground G via resistor Ra, and all command inputs (gates) of switch elements 58b, 60b, 62b, and 64b of printhead 18b are commonly connected via select input 38b and conductor 36b to select output 22b of printhead controller 12 and to ground via resistor Rb. The current inputs (drains) of switch elements 58a, 60a, 62a, and 64a of printhead 18a associated with control inputs 28a, 30a, 32a, and 34a, respectively, are connected via control bus 26 to control outputs 16a-16d, respectively, of printhead controller 12. Likewise, the current inputs (drains) of switch elements 58b, 60b, 62b, and 64b of printhead 18b associated with control inputs 28b, 30b, 32b, and 34b, respectively, are also connected via control bus 26 to control outputs 16a-16d, respectively, of printhead controller 12. The current outputs (sources) of switch elements 58a, 60a, 62a and 64a of printhead 18a are connected to ink jet firing circuits 42a, 44a, 46a, and 48a, respectively. The current outputs (sources) of switch elements 58b, 60b, 62b, and 64b of printhead 18b are connected to ink jet nozzle firing circuits 42b, 44b, 46b, and 48b, respectively.

Although the invention has been described in relation to a printer having two printheads, the application of the invention is not so limited, and could be incorporated in a printer having any number of printheads greater than one. In such a case, as in the embodiments shown in FIGS. 1 and 3, the printhead controller of the printer would include a printhead driver circuit having a set of ink jet nozzle control outputs, which can be individually identified as control outputs 1 to N, wherein N represents a positive integer corresponding to the number of ink jet nozzle firing circuits and ink jet nozzles on each printhead, and further include a printhead selection circuit having a plurality of printhead select outputs, which can be individually identifiable as select outputs 1 to M, wherein M represents a positive integer corresponding to the number of printheads to be controlled. Each of the plurality of printheads would include a printhead enable circuit, for example, of the type shown in FIG. 2 and described above, wherein the control inputs of the printhead enable circuit are individually, electrically coupled to one of the ink jet nozzle control outputs 1 to N. Each output of the enable circuit is coupled to one of the plurality of individually controllable ink jet nozzle firing circuits, and the select input of each printhead is electrically coupled to one of the printhead select outputs 1 to M. In operating such a printer, the printhead controller supplies a select signal via one of the select outputs 1 to M to a printhead enable circuit of one of the plurality of printheads to select that particular printhead for printing. The printhead driver circuit then supplies control signals via the control outputs 1 to N and the enable circuit to control the plurality of individually controllable ink jet nozzle firing circuits of the selected printhead, which in turn controls the ink output of the ink jet nozzles thereof.

Although the invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and in detail without departing from the spirit and scope of the following claims.