EP1197334B1

EP1197334B1 - Printing system

Info

Publication number: EP1197334B1
Application number: EP00308973A
Authority: EP
Inventors: Adam I. Pinard
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 2000-10-12
Filing date: 2000-10-12
Publication date: 2008-03-26
Anticipated expiration: 2020-10-12
Also published as: EP1197334A1; DE60038450D1; DE60038450T2

Description

Field of the Invention

This invention relates to jet printers, including jet printers for direct-to-plate printing systems.

Background of the Invention

Ink-jet printers operate by charging drops of ink with a charging electrode and guiding them to a print substrate through a high intensity electric field. Printers can modulate the charge on an ink drop by changing the charging electrode voltage to select whether each drop is to be printed or instead sent to a gutter. Printers may also adjust the charging voltage to compensate for aerodynamic effects and for the influence of the charge from adjacent drops. Some printers employ a technique known as "swathing" to continuously change the field and thereby direct drops from one or more stationary ink jets to different locations on the printing substrate, instead of moving a print head across the substrate.
Jet printing techniques are applicable to direct-to-plate printers. Such printers typically apply a printing fluid to a sheet of plate stock mounted on a drum. This fluid causes changes in the portions of the surface of the plate on which it is deposited. Although further processing of the plate may be necessary, the result is a printing plate that can serve to print large numbers of pages.
US4,065,773 discloses an ink jet printer for printing different tonal shades onto a substrate. Droplets of ink are charged as determined by an incoming signal and are directed towards to substrate or into a gutter away from the substrate according to the tonal value required in each dot location of the substrate.
US4,525,721 discloses an ink jet recording interlace strategy for a single-pass printer, wherein ink droplets are charged to a selective level and directed towards a substrate. Sequentially generated droplets are directed to non-sequential pixel locations in the pixel locations assigned to that nozzle to improve drop placement accuracy.

Summary of the Invention

There is described herein a jet printer that includes a drum having a print substrate mounted on it, a movable carriage, and a jet printing fluid source attached to the carriage. At least one deflection element is located proximate an output trajectory of the jet printing fluid source, and a carriage mechanism is provided for moving the carriage along a direction of an axis of rotation of the drum. The printer also includes a swathing table, and a control circuit responsive to the swathing table and having an output provided to at least the one deflection element.
The deflection element may advantageously be a charging tunnel surrounding an output of the jet printing fluid source or one of a pair of deflection electrodes. The jet printer may advantageously further include a processor portion operative to drive the printer to print half-tone images on a print substrate. A print substrate placed in the output trajectory of the jet printing fluid source may advantageously be a printing plate. A drum actuation controller may advantageously be provided which is synchronized with the control circuit to cause printing by the printer to take place according to a helical progression.
In one aspect, the invention features a jet printer that includes means for moving a jet printing fluid source relative to a print substrate along a direction of an axis of rotation of a print substrate, means for rotating the print substrate relative to the jet printing fluid source about the axis of rotation such that the combined action of the means for moving and the means for rotating cause the jet printing fluid source to advance in a helical progression with respect to the print substrate during a plurality of drum rotations, and means for guiding a first drop of printing fluid from the jet printing fluid source so that it lands on the print substrate at a first distance along the direction of the axis of rotation of the print substrate from the jet printing source, and for guiding a second drop of printing fluid from the jet printing fluid source so that it lands on the print substrate at a second distance along the direction of the axis of rotation of the print substrate from the jet printing source after the print substrate has rotated, wherein the second distance is different from the first distance.
The means for guiding may advantageously further be for guiding the first and second drops at locations that are spaced apart both longitudinally and radially with respect to the axis of rotation. The printer may advantageously further include means for causing the means for guiding to perform a half-tone printing process.
In a method aspect, the invention features a method of jet printing that includes moving a jet printing fluid source relative to a print substrate along the direction of an axis of rotation of a print substrate, guiding a first drop of printing fluid from the jet printing fluid source so that it lands on the print substrate at a first distance along the direction of the axis of rotation of the print substrate from the jet printing source, rotating the print substrate relative to the jet printing fluid source about the axis of rotation after the step of guiding a first drop, such that the combined action of the step of moving and the step of rotating cause the jet printing fluid source to advance in a helical progression with respect to the drum during a plurality of drum rotations, and guiding a second drop of printing fluid from the jet printing fluid source so that it lands on the print substrate at a second distance along the direction of the axis of rotation of the print substrate from the jet printing source after the print substrate has rotated, wherein the second distance is different from the first distance.
The method may advantageously further include (electromagnetically) guiding further drops of printing fluid from the jet printing fluid source at the first position so that the further drops land on the print substrate at further different distances along the direction of the axis of rotation of the print substrate, after the print substrate has rotated further. The steps of guiding and rotating may advantageously form a part of a half-tone printing process.
There is also described herein a jet printer that includes a jet printing fluid source, at least one deflection element located proximate an output trajectory of the fluid source, a digital filter, and a digital-to-analog converter operatively connected between an output of the filter and at least the deflection element. The filter preferably has inputs responsive to a desired drop position value, to one or more previous desired drop position values, and to one or more previous filter output deflection values.
The printer may advantageously further include a processor portion operative to drive the printer to print half-tone images on a print substrate. The print substrate may be a printing plate. The printer may advantageously further include a drum having a print substrate mounted on the drum, and a carriage mechanism for moving the jet printing fluid source and the deflection element perpendicular to a feed direction of a print substrate, which may advantageously be a printing plate. The printer may advantageously further include a swathing table, and a control circuit responsive to the swathing table and having an output operatively connected to the digital filter. The digital filter may advantageously be constructed and adapted to operate on a desired position for a printing fluid drop, on previous desired positions for printing fluid drops from the jet printing fluid source, and on previous outputs of the filter. The digital filter is preferably an IIR filter. The digital filter may advantageously have a transfer function that includes a sum of previous input position values each multiplied by one of a first plurality of coefficients, and previous output deflection values each multiplied by one of a second plurality of coefficients.
There is also described herein a method of jet printing, that includes (preferably electromagnetically) guiding charged drops of printing fluid to a print substrate (preferably through an electromagnetic field), applying a digital filtering function to a desired input position value, to obtain a guiding value for a further drop of printing fluid, and (preferably electromagnetically) guiding the further charged drop of printing fluid to the substrate.
The step of applying may advantageously apply a transfer function that includes a sum of previous input position values each multiplied by one of a first plurality of coefficients, and previous guiding values each multiplied by one of a second plurality of coefficients.
There is also described herein a jet printer that includes means for (preferably electromagnetically) guiding each of a plurality of charged drops of printing fluid to a print substrate (preferably through an electromagnetic field), means for applying a digital filtering function to a desired input position value and to values of charge on the drops relative to the electromagnetic field, to obtain a deflection value for a further drop of printing fluid, and means for guiding the drop based on the deflection value, the means for guiding preferably comprising means for converting the deflection value to an electromagnetic field intensity to guide the further drop to the substrate.
The means for applying a digital filtering function may advantageously apply a transfer function that includes a sum of previous input position values each multiplied by one of a first plurality of coefficients, and previous deflection values each multiplied by one of a second plurality of coefficients.
There is also described herein a jet printer, comprising a drum constructed and adapted to receive a print substrate, a drum control interface having an output provided to a motor for rotating the drum, a movable carriage, a print head including a first jet printing fluid source attached to the carriage and at least one deflection element located proximate an output trajectory of the first jet printing fluid source, the deflection element having a deflection axis in the direction of an axis of rotation of the drum, a carriage mechanism for moving the carriage in the direction of the axis of rotation of the drum, a swathing table, self-interleaving logic having an output provided to the print head, and a control circuit responsive to the swathing table and having an output provided to at least the one deflection element.
Whilst a drum is greatly preferred, facilitating self-interleaving, particularly in a helical pattern, while reducing the need for abrupt changes of direction, the feature of deflection in the direction of movement of the carriage may be advantageously applied more generally. In the case where a drum is replaced by a platen, references to the axis of rotation of the drum should be modified accordingly. For example, the invention may provide a jet printer, comprising means constructed and adapted to receive a print substrate, a movable carriage, a print head including a first jet printing fluid source attached to the carriage and at least one deflection element located proximate an output trajectory of the first jet printing fluid source, the deflection element having a deflection axis in the direction of motion of the carriage, a swathing table, self-interleaving logic having an output provided to the print head, and a control circuit responsive to the swathing table and having an output provided to at least the one deflection element.
There is also described herein use of a continuously rotatable drum in a jet printer, in combination with self-interleaving and swathing and/or printing along a helical path over a plurality of rotations to deposit spatially adjacent drops from a fluid source on a print substrate non-sequentially, preferably without sudden transitions in motion of the fluid source or print substrate, preferably including delivering drops from a carriage movable along the direction of the axis of the drum and further including deflecting drops in a direction parallel to the axis of the drum. The combination of carriage movement with deflection in the same direction can facilitate precisely controlled and non-sequential deposition without requiring sudden carriage or substrate movements. It will be appreciated that the term sudden is intended to imply movements which may result in jerkiness, deterioration or inconsistency of print quality and typically implies stepwise movements or acceleration or deceleration of a substantial fraction of the relative velocity of the carriage and substrate in a time comparable to the time between deposition of drops; this can readily identified as such but absolute values will of course depend on the size, resolution and print rate of a particular printer.
Aspects and preferred features are set out in the claims.
Systems according to at least preferred embodiments of the invention may be advantageous in that they may provide an inexpensive, accurate and flexible method of controlling the trajectory of drops of printing fluid in jet printing. By treating drops as samples in a sampled-data system, printers can perform swathing, aerodynamic compensation, and adjacent drop compensation in the digital domain using an existing printer control processor or an inexpensive add-on microprocessor. Such printers may also be reconfigurable for different printing applications without requiring a redesigned analog circuit, and they may even be digitally calibrated at start-up or on-the-fly to improve print characteristics. These features may improve the quality of printing, and may reduce the cost and time involved in developing improved printers.
Systems according to the invention may also permit printing operations to take place more quickly and efficiently, in moving-head, direct-to-plate, jet printers. Swathing can permit such printers to deposit individual charged drops that are spaced apart in two polar dimensions on a plate as it rotates. This allows for fine-pitch printing at high speeds with a minimum number of guard drops.

Brief Description of the Drawings

Fig. 1 is a system-level block diagram illustrating elements of a jet printer according to the invention;
Fig. 2 is a flow chart illustrating the operation of the printer of Fig. 1; and
Fig. 3 is an interleaving diagram for a two-nozzle interleaving and three-channel swathing printer.

Detailed Description of an Illustrative Embodiment

In the following description a number of features are disclosed in combination in a particular jet printer having a drum, a preferred application. However, unless otherwise stated below, these features may be provided independently or in other combinations; for example features for controlling the carriage or jet may be used in other printers, for example using a platen, and drum control features may be used in printers without the other advantageous features of jet control disclosed.
A jet printer 10 according to the invention includes a print substrate feed mechanism 12, a print head assembly 14, and a control circuit 16. The feed mechanism includes a print drum 30, which supports a print substrate 32, such as a piece of paper print stock or a printing plate. A motor 34 drives the drum 30 via a coupling mechanism 36.
The print head assembly 14 includes a print head that includes a nozzle assembly 20 having a charging electrode 22, such as a charging tunnel, at its output, with a pair of deflection electrodes 24, 26 located on opposite sides of the path that a drop takes when exiting the nozzle. The deflection electrodes, the charging tunnel, and the nozzle assembly are all mounted on a carriage driven by a carriage actuator 28. The carriage actuator is operative to move the carriage along a path that is parallel to the axis of rotation of the drum.
The control circuit 16 includes a print control processor 40 having a control output provided to a drum control interface 42. The print control processor also has a data port operatively connected to a data port of a storage element 44, and a data port operatively connected to a digital filter 46. The digital filter has an output provided to a digital input of a digital-to-analog converter 48, which has an analog output provided to an input of a high-voltage amplifier 50. The amplifier has an output that is operatively connected to the charging electrode 22. Also provided is a high-voltage source 27 that can be controlled by the print control processor 40 and that has an output operatively connected to one of the deflection electrodes 26. The other deflection electrode 24 can be operatively connected to a fixed voltage source, such as ground.
Fig. 1 is intended as a general illustration of a printer according to the invention, and one of skill in the art would be able to modify its design in a number of ways while still obtaining benefits from the invention for different applications. For example, a number of different mechanisms can be used for the carriage actuator such as toothed-belt or lead-screw mechanisms. And while a drum-based feed mechanism 12 is appropriate for printing directly on lithographic plates, other printing applications may employ different kinds of mechanisms, such as continuous feed paper on a platen.
Features and functionality of the various circuit elements shown in Fig. 1 can also be combined in different ways. For example, the print control processor 40 can incorporate control routines that control the motor 34, allowing a signal from the print control processor or a simple buffered version of that signal to drive the motor. This eliminates the need for a dedicated hardware drum control circuit 42, which receives only a simple on/off signal from the print control processor. The print control processor can be located inside the printer, or it can be located remote from the printer and communicate with the printer, such as via serial cable.
Note that it is also possible to apply the invention to different types of deflection configurations by modulating the excitation provided to one or more of its deflection elements. For example, it is possible to modulate the voltage on the deflection electrodes 24, 26 instead of, or in addition to, modulating the voltage on the charging electrode 22. In addition, it is also possible to operate a jet printer without a charging electrode and modulate only a voltage on one or more deflection electrodes. It is also possible to modulate other approaches to guiding a drop, such as by modulating a magnetic field instead of an electric field. More particularly, while deflection electrodes can be used to generate an electric field between them which serves to deflect charged droplets primarily electrostatically. Additionally or alternatively, a magnetic field may be used to deflect the charged droplets primarily magnetically. Both of these methods rely on electromagnetic interaction and references to electromagnetically deflecting droplets in this specification and claims are intended to encompass any form of guiding making use of the charge of the droplets, unless otherwise stated. Whilst electromagnetic guiding is greatly preferred for accuracy and speed, particularly if the preferred digital filter is employed to control guiding, certain aspects or features, particularly relating to helical printing or interleaving or swathing, may be employed with other guiding mechanisms.
In operation, referring to Figs. 1 and 2, operation of the jet printer 10 begins with operator set-up of the printer and a software start command (step 60). In the case of a direct-to-plate printer that prints on aluminum or plastic plates, an operator first mounts a fresh plate 32 on the printer's drum 30. The operator then causes a host system to download data representing the material to be printed into the print control processor 40. The print control processor can also download coefficients into the digital filter 46, or run a calibration routine to derive these coefficients, if these are not stored locally. Calibration can be performed by depositing printing fluid drops on a calibration needle and adjusting the filter coefficients until an optimal transfer function has been reached. The processor can then instruct the drum control interface 42 to start the motor 34, which causes the drum 30 to rotate. Use of a drum is particularly advantageous in this jet printer as it can minimize the need for changes in direction which may cause droplets to interfere.
After the drum is up to speed, the print control processor 40 instructs the nozzle assembly 20 to generate a series of charged printing fluid drops, which pass through the charging electrode 22 and then between the deflection electrodes 24, 26. The magnitude of the voltage to be applied to the charging electrode 22 by the amplifier 50 depends on whether and where each particular drop is to be printed (step 62). If a drop is not to be printed, such as in the case of a guard drop, the print control processor 40 will select a gutter or knife edge 23 as the destination for the drop (step 66). The print control processor will then compute an appropriate voltage to be applied to the charging electrode given the voltage between the deflection electrodes, to guide the drop into the gutter (step 68). Typically, this voltage is either the maximum or minimum voltage that the amplifier is configured to provide.
If the drop is to be printed, the print control processor 40 retrieves a drop position entry from a swathing table, which can be stored in the storage 44 (step 64). The entries in the swathing table are designed to cause successive, but non-adjacently deposited, drops to be separated from each other on the plate radially due to rotation of the drum and longitudinally due to the swathing. Because the drops are spaced in this way in these two polar dimensions, they will not touch each other. This is particularly important in half-tone printing, where only single, separate drops are deposited. Of course, the order in which the print data is sent to the print head must take the swathing sequence into consideration.
Superimposed on the swathing voltage is a voltage derived by the digital filter 46, which compensates for aerodynamic effects and for the influence of the charge on adjacent drops. The digital filter can be an Infinite-Impulse-Response (IIR) filter implemented using a digital signal processor, such as the TMS 320C203 integrated circuit available from Texas Instruments. The filter function implemented is: $OUT (n) = B 0 * IN (n) + B 1 * IN (n - 1) + B 2 * IN (n - 3) + AI * OUT (n - 1) + A 2 * OUT (n - 2)$
Coefficients used in the function for one embodiment are: TABLE I

IIR Coefficients

b0 0.05

b1 0.67

b2 -0.32

a1 0.6

a2 0
Where IN(n) represents the desired position of drop number n, and OUT(n) represents the electrode voltage for drop number n resulting from the application of the filter. In a system that has sufficient computational capacity, it is contemplated that further coefficients could be included in this function. Digital filter design is discussed in, for example, "Digital Signal Processing," ), which is herein incorporated by reference. The digital filter may be implemented in dedicated hardware or in software; the invention extends to a computer program or computer program product implementing a filter for controlling drop position. The use of a digital filter (particularly an IIR) filter as opposed to a look up table or simple algorithm may improve accuracy of placement of drops and is an advantageous (but not necessarily essential) feature which may be independently provided.

Table 2 illustrates the operation of the digital filter for the initial drops to be printed in a print job. As can be seen from this table, charge interaction between drops and aerodynamic effects cause the filter voltage required to place the drop at a desired position to change from drop to drop.

TABLE 2

Drop Number	Normalized Desired Drop Position	Normalized Charging Voltage
0	1	0.050
1	1	0.750
2	1	0.850
3	1	0.910
4	1	0.946
5	1	0.968
6	1	0.981
7	1	0.988
8	0	0.943
9	0	0.246
10	0	0.147
11	0	0.088
12	0	0.053
13	0	0.032
14	0	0.019
15	0	0.011
16	0	0.007

Once the charging voltage has been computed, the digital filter supplies a code corresponding to that voltage to the digital-to-analog converter 48. The digital-to-analog converter converts this code into an analog voltage, which it presents on its analog output. The amplifier 50 then amplifies the analog voltage to a high level, which is applied to the charging electrode 22 (step 70).
When a final drop has been sent (step 72), the printer can be powered down, or a new print operation can begin (step 74). If drops remain to be printed, the process of determining a charging electrode voltage begins again for the next drop (step 62).
In one particular embodiment, a printer employs a continuous jet head that has multiple jet assemblies and employs swathed bitmap capability to print up to 16 rasters per revolution per channel in a helical progression about the drum. This high resolution bitmap capability allows every drop to be used on halftone images without any of them merging. The provision of a helical printing path can surprisingly improve the quality of jet printed images and is an advantageous (but not necessarily essential) feature of this embodiment which may be provided independently.
It has been empirically determined that 1200 dots per inch (DPI) can be accomplished using a 10 um nozzle at jet velocity of 50 m/s printing a 16 pixel wide swath with a firing order of: 0, 8, 4, 12, 1, 9, 5, 13, 2, 10, 6, 14, 3, 11, 7, 15. This order is stored as a series of charge values in a 32-entry swathing table that also has an entry for non-printing drops, although other types of swathing tables can be used as well. The separation on the individual charges corresponds to a voltage of approximately 4 volts. This requires a total voltage swing of about 128 volts on the charging electrode. A nominal separation of 64 volts between printed and non-printed drops provides sufficient separation for the knife edge to operate properly. The deflection voltage on the nozzle assemblies is programmable by software from 0 to 2200 Volts, and the deflection voltages for each nozzle assembly are to be sensed individually. Stimulation is common for all nozzle assemblies and is a square wave with an amplitude that can be controlled from 2.5 to 41 Volts. The charging voltage output has 1024 discrete levels between +35 and -115 Volts with a settling time of 125ns.
Referring to Fig. 3, it is advantageous to combine interleaving and swathing in printers according to the invention. In such a system, a print head that includes a series of jets spaced along the direction of rotation of the drum simultaneously prints in parallel swathed helical progressions with offset rasters. This combination of swathing and interleaving allows for fast printing and a high degree of separation of the deposited ink drops.
An illustrative printing sequence is shown in Fig. 3 for a printer with two nozzles that each employ three-channel swathing, and that are interleaved with each other and with themselves. In this example, a first nozzle deposits its ink drops at equally spaced intervals during a first revolution. During a second revolution, the first nozzle again deposits its ink drops at equally spaced intervals, but places them between the drops deposited during the first revolution.
At the same time, a second nozzle is also depositing its ink drops at equally spaced intervals, but these are offset from the positions used by the first nozzle, such that they fall in the gaps left by the first nozzle. The result is an interleaved printing sequence where adjacent drops from one jet are printed on different revolutions, and where these drops are also separated by adjacent drops from another jet.
In the illustrated horizontally interleaved print progression, a first jet deposits a first drop A0 in a first stripe α0. It then deposits a second drop A1 in a third stripe α2. Finally, it deposits a third drop A3 in a fifth stripe α4. This pattern begins again as the print head advances with respect to the substrate while printing in even-numbered stripes.
During the same pass of the print head, a second jet is depositing a second swath, at a different position along the direction of rotation of the drum. This second swath begins when the second jet deposits a first drop B0 in a first offset stripe β1. It then deposits a second drop B1 in a third offset stripe β2. Finally, it deposits a third drop B2 in a fifth offset stripe β4. This pattern begins again as the print head advances with respect to the substrate while printing in even-numbered offset stripes.
During the same pass of the next revolution, the first jet will fill in remaining gaps by depositing drops in the odd-numbered stripes (i.e., α1, α3, etc.). Similarly, the second jet will fill in remaining gaps by depositing drops in the odd-numbered offset stripes (i.e., β1, β3, etc.).
The illustrated print order employs horizontal interleaving to separate drops in the direction of the axis of rotation of the drum. This effect can also be accomplished in the direction of rotation of the drum by performing vertical interleaving, in which adjacent print lines are deposited on different passes or even different rotations of the drum. And both horizontal and vertical interleaving can be performed by just a single jet, by interleaving over multiple passes and/or rotations.
For the purpose of clear illustration, the example shown in Fig. 3 employs a left-to-right firing order. It is also advantageous to combine interleaving and jumbled swath order, however, to achieve a high degree of spacing between drops, and to avoid the creation of Moiré patterns. In one embodiment, it is believed that satisfactory 2400 DPI printing can be accomplished using the interleaving presented in connection with Fig. 3 and a 15-drop swath width. The firing order for this embodiment is 1, 8, 4, 13, 0, 6, 10, 3, 14, 7, 11, 2, 9, 5, 12. By appropriate selection of the type of interleaving and the number of swathing and interleaving channels, printing speed and resolution can be optimized for the deposition characteristics of a particular print head, ink, and substrate combination. Preferably, the carriage and drum are advanced continuously to achieve a smooth and precise helical progression, allowing for high precision deposition of ink drops.
The interleaving can be implemented using interleaving logic that directs appropriate pixels to the interleaved jets. This logic can be implemented in a number of ways, including by the use of dedicated logic circuitry, look-up tables, or software running on a processor, such as a print control processor for a multi-source print head. The logic can be separate from the logic implementing the swathing table, or the two functions may be implemented with some overlap.
By appropriate selection of the type of interleaving and the number of swathing and interleaving channels, therefore, printing speed and resolution can be optimized for the deposition characteristics of a particular print head, ink, and substrate combination. Preferably, the carriage and drum are advanced continuously to achieve a smooth and precise helical progression, allowing for high precision deposition of ink drops. The various features mentioned above in relation to swathing and interleaving are advantageous (but not necessarily essential) and may be independently provided or provided in combination with other features. The provision of deflection along the direction of movement of the carriage (as opposed to conventional deflection perpendicular to the direction of movement) is an important advantageous (but not necessarily essential) feature which may be provided independently.

Claims

A jet printer, comprising:
means for moving (28) a jet printing fluid source (14) relative to a print substrate (32) along a direction of an axis of rotation of a print substrate (32),

means for rotating (30) the print substrate relative to the jet printing fluid source (14) about the axis of rotation such that the combined action of the means for moving (28) and the means for rotating (30) cause the jet printing fluid source (14) to advance in a helical progression with respect to the print substrate (32) during a plurality of drum rotations, characterised by

means for guiding (24, 26) a first drop of printing fluid from the jet printing fluid source so that it lands on the print substrate (32) at a first distance along the direction of the axis of rotation of the print substrate from the jet printing source (14), and for guiding a second drop of printing fluid from the jet printing fluid source (14) so that it lands on the print substrate (32) at a second distance along the direction of the axis of rotation of the print substrate from the jet printing source after the print substrate has rotated, wherein the second distance is different from the first distance.
The jet printer of claim 1 wherein the means for guiding (24, 26) are further for guiding the first and second drops at locations that are spaced apart both longitudinally and radially with respect to the axis of rotation.
The jet printer of claim 1 or 2 wherein the means for moving (28) the jet printing fluid source includes means for moving a carriage that supports the jet printing fluid source.
A jet printer according to any preceding claim wherein:
the means for rotating the print substrate comprises a drum (30) constructed and adapted to receive a print substrate (32), and a drum control interface having an output provided to a motor (34) for rotating the drum,

the means for moving the jet printing fluid source comprises a movable carriage (28), wherein the jet printing fluid source is attached to the carriage, and wherein the carriage includes a carriage mechanism for moving the carriage in the direction of the axis of rotation of the drum, such that the combined action of the carriage mechanism and drum control interface cause the jet printing fluid source to advance in a helical progression with respect to the drum (30) during a plurality of drum rotations,

the means for guiding comprises at least one deflection element (24, 26) located proximate an output trajectory of the jet printing fluid source (14), the deflection element having a deflection axis in the direction of an axis of rotation of the drum,

the first distance and the second distance are determined based on a swathing table, and

the printer further comprises a control circuit (16) responsive to the swathing table and having an output provided to at least the one deflection element.
The jet printer of claim 4 wherein the deflection element (24, 26) comprises a charging tunnel surrounding an output of the jet printing fluid source (14) or wherein the deflection element comprises one of a pair of deflection electrodes.
The jet printer of claim 4 or 5 wherein the swathing table includes a series of different firing order entries that define different deflection amounts for the deflection element (24, 26), whereby the deflection element directs drops from the printing fluid source to a succession of different locations on the printing substrate (32), preferably wherein the drop deflection values and the firing order entries represent voltages, and wherein the voltages are superimposed and provided to the deflection element via a digital-to-analog converter.
The jet printer of any of claims 4 to 6 wherein the swathing table is a stored swathing table.
The jet printer of any of claims 4 to 7 further including a drum actuation controller synchronized with the control circuit (16) to cause printing by the printer to take place according to a helical progression.
The jet printer of any preceding claim arranged to perform a half-tone printing process further comprising a processor portion operative to drive the printer to print half-tone images on a print substrate (32).
The jet printer of any preceding claim further including means for causing a third drop to be deposited adjacent the first drop according to an interleaved print pattern.
The jet printer of any preceding claim wherein the jet printing fluid source (14) is part of a print head and further including interleaving logic having an output provided to the print head.
The jet printer of claim 10 or 11 wherein the means for causing includes at least one of:-
(a) means for causing the third drop to be deposited by a second jet printing fluid source (14) between the first and second distances in the direction of the axis of rotation of the print substrate (32);

(b) means for causing the third drop to be deposited by the first jet printing fluid source (14) between the first and second drops in the direction of the axis of rotation of the print substrate (32), and wherein the deposition of the first and third drops are separated in time by at least about a full revolution of the drum (30);

(c) means for causing the third drop to be deposited adjacent the first drop by a second jet printing fluid source at a second distance along the direction of advance of the print substrate (32), and wherein the first and second distances along the direction of advance of the print substrate are different;

(d) means for causing the third drop to be deposited adjacent the first drop by the first jet printing fluid source (14) at a second distance along the direction of advance of the print substrate, and wherein the first and second distances along the direction of advance of the print substrate (32) are different, and wherein the deposition of the first and third drops are separated in time by at least about a full revolution of the drum (30).
A jet printer according to any preceding claim wherein:
the means for rotating the print substrate comprises a drum (30) constructed and adapted to receive a print substrate (32) and a drum control interface having an output provided to a motor (34) for rotating the drum,

the means for moving the jet printing fluid source comprises a movable carriage and a carriage mechanism (28) for moving the carriage in the direction of the axis of rotation of the drum (30),

the means for guiding (24, 26) comprises a print head including a first jet printing fluid source (14) attached to the carriage and at least one deflection element (24, 26) located proximate an output trajectory of the first jet printing fluid source, the deflection element having a deflection axis in the direction of an axis of rotation of the drum,
wherein the first and second distances are determined based on a swathing table and interleaving logic having an output provided to the print head, and
wherein the printer further comprises a control circuit (16) responsive to the swathing table and having an output provided to at least the one deflection element.
The jet printer of Claim 11 or 13 wherein the print head further includes a second jet printing fluid source attached to the carriage and wherein the interleaving logic is operative to provide interleaved portions of data to be printed by the first and second jet printing fluid sources, most preferably wherein the interleaving logic includes horizontal and/or vertical interleaving logic.
The jet printer of any preceding claim wherein the print substrate (32) placed in the output trajectory of the jet printing fluid source (14) is a printing plate.
A method of jet printing, comprising the steps of:
moving a jet printing fluid source (14) relative to a print substrate (32) along the direction of an axis of rotation of a print substrate (32),

guiding a first drop of printing fluid from the jet printing fluid source (14) so that it lands on the print substrate (32) at a first distance along the direction of the axis of rotation of the print substrate from the jet printing source,

rotating the print substrate (32) relative to the jet printing fluid source about the axis of rotation after the step of guiding a first drop, such that the combined action of the step of moving and the step of rotating cause the jet printing fluid source (14) to advance in a helical progression with respect to the drum (30) during a plurality of drum rotations, and

guiding a second drop of printing fluid from the jet printing fluid source (14) so that it lands on the print substrate (32) at a second distance along the direction of the axis of rotation of the print substrate from the jet printing source after the print substrate has rotated, wherein the second distance is different from the first distance.
The jet printing method of claim 16 further including further steps of guiding further drops of printing fluid from the jet printing fluid source at the first position so that the further drops land on the print substrate at further different distances along the direction of the axis of rotation of the print substrate, after the print substrate has rotated further.
The jet printing method of claim 16 or 17 wherein the steps of guiding and rotating form a part of a half-tone printing process.
The jet printing method of any of Claims 16 to 18 further including the step of depositing a third drop adjacent the first drop according to an interleaved print pattern, preferably wherein the step of depositing includes depositing the third drop by a second jet printing fluid source.
The jet printing method of claim 19 wherein the step of depositing includes:-
(a) depositing the third drop by a second jet printing fluid source between the first and second drops in the direction of the axis of rotation of the print substrate; or

(b) depositing the third drop by the first jet printing fluid source between the first and second drops in the direction of the axis of rotation of the print substrate, and wherein the deposition of the first and third drops are separated in time by at least about a full revolution of the drum (30); or

(c) depositing the third drop adjacent the first drop by a second jet printing fluid source at a second distance along the direction of advance of the print substrate, and wherein the first and second distances along the direction of advance of the print substrate are different; or

(d) depositing the third drop adjacent the first drop by the first jet printing fluid source at a second distance along the direction of advance of the print substrate, and wherein the first and second distances along the direction of advance of the print substrate are different, and wherein the deposition of the first and third drops are separated in time by at least about a full revolution of the drum.
A method according to any of Claims 16 to 20 wherein:
rotating the print substrate comprises rotating the substrate on a drum (30) constructed and adapted to receive the print substrate (32) under control of a drum control interface having an output provided to a motor (34) for rotating the drum;

moving the jet printing fluid source comprises moving the source on a movable carriage having a carriage mechanism (28) for moving the carriage in the direction of the axis of rotation of the drum (30);

guiding the first and second drop of printing fluid comprises guiding the printing fluid from a first jet printing fluid source (14) attached to the carriage using at least one deflection element (24, 26) located proximate an output trajectory of the first jet printing fluid source, the deflection element having a deflection axis in the direction of an axis of rotation of the drum;

the method further comprising:
determining the first and second distances based on a swathing table and interleaving logic having an output provided to the print head; and

providing a control circuit (16) response to the swathing table and having an output provided to the at least one deflection element (24, 26).