Patent Application
20080238995
This invention relates to the field of printing, and more particularly to the field of hybrid printing devices which are able to print onto roll-based print media and flat rigid print media.
Printing devices for large format printing can be categorized according to the type of print media they are adapted to print onto and the manner in which the print media is moved during the printing process.
Roll-to-roll printers typically print onto roll-based print media and convey the print media from a first (feed) roller to second roller or basket. Flatbed printers, on the other hand, typically print onto rigid and flat print media with the print media being fixed to a table and the print head of the printer being moved across the print media during the printing process.
In general, a roll-to-roll printer may be preferred for printing onto flexible print media, such as paper, thin plastic film, clothing, etc., whereas a flatbed printer may be preferred for printing onto rigid print media, such as thick plastic, wood, glass, etc.
Advances in the field of large format printing have led to the development of hybrid printers which are able to print onto both roll-based print media and flat rigid print media. Such hybrid printers combine the functionality of a roll-to-roll printer and a flatbed printer in a single machine, thereby reducing cost and space requirements whilst maintaining the advantages associated with each printing type. This is important since large format printers may be over 5 m in width to cater for large format media and, accordingly, may also be very heavy and expensive.
An illustration of an exemplary hybrid printer device is shown in
The scan axis assembly 8 of the exemplary hybrid printer may be over 5.5 metres long and may weigh over 500 kg, for example.
By controlling the movement of the scan axis assembly 8 and the print head 2 along their respective axes whilst the print head 2 is also controlled to print, flat print media 6 secured on the flat surface 4 can be printed onto as required.
The hybrid printer 1 also comprises a feed roller 9 positioned at one end of the table structure and a rear roller (not visible) positioned adjacent to the feed roller 9. Roll-based flexible print media may then be fed from the feed roller 9 past the print head 2. Such roll-based flexible print media can then be printed onto by moving the print head 2 back and forth along the lateral axis L and controlling the print head 2 to print as the flexible print media is fed from the feed roller 9 to the rear roller past the print head 2.
Thus, it will be understood that the hybrid printer 1 of
Despite the advantages associated with hybrid printers, they also exhibit some drawbacks. One such drawback is that existing hybrid printers are generally unable to cater for print media of differing thicknesses due to their size and weight and the positioning accuracy required. In other words, they do not allow the optimization of Print-head to Print-media Spacing (PPS).
Thus, there is a need to design a hybrid printer that can cater for print media of differing thicknesses, and therefore enable a PPS to be adjusted as necessary. It is also desirable that such a printer is able to print with high accuracy, independently of the thickness of the print media.
For a better understanding of the invention, embodiments will now be described, purely by way of example, with reference to the accompanying drawings, in which:
According to an aspect of the invention, there is provided a hybrid printer adapted to print onto roll-based print media and rigid print media, the printer comprising: a print head that is movable along at least one substantially horizontal scan axis; and drive means adapted to drive lifting means, wherein the lifting means are arranged to cause the scan axis to undergo movement in a substantially vertical direction when driven by the drive means, thereby enabling a distance between the print head and the print media to be adjusted.
While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and described presently preferred embodiments. These embodiments are provided so that this disclosure will be thorough and complete, and will convey fully the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.
Referring to
The scan axis assembly 10 comprises an elongate support member 12 that extends laterally between a left end 14a and a right end 14b and is adapted to support the print head in a generally lateral and horizontal scan axis along which the print head is movable.
The scan axis assembly 10 is supported by a base 16 comprising two laterally spaced apart pair of legs 18a and 18b and a cross member 20 bridging the two pairs of legs. Thus, the base 16 is an elongated frame generally extending in a lateral direction (from the left end 14a to the right end 14b), therefore extending in the same general direction as the scan axis assembly 10.
The base 16 also comprises drive means 22 mounted thereon, the drive means being adapted to drive lifting means 24 (see
The lifting means 24 also comprise four nuts (not visible), each nut being threaded on a different bolt. Each nut is also coupled to a respective different corner of the scan axis assembly 10 such that the lifting means 24 cause the scan axis assembly 10 to undergo movement in a substantially vertical direction when driven by the drive means 22.
More specifically, in the example shown, the drive means 22 are adapted to rotate each nut about the vertically arranged shaft axis of the bolt that the nut is threaded on, thereby causing the nut to move along the shaft. By arranging the nuts to be turned in the same direction of rotation at once (assuming the bolts are of the same left-handed or right-handed type), all four corners of the scan axis assembly 10 may be caused to undergo substantially the same vertical movement at the same time. Of course, it will also be understood that the drive means 22 may also be adapted to rotate the nuts independently of each other, and/or in opposing directions, such that the vertical location of each corner of the scan axis assembly 10 may be adjusted as necessary.
By enabling the scan axis assembly 10 to undergo movement in a substantially vertical direction, a vertical distance between the base 16 and the scan axis assembly 10 can be adjusted as necessary. Since the scan axis assembly 10 is arranged to support and guide lateral movement of the print head, and the cross member 20 of the base 16 is adapted to support print media, a distance between the print head and the print media can be adjusted as necessary. In other words, the invention enables a Print-head to Print-media Spacing (PPS) to be optimised.
For hybrid printers a range of PPS is preferably greater than 20 mm, more preferably greater than 50 mm, and most preferably greater than 100 mm. Since the scan axis assembly 10 of a hybrid printer is typically large and heavy (i.e. over 5 m long and over 500 kg in weight), conventional hybrid printers do not provide such preferred PPS ranges, especially to suitable positioning accuracy. A hybrid printer according to the invention, on the other hand, may provide a range of PPS over 220 mm, and more preferably over 120 mm, and enable the PPS to be adjusted to a preferred degree of tolerance or accuracy.
Turning now to
Further, the scan axis assembly (not shown in
The gear arrangement 32 comprises a worm gear 37, a helical gear 38 arranged to engage with the worm gear 37, and first 40 and second 42 spur gears, wherein the first spur gear 40 is arranged to turn with the helical gear 38 and the second spur gear 42 is arranged to engage with the first spur gear 40 while turning around and moving up and down of bolt 24.
The rotor of the motor 30 is adapted to cause the worm gear 37 to rotate about its shaft axis, thereby causing the helical gear 38 and the first 40 and second 42 spur gears to rotate. The second spur gear 42 is coupled to the nut 34 and is adapted to rotate the nut 34 about the shaft axis of the bolt 24 when the second spur gear 42 rotates. It will therefore be understood that the motor 30 is used to drive the gear arrangement 32 which, in turn, causes the nut 34 to be threaded along the shaft of the bolt 24.
In the illustrated embodiment, one revolution of the motor rotor is divided into M subunits of equal angle and the drive means 22 further comprise an encoder unit 44. The encoder unit 44 is adapted to control the motor 30 so that the motor 30 is restricted to rotating the rotor by an integer number of subunits.
Furthermore, the gear arrangement 32 is designed to have a step-down gearing-ratio (i.e. one revolution of the motor rotor causes less than one revolution of the nut 34), and preferably the step-down gearing ratio is of a high value, for example N:1 where N is the number of revolutions of the motor rotor required to cause the nut 34 to undergo one revolution and N is substantially greater than 1. By way of example, the gearing ratio may be greater than 10:1, is preferably greater than 50:1, and is even more preferably greater than 100:1.
Thus, by controlling the rotor of the motor 30 to only turn in subunits of one revolution, and by adapting the gear arrangement such that a plurality of revolutions of the rotor are required to rotate the nut by one revolution, threading of the nut 34 along the shaft of the corresponding bolt 24 can be accurately adjusted and controlled.
By way of example, the drive means of
Control of the motor 30 using the encoder unit 44 may be achieved by using a dedicated electronic board for the motor 30 together with an input/output circuit board which is arranged to interface with a computer via a suitable connection (i.e. a serial connection, a parallel connection, a Universal Serial Bus (USB), wireless connection, etc.). Thus, the drive means 22 may be monitored and dynamically controlled to ensure that resultant movement of the scan axis assembly is as required. Further, if independent drive means 22 are employed for each lifting means 24, the separate drive means may be monitored and controlled so that any loading is equally shared in order to reduce or prevent twisting of the scan axis assembly 10.
It will therefore be understood that the invention enables the position of the nut 34 on the vertically arranged shaft axis of the bolt 24 to be accurately adjusted and controlled, thereby enabling the vertical position of the scan axis assembly 10 (which the nut 34 supports) to also be accurately adjusted and controlled. The invention therefore enables fine adjustment of the PPS.
As shown in
When being driven to move vertically, it is possible that the scan axis assembly 10 may also move laterally and/or longitudinally within the limits of the guidance system. Further, if the lifting means 24 are independently driven, the scan axis assembly may also rotate or twist about a vertical axis. Such small movements prevent jamming of the scan axis assembly 10 for example.
The guidance and braking arrangement 46 is therefore provided with a guide channel 48 within which a flange 50 coupled to the drive means 22 and/or the scan axis assembly 10 extends. The guide channel 48 is adapted to receive the flange 50 so that the guide channel 48 and flange 50 cooperate to restrict large lateral and/or longitudinal movement of the flange 50. Despite closely fitting the flange 50, the guide channel 48 may be formed to have a suitable spacing from the flange 50 so that there is suitable play therebetween, thereby enabling small adjustments in the lateral and/or longitudinal position of the flange (and therefore the drive means 22 and/or the scan axis assembly) to be made.
Once a desired vertical position of the scan axis assembly 10 has been attained by suitably driving and controlling the drive means 22 coupled to the lifting means 24, the longitudinal position of the scan axis assembly 10 can be adjusted to a desirable position by bringing the scan axis to a datum in longitudinal direction by using a clamping arrangement 52 to clamp the flange 50. In the embodiment of
Similarly, a clamping arrangement may be employed secure the scan axis assembly 10 in a desired lateral position and/or desired position in relation to a vertical axis of twist.
While specific embodiments have been described herein for purposes of illustration, various modifications will be apparent to a person skilled in the art and may be made without departing from the scope of the invention.
