WO2007018504A1

WO2007018504A1 - Printing drum having electromechanical sheet attachment

Info

Publication number: WO2007018504A1
Application number: PCT/US2005/026628
Authority: WO
Inventors: Peter Nedelin
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2005-07-27
Filing date: 2005-07-27
Publication date: 2007-02-15

Abstract

A sheet attachment apparatus for attaching a sheet for printing on a revolving drum comprising a sheet gripper mechanism controllably mounted on the revolving printing drum and operated by an electromechanical actuator, also mounted in the printing drum, and engaged with the gripper.

Description

PRINTING DRUM HAVING ELECTROMECHANICAL SHEET ATTACHMENT

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to printing and, more particularly, but not

exclusively to color laser printing.

Color printing requires each sheet to pass through a sequence of printing

stages, typically each stage imprints a single color ink.

Ink drying and curing adds further stages to the printing sequence.

A typical rotational printing machine uses a drum system. A drum rotates

about its axis, and the drum system typically consists of two or three drums.

Typically an image is first created on a first drum called the image drum or PIP.

The image, initially formed from the laser beam, draws ink and is then transferred

to a blanket on a second drum called the printing drum. The image is then

transferred from the blanket onto a page wrapped around the third drum called the

impression drum. Some types of printing systems may have a two-drum system

where the image is created directly on the printing drum. The impression drum

contains a mechanism to catch the sheet to be printed, attach it to the drum, and

eject it when the printing is done.

Color printers usually use several drum systems, wherein each drum system

prints a different color. The result is a large and expensive machine, being larger as

much as more colors can be used. This mechanism requires accurate registration of

the paper on the various drums one after the other to produce a quality image. Subsequently, printing mechanisms were developed that employ a single

printing drum system. Such a mechanism typically requires the drum system to

rotate several times, printing a different color in each rotation. This requires several

rotations before the page is ejected, depending on the number of colors printed.

Color printers with multiple drum systems are inherently faster than color

printers using a single drum system since they print several sheets concurrently,

wherein each sheet is printed by a different drum in a sequence. To achieve the

same speed a single drum color printer has to rotate the drum much faster,

according to the number of colors printed. Hence, the process of receiving and

ejecting a sheet has to be performed much faster and more accurately. Precise

registration of the sheet is doubly difficult due to the increased speed of the drum.

Typically, the drum contains a recess in which a sheet gripper is mounted.

The gripper is opened as the sheet is guided towards the recess and then closed,

thereby attaching the edge of the sheet to the drum. The gripper is typically kept in

the closed position by a spring and is turned open by a cam mounted co-axially with

the drum's axis. The cam normally rotates with the drum. To open the grippers a

stop station, typically an actuator mounted on a fixed frame, extends an arrestor

hook towards the cam which catches the cam and stops the cam rotation. The

gripper is connected to a lever that is in turn connected at its far end to a cam

follower that rides on the cam on the other end. The perimeter of the camhas

extensions in the radial direction of the drum and the cam follower rides over the

extensions of the cam as it is stopped and forces the gripper to open. The cam follower then travels down the curve of the cam and enables a spring to close the

gripper. The rotary actuator releases the cam before the cam follower reaches the

next extension on the cam and the cam returns to rotate with the drum. The gripper's

opening and closing trajectories are determined by the profile of the cam. A further

description of the prior art is provided below with reference to Figs. 4 and Fig. 5.

Several stop stations may be used to allow the gripper to be opened at

different places along the drum rotation. To enable feeding sheets of different

thickness the cam may be provided with various profiles or may be replaced with a

cam of a different profile, say by operating an external setting.

The cam mechanism is limited by its ability to open the gripper only at

predefined locations on the rotation of the drum. Furthermore, at high speed, the

abrupt stoppage of the cam and the induced trajectory of the gripper create a

vibration that may interfere with the required precision high speed sheet

registration, and the vibration may be passed on to the printing heads, thus

adversely affecting printing.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a sheet

attachment apparatus for attaching a sheet for printing on a revolving drum, the

sheet attachment apparatus containing a sheet gripper mechanism controllably

mounted on the revolving drum and operated by an actuator mounted to rotate with

the revolving drum. According to another aspect of the present invention there is provided a sheet

attachment apparatus wherein the actuator is engaged in non-contact manner with

the 5 gripper mechanism.

According to yet another aspect of the present invention there is provided a

sheet attachment apparatus wherein the actuator is an electromagnetic actuator.

According to still another aspect of the present invention there is provided a

sheet attachment apparatus wherein the_^ electromagnetic actuator contains a

solenoid.

Further according to another aspect of the present invention there is provided

a sheet attachment apparatus wherein the actuator is an electromechanical actuator.

Still further according to another aspect of the present invention there is

provided a sheet attachment apparatus wherein the actuator is constantly engaged

with the gripper mechanism.

Even further according to another aspect of the present invention there is

provided a sheet attachment apparatus wherein the actuator is controlled by a

microcontroller, the microcontroller being operative to instruct the actuator to

execute at least one of closing and opening of the sheet attachment apparatus in a

substantially continuously selectable position along a revolution of the printing

drum.

Even further according to yet another aspect of the present invention there is

provided a sheet attachment apparatus wherein the actuator has an automatically

variable travel length, thereby to permit a selectable spacing for gripping. Even further according to still another aspect of the present invention there is

provided a sheet attachment apparatus wherein the actuator is controlled by a

microcontroller configured to select the spacing.

Additionally according to another aspect of the present invention there is

provided a sheet attachment apparatus wherein the actuator has automatically

variable force affecting at least one of a selectable variable gripping force and a

selectable variable ejection force.

According to further another aspect of the present invention there is provided

a sheet attachment apparatus wherein the actuator is controlled by a microcontroller

configured to select the force.

According to yet another aspect of the present invention there is provided a

sheet attachment apparatus wherein the actuator contains a plurality of coils and

wherein activating different selections of the coils produces at least one of different

travel lengths and different forces.

According to still another aspect of the present invention there is provided a

sheet attachment apparatus wherein the activating the different selections produces

the different travel lengths, and wherein the different travel lengths provide

selectable gripping spacing.

Further according to another aspect of the present invention there is provided

a sheet attachment apparatus wherein the mechanism additionally containing: a

gripper pivotally mounted about an axis to attach a sheet to the drum; and a lever co-pivotally mounted with the gripper and operative to effect the gripper to pivot;

and the actuator containing a shaft mounted to pivot the lever.

Still further according to another aspect of the present invention there is

provided a sheet attachment apparatus wherein the gripper mechanism contains: a

gripper arm pivotally mounted on the drum, a lever, co-pivotally mounted with the

gripper arm; and a spring connected on one end to the lever and on a second end to

the drum, the spring operative to exert force opposite to the actuator; and the

actuator containing a controllably movable shaft pivotally engaged with the lever.

Even further according to another aspect of the present invention there is

provided a printing apparatus containing an image drum; a printing drum; an

impression drum; and a sheet attachment apparatus for attaching a sheet to the

impression drum; and the sheet attachment apparatus containing a sheet gripper

mechanism controllably mounted on the impression drum and operated by an

electromechanical actuator mounted to rotate with the impression drum and to

engage with the gripper mechanism, the actuator operative to open and close the

sheet gripper mechanism.

Even further according to yet another aspect of the present invention there is

provided a printing apparatus wherein the electromechanical actuator is at least one

of: constantly revolving with the impression drum; and constantly engaged with the

gripper mechanism.

Even further according to still another aspect of the present invention there is

provided a printing apparatus wherein the electromechanical actuator is controllable to execute at least one of closing and opening of the sheet attachment apparatus in a

continuously selectable position along a revolution of the impression drum.

Additionally according to another aspect of the present invention there is

provided a printing apparatus wherein the electromechanical actuator is controllable

to open the sheet attachment apparatus to an automatically selectable width, thereby

to adjust for paper thickness.

According to further another aspect of the present invention there is provided a

printing apparatus wherein the electromechanical actuator is controlled by a

microcontroller to execute at least one of closing and opening of the sheet

attachment apparatus with a software selectable force.

According to yet another aspect of the present invention there is provided a

printing apparatus wherein the actuator contains a shaft and a plurality of coils and

wherein a number of the coils is selectably activatable to provide different travel

lengths of the shaft.

According to still another aspect of the present invention there is provided a

printing apparatus wherein the different travel lengths effect at least one of closing

and opening of the sheet attachment apparatus to a selectable opening width.

Further according to another aspect of the present invention there is provided a

printing apparatus wherein the gripper mechanism is operative to pivot about an

axis and grip a sheet on the drum, the gripper mechanism additionally containing a

lever to effect the pivoting, the actuator containing a shaft that is constantly

engaged with the lever. Still further according to another aspect of the present invention there is

provided a printing method for printing on a sheet attached on a revolving drum, the

printing method containing a step of sheet attachment for attaching the sheet to the

drum, the step of sheet attachment containing the steps of: opening a sheet gripper

to receive a sheet; closing the sheet gripper to attach the sheet to the drum; and

opening the sheet gripper to eject the sheet; wherein at least the opening is executed

using a substantially continuously selectable opening position along a revolution of

the drum.

Even further according to another aspect of the present invention there is

provided a further containing setting at least one of: a substantially continuously

selectable opening width; a substantially continuously selectable speed; and a

substantially continuously selectable force.

Unless otherwise defined, all technical and scientific terms used herein have

the same meaning as commonly understood by one of ordinary skill in the art to

which this invention belongs. The materials, methods, and examples provided

herein are illustrative only and not intended to be limiting.

Implementation of the method and system of the present invention involves

performing or completing certain selected tasks or steps manually, automatically, or

a combination thereof. Moreover, according to actual instrumentation and

equipment of preferred embodiments of the method and system of the present

invention, several selected steps could be implemented by hardware or by software

on any operating system of any firmware or a combination thereof. For example, as hardware, selected steps of the invention could be implemented as a chip or a

circuit. As software, selected steps of the invention could be implemented as a

plurality of software instructions being executed by a computer using any suitable

operating system. In any case, selected steps of the method and system of the

invention could be described as being performed by a data processor, such as a

computing platform for executing a plurality of instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to

the accompanying drawings. With specific reference now to the drawings in detail,

it is stressed that the particulars shown are by way of example and for purposes of

illustrative discussion of the preferred embodiments of the present invention only,

and are presented in order to provide what is believed to be the most useful and

readily understood description of the principles and conceptual aspects of the

invention. In this regard, no attempt is made to show structural details of the

invention in more detail than is necessary for a fundamental understanding of the

invention, the description taken with the drawings making apparent to those skilled

in the art how the several forms of the invention may be embodied in practice.

In the drawings:

Fig. 1 is a simplified illustration of a sheet attachment apparatus according to a

preferred embodiment of the present invention;

Fig. 2 is a simplified illustration of a sheet attachment apparatus according to

another preferred embodiment of the present invention; Fig. 3 is a simplified illustration of the sheet attachment apparatus of Fig. 1

in the sheet ejection position;

Figs. 4 is a simplified illustration of a sheet attachment apparatus according

to the prior art;

Figs. 5 is a simplified illustrations of the sheet attachment apparatus of Fig. 4

in the open position; and

Fig. 6 is a simplified illustration of a preferred embodiment of the present

invention comprising a printing assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The principles and operation of a sheet attachment apparatus and method

according to the present invention may be better understood with reference to the

drawings and accompanying description.

Before explaining at least one embodiment of the invention in detail, it is to

be understood that the invention is not limited in its application to the details of

construction and the arrangement of the components set forth in the following

description or illustrated in the drawings. The invention is capable of other

embodiments or of being practiced or carried out in various ways. Also, it is to be

understood that the phraseology and terminology employed herein is for the purpose

of description and should not be regarded as limiting.

Reference is now made to Fig. 1, which is a simplified illustration of a sheet

attachment apparatus according to a first embodiment of the present invention. As shown in Fig. 1, an impression drum 10, revolving around axis 11, comprises a

recess 12, in which a gripper 13 is mounted. The gripper 13 (also referred to

hereinbelow as a gripper arm or a clamping arm) is shown in the open position and

is operative to clamp an edge of a sheet to the floor of the recess 12. The gripper 13

comprises a lever 14 operative to maneuver the gripper about a pivot 15. The

gripper 13 is typically kept in the closed position by a spring 16 pulling lever 15. In

the closed position the gripper attaches a sheet 17 to the recess 12 of the drum 10 by

the edge of the sheet 17 as shown in Fig. 22. An electromechanical actuator 18 is

operative to push the lever 14, against the pull of the spring 16, and cause the

gripper 13 to open to accept or release the sheet. The electromechanical actuator 18

is typically constantly engaged with the lever 14 via a pivot 19.

It is appreciated that several types of actuators are useful to operate the

gripper. Such devices may be a linear actuator, a rotary actuator, a stepping motor,

etc. The gripper, lever and the spring are referred to hereinbelow as a gripping

mechanism.

The lever 14, the spring 16 and the actuator 18 are typically mounted inside

the drum 10. The drum is typically a cylinder with two side panels and the actuator

is typically mounted on the inner side of the cylinder's side panel. Alternatively the

lever 14, the spring 16 and the actuator 18 can be mounted on the outer side of the

side panel of the drum. As a further alternative, the lever 14, the spring 16 and the

actuator 18 can be mounted on a special mount inside the cylinder, typically at the center of the cylinder. In all these alternatives the actuator 18 is continuously

rotating with the drum 10.

The gripper may be held in the closed position by the spring and is forced

open by activating the actuator. Alternatively the gripper is held in the closed

position by the actuator and is opened by the spring when the actuator is

deactivated. As a further alternative, the actuator comprises a pair of solenoids, or a

bipolar solenoid, able to force the gripper to open and to close. The actuator 18 is

activated by inducing an electric current via the actuator's conductors 20. The

conductors 20 are connected between the actuator and a pair of conductive rings 21.

A pair of brushes 22 provides electrical contacts between the rings 21 and another

pair of conductors 23 that connects to a controller 24. The controller 24 provides

the current that energizes the actuators to switch the gripper's position in the

required time. The controller is typically mounted on a fixed frame.

The controller 24, typically comprising a microcontroller, is able to operate

the actuator and thereby open or close the gripper at any point along the rotation of

the drum without being limited by stopping stations and the like. By controlling the

amount of current in one embodiment the controller is able to control the width of

the opening of the gripper, for example to adapt the opening to different sheet

thickness. Additionally, different current values induce different opening forces.

The opening force effects the ejection of the sheet, giving the sheet the velocity

required to travel away from the drum and into the sheet collection tray. Different sheets, having different weights, require different ejection

forces. Additionally, the shape of the pulse of the current applied to the actuator

also affects 30 the acceleration and the speed of opening and closing the gripper.

Similarly, if the actuator is arranged to force the gripper closed the amount

of current determines the force applied on the sheet, thus adapting the force to the

sheet's softness, weight, smoothness, etc. ;

Reference is now made to Fig. 2, which is a simplified illustration of a sheet

attachment apparatus according to another preferred embodiment of the present

invention. The embodiment of Fig. 2 is similar to the embodiment of Fig. 1 except

for the following differences. In Fig. 2, the spring 16 is mounted in-line with the

lever 14 and holds the lever in position whether closed or open. Additionally, the

gripper mechanism of Fig. 2 is activated by an actuator 25 that comprises a pair of

solenoids 26 and is operative to force the lever to change positions between the

open and closed positions.

As shown in Fig. 2, the actuator 25 has two pairs of conductors 20 and

accordingly there are two pairs of rings 21, two pairs of brushes 22 and two pairs of

conductors 23 connecting to two output ports of the controller 24.

When changing positions the actuator pushes the lever, which depresses the

spring, and after the spring passes its maximum tension it pushes the lever to the other

position. Alternatively the spring can be mounted to pull the lever into the closed or

open positions. Alternatively, the actuator may comprise two coils 27, typically of different

size, activating the shaft of the actuator in the same direction, however, effecting a

different stroke length. This configuration requires the spring arrangement of Fig. 1.

In this configuration the controller can selectively activate the smaller coil to cause

the gripper to open to a small width or force. Alternatively the controller can

selectively activate the larger coil to cause the gripper to open to a medium width or

force. Further alternatively the controller can activate both coils and open the

gripper to a maximum width or force. Thus the controller can adjust the opening

width to the thickness or weight of the sheet (or the closing force if configured to

close the gripper).

Reference is no made to Fig. 3, which is a simplified illustration of a sheet

30 attachment apparatus according to the preferred embodiment of the present

invention described with reference to Fig. 1. As shown in Fig. 3, the gripper 13 is

opened to eject the sheet 17. An ejector 28, which is a part of the gripper, rotates

and pushes the edge of the sheet 17 away from the drum 10 and into a collection

tray (not shown).

Reference is now made to Fig. 4, which is a simplified illustration of a

typical sheet attachment apparatus according to the prior art

Figs. 4 shows a drum 29, with a recess 30, in which a gripper 31 is mounted.

A lever 32 and a spring 33 hold the gripper in a normally closed position. A cam 34

is mounted on the axle 35 of the drum 29 and freely rotates with the drum. At least one actuator 36 is mounted on a fixed frame 37 (and not on the drum). The

controller 38 controls the actuator 39.

Reference is now made to Fig. 5, which is a simplified illustration of the

sheet attachment apparatus described with reference to Fig. 4 in the open position.

As shown in Fig. 5, the controller 40 activated the actuator 41, which extended an

arrestor 42, which stopped the cam 34 by catching a cam stopper 43. As the drum

29 continues to rotate, a cam follower 44 that rides on the perimeter of the cam 34

pushes the lever 32 against the pull of the spring 33. The lever 32 rotates and opens

the gripper 31. After the lever 32 reaches the apex of the cam 34 the lever 32

continues to travel down the curve of the cam 32 and enables the spring 33 to close

the gripper 31. The controller 45 deactivates the actuator 46, which releases the cam

34, typically before the cam curves up again. The cam 34 then returns to rotate with

the drum 29.

Therefore the actuator 42 is able to open the gripper 31 only at a few discrete

positions, according to the number and positions of the cam stoppers 43 along the

cam circumference. Furthermore, the gripper 31 can be opened only to a specific

width defined by the shape of the cam 34. To have more opening positions, more

actuators, such as actuator 47, are required. To enable different opening widths the

cam may either be replaced with a cam of an adequate shape or a mechanical

adjustment may be made to the shape of the lever.

Contrary to the prior art, the preferred embodiment of the present invention,

as described in Figs. I and 22 use a single actuator 18, typically mounted to rotate with 30 the drum 10. The solenoid operates directly on the lever and is thus

operative to open or close the sheet gripper 13 at any point along the rotation of the

drum 10. The solenoid 18 is in this sense typically constantly engaged with the

sheet gripper 13 and typically continuously rotates with the drum 10. As can be seen

in Figs. 4 and 5, the rotary solenoid 36 of the prior art is mounted on the fixed

frame 37 and not on the drum 29. In the prior art it is the shape of the cam and the

location of the stopping stations that determines the possible opening positions and

the width of the opening. However, in the present embodiments the controller is

able to activate the opening of the gripper practically at any point along the rotation

of the drum and to effect different opening width, or ejection force, by selecting one

of the actuator's coils, or 10 by inducing a different electrical current. Reference is

now made to Fig. 6, which is a simplified illustration of a further embodiment of

the present invention comprising a printing assembly 48 for printing on a sheet. The

printing assembly 48 comprises an image drum 49 on which writing heads 50 create

a static image that collects color ink from ink dispensers 51. Excess ink is removed

by element 52. Typically, the image drum transfers the ink comprising the image to

be printed to a printing drum 53. A sheet 54 that is to be printed is fed from a sheet

dispenser 55 to an impression drum 56. A sheet gripper 13 catches the edge of the

sheet and wraps the sheet around the impression drum. The printing drum then

transfers the ink onto the sheet. The three drums rotate together. As can be seen in

Fig. 6 and in accordance with Figs 1 and 2, the gripper 13 is operated by a solenoid 18 mounted inside or on the side of the impression drum 56. Typically the solenoid

18 rotates continuously with the drum 56.

Alternatively the printing assembly comprises only the image drum and the

impression drum, so that the image drum transfers the ink directly onto the sheet

wrapped around the impression drum.

It is expected that during the life of this patent many relevant sheet

attachment devices and printing systems will be developed and the scope of the

terms herein is intended to include all such new technologies a priori.

It is appreciated that certain features of the invention, which are, for clarity,

described in the context of separate embodiments, may also be provided in

combination in a single embodiment. Conversely, various features of the invention,

which are, for brevity, described in the context of a single embodiment, may also be

provided separately or in any suitable sub-combination.

Although the invention has been described in conjunction with specific

embodiments thereof, it is evident that many alternatives, modifications and

variations will be apparent to those skilled in the art. Accordingly, it is intended to

embrace all such alternatives, modifications and variations that fall within the spirit

and broad scope of the appended claims.

All publications, patents and patent applications mentioned in this

specification are herein incorporated in their entirety by reference into the

specification, to the same extent as if each individual publication, patent or patent

application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application

shall not be construed as an admission that such reference is available as prior art to

the present invention.

Claims

WHAT IS CLAIMED IS:

1. A sheet attachment apparatus for attaching a sheet for printing on a _;

revolving drum, said sheet attachment apparatus comprising a sheet gripper

mechanism controllably mounted on said revolving drum and operated by an

actuator mounted to rotate with said revolving drum.

2. A sheet attachment apparatus according to claim 1 wherein said

actuator is engaged in non-contact manner with said gripper mechanism.

3. A sheet attachment apparatus according to claim 1 wherein said

actuator is an electromagnetic actuator.

4. A sheet attachment apparatus according to claim 3 wherein said

electromagnetic actuator comprises a solenoid.

5. A sheet attachment apparatus according to claim 1 wherein said

actuator is an electromechanical actuator.

6. A sheet attachment apparatus according to claim 1 wherein said

actuator is constantly engaged with said gripper mechanism.

7. A sheet attachment apparatus according to claim 1 wherein said

actuator is controlled by a microcontroller, said microcontroller being operative to instruct said actuator to execute at least one of closing and opening of said sheet

attachment apparatus in a substantially continuously selectable position along a

revolution of said printing drum.

8. A sheet attachment apparatus according to claim 1 wherein said

actuator has an automatically variable travel length, thereby to permit a selectable

spacing for gripping.

9. A sheet attachment apparatus according to claim 8 wherein said

actuator is controlled by a microcontroller configured to select said spacing.

10. A sheet attachment apparatus according to claim 1 wherein said

actuator has automatically variable force affecting at least one of a selectable

variable gripping force and a selectable variable ejection force.

11. A sheet attachment apparatus according to claim 10 wherein said

actuator is controlled by a microcontroller configured to select said force.

12. A sheet attachment apparatus according to claim 1 wherein said

actuator comprises a plurality of coils and wherein activating different selections of

said coils produces at least one of different travel lengths and different forces.

13. A sheet attachment apparatus according to claim 12 wherein said

activating said different selections produces said different travel lengths, and wherein said different travel lengths provide selectable gripping spacing.

14. A sheet attachment apparatus according to claim 1 wherein said

mechanism additionally comprising:

a gripper pivotally mounted about an axis to attach a sheet to said drum; and

a lever co-pivotally mounted with said gripper and operative to effect said

gripper to pivot;

said actuator comprising a shaft mounted to pivot said lever.

15. A sheet attachment apparatus according to claim 1 wherein:

said gripper mechanism comprises:

a gripper arm pivotally mounted on said drum,

a lever, co-pivotally mounted with said gripper arm; and

a spring connected on one end to said lever and on a second end to

said drum, said spring operative to exert force opposite to said actuator;

said actuator comprising a controllably movable shaft pivotally engaged

with said lever.

16. A printing apparatus comprising:

an image drum;

a printing drum;

an impression drum; and

a sheet attachment apparatus for attaching a sheet to said impression drum; said sheet attachment apparatus comprising a sheet gripper mechanism

controllably mounted on said impression drum and operated by an

electromechanical actuator mounted to rotate with said impression drum and to

engage with said gripper mechanism, said actuator operative to open and close said

sheet gripper mechanism.

17. A printing apparatus according to claim 16 wherein said

electromechanical actuator is at least one of:

constantly revolving with said impression drum; and

constantly engaged with said gripper mechanism.

18. A printing apparatus according to claim 16 wherein said

electromechanical actuator is controllable to execute at least one of closing and

opening of said sheet attachment apparatus in a continuously selectable position

along a revolution of said impression drum.

19. A printing apparatus according to claim 16 wherein said

electromechanical actuator is controllable to open said sheet attachment apparatus

to an automatically selectable width, thereby to adjust for paper thickness.

20. A printing apparatus according to claim 16 wherein said

electromechanical actuator is controlled by a microcontroller to execute at least one

of closing and opening of said sheet attachment apparatus with a software

selectable force.

21. A printing apparatus according to claim 16 wherein said actuator

comprises a shaft and a plurality of coils and wherein a number of said coils is

selectably activatable to provide different travel lengths of said shaft.

22. A printing apparatus according to claim 21 wherein said different

travel lengths effect at least one of closing and opening of said sheet attachment

apparatus to a selectable opening width.

23. A printing apparatus according to claim 16 wherein said gripper

mechanism is operative to pivot about an axis and grip a sheet on said drum, said

gripper mechanism additionally comprising a lever to effect said pivoting, said

actuator comprising a shaft that is constantly engaged with said lever.

24. A printing method for printing on a sheet attached on a revolving

drum, said printing method comprising a step of sheet attachment for attaching said

sheet to said drum, said step of sheet attachment comprising the steps of:

opening a sheet gripper to receive a sheet;

closing said sheet gripper to attach said sheet to said

drum; and opening said sheet gripper to eject said sheet;

wherein at least said opening is executed using a substantially continuously selectable opening position along a revolution of

said drum.

25. The printing method of claim 25 further comprising setting at least one

of a substantially continuously selectable opening width;

a substantially continuously selectable speed; and

a substantially continuously selectable force.