GB2298821A

GB2298821A - A ribbon winding mechanism

Info

Publication number: GB2298821A
Application number: GB9505216A
Authority: GB
Inventors: Steven Buckby; Keith Buxton
Original assignee: Prestek Ltd
Current assignee: Markem Imaje Industries Ltd
Priority date: 1995-03-15
Filing date: 1995-03-15
Publication date: 1996-09-18
Also published as: DE69602524T2; EP0814960B1; WO1996028304A1; ATE180213T1; DE69602524D1; GB9505216D0; ES2132902T3; GB9710372D0; GB2310405A; GB2310405B; EP0814960A1

Abstract

A winding mechanism (10) capable of winding a ribbon (13) or similar in for example, a printing apparatus, comprises a supply spool (11) and a take-up spool (14). A ribbon path exists between the ribbon (13) and the spools (11, 14), along which a printing station (20) may be situated, a motive means causes the ribbon (13) to move along said path and wind onto the take-up spool (14). A sensing means (22) senses the movement of the ribbon (13) as the take-up spool (14) rotates and provides an input to a control means (25) which provides a signal along line (26) and thus controls the motive means.

Description

Title: Winding Mechanism Description of the Invention This invention relates to a ribbon winding mechanism for a printing apparatus, the mechanism being of the kind in which ribbon on a storage spool is fed along a path, for example past a printing station, onto a take-up spool.

The ribbon may for example be thermal transfer ribbon used in a thermal printing apparatus as described in detail in our previous published International patent application number W094/26526, or an inked ribbon or any other ribbon used in printing or similar processes. In another example the ribbon may comprise a backing web carrying a plurality of labels which are removed from the web as the web is fed along the path between the storage and take-up spools.

It is desirable in many printing apparatus, to be able to advance the ribbon from the storage onto the take-up spool, in accurate incremental amounts.

For example in a thermal printing apparatus the ribbon used is an expensive consumable and hence it is desirable to advance the ribbon a minimum amount between printing operations to save on wastage of ribbon.

Presently there are a number of methods utilised in a thermal printing apparatus for achieving winding of ribbon between printing operations. Such ribbon can be provided on a cassette which is removed when all the ribbon is used up, and another cassette containing a full ribbon storage spool is inserted into the apparatus.

A first known method of achieving ribbon winding is by directly driving the take-up spool and controlling the amount of rotation of the take-up spool.

The advantages of this are: 1) despite space constraints if the winding mechanism is designed correctly, the mechanics of it can be relatively simple and reliable; 2) the simplicity means that the solution is low cost.

However this method has clear disadvantages in that the system to drive the take-up spool appropriately in order to advance the ribbon a desired amount, is complex, and in fact, not practically possible to do with a desired accuracy in a foolproof manner. The system is open to operator intervention leading to ribbon advance errors. This is because the diameter of the take-up spool will increase as the ribbon is wound onto it.

Although the relationship between the effective increase in spool diameter and the amount of rotation of the take-up spool can theoretically be calculated, this relies on the ribbon being of a constant thickness, and there being assumed constant and repeatable ribbon tension. In practice it is not realistic to assume a constant tension, or that different ribbons all have the same thickness.

Furthermore, if an operator removes a roll or modifies the effective diameters of the spools by hand winding ribbon, which can often occur in a production run due to printer faults and ribbon breakage, then the method is wide open to errors.

If for example an operator intervenes, by fitting a new supply spool of ribbon, but does not reset the control system mechanism, the calculation performed may assume an effective starting diameter of the take-up spool which is nothing like the actual effective diameter, so that the amount of ribbon advanced will be significantly in error compared with what is required.

A second known method of achieving accurate ribbon winding, is to advance the ribbon through the path between the supply and take-up spools, by means of a drive roller assembly and to control the drive roller assembly.

The advantage of this method is that it drives the ribbon very accurately, independently of the supply and take-up spools and hence irrespective of ribbon diameter on the spools, and is hence not prone to the errors arising in the first known method.

The disadvantage however is that the mechanism is more complex, having more components such as the drive roller etc. Hence it is more expensive in general terms than a mechanism which operates according to the first method.

Furthermore, in apparatus where available space is highly constrained, in order to avoid reliability problems, a high standard of engineering is required which can further increase costs.

According to a first aspect of the invention we provide a ribbon winding mechanism for a printing apparatus, the mechanism comprising a supply spool and a take-up spool and there being a ribbon path between the supply and take-up spools, a motive means to cause the ribbon to be moved along the path and wound onto the take-up spool, characterised in that a sensing means is provided to sense movement of the ribbon as the take-up spool is rotated and to provide a signal to a control means which thus controls the motive means.

Hence using the simpler mechanics of the existing ribbon wind mechanism which operates according to the first prior art method described, in combination with a sensing means to sense ribbon movement e.g. along the path, a ribbon wind mechanism having the advantages of the mechanism which operates according to the second prior art method described, can be achieved.

The take-up spool may conveniently be driven by a stepper motor for example, so that the number of steps stepped by the motor can be controlled by the control means in response to the sensing means, to advance the ribbon an accurate amount.

The sensing means may comprise an idler roller which is in contact with the ribbon as the ribbon is wound onto the take-up spool and is thus rotated as the ribbon moves, there being means to determine the amount of rotation of the idler roller for a given amount of movement of the take-up spool so that rotation of the idler roller can be related to the amount of ribbon movement.

In one arrangement, there is provided a magnetised element which is rotatable with and may be mounted on the idler roller and there is at least one magnetic sensor to sense movement of the magnetised element thus to determine the amount of rotation of the idler roller.

In another example, the amount of rotation of the idler roller may be sensed by an optical system which for example includes an optical element carried for rotation with the idler roller, and an optical sensor operable to sense when the optical element moves past the sensor.

In each case, the idler roller may be coated with a high friction material to ensure that there is no slippage between the ribbon and the roller.

If desired, the idler roller may be mounted to rotate with a spindle which may carry the magnetic, optical or other element the movement of which is sensed by an appropriate sensor.

Preferably the mechanism is initially calibrated when the ribbon is loaded (or reloaded) into the mechanism, by the motive means advancing a portion of the ribbon onto the take-up spool whilst a known amount of rotation of the take-up spool caused by the motive means is related by the control means to the amount of ribbon movement sensed by the sensing means and the outside diameter of the idler roller. Thereafter, as the effective diameter of the take-up spool increases as ribbon is used up and wound onto the take-up spool, the control means repeatedly relates the amount of rotation of the take-up spool caused by the motive means to the amount of ribbon movement sensed by the sensing means so as to achieve a required amount of ribbon movement in each incremental step.

According to a second aspect of the invention we provide a printing apparatus having therein a ribbon winding mechanism according to the first aspect of the invention.

The printing apparatus may comprise an apparatus of the thermal transfer printing type, in which case the ribbon may comprise a thermally sensitive ribbon comprising a backing and ink deposited upon the backing, the ink being transferable by means of a thermal print head from the backing onto a substrate.

During a printing operation, the print head may be moveable relative to a stationary ribbon and substrate, or alternatively during printing, the print head may be stationary and the ribbon and substrate moved past the printing head.

In each case, between printing operations, the ribbon may be wound onto the take-up spool an accurately determined amount, by the method of the first aspect of the invention.

The invention will now be described with reference to the accompanying drawings in which: Figure 1 is a purely illustrative view of a ribbon winding mechanism operable by a method in accordance with the invention; Figure 2 is a plan view of an idler roller of the mechanism of Figure 1; Figure 3 is a side view of an alternative form of an idler roller which may be used in the mechanism of Figure 1.

Referring to the drawings, a ribbon winding mechanism 10 comprises a ribbon supply spool 11 including a hub 12 around which ribbon 13 is wound.

The mechanism 10 further comprises a ribbon take-up spool 14, having a hub 15 onto which the ribbon 13 is wound. Hence there is a ribbon path between the supply spool 11 and the take-up spool 14 around a plurality of simple idler rollers indicated at 16 to guide the ribbon 13, and an idler roller indicated at 17, of a sensing means 22, such that the ribbon path is through a printing station indicated at 20.

In one embodiment of the invention, the ribbon winding mechanism 10 is utilised in a printing apparatus in which the ribbon 13 comprises a thermally sensitive ribbon having a backing web and ink deposited on the web.

During printing, relative movement occurs between a print head at the printing station 20, and the ribbon 13 and individually energisable heating elements of the print head cause ink to be deposited from the ribbon 13 onto an adjacent substrate.

The print head may be moveable relative to a stationary ribbon and substrate during printing, or else the ribbon and substrate may be moved relatively to a stationary print head.

A fuller description of one such printing apparatus which operates according to these principles is contained in our co-pending International patent application number WO94/26526.

During the printing operation or between printing operations as appropriate, the ribbon 13 is unwound from the supply spool 11, moved along the ribbon path and fed onto the take-up spool 14, by rotating the take-up spool 14 using an appropriate motive means. One appropriate motive means would be a stepper motor, such that movements of the take-up spool 14, and hence the amount of ribbon 13 moved can accurately be controlled.

In accordance with the present invention, the idler roller 17 and an appropriate sensor system 21 together comprise the sensing means 22 which senses ribbon movement, in this example, along the ribbon path. The outer diameter of the idler roller 17 is accurately known and hence the amount of ribbon movement for a given rotation of the take-up spool 14 can be determined.

Hence the ribbon 13 can be advanced along the ribbon path an accurate amount by rotating the take-up spool 14 an appropriate amount.

The idler roller 17 is preferably carried on a spindle 18. In the arrangement shown in Figure 2 there is an example of idler roller 17 which may be used. The idler roller 17 is coated with a coating 23 which is an antislip coating to prevent slippage occurring between the ribbon 13 and the idler roller 17 when the ribbon 13 is moved. The outer diameter of the coated roller 17 is measured at the outside surface of the coating for optimum accuracy in the mechanism.

In the example of Figure 2, the idler roller 17 is carried on a spindle 18 and may rotate relative to the spindle 18. On an end surface of the idler roller 17 there is provided a magnetic disc 24, which will have a north and south pole as indicated in Figure 2.

Nearby roller 17, there is a magnetic sensor 21 which can monitor rotation of the idler roller 17 by determining when a north and/or south pole of the disc 24 passes the sensor 21. In another arrangement, a pair of magnetic sensors may be provided which, as the idler roller 17 rotates, gives two phase shifted sine waves, which, if the phase difference of which is signal processed at a high frequency by a control means 25 will give a very accurate measure of the rotational movement of the idler roller 17.

The sensor 21 or sensors provide an input to the control means 25 which for a subsequent ribbon movement provides a signal e.g. along line 26 to the stepper motor driving the take-up spool 24, to cause the stepper motor to step a calculated number of steps to achieve a desired amount of ribbon movement.

For each subsequent movement of ribbon 13, the control means 25 is able to determine by the sensor means 22, the amount of ribbon movement which has occurred for a given number of steps stepped by the stepper motor during the previous ribbon movement. Hence for each subsequent movement of the take-up spool, the number of steps stepped may be adjusted to ensure that the amount of ribbon movement will be, accurately, a desired amount.

It will be appreciated that in a printing apparatus such as described in our prior International patent application number W094/26526 the ribbon 13 would be carried on spools 11 and 14 on a cassette which is inserted into the main printing apparatus. It is arranged such that upon the or each occasion when a ribbon cassette is inserted into the printing apparatus the stepper motor which drives the take-up spool 14 is rotated a predetermined number of steps to wind a portion of the ribbon onto the spool 14, and the corresponding amount of ribbon movement sensed by sensor 22 to provide an initial calibration. If the ribbon is not provided on a cassette, this initial calibration needs to be performed each time the ribbon is rethreaded along the ribbon path, or otherwise attended to by an operator.

Another arrangement, of idler roller 17a is shown in Figure 2.

Attached to the roller 17a is a gear 24a which has a plurality of teeth 24b. Such a idler roller 17a may be used in conjunction with an optical sensing system so that the number of teeth 25 passing for example an optical sensing element can be counted, so that again an accurate determination of the rotational movement of the driven roller 17a can be determined by knowing the external or outer diameter of the roller 17a and a signal fed to the control means 25 which thus adjusts the number of steps stepped by a stepper motor driving the take-up spool 14 in à subsequent ribbon movement. One tooth 24c may be bigger than the other teeth, as a check on the number of full rotations occurring.

Various modifications may be made without departing from the scope of the invention. For example, the sensing means described with reference to Figures 1 and 2 or Figures 1 and 3 are only examples of appropriate sensing means for sensing movement of the ribbon 13 as the take-up spool 14 is rotated.

For example, a more sophisticated optical encoding system may be used to determine the amount of rotational movement of the idler roller 17.

It is not essential that there is provided a stepper motor to provide driving power to the take-up spool 14, but another motive means could instead be provided, such as a servo controlled motor, which allows for accurate control of the rotation of the take-up spool 14.

Although the invention has been described with reference to a ribbon winding mechanism 10 for a thermal printing apparatus, the invention may be applied to any other kind of printing apparatus, in which there is a ribbon winding mechanism for winding ribbon from a supply spool 11 onto a take-up spool 14 and where it is desired to advance the ribbon incrementally by accurate amounts.

It will be appreciated that the invention does not preclude rewinding the ribbon 13 from the take-up spool 14 onto the supply spool 11 in an arrangement where for example it is desired to rewind ribbon onto the supply spool 11 for example to allow a particular area of ribbon repeatedly to be used for printing or to allow for use of multi-pass ribbons. The sensing means 22 may provide a measure of the amount of ribbon movement in a direction opposite to that indicated by the arrows A in the drawing which is the normal direction for ribbon movement. In this event, of course the take-up spool 14 would perform the function of a supply spool, and the supply spool 11 would be performing the function of a take-up spool with there being a motive means which allows for the selective driving of the take-up and supply spools 14, 11.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A ribbon winding mechanism for a printing apparatus, the mechanism comprising a supply spool and a take-up spool and there being a ribbon path between the supply and take-up spools, a motive means to cause the ribbon to be moved along the path and wound onto the take-up spool, characterised in that a sensing means is provided to sense movement of the ribbon as the take-up spool is rotated and to provide a signal to a control means which thus controls the motive means.

2. A ribbon winding mechanism according to claim 1 wherein the take-up spool is driven by a stepper motor such that the number of steps stepped by the motor is controlled by the control means in response to the sensing means, to advance the ribbon an accurate amount.

3. A ribbon winding mechanism according to claim 1 or 2, wherein the sensing means comprises an idler roller which is in contact with the ribbon as the ribbon is wound onto the take-up spool and is thus rotated as the ribbon moves, there being means to determine the amount of rotation of the idler roller for a given amount of movement of the take-up spool so that rotation of the idler roller can be related to the amount of ribbon movement.

4. A ribbon winding mechanism according to claim 3 wherein the outside diameter of the idler roller is known.

5. A ribbon winding mechanism according to claim 3 or 4 wherein the idler roller is coated with a high friction material to ensure that there is no slippage between the ribbon and the roller.

6. A ribbon winding mechanism according to claim 3,4 or 5, wherein the sensing means comprises a magnetised element which is rotatable with the idler roller and there is at least one magnetic sensor to sense movement of the magnetised element thus to determine the amount of rotation of the idler roller.

7. A ribbon winding mechanism according to claim 3, 4 or 5, wherein the sensing means comprises an optical element which is rotatable with the idler roller, and an optical sensor operable optically to sense when the optical element moves past the sensor.

8. A ribbon winding mechanism according to claim 6 or 7 wherein the idler roller is mounted to rotate with a spindle which carries the magnetised or optical element.

9. A ribbon winding mechanism according to claim 6 or 7 wherein the magnetised or optical element is mounted on the idler roller.

10. A ribbon winding mechanism according to any preceding claim wherein the mechanism is initially calibrated when the ribbon is loaded (or reloaded) into the mechanism, by the motive means advancing a portion of the ribbon onto the take-up spool whilst a known amount of rotation of the take-up spool caused by the motive means is related by the control means to the amount of ribbon movement sensed by the sensing means and the outside diameter of the idler roller.

11. A ribbon winding mechanism according to claim 10 wherein during operation, as the effective diameter of the take-up spool increases as ribbon is used up and wound onto the take-up spool, the control means repeatedly relates the amount of rotation of the take-up spool caused by the motive means to the amount of ribbon movement sensed by the sensing means so as to achieve a required amount of ribbon movement in each incremental step.

12. A printing apparatus having therein a ribbon winding mechanism according to any one of claims 1 to 11.

13. A printing apparatus according to claim 10 wherein it comprises an apparatus of the thermal transfer printing type, the ribbon being a thermally sensitive ribbon comprising a backing and ink deposited upon the backing, the ink being transferable by means of a thermal print head from the backing onto a substrate.

14. A printing apparatus according to claim 12 or 13 wherein during a printing operation, the print head is moveable relative to a stationary ribbon and substrate, or alternatively during printing, the print head is stationary and the ribbon and substrate are moved past the printing head.

15. A ribbon winding mechanism substantially as hereinbefore described with reference to the drawings of Figures 1 to 3.

16. Any novel feature or novel combination of features as herein defined and/or shown in the accompanying drawings.