Description of Invention

This invention relates to a printing apparatus, and more particularly to a printing apparatus in which a marking medium is carried on a carrier such as a ribbon which is fed along a ribbon feed path past a printing station from a storage spool onto a take-up spool.

In general, the ribbon will be a thermal transfer ribbon comprising a continuous web having thereon a coating of marking medium e.g. ink.

Prior art printers are known, being of the so-called hot foil type. They are simple and relatively cheap. They carry a whole image to be printed in the form of a printing block. During a printing cycle, the printing block is moved out into contact with a carrier such as an inked ribbon such that under the pressure thus applied, in combination with heat also applied to or by the printing block, ink is transferred from the ribbon onto the substrate. The movement of the printing block may be effected by a simple piston and cylinder arrangement. However, such printers are not flexible or adaptable. To change the image to be printed, the printing block must be replaced or physically modified. In addition, the ribbon and substrate to be printed on, must be stationary at the printing station when a printing cycle occurs.

An alternative form of printing apparatus currently available also uses carrier comprising thermal transfer ribbon, but in such printers, the print head comprises a, usually linear, array of selectively energisable heating elements which are successively energised, or not energised, as the print head moves relative to the ribbon and substrate along the ribbon and substrate to transfer pixels of ink or other marking medium onto the substrate to print the image. Such printers are considered to be intelligent, since the image to be printed is infinitely variable and alterable by computer controlled means. In addition, the substrate and ribbon

need not be stationary during a printing operation.

However, accurate synchronisation of relative motion between the print head, and the ribbon and substrate with the incremental pixel patterns set up on the print head is necessary. This is typically achieved by means of a computer control to control the energisation of the printing elements, and one or more stepper motors to effect the relative motion between the print head, and the ribbon and substrate. That is, computer control sets up a first line pattern in the print head, the printing elements of the head are energised and pixels of ink are transferred from the ribbon to the substrate. Then, the computer control instructs the or one of the stepper motors to increment one or more steps of relative motion, and the next pattern is set up on the print head and then further pixels of ink are transferred.

This continues until the entire image has been printed. Such apparatus is considered to be intelligent since the image is set by computer control and is readily alterable. The ability to alter the image, means that the apparatus is flexible but the electronics and mechanics required to effect this process are relatively expensive compared to known hot foil type printers, resulting in the disadvantage of higher cost of such apparatus.

It is an object of the present invention to overcome the above identified disadvantage.

According to a first aspect of the invention there is provided a printing apparatus comprising a print head which is operable at a printing station, to transfer print medium from a carrier onto an adjacent substrate, actuating means having an actuating member which is movable generally bi-directionally, chararacterised in that the print head is of the kind which has a plurality of printing elements each of which is selectively operable during printing to transfer a pixel of print medium from the carrier onto the adjacent substrate and that a mechanical transmission is provided which is adapted to convert the movement of the actuating member in one direction into movement of the print head from a start position towards the substrate and carrier, and then along the substrate

and carrier at the printing station whilst a control means selectively operates the printing elements of the print head to effect printing, and subsequent to printing, to convert movement of the actuating member in the second direction into movement of the print head back to the start position.

The invention thus provides a printing apparatus of greater flexibility than for prior art hot foil printers but at reduced cost compared to known thermal transfer printers. This is achieved since the need for expensive components is reduced, the transmission achieving by mechanical means, movement previously requiring complex and expensive electronic control.

The actuating means may comprise a piston and cylinder arrangement, the piston of which may comprise the actuating member which may be extended and retracted. The piston and cylinder may be activated by compressed fluid, preferably air.

In each case, the actuating means may comprise a linear actuator, and the bi-directional movement of the actuating member may be generally towards and away from the printing station.

Conveniently, the transmission, whilst converting the second movement of the actuating member into movement of the print head back to the start position, utilises the actuating member movement to cause the carrier to be advanced to provide a fresh area of carrier at the printing station for subsequent printing. Thus no separate drive means is required.

For example, the transmission may comprise an input member which is coupled to the actuating member and an output member on which the print head is mounted.

According to a second aspect of the invention we provide a method of printing utilising a printing apparatus according to the first aspect of the invention characterised in that the method comprises operating the actuating means to cause movement of the actuating member in the one direction, converting the movement of the actuating member in the one direction into movement of the print head towards the substrate and carrier at the printing station, and then

along the substrate and carrier whilst the printing elements of the print head are selectively operated to effect printing, operating the actuating means to cause movement of the actuating member in the second direction, and converting the movement of the actuating means in the second direction into a movement of the print head back to the start position.

Although most usually an apparatus in accordance with the invention would be constructed as original equipment, an apparatus in accordance with the invention may be made by converting an existing hot-foil type of apparatus, utilising the mechanics of that apparatus and exchanging the printing block thereof with a mechanical transmission and prim head.

Thus according to a third aspect of the invention we provide a method of converting a printing apparatus of the kind adapted to utilise a printing block mounted on an actuating member which is movable by an actuating means towards a printing station where the printing block contacts a carrier to transfer print medium from the carrier onto an adjacent substrate into a printing apparatus of the kind comprising a print head which is moved along a carrier at the printing station whilst a plurality of printing elements are selectively operated to transfer pixels of print medium from the carrier onto an adjacent substrate, the method comprising interposing a mechanical transmission between the actuating means and the printing station, the mechanical transmission being operable to convert the movement of the actuating member generally towards the printing station into movement of the print head from a start position towards the substrate and carrier, and then along the substrate and carrier at the printing station, and utilising a control means selectively to operate the printing elements of the print head to effect printing as the print head moves along the carrier, and to convert movement of the actuating member generally away from the printing station subsequent to printing, into movement of the print head back to the start position.

According to a fourth aspect of the invention we provide a printing apparatus comprising a print head which has a plurality of printing elements each

of which is selectively operable during printing at a printing station to transfer a pixel of print medium from a carrier onto an adjacent substrate, means to cause relative movement between the print head and the substrate during printing whilst selectively operating individual printing elements of the print head characterised in that the apparatus comprises an actuating means having an actuating member movable bi-directionally, and a mechanical transmission adapted to convert movement of the actuating member in one direction into movement of the print head from a start position towards the substrate and carrier, and then along the substrate and carrier at the printing station whilst a control means selectively operates the printing elements of the print head to effect printing, and subsequent to printing, to convert movement of the actuating member in the second direction into movement of the print head back to the start position.

The invention will now be described, by way of example only, with reference to the accompanying drawing which is a purely illustrative view of a printing apparatus according to the invention.

A printing apparatus 10 comprises a storage spool 11 and take-up spool 12 for printing ribbon 13. There is a ribbon path through the apparatus 10 between the storage spool 11 and take-up spool 12 for the ribbon 13. In this example, the ribbon 13 is of the so-called thermal transfer type.

The ribbon path is through a printing station 14 where a print head 15 is operable to transfer pixels of ink from the ribbon 13 onto an adjacent substrate 16.

The print head 15 has at an edge 15a thereof a plurality of selectively energisable printing elements in this case in a linear array, each of the printing elements, when energised, being operable to melt and remove a pixel of print medium i.e. thermal transfer ink, from the ribbon 13 and transfer it onto the substrate which is indicated in the drawing at 16. In another arrangement the array of printing elements need not be linear.

Selection of the printing elements is made by a computer or other control means C, which may be considerably simpler than the kind of control means

required in a conventional intelligent thermal transfer printer, since it is not required to perform complex control and synchronisation operations in addition to the image control.

A backing pad 17 is provided against which the print head 15 bears as in this arrangement the ribbon 13 and substrata 16 are stationary at the printing station 14 during a printing operation. This ensures close contact of the ribbon 13 with the substrate 16.

In another arrangement though, in place of the backing pad 17, a roller or similar may be provided, for example in an arrangement in which during printing, the substrate 16 and ribbon 13 move as well as the print head 15.

The ribbon guide path further includes idler rollers 18 and 19. The printing apparatus 10 further comprises an actuating means 21 which in this example is a linear actuator in the form of a piston and cylinder 21 which is provided with a supply of compressed air (not shown). The actuating means 21 may alternatively, be hydraulically operated, or may be an electrical actuating means. In each case the actuating means 21 comprises an actuating member 22, which in this case is the piston of the cylinder and piston arrangement, which when the actuating means 21 is operated, is moved bi-directionally only, towards or away from the printing station 14 and is connected to an input member of a transmission 20.

In a conventional hot foil type printer, a printing block would be moved towards and into contact with the ribbon 13 at the printing station 14 by such a linear actuator 21, to effect printing, and then away from the printing station 14 to permit the ribbon 13 to be moved on and fresh substrate 16 presented at the printing station.

In accordance with the invention, such simple mechanical arrangement, i.e. the use of an actuating means 21 rather than one or more stepper type motors, can be utilised with the "intelligent" print head 15. To achieve this, a transmission 20 is provided between the actuating means 21 and the print head 15, which uses the linear or other bi-directional movement of the actuating

member 22 to move the print head 15 both towards the ribbon 13 and substrate 16 at the printing station 14, and then along the ribbon 13 and substrate 16 whilst printing is effected under the control of the control means. The print head 15 is thus connected to an output member 23 of the transmission 20. The transmission 20 also uses actuating member 22 movement to drive the take-up spool 12 to advance the ribbon 13 inbetween printing operations.

The printing apparatus 10 operates as follows. At the start of a print cycle the piston 22 is extended in the direction of arrow A towards the printing station 14. This linear motion, by means of the transmission 20, moves the print head 15 in the direction of arrow B towards the substrate 16 and ribbon 13 and into contact with the ribbon 13. Due to the presence of the print pad 17, the ribbon 13 is thus moved into close contact with the substrate 16. Once in contact with the ribbon 13 the transmission 20 causes the print head 15 to execute print head motion, that is, to move the print head 15 along the length of the ribbon 13 and relative to the substrate 16, at the print station 14, in the direction of arrow C. The distance the print head 15 moves substantially parallel to the ribbon 13 and substrate 16 may be fixed, or user adjustable.

During the print head motion along the ribbon 13 and substrate 16, the plurality of printing elements are selectively energised to effect printing of the required image. The manner of selection of the energisable printing elements to form the required image is discussed below.

The piston 22 is then retracted, in the opposite direction away from the printing station 14, in a direction opposite to arrow A, and this motion is converted by the transmission 20 to move the print head 15 away from the ribbon 13 in the direction of arrow D and back to its starting position in the direction of arrow E. In addition, the retraction of the piston 22 causes the take-up spool 12 to rotate thus advancing the ribbon 13 to present a fresh area of ribbon 13 at printing station 14 ready for the next print cycle. The distance the ribbon 13 is advanced may be a fixed or user adjustable distance.

Selection of the printing elements to be energised to form the image to be

printed, may be set by user adjustable means. Thus the user may input to the control means C information concerning the image to be printed, and the control means C determines the appropriate elements to be energised at a plurality of positions along the path of print head 15 during print head motion. The rate at which the energised elements are changed i.e. the same/different printing elements are switched on and off, may be user adjustable, in which case the user may make adjustments until the rate "matches" the speed of motion of the print head 15 and a satisfactory image is printed. That is, the user may adjust the rate at which the printing elements are switched on and off until the printed image "looks good".

In an alternative embodiment, a feed back device, such as an encoder which is shown in dotted lines at E in the drawing, may be linked to the stroke of the piston 22 to provide the control means C with a means by which it can automatically synchronise the energisation of the printing elements on the print head 15 to the print head motion.

Whilst the substrate 16 is illustrated in the figure as a continuous length of material, the printing apparatus 10 may, for examples, equally be used to overprint onto discrete articles conveyed past the printing station 14, or onto discrete labels carried onto a continuous backing web.

A printing apparatus 10 according to the invention may comprise other forms of, preferably linearly acting, actuating means 21. For example, an electromagnetic solenoid may be employed in place of a piston and cylinder.

Currently available intelligent thermal transfer printers require microprocessor control, not only of the energisable printing elements of the print head 15, but also of all the stepper control motor or motors and clutches associated therewith to effect the print head motion and the winding on of the ribbon 13. The printing apparatus 10 according to the invention still requires microprocessor control of the energisable printing elements on the print head 15, but does not require microprocessor control of the mechanical movement of the print head 15 which is effected by the transmission 20. The task of the

microprocessor control means 20 is thus reduced, thus significantly reducing the cost of the printing apparatus 10 in comparison with current intelligent thermal transfer printers.

Various other modifications to those indicated above may be made without departing from the scope of the invention as will be apparent to those skilled in the art.

An apparatus in accordance with the invention may be made as original equipment in which case the actuating means 21 may be positioned otherwise than as described above and as shown in the drawing, to be compatible with the transmission 20. Alternatively, an apparatus in accordance with the invention may be provided using at least some components of an existing hot foil type printing apparatus.

The features disclosed in the foregoing description 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, or a class or group of substances or compositions, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.