GB2139964A - A printer - Google Patents

Abstract

A printer (1) comprises a thermal print head (17), a platen roller (11), a thermal ribbon supply spool (14) and a thermal ribbon take-up spool (15). Paper to be printed is fed between the platen roller (11) and the print head (17) by means of a friction feed mechanism and the print head (17) is raised to trap the paper and a thermal ribbon (13) between the platen roller (11) and the print head (17). The thermal ribbon (13) is pulled along with the paper and the printing operation is carried out, with the thermal print head (17) printing through the thermal ribbon (13) onto the paper. The printer (1) is provided with sensing and actuating means (16) for detecting a reduction in ribbon tension between the printing zone and the ribbon take-up spool (15) and rotating the ribbon take-up spool (15) in the ribbon take-up direction thereof. Sensing and actuating means (not shown) may also be provided for detecting an increase in ribbon tension between the printing zone and the ribbon supply spool (14) and rotating the ribbon supply spool (14) in the ribbon supply direction thereof. The ribbon is only fed during printing and the printhead only contacts the ribbon during printing which reduces ribbon wear. <IMAGE>

Description

SPECIFICATION A printer This invention relates to a printer which is suitable for use in conjunction with a computer, as part of a dedicated word processor or teleprinter or the like. It is envisaged that the printer of the present invention will be particularly suitable for use, by mail order business orthe like for address printing.

A number of types of printer have been previously proposed, and these include the daisy-wheel, dotmatrix, electrosensitive, thermal, ink-jet and graphplotter types. A dot-matrix comprises a print head consisting of a row of fine rigid wires each of which is arranged to be activated separately by a respective solenoid. The wires print through a pressuresensi- tive ribbon and the paper is fed over a roller as in a conventional typewriter. The print head is scanned across the paper transversely of the row, which typically comprises between six and nine wires, and the wires are activated in response to instructions which are extracted from read only memory (ROM) in the printer. The image produced thus comprises a band of dots which is between six and nine dots in depth. In a typical printout, an 80 character band has more than 400 dots per line.A conventional dotmatrix printer can be used for addressing envelopes.

However, this is time consuming, becuase the address occupies only a small part of the available printing area on each envelope. Therefore, it has been proposed to use a dot-matrix printer to print addresses on a plurality of adhesive labels which are arranged edge-to-edge so as to extend across the entire line width of the printer. Such labels are expensive and additional labour is required to apply the labels to the envelopes. Dot-matrix printers have also been proposed having a number of print heads which operate simultaneously so as to print every line of an address simultaneously. Such printer have been found to be expensive to produce, complex and noisy.

A previously proposed electrosensitive printer utilises special paper comprising a layer of ink sandwiched between a layer of aluminium foil and a layer of ordinary paper. The print head comprises a wire which is brought into contact with the foil. A high voltage is then applied to the wire, as a result of which the foil melts, exposing the ink beneath. As in the dot-matrix printer, the print head scans across the paper to produce the image, but the image comprises only a single line of dots. In order to produce a line of characters, it is necessary for the print head to scan across the paper, say, between six and nine times. Thus, the electrosensitive printer has a potentially lower printing speed than the dotmatrix printer described above. Also, the special paper may be difficult to obtain or expensive and may be unsuitable for commercial use, because unaesthetic.However, an electrosensitive printer is generally less noisy in use than a dot-matrix printer, because it is not necessary for the wire to strike a pressure-sensitive ribbon.

Thermal printers have also been proposed, which utilise heat sensitive paper that changes colour, for example from white to blue, when heated. The print head comprises a line of wires, extending transversely of the paper feed direction, which are brought into contact with the paper. The wires are then selectively heated to produce a pattern of dots on the paper. A typical print head is about 2 inches (5 cm) in width. Thus, to obtain a line length of 8 inches (20 cm), for A4 page printing, four print heads are placed side by side. A thermal printer is generally less noisy and has a higher printing speed than a dot-matrix printer, but it is necessary to use special paper and it is not, therefore, suitable for address printing.The heat sensitive paper which is currently available suffers from the disadvantage that the image tends to fade after a period of time and that the paper may be heated, and thus marked, accidentally.

Thermal printers have also been proposed, for example in GB-A-1473870 and EP-A-0029313, wherein the heat sensitive paper is replaced by a ribbon carrying a heat actuable substance. However, although such printers are relatively quiet, like other printers using ribbon carrying material transferable to a substrate, problems occur with the tensioning of the ribbon which may lead to less than precise printing and, moreover, smudging may occur if, for example, the ribbon moves relative to, and is thereby rubbed over, the substrate.

It is an object of the present invention to enable the provision of a printer whereby the above disadvantages may be overcome, or at least mitigated.

According to a first aspect of the present invention there is provided a printer, which comprises: a ribbon; means for bringing a substrate into contact with the ribbon in a printing zone; a print head comprising means for selectively transferring a medium on the ribbon to the substrate so as to produce an image on the substrate, and drive means for moving the ribbon past the print head, the print head being movable between a non-printing position remote from the ribbon and a printing position in which the print head brings the ribbon into driving engagement with the ribbon drive means. Thus, a printer in accordance with the invention enables an arragement whereby the ribbon is driven only during printing and the print head contacts the ribbon only during printing so that wear on the ribbon may be reduced.

Preferably, the ribbon drive means comprises means for moving a substrate through the printing zone and the print head is arranged to bring part of the ribbon into engagement with the substrate moving means when the print head is in the printing position and usually the ribbon drive means comprises a first rotatable bearing surface for engaging a substrate, which first bearing surface is rotatably drivable by a motor and wherein the print head has a second bearing surface freely rotatably mounted thereto so that, in the printing position of the print head, the ribbon is trapped between the drive bearing surface and the print head bearing surface.

Generally, the printer comprises a ribbon supply spool and a ribbon take-up spool and means responsive to a decrease in ribbon tension between the printing zone and the ribbon take-up spool for rotating the ribbon take-up spool in the ribbon take-up direction thereof to maintain the tension in at least part of the ribbon substantially constant and usually, the means for maintaining the tension in at least part of the ribbon substantially constant further comprises means responsive to an increase in ribbon tension between the printing zone and the ribbon supply spool for rotating the ribbon supply spool in the ribbon supply direction thereof.Preferably, the tension responsive means comprises an elongate arm one end of which is pivotally mounted to one of the ribbon spools and the other end of which rests freely on the ribbon, movement of the arm being arranged to activate means for rotating one of the ribbon spools so as to maintain the ribbon tension substantially constant. Such an arrangement assists in preventing the wear which may otherwise occur if the ribbon is subjected to undesired tension changes.

Generally, ribbon moving means are provided for reducing the ribbon tension in response to move ment of the print head toward the printing position thereby causing movement of the ribbon past the head prior to the ribbon being brought into engag ment with the drive means. In a preferred arrange ment, the ribbon moving means comprises a rotatable bearing surface of the ribbon, which bearing surface is connected via a mechanical linkage to the print head so that the bearing surface is movable with the print head. Such an arrangement allows the speed differential between the ribbon and the substrate to be reduced prior to the ribbon being trapped by the raising of the head to the printing position and so has the effect of preventing or at least reducing, smudging of the substrate caused by the ribbon rubbing over the substrate.

The ribbon moving means usually carries or is formed by a heat activatable substance and the means for selectively transferring a medium on the ribbon to the substrate comprises means for selec tively heating the heat activatable substance.

According to a second aspect of the present invention there is provided a printer suitable for addressing labels, which printer comprises: a hous ing; a ribbon which carries or is formed by a heat activatable substance; a feed tray for supplying paper to the printer; a friction feed mechanism for bringing paper into contact with the ribbon, the friction feed mechanism comprising wheels for engaging a substrate supplied to the printer via the feed tray and a platen roller for contacting the paper during printing; a print head; means pivotally mounting the print head to the housing so that the print head is movable between a non-printing posi tion remote from the ribbon and a printing position; means four pivoting the print head; means for sensing paper fed into the friction feed mechanism and for producing an output signal in response thereto; means for actuating the print head pivoting means in response to the sensing means output signal to pivot the print head to the printing position; a ribbon feed mechanism comprising a ribbon supply spool, a ribbon take-up spool, a first rotatable bearing surfaceforthe ribbon, means mounting the first rotatable bearing surface to the print head, a second rotatable bearing surface for the ribbon, a support arm having first and second ends, the first end of the support arm being pivotally connected to the housing and the second end of the support arm rotatably carrying the second rotatable bearing surface; a mechanical linkage connecting the print head to the support arm so that the support arm is pivotable with the printing head; and a tensioning mechanism including an elongate arm with first and second ends, the first end of the elongate arm being pivotally mounted to the ribbon take-up spool and the second end of the elongate arm resting on the ribbon, and means for rotating the ribbon take-up spool in response to lowering of the arm caused by a decrease in the ribbon tension.

For a better understanding of the present invention, and to show how the same may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a vertical cross-sectional view of a thermal printer in accordance with the invention, and Figure 2 is a block diagram of part of the printer of Figure 1.

A printer 1 which is capable of receiving and printing characters from a computer comprises a housing 2, a lid 3 which is hinged to the housing 2 at 4 and a feed tray 5 which is hinged to the housing 2 at 6. Apertures 7 and 8 are formed in a lower front part and in the bottom, respectively, of the housing 2 and a slot 9 is formed in the hinged lid 3. The printer 1 is of such a size as to be suitable for desk top use. A friction feed mechanism is provided which comprises wheels 10 for engaging paper fed into the printer from the feed tray 5, a platen roller 11 for contacting the paper during printing and large paper inverting wheels 12, which are rotatable by means of a stepper motor 28 (Figure 2) and a gear and belt drive arrangement (not shown) under the control of a microprocessor 27 (Figure 2) in the printer.Also, a feed mechanism for a heat activatable printing ribbon 13 is provided which comprises a ribbon supply spool 14 and a ribbon take-up spool 15, which are mounted for rotation in the housing 2, and a sensing and actuating means 16 which will be described in detail hereinafter. A thermal print head 17 is mounted in the housing 2 and the ribbon 13 extends over a roller 18 which is mounted on the print head 17. The print head 17 is pivotally movable about the axis of a pivot pin 19 between a raised and a lowered position by means of a half-revolution spring-wrap clutch and a cam (not shown) and is shown in its raised position. The printer 1 further comprises a photoelectric cell 20, a paper deflector 21 and a conveyor 22.

Referring now to the thermal ribbon feed mechanism in more detail, the sensing and actuating means 16 comprises a pivotal arm 23 and a roller 24 which is rotatably mounted to the free end of the pivotal arm 23 and which rests on the thermal ribbon 13. As the thermal ribbon 13 is drawn through the printing zone during printing, the arm 23 is lowered thereon.

The movement of the arm 23 is sensed by an arm sensor 29 which may be, for example, a photoelectric sensor, and the sensor 29 activates a motor 30 (Figure 2) which rotates the ribbon take-up spool 15 until the arm 23 is raised to its original position. The ribbon supply spool 14 may be provided with a similar sensing and actuating means (not shown) for rotating the ribbon supply spool 14, and thus unwinding the ribbon 13, as the ribbon 13 is drawn through the printing zone. Alternatively, the means (not shown) for rotating the ribbon supply spool 14 may be actuated by raising of the arm 23 from its original position. This ensures that the tension in the ribbon 13 remains substantially constant, regardless of the amount of ribbon 13 left on the supply spool 14.

The Figure illustrates two alternative paths of travel for the ribbon 13 from the ribbon supply spool 14 to the printing zone. Thus, in one arrangement as shown in dotted lines in the Figure, the ribbon 13 travels directly from the supply spool 14 to the region of the print head 17. In the alternative preferred arrangement shown in the Figure, the ribbon 13 travels from the supply spool 14 over a bearing surface in the form of a roller 26 rotatably mounted to one end of a support arm 25, the other end of the support arm 25 being pivotally mounted to the housing. The support arm 25 is connected by a mechanical linkage (not shown) to the print head 17 so that the support arm 25 pivots with the print head.

The mechanical linkage may be, for example, a gear and belt drive arrangement for causing the arm 25 to pivot with the print head 17 ora push/pull rod arrangement connecting the print head 17 to the support arm 25. Thus, when the print head 17 is raised to the printing position shown in the Figure, the arm 25 pivots to the left in the Figure and when the print head 17 is lowered to the non-printing position (not shown), the support arm 25 pivots to the right in the Figure.

In use, paper is fed from the feed tray 5 and advances towards the moving platen roller 11.

Immediately before the leading edge of the paper reaches the platen roller 11, the photoe-electric cell 20 is activated thereby and the microprocessor then allows the paper to move through the printer by a further amount, which can be preset, depending on the desired position of the print on the paper. When the paper has reached the desired position, the paper feed velocity is reduced and the print head 17 is raised from the lowered to the raised position thereof. This traps the paper and the thermal ribbon 13 against the platen roller 11, as a result of which the thermal ribbon 13 is pulled along with the paper.

The printing operation is then carried out, as will be discussed in more detail hereinafter. On receipt of a command from the computer, the print head 17 is lowered and the stepper motor is ramped up to the higher paper feeding speed. When the trailing edge of the paper passes the photoelectric cell 20, the cycle recommences, unless no further characters have been received from the computer. Because the paper is printed on the underside thereof, it is desirable to invert the paper so that the printing can be read as it emerges from the printer 1, and this is done using the paper inverting wheels 12 and deflector 21. The deflector 21 guides the paper around the inverting wheels 12 and the paper is thus fed out of the printer 1 through the aperture 8 in the bottom of the housing 2. An alternative position for the paper deflector 21 is shown in phantom lines.In this alternative arrangement the paper is fed to the conveyor 22 and is then conveyed to the aperture 7 in the front of the housing 2, whence it emerges from the printer 1. If it is not desired that the printed paper be inverted before being fed out of the printer 1, a slot 9 may be provided in the hinged lid 3 and the deflector 21 removed so that the paper exits via the slot 9 in the hinged lid 3.

In the preferred arrangements mentioned above where the ribbon 13 passes over the roller 26, the mechanical linkage (not shown) between the print head 17 and the support arm 25 causes the support arm 25 to pivot about the other end thereof toward the left in the Figure as the print head 17 is raised.

This pivoting of the support arm causes the tension in the ribbon to be reduced, lowering the arm 23 and thereby causing the take-up spool 15 to be rotated to return the ribbon to the desired tension. Thus, the ribbon is moved prior to being trapped against the platen 11 by the roller 18 so that the speed differential between the paper being fed to the printer and the ribbon is reduced and rubbing of the paper along the ribbon which causes unsightly smudges on the paper is prevented or at least reduced.

The printer 1 can be used to print on individual sheets of paper or sprocket-punched paper, labels, envelopes or the like, and is particularly suitable for printing addresses directly onto envelopes, there being no need to use a separate address label for each envelope. The large paper inverting wheels 12 can be replaced with wheels which are provided with sprocket pins when printing on continuous stationary.

The print head 17 comprises a single row of individually actuable heating elements extending across the printing zone transversely of the paper feed direction, which prints through the heat sensitive ribbon 13 onto the paper to produce a pattern of dots. Each line of characters produced consists of seven or nine such rows of dots, each row corresponding to a separate activation of the print head 17.

Alternatively, the print head 17 can be used to print a number of lines of characters simultaneously, the lines extending in the paper feed direction, for example when printing labels or addresses. The print head 17 may be about 2 inches (5 cm) wide and comprise 150 heating elements. Thus, to produce a line length of 4 inches (10 cm), for label or address printing, two print heads are placed side by side, and to produce a line length of 8 inches (20 cm), for A4 page printing, four print heads are placed side by side. The heat sensitive ribbon 13 must be at least as wide as the total width of the heads. It should be appreciated that because each heating element is individually addressable by software and an external computer (not shown) connectable to the printer microprocessor via an appropriate interface 31 for example an RS232 or centronics interface, any characters or designs may be produced under software control. In particular, the printer may be used to produce bar codes and different sizes or styles of printing as well as designs or pictures, the software necessary for producing each different style or type of printing being stored in a memory 32 for example, an eraseable programmable memory, of the printer and being accessible by means of an external computer connected to the interface 31.

The printer 1 is capable of attaining a printing speed of 2,000 characters per second (c/s) and produces litte noise during printing other than that of the stepper motor. It has been found that the printer 1 can be used for addressing envelopes at considerably reduced overall cost when compared to a previously proposed dot-matrix printer.

The features disclosed in the foregoing description, in the following claims and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realising the invention in diverse forms thereof.

Claims (12)

1. A printer, which comprises: a ribbon; means for bringing a substrate into contact with the ribbon in a printing zone; a print head comprising means for selectively transferring a medium on the ribbon to the substrate so as to produce an image on the substrate; and drive means for moving the ribbon past the print head, the print head being movable between a non-printing position remote from the ribbon and a printing position in which the print head brings the ribbon into dirving engagement with the ribbon drive means.

2. A printer according to Claim 1, wherein the ribbon drive means comprises means for moving a substrate through the printing zone and the print head is arranged to bring part of the ribbon into driving engagement with the substrate moving means when the print head is in the printing position.

3. A printer according to Claim 2, wheren the ribbon drive means comprises a first rotatable bearing surface for engaging a substrate, which first bearing surface is rotatably drivable by a motor and wherein the print head carries a second bearing surface freely rotatably mounted thereto so that, in the printing position of the print head, the ribbon is trapped between the drive bearing surface and the print head bearing surface.

4. A printer according to Claim 1, 2 or 3, which comprises a ribbon supply spool and a ribbon take-up spool and means responsive to a decrease in ribbon tension between the printing zone and the ribbon take-up spool for rotating the ribbon take-up spool in the ribbon take-up direction thereof to maintain the tension in at least part of the ribbon substantially constant.

5. A printer according to Claim 4, wherein the means for maintaining the tension in at least part of the ribbon substantially constant further comprises means responsive to an increase in ribbon tension between the printing zone and the ribbon supply spool for rotating the ribbon supply spool in the ribbon supply direction thereof.

6. A printer according to Claim 4 or 5, wherein the tension responsive means comprises an elongate arm one end of which is pivotally mounted to one of the ribbon spools and the other end of which rests freely on the ribbon, movement of the arm being arranged to activate means for rotating one of the ribbon spools so as to maintain the ribbon tension substantially constant.

7. A printer according to any one of Claims 4to 7, wherein ribbon moving means are provided for reducing the ribbon tension in response to movement of the print head toward the printing position thereby causing movement of the ribbon past the print head prior to the ribbon being brought into engagement with the drive means.

8. A printer according to Claim 7, wherein the ribbon moving means comprises a rotatable bearing surface of the ribbon, which bearing surface is connected via a mechanical linkage to the print head so that the bearing surface is movable with the print head.

9. A printer according to any precding claim, wherein the ribbon carries or is formed by a heat activatable substance and wherein the means for selectively transferring a medium on the ribbon to the substrate comprises means for selectively heating the heat activatable substance.

10. A printer suitable for addressing labels, which printer comprises: a housing; a ribbon which carries or is formed by a heat activatable substance; a feed tray for supplying paper to the printer; a friction feed mechanism for bringing paper into contact with the ribbon, the friction feed mechanism comprising wheels for engaging a substrate supplied to the printer via the feed tray and a platen roller for contacting the paper during printing; a print head; means pivotally mounting the print head to the housing so that the print head is movable between a non-printing position remote from the ribbon and a printing position; means for pivoting the print head; means for sensing paper fed into the friction feed mechanism and for producing an output signal in response thereto; means for actuating the print head pivoting means in response to the sensing means output signal to pivot the print head to the printing position; a ribbon feed mechanism comprising a ribbon supply spool, a ribbon take-up spool, a first rotatable bearing surfaceforthe ribbon, means mounting the first rotatable bearing surface to the print head, a second rotatable bearing surfaceforthe ribbon, a support arm having first and second ends, the first end of the support arm being pivotally connected to the housing and the second end of the support arm rotatably carrying the second rotatable bearing surface; a mechanical linkage connecting the print head to the support arm so that the support arm is pivotable with the printing head; and a tensioning mechanism including an elongate arm with first and second ends, the first end of the elongate arm being pivotally mounted to the ribbon take-up spool and the second end of the elongate arm resting on the ribbon, and means for rotating the ribbon take-up spool in response to lowering of the arm caused by a decrease in the ribbon tension.

11. A printer substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings.

12. Any novel feature or combination of features described herein.