GB2315044A - A drive mechanism for tape - Google Patents

Abstract

A drive mechanism particularly for a tape printer is described which allows different width tapes to be driven with an optimum torque. A capstan is provided for engagement with a take-up spool on which the tape is taken up, the capstan having a capstan gear. A main drive gear is arranged to be driven by a motor, and first and second intermediate drive gears can be selectively engaged between the capstan gear and the main drive gear to supply different torques in dependence on the width of the tape. A printing device and a set of tape holding cases using this concept is also described herein.

Description

A DRIVE MECHANISM FOR TAPE This invention relates to a drive mechanism for taking up tape, particularly but not exclusively for thermal transfer ribbon in a thermal printing device.

Thermal printing devices of the general type with which the present invention is concerned are known. They operate with a supply of tape arranged to receive an image and means for transferring an image onto the tape. In one known device, a tape holding case holds a supply of image receiving tape and a supply of an image transfer ribbon, the image receiving tape and the transfer ribbon being passed in overlap through a printing zone of the printing device. At the print zone, a thermal print head cooperates with a platen to transfer an image from the transfer ribbon to the tape. A printing device operating with a tape holding case of this type is described for example in EP-A0267890 (Varitronics, Inc.). Other printing devices have been made in which letters are transferred to an image receiving tape by a dry lettering or dry film impression process. In all of these printing devices, the construction of the image receiving tape is substantially the same. That is, it comprises an upper layer for receiving an image which is secured to a releasable backing layer by a layer of adhesive.

Once an image or message has been printed on the tape, that portion of the tape is cut off to enable it to be used as a label. The releasable backing layer is removed from the upper layer to enable the upper layer to be secured to a surface by means of the adhesive layer.

In another known printing device, described in EP-A-0322918 (Brother Kogyo K.K.), a tape holding case houses a supply of a transparent image receiving tape and a supply of an image transfer ribbon. The tape holding case also houses a supply of backing tape which comprises a carrier layer having an adhesive layer on its underside to which is secured a releasable backing sheet and an adhesive layer on its upper side which can be secured to the image receiving tape after an image has been printed thereon. In this device, the image is printed onto the image receiving tape as a mirror image which, when viewed through the image receiving tape, is the correct way round. With this device, the print is protected when the label is used.

In all of these devices, the colour of the label and the colour of the print are predetermined by the contents of the tape holding case. By the colour of the label reference is made to the upper layer of the image receiving tape of the apparatus described in EP-A-0267890 and to the carrier layer of the device described with reference to EP-0322918. The colour of the print is determined by the colour of the image transfer ribbon. Thus labels of one particular colour can only be printed with ink of a particular colour. Moreover, because the image receiving tape and image transfer tape are in the same tape holding case, they will run out together.

Other printing devices exist in which two separate cassettes hold respectively ink ribbon and substrate tape.

In one device in particular, there are two cassette receiving portions located on opposed sides of a printing zone. The first cassette receiving portion receives a first tape holding case housing a supply of an image transfer ribbon. The second cassette receiving portion receives a second tape holding case housing a supply of image receiving tape. The image receiving tape is of the type having an upper image receiving layer and a backing layer secured to the upper layer via an adhesive layer.

The first and second tape holding cases can be individually removable and replaceable whereby different combinations of ink ribbon and image receiving tape can be selected.

This allows for the use of image receiving tape of differing widths. For example, widths of 6mm, 9mm, 12mm, l9mm and 24mm or 32mm are possible. If a common width of image transfer ribbon is utilised, this presents difficulties. If the ink ribbon has a width wide enough to accommodate the full extent of the widest image receiving tape, then it will extend beyond the boundaries of narrow image receiving tape and ink will be transferred to the platen. This makes the platen dirty and inefficient. In contrast, if ink ribbon of a narrower width is used, this will not be sufficient for the full width of image transfer tape.

Therefore, it is desirable to provide ink ribbons of different widths, according to the different widths of image receiving tape.

For example, two different widths of ink ribbon can be provided, l9mm and 28mm. These are referred to herein as narrow ink ribbon and wide ink ribbon respectively. A problem then arises however since the ink ribbons of different widths are nevertheless to be used in a common printing device having a single drive mechanism.

The drive mechanism is set up to supply a certain torque to drive a take-up spool for the ink ribbon. If the torque is set sufficiently high to drive satisfactorily a wide ink ribbon, then a narrow ink ribbon can easily be broken accidentally due to an excessive torque being applied to it. Moreover, the ink ribbon can slip relative to the substrate tape because the speed is too high. If on the other hand the torque is set so that it is suitable for narrow ink ribbon, then it may be insufficient to satisfactorily drive a wide ink ribbon. In particular, it can fail to feed at a sufficient speed. In any case, if the ink ribbon is fed at the wrong tension (whether too high or too low), the ink ribbon can wrinkle or fold causing a deterioration in print quality.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: Figure 1 is a plan view showing two cassettes inserted in a printing device; Figure 2 is a diagrammatic sketch showing the control circuitry for the printing device; Figure 3 is a plan view of a drive mechanism in a position for narrow ink ribbon; Figure 3A is an enlarged portion showing the configuration of gear teeth; Figure 4A is a simplified side view of the mechanism of Figure 3 in the direction of arrow IV; Figure 4B is a side view like that of Figure 4A, but showing the drive components in more detail, and with the main drive gear "unfolded"; Figure 5 is a plan view like that of Figure 3 but showing the drive mechanism in a position for wide ink ribbon; Figure 6 is a simplified side view of the mechanism of Figure 5; Figure 7 is a side view in the direction of arrow VII in Figure 5 showing the drive components in more detail; and Figure 8 shows the slipping clutch mechanism for the main drive gear.

Figure 1 shows in plan view two cassettes arranged in a printing device 1. The upper cassette 2 is located in a first cassette receiving portion 26 and contains a supply of image receiving tape 54 which passes through a print zone 3 of the printer to an outlet 5 of the printer. The image receiving tape 54 comprises an upper layer for receiving a printed image on one of its surfaces and having its other surface coated with an adhesive layer to which is secured a releasable backing layer. The cassette 2 has a recess 6 for accommodating a platen 8 of the printer, and guide portions 22,24 for guiding the tape 4 through the print zone. The platen 8 is mounted for rotation within a cage moulding 10. As an alternative, the platen 8 could be mounted for rotation on a pin.

The lower cassette 4 is located in a second cassette receiving portion 28 and contains a thermal transfer ribbon which extends from a supply spool 30 to a take-up spool 32 within the cassette 4. The thermal transfer ribbon 12 extends through the print zone 3 in overlap with the image receiving tape 54. The cassette 4 has a recess 14 for receiving a print head 16 of the printer and guide portions 34,36 for guiding the ink ribbon 12 through the print zone 3. The print head 16 is movable between an operative position, shown in Figure 1, in which it is in contact with the platen and holds the thermal transfer ribbon 12 and the image receiving tape in overlap between the print head and the platen and an inoperative position in which it is moved away from the platen to release the thermal transfer ribbon and image receiving tape. In the operative position, the platen is rotated to cause image receiving tape to be driven past the print head and the print head is controlled to print an image onto the image receiving tape by thermal transfer of ink from the ribbon 12.

The print head is a conventional thermal print head having an array of pixels each of which can be thermally activated in accordance with the desired image to be printed.

The printing device has a lid which is not shown but which is hinged along the rear of the cassette receiving portion and which covers both cassettes when in place.

A motor 7 (Figure 2) drives the platen 8 which drives the image receiving tape in overlap with the ink ribbon through the print zone under the action of its own rotation. Columns of print are printed on the image receiving tape 54 at adjacent locations as the tape 54 is driven through the print zone. The rotation of the platen and the energisation of the print head 16 are controlled by a microprocessor as described in our European Applications Nos. 93304436.4 and 93305336.5 the contents of which are herein incorporated by reference.

The basic circuitry for controlling the printing device is shown in Figure 2. There is a microprocessor chip 100 having read only memory (ROM) 102, a microprocessor 101 and random access memory capacity indicated diagrammatically by RAM 104. The microprocessor is connected to receive data input to it from a data input device such as a keyboard 106. The microprocessor chip 100 outputs data to drive a display 108 via a display driver chip 109 and also to drive the print head 16 and the motor 7 for controlling the platen 8. The microprocessor chip also controls a cutting mechanism including a cutter 17 to cut off lengths of printed tape. The keyboard and display are located on the upper surface of the printing device to the right hand side of the cassette receiving portion as indicated by the dotted lines. It would be possible instead to having the keyboard and display provided as a remote unit, such as a conventional PC, and to download information to the printing device.

The operation of the printer will now be described. Data to be printed is typed into the printing device using data input keys as on the keyboard 106. The data input keys are designated generally by the block 109 but will in practice comprise a plurality of lettered and numbered keys. As the data is entered into the keyboard 106 it is supplied to the microprocessor 101 which drives the display 108 to display the data as it is entered. To do this, for each character which is entered, the microprocessor calls up a stored version of the character from the ROM 102. As the character is stored in compressed form this font data is stored temporarily in the RAM 104 and is manipulated by the microprocessor 100 to generate pixel data to form the character. This pixel data is transmitted in one form to the display 108 and in another form to the print head for printing.

Character data is not passed to the print head for printing until a print operation is executed. Firstly, the characters for the label are entered and edited using function keys on the keyboard 106 in conjunction with the display 108. When a label has been completed, data defining the label is held in the form of a character string and is used to generate pixel data for the print head for printing a label.

Reference will now be made to Figures 3 to 8 to describe the present drive mechanism. Figure 3 is a plan view of the drive mechanism located in the cassette receiving portion 28 for receiving the thermal transfer ribbon cassette 4. In Figure 3, reference numeral 23 denotes a capstan of the drive mechanism.

The capstan 23 carries a capstan gear 25. When a cassette 4 is inserted into the cassette receiving portion 28, the capstan 23 engages the take-up spool 32 in a known manner. Reference numeral 27 denotes a main drive gear which is driven from the motor 7 via a platen gear 21 mounted on a common shaft with the platen 8. As illustrated in Figure 8, the platen gear 21 is connected to the main drive gear 27 via a slipping clutch mechanism 19. Thus, when the platen 8 is driven to rotate, the main drive gear 27 also rotates in the direction of arrow A with a constant torque. The speed of the ink ribbon through the printing mechanism is to be governed by the platen, which feeds ink ribbon and substrate tape in overlap through the print zone.

The take-up roller is thus driven at a faster speed to ensure that it is always adequately fast, and the slipping clutch takes up the difference.

The drive mechanism includes first and second intermediate drive gears 29,31. The first intermediate drive gear 29 is configured to transfer a lower torque from the motor to the capstan 23 than the second intermediate drive gear 31. The lower torque is intended for ink ribbon of a narrower width, for example 19mm.

An actuator arm 33 selectively places into engagement between the main drive gear 27 and the capstan gear 25 one of the first and second intermediate gears 29,31. The actuator arm 33 has a base part 37 which carries an upstanding actuator piece 35. The base part 37 also carries the first and second intermediate gears 29,31 rotatively mounted about respective pins 29a and 31a. The actuator arm 33 is biased in the position illustrated in Figure 3 against a stop 41 by a spring 39 which is connected between the base part 37 of the actuator arm 33 and the base of the cassette receiving portion 28.

The actuator arm 33 is provided with a slot 43 which engages a guide pin 45 mounted on the floor of the cassette receiving portion 28.

Figure 4A is a simplified view taken from the side of the drive mechanism of Figure 3. Thus, the base part 37 of the actuator arm 33 can readily be seen, together with the upstanding actuator piece 35. Moreover, the profile of the actuator piece 35 can be seen in Figure 4. It has a wide upstanding base portion 35a, an angled portion 35b and a narrow, top portion 35c. Figure 4 also illustrates how the gear 29 has upper and lower cogs 29',29" which rotate together about pin 29a. A similar arrangement exists for the second intermediate gear 31, as illustrated in Figure 7. For reasons set forward in more detail hereinafter, cogs 29',29" have the same radius whereas the upper cog 31' has a smaller radius than the lower cog 31' on the gear 31.

Figure 3a illustrates the tooth profile of the main drive gear 27 and the intermediate drive gears 29,31. Each gear tooth 51, instead of having a conventional involute profile, has one side of the tooth 51a formed with an involute profile and another side of the tooth 51b formed as a flat surface. This creates a point 51c at the tip of the gear tooth. This eases engagement between the gears when a new cassette is inserted and the base part 37 is caused to rotate.

Operation of the drive mechanism to supply different drive torques for different widths of ink ribbon will now be described.

Figure 3 shows the position where a cassette holding an ink ribbon having a width of l9mm is inserted into the cassette receiving portion 28. The base of such a cassette has an aperture 53 sized to accommodate the narrower top part 35c of the upstanding actuator piece 35. The actuator arm 33 is held in the position shown in Figure 3 under the action of the spring 39, and is locked into position by the aperture 53 engaging the narrow top portion 35c. In this position, as can be seen from Figure 4B, the lower cog of the first intermediate drive gear 29 engages the main drive gear 27 and the upper cog of the first intermediate drive gear 29 engages the capstan gear 25. Thus, the same torque supplied by the main drive gear 27 is supplied to drive the capstan gear 25 and thus the capstan 23. This torque is just sufficient to draw the ink ribbon of narrow tape width through the print zone, but is not so great as to break it or cause it to slip through at a greater speed than the platen.

Reference will now be made to Figures 5, 6 and 7 to illustrate the situation when a cassette holding a wide tape width of ink ribbon, for example 28mm, is inserted into the cassette receiving portion 28. In Figures 5 and 6, like numerals denote like parts as Figures 3 and 4. The base of the cassette 4 holding wide ink ribbon has an aperture 55 which is wider than the aperture 53 in the base of the cassette of narrow ink ribbon. As the cassette is inserted into the cassette receiving portion, the aperture 55 engages the top narrow portion 35c of the upstanding actuator piece (see the top part of Figure 6). Subsequently, as the cassette is pushed further into the cassette receiving portion, the edge of the aperture 55 engages the angled portion 35b and causes the actuator piece to move to the left thus moving the actuator arm 33 in the direction of arrow B (Figure 5). The final, locked position of the cassette is illustrated in the lower part of Figure 6, where it can be seen that the aperture 55 is now engaged against the wide portion 35a. Thus, the actuator arm 33 has moved to the position shown in Figure 5, guided by the guide pin 45 in its slot 43. This moves the first intermediate drive gear 29 out of engagement from the main drive gear 27 and inserts instead the second intermediate drive gear 31. In this position, the upper cog 31' is in engagement with the capstan gear 25 and the lower cog 31" is in engagement with the main drive gear 27. As explained above, the upper cog 31' has a smaller radius than the upper cog 29' of the first intermediate drive gear 29". Thus, torque supplied to the capstan gear 25 from the main drive gear 27 is greater than the torque supplied via the first intermediate drive gear 29. This torque is sufficient to drive the wide ink ribbon through the print zone.

The ratio of torques supplied can be for example 1.5 (wide ribbon): 1 (narrow ribbon). In this way, it is possible to prevent breakages or slipping of narrow ink ribbons, or deficient winding of wide ink ribbons because insertion of the cassette automatically selects the correct position of the actuator arm, and therefore the correct intermediate drive gear.

It will readily be appreciated that it would in principle be possible to provide three different torques for three different widths of ink ribbon by providing three intermediate drive gears with respectively selectable positions using the principles of the present invention.

Claims (12)

CLAIMS:

1. A drive mechanism for taking up tape comprising: a capstan for engagement with a take-up spool onto which tape is taken up and having a capstan gear; a main drive gear arranged to be driven by a motor; first and second intermediate drive gears mounted for selective engagement between the capstan gear and the main drive gear and supplying respectively different torques from the motor to the capstan gear; and means for selecting one of said first and second intermediate drive gears for engagement in dependence on the width of the tape to be taken up on the take-up spool.

2. A drive mechanism according to claim 1 wherein said selecting means comprises a selection member on which said first and second intermediate drive gears are mounted, said selection member being selectively movable between first and second positions in dependence on the width of the tape.

3. A drive mechanism according to claim 2 wherein said selection member is movable against the action of biasing means, arranged to bias said selection member in said first position.

4. A drive mechanism according to claim 2 or 3 which comprises a guide pin for guiding movement of said selection member between said first and second positions.

5. A drive mechanism according to any preceding claim wherein said selecting means is cooperable with a selected one of first and second tape holding cases holding respectively tapes of different widths whereby insertion of one of said tape holding cases causes said selecting means to adopt an appropriate one of first and second positions.

6. In combination, a drive mechanism according to any of claims 1 to 4 with a tape holding case cooperable with said selecting means to select an appropriate one of first and second positions in accordance with the width of tape held in the tape holding case.

7. A combination according to claim 6, wherein the tape holding case holds ink ribbon for a tape printer.

8. A set of tape holding cases, each tape holding case comprising a supply spool and a take-up spool onto which tape is taken up when the take-up spool is driven, each tape holding case of said set holding a tape having a width different to tape in another tape holding case of said set, each tape holding case having a locking part, the configuration of which depends on the width of tape in the tape holding case, said locking part being for cooperation with a drive mechanism to select a proper torque for driving in dependence on the width of tape in the tape holding case.

9. A set according to claim 8, wherein each tape holding case holds ink ribbon for a tape printer.

10. A printing device comprising: a receiving zone for receiving a supply of tape and a takeup spool onto which said tape is taken up; a printing mechanism for printing an image onto an image receiving medium arranged in overlap with said tape at a print zone of the printing device; and a drive mechanism comprising a capstan for engagement with the take-up spool and having a capstan gear; a main drive gear arranged to be driven by a motor; first and second intermediate drive gears mounted for selective engagement between the capstan gear and the main drive gear and supplying respectively different torques from the motor to the capstan gear; and means for selecting one of said first and second intermediate drive gears for engagement in dependence on the width of the tape to be taken up on the take-up spool.

11. A printing device according to claim 10 which includes a display for displaying said image prior to printing.

12. A printing device according to claim 11 or 12 which includes an input device for entering data to define said image to be printed.