GB2095181A - Character selection in type wheel printer - Google Patents

Abstract

In order to select types (201) on each type wheel of a set, (as shown each set comprises two wheels 2a, 2b), each wheel being associated with selector pawls (4a,4b) operable by a single electromagnet (5), a driver (6) firstly moves one pawl (4b) for the set into operative position to back the associated type wheels (2b), the into operative position to lock the associated type wheel (2b), the wheel in selected position. Then the driver releases the paw (4b) and associated wheel (2b) so that further actuation of the electromagnet selects the type on that wheel. More than two type wheels may be provided per set, in which case they are released in turn for selection by plural drivers. <IMAGE>

Description

SPECIFICATION Printer The present invention relates two a printer, e.g. a miniaturised or other small printer.

U.S. Patent Specification No. 3,848,527 discloses a mechanism for small printers which mechanism includes fewer electro-magnets than there are figure positions. As shown in Figures 4 and 5 of U. S. Patent Specification No. 3,848,527 for every three figure positions there are provided an electromagnet and a selector roll for controlling the electromagnet to select a type wheel at a desired figure position. Since the selector roll makes one-third of a complete revolution to select a single type, the selector roll is required to make one revolution before it covers three figure positions. Assuming that it will take 5 ms to select one type, the selector roll will make one revolution in 1 5 ms, and hence it will rotate at a high speed of 4,000 rpm.Such high-speed rotation tends to cause the printer to produce vibrations and noise, and business machines such as desktop calculators incorporating such a printer have proved unsatisfactory. In addition, the types on the type wheels are displaced for every three figure positions, a feature that -prohibits use of type wheels fabricated by injection-moulding a material in a common mould. Production of such type wheels requires three different moulds and hence is very costly.

Moreover, different moulds are likely to manufacture type wheels having varying type positions.

According, therefore, to the present invention, there is provided a printer comprising: a plurality of type wheels providing figure positions and each having types on its peripheral surface and a ratchet on a side thereof, said ratchet having teeth corresponding in position to said types; a shaft rotatably supporting said type wheels thereon; slipping clutch means for transmitting drive between said shaft and each of said type wheels; selector pawls which are movable into and out of an operative position in which they respectively engage said ratchets on said type wheels for locking desired types in a printing position; electromagnets each of which, when energized, is arranged to attract a respectively plurality of said selector pawls towards their operative positions; a plurality of pawl drivers which are arranged to engage and move all but one selector pawl of each said respective plurality of selector pawls into their operative positions; means for releasably holding each selector pawl in an inoperative position; and printing means for pressing a sheet of printing paper or other material against selected types on said type wheels, which selected types are arranged in a row at said printing position.

Thus the present invention provides a printer having fewer electromagnets than figure positions and having a reduced amount of vibration and noise, the printer being capable of being manufactured at reduced cost.

Preferably, each selector pawl of the said all but one selector pawls, when in its operative position, is engageable in a recess in the respective ratchet.

Control means are preferably provided such that, during a first revolution of said shaft, selected type wheels are stopped by the movement of the respective selector pawls into their operative positions, while each of the other type wheels is moved to and locked in its printing position by rotating it until an energizing signal is transmitted to the respective electromagnet, and during a subsequent revolution of said shaft each of the said selected type wheels is no longer so stopped and is moved to and locked in its printing position by rotating it until an energizing signal is transmitted to its respective electromagnet.

Each electromagnet may be arranged to attract two selector pawls, the pawl drivers being engageable only with alternate selector pawls.

Each ratchet may have lands which move the selector pawls back to their inoperative positions when the said shaft is rotated in a direction opposite to that in which it moves the type wheels to their printing positions.

Preferably, the slipping clutch means comprises, for each of the type wheels, a spring one end of which is engageable in a slot in the said shaft and the other of which is mounted in a recess in the respective type wheel, the arrangement being such that, in operation, when a type wheel is stopped while the shaft is being rotated, the said one end of the respective spring is forced out of the slot, and when a type wheel is not so stopped, the said one end can re-enter the said slot, when the said shaft is in a predetermined angular position, to transmit drive from the said shaft to the said type wheel.

The invention is illustrated, merely by way of example in the accompanying drawings, in which: Figure 1 is a side elevational view of a small printer according to the present invention, Figure 2 is a perspective view of the small printer shown in Figure 1, and Figure 3 is a timing chart illustrative of operation of the small printer of Figure 1.

As shown in Figures 1 and 2, a plurality of printing or type wheels 2 are rotatably on a shaft 1 having an axial slot 101. The type wheels 2 comprise odd-numbered type wheels 2a and even-numbered type wheels 2b. Each type wheel 2 has a plurality of printing indicia or types 201, such as characters or symbols, on its peripheral surface and has a selector ratchet 202 on a side thereof, the type wheels 2 collectively providing a required number of figure positions.Each ratchet 202 has teeth 202a corresponding in position to the types 201 on the respective type wheel 2.

A resilient type wheel spring 3, one of which is provided for each type wheel 2 has one end 301 received in the slot 101 and the other end 302 received in a recess 203 in the respective type wheel 2. Each spring 3 constitutes a slipping clutch for transmitting drive from the shaft 1 to the respective type wheel 2. The arrangement is -such that, in operation, when a type wheel 2 is stopped while the shaft 1 is being rotated, the end 301 of the respective spring 3 is forced out of the slot 101, and when the type wheel is not so stopped, the end 301 can re-enter the slot 101 when the parts are positioned as shown in Figure 1.

A plurality of selector pawls 4 are mounted for oscillatory movement on a shaft 4c and are adapted to engage the respective ratchets 202 of the type wheels 2 to bring selected types 201 into a printing position 9. The selector pawls 4 comprise pawls 4a, 4b for engagement respectively with the ratchets 202 of the type wheels 2a, 2b.

A plurality of electromagnets 5 are disposed adjacent to the selector pawls 4 for angularly moving the latter in the direction of the arrow a upon energization of the electromagnets so that the selector pawls 4 are attracted towards their operative positions (shown by dot and dash lines) in which they engage their respective ratchets. A leaf spring 10 (shown only in Figure 1) engages each of the selector pawls 4 to hold the latter in an inoperative position (shown by full lines) after it has turned in the direction of the arrow a. One of the electromagnets 5 acts on every two selector pawls 4 and hence crresponds to two figure positions. Thus, the number of electromagnets 5 required is only half as many as that of the selector pawls 4 or figure positions.A plurality of pawl drivers 6 are mounted on a shaft 6a for driving every pawl 4b, and thus every other pawl 4, into locking engagement in recesses 205 in the type wheel 2b to prevent the latter from being rotated.

A printing means 8 is located parallel to the type wheels 2 and is movable toward the latter for pressing a sheet 7 of printing paper or other material against selected types 201 arranged in a row at the printing position 9.

Operation of the printer thus constructed will be described with reference to Figure 3. The operation of the printer comprises three modes, that is, a type selection mode, a printing mode, and a type resetting mode.

In the type selection mode of operation, a motor (not shown) is energized in response to a printing command for rotating the shaft 101 in the direction of an arrow d. At this time, a cam (not shown) is actuated to turn the pawl drivers 6 in the direction of an arrow b to a position indicated by dot-and-dash-lines, in which the pawls 4b engage in recesses 205 in even-numbered type wheels 2b. When the shaft 1 is rotated, the even numbered type wheels 2b are prevented by the pawls 4 from being rotated with the result that the ends 301 of the springs 3 come out of the slot 101 in the shaft 1. However, odd-numbered type wheels 2a are caused to rotate with the shaft 1 due to the springs 3 being held in frictional engagement with the shaft 1.The shaft 1 is provided with a detector (not shown) for producing timing pulses upon rotation of the shaft 1 to detect the position of the types 201. When a desired type 201 on an odd-numbered type wheel 2a is about to be located at the printing position 9, the corresponding electromagnet 5 is briefly energized in synchronization with a timing pulse to cause the corresponding odd-numbered selector pawl 4a to turn in the direction of the arrow a, whereupon a distal end of the selector pawl 4a engages the ratchet 202 of the type wheel 2a to stop the latter. Therefore, the oddnumbered type wheels 2a can be selected at this time while the shaft 1 makes one complete revolution.

When the ends 301 of the springs 3 attached to the even-numbered type wheels 2b are allowed to drop again into the slot 101 in the shaft 1 as a result of the shaft 1 having made the -said complete revolution, the shaft 6a is turned further in the direction of the arrow b to return the drivers 6 to their starting position, thereby turning the pawls 4b back out of engagement with the ratchets 202. Continued rotation of the shaft 1 for making another revolution of the type wheels causes the even-numbered type wheels 2b which have thus been unlocked to rotate with the shaft 1 since the ends 301 of the springs 3 are received in the slot 101. At this time, the odd-numbered type wheels 2a are prevented from rotation by the selector pawls 4a which engage the ratchets 202 of the odd-numbered type wheels 2a.Desired types 201 on the even-numbered type wheels 2b are selected in response to energization of the electro-magnets 5 in the manner described above for selection of desired types on the oddnumbered type wheels 2a. When the shaft 1 makes two complete revolutions, the desired types 201 on the odd and even type wheels 2a, 2b are selected and locked at the printing position 9. The type selection mode of operation is thus finished.

In the succeeding printing mode of operation, the printing means 8 is moved in the direction of an arrow c to press the sheet 7 uniformly against the types 201, whereby selected characters are printed on the sheet 7. The shaft 1 is held against rotation (by means not shown) during the printing mode of operation. Printing of the characters may be effected either by an ink roll or by an ink ribbon.

In the type resetting mode of operation, the direction of rotation of the shaft 1 is reversed so that it rotates in the direction of an arrow e. As the shaft 1 is thus rotated, the end 301 of the springs 3 drop successively into the slot 101 in the shaft 1 to cause the type wheels 2 to rotate with the shaft 1 until all of the type wheels 2 are brought back to their starting position. The oddand even-numbered type wheels 2a, 2b are all reset while the shaft 1 makes approximateiy one revolution.

Moreover, the rotation of the shaft 1 in the direction of the arrow e will cause the distal ends of the selector pawls 4, 4b to travel up inclined surfaces 202b of the ratchet teeth 202a to the radially outer ends thereof so as to rotate the selector pawls 4a, 4b in the direction of the arrow f.Furthermore, each of the selector pawls 4a, 4b are also turned in the direction of the arrow f by a respective projection 204 so that they are moved to their inoperative positions shown in Figure 1 in which they are releasably held by the leaf springs 1 0. Figure 1 does not, however, show the selector pawls 4 as being engaged with the projections 204 because, after the projections 204 make the selector pawls 4 turn in the direction of the arrow f, the type wheels 2 rotate a little in the direction of the arrow dto provide space between each projection 204 and the respective selector pawl 4 and this condition is maintained.

With the arrangement described above, a single electromagnet 5 can select types on two odd- and even-numbered type wheels 2a, 2b during the type selection mode of operation, and hence the number of expensive electromagnets 5 required is only half as many as the number of type wheels 2 used. Desired types can be selected while the shaft 1 makes about two revolutions. Types on the odd-numbered type wheels 2a are selected during a first revolution of the shaft 1, and those on the even-numbered type wheels 2b are selected during a next revolution of the shaft 1 under the control of the pawl drivers 6 which are selectively engageable with every other selector pawl 4 to stop corresponding type wheels 2.The pawl drivers 6 are required to be actuated only twice, that is, before the shaft 1 starts to rotate (as indicated at g in Figure 3), and when the shaft 1 starts to make a second revolution (as indicated at h in Figure 3). Thus, the pawl drivers 6 produce little vibration and noise.

Moreover, the type wheels 2 are of the same configuration and can be inexpensively moulded using one mould. The types 201 on such type wheels 2 may be uniform and of high quality and hence can print characters which are positionally aligned or neatly arranged in a row.

Although in the illustrated embodiment each electromagnet 5 covers two type wheels or figure positions, it may alternatively be arranged to actuate three or four type wheels. Thus if, for example, each electromagnet 5 is associated with a group of three selector pawls 4, pawl drivers 6 are provided only for the second and third selector pawls of each group.In this case, during the first revolution of the shaft 1 in the direction of the arrow d, the second and third selector pawls of each group are moved into their operative positions to stop their respective type wheels, while the first selector pawl of each group remains in its inoperative position until its respective solenoid 5 is energized to lock the respective type wheel in the desired printing position. the pawl driver 6 of the second selector pawl of each group is then operated to move its respective selector pawl to its inoperative position and during a subsequent revolution of the shaft 1, the second selector pawl of each group is moved back into its operative position when its respective solenoid 5 is energized. The pawl -driver 6 of the third selector pawl of each group is then operated to move its respective selector pawl to its inoperative position and, during yet a further revolution of the shaft 1, the third selector pawl of each group is moved back to its operative position when its respective solenoid 5 is energized.

Although certain preferred embodiments have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Claims (9)

Claims

1. A printer comprising: a plurality of type wheels providing figure positions and each having types on its peripheral surface and a ratchet on a side thereof, said ratchet having teeth corresponding in position to said types; a shaft rotatably supporting said type wheels thereon; slipping clutch means for transmitting drive between said shaft and each of said type wheels; selector pawls which are movable into and out of an operative position in which they respectively engage said ratchets on said type wheels for locking desired types in a printing position; electromagnets each of which, when energized, is arranged to attract a respective plurality of said selector pawls towards their operative positions; a plurality 6f pawl drivers which are arranged to engage and move all but one selector pawl of each said respective plurality of selector pawls into their operative positions; means for releasably holding each selector pawl in an inoperative position; and printing means for pressing a sheet of printing paper or other material against selected types on said type wheels, which selected types are arranged in a row at said printing position.

2. A printer as claimed in claim 1 in which each selector pawl of the said all but one selector pawls, when in its operative position, is engageable in a recess in the respective ratchet.

3. A printer as claimed in claim 1 or 2 comprising control means such that, during a first revolution of said shaft, selected type wheels are stopped by the movement of the respective selector pawls into their operative positions, while each of the other type wheels is moved to and locked in its printing position by rotating it until an energizing signal is transmitted to the respective electromagnet, and during a subsequent revolution of said shaft each of the said selected type wheels is no longer so stopped and is moved to and locked in its printing position by rotating it until an energizing signal is transmitted to its respective electromagnet.

4. A printer as claimed in any preceding claim in which each electromagnet is arranged to attract two selector pawls, the pawl drivers being engageable only with alternate selector pawls.

5. A printer as claimed in any preceding claim in which each ratchet has lands which move the selector pawls back to their inoperative positions when the said shaft is rotated in a direction opposite to that in which it moves the typewheels to their printing positions.

6. A printer as claimed in any preceding claim in which the slipping clutch means comprises, for each of the type wheels, a spring one end of which is engageable in a slot in the said shaft and the other of which is mounted in a recess in the respective type wheel, the arrangement being such that, in operation, when a type wheel is stopped while the shaft is being rotated, the said one end of the respective spring is forced oust of the slot, and when a type wheel is not so stopped, the said one end can re-enter the said slot, when the said shaft is in a predetermined angular position, to transmit drive from the said shaft to the said type wheel.

7. A printer substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

8. A printer comprising: a plurality of type wheels providing figure positions and each having types on its peripheral surface and a ratchet on a side thereof, said ratchet having teeth corresponding in position to said types; a shaft rotatably supporting said type wheels thereon; a member held in frictional engagement between said shaft and each of said type wheels; selector pawls engageable respectively with said ratchets on said type wheels for selecting and locking desired types in a printing position; electromagnets disposed in the ratio of a plurality of said selector pawls to one electromagnet and energizable at a desired timing for actuating the latter; pawl drivers for forcibly driving said selector pawls; and printing means for pressing a sheet of printing paper against selected types on said type wheels, which are arranged in a row at said printing position, the arrangement being that said pawl drivers will drive selector pawls for unselected figure positions into engagement with type wheels for the unselected figure positions against rotation whereof in the first revolution of said shaft, allowing types on the type wheels other than the engaged type wheels to be selected, and in the following revolutions of said shaft the engaged type wheels are selected and types for all of the figure positions will be selected when said shaft makes a plurality of revolutions.

9. A printer comprising: a plurality of type wheels providing figure positions and each having types on its peripheral surface and a ratchet on a side thereof, said ratchet having teeth corresponding in position to said types and a recess; a shaft rotatably supporting said type wheels thereon; a member held in frictional engagement between said shaft and each of said type wheels; selector pawls engageable respectively with said ratchets on said type wheels for locking desired types in a printing position and also engageable in said recesses for stopping said type wheels against rotation; electromagnets disposed in the ratio of a plurality of said selector pawls to one electromagnet and energizable at a desired timing for actuating the latter into engagemunt with said ratchets; pawl drivers for forcibly driving said selector pawls into engagement in said recesses; and printing means for pressing a sheet of printing paper against selected types on said type wheels, which are arranged in a row at said printing position, the arrangement being that said pawl drivers will drive selector pawls for unselected figure positions into engagement with said recesses of type wheels for the unselected figure positions against rotation thereof in the first revolution of said shaft, allowing types on the type wheels other than the engaged type wheels to be selected, and in the following revolutions of said shaft the engaged type wheels are selected, and types for all of the figure positions will be selected when said shaft makes a plurality of revolutions.