WO1983002752A1

WO1983002752A1 - Print carriage mounting for daisywheel printer

Info

Publication number: WO1983002752A1
Application number: PCT/GB1983/000040
Authority: WO
Inventors: Office Systems Limited Panorama
Original assignee: Poley, John; Joy, Brian, Richard
Priority date: 1982-02-10
Filing date: 1983-02-10
Publication date: 1983-08-18
Also published as: JPS59501351A; AU1225383A; EP0101480A1

Abstract

A print carriage (16) can be swivelled downwardly to give access to a print member such as a daisy wheel (10). The print carriage (16) may bear means for advancing ribbon or tape in a cassette past a print member. An innovative intermittent motion device is described for effecting such movement.

Description

PRINT CARRIAGE MOUNTING FOR DAISYWHEEL PRINTER

This invention relates to printers and in particular to daisy wheel printers.

In recent years major developments have occurred in the development of printer output devices for computers. Among the most important developments has been that of the daisy wheel printer which produces a printed output like a typewriter, but operates very much faster. Such printers are used in particular in word processing equipment, though their use is not so restricted...

In a printer of this type, the individual letter and symbol shapes are formed in relief on the ends of the petals of the daisy wheel. This wheel is mounted on a spindle so that it can be rotated to bring the desired petal^"" end in between a print solenoid and a platen, >conventionally in the form of a rubber covered roller. Between the petal end and the roller are arranged a suitable inking member such as an inked fabric ribbon or a carbon film ribbon and the paper or other stationery on which it is desired to print. When the desired petal has been brought into position, the print solenoid is actuated to push the end of the petal sharply towards the platen, the raised symbol shape on the end of the petal then making a mark where desired on the paper or the like.

OMPI The assembly of daisy wheel, positioning mechanism for the daisy wheel and print solenoid is formed on a carriage which can be tracked along a path parallel to the axis of the platen in order to produce a line of printing. The carriage carries the inking ribbon or film ribbon, usually in the form of a cassette containing a supply and a take-up spool, and the ^{• •} carriage may also carry one or more^'paper guides which act in conjunction with the platen to keep the paper or the like round the platen in contact therewith both to increase the quality of printing and to reduce noise.

It is evident from the above description and from an inspection of known daisy wheel printers that - there is a large number-of individual components in close proximity to one another in and around the carriage in front of the platen, and of course the carriage and platen must be close together to minimise the amount of travel that the end of each petal has to move through, both to improve speed and print quality.

This congestion leads to substantial disadvantages in connection with maintenance; daisy wheels need to be cleaned periodically,for which purpose they are removed from the printer and then replaced, and additionally daisy wheels can be changed if it is desired e.g. to print successive- documents using different typefaces. This can be a problem area particularly in the case of office word processing machinery. In this area of use, ease of operation and maintenance are of prime importance.

According to a first feature of the present invention there is provided a printer including an elongate platen for supporting material to be printed and a print carriage, the carriage being mounted for movement parallel to the platen and including a daisy wheel, means for bringing the daisy wheel into the desired position, and a print solenoid adapted when actuated to move one petal of the daisy wheel towards the platen, wherein the carriage is mounted in a frame pivotal about an axis parallel to and spaced from the platen, and including means for maintaining the carriage in a printing position closely adjacent the platen and or enabling it to be swung away from the platen to facilitate access to the daisy wheel. Normally the platen takes the form of a rubber covered roller and the. carriage is mounted on a track parallel to the axis of the roller. This track may be supported in a frame which can be pivoted about an axis likewise parallel to the axis of the roller and spaced therefrom. Preferably the frame is pivoted to a second frame in which the roller itself is mounted, the frame and second frame having cooperating stop means defining a position in which carriage and platen are close together. The axis about which the frame and second frame pivot relative to one another may be defined by an axle along which the carriage itself is slideable. A part of the carriage remote from the platen may carry a foot slideable-along a rail forming part of the frame. In a particularly preferred embodiment the frame and sub-frame are held with their respective stop members abutting- one another under. a spring bias. One particularly preferable way of arranging that spring bias is to provide tension springs pivotally connected at each end to parts of the frame and second frame respectively, the pivotal connection points and the hinge axis between frame and sub-frame being substantially collinεar when the carriage is swung away from the platen. Such^" a system is particularly advantageous, since it requires no separate locking means to hold the frame

^ and sub-frame relative to one another.

The front of the carriage may bear paper guide ^' means which when the carriage is adjacent the platen cooperate with the platen to define a narrow path for paper or the like and accordingly to hold the paper or the like firmly against the platen during printing.

The upper surface of the carriage may be appropriately configured to receive a tape or ribbon cartridge containing for example an inked fabric ribbon or a carbon film ribbon. The cartridge may be held in place by suitable frictional or spring clip engagement in known fashion and being on top of the carriage it is easily accessible for changing. The carriage may include means for advancing the^' ribbon in such a cartridge. In the past, this has generally been effected using a stepping motor or like drive mounted in the carriage and actuated in - correspondence to actuation of the print solenoid to advance the ribbon. This is an expensive and cumbersome mechanism which in addition requires the provision of suitable power supply.

According to a further feature of the present invention there is provided a drive mechanism for advancing the take up spool in a printer, the drive^*" mechanism comprising:

1. continuously rotating drive- means

2. a drive take-up mechanism normally disengaged from the continuously rotating drive means 3. an escapement mechanism having a rest position in which the drive take-up mechanism is disengaged from the continuously rotating drive and an active position in which the drive take- up means engages the continuously rotating drive, the escapement mechanism permitting only a given rotation of the drive take-up mechanism before reverting to its rest position and 4. means for triggering the escapement mechanism into its active state in response to movement of a thrust member. Such a mechanism may be actuated e.g. at the same time the print solenoid is actuated (where the solenoid itself may be the thrust member referred to) to give satisfactory tape or ribbon drive in printers of the type described above. It should be observed, however, that the ribbon drive mechanism just defined is not restricted to use in such printers but may be used in any analogous apparatus where it is desired to feed a print ribbon or the like forward intermittently in response to another operation. Examples of such other apparatus are electric and electronic typewriters, accounting machines, telex machines and other electronically controlled print output devices.

The drive take-up mechanism may bear a suitable drive dog for the take-up spool in a cassette or for a separately mounted take-up spool if cassettes are not used.

Generally it is desirable to have a standard angular movement for the take-up spool in a cassette through v/hich it is to be moved each time the print" solenoid is actuated. This can be achieved in a drive mechanism as just defined by providing on the output drive shaft an evenly toothed ratchet wheel and arranging that each time the intermittent drive is actuated the ratchet wheel is advanced by one or more teeth. In a particularly preferred embodiment of the drive mechanism, it comprises: a. motor drive means for continuously rotating a driving pinion b. a ratchet wheel mounted on the output drive shaft for the εoool c. a driving wheel engageable with the driving pinion and rotatable about an eccentric axis defined by a stub shaft which extends from one end of a crank which is pivotable about the ratchet wheel axis

•d. a pawl mounted on the crank v/hich engages the ratchet teeth and indexes the ratchet wheel by one tooth in response^'to arcuate movement of the crank- e. a stop on the driving wheel . an abutment engageable with the stop to inhibit rotation of the wheel, the abutment being movable in response to actuation of the printer out of engagement with the stop to permit the wheel to be rotated by the continuously driven pinion until the stop and abutment engage once again and g. spring means adapted to provide a force for moving the wheel out of engagement with the -driving pinion after the stop and abutment have become engaged and for moving the wheel back into engagement with the driving pinion when the abutment is moved out of engagement with the stop. In such an arrangement the pinion and driving wheel may be toothed gears with the driving gear having a section without teeth so that at one angular position relative to the shaft of the pinion, it cannot be driven. Preferably a stop is provided on the crank v/hich engages a fixed member to define a permissible arcuate displacement of the crank member on which the driving wheel is mounted. The position should be such that the stop on the crank member limits movement of the latter slightly in advance of the position in which the driving wheel stoτj member engages the abutment

__ O PI so that the spring means acting on the driving wheel so as to rotate the driving wheel about the eccentric ^' axis thereof in order to rotate the stop on the driving wheel into engagement v/ith the abutment. The stop may be directly connected to the print solenoid to ensure that each time .the print solenoid^' is actuated the stop is moved and the drive mechanism indexes the ribbon forward by the desired degree. The continuous drive should be -sufficiently fast that the intermittent drive mechanism is able to complete a single cycle in less than the minimum time between successive^' actuations of the solenoid. This ensures that a fresh segment of ribbon or type is available for the printing of each successive character. The pinion and driving v/heel may be toothed gears or one may be a plain capstan and the other a tyred wheel, or both may be tyred wheels.

As noted above, the principal advantage of the present invention is the ease with v/hich daisy wheels may be exchanged. This may be further facilitated by locating on the carriage a lift-off lever having a central fulcrum, arms to one side of the fulcrum located adjacent to the rear face of a daisy wheel positioned-en the carriage and adapted to move in a direction substantially perpendicular to the plane of the daisy wheel and having its end the other side of the fulcrum accessible to effect . such movement. Most conveniently the two arms lie either side of a central support hub on which the daisy wheel is engaged and are adapted to push the daisy wheel out of engagement with the hub when the other end of the lever ^"is moved e.g. by a fingertip.. The lever is preferably sprung biased to a position in v/hich the arms lie spaced from the rear of the daisy v/heel by a maximum extent e.g. of 1 to 2 mm. By suitable positioning and design, - 8 -

such a lever may very substantially facilitate daisy wheel removal effectively by moving the daisy wheel from an engaged position on its standard supporting hub to a loose position in which it is resting on the 5. hub but can easily be lifted therefrom. In particular the conventional drive dog on the hub is disengaged from the matching slot on the daisy wheel.

The invention is further described by way of example with reference to the accompanying drawings 10 in which:

Figure 1 is a diagrammatic side view of part of a daisy v/heel printer according to the present invention Figure 2 is an opposite side view of part of a 15 daisy wheel printer also constructed in accordance with the invention Figure 3 is a view from above of the part of the printer shown in Figure 2 Figure 4 is a diagrammatic side view of an 20 ^' alternative embodiment

Figure 5 is an elevational view seen from the right-hand side of Figure 4, of the embodiment of Figure 4 Figure 6 is a plan view of the embodiment of 25 Figures 4 and 5, and

Figure 7 is a diagrammatic underneath plan view of the ribbon advance- mechanism on the carriage of the printer shown in Figures 4 to 6. In Figure 1 a daisy v/heel 10 is shown mounted on a spindle 12 of a drive unit such as a stepper motor 14 which is mounted within a carriage 16 within a printer main frame. The carriage is slideable along a circular section rod or axle 18 and is mounted thereon by means of-bearings one of which is shown at 20.

Behind the daisy wheel 10 is located a solenoid 22 for moving the uppermost daisy wheel petal towards a platen 24.

The carriage 16 is maintained in the position shown in Figure 1 by means of a foot 26 which runs in a rail 28 v/hich is located along the upper edge of a pivotable frame member 30. ^' The latter,pivots about an axle 3 and is urged in an anti-clockwise direction about that axle by means of a spring 34.

The frame member 30 can be gripped and urged in a clockwise direction about the axle 3 so as to release the foot 26 from the rail 28 so allowing the carriage to tilt about the axis of the rod 18 so that the foot 26 drops and the daisy wheel 10 is in turn moved away from the platen 24 and tilted so as to give better access thereto. A locking mechanism (not shown) holds the frame member 30 in its clockwise pivoted position and an interlock or similar mechanism between the locking _. mechanism and the carriage 16 causes the locking mechanism to become unlocked when the carriage is lifted as by rotating the carriage around the rod 18 so that the foot 26 is once again engaged by the rail 28.

An alternative arrangement is shown in Figures 2 and 3- Here, a sub-frame comprises two parallel spaced apart side plates one of which- is shown at 34 and two rods 36 and 38 which extend between the two side plates 34. Rod 36 is circular in cross-section and protrudes through bearings carried in main frame side panels one of which is shown at 40 so as to be pivotable about the axis of the rod 36 relative to the main frame 40.

Referring to Figure 3_» the. sub-frame also includes outboard^" sideplates one of which is denoted by reference numeral 42. A similar such plate is provided at the opposite end of the rods 36 and 38 outboard of the sub-frame sideplate corresponding to plate 34.

Each of the outboard plates 42 includes a turned over upper edge to form outwardly facing flanges such as 44, the purpose of which is described below. An L-shaped locking member generally designated 46 is pivotally joined to each outboard plate 42 by means of a rivet or the like 48 and each L-shaped member includes a sloping leading edge 50 behind which is a slot 52 adapted to engage a pin 54 fixed -^* to the main frame panel 40.^'

The engagement of the pin 54 in the slot 52 prevents the outboard plate 42 from pivoting about the axis of rod 36 in a anti-clockwise direction (as seen in Figure 2). A spring 56.is attached to the upstanding . section of the L-shaped member 46 at 58 and is

. attached at its other end tc the sideplate of the sub- frame at 60. The sideplate is conveniently cut away at 62 to accommodate the spring.

The tension in the spring urges the sub-frame made up of the plates 34 and rods 36 and 38 in a generally clockwise direction about the axis of rod 36 and the upper front end of each sideplate 34 is bent outwardly to form a first stop 64 and the similar corresponding rear edge of the main frame side panel 40 is similarly bent around at 66 to form a second stop. When the pin 54 is engaged in the slot

OMPI 52 of the L-shaped locking device 46, the two stops 64 and 66 are in close abutting relationship and are maintained tightly one against the other by the action of the spring 56. .The sub-frame can be tilted in an anti-clockwise direction around the axle 36 by,pushing forward in the direction of the arrow 68 on the upwardly protruding section of the L-shaped lever. In so doing, both sideplates at opposite ends of the sub-frame become free to move as one in an anti-clockwise pivoting movement about the axis of the rod 3 until the lower edges of the plates such as 34 abut stops (not shown) which dictate the lowermost position for the sub-frame. In this position the carriage (not shown) carried by the sub-frame and slideable along the two rods 36 and 38, is tilted by the same amount by which the sub-frame is tilted about the axis of the rod 36 so as to make the part of the carriage containing the daisy wheel that much more accessible.

The outwardly directed flanges 44 allow the sub-frame to be lifted and tilted in an opposite direction around the axis of the rod 36 so as to cause the L-shaped lever to once again engage the pin 54.

By providing that a cut-out in the leading edge of the outboard plate 42 registers with the stop 60, and is normally spaced therefrom, there is. no tendency for the outboard plates 42 to determine the home position for the inboard plates 34, the position of which is dictated solely by the abutting of the stops 64 and 66.

The gap between the cut away edge 70 and the „ stop 66 also permits the outboard plates 42 to be pivoted slightly more than the inboard plates such as 34 when they are lifted so as to allow for the engagement of the L-shaped levers 46 with the pins 54.

As soon as the outboard plates are let go, the action of the spring 56 causes the outboard plates 42 to revert to their normal position as shown in Figure 2 and this maintains through the action of the spring

56, the sub-frame formed by the inboard sideplate 44 and rods-36 and 38 in its correct position in which the carriage mounted thereon is in close proximity to the platen (not shown) Referring now to Figures 4 to 6 these show diagrammatically the preferred embodiment of a printer in accordance-with the present invention.

The printer has a platen 200 mounted for rotation in a main frame having endplates 202. Mounted adjacent one of these plates is a platen drive motor

204 which is arranged to drive the platen in known fashion.

Mounted adjacent the platen are paper guides 206 and 208 and guide 206 has a number of free rollers 210 and 212 set in it. The platen consists of a metal tube foam filled for noise suppression and having an outer rubber coating.

Attached to the main frame is a sub-frame having endplates 220 connected^""together by a rail 222 and pivotally mounted on a shaft 224 v/hich hinges the main frame and sub-frame together.

A carriage is mounted so that it may be slid along shaft 224. The carriage consists basically of two sideplates 230 and a roofplate 232. Attached to the edge of the roofplate remote from platen 200 is a plastics block 234 having a slot in it which engages on rail 222. Each of plates 230 has a bush set in ^" it through which shaft 224 passes. Located with its axis vertical within the carriage is a continuously driven DC motor 236 for advancing a ribbon in a cassette. Motor 236 has on its output shaft a continuously driven roller 238 which constitutes the power source for an intermittent drive mechanism of a type explained below with reference to Figure 7. Mounted above plate 232 is a print solenoid 240 having an actuation member 242 which constitutes a print hammer.

Mounted between plates 230 is a frontplate 244 having a depending portion 246 to which is attached a wire 248 which runs in a.loop between spindles 250, 252. Spindle 252 is an idler spindle and spindle 250 is driven by a carriage drive motor 25 ^r to move the carriage back and forth .along shaft 224.

Also mounted on plate 244 is a drive motor 256 for driving a daisy wheel the outer periphery of v/hich is indicated at 258 on Figure 5. The end of each petal may be brought to lie immediately in front of the print hammer 242 of solenoid 240.

The front of the carriage has two plastics paper guides 260 mounted on it which have a concavely curved surface adapted to lie closely adjacent platen 200 when the carriage is in its operative position as shown in Figure 4.

Each plate 220 is hinged effectively by bar 224 to one of the two plates 202. Plates 220 and 202 are each formed with an abutment flange 270 and 272 respectively. The abutment of these flanges defines the working position of the carriage relative to the platen in consistent and repeatable fashion. Abutment is maintained by means of a tension spring 274 attached between spigots 276 and 278 on plates 220 and 2Q2 respectively. If plates 202 are pushed downwards i.e. rotated clockwise about the centre of shaft of 224 as shown in Figure 4, spigot 276 moves down as shown in that Figure to a point at which the two spigots and the axis of shaft 224 are essentially collinear. In this position the spring does not tend to move the plate 202 back up and the carriage front is accessible by hand. The daisy v/heel can then be removed from the standard shaft on the motor 256 and replaced with another or replaced after cleaning. In

5 order to facilitate the removal a cranked lever is conveniently provided, the level pivoting about a vertical^"hinge pin mounted on the frontplate 244. The lever is preferably of generally Y shape with the two arms of the Y coming to lie between plate 244- and

-10 the rear face of the daisy wheel itself. The other end of the lever may be brought out from the side of the carriage and indeed may be wrapped round the side as shown at 282 on Figure 5. Pulling the end of lever 282 away from the platen or, if the lever is cranked

15 round the corner of the frame of the carriage, moving its end_. to the left as shown in Figure 5 causes the arms of the Y to ease the daisy wheel out of . engagement with the hub.. It can then be simply lifted r.^'out easily by hand,

20 A particular feature of the construction shown in Figures 4 to 6 is that the whole unit may be incorporated in an outer casing, schematically indicated at 288 on Figure -^ but be adequately isolated from that casing acoustically. For example the

25 bottoms of the main frame at 292 may be mounted via acoustically damping rubber bushes on a casing base. The casing may have a front portion which is adapted to hinge down and which has on its interior walls a pair of niches adapted to catch and move spigots 290,

30 one of which is fixed to each plate 220. The niches are so configured that v/hen the casing section identified as 288 in Figure 4 is in the position shewn and plates 220 are in the position shown, spigot 290 lies within the niche but does not contact any wall of

35 the niche. However, v/hen the front of the casing is swung down, just after the swinging movement, one wall

O H of the niche comes to bear against spigot 290 at each end and the continued downward movement of casing portion 288 then carries down plates 220 until the neutral position with spring 274 intersecting the axis of shaft 224 is reached, at which point the interior is available for e.g. changing or cleaning the daisy wheel or for replacing the ribbon cartridge which fits on top of the carriage. " The ribbon cartridge may simply sit on plate 232, through which a drive shaft for the take-up spool thereon may project.

Drive of the ribbon in the cassette is effected as noted above by means of a continuously driven motor 26 via an intermittent motion device. Actuation of the intermitteitmotion device is effected by means of a releasing lever which is pivoted about a point 296 which has an arm 298 extending towards the drive roller 238 of motor 236 and an arm -which extends upwardly and has a cranked end engaging in a transverse hole 300 formed in the print h-ammer.

Referring now to Figure 7, this shows the intermittent ribbon forwarding mechanism which is located on the underside of the carriage, seen from below. In the drawing reference numeral 110 designates a continuously rotating drive pinion 1 0 mounted on a motor shaft 112. The motor is a- simple inexpensive DC motor which is continuously driven in use of the printer. The pinion is formed v/ith teeth 114 which are complementary to teeth 116 formed around a v/heel 118 which is mounted for rotation about an eccentric axis and is carried by a stub shaft 120 v/hich extends from a crank 119. Crank 119 pivots about a fixed axis relative to the carriage, as does a ratchet wheel 122. Both the ratchet v/heel 122 and the crank

OMH 119 are mounted on a shaft 124 (shown in dotted outline) which constitutes the output drive shaft for the mechanism. The upper end of shaft 124 carries a- drive dog which engages the take-up spool -in the ribbon cartridge.

The ratchet wheel 122 can rotate in the direction of the arrow 126 but is prevented^ rom rotating in the reverse direction by means of a pawl 128 carried at the end of a cranked lever 170 which is pivoted at 132 and is prevented from moving out of engagement with.the teeth by virtue of the natural resilience of the arm 130 and a stop in the .form of a pillar 136. A spring 34 is secured to and extends between pillar 136 and a central spigot 138 which extends axially from wheel 1 8. The - spring 134.not only provides a degree of restoring force for the crank 119 but also serves to rotate the wheel 118 about is eccentric axis 120 v/hen the crank 119 is prevented from anti-clockwise movement by a stop 121.

An abutment member 142 pivotable about an axis designated 144 normally serves as a stop for a pin 140 so preventing rotation of the wheel 118. ^• The pin 140 is shown abutting the end 146 of the member 142. End 146 when actuated moves in a direction perpendicular to the plane of the drawing, away from wheel 1 8.

The teeth 116 do not extend completely around the pinion 118 and an untoothed region 148 is left v/hich registers with the toothed pinion 110 as the pin 140 approaches the end 146 of the member 142.

The disengagement of the teeth 116 from the teeth 114 would normally inhibit further rotation of the wheel 1 8 actually intc the position shown in the drawing but since the teeth disengage* only after the spindle 138 has moved beyond the eccentric axis 120

Oλ-TH of the pinion 118, the spring force of spring 134 v/ill continue to rotate the wheel 118 until the pin 1 0 abuts the end 146 of member 142.

^" Left in this condition, there will be no drive transmitted to the wheel 118 and the output shaft 124 will remain stationary. ^* _.

Member 142 is one end of a lever, the other end of which is pivoted in the plunger of the print solenoid. Thus, when the print solenoid is actuated, this lever is moved so as to rotate about axis 144 and to lift the end 146 sufficiently away from wheel 118 to disengage spindle 40. The spring force of spring 34 now starts wheel 118 rotating clockwise about axis 120. in the direction of the arrow 152. This rotation of^' the wheel 118 brings the toothed section of the wheel into engagement once again with the teeth around the pinion 110 and since the latter is rotating, this then causes the v/heel 118 to continue to rotate through a full circle until the untoothed region 148 once again registers with the pinion 110.

Since the wheel 118 is mounted eccentrically about the axis 1 0, rotation of the wheel around the axis 120, as a result of the force exerted by the spring 134, which tends_to keep the wheel 118 in meshing engagement with the pinion 110, v/ill cause ^'the axis 120 to be displaced away from the pinion 110 and then back towards it again during the full circle of rotation. The result is that the crank 119 will be arcuately displaced relative to its fixed stop 121 and a spring pa l 139, carried on the crank 119, indexes the ratchet wheel 122 in the direction of the arrow 126 during the first half of the circular movement of the wheel 118. The return movement of the wheel through the other half-circle will produce a reverse movement of pawl^' 139 but pawll2S prevents ratchet wheel 22 rotating in the reverse direction (i.e. anti-clockwise

OMPI WIPO as shown).

In place of spring pawl139, spring means may be provided for engaging a separate pawl in the ratchet teeth on ratchet wheel122. However, rather than provide spring means separate from the pawl, the pawl itself is preferably formed of a resilient material -having a natural springiness which causes it to maintain engagement with the teeth around ratchet wheel122. _ - It will be seen that by altering the eccentricity of the axis 120 relative to the centre of the Λvheel 18, the angular movement of the crank 119 may be varied; an eccentricity should be chosen such that a sufficient arcuate displacement of the crank 119 is obtained to index the ratchet wheel122 by.a whole number of ratchet tooth pitches. In this way there will be no tendency for any backlash to occur since the retaining pawl 128 will have just engaged a new ratchet tooth at the end of the forward stroke of the crank 119.

It v/ill be seen that if the teeth are removed from the pinion 110 and wheel 118, and a tyre is fitted around one or other (or both) of the pinion and wheel, drive will be transmitted in the same way relying on friction between the tyre and the smooth- cylindrical surface or tyre of the other member. •Where this approach is adopted, it is necessary to ensure that the minimum radius from the eccentric spindle 120 of the wheel 118 is less than that required to effect driving engagement between the wheel and pinion so that in that one position, and preferably in a range of positions immediately on either side of that minimum radius, the pinion makes no driving engagement with the wheel. It is also necessary to ensure that the wheel 118 comes to rest with the pin ^' 140 against the stop 146 with the position of minimum radius lying between the eccentric axis 120 and the axis 112 of the pinion 110.

Stop 121 is preferably positioned such that.the crank 119 engages this stop at the end of its return stroke at a position well before the rotation of the wheel 118 has caused the latter to move out of engagement with the pinion110.but such that the point 138 is beyond the eccentric centre of rotation 120 so that continued rotation of the wheel 118 is ensured under the restoring force of the spring 134, bringing the pin 140 finally into contact v/ith the stop 146.

Claims

C L A I M S

1. A printer including an elongate platen for supporting material to be printed and a print carriage, the carriage being mounted for movement parallel to the platen and including a daisy wheel, means for bringing the daisy wheel into the desired position, and a print solenoid adapted when actuated to move one petal of the daisy wheel towards the platen, wherein the carriage is mounted in a frame pivotal about an axis parallel to and spaced from the platen, and including means for maintaining the carriage in a printing position closely adjacent the platen and for enabling it to be swung away from the platen to facilitate access to the daisy wheel.

2. A printer according to claim 1 wherein the platen is a resiliently covered roller and the carriage is mounted on a track parallel to the axis of the roller, the track being supported in a frame which can be pivoted about an-axis parallel to the axis of the roller and spaced therefrom.

3 - A printer according to claim 2 wherein the frame is pivoted to a second frame in which the roller itself is mounted, the frame and second frame having cooperating stop means defining -a position in v/hich carriage and platen are close together.

4. A printer .according to claim 3 wherein the frame and second frame are held with their respective stop members abutting one another under a spring bias.

5. A printer according to claim 4 wherein the spring bias is provided by tension springs pivotally connected at each end to parts of the frame and second frame respectively, the pivotal connection points and the hinge axis between frame and sub-frame being substantially collinear when the carriage is swung away from the platen.

5 &. A printer according to any one of claims 1 to 5 wherein the front of the carriage bears paper guide means which, when the carriage is adjacent the platen, cooperate with th platen to define a narrow path for paper or the like and accordingly to hold the 10 paper or the like firmly against the platen during printing.

7. A drive mechanism for advancing the take-up spool in a printer, the drive mechanism comprising: 1. continuously rotating drive means 15 2. a drive take-up mechanism normally disengaged from the continuously rotating drive means 3. an escapement mechanism having a rest position in which the drive take-up mechanism is disengaged fro .the continuously rotating drive 0 and an active position in which the drive take-up means engages the continuously rotating drive, the ^{• '} . escapement mechanism permitting-only a given rotation of the drive take-up mechanism before reverting to its rest position, and 5 4. means for triggering the escapement mechanism into its active state in response to movement of a- thrust member.

8. A printer including a drive mechanism according to claim 7 and arranged to be actuated at the same 0 -time as a print solenoid is actuated, the solenoid itself being thrust member.

QMPI

9. A drive mechanism according to claim 7 and including on the output drive shaft, an evenly toothed ratchet wheel, the arrangement being such that each time the intermittent drive is actuated the ratchet wheel is advanced by one or more teeth.

10. A drive mechanism according to claim 7 or 9 and comprising: a. motor drive means for continuously rotating a driving pinion b. a ratchet wheel .mounted on the output drive shaft for the spool c. a driving v/heel engageable with the driving pinion and rotatable about an eccentric axis defined by a stub shaft which extends from one end of a crank which is pivotable about the ratchet wheel axis d. a pawl mounted on the crank which engages the ratchet teeth and indexes the ratchet wheel by one tooth in response to arcuate -movement of the crank e. a stop on the driving wheel ^"f• an abutment engageable with the stop to inhibit rotation of the.wheel, the abutment being movable in response to actuation of the printer out of engagement with the stop to permit the wheel to be rotated by the continuously driven - pinion until the stop and abutment engage once ^"again and g_* spring means adapted to provide a force for moving the v/heel out of engagement with the- driving pinion after the ^'stop and abutment have _.become engaged and for moving the wheel back into engagement with the driving pinion v/hen the ^" abutment is moved out of engagement with the stop.

11. A drive mechanism according to claim 10 and

. wherein a stop is provided on the crank which.engages a fixed member to define a permissible arcuate displacement of the crank member on which the driving 5 wheel is mounted.

12. A printer according to any one of claims 1 to .11 and including on the carriage a lift-off lever having a central fulcrum, arms to one side of the fulcrum located adjacent to the rear face of a • 10_. daisy wheel positioned^' on the carriage and adapted to move in a direction subsequently perpendicular to the plane of the daisy wheel and having its end the other side of the fulcrum accessible to effect such movement.

5 13. printer according to claim 12 wherein the lever is sprung biased to a position in which the arms lie spaced from the rear of the daisy wheel by a maximum extent.

OMPI