CA1046005A - Single element printer - Google Patents

Abstract

SINGLE ELEMENT PRINTER
Abstract of the Disclosure A printer has a carrier having a rocker which supports a print shell on which are disposed type characters in a two dimensional array with the shell controllably movable in two degrees of freedom (rotate and tilt) to selectively position each type character opposite a record-medium-carrying platen for printing. The rotation is per-formed by a motor on the rocker and directly connected to the print shell. The tilt is performed by a motor on the carrier and connected via a particular link configuration to the print shell. In addition, during printing the shell is driven against the platen with a force related to the particular character being printed by virtue of a controllably rotatable shaft which via a cam drives the rocker.

Description

This invention pertains to printers and more particu-la:rly to single element printers which are electronically con-trolled.
Of the many uses for printers there are two which prledominate in number. They are keyboard controlled t~pewriters and signal controlled output devices for computers, communi-cations terminals and the like. In fact, many such output devices utilize conventional electric typewriters. Of the con-ventional electric typewriters the single element print head variety as exemplified by the IBM Selectric family have become the most popular. While such typewriters are adequate for many tasks, it should be realized they are highly complex machines containing innumerable mechanical drives, linkages and the like. This complexity results in an initially expensive machine.
In addition, while a typewriter is satisfactory for use by a typist, it not only has a too low upper limit of speed when driven by a computer or the like, but also is not sufficiently rugged for the extended period of continued use required in many computer, word processing and communications applications.
Furthermore, such machines are noisy. These limitations arise from the mechanical complexity of presently avallable type-writers.
It is accordingly, a general object of the invention to provide an improved printer.
It is another object of the invention to provide an improved printer wherein coded combinations of signals represent the characters to be printed and these coded com-binations of signals are processed to select the type characters for printing.
It is a further object of the invention to provide an improved single element print head printer.

J~ J;c~ rk In such a machine all the type characters of a font are located on the surface of one print device which may be positioned for printing en-gagement with a platen. Of such devices the most common and versatile is a printing head having a truncated spherical print shell with characters arranged in rows and columns about the peripheral surface of the shell.
A character is selected for printing by rotating and tilting the shell. In particular, there is actuated by a displacement mechanism having two principal portions, one for titling and another for rotating the shell.
More specifically, selecting links are operated which determine the pivot points of connecting members to produce an output of predetermined displace-ment and direction. In each portion of the displacement mechanism, the value of output is determined by the links selected either singly or in combination. When the links are selected in combination the displacement is the sum of the individual displacements of the links. A tape and pulley mechanism to the printing head to locate the selected character in a re-ference position. Thereafter, the head is caused to strike the platen to print the chosen character. A more complete discussion of such machines can be found in United States Patent No. 2,919,002 issued December 29, 1959 to International Business Machines Corporation, New York, New York.
There have been attempts to dispense with the complicated linkages to rotate the print shell. See for example, United States Patent No~
3,788,443 issued January 29, 1974 to Paillard S.A., Sainte-Croix, Vaud, Switzerland and United States Patent No. 3,838,764 issued October 1, 1974 to Triumph Werke Nuernberg A.G., Nuernberg, Germany. Here, reel and pulley arrangements have been used. However, such reel and pulley arrangements are not reliable and are slow operating since the reels and pulleys have considerable play.
It is another object of the invention to replace such mechanisms with a motor directly connected to the print shell wherein both the print shell and the motor are carried on the rocker which is thrown toward the platen. Such an arrangement provides the simplest rotate ~r~

10~005 mechanism possible In addition, the added mass on the rocker permits slower drive velocities of the rocker for a given amount of impact momentum. Con-sequ,ently, much quieter printing is possible since impact noise is related to the energy of the rocker on impact and such energy is proportional to the square of the velocity on impact.
In such previously available printers there is an impression or impact control to insure that each character when printed has the same shading.
In other words, when printing a "period~ or a "comma" less impact is required than when printing an m or a w. The usual impression control utilizes a con-stant speed cycle motor and a plurality of selectable cams which drive theprint element against the platen. While this configuration adequately performs the impact control function, it is apparent that the utilization of selectable cams again complicates the mechanism and slows down the printing speed.
It is, accordingly, another object of the invention to simplify the impression or impact control portion of the printer by connecting the drive motor via a single cam on the shaft of the drive motor to ~he print head or rocker and control the speed of rotation of such motor to control the impact force.
With such single element prin* head devices the high print quality is obtained because the print shell is mechanically detented before impact.
The nature of detenting limits the possible speed of operation as well as submitting several elements to wear.
It is, accordingly, another object of the invention to modify the presently known detenting arrangement to permit high speed operation and longer life for the print head.
According to one aspect of the present invention, there is disclosed a printer comprising: a platen; a print carrier opposite said platen, said print caTrier comprising a print head, said print head having a print element upon which are type characters, positioning means for selectively moving said print element to position a particular type character operatively opposite said platen for printing, a rocker means for supporting said print element, a cam follower connected to said rocker means and means for mounting said ~ _ 3 _ .~

l046Qas rocker means to pivot so that said print element can move against said platen, a drive shaft, a cam on said drive shaft and operatively cooperative with said cam follower so that as said drive shaft rotates said print element is driven toward said platen, and a motor for rotating said shaft; and means for moving said print carrier along a path parallel to said platen.
According to a further aspect of the invention, there is disclosed a printer comprising a platen, a print head, said print head having a print element upon which are type characters, said characters being grouped in a plurality of sets according to size, positioning means for selectively moving said print element to position a particular type character operatively opposite said platen for printing, a rocker means for supporting said print element, a cam follower connected to said rocker means, and means for mounting said rocker means to pivot so that said print element can move against said platen, a drive shaft, a cam on said drive shaft and operatively cooperative with said cam follower so that as said drive shaft rotates through a single rotational cycle said print element is driven toward said platen, a motor means when energized rotating said drive shaft through a single rotational cycle at selectively different speeds, and control means for energizing said motor means each time a character is to be printed, said control means energizing said motor means to rotate said drive shaft during one portion of the single rotational cycle at a first speed and during another portion of the same single rotational cycle at a different speed selected in accordance with the set to which the character to be printed belongs.
According to yet a further aspect of the invention, there is dis-closed a printer comprising a platen, a rocker means, a print shell on said rocker means having a plurality of type characters, means on said rocker means for driving said print shell to rotate about a first axis, means for pivoting said rocker means about a pivot axis to drive a type character on said print shell against said platen, a support means on said rocker means to support said print shell to tilt about a second axis, a motor supported remotely from said rocker means, an arm connected to said motor, a link having one end pivotably connected at a first point to said arm and a second end ~ - 3a -1046~05 pivotably connected at a second point to said support means, the line connect-ing said points passing through said pivot axis.
According to a further aspect of the inven~ion there is disclosed a printer comprising a platen, a print shell having a plurality of type characters and being in the form of a truncated sphere, said print shell having a plurality of rotate detents along a peripheral edge of the truncated sphere, support means for supporting said print shell to rotate about a first axis and tilt about a second axis, a plurality of tilt detents in said support means, a slotted sector arm pivotably connected to said support means and having a detent nose positioned opposite said rotate detents, a detent arm, means for moving said detent arm between first and second positions, said detent arm passing through the slot of said slotted sector arm and opposite said tilt detents to apply pressure to said sector arm to move it away from said rotate detents when said detent arm is in the first position and to remove such pressure whereby said detent nose can engage one of said rotate detents and also engage one of said tilt detents when said detent arm is in the second position, a plunger having a first shoulder resting against said sector arm, a spring for biasing said plunger to move in a given direction to urge said detent arm into engagement with one of said tilt detents and to urge said detent nose into engagement with one of said rotate detents, means for impell-ing said print shell against said platen, and means for driving said detent arm into said second position when said print shell is being impelled.
Other objects, the features, and advantages of the - 3b -'~`

1046005 ~ y_ invention will be apparent from the followinq detailed des-cription when read with the accompanying drawinq which shows by way of example, and not limitation, an exemplary embodiment of the invention.
Fig. 1 is a plan view of the printer accordinq to the invention, the view omitting unrelated parts and being partially c~iagrammatic;
Fig. 2 is a diagrammatic side view of the printer of Fig. 1 showing cooperating elements and their logic-controlled energizing means;
Fig. 3 is a view similar to Fig. 2 except that struc-ture is clarified, energizing means are omitted or shown schematically and the print head or rocker assembly is re-tracted;
Fig. 4 is a front view taken on line 9-9 in Fiq. 3 with parts broken away or in phantom and the rocker assembly in the print position;
Fi~. 5 is a fragmentary plan view taken on the line 10-10 ln Fig. 4;
Fig. 6 is an enlarged fragmentary view of Fig. 4;
Fiq. 7 is a side view thereof;
Fig. 8 is a bottom view taken on line 13-13 in Fig, 7;
and Fig. 9 is an enlarged fragmentary view of Fig. 7 except that the mechanism is shown in the position wherein the printing element detents are retracted.
The printer in accordance with the invention is controlled by electronics (not shown). In particular, there can be a rotation control which sends pulse signals along a cable DR to cause rotation of the print shell, and receives signals on lines FR and SR to indicate the instantaneous rotational position of the print shell. There can be a tilt control which emits pulse signals on a cable DT
to cause tilting of the print shell, and receives signals on lines FT ànd DT to indicate the instantaneous tilt 104f~0()5 position of the print shell. These can be a print control which feeds pulses at controllably variable repetition rate on a cable DP to control the impact velocity of the print shell against a platen, and which receives signals on lines EP, Cl and C2 to indicate different positions in a print cycle so that the repetition rate of the pulses on cable DP can be changed. These can be an index control which feeds signals on a cable DI to control horizontal indexing of the print carrier and which receives signals on lines FI and SI to in-dicate the instantaneous position of the carrier. The printer will also have a line feed mechanism (not shown) for vertically moving paper past the print shell.
Referring to Figs. 1 to 6 and to Figs. 1 and 2 in particular, printer PR is shown having a frame 14 spindling a platen 16.
Carrier 20, comprising a ribbon feed 30, a print head 32 and a step motor 50, is horizontally moved via a cable means 34, by a step motor 36 in response to pulses on cable DI
A transducer 38, on motor 36 relays information viat line SI
to a (not shown) indextcontrol.
In particular, when step motor 36 receives the stepping signals on cable DI from the index control (not shown) the motor rotates pulley 34A causing the cable means 34 to move the carrier 20 to the left or right. At the same time, transducer 38 which can comprise a disc 38A with a band of slots, and a light source-light sensitive cell, such as a light emitting diode-photosensitive solid state device strad-ling the band indicated generally as combination 38B, emits a pulse on line SI each time a slot of disc 38A is operatively opposite combination 38B. In addition, carrier 20 carries a light interposer 39A which interrupts a light path estab-lished between a light source and a light sensitive cell in-10460()5 dicated generally at 39B to cause the transmission of a pulse on line FI to index control when the pr;nt carrier 20 is at the left hand margin.
The print head has rotate step motor 42 which rotates in a clockwise or counter-clockwise direction as viewed in Fig.
1 in response to the step signals received on cable DR from a not-shown rotation control. Connected to the shaft of motor 42 is a slotted disc having one band of twenty-two equispaced slots (one for each character in a row) and a second band with a single slot. Each of the bands is straddled by light source-light sensitive cell combinations indicated generally by box 44. Thus as the motor 42 is stepped in response to pulses on cable DR from the rotational control, a pulse is emitted on line SR as each of the slots of the first band is sensed. In addition, whenever the slot of the second band is sensed a pulse is emitted on line FR to the rotation control. The details of how step motor 42 rotates print head 40 will be describedhereinafter in detail.
A tilt step motor 46 rotates clockwise or counter-clockwise in response to step signal or pulses received on cable DT from a not-shown tilt control. Connected to the shaft of motor 46 is a slotted disc haviny one band with four slots one for each row of characters and a second band with a single slot, each of the bands is straddled by a light source-light sensitive cell combination indicated generally by box 48.
Thus as the motor 46 is stepped in response to pulses on cable DT a pulse is emitted on line ST as each slot d the first band is sensed, and whenever the slot of the second band is sensed a p~lse emitted on line FT to tilt control TC of Fig. 1.
Shaft 18 is driven by step motor 50 in response to stepping signals or pulses received on cable DP from the print control. Connected to the shaft of motor 50 is a disc having three slots, each in different bands, straddling each band is a light source, light sensitive cell combination in-dicated generally by box 52. Thus, as the motor 46 is stepped a pulse is emitted sequentially on lines Cl, C2 and EP. The positions of the slots associated with lines Cl and C2 are chosen to indicate when the actual printing is being performed as will hereinafter become apparent.
The platen-rotation means 54 and ribbon-feed means 56, although linked operatively through manual, mechanical and logic control, are not a part of the invention, and there-fore are referred for edification only.
The basic operations and logic references shown in Fig. 2 center around velocity-controlled cam 58 which co-operates with follower 66 to impel the rocker assembly 60 of print head 32 clockwise around bearing 62 driving the print shell 40 toward platen 16. Cam 58 is fixed on shaft 18 which is spindled on carrier 20. Shaft 18 is rotated by motor 50 which is preferably mounted on carrier 20. In fact~ shaft l8 can-be the shaft of motor 50. In this way, the print head driving mechanism is greatly simplified over previously known driving mechanism. (Two additional cams, described herein-after, are also mounted on shaft 18.) As best seen in Figs. 3, 4 and 5, the print head 32 comprises the rocker assembly 60 and the tilt means 68.
The rocker assembly includes pivotable base member 60, mounted for rotation about bearing 62. The member 60 has a yoke 104 and an arm 102 which carries cam follower 66.
Yoke 104 spindles print shell 40 at bearings 40B, spindles shaft 74 in a bearing 106 (see also Fig. 6) and arm 96 in a bearing 108.
Passing through the base of rocker 60 is shaft 74 of motor 42 having one end connected to universal joint 76.
(See particularly Fig. 4). Above universal joint 76, the upper section 74a of shaft 74 is journaled through a housing 40c, tiltable on bearings 40b, to connection with print shell 40.
The other end of shaft 74 is the shaft of motor 42 whose hous-in~ is mounted on the rocker. Thus rotation of motor 42 presents the twenty-two different angular positions each associated with a different character in the rows of characters on print shell 40 to platen 16.
In this way there is a minimum of mechanical con-nections between the rotate motor 42 and the print shell 40.
Thus, leading to a simplification of structure which increases the potential life of the device and permits higher speed operation of the device. In addition, by supporting the rotate motor on the rocker assembly increases the mass of the assembly.
Therefore, lower impact velocities can be used to control the print impression, Cons~quently, less noise is generated upon impact.
The tilt means 68 comprises the motor 46 mounted on carrier 20. The shaft of motor 46 is connected via arm 70 and link 72 to bearing 40a in housing 40c. By this means, the rotation of motor 46 selects which of the rows of char-acters on shell 40 is to be presented to platen 16. It should be noted that since l~nk 72 connected between bearing 40a and pin 70a passes through the pivot point of rocker 60.
(i.e. bearing 62) as shown in Figs. 2 and 3 the differential linkage length is minimized during the pivoting of the rocker assembly 60.
In Figs 4 and 5 there is shown on shaft 18 a ribbon feed cam 80 for controlling the ribbon 82. Since the ribbon feed portion of the printer forms no part of the present invention and will not be discussed further.

In addition, shaft 18 has a detent-control cam 84.
An arm 86, spindled at a bearing 88 spindles a roller 86a engaged by a second arm 92 spindled at a bearing 94. Arm 92, in turn, is engaged by a detent arm 96 that is biased counter-clockwise by a first spring 98 and by a second spring to be described.
As practiced in the prior art, arm 96 engages one of four tilt detents 110 directly and disengages one of twenty-two rotation detents 112, indirectly, by downward pressure on a slotted sector 114. However, to obtain high operative speeds, through logic control, without adding wear, and de-terioration of reliability, positive engagement of the detents i8 increased and friction at the arcuate contact surface 114a of sector 14 during disengagement is decreased in a new and novel manner.
In Figs. 4 to 9, a plunger 116, slidably fitted in a hole 118 has a high shoulder 116a and a low shoulder 116b (See especially Fig. 9). A spring 120 biases plunger 116b up-wards, and through contact at shoulder 116a, cooperates with spring 98 to obtain positive engagement of arm 96 in tilt detent 110. Additionally, through contact of shoulder 116b with sector 114, spring 120 operates to obtain positive en-gagement of arm 114 in rotate detent 112 (3CC ~ig. 13).
By this means, it will become evident that arm 114 can be made rapidly, yet reliably responsive without friction between the bottom surface of finger 96b and the surface 114a.
The height of sector 114 at this point is less than the spacing 116c between the shoulders 116a and 116b so that in the un-detented position of finger 96b no friction exists betweeen the aforesaid surfaces. However, when finger 96b seats in detent 110 sufficient over travel of nose 114b is available to seat it in rotate detent 112.

11~46005 In operation, rotate motor 42 rotates shaft 74 to select the "column" of the desired character on print shell 40 while at the same time tilt motor 46 operative via link 72 ti~ts print shell 40 to the row of the desired character.
As these motions are ending print motor 50 drives shaft 18 to perform one revolution. During the revolution three motions are performed, the rotation of cam 58 to drive rocker number 60, a rotation of cam 80 to move ribbon 82 and a rotation of cam 84 to control the deten~ing of the print shell 40. It is the de-tenting ~ the print shell before and during impact which en-hances the print quality.
Normally, i.e. with shaft 18 in its rest position, roller 90 rests on crest 84a of cam 84, arm 86 is pivoted counterclockwise (see Fig. 4) pressing against finger 96a of arm 96. Thus arm 96 is rotated clockwise about pin 108 caus-ing its other finger 96b to be clear of detents 110~ This inger also presses down on sector 114 (see Fig. 9) causing nose 114b to clear detents 112 (See Fig. 8). In ~is position the print shell 40 is fully tiltable and rotatable in res-ponse to its associated motors. Now as the sha~t rotates roller 90 assumes the position shown in Figs. 4 and 5. Then finger 96b is driven up into a detent 110 by virtue of spring 98 rotating arm 96 counter-clockwise about pin 108 and by spring 12~ Jpushing the shoulder 116a against finger 96b.
In addition, detent nose 114b is driven into detent 112 by spring 120 actin~ via the second shoulder 116b pushes arm 114 in the clockwise direction. Now the print shall 40 is mechani-cally locked in position.
Inspection will further show that particularly at high speeds, the vertical spacing 116c, between shoulders 116a and 116b ensures that engagement of arm 96 in detent 110 and rotational positioning of element 40 are completed before nose 114b moves into detent 112. Thus,detent nose 114b moves in with greater reliability and less wear.
At the same time rocker assembly 60 responds to fol-lower 66 mounted thereon. This response moves print shell 40 towards platen 16 in two separate velocity patterns. Follower 66 is first accelerated by the rise in cam 58 from the dwell 58a to, substantially, the peak 58b, from which point velocity is imparted to the mass of print head 32. In this manner, print shell 40 prints characters at variable pressure dependent upon acceleration changes in motor 50.
Finally cam 80 causes the indexing of ribbon 82.
Then all motions ceases until another character is called for.
The overriding observation in comparing the mechanical embodiment of the present invention to the present art,in printing element articulation, is the great reduction in parts with its obvious advantages consonant with high speed operation.
Printing speed is thereby brought closer to the speeds available with logic and servos above-described.
While only one embodiment of the invention has been shown and described in detail there will now be obvious to those skilled in the art many modifications and variations satisfying many or all of the objects of the invention but which do not depart from the spirit thereof.

2, 1 l _ ~J

Claims (15)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1, A printer comprising: a platen; a print carrier opposite said platen, said print carrier comprising a print head, said print head having a print element upon which are type characters, positioning means for selectively moving said print element to position a particular type char-acter operatively opposite said platen for printing, a rocker means for supporting said print element, a cam follower connected to said rocker means and means for mounting said rocker means to pivot so that said print element can move against said platen, a drive shaft, a cam on said drive shaft and operatively cooperative with said cam follower so that as said drive shaft rotates said print elements is driven toward said platen, and a motor for rotating said shaft; and means for moving said print carrier along a path parallel to said platen.

2, The printer of claim 1 further comprising control means to energize said motor to operate at controllably variable speeds.

3. The printer of claim 1 wherein said drive shaft is the shaft of said motor.

4. A printer comprising a platen, a rocker means, a print shell having a plurality of type characters thereon, a support means on said rocker means to support said print shell to rotate about a first axis and to tilt about a second axis, a first motor having a shaft, said first motor and shaft being carried by said rocker means, means for connecting the shaft of said first motor to said print shell for rotating the latter whereby a unitary structure is obtained, means for pivoting about a third axis said rocker means carrying said print shell and said first motor to drive a type character on said print shell against said platen, a second motor supported remotely from said rocker means, an arm connected to said second motor, and a link having one end pivotably connected to said arm and a second end pivotably connected to said support means, a straight line joining the ends of said link passing through said third axis about which said rocker means pivots.

5. A printer comprising a platen, a print head, said print head having a print element upon which are type characters, said characters being grouped in a plurality of sets according to size, positioning means for selectively moving said print element to position a particular type character operatively opposite said platen for printing, a rocker means for supporting said print element, a cam follower connected to said rocker means, and means for mounting said rocker means to pivot so that said print element can move against said platen, a drive shaft, a cam on said drive shaft and operatively cooperative with said cam follower so that as said drive shaft rotates through a single rotational cycle said print element is driven toward said platen, a motor means when energized rotating said drive shaft through a single rotational cycle at selectively different speeds, and control means for energizing said motor means each time a character is to be printed, said control means energizing said motor means to rotate said drive shaft during one portion of the single rotational cycle at a first speed and during another portion of the same single rotational cycle at a different speed selected in accordance with the set to which the character to be printed belongs.

6. The printer of claim 5 wherein said control means controls said motor means to rotate said drive shaft during a third position of the single rotational cycle at a further different speed.

7. The printer of claim 5 wherein said one portion commences at the start of the single rotational cycle.

8. The printer of claim 5 wherein said one portion ends at the end of the single rotational cycle.

9. The printer of claim 5 further comprising a print carrier movable opposite said platen for supporting said rocker means and said motor means.

10. The printer of claim 5 wherein said print element comprises a print shell and support means for supporting said print shell to rotate about a first axis and to tilt about a second axis; and said positioning means comprises a first motor mounted on said rocker means and having a shaft for rotating said print shell, and means for tilting said print shell.

11. The printer of claim 5 wherein said print element comprises a print shell and means for supporting said print shell to rotate about a first axis and to tilt about a second axis and said positioning means com-prises rotating means for rotating said print shell, and tilting means for tilting said print shell, said tilting means comprising a motor supported remotely from said rocker means, an arm connected to said motor, and a link having one end pivotably connected to said arm and a second end pivotably connected to said support means, said link passing through the pivot axis of said rocker means.

12. The printer of claim 5 wherein said print element comprises a print shell in the form of a truncated sphere and having a plurality of rotate detents along a peripheral edge of the sphere and support means for supporting said print shell to rotate about a first axis and to tilt about a second axis, a plurality of tilt detents in said support means, a slotted sector arm pivotably connected to said support means and having a detent nose positioned opposite said rotate detents, a detent cam on said drive shaft, a detent cam follower operatively opposite said detent cam, a detent linkage connected to said cam follower and having a detent arm passing through the slot of said slotted sector arm and opposite said tilt detents to apply pressure to said sector arm to move it away from said rotate detents when said drive shaft is in a first position and to remove such pressure when said drive shaft is in second position, and a plunger having a first shoulder resting against said detent arm and a second shoulder resting against said sector arm, and a spring for biasing said plunger to move in a given direction to urge said detent arm into engagement with one of said tilt detents and to urge said detent nose into engagement with one of said rotate detents.

13. A printer comprising a platen, a rocker means, a print shell on said rocker means having a plurality of type characters, means on said rocker means for driving said print shell to rotate about a first axis, means for pivoting said rocker means about a pivot axis to drive a type character on said print shell against said platen, a support means on said rocker means to support said print shell to tilt about a second axis, a motor supported remotely from said rocker means, an arm connected to said motor, a link having one end pivotably connected at a first point to said arm and a second end pivotably connected at a second point to said support means, the line connecting said points passing through said pivot axis.

14. The printer of claim 13 wherein said print shell is in the form of a truncated sphere and having a plurality of rotate detents along a peripheral edge of the truncated sphere and wherein there are a plurality of tilt detents in said support means, further comprising a slotted sector arm pivotably connected to said support means and having a detent nose positioned opposite said rotate detents, a detent arm, means for moving said detent arm between first and second positions, said detent arm passing through the slot of said slotted sector arm and opposite said tilt detents to apply pressure to said sector arm to move it away from said rotate detents when said detent arm is in the first position and to remove such pressure whereby said detent nose can engage one of said tilt detents when said detent arm is in the second position, a plunger having a first shoulder resting against said detent arm and a second shoulder resting against said sector arm, and a spring for biasing said plunger to move in a given direction to urge said detent arm into engagement with one of said tilt detents and to urge said detent nose into engagement with one of said rotate detents.

15. A printer comprising a platen, a print shell having a plurality of type characters and being in the form of a truncated sphere, said print shell having a plurality of rotate detents along a peripheral edge of the truncated sphere, support means for supporting said print shell to rotate about a first axis and tilt about a second axis, a plurality of tilt detents in said support means, a slotted sector arm pivotably connected to said support means and having a detent nose positioned opposite said rotate detents, a detent arm, means for moving said detent arm between first and second positions, said detent arm passing through the slot of said slotted sector arm and opposite said tilt detents to apply pressure to said sector arm to move it away from said rotate detents when said detent arm is in the first position and to remove such pressure whereby said detent nose can engage one of said rotate detents and also engage one of said tilt detents when said detent arm is in the second position, a plunger having a first shoulder resting against said sector arm, a spring for biasing said plunger to move in a given direction to urge said detent arm into engagement with one of said tilt detents and to urge said detent nose into engagement with one of said rotate detents, means for impelling said print shell against said platen, and means for driving said detent arm into said second position when said print shell is being impelled.