Patent GB-997132-A (GB)
IPC: B41J19/64
Filed: 1963-09-23
Abstract: 997,132. Typewriters. INTERNATIONAL BUSINESS MACHINES CORPORATION. Sept. 23, 1963 [Sept. 25, 1962], No. 37244/63. Heading B6F. Differential letter-spacing mechanism.-A typewriter is provided with a differential letterspacing arrangement, permitting the use of characters of different widths, which includes a carriage 4, Fig. 1, movable in fixed increments E in one direction #<SP>1</SP> relating to an escapement rack 1, movable relatively to the frame of the typewriter in the opposite direction f<SP>2</SP> and electromagnetically-operated ratchet means to move the carriage with the rack in the said opposite direction during the interval between actuation of a key lever and the actual strike of a type head by a distance NdE, which corresponds to the width of the character to be typed. The carriage 4 is positioned relatively to the chain rack 1 by escapement pawl 7 and a positioning pawl 8 engaging toothed racks 1a and 1b, respectively, the teeth facing in opposite direction. The chain rack 1 is carried by a drive wheel 2a and idle wheel 2b and guided by a slide bar 3. The pitch of the rack teeth corresponds to maximum spacing E between two characters, which is divided into N intervals dE. Wheel 2a is driven selectively or collectively by axially spaced ratchet wheels R1, R2 and R3 through one way clutches 2c. Immediately following the strike of the type head or a space bar movement the single pawl 7 is lifted, allowing carriage 4 to escape by one pitch length E of the rack 1a in the direction f<SP>1</SP> and movement of the carriage is arrested by the face 7<SP>1</SP> of pawl 7 coming into contact with the next tooth of the rack. Play of the carriage in the opposite direction f<SP>2</SP> is limited by pawl 8 which coaots with rack 1b. At this stage on depression of the subsequent key lever the actual spacing corresponding to the character is determined in that the maximum spacing E determined by the carriage advance is reduced by the required amount in accordance with the width of the next character to be typed. This reduction is obtained by moving the carriage which is now engaged to the rack the appropriate amount in the direction f<SP>2</SP> before the moment of actual strike of the selected character. The selected amount of carriage and rack movement is obtained by rotation of the drive wheel 2a in an anticlockwise direction, by actuation of one or more of electromagnets ERI . . . ER3, whose pawls C1 . . . C3, control and limit the angular displacement of ratchet wheels R1 . . .R3. The selection of an electromagnet or electromagnets specific to a selected character is achieved by electrical contacts placed on the respective key lever. The pitches of the ratchet wheels R1, R2, R3 correspond to one, two or three dE intervals, respectively. The actions of the ratchet wheels R1 . . . R3 may be cumulative by arranging for them to be operated in sequence by delaying selectively the action of the respective electromagnets. In another embodiment (in Fig. 2, not shown), ratchet wheels R1 . . . R3 are replaced by a single ratchet wheel R<SP>1</SP>1 and the spacing E is divided into four elementary intervals dE. The armature movements of the electromagnets E<SP>1</SP>R1 and E<SP>1</SP>R2 are such that their associated pawls C1, C2 can displace the ratchet wheel R<SP>1</SP>1 one or two tooth pitches selectively or three pitches cumulatively. In a further embodiment in Figs. 3a and 3b, a ratchet wheel R<SP>11</SP>1, which drives a shaft 2d of the chain drive wheel 2a by a clutch has three similar elements 12a provided with electromagnets E<SP>11</SP>1 operating a pawl 13. Each of the elements is controlled by levers 14, 15, 16 pivotally mounted on a lever 21 following a cam 18 mounted on a camshaft 20. The elements such as 12a have an oscillatory movement about the shaft 2d which corresponds to one, two or three tooth pitches of the ratchet wheel R<SP>11</SP>1, and drive the wheel when the respective pawl is moved by the respective armature. By phasing the action of the electromagnets it is possible to displace the ratchet wheel R<SP>11</SP>1 angularly in a cumulative manner. Alignment for impression.-Following displacement of the carriage and rack in the direction f<SP>2</SP>, Fig. 1, by ratchet wheels R1 . . . R3, or R<SP>1</SP>1 or R<SP>11</SP>1, which displace the carriage in the said direction slightly more than an integral interval dE, the electromagnets associated with the ratchet wheels are released and the carriage moves in the direction f<SP>1</SP> under the action of its bias until pawl 6, 61 or 6<SP>11</SP> engages its respective ratchet wheel R5, R<SP>1</SP>4 or R<SP>11</SP>4 fast with the shaft 2d and aligns the carriage for impression. Keys operating electrical contacts.-Each of the key levers (not shown) is provided with several contacts of which each corresponds to a different proportional spacing and of which only one is operative at a time. A similar selection is carried out to accommodate the use of upper and lower case characters of different width.