US3927753A

US3927753A - Solenoid system for moving a type member

Info

Publication number: US3927753A
Application number: US852168A
Authority: US
Inventors: Timothy F Donovan; William P Ryan
Original assignee: Mite Corp
Current assignee: NEW HAVEN MANUFACTURING CORP A CORP OF; USM Corp
Priority date: 1969-08-22
Filing date: 1969-08-22
Publication date: 1975-12-23
Anticipated expiration: 1992-12-23
Also published as: DE2039601A1; FR2057664A5; DE2039601B2; GB1306514A

Abstract

A printer which includes a movable type body and a solenoid system to move the type body is provided. The solenoid system comprises a plurality of opposing pairs of solenoids, each pair being connected together so as to provide simultaneous displacement of both solenoids in a pair when one of the solenoids of a pair is energized. The several pairs of solenoids are interrelated with respect to their relative displacements and the sum of all of the displacements is transmitted to the type body for selection of a position on the type body. The solenoid system may include a pulley system or a differential lever system for the purposes of transmitting the sum of the displacements to the type body.

Description

United States Patent [191 Donovan et a1.

[ Dec. 23, 1975 1 SOLENOID SYSTEM FOR MOVING A TYPE MEMBER [75] Inventors: Timothy F. Donovan, Huntington;

William P. Ryan, Bethany, both of Conn.

[73] Assignee: Mite Corporation, New Haven,

Conn.

[22] Filed: Aug. 22, 1969 [21] Appl. No.: 852,168

[52] US. Cl. 197/49; 101/93.16; l0l/93.17; 101/93.2l; 101/93.48

[51] Int. Cl. 341.1 l/32 [58] Field of Search 197/49, 18, 55; 178/34;

[56] References Cited UNITED STATES PATENTS 1,548,168 8/1925 Pfannenstiehl 178/34 2,727,944 12/1955 Howard 1. 2,757,775 8/1956 Hickers0n..... 2,769,029 10/1956 Howard 3,139,820 7/1964 Kittler 101/93 C 3,227,259 1/1966 Howard 197/49 3,256,969 6/1966 Bretti 197/49 3,279,576 lO/1966 Howard 197/49 3,309,989 3/1967 Solheim et a1. lOl/93 C 3,374,873 3/1968 Takenaka 197/49 Primary Examiner-Clifford D. Crowder [57] ABSTRACT A printer which includes a movable type body and a solenoid system to move the type body is provided. The solenoid system comprises a plurality of opposing pairs of solenoids, each pair being connected together so as to provide simultaneous displacement of both solenoids in a pair when one of the solenoids of a pair is energized. The several pairs of solenoids are interrelated with respect to their relative displacements and the sum of all of the displacements is transmitted to the type body for selection of a position on the type body. The solenoid system may include a pulley system or a differential lever system for the purposes of transmitting the sum of the displacements to the type body.

39 Claims, 19 Drawing Figures US. Patent Dec. 23, 1975 3,927,753

Sheet 1 of 5 INVENTORS TIMOTHY E DONOVAN WILLIAM P. RYAN ATTORNEYS US. Patent Dec. 23, 1975 Sheet2of5 3,927,753

74 247 on Q O 0* O II 230 {236 240? H 194 u 272 266 E Z 280 a 4 In 283 262 74 276 ll 26! INVENTORS Z74 n/27o TIMOTHY E DONOVAN WILLIAM E RYAN 267 BY ATTORNEYS US. Patent Dec. 23, 1975 Sheet 3 of5 3,927,753

INVENTORS TIMOTHY E DONOVAN WILLlAM P. RYAN ATTORNEYS US. Patent Dec. 23, 1975 Sheet 5 of 5 w 5 :13 m a h Q m z n "5 q W :2

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INVENTORS TIMOTHY E DONOVAN WILLIAM T. RYAN ATTORNEYS SOLENOID SYSTEM FOR MOVING A TYPE MEMBER This invention relates to communications apparatus, and more particularly to printers which operate in response to coded or telegraphed signals.

Telegraph printers sometimes employ solenoid systems to move a type body which contains the characters to be printed. The solenoid systems are usually connected to movable means such as pulleys which in turn are connected by means of a cable or belt to the type body. During operation, each pulley is displaced linearly to either of two positions in response to the motion of the solenoid to which it is connected. One of the positions is commonly termed an in position and it results in a lengthening of the cable or belt which is trained about the pulley and connected to the type body. As a result, the type body moves axially to the selected position at which it is ready for printing. The other of the two pulley positions is called an out position, and results in the type body being spring restored axially to its initial print position. A group of such pulleys are generally interconnected and the total displacement of the cable or belt to which the type body is affixed is a function of the total displacement of the various pulleys in the group. By a careful selection of the in and out positions of each pulley, proper positioning of any number of characters on the type body will be effected.

The kind of pulley system above-described is generally termed on open system since each of the solenoids and/or the cable or belt is provided with a Spring return mechanism so that the attached pulley returns to its out position when the solenoid is deenergized. As a result, the type body by returning to its original position after each character is printed is forced to traverse the same distance twice. While this kind of system has been employed in the industry, there is still need for further improvement so that the speed and life of the system can be improved and to avoid the need for the solenoids towork against springs with the resulting duplication of travel and unwanted dynamic oscillations.

It is a primary object of the present invention to provide an improved printer which is faster and has a longer life expectancy than the previously developed printers. Another object of this invention is to provide a printer which includes an improved solenoid system whereby the type body undergoes a minimum amount of movement during the operation of the printer.

Broadly, the invention is directed to a printer comprising a movable type body, a solenoid system to move the body, the solenoid system comprising a plurality of opposing pairs of solenoids, each of the solenoids in a pair being connected together so as to provide simultaneous displacement of both when one of the solenoids of a pair is energized, means to sum the solenoid displacement, and means to apply the sum of such displacements to the type body for the selection of a new position of the type body. The displacement of the solenoid pairs are interrelated and in the preferred embodiment the displacement relationship is a geometrically progressive ratio of two, that is, each of the solenoid pairs is displaced twice the distance of another of the solenoid pairs.

The solenoid system of the invention operates with pulleys or levers either of which is connected directly to the solenoids. The type body is secured to the pulleys or the lever system by means of a belt, gearing mechanism, or the like, so that upon movement of the solenoid system the type body is moved a distance which is proportional to the sum of the solenoid displacements. When a pulley system is employed, two pulleys are connected to a solenoid pair. Two belts are trained about the various pulleys, one belt being trained about one-half of the pulleys which are usually placed slightly above and opposite the other half of the pulleys and the other belt being trained about the remaining pulleys. Each belt terminates at a feed drum at one end and at opposite sides of the type body at the other end to thereby form a closed loop. Thus, when one of the solenoids of a pair is energized, the pulleys move simultaneously and the displacement thereof is translated directly to both belts and to the type body. The movable ends of the belts are thus positioned in complementary directions by the same amount, maintaining a constant distance across the attachments on the type body.

To the accomplishment of the foregoing general objects, and other more specific objects which will hereinafter appear, our invention resides in the telegraph printer elements and their relation one to another, as

are hereinafter more particularly described in the following specification. The specification is accompanied by drawings in which:

FIG. 1 is a perspective view of part of a telegraph printer embodying the improvements of the invention;

FIG. 2 is a front elevational view of a printing hammer which is employed in the printer shown in FIG. 1;

FIG. 3 is a plan view of a telegraph printer shown in FIG. 1;

FIG. 4 is a simplified schematic diagram showing one of the two pulley and belt systems which is combined in the invention;

FIG. 5 is a simplified schematic diagram showing the other pulley and belt system which is combined;

FIG. 6 is a simplified schematic diagram showing the belt systems of FIGS. 4 and 5 combined;

FIG. 7 is a simplified schematic diagram similar to FIG. 4 with some modifications;

FIG. 8 is a simplified schematic diagram similar to FIG. 5 with some modifications;

FIG. 9 is a simplified schematic diagram showing the belt and pulley systems in FIGS. 7 and 8 combined;

FIG. 10 is a fragmentary plan view of the paper roll and several solenoids employed in the printer of the invention;

FIG. 11 is a schematic illustration of a lever system employed for rotary motion of the type body;

FIG. 12 is a side elevational view of the printer illustrated in FIG. 3 looking from the left of FIG. 3;

FIG. 13 is also a side elevational view of the'structure illustrated in FIG. 3, as seen looking from the right of FIG. 3;

FIG. 14 is a detailed plan view of the system for character advance, that is, stepping the type body axially to locate the next character to be printed;

FIG. 15 is a detailed view of the mechanism employed to line feed the paper;

FIG. 16 is a bottom plan view of the device shown in FIG. 15 looking in the direction of the arrows 16- 16;

FIG. 17 is a perspective view of part of the printer illustrated in FIG. 1 with temperature compensating apparatus added;

FIG. 18 is a side elevational view of a printing hammer having a self-aligning hammer head; and

FIG. 19 is a plan view of part of the printing hammer mechanism of FIG. 18.

The broad concept of the invention is shown in FIG. 6, but will be best understood by referring first to FIGS.

4 and 5, wherein several pulley configurations are 5 shown. In FIG. 4 there is illustrated an array of

pulleys

10, 12, 14, 16, 18, all connected by a belt terminating at feed drum 20. The pulleys 16 and 18 are fixed guide pulleys, while the pulleys l0, l2 and 14 are movable in different amounts usually in a ratio of 2. A belt 22 is trained about the pulleys and is secured to type body 24 at one end. The various positions of the pulleys which are obtained after movement by the solenoids (not shown) to which they are affixed, are termed in and out positions as has hereinbefore been mentioned. The change of belt position is double the pulley changeand therefore if the characters are spaced say Vs inch, the pulley motion of pulley 10, for example, should be 1/16 inch. In addition the predetermined displacement of pulley 14 is double that of pulley 10, while the pulley 12 is double that of pulley 14. Thus the pulley motions may be I/ l 6 inch, /4 inch, inch, and so on. After the type body 24 is properly positioned, a hammer (not shown) strikes a ribbon and paper (also not shown) to print the character on the paper.

FIG. 5 illustrates a similar but opposed arrangement to that shown in FIG. 4 and includes

pulleys

26, 28, 30, 32 and 34, which are also connected in series. Guide pulleys 32 and 34 are fixed, while

pulleys

26, 28 and 30 are movable in different amounts similar to the displacement of pulleys 10, 12 and 14 in FIG. 4. A belt 36 terminates at one end at feed drum 38, and is secured at the other end to the type body 40. This belt is shown in a dashed form in FIGS. 5 and 6 to distinguish it from belt 22 in FIG. 4. The operation of the system shown in FIG. 5 is identical to that illustrated in FIG. 4.

The combination of the system shown in FIGS. 4 and 5 is depicted in FIG. 6 which represents an embodiment of the present invention. Referring to FIG. 6 it is apparent that the several pulleys illustrated in FIG. 4 are similarly placed, but in view of their combined arrangement are now positioned opposite each other in pairs. What is not schematically shown in FIG. 6 is the fact that the pulleys are mechanically secured together and to the movable cores of the solenoids. Thus the pulleys illustrated by the

numerals

42 and 44 form a pair which are simultaneously displaced by the action of their opposed solenoids. The same is also true for

pulleys

46 and 48, and for pulleys 50 and 52. Cables 54 and 55 form a closed loop as they are trained about the various pulleys. Feed drum 56 and fixed guide pulleys 58, 60 and 62 are positioned within the closed loop to assist the motion of the cables 54, 55. A type body 64 is secured to the cables 54 and 55 and moves axially with the displacement of the cables. In the operation of the system shown in FIG. 6, a solenoid of any of the pairs of pulleys is activated and its core is displaced a prescribed distance. The two pulleys connected to the energized solenoid are also displaced causing the cables 54, 55 to move a predetermined distance and carry the type body to a new position. In this manner, the type body 64 is properly positioned along its axial path of travel. When the solenoids are deenergized the type body remains in its new position.

FIG. 9 also illustrates the features of the present invention and is best described by referring first to FIG. 7 which shows a series of movable pulleys 66, 68, and 70, and fixed guide pulleys 72 and 74 positioned in series with a cable 76 trained thereabout. The cable 76 terminates at one end at feed drum 78 and at the type body 80 at the other end. The type body moves in conjunction with the motion of the pulleys as described with respect to FIG. 4. In FIG. 8 illustrates the other half of the movable pulleys of the system shown in FIG. 9. These pulleys are indicated by the

numerals

82, 84 and 86. Fixed guide pulleys 88 and 90 are also included. Cable 92 which is connected to type body 94 terminates at feed drum 96. Again the motion of the solenoids (not shown) and respective pulleys is similar to that of FIGS. 4, 5 and 7, and FIG. 8 illustrates a configuration opposed to that of FIG. 7. FIG. 9 represents another embodiment of the invention, and is a combination of the configurations illustrated in FIGS. 7 and 8. This embodiment includes the additional feature of superimposed pulleys shown at 96 and 98. Opposing pairs of

movable pulleys

100 and 102, and 104 and 106 are secured to solenoids and operate in the manner described with respect to FIG. 6. Pulley 96, however, is actually a combination of two pulleys placed one above the other and connected to each other and to a solenoid pair (not shown). The advantage of this type of pulley construction is that the pair of solenoids having the longer stroke in the group can be connected advantageously to double pulley 96, and less space will be required to house the solenoids as hereinafter will be more fully explained. Fixed guide pulleys 108 and 110 direct cables 111 and 112 which are secured to type body 114. As explained with reference to FIG. 6, the operation of the solenoid pairs, is essentially that of a push-pull system resulting in the axial motion of type body 114.

FIG. 1 is a partial perspective view of a printer embodying the principles schematically shown in FIG. 9. In FIG. 1 a plurality of solenoids are oppositely disposed in pairs. Solenoid 116 forms a pair with solenoid 118, solenoid 120 with solenoid 122, and solenoid 124 with solenoid 126. As shown, each pair of solenoid cores or plungers is connected to a pair of pulleys. Pulley 128 is secured to the core of solenoid 116, pulley 130 to the core of solenoid 118, pulley 132 to the core of solenoid 124 and pulley 134 to the core of solenoid 126. However, pulleys 136 and 138 are superimposed, and are connected to the plungers of

solenoids

120 and 122. A fixed guide pulley 140 which actually consists of superimposed

pulleys

142 and 144, and fixed guide pulleys 146 and 148 are positioned so as to enable the

belts

150 and 151 to form a closed loop. The belt 150 is trained about the

movable pulleys

130, 134, 136 and is secured at one end to a feed drum 152. Belt 151 is trained about

movable pulleys

128, 132 and 138, and also terminates at drum 152. Belt 151 traverses a path opposite to that of belt 150 and is vertically below belt 150 due to the lower position of

pulleys

128, 132, 138. A connecting member 154 is secured to the

cores

156 and 158 of

solenoids

124, 126, and also connects the

pulleys

132 and 134. A second connecting member 160 connects

solenoids

116 and 118 and

pulleys

128 and 130 in the same manner. However, pulleys 136 and 138 are connected to cores of

solenoids

120 and 122 and to each other by pin 161 and connecting member 164.

A collar 166 and yoke 168 is immovably affixed to the

belts

150, 151 whose loops are attached to pins 171 and 173 riveted on yoke 168. A yoke support rod 172 passes freely through the collar 166 and aids in the support thereof. A splined rod 174 supports a type cylinder 176 which may be solid but which is illustrated as being divided into a plurality of beaded extensions each containing the indicia or characters which are to be printed. The rod 174 may be keyed or splined, or as shown, may be a pinion rod. For a detailed description of the rod and type body here shown, reference is made to U.S. Pat. No. 3,279,576, issued October 18, 1966 and assigned to the assignee of the subject application. The type cylinder 176 moves axially relative to the splined rod 174 due to the motion of the

belts

150, 151 as transmitted through collar 166 and yoke 168. The yoke 168 is secured in the groove 178 which is shown as being centrally positioned in the type cylinder. As a result of this construction the type cylinder travels a predetermined distance along the splined rod 174 in direct relation to the displacement of the

belts

150, 151.

Printing is effected by a hammer 180 which comprises a hammer head 182, a support member 184 for the hammer head and further includes rod 186 and shaft 188. A clearer illustration of this mechanism is shown in FIG. 2, wherein it can be seen that the rod 186 is secured at its end to a linkage arm 270 which is instrumental in the rocking movement of the hammer, as will be more fully described hereinafter. A retaining ring 190 is secured next to arm 270 to position the arm on rod 186.

Members

185 and 187 bridge shaft 188 and rod 186 to further support and align these components so that they move together as a single body about the axis of shaft 188.

Reverting to FIG. 1, a cord 192 passes through and is secured to the support member 184 and carries the hammer system axially in conjunction with the movement of the type cylinder 176. The end of the splined rod 174 is provided with a gear 194 which as will be hereinafter further explained, is employed for rotary movement of the type body.

During operation of the printer the type cylinder 176 moves along the splined rod 174 directly with the movement of the

belts

150, 151. The belts are positioned axially in response to the displacement of the various solenoids 116 through 126. As before indicated, the solenoids operate in pairs in the preferred embodiment. Therefore, if solenoid 116 is energized it will displace pulley 128 and also pulley 130 because of its connection to pulley 130 through member 160. As a result, belt 151 is lengthened while belt 150 is shortened an equal amount, the displacement being sufficient to move an indicia or character on the type cylinder into a position for print. The hammer head 182 is then rocked so that it strikes an inked ribbon or the like against a paper (not shown) interposed between the hammer head and the type cylinder. If further movement of the type cylinder is desired to position a different character in front of the hammer head, other solenoids will also be activated so that the belts are further displaced. Obviously a variety of displacements can be accomplished with a variety of signals to the solenoids particularly in view of the fact that each pair of solenoids is preferably designed to provide a displacement which differs from that of any other pair. Thus, with the arrangement illustrated, a type cylinder having eight characters along its length can readily be moved to the eight axial positions by properly displacing the various solenoids in a ratio of 1:2:4.

It will be noted that the rear edges of the two banks of solenoids shown in FIG. 1 are aligned despite the fact that

solenoids

120 and 122 are larger than the other solenoids. The larger solenoids are required for longer displacement strokes. The edge alignment is made possible by locating the double or

superposed pulleys

136, 138 in combination with the longer displacement solenoid. Thus, a compact assembly is assured, thereby providing an important advantage in the printer of the invention.

FIG. 3 is a plan view of the device shown in FIG. 1. The relative positioning of the various solenoids employed in the lateral displacement of the type cylinder 176 as well as the arrangement of the pulleys is clearly shown. Feed drum 152 is illustrated as being combined with auxiliary equipment which will be later described in detail with reference to the step-by-step advance of the type cylinder. Cable 192 which winds about an extension of feed drum 152 at a level below that shown in FIG. 1 (best shown in FIG. 12) is trained about several pulleys such as at 196 and 198, 200 and 202, which are below deck 262. The rocking motion of the print hammer 180 is provided by a print solenoid 266 and a link mechanism generally designated at 206 which are also below deck 262.

As so far described the ends of the cables may be secured together and the type cylinder may be axially shifted back and forth about a point such as when printing on a narrow tape which moves continuously past the type cylinder. However, for page printing, as here shown, in addition to the axial character selection for the type cylinder which has been described as a function of the solenoid system of FIG. 1, there is provided a mechanism which axially advances the type cylinder on a step-by-step basis. This movement is necessary so that each character printed be spaced across the page from the one just previously printed. The mechanism for this movement is most clearly detailed in FIG. 14; moreover, it is shown positioned below the upper deck 262 (FIG. 3), and rotatively secured to the feed drum shaft (264 in FIG. 12). A torsion spring 208 is tied at one end to a fixed pin 210 and at the other end to a hub 212 which is splined to the same shaft as that to which ratchet 216 is splined, thus keying the hub and ratchet together. As viewed in FIG. 14 the feed drum is rotated clockwise to feed the type cylinder one step in the proper direction for a line of print. For this purpose solenoid 214 is connected to ratchet teeth 216 by means of feed pawl 218 which engages the ratchet teeth. Upon activation of the solenoid 214 the feed pawl is moved linearly and engages a tooth, thus moving the spacer drum a predetermined increment. This movement is translated to the type cylinder by means of the cables shown in FIG. 1. The type cylinder is then in a position to print the next character to be selected by the action of solenoids 116 through 126. At the end of a printed line, that is for so-called carriage return, the feed drum must return to its original position along with the type cylinder and hammer. For this purpose a solenoid 220 is activated. The displacement of the solenoid causes release lever 222 to lift feed pawl 218 such that it is disengaged from the ratchet teeth 216. Slightly later check pawl 226 is engaged by lever 222 and is disengaged from the ratchet teeth. Torsion spring 208 then unwinds so that the ratchet and drums quickly rotate in a counterclockwise direction to return to the original starting point. Because solenoid 214 is only momentarily activated a latching device is required to keep feed pawl 218 and check 'pawl 224 disengaged from ratchet teeth 216 until the ratchet reaches its initial position. When the solenoid 214 is activated, lever 222 is rotated so that it becomes engaged with lever arm 217 which is urged into this engagement by tension spring 221. The lever arm 217 keeps the

pawls

226 and 218 disengaged until the ratchet reaches its initial position. Pin 215 then deflects arm 217, disengaging lever 222 and allowing the pawls to be restored to operating position. A pad 213 is employed to cushion the force occurring when the drums returns to the starting position. The force is transmitted to the pad through pin 215 and lever arm 217, the latter being pivotally secured at pivot 219.

For character selection the type cylinder 176 is moved both axially and rotatively. In the present case the cylinder or boody 176 is eight characters long and has a circumference sufficient to carry eight characters about the circumferential periphery, thus providing sixty-four characters in all. To impart the rotary motion to the cylinder we provide an apparatus which can best be described by referring initially to FIG. 11 which is a schematic illustration of the mechanism employed. The operation of the mechanism is similar to that of the pulley system described in FIG. 1. It will be noted that in FIG. 11 there are a plurality of opposed solenoid pairs. For example, solenoid 228 and solenoid 230 which are connected to the lever 232 form a pair of solenoids which function in the manner described with reference to the solenoid pairs in FIG. 1. In addition, solenoid 234 coupled with solenoid 236, and solenoid 238 with solenoid 240 to form solenoid pairs. Lever 242 and lever 244 are each secured to a solenoid pair as shown. The three

levers

232, 242 and 244 are pivotally linked together by

members

246 and 248. The end of lever 232 is secured to pivotal mount 235. The end of lever 244 is joined by pivot member 249 with a gear rack 250 which is connected through an idler gear to gear 194. As illustrated in FIG. 1 the gear 194 is integrally connected to the splined rod 174, and thus the type cylinder 176 is rotated by the displacement of the solenoid system shown in FIG. 11. The operation of the system in FIG. 11 is similar to the operation of the pulley system in FIG. 1, that is, the displacement of a solenoid pair is transmitted through the levers and the various linkages members to the gear rack 250 and the gear 194. The levers are so arranged to enable the movement of each of the pairs to be summed and applied to the gear rack. For example,

solenoids

238 and 240 are interconnected by member 247 which is tied to lever 244 by pin 251. The other solenoids and levers are similarly connected. In this way the displacement of each of the pairs is added and the total displacement is transmitted to the type cylinder 174.

The accuracy of movement of the type cylinder in a rotary direction is quite important if accurate reproduction of the characters is expected. A slight error in the rotary direction will appear prominently on the printed page since the character printed will be displaced in a vertical direction. As a result, we provide a device which is intended to ensure proper alignment of the character whenever a movement of the type body in the rotary direction is carried out. This device or mechanism can best be explained by referring to FIG. 13 wherein the device is shown to consist of a rotary lock solenoid 252 which is secured to bell crank lever 254 the end of which is provided with a detent 256. The detent 256 engages a detent wheel 258 which is secured to splined rod 174. The rack 250 engages gear 194 through idler gear 253. In operation, solenoid 252 is energized after the type body is rotated and assumes its final position. The movement of the solenoid plunger 260 is translated through lever arm 254 which locks the detent wheel 258 by means of the detent 256. Further movement of the mechanism is prohibited by this locking action until the solenoid 252 is deenergized and spring returned. This occurs after the printing operation.

The hammer must move axially with the type body 176 in order that it be in position to strike the paper which is interposed between the type body and the hammer as before explained. The axial movement of the hammer is effected by a pulley system described with reference to FIG. 3 and cord 192 which is most clearly illustrated in FIG. 1. The cord is secured to the hammer support member 184 and movement of the cord causes the consequent lateral movement of the hammer head 182. In order that the lateral movement of the hammer follow exactly the movement of the type body, the cord 192 is trained about a drum 260 which is best illustrated in FIG. 12. This drum is below the deck surface 262 and is directly connected to the feed drum 152 at the shaft 264.

Drums

152 and 260 have the same effective diameter and therefore the rotation of the drum 152 by means of character advance solenoid 214 is directly translated to the hammer by means of cord 192 which forms a closed loop about drum 260 and

pulleys

196, 198, 200 and 202.

The printer includes a mechanism to cause the hammer head 182 to strike the paper at the proper time in the printing cycle. Such a mechanism is also shown in FIG. 12 and consists mainly of the print solenoid 266 which is directly connected at its plunger 268 to link 270. The other end of the link 270 is secured to the rod 186. As shown in FIGS. 1 and 2, the rod 186 passes slidably through the hammer support member 184. Thus the movement of the solenoid plunger 268 is translated through the link 270 to the

arms

185, 187 and shaft 186 and causes the hammer head 182 to move toward and strike the paper to thereby effect the printing of a character.

At the end of each printed line the paper which is fed to the printing mechanism is moved a distance sufficient to begin a new ine of print. This movement coincides with the carriage return movement explained with reference to the spacer drum 152 and is most clearly shown in FIG. 15. For the purposes of transmitting the paper to a new position as required there is shown in FIG. 15 still another solenoid 272 which is directly connected to a U-shaped lever member 274, which comprises

lever arms

280 and 283 and cross member 281 pivotally secured to each of the

lever arms

280 and 283 and mounted on shaft 285. A paper feed roll 282 is provided at its end with a ratchet wheel 284. Lever arm 276 has affixed to its end a roller 286 which meshes with ratchet wheel 284 to function as a lock detent. Lever arm 278 is a feed pawl so that upon the activation of solenoid 272 linkage arm 278 acts upon ratchet wheel 284 so that it rotates an increment. This motion is translated to the paper roll 282 which is secured to the same shaft 287. Thus at predetermined intervals the activation of solenoid 272 will cause the paper to be moved a distance sufficient to begin a new line of print. When feed pawl 278 advances ratchet 284 one increment, the tip 294 of feed pawl 278 contacts the backstop of member 292. This enables the tip at the other end of the feed pawl 278 to apply a braking action on ratchet 284 at the completion of the stroke. When feed pawl 278 is spring restored to its initial position, tip 294 of feed pawl 278 contacts the forward stop of member 292 causing the tip at the other end of pawl 278 to be cammed out of engagement with ratchet 284, thus permitting manual rotation of feed roll 282, if desired.

FIG. and FIG. 16 illustrate the configuration shown in FIG. with respect to the location of the various components in greater detail. These figures indicate that the print solenoid 266 and its associated mechanism are positioned adjacent line feed solenoid 272 and its mechanism and both solenoids are below deck 262.

To assist in the printing of the characters, self-inking paper may be employed. In the alternative, an ink ribbon is used. To ensure a fresh supply of ribbon so that the characters may be properly reproduced, the ribbon is passed lengthwise at regular intervals. Any of a number of well known ribbon moving devices can be employed for this purpose, and FIG. 3 indicates that such a mechanism 300 may include a ribbon advance spool 302 and a ribbon takeup spool 304, one or the other of which is operated by a pawl member 306 positioned therebetween. The step by step ribbon movement may be activated by a solenoid 308. The mechanism used for returning the ribbon from the takeup spool to the advance spool at the end of the ribbon is not shown, but any of the well known mechanisms readily apparent to one skilled in the art may be used.

Belts or

cables

150 and 151 in FIG. 1 generally comprise a material having a low coefficient of thermal expansion. One example of such a material is a tetrafluoroethylene coated continuous filament fiberglass. This particular material is useful because of its stability through variations in humidity, pressure loading, and temperature during the operation of the system. However, the .materials selected for the

pulleys

128, 130, 132, 134, 136, 138, 142 and 144, and for the drum 152 are lightweight materials such as fiberglass filled plastics. The lightweight character of these materials renders them quite desirable to use for working parts in the highly dynamic system here described, and also to enable the printer to be portably carried. Although the fiberglass content in the pulleys and the drum reduces the coefficient of thermal expansion of these parts, this parameter is still approximately about two to about four times as great as that of the continuous

filament fiberglass cables

150 and 151. When the printer is exposed to elevated temperatures therefore, the greater coefficient of thermal expansion of the pulleys and drums causes a variation in the positioning of the type cylinder 176, and also causes the cables or belts to tighten on the pulleys, thereby increasing the friction at the pulleys.

To avoid errors in the positioning of the type cylinder 176 and the increased friction at the several pulleys, a temperature compensating device such as that shown in FIG. 17 may be employed. Referring to FIG. 17,

expander arms

300 and 302 which are composed of a plastic material having a relatively high coefficient of thermal expansion, i.e., seven or eight times as much as fiberglass, are mounted on

metal pins

304 and 306 which are fixed to the main (metal) frame of the printer (not shown). Pulley 142 is set on a pin 308 which is attached to a metal strip 310 and movable in a slot 311 in arm 300. Strip 310 is composed of a metal which is relatively thermally stable compared to the plastic material of the pulleys and is attached to the end of the arm 300 by a pin 312. The distance between the center of the pin 304 and the center of the pulley 142 is illustrated as being D while the distance between the center of the pin 304 and the center of the pin 312 is shown as D,. The differential thermal expansion of the entire arm 300 relative to the metal frame to which it is attached through pin 304 occurs over the distance D,. Only part of this expansion occurs over the distance D The use of the relatively thermally stable metal strip 310, however, enables the total relative expansion of arm 300 (D to occur at the pulley 142 since this expansion is transmitted through the metal strip 310 to pulley 142. The change of position of the pulley 142 due to the expansion of the arm 300 is in a direction which reduces the distance that the cable must traverse between

pulleys

134 and 148. Therefore the thermal expansions of

pulleys

134 and 148 as well as that of the other pulleys in the system about which the cable 150 is trained which increase the distance that the cable 150 must travel are neutralized by the amount of movement of pulley 142 and thus the position of type body 176 is relatively unaffected by thermal variations.

A similar arrangement of compensating parts may be provided for the pulleys carrying cable 151 by placing pulley 144 on a separate shaft 318 and employing a similar expandable arm 302. A metal strip 314 which is also composed of a material having a low coefficient of thermal expansion compared to the pulleys is attached to the end of the arm 302 by pin 316 and to the pulley 144 by shaft 318. These components function in the same manner as described with reference to expander arm 300 and thus the variation in dimensions of

pulleys

132 and 146 due to thermal changes and the consequent altering of the position of the cable 151 is also compensated for by the expansion of arm 302 acting in conjunction with the metal strip 314.

Slots are provided in the arm 300 at 313 and in the arm 302 at 315 and 317 to allow for the relative lateral movement of

pins

316, 312 and 318 respectively. Pins 312 and 316 and their respective slots form guide means for the movement of

pulleys

142 and 144.

Still other modifications of the printer herein shown may be made. For example, the position of the hammer head when it strikes relative to the position of the type cylinder surface is important in the operation of the printer. In order to ensure that the hammer head is flush with the type cylinder surface when printing occurs, the apparatus illustrated in FIGS. 18 and 19 may be provided. As there shown, a tubular type cylinder 322 with fixed type strips having projecting surfaces such as that illustrated by the numeral 324 is positioned adjacent a hammer mechanism 326 comprising a movable hammer head 328 and a supporting plate 330. The supporting plate 330 is itself supported on a frame 334 such as by the large hexagonal headed screw 335. The supporting plate 330 is provided with a projecting member 336 which is placed within the receptacle 338 in hammer head 328. A pin 340 is closely fitted within the hammer head 328 and loosely rests in an enlarged hole 342 in support plate 330. A similar pin 344 is closely fitted in the support plate 330 at the lower portion thereof. The hammer head 328 is freeto rock or rotate at the joint between the projecting member 336 and the receptacle 338 by virtue of the movement of the pin 340 within the enlarged hole 342. A U- shaped spring 346 is held in a notch 348 in the support plate 330 at one end and is further supported in

grooves

354 and 356 in

pins

340 and 344 respectively.

1 1 The spring 346 is effective to press the hammer head 328 against the projecting member 336 on support plate 330. Thus, when the support frame 334 pivots about a shaft such as shaft 188 in FIG. 2, the hammer head 328 strikes a paper and ribbon (not shown) against the surface 324 of the type cylinder 322. If the front face 352 of the hammer head 328 is not flush against the surface 324 of the type cylinder 322 when the striking occurs then the hammer head 328 automatically rotates at the joint formed by member 336 and receptacle 338 to align itself with this surface. Some resistance to the relative motion of the hammer head 328 is provided by the friction between the pin 340 and the spring 346. This friction has only a negligible effect during the aligning operation and actually aids in keeping the hammer head 328 in the newly aligned position after the printing is effected. Since the misalignment of the type cylinder varies little from character to character after the initial aligning occurs, it is advantageous to maintain the hammer head at its last aligned position since this minimizes the wear which would occur if the hammer head were to return to the same position after each printing operation.

It will be noted that the solenoid systems have been described and illustrated herein as being operatively connected to a pulley system or a lever system. While the pulley system has been described with reference to the axial displacement of a type body it will be appreciated that it may be used for either axial or rotary movement. In addition, it will be further appreciated that only one of such pulley or lever systems need be employed with certain type body configurations.

It is believed that the construction and operation of our improved printer for operation in response to coded signals, as well as the advantages thereof will be apparent from the foregoing detailed description. It will also be apparent that while we have shown and described the invention in preferred form, changes may be made in the structure shown without departing from the scope of the invention.

The terms cable and belt have been interchangeably employed throughout the specification to refer to the parts used to carry the type body to new positions. The term cable in the appended claims is generically directed to any strip of material suitable for operative connection to and movement of the type body.

We claim:

1. In a printer having a movable type body, a solenoid system to move the type body, said solenoid system comprising a plurality of pairs of opposing solenoids, a plurality of displacement means each operatively connected to a pair of solenoids, said displacement means being movable in a first direction, by one of said solenoids of a pair, to a first position and movable in a second direction, by the other solenoid of said pair, to a second position, said plurality of displacement means having different displacements which are interrelated in a predetermined ratio, means to sum the displacements of said displacement means, and means to transmit the sum of said displacements to the type body for selection of a position on the type body.

2. The printer of claim 1, wherein the means to sum the displacements of said solenoids comprises a plurality of pulleys operatively connected to said displacement means and movable therewith and cable means trained around said pulleys and operatively connected to said type body.

3. The printer of claim 2, wherein said plurality of displacement means have different displacements, the pair of pulleys connected to said displacement means having the largest displacement being arranged in superposed positions.

4. The system of claim 2, wherein said pulleys are arranged in pairs, each pair being operatively connected to one of said displacement means and movable therewith, and wherein said cable means comprises a first cable operatively connected at one end to said type body and trained successively around one pulley of each pair and second cable operatively connected at one end to said type body and trained successively around the other pulley of each pair.

5. A printer as defined in claim 4 for page printing, in which there is a double spacer drum, the unconnected end of one cable being wound on one drum, the unconnected end of the other cable being wound in opposite direction on the other drum, and pawl and ratchet mechanism to rotate the drums, whereby the cables serve for step-by-step movement of the type body across the page as well as for character selection.

6. A printer as defined in claim 5, in which the type body is a type cylinder splined to and slidable along a rotatable shaft, said cylinder being eight characters long.

7. In the system of claim 4, a temperature compensating device comprising an expandable arm having a high coefficient of thermal expansion relative to that of said pulleys, said arm having a part movable in a first direction in response to a thermal expansion of said arm, and means for operatively connecting said part of said arm to one of said pulleys about which said first cable is trained and effective to carry said pulley with said part in said given direction, thereby to alter the position of said first cable in said first direction opposite to the direction of alteration of the position of said first cable due to the thermal expansion of the pulleys about which said first cable is trained.

8. In the printer of claim 7, a member having a low coefficient of thermal expansion relative to that of said expandable arm operatively connected to and extending from said part of said arm, said pulley being operatively connected to said member whereby said pulley is moved a distance substantially equal to the movement of said part in said first direction.

9. In the printer of claim 8, said expandable arm comprises a plastic material and said member comprises metal.

10. In the printer of claim 7, a second expandable arm having a high coefficient of thermal expansion relative to that of said pulleys and having a part which is movable in a second direction in response to a thermal expansion of said arm, and means for operatively connecting said part of said second arm to a second pulley about which said second cable is trained, said means being effective to carry said second pulley with said part in said second direction, the position of said second cable thereby being altered in said second direction opposite to the direction of alteration of the position of said second cable due to the thermal expansion of the pulleys about which said second cable is trained.

11. In the printer of claim 10, a member having a low coefficient of thermal expansion relative to that of said second expandable arm operatively connected to and extending from said part of said second arm, said second pulley being operatively connected to said member whereby the second pulley is moved a distance substantially equal to the movement of said part of said second arm in said second direction. 12. The system of claim 4, further comprising means operatively connecting the other ends of said cables, said cables thereby forming a closed loop, whereby displacement of one of said cables by said solenoid system is accompanied by an equal displacement of the other of said cables, whereby said type body is displaced in an amount proportional to the sum of the displacements of said pulleys.

13. The system of claim 4,'wherein there arethree pairs of opposed solenoids, said displacement means each being movable in different amounts in a ratio of 12:4, whereby said type body may be moved t'oany one of eight positions.

14. The system of claim 13, wherein each pair of pulleys has an upper pulley and a lower pulley, saidfirst cable being trained back and forth around said upper pulleys and said second cable being trained back andforth in an opposite direction around said lower pulleys.

15. A printer as defined in claim 14, for page print ing, in which there is a double spacer drum, the other end of said first cable being wound on said drum, the

other endof said second cable 16. In the system of claim 2, a temperature compen.- sating device comprising an expandable arm having a high coefficient a thermal expansion relative to that of.

cable is'trained and effective to carry said pulley ,with

said part in said first direction thereby to alter the position of said cable means in said first direction opposite to the direction of alteration of the position of said cable means due to the thermal expansion of the pulleys about which said cable means is trained.

17. In the system of claim 16, a member having a low coefficient of thermal expansion relative to that of said expandable arm operatively connected to and extending from said part of said arm, said pulley being operatively connected to said member whereby said pulley is moved a distance substantially equal to the movement of said part in said first direction.

18. In the printer of claim 1, hammer means p ositioned adjacent said type body and effective to apply a force to said type body each time a printing operation is to be effected, said hammer means comprising a frame, a hammer head having a front face, a support member operatively connected to said hammer head and pivotally mounted on said frame for movement towards and away from said type body, and means pivotally mounting said hammer head on said support member and effective to automatically pivotally align said front face with the surface of said type body when a printing operation is effected.

19. In the printer of claim 18, in which said support member has an opening therein, said pivot means comprising a projecting part extending outwardly from said support member, a receptacle in said hammer head effective to receive said projecting part in a movable engagement therewith, and a member affixed to said hammer head and rotatably mounted in said opening in said support member, said hammer head member being laterally movable in said opening thereby to allow relative movement of said part in said receptacle.

20. In the printer of claim 19, in which said hammer head member comprisesa pin and further comprising resilient means operatively connected to said pin and to. said support member effective to force said hammer head receptacle into engagement with said projecting part. i

21. The printer of claim 1, wherein the means to sum the displacements of said displacement means comprises a differential lever system comprising a plurality of levers operatively connected together, each displacement means being operatively connected to a lever.

22. The systemof claim 21, wherein said plurality of levers are operatively pivotally connected together, one of said levers being pivotally mounted at a fixed point and another of said levers being operatively connected to said type body and adapted to move same.

23. The printer of claim 1, wherein the type body is to be moved both axially and in rotation, comprising a second solenoid system identical to said first solenoid system, one of said solenoid systems imparting axial movement to said type body and the other of said solenoid systems imparting rotary movement to said type body. 7

24. The system of claim 23, wherein the means to sum the displacements of said displacement means in one. of said solenoid systems comprises a plurality of pulleys operatively connected to said displacement means and movable therewith and cable means trained around said pulleys and operatively connected to said type body.

'25. The system of claim 24, wherein said pulleys are arranged in pairs, each pair being operatively-connected to one of said displacements means and movable therewith, and wherein said cable means comprises a first cable operatively connected at one end to said type body and trained successivelyaround one pulley of each pair and secohdcable operatively connected at one end to said type body and trained successively around the other pulley of each' pair.

26. The system of claim 23, wherein the means to sum the displacements of saiddisplacement means of one of said solenoid systems comprises a differential lever system comprising a plurality of levers operatively connected together, each of said displacement means being operatively connected to a lever.

27. The system of claim 26, wherein the means to sum the displacements of said displacement means of said other solenoid system comprises a plurality of pulleys operatively connected to said displacement means and movable therewith and cable means trained around said pulleys and operatively connected to said type body.

28. The system of claim 27, wherein said type body is of a length sufficient to carry eight characters, said first solenoid system comprising three pairs of opposed solenoids, each of said displacement means being movable in different amounts in a ratio of 1:224, whereby said type body may be moved axially to any of eight 30. The system'of claim 27, wherein saidpulleys are arranged in pairs, each pair being operatively connected to one of said displacement means and movable therewith, and wherein said cable means comprises a first cable operatively connected at one end to said type body and trained successively around one pulley of each pair and second cable operatively connected at one end to said type body and trained successively around the other pulley of each pair.

31. The system of claim 30, wherein each pair of pulleys has an upper pulley and a lower pulley, said first cable being trained back and forth around said upper pulleys and said second cable being trained back and forth in an opposite direction around said lower pulleys.

32. The system of claim 1, wherein there are three pairs of opposed solenoids, said displacement means each being movable in different amounts in a ratio of 1:2:4, whereby said type body may be moved to any one of eight positions.

33. The system of claim 32, wherein the means to sum the displacements of said displacement means comprises a differential lever system comprising a plurality of levers operatively connected together, each displacement means being operatively connected to a lever.

34. The system of claim 33, wherein said plurality of levers are operatively pivotally connected together, one of said levers being pivotally mounted at a fixed point and another of said levers being operatively connected to said type body and adapted to move same.

35. In a printer having a movable type body, a solenoid system to move said type body, a plurality of pulleys operatively connected to said solenoids in said solenoid system, a feed drum positioned proximate said solenoid system,a first cable trained about several of said pulleys and terminating at one end of said feed drum and at the other end at said type body, a second cable trained about the remainder of said pulleys in an opposite direction to said first cable and terminating at said feed drum at one end and at said type body at the other end, said cables thereby forming a closed loop and being trained about said pulleys such that the displacement of said first cable by said solenoid system causes an equal displacement of said second cable, whereby said type body is displaced an amount proportional to the sum of the displacements of said pulleys, a

temperature compensating device comprising an expandable arm having a high coefficient of thermal expansion relative to that of said pulleys, said arm having a part movable in the first direction in response to a thermal expansion of said arm, and means for operatively connecting said part of said arm to one of said pulleys about which said first cable is trained and effective to carry said pulley with said part in said given direction, thereby to alter the position of said first cable in said first direction opposite to the direction of alteration of the position of said first cable due to the thermal expansion of the pulleys about which said first cable is trained.

36. In the printer of claim 35, a member having a low coefficient of thermal expansion relative to that of said expandable arm operatively connected to and extending from said part of said arm, said pulley being operatively connected to said member whereby said pulley is moved a distance substantially equal to the movement of said part in said first direction.

37. In the printer of claim 35, a second expandable arm having a high coefficient of thermal expansion relative to that of said pulleys and having a part which is movable in a second direction in response to a thermal expansion in said arm, andmeans for operatively connecting said first part of said second arm to a second pulley about which said second cable is trained, said means being effective to carry said second pulley with said part in said second direction, the position of said second cable thereby being altered in said second direction opposite to the direction of alteration of the position of said second cable due to the thermal expansion-of the pulleys about which said second cable is trained.

38. In the printer of claim 37, a member having a low coefficient of thermal expansion relative to that of said second expandable arm operatively connected to and extending from said part of said second arm, said second pulley being operatively connected to said member whereby the second pulley is moved a distance substantially equal to the movement of said part of said second arm in said second direction.

39. In the printer of claim 38, said expandable arm comprises a plastic material and said member comprises metal.

Claims

11. In the printer of claim 10, a member having a low coefficient of thermal expansion relative to that of said second expandable arm operatively connected to and extending from said part of said second arm, said second pulley being operatively connected to said member whereBy the second pulley is moved a distance substantially equal to the movement of said part of said second arm in said second direction.

12. The system of claim 4, further comprising means operatively connecting the other ends of said cables, said cables thereby forming a closed loop, whereby displacement of one of said cables by said solenoid system is accompanied by an equal displacement of the other of said cables, whereby said type body is displaced in an amount proportional to the sum of the displacements of said pulleys.

13. The system of claim 4, wherein there are three pairs of opposed solenoids, said displacement means each being movable in different amounts in a ratio of 1:2:4, whereby said type body may be moved to any one of eight positions.

14. The system of claim 13, wherein each pair of pulleys has an upper pulley and a lower pulley, said first cable being trained back and forth around said upper pulleys and said second cable being trained back and forth in an opposite direction around said lower pulleys.

15. A printer as defined in claim 14, for page printing, in which there is a double spacer drum, the other end of said first cable being wound on said drum, the other end of said second cable

16. In the system of claim 2, a temperature compensating device comprising an expandable arm having a high coefficient a thermal expansion relative to that of said pulleys, said arm having a part movable in a first direction in response to a thermal expansion of said arm, and means for operatively connecting said part of said arm to one of the said pulleys about which said cable is trained and effective to carry said pulley with said part in said first direction thereby to alter the position of said cable means in said first direction opposite to the direction of alteration of the position of said cable means due to the thermal expansion of the pulleys about which said cable means is trained.

18. In the printer of claim 1, hammer means positioned adjacent said type body and effective to apply a force to said type body each time a printing operation is to be effected, said hammer means comprising a frame, a hammer head having a front face, a support member operatively connected to said hammer head and pivotally mounted on said frame for movement towards and away from said type body, and means pivotally mounting said hammer head on said support member and effective to automatically pivotally align said front face with the surface of said type body when a printing operation is effected.

20. In the printer of claim 19, in which said hammer head member comprises a pin and further comprising resilient means operatively connected to said pin and to said support member effective to force said hammer head receptacle into engagement with said projecting part.

22. The system of claim 21, wherein said plurAlity of levers are operatively pivotally connected together, one of said levers being pivotally mounted at a fixed point and another of said levers being operatively connected to said type body and adapted to move same.

23. The printer of claim 1, wherein the type body is to be moved both axially and in rotation, comprising a second solenoid system identical to said first solenoid system, one of said solenoid systems imparting axial movement to said type body and the other of said solenoid systems imparting rotary movement to said type body.

24. The system of claim 23, wherein the means to sum the displacements of said displacement means in one of said solenoid systems comprises a plurality of pulleys operatively connected to said displacement means and movable therewith and cable means trained around said pulleys and operatively connected to said type body.

25. The system of claim 24, wherein said pulleys are arranged in pairs, each pair being operatively connected to one of said displacements means and movable therewith, and wherein said cable means comprises a first cable operatively connected at one end to said type body and trained successively around one pulley of each pair and second cable operatively connected at one end to said type body and trained successively around the other pulley of each pair.

26. The system of claim 23, wherein the means to sum the displacements of said displacement means of one of said solenoid systems comprises a differential lever system comprising a plurality of levers operatively connected together, each of said displacement means being operatively connected to a lever.

28. The system of claim 27, wherein said type body is of a length sufficient to carry eight characters, said first solenoid system comprising three pairs of opposed solenoids, each of said displacement means being movable in different amounts in a ratio of 1:2:4, whereby said type body may be moved axially to any of eight positions.

29. The system of claim 27, wherein said type body has a circumference sufficient to carry eight characters thereabout, and wherein said second solenoid system comprises three pairs of opposed solenoids, each of said displacement means being moved in different amounts in a ratio of 1:2:4, whereby said type body may be rotated to any one of eight positions.

30. The system of claim 27, wherein said pulleys are arranged in pairs, each pair being operatively connected to one of said displacement means and movable therewith, and wherein said cable means comprises a first cable operatively connected at one end to said type body and trained successively around one pulley of each pair and second cable operatively connected at one end to said type body and trained successively around the other pulley of each pair.

35. In a printer having a movable type body, a solenoid system to move said type body, a plurality of pulleys operatively connected to said solenoids in said solenoid system, a feed drum positioned proximate said solenoid system, a first cable trained about several of said pulleys and terminating at one end of said feed drum and at the other end at said type body, a second cable trained about the remainder of said pulleys in an opposite direction to said first cable and terminating at said feed drum at one end and at said type body at the other end, said cables thereby forming a closed loop and being trained about said pulleys such that the displacement of said first cable by said solenoid system causes an equal displacement of said second cable, whereby said type body is displaced an amount proportional to the sum of the displacements of said pulleys, a temperature compensating device comprising an expandable arm having a high coefficient of thermal expansion relative to that of said pulleys, said arm having a part movable in the first direction in response to a thermal expansion of said arm, and means for operatively connecting said part of said arm to one of said pulleys about which said first cable is trained and effective to carry said pulley with said part in said given direction, thereby to alter the position of said first cable in said first direction opposite to the direction of alteration of the position of said first cable due to the thermal expansion of the pulleys about which said first cable is trained.

37. In the printer of claim 35, a second expandable arm having a high coefficient of thermal expansion relative to that of said pulleys and having a part which is movable in a second direction in response to a thermal expansion in said arm, and means for operatively connecting said first part of said second arm to a second pulley about which said second cable is trained, said means being effective to carry said second pulley with said part in said second direction, the position of said second cable thereby being altered in said second direction opposite to the direction of alteration of the position of said second cable due to the thermal expansion of the pulleys about which said second cable is trained.