US3599774A

US3599774A - Platen line-spacing mechanism

Info

Publication number: US3599774A
Application number: US871623A
Authority: US
Inventors: Carl P Anderson
Original assignee: SCM Corp
Current assignee: Smith Corona Corp
Priority date: 1969-11-10
Filing date: 1969-11-10
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17

Abstract

A mechanism for line spacing the platen of a business machine carriage in the rotational direction when in the left margin position without causing any movement of the carriage in the lateral direction. The mechanism includes a drum and cord arrangement which is momentarily clutched to the machine power supply for line spacing the platen through a crank device wherein the clutching time is controlled by a cyclic cam so as to disengage the clutch at a precise time just after line spacing has occurred and just prior to the time the crank mechanism would reach its abutment and move the carriage laterally.

Description

United States Patent [72] Inventor Carl P. Anderson Homer, N.Y.

[21] Appl. No. 871,623

[22] Filed Nov. 10, 1969 [45] Patented Aug. 17, 1971 [73] Assignee SCM Corporation Continuation of application Ser. No. 669,032, Oct. 20, 1967, now abandoned.

[54] PLATEN LINE-SPACING MECHANISM 2 Claims, 13 Drawing Figs.

1,784,047 12/1930 Degener Primary Examiner lirnest '1'. Wright. Jr. Attorney-Milton M. Wolson ABSTRACT: A mechanism for line spacing the platen of a business machine carriage in the rotational direction when in the left margin position without causing any movement of the carriage in the lateral direction. The mechanism includes a drum and cord arrangement which is momentarily clutched to the machine power supply for line spacing the platen through a crank device wherein the clutching time is controlled by a cyclic cam so as to disengage the clutch at a precise time just after line spacing has occurred and just prior to the time the crank mechanism would reach its abutment and move the carriage laterally.

PATENTED AUG] 71371 SHEET 1 0F 4 INVENTOK CARL F? ANDERSON MHZ AGENT PATENTED AUG 1 7 I971 SHEET 3 OF 4 INVENTOR. CARL F! ANDERSON PATENTED we I 7 Ian SHEET ll 0F 4 N R0 S in D N A WP L R A C AGENT PLATIEN LINE-SPACING MECHANISM RELATED APPLICATION This application is a continuation of my copending application, Ser. No. 669,032 filed Sept. 20, 1967 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to powered carriage return mechanisms for business machines and more particularly to the type which line space the carriage platen in a rotational direction without moving the carriage in a lateral direction when the carriage is in its left margin position.

In most powered carriage return mechanisms for business machines, a tape or draw cord is wrapped onto a drum through the use of a large friction clutch to return the carriage when the carriage return button is depressed. The tape is connected to the carriage in such a manner that initial wrapping onto the drum actuates the platen rotational line-spacing mechanism and further wrapping pulls the carriage along its tracking rail to the left margin position. The moving carriage is decelerated by any suitable mechanism as it approaches this position and is allowed to move slightly beyond this position so that it may be more easily and properly registered at the beginning of the writing line. This overbanking motion of the carriage is generally used in any appropriate manner to release the friction clutch and cause the conventional carriage escapement mechanism to arrest the carriage in proper registration position.

If the operator desires to line space the carriage platen while in the left margin position, the overbank motion just described must also occur in order to accomplish the function thereby causing a sudden jerk of the carriage and an undesirable noise and vibration.

SUMMARY OF THE INVENTION This invention provides a carriage return mechanism capable of accomplishing a rotary line space function of the carriage platen when in the left margin position without causing any lateral movement of the carriage thereby overcoming the above-mentioned disadvantage of noise and vibration.

This is accomplished by use of a cyclic cam in combination with the carriage return clutch and the line-spacing mechanism wherein the clutch is a positive clutch, the cyclic cam controls the engagement time, and the line space mechanism produces substantially a harmonic rotational motion on the carriage platen.

A line space mechanism pawl which drives the platen in a rotational direction is first accelerated, then decelerated during its driving stroke by a crank device. The deceleration of the pawl in combination with a dwell provision in the crank device allows for a precise time of clutch disengagement whereby the line-spacing function is completed and released before the mechanism reaches the point at which it would move the carriage laterally.

DESCRIPTION OF THE DRAWING FIG. 1 is a bottom perspective view showing the novel carriage return mechanism and its association with the machine rear framework and a power source;

FIG. 2 is a perspective view of the carriage platen and the line space crank assembly;

FIG. 3 is a perspective view of a carriage return trip assembly;

FIG. 4 is an exploded view of the cyclic cam and two of the carriage return mechanism clutches;

FIG. 5 is a portion of FIG. 1 illustrating the mechanism used to couple the carriage return mechanism to the machine power supply;

FIG. 6 is a perspective view illustrating the association between the cyclic cam an the cord drum clutch;

FIG. 7 is a front elevational view of a portion of a carriage return latch mechanism;

FIGS. 8, 9, and 10 are front elevational views of a portion of FIG. 5 as it appears at different stages of a carriage return operation;

FIG. 11 is a left elevational view of a portion of the crank assembly in a normal unactuated position;

FIG. 12 is a left elevational view of a portion of the crank assembly in a fully actuated position for line spacing the platen without effecting carriage return movement; and

FIG. 13 is a left elevational view of the crank follower and the platen ratchet wheel as they appear in their rest position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring briefly to FIG. 1, which shows the carriage return mechanism in its rest position when the carriage is in the left margin position, the general operation of the invention is as follows:

A trip assembly 10 is activated by depression of the carriage return button for effecting a counterclockwise motion of an actuator bellcrank 12. The bellcrank 12, through mechanism 14, clutches the machine motor to a driving pinion l6 and clutches a cyclic cam 18 to a hypoid gear 20 through mechanism 22. The hypoid gear 20 is coaxially mounted on a shaft 74 cyclic with cam 18 and is constantly in mesh with the pinion 16. The cam 18 which rotates clockwise, pivots a cam follower 24 which in turn engages a spring clutch 82 between the hypoid gear 20 and a cord drum 78 (FIG. 4). The cord drum 78 and the spring clutch 82 are both coaxially mounted with and are behind the hypoid gear 20. A cord 26 is then wrapped onto the cord drum 78 as the drum 78 rotates whereupon the cord 26 first rotationally line spaces the carriage platen 38 and then pulls the carriage along its tracking rail to the left margin position.

Referring to FIG. 2, the cord 26, which is guided by pulleys 27, when wrapped onto the cord drum 78 pivots a crank 28, which is pivotally mounted in the left carriage end frame 29 by a shaft 31, and crank follower 30 counterclockwise, which in turn drives the platen 38 counterclockwise about its axis 33 by way of a crank follower pawl 32 and a platen ratchet wheel 34. The cord 26 which is fixed at one end to a crank-keyed pulley 36 and fixed at its other end to the cord drum 78, pivots the pulley 36 counterclockwise causing a like movement of the platen 38 until a projection 40 of the pulley 36 contacts the left side of a carriage frame mounted rubber abutment 42. After the abutment contact is made, further wrapping of the cord 26 pulls the carriage to the right along its tracking rail (not shown).

When the carriage reaches its left margin position or all the way to the right, the driving force to the cord drum 78 is released and the carriage is decelerated by a conventional shock-absorbing dashpot 43 (FIG. 1) and the carriage escapement is conventionally engaged thereby arresting the carriage at the left margin registration. The cord 26 is now free from being wrapped and the pulley 36 is moved clockwise by a return cord 44 which is appropriately fixed at one end to the hub of pulley 36, guided by pulley 45, and fixed at its other end to a long but light carriage frame mounted tension spring 46.

More specifically and with reference now to FIG. 3, the trip assembly 10 consists of a trip bellcrank 48 which is pivotally mounted on a rigid shaft 50 and is biased clockwise by a tension spring 52. The shaft 50 is rigidly mounted at its right end on a frame bracket 54. A stop finger 56 is pivotally'mounted on a lower portion of bracket 54 by a pin 57. A link 58, which is pulled when the carriage return button is depressed, rotates the trip bellcrank 48 counterclockwise until an extension 60 of the bellcrank 48 contacts an abutment 62 of the stop finger 56. A trip dog 64 is pivotally mounted on the trip bellcrank 48 by a pin 63 and is biased counterclockwise by spring 65 so that a formed arm 66 abuts the forward portion 68 of the trip bellcrank 48. When the bellcrank 48 is pivoted counterclockwise the trip dog 64 pivots the actuator bellcrank 12 counterclockwise.

The stop finger 56 is biased counterclockwise by a spring 70 so as to normally allow only a limited motion of the trip bellcrank 48 via the stop finger abutment 62. In the event that the carriage return button is held depressed, the actuator bellcrank 12 must be returned to its normal rest position shortly after being pivoted counterclockwise by the trip dog 64 in order to insure only a single actuation of the cyclic cam 18.

This is accomplished by an extension 69, operated by cam fol- I lower 24 which moves upwards and under arm 250 of trip dog 64 as soon as the carriage return operation begins and thereby pivots the trip dog 64 clockwise thereby allowing the actuator bellcrank 12 to be pivoted clockwise to its rest position by a spring 206 and rest upon the forward portion 68 of the trip bellcrank 48 until the carriage return button is released. However, as the carriage moves into its left margin position, a margin abutment plate finger 72 of margin abutment plate 191 pivots the stop finger 56 far enough clockwise to permit further motion of the trip bellcrank 48 in response to further depression of the carriage return button. This in turn causes further counterclockwise motion of the actuator bellcrank 12 and provides as will be hereinafter described, a repeat vertical line-spacing operation.

Referring now to FIG. 4, the shaft 74 which is rigidly mounted in a frame casting 76, provides pivotal support for the hypoid gear and the cord drum 78 each of which has a hub 80 and hub 81 respectively upon which a coiled spring clutch 82 is supported. The spring clutch 82 is fixed to the hypoid gear hub 80 by way of a formed spring end 84 that extends into an appropriate hole 85 in the gear hub 80 while the opposite end of the spring clutch 82 is loose on the cord drum hub 81. This arrangement normally allows the gear 20 to rotate in a clockwise direction when driven by the pinion 16 without effecting rotation ofthe cord drum 78.

The gear 20 has another hub consisting of two

portions

86 and 88; the smaller portion 86 upon which the cam 18 is pivotally supported and a larger toothed portion 88. The toothed portion 88 provides a means of clutching the cam 18 to the gear 20 when the toothed portion 88 is engaged by a cam mounted dog 90. The dog 90 is pivotally mounted on a pin 92 which is rigidly mounted on cam 18 and is biased clockwise by a light tension spring 94 to engage the toothed hub portion 88 but is normally held disengaged by a formed finger 96 of the actuator bellcrank 12. Thus the gear 20 may also be normally rotated clockwise when driven by the pinion 16 without effecting a rotation of the cam 18.

A spiral spring housing 98 is rigidly mounted to the casting 76 by screws 100 and provides an anchor for an outer formed end 102 of a spiral spring 104 while the inner end of the spiral spring 104 is fixed to a cord drum hub (not shown) for providing a clockwise biasing force on the cord drum 78. This force keeps the cord 26 from becoming slack and also minimizes cord backlash when the mechanism is suddenly stopped at the end ofa carriage return operation.

A cam plate 106 which is supported on a cam hub 108 is adjustably secured to the outer face of the cam 18 by a screw 110 and provides a method for altering that portion ofthe cam profile which is instrumental in timing the disengagement of the spring clutch 82 as will be described shortly. A collar 112 is rigidly fixed to the end of shaft 74 by means of a setscrew 113 for retaining the associated parts on the shaft 74.

It can now be seen that ifthe cam dog 90 is engaged with the toothed hub 88 and if the coils of the free end of the spring clutch 82 are pressed against the cord drum hub 81, the cord drum 78 and the cam 18 would rotate clockwise with the gear 20 as it is driven by the pinion 16.

Referring now to FIG. 5, the pinion 16 is driven by the machine motor shaft 114 through both a centrifugal clutch 116 and a friction clutch 118. The friction clutch 118 is comprised of a plate 120 which is pivotally mounted on the pinion shaft 122 and is straddled by a pair of friction pads 124. A pair of metal discs 126 are keyed to the shaft 122 by having square center holes which circumscribe a like portion of the shaft 122. The friction clutch assembly 118 is retained between a keeper 128 at its left end and a relatively heavy compression spring 130 at its right end. The compression spring 130 is disposed between a shaft collar 132 and the right metal disc 126 thereby providing the frictional force on the opposite faces of the plate 120. The collar 132 is adjustable on shaft 122 to vary the compression of spring 130. After collar 132 is adjusted on shaft 122, fastening means (such as screws) located in collar 132 permit collar 132 to be rigidly mounted in position on shaft 122. The plate 120 is keyed by way of a tongue and groove arrangement to a finger 134 which is brazed to the right end ofa sliding sleeve 136 while the sleeve 136 is pivotally mounted on the right end of the motor shaft 114 and also provides an internal pivotal support for the left end of the pinion shaft 122. The right end of the pinion shaft 122 is pivotally supported in a bushing 138 which is keyed to a slotted frame member 140. A collar 141 is rigidly mounted to the pinion shaft 122 and provides for proper positioning of the pinion 16 during assembly.

At the left end of the sleeve 136 is a rigidly mounted toothed member 142 having teeth which cooperate with two centrifugal dogs which pivot about pins 147 within a centrifugal clutch 116 when the sleeve 136 is moved laterally to the left. More specifically, the centrifugal dogs 145 are normally spring urged out of the path of the teeth of toothed member 142. Rotation of centrifugal clutch 116 causes the centrifugal dogs 145 to turn inwardly into engagement with the teeth of toothed member 142 when sleeve 136 is moved laterally to the left. The sleeve 136 is normally held to the right as shown by a yoke 143 which is pivotally mounted on a frame bracket 144 by a stud 146 and straddles a circular plate 148 which is rigid on sleeve 136. A long link 150 is pivotally mounted to the lower end of the yoke 143 and is biased to the right by a tension spring 152. The force exerted by spring 152 is normally held from effecting engagement of the sleeve toothed member 142 with the normally rotating centrifugal clutch 116 by a finger 154 which is abutted by a link latch finger 156 at its right end and restricts the link 150 from lateral movement to the right. An upper extension 158 oflink 150 has an elongated slot 160 through which a pin 162 extends, the pin 162 being rigidly mounted on an arm 164 of the actuator bellcrank 12 (FIG. 4).

When the actuator bellcrank 12 is pivoted counterclockwise by the trip assembly 10, the pin 162 of the bellcrank arm 164 causes a downward motion of the right end of link 150. This motion causes the link latch finger 156 to step off the holding finger 154 whereupon the tension spring 152 drives the link 150 to the right and engages the sleeve toothed member 142 with the rotating centrifugal clutch 116 to rotate the pinion 16 counterclockwise (FIG. 4) through the friction clutch 118. At the same time the link 150 is moved downward, the cam dog 90 (FIG. 4) is released by the actuator bellcrank arm 96 and the cam 18 is clutched to the gear 20.

Referring now to FIG. 6, a cam follower assembly 166 is pivotally mounted on a rigid shaft 168 and comprises a latch lever 170 and a follower bellcrank 172, which are brazed at opposite ends to a sleeve 174. The sleeve 174 1;; pivotally mounted on the rigid shaft 168 and the assembly 166 is heavily biased in a clockwise direction by tension spring 176 so that a roller 178 which is pivotally mounted on the follower bellcrank 172 is held against the periphery of the cam 18. The latch lever 170 provides the finger 154 against which the link latch finger 156 abuts (FIG. 5). The iatch lever 170 has, pivotally mounted at its left end, a trip member 180 which effects both the release of the carriage escapement upon initial movement of the follower assembly 166 and the reengagement of the escapement as the carriage moves into its left margin position. This is accomplished by two formed

fingers

182 and 184 of the trip member 180 in that the formed finger 182 contacts and pivots the escapement holding dog 186 (FIG. 1) out of the path of the escapement star wheel teeth 188 when the follower assembly 166 is rocked by the cam 18 while the formed finger 184 is driven to the right by a margin abutment extension 190 attached to margin abutment plate 191 to efiect reengagement of the holding dog 186 as the carriage moves into the left margin position and drives the margin abutment plate 191 to the right.

Referring again to FIG. 6, a spring clutch engaging member 192 which is also pivotally mounted on shaft 168 has an upstanding arm 194 and is normally biased counterclockwise by a tension spring 196 which is connected between a lower extension of the clutch-engaging member 192 and a formed ear I' 198 of the latch lever 170. A finger extension 200 of the engaging member 192 overlies and contacts a formed finger 202 of the follower bellcrank 172 so as to insure counterclockwise movement of the engaging member 192 in response to alike movement of the follower bellcrank 172 as the cam 18 begins to rotate. As this happens, the end of the engaging member upstanding arm 194 presses against the free end of spring clutch 82 and clutches the cord drum 78 to the already rotating hypoid gear (FIG. 4) to effect wrapping of the cord 26 thereon.

The cam 18 makes only a single revolution as will be described hereinafter, while the cord 26 must be wrapped until the carriage reaches its left margin position. Therefore the follower assembly 166 must be latched in a position so as to insure a continuous engagement of the spring clutch 82 until the carriage is in its left margin position. This is accomplishedby a latch member 204 which is pivotally mounted on the same rigid shaft 205 as is the actuator bellcrank 12 (FIG. 1). The latch member 204 is biased counterclockwise by the tension spring 206 which interconnects the latch member 204 and the actuator bellcrank 12 (FIG. 1). The latch member 204 is limited in its normal inoperative position as shown by a formed car 208 on the latch lever 170.

When the latch lever 170 is pivoted counterclockwise by the cam 18, the formed car 208 (FIG. 7) is raised to a position 210 whereby a step portion 212 of the latch member 204 will move under and hold the latch lever 170 in a latched position against the influence of the follower assembly spring 176. The cam 18 may now complete its revolution and return to its normal inoperative position without causing a return motion of the follower bellcrank 172 thereby insuring the continuous engagement of the spring clutch 82 until the carriage reaches the left margin position. When this occurs, an extension 214 of the margin abutment plate 191 contacts the upper extension 216 of the latch member 204 and pivots the member 204 clockwise to release the latched condition of the latch lever 170 and thereby effect release of the spring clutch 82.

The mechanism is such that latching of the latch lever 170 will occur any time the carriage is one or more letter spaces away from the left margin and the mechanism is actuated. However, when the carriage is in the left margin position, the latch member 204 is held in its clockwise pivoted condition by margin abutment plate extension 214 contacting latch member extension 216 whereby the step portion 212 of the latch member 204 will not prevent the formed ear 208 from rising and falling in response to a cycling of the cam 18. Thus, if the carriage is in the left margin and the carriage return but ton is depressed beyond its normal actuating position thereby causing further counterclockwise rotation of the actuator bellcrank 12 as previously described in reference to FIG. 3 and being that the latch member 204 is held ineffective with respect to the latch lever 170, the actuator bellcrank arm 96 will not effect reengagement with the cam dog 90 and the continuously rotating cam 18 will effect intermittent engagement and disengagement of the cord drum spring clutch 82 thereby providing intermittent rotary line spacing of the platen 38. The cord 26 is alternately pulled in the actuating direction by the above mentioned action, and pulled in the return direction by the spring biased return cord 44 (FIG. 2). Thus the engagement time of the spring clutch 82 is dependent upon the profile of the cam 18 which is basically a rise, dwell, and return profile. It should be noted that by adjusting the cam plate 106 clockwise or counterclockwise with respect to the cam 18, that, the.:dwell portion of the cam profile will accordingly be shortened or lengthened respectively thereby providing a more precise timing for the engagement of the spring clutch 82, the provision of which will soon be evident.

Referring now to FIGS. 8 thru 10, the singlerotation of the cam 18 is accomplished through the controlledmovement of the long link 150 by the latch lever finger 154. More specifically, after the long link 150 has been driven both downward and to the right as previously described and as illustrated by full lines in FIG. 8, the link 150'is'raised to the position illustrated by full lines in FIG. 9 by both the actuator bellcrankbiasing spring 206 (FIG. 1) through pin 162 and the long linkbiasing spring 152 (FIG. 5) when the latch lever 170 is pivoted by the cam 18 and the latch lever finger 154 moves to the position illustrated by full lines in FIG. 9. When the link 150 is raised, the actuator bellcrank arm 96 pivots clockwise to its normal inoperative position as shown in FIG. 4 and is in position to contact and disengage the approaching cam dog from the toothed gear hub 88 thereby rendering the clutch engagement between the cam 18 and the gear 20 ineffective.

The latch lever finger 154 remains in the position shown in FIG. 9 until the latch member 204 (FIG. 6) is pivoted by the margin abutment extension 214 whereupon the heavy follower assembly spring 176 pivots the assembly 166 clockwise and the latch lever finger 154 (FIG. 10) drives the long link to the left via the link latch finger 156 to disengage the pinion driving centrifugal clutch 116 (FIG. 5).

Referring now to FIG. 11, a cord knot 218 at the end of the cord 26 which lies within an appropriate knot retaining aperture 219 in the pulley 36 provides the means by which the cord 26 is anchored to the pulley 36 while a like knot and aperture arrangement (not shown) also provides the anchor means for the spring biased return cord 44 on pulley 36. The two

cords

26 and 44 are wrapped in opposite directions onto their respective hub grooves whereby the pulley 36 moves counterclockwise when cord 26 is pulled and clockwise when cord 44 is pulled.

The pulley 36 is normally held in its inoperative position with its projection 40 abutting the right side of the rubber abutment 42 by the spring biased return cord 44. As the cord 26 wraps onto the cord drum 78 and moves the crank 28 counterclockwise about its shaft 31, a crank roller 220, which is pivotally mounted to the crank 28 and lies within a suitable slot 222 in the crank follower 30, first moves parallel to and outwardly within the slot 222 thereby causing an accelerated counterclockwise motion of the follower 30. This acceleration reaches a maximum when the roller 220 is in line with the axis of shaft 31 and platen axis 33 respectively.

As the crank 28 rotates further, the roller 220 moves parallel to and inwardly within the slot 222 thereby causing a decelerating motion of the crank follower 30 until it reaches the position shown in FIG. 12.

The inward most portion 224 of the slot 222 comprises an arc and provides a dwell for the crank follower 30 during the last portion of pulley movement and is so positioned that the roller 220 enters the dwell portion 224 (FIG. 12) just before the pulley projection 40 contacts the left side of rubber abutment 42. Consequently, further movement of the pulley 36 does not effect movement of the follower 30 and provides a time interval during which the spring clutch 82 on the cord drum hub 81 may be disengaged.

Being that the follower 30 is first accelerated and then decelerated during its counterclockwise motion, substantially a harmonic motion is transmitted to the platen 38 by way of the crank follower pawl 32 (FIG. 13). The pawl 32 is pivotally mounted on the crank follower 30 and is biased counterclockwise by a tension spring 226 for engagement with the peripheral teeth 35 on the platen ratchet wheel 34. A shelf 228 prevents the pawl 32 from engaging the teeth 35 when the mechanism is normally inoperative as shown and is conventionally adjustable between a plurality of positions about the periphery of the ratchet wheel 34 for selectively providing different degrees of platen rotation during the line-spacing operation.

As the follower is driven counterclockwise, the pawl 32 drops off the end of the shelf 228 and enters the appropriate tooth 35 opening on the ratchet wheel 34 causing the ratchet wheel 34 and the platen 38 to move counterclockwise. A conventional heavily biased detent roller 230 is provided for insuring proper registration of the platen 38 after it has been linespaced.

Being that the crank follower 30 has completed its counterclockwise motion prior to the time that the pulley projection 40 would contact the rubber abutment 42 and being that the spring clutch 82 on the cord drum hub 81 is disengaged prior to said abutment contact, the rotary line-spacing function of the carriage platen 38 is therefore completed without causing any lateral movement of the carriage.

Referring again to FIG. 1, the left margin abutment plate 191 is shown in its left margin position just after a carriage return operation has been performed and the carriage has driven plate 191 all the way to the right via contact of an upper slide extension 232 of margin abutment plate 191 by the left margin button extension 234. The plate 191 is slideably mounted on a long rigid shaft 236 and is driven to the left by the dashpot piston rod 238 under the influence of a piston rod compression spring 240 as typing occurs and the carriage is spaced to the left. A self-locking nut 242 toward the left end of the shaft 236 limits the travel of the margin abutment plate 191 and the dashpot piston rod 238 as typing continues and positions the margin abutment plate 191 for the subsequent carriage return operation.

The ability of the line-spacing mechanism to effect substantially a rotary harmonic motion to the carriage platen 38 results in a smoother acting line-spacing feature with more controllability for proper platen registration while the ability of the carriage return mechanism in cooperation with the dwell provision within the line space crank mechanism to effect a more timely disengagement of the cord drum spring clutch 82 results in a quieter and nonjerking carriage linespacing feature when the carriage is positioned at the left mar- What I claim and desire to be secured by Letters Patent is:

1. In an electric machine, having a rotatable platen supported on a traversable carriage, a mechanism which either indexes the platen and returns the carriage to its left-hand margin position or, when the carriage is in its left-hand margin position, indexes the platen only, such mechanism comprising:

a. a rotatable pulley supported for movement with the carriage,

b. stop means on said carriage which limits rotation of said pulley,

0. means which impart rotatable movement of said pulley to the platen,

a rotatable cord drum,

e. a cord, having one end wrapped on said rotatable cord drum and the other end attached to the pulley so that initial rotation of said cord drum will cause the pulley to be rotated to its rotative limit and further rotation of said cord drum will cause the carriage to be returned to its left-hand margin position,

e. a driving member operable by a power source,

a clutch which transmits rotation from said driving member to said cord drum,

. a cyclic cam for actuating said clutch to cause initial rotation of said cord drum so that the pulley is rotated to its rotative limit,

. means for further actuating said clutch to cause further rotation of said cord drum so that the carriage will be returned to its left-hand margin position, and j. an extension mounted on the carriage which is effective without movement of the carriage or any carriage-associated part to prevent said means for further actuating said clutch from further actuating said clutch when the carriage is in its left-hand margin position.

2. In an electric machine, as set forth in claim 1 wherein said means for further actuating said clutch comprises a latch lever and latch.

Claims

1. In an electric machine, having a rotatable platen supported on a traversable carriage, a mechanism which either indexes the platen and returns the carriage to its left-hand margin position or, when the carriage is in its left-hand margin position, indexes the platen only, such mechanism comprising: a. a rotatable pulley supported for movement with the carriage, b. stop means on said carriage which limits rotation of said pulley, c. means which impart rotatable movement of said pulley to the platen, d. a rotatable cord drum, e. a cord, having one end wrapped on said rotatable cord drum and the other end attached to the pulley so that initial rotation of said cord drum will cause the pulley to be rotated to its rotative limit and further rotation of said cord drum will cause the carriage to be returned to its left-hand margin position, e. a driving member operable by a power source, g. a clutch which transmits rotation from said driving member to said cord drum, h. a cyclic cam for actuating said clutch to cause initial rotation of said cord drum so that the pulley is rotated to its rotative limit, i. means for further actuating said clutch to cause further rotation of said cord drum so that the carriage will be returned to its left-hand margin position, and j. an extension mounted on the carriage which is effective without movement of the carriage or any carriage-associated part to prevent said means for further actuating said clutch from further actuating said clutch when the carriage is in its left-hand margin position.