US3455430A

US3455430A - Back spacing mechanism

Info

Publication number: US3455430A
Application number: US552178A
Authority: US
Inventors: Horst Schweizer
Original assignee: Olympia Werke AG
Current assignee: Olympia Werke AG
Priority date: 1965-05-21
Filing date: 1966-05-23
Publication date: 1969-07-15
Anticipated expiration: 1986-07-15
Also published as: DE1436698A1; GB1153521A; DE1436698B2; CH445527A

Description

6 Sheets-Sheet 1 Fi led May 23, 1966 .mm N

' INVENTOR filo-:1 W4? BY d J fl'M ATTORNEY July 15, 1969 H. SCHWEIZER 3,455,430-v BACK SPACING MECHANISM Filed May 25, 1966 6 Sheets-Sheet 2 INVENTOR WA,

BY w/ JiJk a/ ATTORNEY July 15, 1969 H. SCHWEIZER BACK SPACING MECHANISM Filed May 25, 1966 6 Sheets-Sheet 5 Fig.2!) 43 INVENTOR ATTORNEY I July 15, 1969 H. SCHWEIZER 3,455,430

BACK SPACING MECHANISM Filed May 23, 1966 6 Sheets-Sheet 4 INVENTOR ATTORNEY y 15, 1959 H. SCHWEIZER 3,455,430

BACK SPACING MECHANISM Filed May 25, 1966 6 Sheets-Sheet 5 ATTORNEY July 15, 1969 H, SCHWEIZER 3,455,430

BACK SPAC ING MECHANI SM Filed May 23, 1966 6 Sheets-Sheet 6 l United States Patent U.S. Cl. 19791 Claims ABSTRACT OF THE DISCLOSURE A set of escapement pawls cooperates with the rack of a carriage to block carriage movement after steps of different length, and are connected by coupling means to backspacing means which shift coupled pawls forward and rearward, and into and out of recesses of the rack to obtain backspacing of the carriage.

The present invention invention relates to a back spacing mechanism for the escapement mechanism of a carriage, and more particularly to mechanism for moving the paper carriage of a typewriter in steps which are proportional to the dimensions of the typed characters.

The escapement mechanism includes a set of escapement pawls, preferably three pawls, which sequentially cooperate with the teeth and recesses of a rack secured to the paper carriage. The escapement pawls are mounted on a stationary shaft for turning movement into and out of the recesses, and for longitudinal movement along the rack of the paper carriage. Each pawl cooperates with two releasing members which, in accordance with the selected type character and corresponding step, release the corresponding pawls so that only one pawl stops the carriage after a step of a desired length. Consequently, assuming that three escapement pawls are provided, the pawls have three different positions relative to each other, one pawl enaging a blocking means to stop the carriage, while the other pawls are spaced distances corresponding to one and two steps, respectively, from the stop means.

It is one object of the invention to combine a proportional escapement mechanism of this type with a back spacing device permitting the correction of errors by moving the paper carriage rearward.

Another object of the invention is to combine an escapement mechanism which permits the carriage to move steps of different length, with a back spacing de vice which back spaces the paper carriage for a distance corresponding to the shortest step.

It is another object of the invention to provide a combined back spacing and escapement mechanism using the escapement pawls for the back spacing operation.

With these objects in view, the present invention relates to a back spacing mechanism, and more particularly to a combined back spacing and escapement mechanism for a paper carriage which is movable forward in a writing direction and rearward in a back spacing and return direction.

One embodiment of the invention comprises a set of escapement pawls, preferably three pawls, cooperating with the teeth and recesses of the rack of the carriage, and having stop portions staggered relative to each other a predetermined distance in the direction of the carriage movement; blocking means engage the stop portion of the leading pawl for blocking forward movement of the carriage while the stop portions of the other pawls are rearwardly spaced from the leading stop portion and from the blocking means; a set of coupling means respectively correlated with the pawls and being individually 3,455,430 Patented July 15, 1969 and independently movable between a position of rest, a first coupling position coupled with the leading pawl which engages the blocking means, and a second coupling position coupled with another pawl, preferably with the second trailing pawl; actuating means for moving the coupling means to the coupling positions, and for moving the coupling means in the first coupling position together with the respective pawl rearward so that the carriage is rearwardly moved and for moving the coupling means in the second coupling position forward so that the respective pawl moves out of an engaged recess and forward relative to the rearwardly moving rack and then engages the next leading recess while the stop portion thereof engages the blocking means for blocking forward movement of the carriage; and back spacing means for operating the actuating means.

The predetermined distance between the stopping portions of the escapement pawls, which corresponds to the minimum carriage step, is the distance between adjacent recesses of the rack of the paper carriage, divided by the number of pawls in the set. The coupling means in the second coupling position engages the pawl whose stop portion trails the leading stop portion of the leading stop, two of these distances.

In the preferred embodiment of the invention, the actuating means include biassing means for urging the coupling means whose associated pawls are in the corresponding positions into the first and second coupling positions respectively, and a turnable drive means having rearwardly and forwardly acting parts for moving the coupling means in the first coupling position rearward, and the coupling means in the second coupling position for ward, respectively. The drive means has a normal position for holding the coupling means in the position of rest, and an actuating position for releasing the coupling means for movement under the action of the biassing means to the first or second coupling positions. Further turning of the drive means causes forward and rearward movement, respectively, of the coupling means in the coupling positions with the respective pawls, to effect back spacing of the carriage and blocking of the same after the step in rearward direction. The back spacing key is operatively connected with the drive means for operating the same. 4

In the preferred embodiment of the invention, the several pawls have staggered stepped recesses with staggered shoulders, which are engaged by the respective coupling means in accordance with the staggered positions of the pawls so that different shoulders of a stepped recess are engaged in the first and second coupling positions, causing a relative displacement between the respective coupling means in coupling positions and the rearwardly and forwardly acting parts of the drive means. Consequently, only one pawl is shifted in forward writing direction, and another pawl is shifted backward, while the remaining pawl or pawls are not actuated but follow the movement of the other pawl in backward direction.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1a is a fragmentary elevation, partially in section along line 1a-1a in FIG. lb, illustrating an escapement mechanism combined with a back spacing mechamsm;

FIG. 1b is a fragmentary plan view of the embodiment of FIG. 1a;

"ice

FIG. 2a is a fragmentary elevation, corresponding to FIG. 1a, but omitting parts of the same for the sake of simplicity, and illustrating the mechanism in a first operational position in which the longest pawl blocks the can riage movement;

FIG. 2b is a plan view illustrating the mechanism in the position of FIG. 2a;

FIG. 3a is a fragmentary elevation partly in section taken along line 3a3a in FIG. 3b and corresponding to FIG. 2a, but illustrating the mechanism in another operational position in which the shortest pawl blocks the carriage movement;

FIG. 3b is a fragmentary plan view illustrating the mechanism in the position of FIG. 3a;

FIG. 4 is a fragmentary elevation illustrating on an enlarged scale, a detail of the mechanism in an operational position assumed between the positions of FIG. 2a and FIG. 3a;

FIG. 5 is a fragmentary elevation illustrating on an enlarged scale a detail of the mechanism in another operational position in which the shortest pawl is operative to block carriage movement; and

FIG. 6 is a fragmentary elevation illustrating on an enlarged scale a detail of the mechanism in a further operational position in which a pawl of intermediate length blocks the carriage movement.

Referring now to the drawing, and more particularly to FIGS. 1a and 1b, the paper carriage of a typewriter, not shown, carries the escapement rack 1, and is urged by the carriage spring, not shown, to move in a forward writing direction indicated by the arrow 2. During the carriage return or during a back spacing operation, the carriage with rack 1 moves in the opposite rearward direction.

The teeth 3 of the rack 1 are spaced at distance t which is equal to three smaller distances 0. An escapement mechanism P includes three pawls 4 whose engaging portions 5 cooperate with the recesses between teeth 3 of rack 1. The pawls 4 are operated in a manner which is not an object of the invention, to permit the carriage to move steps of different length proportionate to the dimensions of a typed character, the steps having a length of one, two or three distances 2. FIGS. 1a and lb also show parts of a return mechanism R which is not an object of the invention, and a back spacing mechanism S which, in accordance with the invention, is combined with the escapement mechanism P. The set of escapement pawls 4 is mounted on a stationary rod or shaft 7 for turning movement into and out of the recesses between teeth 3, and for movement in the direction of rack 1 and of the carriage movement. Pawls 4 have slots 6, open at one end, and closed at the other end by semicircular stop portions 6', which are spaced different dis tances L L L from the tip of the respective engaging portion 5, and since the pawls 4 are of a corresponding length, the foremost pawl 4 is the longest, and the rearmost pawl 4 is the shortest. Distance L +e is distance L and distance L, is distance L +e, as diagrammatically indicated in the upper portion of FIG. 1a. In the position of FIG. 1a, the longest pawl 4 blocks movement of the carriage since its stop portion 6 abuts blocking shaft 7. Stop portion 6' of the intermediate pawl 4 is spaced the distance :2 from the blocking shaft 7 and stop portion 6 of the rearmost pawl 4 is spaced the distance e from the stop portion 6 of the intermediate pawl 4 and a distance 2e from the blocking shaft 7. Consequently, the intermediate and rearmost pawls 4 do not block carriage movement in the position of FIG. la. The stop portions 6 have substantially the same diameter as shaft 7.

FIG. 1a shows the foremost longest pawl 4 in dash and dot lines and may be considered as a section along line 1a1a in FIG. lb, with the foremost pawl 4 shown in phantom lines.

Each of the pawls 4 is biased by a spring 8 engaging an arm 9 to turn in counterclockwise direction about blocking shaft 7, and also to move rearward along the rack 1. The force of any spring 8 urges the respective pawl 4 to engage the rack 1 with its engaging portion 5. FIGS. 1a and 2:: show the engaging portions 5 of all three pawls 4 located in the same recess between adjacent teeth 3' and 3", and since the carriage spring urges rack 1 in the direction of the arrow 2, the flank of tooth 3 urges all three pawls 4 towards the left, overcoming the weaker springs 8, so that the longest pawl 4 abuts blocking shaft 7 with its stop portion 6, while stop portions 6 of the shorter pawls 4 are spaced from the blocking shaft 7. Only the foremost pawl 4 blocks movement of the carriage. The staggered position of stop portions 61 is also shown in FIGS. 2a and 212.

Each pawl 4 has a projecting lug 10, having a shoulder 10, and the shoulders 10' of the three pawls 4 are spaced predetermined distances 0 from each other so that shoulders 10' are spaced the same distance from stop portions 6' of the respective pawl 4. Shoulders 10' cooperate with engaging edges 11, '11'a of pairs of releasing members 11, 110, one pair of releasing

members

11, 11;a being respectively associated with each pawl 4. Releasing

members

11, 11a have slots '12 open to the right as viewed in FIG. la, and embracing shaft 7 so that the releasing

members

11, 11a are guided for longitudinal and turning movement. Springs 13 and 13:: are respectively connected with each pair of releasing

members

11, 11a and urge the same to turn in counterclockwise direction until a stop 14- abuts a stationary abutment 15, schematically indicated in FIG. la, and preferably mounted on the frame 50 of the machine. The action of springs 13, 13a urges releasing

members

11, 11a to the right until edges 11', 11'a abut shoulders 10 of lugs 10 of. pawls 4.

Each releasing member 11, 11:: has a projecting portion 16, 16a. Projecting portions 16, 16a project over the respective lug 10 of the associated pawl 4. Projecting portion 16 of each releasing member 11 projects over the respective lug 10 substantially the distance 2 so that when releasing member 11 turns in clockwise direction, engagement of lug 10 is assured. Projecting portion 16a of each releasing member 11a is a distance 1 longer than projecting portion 16, the distance t being the spacing between adjacent teeth of rack 1. A locking member 48 with a locking portion 31 cooperating with locking teeth 30 in releasing

members

11, 11a is biased by spring 49.

Parts

11, 11a, 48 belong to an escapement mechanism P which is not an object of the present invention, and these parts have been shown and illustrated only for the sake of completeness, and have no bearing on the present invention. It will be understood that pawls 4 can be operated under the control of the releasing

members

11, 11a and of the locking member 48 to release and engage the teeth of the rack 1 to cause stepwise movement of the carriage under the action of the carriage spring, not shown, for steps whose lengths are either e or 2e or 3e, depending on the width of the last typed character.

The present invention is concerned with the use of the escapement pawls 4 to obtain a back spacing of the carriage in steps having the length of the predetermined distance e which is one-third of the spacing t of two teeth 3 of rack.

As also shown in FIGS. 2a to 6, each pawl 4 is provided in accordance with the invention with a stepped recess bounded by a first coupling shoulder 44', a first abutment 44, another shoulder 45", a second abutment 45, and a second coupling shoulder 45'. The stepped recesses are staggered the above-defined distance e relative to each other. The deeper portion 45a of each recess is bounded by

edges

45, 45, 45" and the shallower portion of each recess is bounded by

edges

44 and 44. The recesses cooperate with coupling portions 35 of a set of three coupling levers 35 and a coupling portion 35 cooperates with the first coupling shoulder 44' of the associated pawl 4 to shift the same toward the right for moving the carriage in the back spacing direction, and cooperates with a second coupling shoulder 45 of the associated pawl 4 for moving the same in a forward direction while the engaging portion 5 of the respective pawl 4 moves forwardly into the next following recess as will be described in greater detail hereinafter.

Coupling shoulders 44 and 45' are spaced equal distances from the stop portions 6' of the respective asso ciated pawls 4, so that the coupling shoulders 44 and 45' of the pawls 4 are staggered relative to each other, respectively, distances e.

Each coupling lever 35 has a forked end with a slot in which a fulcrum pin 43 is located for supporting the coupling levers 35 for turning movement, and also for movement in the longitudinal direction of the rack 1. Fulcrum pin 43 is mounted on a rocking member 52 of U-shaped configuration, best seen in FIG. 1b. Rocking member 52 is mounted on a stationary shaft 53 supported on frame wall 50 and is turnable together with fulcrum pin 43. Springs 8 connect arms 9 of pawls 4 with rocking member 52 so that the latter is biassed to turn in clockwise direction about shaft 53 until shaft 43 abuts a stationary abutment surface 50" which is part of the frame 50 of the machine. One wall of the frame 50 is shown in FIG; lb, and another wall 5-9 schematically indicated in hatched section, the walls 50 supporting a shaft 53. When a coupling lever 35 is displaced to the right, rocking member 52 is turned in counterclockwise direction against the action of spring 8 with fulcrum pin 43.

Actuating means are provided for coupling levers 35 and include springs 42 connecting the coupling levers 35 with a holding portion 36 of a drive means 36 which has a sleeve 38 mounting drive means 36 for turning movement on a stationary shaft 38. Springs 42 suspend the three coupling levers 35 in engagement with fulcrum pin 43, but permit independent movement of coupling levers 35. While springs 42 urge coupling levers 35 into engagement with fulcrum pin 43, the stronger springs 8 acting on rocking member 52 and fulcrum pin 43, do not permit turning of rocking member 52 by springs 42.

A stud 39 on arm 37 of drive means 36 abuts a stationary abutment 50' on the frame of the machine under the action of springs 42. A back spacing means 41, connected to the back spacing key of the typewriter, not shown, embraces bolt 39, as also shown in FIG. 112, so that upon operation of the back spacing key, arm 37 with drive means 36 is turned in counterclockwise direction about shaft 38.

In the normal position of rest of drive means 36, illustrated in FIG. 1a, its holding part 36' holds the coupling levers in a position of rest in which one of the superimposed coupling portions 35' is located opposite the deep recess portion a between shoulders 45' and 45 of one of pawls 4. When this coupling lever 35 is turned about fulcrum pin 43, its coupling portion 35' moves into the deep recess portion 45a until abutting abutment 45 in the position of FIG. 4 which shows the three pawls 4 in the same position as FIG. 1a, and coupling portion 35 of the rearmost coupling lever 35 between shoulders 45' and 45" of the shortest rearmost pawl 4 which has a stop portion 6' which is spaced two distances 0 from the blocking shaft 7. Coupling portion 35' of the foremost coupling lever 35 is located opposite coupling shoulder 44 of the longest pawl 4, while coupling portion 35 of the intermediate coupling lever 35 is spaced from coupling shoulder 44 of the associated intermediate pawl 4.

Drive means 36 is turned by back spacing means 41 in counterclockwise direction, and during such movement a transversely projecting drive part 36" moves in forward direction, and a transversely projecting drive part 36" moves in the rearward direction. Coupling members 35 have

abutments

35 and 35" respectively cooperating with the forwardly acting drive part 36" and the rearwardly acting drive part 36". In the position of FIG. 1a, in which coupling levers 35 are in the position of rest, abutments 35" are all located opposite the rearwardly acting drive part 36", whereas abutments 35" are not located in the path of movement of the forwardly acting drive part 36". However, when coupling portion 35' of one of the coupling levers 35, for example of the rearmost coupling lever 35 is moved into the deep recess portion 45a until abutting abutment 45, as shown in FIG. 3a, the respective abutment 35" is located opposite the forwardly acting drive portion 36, while the abutment 35" is no longer located in the path of movement of the rearwardly acting drive part 36".

FIG. 1a shows in its right portions a number of parts which have not been described since these parts belong to a carriage return device R cooperating with the escapement mechanism P which are not objects of the present invention. All these parts are omitted for the sake of clarity in FIGS. 2a and 2b, which show the position of rest, and FIGS. 3a and 3b which show an operational position of the back spacing mechanism S according to the present invention.

FIG. 1a and FIG. 2a show a basic operational position in which all three engaging portions 5 are located in the same recess between teeth 3' and 3". FIGS. 3a and 3b show the mechanism in an operational position in which a back spacing step of the carriage for a distance 2 has been accomplished by operation of the back spacing means 41. For a better understanding a system of parallel lines 34 indicates the spacing t between adjacent recesses, each distance r being the sum of three distances e so that e is one-third of distance t.

In the position of FIGS. 2a and 2b, in which stop portion 6 of "the foremost pawl 4 abuts blocking means 7 and blocks carriage movement, the other two pawls 4 are held by the respective springs 8 in engagement with the leading flank of tooth 3. Coupling portion 35' of the rearmost coupling lever 35 is located opposite the deep recess portion 45a of the rearmost pawl 4.

When back spacing means 41 is moved to the right, drive means 36 is turned in counterclockwise direction and holding portion 36' releases all three coupling levers 35 so that coupling levers 35 are raised by springs 42, and coupling portions 35' try to enter into the recesses in the corresponding pawls 4. Coupling portion 35 of the rearmost coupling lever 35 enters the deep recess portion 45a of the respective rearmost pawl 4, abutting the coupling edge 45, while abutments 44 limit the movement of coupling portions 35 of the other two coupling levers 35. The rear edge of the foremost coupling portion 35' is located opposite the foremost coupling shoulder 44' as best seen in FIG. 4.

Since the rearmost coupling lever 35 has moved to a higher position, its abutment 35", see FIG. 3a, is located opposite the forwardly acting drive part 36", while its abutment 35" is no longer located in the path of movement of the rearwardly acting drive part 36- of drive means 36.

In this manner, a selective coupling between drive means 36 and pawls 4 has been obtained, and when under the control of back spacing means 41, drive means 36 is further turned in counterclockwise direction, the forwardly acting drive part 36" moves through coupling means 35, 35 and 45' the rearmost escapement pawl 4 from the trailing position shown in FIG. 2a to the leading position shown in FIG. 3a so that this pawl 4 has moved two distances e until its stop portion 6' abuts blocking shaft 7, as shown in FIG. 30.

At the same time, the rearwardly acting drive part 36" engages abutments 35" of the two forward coupling levers 35 and shifts the same in rearward direction to the right as viewed in the drawing so that rocking member 52 is displaced against the action of springs 8. Coupling portion 35' of the foremost coupling lever 35 engages coupling shoulder 44 and moves the foremost largest escapement pawl 4 back for about two distances e so that rack 1 with the paper carriage is shifted back a corresponding distance in rearward direction, while the respective stop portion 6' moves away from blocking shaft 7.

While engaging portion of the rearmost pawl 4 moves forward toward the left, it is urged by a flank of tooth 3" out of the recess between teeth 3' and 3", and while the foremost pawl 4 moves the carriage in rearward direction, engaging portion 5 of the rearmost pawl 4 moves over tooth 3" and falls into the next following recess under the action of the respective spring 8. The shortest pawl 4 moves forward to lead the other pawls 4 and stops the carriage movement when stop portion 6- abuts blocking shaft 7 in the position shown in FIGS. 3a and 3b.

When the back spacing means 41 are released, and drive means 36 is returned by springs 42 in clockwise direction to the normal position of rest shown in FIGS. 2a, 2b, the shortest rearmost pawl 4 is in the leading position abutting blocking means 7 and blocking carriage movement. The position of the three pawls 4 is the same as if, starting from the position of FIG. 2a, a step of two distances e would have been performed in the forward writing direction, that is to the left as viewed in the drawing, the difference being that in this event tooth 3' would be in the position in which tooth 3" is in the position of FIG. 3a which shows the corresponding position after a backward step.

The three possible relative positions of escapement pawls 4 are shown in FIGS. 4, 5 and 6. In the position of FIG. 5, the rearmost pawl 4 leads the other pawls 4, and in the position of FIG. 6, the middle pawl 4 leads. In all relative positions of pawls 4, the deeper recess portion 45a of a pawl 4 which trails the other two pawls 4 two distances 2, is located opposite the coupling portion 35 of the respective coupling lever 35, so that this trailing pawl 4 is engaged at the coupling shoulder 45 and forwardly shifted to become the blocking pawl 4, while the previously blocking pawl 4 is engaged at the coupling shoulder 44' by the respective coupling lever 35 and shifted rearwards together with the paper carriage. The respective third pawl 4, which trails the blocking pawl 4 only one distance e, follows the originally blocking pawl 4 which moves the carriage rearward due to its engagement with the teeth 3 of the rack 1, without any influence on the back spacing operation.

FIGS. 4, 5 and 6 illustrate the coupling positions of coupling levers 35 depending on the relative positions of the escapement pawls 4.

In the position of pawls 4 shown in FIGS. 2a and 4, the foremost pawl 4 is the blocking pawl and is shifted rearward by coupling portion 35' engaging coupling shoulder 44 while the carriage is stopped by the rearmost pawl 4 which is shifted in writing direction by coupling portion 35 engaging coupling shoulder 45 of the rearmost pawl 4.

In the pawl position shown in FIGS. 3a and 5, the rearmost blocking pawl 4 is shifted backward by the rearmost coupling portion 35 which engages coupling shoulder 44 of the respective pawl 4, while the carriage is stopped by the middle pawl 4 forwardly shifted by the intermediate coupling portion 35' engaging coupling shoulder 45'.

In the position of FIG. 6, the middle pawl 4 is the blocking pawl and is shifted rearwardly by the respective coupling portion 35 which engages coupling shoulder 44' while the carriage is stopped by the foremost pawl 4 shifted in writing direction by coupling portion 35 engaging coupling shoulder 45.

In the illustrated embodiment, three pawls 4 are provided, and the smallest step e is one-third of the spacing between adjacent rack teeth 3. As explained above, a coupling lever 35 must move the blocking pawl 4 in rearward direction, and the pawl 4 whose stop portion 6' trails the stop portion 6 of the leading blocking pawl 4 two distances e, must be forwardly moved in order to stop the movement of the carriage. The remaining pawl 4 follows the motions without having any influence on the displacement of the carriage.

From the above description it will become apparent that a set of coupling means 35, is provided and that each coupling means 35, 35' can be individually moved between a position of rest shown in FIG. 1a, a first coupling position coupled with the leading pawl 4 which initially blocks carriage movement along the coupling shoulder 44', and a second coupling position coupled with the pawl 4 which trails the leading pawl 4 two distances e by engaging its coupling shoulder 45. In the first coupling position, the rearwardly moving drive part 36 of drive means 36 effects through the coupling means 35, 35' in the first coupling position a back spacing movement of the leading pawl 4 and of the carriage, while drive part 36 moves the trailing pawl 4, which is coupled with the coupling means 35, 35 in the second coupling position, in writing direction.

What is claimed as new and desired to be secured by Letters Patent is:

1. Back spacing mechanism for a carriage which is movable forward and rearward in one direction and has a rack with teeth and recesses, comprising, in combination, a set of escapement pawls cooperating with said rack and having stop portions staggered relative to each other a predetermined distance in said one direction and being individually movable forward and rearward in said one direction and into and out of said recesses; resilient means urging said pawls into said recesses; blocking means engaging said stop portion of the pawl leading in said one direction for blocking forward movement of said carriage while said stop portions of the other pawls are rearwardly spaced from the leading stop portion and from said blocking means; a set of coupling means respectively correlated with said pawls, each coupling means being mounted for movement in said one direction, and for individual movement between a position of rest, a first coupling position coupled with the leading pawl which engages said blocking means, and a second coupling position coupled with another pawl whose stop ortion trails said leading stop portion; actuating means for moving said set of coupling means to said first and second coupling positions, and for moving the coupling means in said first coupling position together with the leading pawl rearward so that said leading pawl moves said rack and said carriage rearward, and for moving the coupling means in said second coupling position forward so that the respective other pawl moves out of an engaged recess and forward relative to the rearwardly moving rack, and then engages the next leading recess of said rack while the stop portion thereof engages said blocking means for blocking forward movement of said carriage; and back spacing means for operating said actuating means.

2. Back spacing mechanism according to claim 1 wherein said predetermined distance is the distance between adjacent recesses of said rack divided by the number of pawls in said set of escapement pawls; wherein said number of pawls is at least three; and wherein the coupling means in said second coupling position engages the pawl whose stop portion trails said leading top portion a distance equal to twice said predetermined distance.

3. Back spacing mechanism according to claim 1 wherein said actuating means include biassing means for urging each of said coupling means into said first and second coupling positions and a drive means having rearwardly and forwardly acting drive parts for respectively moving the coupling means in said first coupling position backward, and the coupling means in said second coupling position forward, said drive means having a normal position for holding said set of coupling means in said position of rest and being movable to an actuating position for releasing said set of coupling means for movement to said first and second coupling positions, and for moving said set of coupling means in said first and second coupling positions in said one direction rearward and forward, respectively, with the respective pawls; and wherein said back spacing means moves said drive means to said actuating position.

4. Back spacing mechanism according to claim 1 wherein said predetermined distance is the distance between adjacent recesses of said rack divided by the number of pawls in said set of escapement pawls; wherein said number of pawls is at least three; wherein the coupling means in said second coupling position engages the pawl whose stop portion trails said leading stop portion two of said predetermined distances; wherein said actuating means include biassing means for urging said set of coupling"means into said first and second coupling positions, and a drive means having rearwardly and forwardly acting drive parts for respectively moving a coupling means in'said first coupling position rearward, and a cou pling means in said second coupling position forward, said drive means having a normal position for holding said setjaof coupling means in said position of rest and being movable to an actuating position for releasing said set of coupling means for movement to said first and second coupling positions, and for moving said set of coupling means in said first and second coupling positions in said one direction rearward and forward, respectively, with therespective pawls; and wherein said back spacing means moves said drive means to said actuating position. 1

5. Back spacing mechanism according to claim 4 wherein each of said pawls has a coupling recess, each coupling recess having a first coupling shoulder and a second coupling shoulder and a shallower recess portion bounded by said first coupling shoulder and a deeper recess portion bounded by said second coupling shoulder, wherein jsaid first and second coupling shoulders of each of said pawls are staggered relative to the corresponding coupling shoulders of the other pawls said predetermined distance; wherein said set of coupling means have coupling portions registering in said position of rest, one of said coupling portions being located opposite said deeper recess portion, and the other coupling portions being located opposite said shallower recess portions of the corresponding pawls, and one of said other coupling portions having a face aligned with said first coupling shoulder of the respective pawl so that upon movement of said drive means to said actuating position, said one coupling portion enters said deeper recess portion and engages said second coupling edge of the respective pawl in said second coupling position while said one of said other coupling portions engages said first coupling shoulder.

6. Back spacing mechanism according to claim 5 wherein each of said set of coupling means has first and second abutments respectively cooperating with said rearward and forwardly acting drive parts, said first abutments being located in the path of movement of said rearward acting drive part in said position of rest and in said first coupling position of said set of coupling means, and said second abutments being located outside of the path of movement of said rearward acting drive part in said position of rest and in said first coupling position, and in the path of movement of said forwardly acting drive part in said second coupling position so that upon movement of said drive means to said actuating position, the coupling means in said second coupling position shifts the trailingpawl to a leading position, while the coupling means in said first coupling position shifts the leading pawl twice said predetermined distance rearward in said one direction.

7. Back spacing mechanism according to claim 6 wherein said set of coupling means are coupling levers; wherein said biassing means of said actuating means include a set of springs respectively connecting said coupling levers with said drive means; and a support supporting said coupling levers for turning movement between said position of rest and said first and second coupling positions, and for movement in said one direction together with the pawls coupled thereto.

8. Back spacing mechanism according to claim 7 wherein said support is a rocking member mounted for angular movement; and wherein said resilient means include a set of springs respectively connecting said pawls with said rocking member and urging said pawls to move rearward in said one direction and into said recesses of said rack.

9. A back spacing mechanism according to claim 8 wherein said blocking means is a stationary shaft; and wherein said pawls have slots extending in said one direction and being closed at one end by said stop portions, respectively, said stop portions being semi-circular and having substantially the same diameter as said stationary shaft; and wherein said stationary shaft is located in said slots for supporting said pawls for forward and rearward movement in said one direction, and for angular movement into and out of said recesses of said rack; and wherein said semi-circular stop portion of the leading pawl slidingly abuts said stationary shaft, and the other stop portions are spaced in multiples of said predetermined distance rearward in said one direction from said stationary shaft.

10. Back spacing mechanism according to claim 8 and including a shaft supporting said drive means for turning movement between said position of rest and said actuating position; and wherein said drive means has an arm with a projecting stud; and wherein said back spacing means has a member embracing said stud for turning said drive means; and comprising a stationary stop engaged by said stud in said position of rest of said drive means.

11. A back spacing mechanism according to claim 1 wherein said blocking means is a stationary shaft; wherein said pawls have slots extending in said one direction and being closed at one end by said stop portions; wherein said stop portions are semi-circular and have substantially the same diameter as said stationary shaft; wherein said stationary shaft is located in said slots and supports said pawls for forward and rearward movement in said one direction, and for angular movement into and out of said recesses of said rack; wherein said resilient means urge said pawls to move rearward in said one direction and to turn into said recesses; and wherein said carriage and rack are biased to urge said pawls against the action of said resilient means toward said stationary shaft so that said semi-circular stop portion of said leading pawl abuts said stationary shaft.

12. Back spacing mechanism according to claim 1 wherein said pawls have recesses bounded by first and second coupling shoulders, said coupling shoulders of said pawls being staggered multiples of said predetermined distance; wherein said sets of coupling means engage said first coupling shoulder of the respective pawl in said first coupling position, and said second coupling shoulder in said second coupling position; and wherein said actuating means include a set of biassing springs respectively urging said set of coupling means into said first and second coupling positions, and drive means operated by said back spacing means to move the coupling means in said first coupling position rearward in said one direction with the respective pawl, and the coupling means in said second coupling position forward in said one direction with the respective pawl.

13. Back spacing mechanism according to claim 12, wherein said biassing springs connect said drive means with said set of coupling means, respectively; wherein said drive means is mounted for turning movement and is urged by said biassing springs to turn in one direction of rotation; and including stop means for stopping turning movement of said drive means in a normal position in which said set of coupling means are in said position of rest.

14. Back spacing mechanism according to claim 1.

wherein said predetermined distance is the distance between adjacent recesses of the rack divided by the number of pawls in said set of escapement pawls; wherein said number of pawls is at least three; wherein said blocking means is a stationary shaft supporting said pawls for forward and rearward movement in said one direction, and

for angular movement into and out of said recesses; wherein said staggered stop portions cooperate with said stationary shaft for blocking carriage movement; wherein the coupling means in said first coupling position engages said leading pawl whose stop portion abuts said stationary shaft, and the coupling means in said second coupling position engages the pawl whose stop portion is located rearward of said stationary shaft and of said stop portion of the leading pawl a distance equal to twice said predetermined distance.

15. Back spacing mechanism according to claim 1 and including a rocking member having a shaft supporting said set of coupling means for forward and rearward movement and for independent turning movement between said position of rest and said first and second coupling positions; and wherein said resilient means include a set of springs respectively connecting said pawls with said rocking member so that said pawls are biassed to move rearward in said one direction and said set of coupling means are biassed to move forward in said one direction.

References Cited UNITED STATES PATENTS 2,547,449 4/1951 Dodge 19784 2,701,045 2/1955 Madsen 19791 2,753,973 7/1956 Dodge et al. 197-84 2,905,303 9/1959 Palmer et al. 19784 2,972,401 2/1961 Salto 19784 3,288,262 11/1966 Salto 197-9l X ERNEST T. WRIGHT, JR., Primary Examiner US. Cl. X.R. 197-84