US3799316A

US3799316A - Automatic erase mechanism

Info

Publication number: US3799316A
Application number: US00102696A
Authority: US
Inventors: R Davidge; J Schaefer; C Davis; S Okcuoglu
Original assignee: International Business Machines Corp
Current assignee: IBM Information Products Corp
Priority date: 1970-12-30
Filing date: 1970-12-30
Publication date: 1974-03-26
Anticipated expiration: 1991-03-26
Also published as: DE2164763A1; CA935776A; NL7117319A; AU456531B2; JPS534441B1; AU3654171A; BR7108646D0; GB1316532A; AR202172A1; JPS5316419B1; FR2120737A5; DE2164763C2; BE776086A

Abstract

A mechanism is disclosed for the automatic erasing of typing errors utilizing a fully serialized and automated correction apparatus where the correction is accomplished by a single backspace operation allowing both the erasure of the erroneously typed letter and the typing of the proper letter. The backspace operation repositions the typewriter carriage for the correction of the erroneous letter and at the same time inhibits the escapement of the carriage for a single print cycle allowing the corrected letter to be printed over the correction without requiring an additional backspace operation. The escapement mechanism is re-engaged during the correction cycle so that the carriage advances of the print cycle.

Description

[ Mar. 26, 1974 Wolowitz........................ 197/157 FOREIGN PATENTS OR APPLICATIONS 921,857 Canada 1,097,843 Great 197/91 OTHER PUBLICATIONS Typewriter, Form No.

, Selectric Typewriter, Form 7X5, November,

ABSTRACT A mechanism is disclosed for the automatic erasing of typing errors utilizing a fully serialized and automated peration allowing both y typed letter and the Selectric 7, October, 1968, pp. 9, 33. IBM Service Manual No. 241

IBM Parts Catalog, 241-5102- 56l5-0, Models 7X1-7X3 Primary Examiner-Ernest T. Wright, Jr. Attorney, Agent, or Firm-Laurence R. Letson correction apparatus where the correction is accomplished by a single backspace o the erasure of the erroneousl O United States Patent [191 Davidge et al.

[ AUTOMATIC ERASE MECHANISM [75] Inventors: Ronald V. Davidge; Clayton J.

Davis; Selahattin A. Okcuoglu; John O. Schaefer, all of Lexington, Ky. [73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: Dec. 30, 1970 21 Appl. No.: 102,696

[52] U.S. Cl... 197/181, 197/82, 197/83, 197/86, 197/91, 197/156, 197/159 [51] Int. B4lj 29/16 [58] Field of Search............. 197/65, 66, 67, 68, 82, 197/83, 84, 84 A, 84 B, 91, 92, 94, 96, 157, 158,159,172,181,156, 98

[56] References Cited UNITED STATES PATENTS S e 6 ed mmk hcem u n. mv. ac cfww pc r e e g 8 r.m t v n a P .m 0 C ei O a vr.

c m d r m e .l e. C cm wt a W wa mmm umm m a n a e a l eeb h F g o unt e atf O n C 2 n .m m mgr m W a ae .C .l. nth m f ro n mflmmn u an e m 7 l r a e e 0.6 n C r. th m 0 W m 6 ea 1 C 1 .1 pD- na o on c IS 0 CTC r uto r. mwm .m nmewfi tm t S 0 a U e f fip m fim m mmcm w m mewm fmc p e mr n ef llo a IfOtflCOdV 132111111 mm wmmwmmww 11 777777 WWWNW999999. 11 7 l l l I I I19 79 1 9 m mmmmmmmmm H H u n n n m m m mmmmu u r r .w r e d w e e w o om wkm mmn e mm 0 BHOAWPPWWWFH 339424455600 NHL-1466666666 999999999999 UWM JWWNWWWWW 1.33 8 5627 %7co3oo59 4456 3 92496944O7 626552400 9 ATENTED MR 2 51974 SHEET 1 BF 2 INVENTORS SELAHATTIN A. OKCUOGLU RONALD V DAVIDG CLAYTON J. DAVIS,

JOHN O. SCHAEFER BY LAURENCE R. LETSON AGE/VT AUTOMATIC ERASE MECHANISM BACKGROUND OF THE INVENTION When a typist makes an error and the error is to be corrected on the document being typed it is necessary for the typist to erase the error with an eraser or to cover the error with a correction liquid which then dries and obliterates the error or by overstriking the error with a correction media which covers the error with a white material thereby rendering the erroneously typed letter semi-invisible.

Efforts in theprior art have been made to try to mechanize the error correction operations on a typewriter.'The prior art discloses apparatuses in which the escapement of the carriage of the typewriter is manually disabled so that the correction may be made on the next print cycle after the obliteration of the erroneous letter. After the correction and overprinting the disability is removed manually to allow letter feed in the normal manner. This, of course, is a mechanism which requires the operator to remember to disengage the manual inhibit mechanism after the correction has been made in order to prevent further typing of additional letters over the corrected letter. Further it requires the operator to make several additional manual strokes over and above that required for a fully automated mechanism.

The prior art likewise discloses a semiautomatic correction apparatus where the correction media, whether it be an obliterating tape or an adhesive erasing tape, is conditioned for correction by the operation of a correction backspace key. This correction apparatus remains in the correction mode until such time as a second backspace is accomplished. Thus the semiautomatic error correction devices require one backspace operation to place the carriage in the proper position for making the correction and then a correction cycle followed by a second backspace operation to again position the carriage in the proper position and disengage the correction apparatus which had conditioned the a minimum of two backspace operations is required in such an apparatus andis not as efficient or automated asa fully automated single cycle backspace correction apparatus. i

Other prior. art discloses the manual selection of the mode of the typewriter, i.e., correction or print, and thus the shifting into the appropriate mode when the backspace or correction key is operated. This has much the same disadvantage as the other nonautomated correction mechanisms.

All of the above prior art approaches to the correction of erroneously typed characters have been shown to be unsatisfactory from a human engineering standpoint. The operator must be able to correct the error and replace it with a correct letter with a minimum number of typing strokes and with a minimum amount of alert thought as to the sequence of steps required. An advantage will flow from the apparatus disclosed in that a typist will increase her speed and accuracy by not breaking her typing operation to secure some correction media or operate additional controls to control the sequence of the correction strokes.

correction media for positioning next to the page. Thus OBJECTS OF THE INVENTION It is the primary object of this invention to automate and sequence the error erasure and correction steps necessary to correct erroneously typed letters.

It is another object of this invention to eliminate steps in the error correction sequence in an efficient manner on a typewriter by automating and sequencing the typewriter mechanisms.

It is a further object of this invention to fully sequentialize and automate the conditioning of the correction media and the carriage spacing control to eliminate unnecessary typing strokes and operations in an efficient manner.

It is an additional object of this invention to simplify the mechanism necessary to fully automate and sequentialize the error correction operations of a typewriter.

SUMMARY OF THE INVENTION The foregoing objects are accomplished by simultaneously conditioning the correction media for movement between the letter printing elements and the paper being typed upon while backspacing one letter space increment and inhibiting the escapement mecha nism of the typewriter such that the inhibition is only effective for one print cycle and automatically reengages it for proper escapement on subsequent cycles. This is accomplished by unlatching cam followers which will respond to a cam rotation during the correction cycle activating the correction media while at the same time disengaging the escapement mechanism in such a manner that it remains inoperative only during the one cycle and the normal operation of the escapement mechanism will re-engage the disabled member during the correction cycle so that when the corrected letter is printed on the next printing cycle the escapement functions properly causing letter feed in the normal manner.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of the correction control mechanism illustrating an additional key on the keyboard for backspacing in order to implement error correction.

FIG. 2 is an alternate control mechanism for accomplishing the error correction backspacing and inhibiting letter feed in a fully automated power operated error correction mechanism.

FIG. 3 is a perspective view of the control mechanism of the invention where the existing backspace train of a prior art typewriter is utilized.

FIG. 4 is a right hand side view of the mode control and conditioning mechanism for positioning the error correction media between the print element and the platen.

FIG. 5 is a left hand side view of the tape lift mechanism for lifting the tape during the error correction cycle, a part of the mode control means.

FIG. 6 is a perspective viewof the escapement inhibit mechanism latched in its inhibit mode.

FIG. 7 shows a typewriter on which the error correction mechanism is embodied.

DESCRIPTION OF THE INVENTION A typewriter 1, having a keyboard 2, a character defining element 3, character keys 4, and writing sheet 5, and having normal prior art functions as illustrated in 7. The typewriter 1 also has the improvement more fully disclosed in FIGS. 1 through 6.

Referring to FIG. 1, in accordance with normal practice, the typewriter keyboard 2 is provided with a standard backspace key as one of two backspace keys, the first being the normal backspace key 10 and the second being the erase backspace key 22. Backspace key 10 controls the normal backspace cycle and is, in and of itself, not part of this invention. Erase backspace key 22 is operatively interconnected with backspace key 10 through erase backspace lever 26. Erase backspace lever 26 is connected to erase backspace key 22 by rod 26" and has an appendage 26' positioned to engage pin 30 on the backspace pawl 14 to cause movement of pawl 14. Backspace pawl 14 is part of the normal backspace train of elements. Erase backspace key 22, through erase backspace lever 26 and appendage 26' interacts with and engages pin 30 thereby making the erase backspace key 22 operative through the normal backspace train.

To transmit motions of erase backspace key 22 to link 38 erase backspace key 22'is operatively connected to bell crank 34 by lip 22" such that the up down movement of erase backspace key 22 is converted to a front-back movement of link 38.

Backspace pawl 14 engages backspace interposer 18 to transmit any motion of the backspace pawl 14 through the backspace train thereby activating the backspace function.

To provide movement of torque bar 42 for error correction media conditioning, link 38 is connected to torque bar 42 to rotate it around its pivot point 43. Torque bar 42 is pivotally supported by a frame member not shown, and functions as a control means. Torque bar 42 has two functional positions, its nominal position and a second position where it is in a rotated position controlling the mode of the correction media mechanism. Extending rearward from torque bar 42 is link 46. Link 46 may, if desired, be an extension of link 38. Link 46 interconnects torque bar 42 to escapement trigger 50. Escapement trigger 50 is biased by escapement trigger spring 74 extending between the lower extremity of escapement trigger50 and the rearward portion of escapement trigger lever 54 for restoring the trigger 50 and providing forces to reset torque bar 42 at the end of a correction cycle. Escapement trigger 50 normally engages the escapement torque bar lip 56 under the influence of escapement trigger spring 74, as seen in FIGS. 1 and 2. Escapement torque bar lip 56 is an integral part of the escapement torque bar 58 which when rotated controls escapement pawl 62. The rotation of escapement torque bar 58 pulls the escapement pawl 62 out of engagement with the escapement rack not shown allowing a letter feed motion. The escapement torque bar 58, pawl 62 and rack (not shown) comprise a letter feed means which is responsive to key board operation as is well known in the art.

Escapement trigger spring 74 serves to pull trigger 50 back into engaging relation with lip 56 when trigger lever 54 is rotated by shaft 55 and restored as is well known in the prior art. As trigger 50 is reengaged with lip 56 by trigger spring 74 spring 74 also acts to restore torque bar 42 to its nominal or primary position and also restore other linkages connected to torque bar 42 to their nominal positions.

An escapement trigger latch 66 is provided for holding escapement trigger 50 out of engagement with escapement torque bar lip 56 when the error correction mechanism is activated. Escapement trigger latch spring 70 biases escapement trigger latch 66 into contact with escapement trigger 50. The trigger latch 66 and trigger 50 together with associated links 46 and- /or 38 are referred to as the letter space or letter feed inhibit means.

The foregoing description describes the elements of one of the variations of the invention disclosed herein.

Now referring to FIG. 2, a fully serialized erase mechanism will be described as an alternate variation. This variation is a fully powered version where the activating force required on the key 22' is reduced because the power required is supplied by spring 20. Erase key 22' is added to a standard key board and is pivotally mounted on pivot point 19. Erase key 22' engages by lip 22" an erase trigger 23 for rotational movement in response to the up-down movement of the erase key 22'. Erase trigger 23 has a small finger 23' on the end opposite that engaged by erase key 22. To prevent the rotation of sear 24, this finger 23' engages the erase sear 24 and depends upon the surface of sear 24. Erase sear 24 is rigidly connected to bell crank 27 or may be a part of bell crank 27. Erase sear 24 has a window or notch 25 formed into sear 24, which will seat over the finger 23' of erase trigger 23 when they are coaligned. Bell crank 27 has two crank

arms

27, 27", one arm 27 connected to link 28 which in turn is connected to a crank arm 29' of bell crank 29. The arm 29 of bell crank 29 engages pin 30 on backspace pawl 14 for controlling the movement of pawl 14' to cause engagement of link 18 by lip 15'. The second arm 29" of bell crank 29 is interconnected to torque bar 42 by link 38 as discussed with reference to FIG. 1.

Again referring to FIG. 2, bell crank 27 and its second crank arm 27" is interconnected with reset crank 32 by a link 31. Reset crank 32 acts to reset backspace interposer 18 and bell crank 27 at the end of a backspace cycle, by rotating clockwise. The remainder of the structure disclosed in FIG. 2 has been described with respect to FIG. 1 and the mechanisms are identical.

In referring to FIG. 3 a third variation of the automated erase mechanism will be described. The third variation is one which utilizes the existing backspace train within the typewriter l and controls the escapement inhibit and error correction media conditioning from the output of the backspace train. To eliminate redundancy, backspace and erase keys are combined in key 10' which is connected to backspace pawl 14" by connection 13. Backspace pawl 14" interacts upon movement of the backspace key 10 through lip 15", with backspace interposer 18. The cam surfaces l5, l5, l5", 16 of backspace pawl l4, l4 and 14" and backspace interposer 18 respectively are complementary for moving backspace interposer 18. The rearward terminus 17 of backspace interposer 18 engages latch 98 which is pivotally connected at 91 to backspace bell crank 90. Backspace bell crank has a lug 86 extending rearwardly therefrom. Bell crank 82 is pivotally supported on the frame member around the indicated axis 83 and one arm 81 of the bell crank 82 is engageable with lug 86 to receive the input and the other arm 84 of hell crank 82 is interconnected to escapement trigger 50 through link 78.

The description of torque bar 42, link 46, escapement trigger 50, escapement trigger latch 66 and latch spring 70 is the same as the corresponding parts previously described with respect to FIG. 1. Cam follower 94 follows the backspace cam (not shown) which is operated in response to the backspace cycle clutch, not shown, and rotates about its axis 95. The arm 96 of cam follower 94 may engage the lower lip 98' of latch 98 when latch 98 is moved rearwardly by backspace interposer 18.

Cam follower 94, latch 98, and bell crank 90 combined, illustrate a backspace operating means responsive to depression of a backspace key Referring to FIG. 4, a description of the correction media feed trigger mechanism will follow. To activate the correction media mechanism at the appropriate time the driving force is supplied by cam 110. Cam 110 is positively driven in response to the activation of the cycle clutch of the typewriter for each print cycle. Pivotally supported at 101 either on the print element carrier of a single element typewriter or on the frame of the type bar basket ina type bar typewriter is catch lever 102. Catch lever 102 is biased toward a rigid frame element 100 by catch lever spring 104 to latch up cam follower 106. Catch lever 102 has a lower arm 102' which is selectively engageable by the torque bar 42 in response to the movement of link 46. Cam follower 106 is pivotally mounted such that the follower lobe 106' may make contact with cam 110. An extension lug 108 of cam follower 106 is formed to interact with the upper end 103 of catch lever 102. During normal printing operation catch lever 102 prevents cam follower lobe 106 from following the cam profile of cam 110 and thus disables the correction media feed driven by the upper arm 106" of follower 106.

Referring to FIG. 5, cam 110 likewise controls cam follower 142. Cam follower 142 is rigidly attached to liftfollower 138 which is pivotally mounted at 139 to oscillate in response to the change in the cam profile of cam 110. A push lever 114 is pivotally mounted at 115 and has two arms 114', 114". The lower of the two arms 114' is engageable by torque bar 42 in response to movement of link 46 to condition correction media lifter 150. The upper arm 114" of push lever 114 engages the right h andportion of lift arm 130 to control its engagement with lift follower 138. Lift arm 130 is spring biased toward the left in FIG. 5 by leaf spring 122 to prevent such engagement. The rotation of push lever 114 will move lift arm 130 toward the right sliding the lift arm 130 in the slot 117 over pin 118. Lift arm 130 is provided with a lug 134 which is selectively engageable with liftfollower 138. Further lift arm 130 is provided with lift arm extension 146 extending into engagement with correction media lifter 150. Correction media lifter 150 is capable of lifting and supporting a correction tape 152 and is referred to as a means for placing or conditioning the correction tape 152. A more full explanation of how the sequence of steps and a more detailed explanation of the operation of the mechanism will follow. Torque bar 42 and catch lever 102 comprise a feed mode control for controlling the correction medium in either print or correct modes, to initiate ribbon feed in conjunction with an error correction cycle.

Referring again to FIG. 1 the necessary steps to correct a mistake in typing with the above-described apparatus are: (l) depress the erase backspace key 22; (2) depress the erroneous letter key 4 thereby obliterating the erroneous letter from the typed page 5; (3) depress the key 4 for the correct letter; (4) continue typing. It will become clearer how the above sequence of steps is permitted as the explanation of the operation of the mechanism below.

1. Depress the erase key 22.

Upon the depression of the erase backspace key 22 the erase backspace lever 26 moves in unison therewith and the lug or appendage 26' of erase backspace lever 26 engages pin which is rigidly attached to backspace pawl 14. This movement of erase backspace key 22 then forces backspace pawl 14 downward engaging the cam surface 15 on its lower end with the cam surface 16 on the backspace interposer 18. This operation initiates the backspace cycle of the typewriter in its normal fashion as in the prior art.

The depression of erase backspace key 22 also causes bell crank 34 to pivot around its pivot point 35 and pull link 38 forward. Link 38 in turn pulls link 46 forward and simultaneously rotates torque bar 42 a fraction of a revolution in a clockwise direction as viewed in FIG. 1 to its secondary position. Torque bar 42 conditions the correction media mechanism as will be discussed more fully later.

Link 46 causes escapement trigger 50 to rotate about its pivot point 51 in a clockwise direction and against the force of escapement trigger spring 74. As escapement trigger 50 rotates in a clockwise direction around its pivot point 51 escapement trigger latch 66 is caused to drop into the notch 49 in the upper portion of escapement trigger 50, under the influence of latch spring 70. This latched condition is clearly illustrated in FIG. 6. With the escapement trigger 50 rotated clockwise and retained by latch 66 it no longer engages escapement torque bar lip 56 of torque bar 58 and is in its inhibit mode. The above sequence of actions has now conditioned the machine to correct the erroneously typed letter. The carriage has been returned to a position over the erroneous letter and the correction media 152 conditioned to be moved between the type elements 3 or character defining application andthe paper 5 by the rotation of torque bar 42. et

Referring to FIG. 4 when torque bar 42 is rotated partially clockwise by the movement of link 46 it engages the lower arm 102 of catch lever 102. This engagement causes catch lever 102 to rotate in a counterclockwise direction against the bias of spring 104 and allows cam follower lug 108 to disengage from the upper end 103 of catch lever 102. This allows cam follower lobe 106' to follow the profile of cam 110 during the next print cycle of the typewriter when cam 110 will be positively driven. The upper arm 106" of cam follower 106 is connected to an incrementing mechanism to increment the correction tape 152 and present a new portion to the appropriate point on the carriage for a subsequent correction cycle. A more complete description of the operation of the correction media feed and conditioning mechanism may be found in cofiled aplication titled, Feed System for an Adhesive Ribbon and the Like, F. S. Korb, et. al., filed Dec. 30,

I970, Ser. No. 102,695, now US. Pat. No. 3,724,633 issued Apr. 3, 1973 and assigned to the same assignee as this invention. Referring to FIG. 5, the rotation of the torque bar 42, now characterized as a counterclockwise rotation, as viewed from the left side of the typewriter 1 causes the oscillation of push lever 114 in a clockwise direction. The upper arm 114" of push lever 114 engages the right hand portion of lift arm 130 causing it to slide to the right over pivot pin 118, and pin 126 fixed to arm 130, in slot 127. The movement of lift arm 130 is opposed by leaf spring 122. This lateral shift of lift arm 130 brings lug 134 into an operative relationship with lift follower 138 by screw 133 being contacted by the end of slot 135, in which screw 133 may slide. Lift follower 138 being rigidly attached to cam follower 142 will respond to the cam profile of cam 110 on the next succeeding print cycle of the typewriter causing the lift arm 130 to be elevated. Because of the elevation of lift arm 130, lift arm extension 146 moves upward. Lift arm extension 146 is engaged with correction media lifter 150 and moves correction media lifter 150 upward thereby causing the correction tape 152 to be elevated and placed within the printing zone between the type elements and the platen.

2. Depress the erroneous letter key 4.

As the key 4 of the erroneously typed letter is depressed, the type element 3 strikes the correction tape 152 with the same letter as that previously erroneously typed and thereby causes obliteration of the erroneous letter. As cam 110 continues to rotate through the remainder of the print cycle it allows cam follower 142 to return to its lower position and disengage from lug 134. With no resistance encountered by lug 134 spring 122 forces lift arm 130 leftward in FIG. 5 thereby removing lug 134 from the active zone of movement of lift follower 138. Thus lift follower 138 and cam follower 142 may follow the cam profile through succeeding printing operations without lifting the correction tape 152. Again referring to FIG. 4, the cam follower 106 has been released by the disengagement of the upper end 103 of catch lever 102 in response to the partial revolution of torque bar 42. This allows cam follower lobe 106' to engage the surface of cam 110 and during the correction print cycle of the typewriter cam 110 on' shaft 111, will make one complete revolution causing cam follower 106 to rotate about its pivot point 107 in a clockwise direction. As lug 108 moves upward in response to the larger cam profile, catch lever 102 acting under the influence of spring 104 will again rotate in a clockwise direction securing cam follower 106 and again preventing it from following the cam surface. Cam 110 is mounted on a rotatable shaft 111. Torque bar 42 is restored to its primary or nominal position by the reengaging of escapement trigger 50 with lip 56 at the completion of the obliterating portion of the sequence.

Referring to FIG. 1, during a normal print cycle escapement trigger lever 54 is rotated.about its pivot 55 in a clockwise direction. This normally pulls escapement trigger 50 downward and in so doing causes escapement torque bar 58 to rotate partially in a clockwise direction in response to the engagement of escapement trigger 50 and escapement torque bar lip 56. However, in response to the depression of erase backspace key 22 escapement trigger 50 has been retracted from escapement torque bar lip 56 and is retained by latch 66. During the next print cycle which would be the correction cycle where the erroneous letter is typed again to erase the erroneous letter escapement trigger lever 54 is rotated about its pivot point 55 pulling escapement trigger 50 downward. As it is not in engagement with escapement torque bar lip 56 no movement of the escapement torque bar 58 is caused and the escapement is not activated during this one print cycle. As escapement trigger lever 54 is returned, through the normal linkages of the typewriter, to its home position escapement trigger 50 is likewise moved upward and allowed to re-engage escapement torque bar lip 56. As escapement trigger 50 has been disengaged from latch 66 during the previous movement of escapement trigger lever 54, the latch 66 is forced upward and is ineffective in retaining escapement trigger 50 in its inhibited position.

The operational sequence is ready for depression of the correct key lever.

3. Depress the key for the correct letter.

At this point of the operation the error backspace key 22 has been depressed and the carriage returned to the print position over the erroneous letter. The erroneous letter key 4 is depressed to obliterate the printed letter on the page which is accomplished through the conditioning of the correction media feed and conditioning mechanism illustrated and explained with respect to FIGS. 4 and 5. As this print cycle ends, the escapement trigger 50 which has been disengaged from escapement torque bar lip 56 is allowedto reengage escapement torque bar lip 56 and when the correct letter is printed in the next succeeding print cycle the rotation of escapement trigger lever 54 clockwise about its pivot 55 will cause the escapement trigger 50 to move downward interfering with escapement torque bar lip 56. The small rapid rotation of escapement torque bar 58 retracts escapement pawl 62 from the escapement rack and relases it in response to escapement torque bar 58 being released and allows the escapement pawl 62 to restore into the next succeeding tooth in the escapement rack (not shown).

Referring to FIG. 2, a fully serialized and automated operation of the mechanism is as follows. The erase key 22' is depressed and causes erase trigger 23 to rotate a slight amount in a counterclockwise direction. The finger 23' on the end of erase trigger 23 is moved upward and encounters the window or notch 25 in erase sear 24. Erase sear 24 then is permitted to move in a slightly counterclockwise direction with the finger 23 of erase trigger 23 extending through window 25. This permits bell crank 27 to rotate in a counterclockwise direction in response to the force exerted by spring 20. The counterclockwise rotation of bell crank 27 causes link 28 and link 31 to rotate bell crank 29 and reset crank 32, respectively. Bell crank 29 rotates in a counterclockwise direction in response to the movement of link 28. One arm 29' of bell crank 29 is engaged with pin 30 of backspace pawl 14. The movement of bell crank 29 forces pin 30 and pawl 14 downward engaging the cam surface 15 on the lower end of backspace pawl 14' with cam surface 16 on the left end of backspace interposer 18. This activates the backspace cycle as previously described and as in the prior art machines. The rotation of bell crank 29 causes link 38 to move toward the left in FIG. 2 thereby rotating torque bar 42 and pulling link 46 as described earlier with respect to FIG. 1.

As can be seen from this explanation, the effort required to depress erase key 22' is reduced from that illustrated in FIG. 1 because the only resistance to the depression of erase key 22 is the friction between the finger 23' of erase trigger 23 and erase sear 24, and any return springs 21 for returning erase key 22' to its restored position. The entire remainder of the force r'equired to activate bell crank 27, links 28, 31, bell crank 29 and the remainder of the mechanism is supplied by the spring 20. Upon restoration of backspace interposer 18 in response to the clockwise motion of reset crank 32, by engagement of interposer l8 and lug 32' as is known in prior art typewriters, link 31 is moved toward the upper right and causes bell crank 27 to rotate in a clockwise direction thereby withdrawing sear 24 from around the finger 23 of erase trigger 23 thereby permitting erase trigger 23 to reset for subsequent cycles. The conditioning and operation of the correctionmedia mechanism and the escapement inhibit mechanism is identical to that described previously. 1

If so desired, the existing backspace train in the typewriter may be fully utilized and eliminate the need for a redundant operational chain of parts. This also permits the elimination of a separate erase backspace key as shown in FIGS. 1 and 2 Referring to FIG. 3, the backspace and erase keys have been combined as backspace key The depression of backspace key 10' will force backspace pawl l4" downward triggering the backspace cycle through backspace interposer 18 as described earlier. This is accomplished 'by backspace interposer 18 engaging the latch 98 of backspace bell crank 90. Latch 98 is pivotally attached at 91 to backspace bell crank 90 such that it may be moved forward and backward by a contact between .it and backspace interposer 18. The backspace cam-follower 94 is pivotally mounted at 95 and follows a backspace cam which is triggered by the backspace chain. As backspace cam follower 94 rotates about its axis 95 its arm 96 is moved downward and engages the lip 98' of latch 98 and in so doing pulls the backspace bell crank 90 in a clockwise direction around-its pivot point 89 when viewed from the front of the typewriter. As backspace bell crank 90 rotates in a clockwise direction, dog 86 moves downward engaging the arm 81. of bell crank 82. As bell crank 82 is rotated in response to the downward motion of dog 86 the link 78 attached to bell crank 82 is moved rearward and in so doing retracts escapement trigger 50 away from the escapement torque bar lip 56 of escapement torque bar 58, as illustrated in FIG. 6. This is analogous to the retraction accomplished in FIGS. 1 and 2. As trigger'50 is retracted latch 66 engages it and retains it in its retracted position. Extending from the bottom of escapement trigger 50 is link 46 interconnecting trigger 50 and torque bar 42. In this arrangement link 46 is identical to link 46 in FIGS. 1 and 2 but performs a push function as opposed to a pull function in the previous embodiments.

The immediately above described embodiment has the advantage of utilizing the existing backspace train to the point where the output of backspace bell crank 90 is transmitted to bell crank 82. The bell crank 82, link 78 and latch 66, spring 70, link 46, and torque bar 42 are the only essential additional parts added to the pre-existing typewriter l in order to accomplish the escapement inhibit function and the conditioning of the correction media mechanism. One can immediately appreciate that the utilization of the backspace train up to the point of lug 86 is one of simplicity and economy while the other mechanisms are advantageous in that they provide a separate erase backspace key 22 which conditions the correction media mechanism while the operation of the standard backspace key 10 will not condition the correction tape 152. One will also appreciate that in the embodiment illustrated in FIG. 3 where it is desired to backspace for a function not requiring erasure of the previously printed letter such as the underscoring of a letter, if the underscore key is depressed the typewriter 1 will function as if it is erasing an underscore which had not been printed. This will merely waste one print cycle of the typewriter and when the underscore key is depressed for a second time the print function will occur. If the operator desires to cancel the correction mode prior to touching a key 4 for printing this may be accomplished by activating the space bar as the space bar activates the escapement mechanism. Any operation of the escapement trigger lever 54 through one cycle will reengage the escapement trigger 50 with the escapement torque bar lip 56. Thus by touching the space bar and actuating the escapement chain then the single cycle inhibit is cancelled and the next machine operation will be in response to any key 4 depressed and the mode of operation will be the print mode.

It will be apparent to one skilled in the art that although this invention has'been disclosed in detail with respect to a single element typewriter 1 it would be only a minor modification to embody the invention in a type bar typewriter. This would readily be accomplished by latching out of engagement for one cycle that element in a type bar typewriter which acts against the escapement pawl removing the escapement pawl from the engagement rack. Thus during the one cycle the escapement pawl would not be removed and would prevent any escapement relative to the print basket of the escapement rack and carriage. Further a correction media or correction tape lifter mechanism would be required and actuated from a torque bar essentially the same as disclosed with respect to the single element typewriter 1.

Further one skilled in the art would recognize that latch 66 may be replaced by a flat, stiff spring attached to escapement torque bar 58 and which normally does not interfere with escapement trigger 50 but drops down and blocks trigger 50 when trigger 50 is rotated by link 46.

As can be seen from the foregoing, the above described invention allows the overcoming of the disadvantages of the prior art in that a typist may now correct a letter erroneously typed with a minimum of lost motion and a minimum of conscious concentration upon the sequence of steps necessary. The typist to correct the letter erroneously printed would backspace using the erase backspace key 22 if it is separate from the standard backspace key 10, strike over the erroneous letter and print the corrected letter requiring only three typing strokes to correct the erroneous letter immediately preceding on the page. This overcomes the double backspace or the manual operation required to inhibit spacing or the requirement that a second backspace key must be activated to return the typewriter l to a print mode, all of which were disadvantages in the prior art.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. A typewriter having a keyboard, impacting means including character defining means operatively connected with said keyboard and responsive to individual key depression for impacting individual characters on a writing sheet and causing letter feed motion relative to said writing sheet upon each character printed, said impacting means further comprising an escapement trigger operatively engageable with an escapement torque bar for causing said letter feed motion, the typewriter further having backspace operating means responsive to a backspace key at said keyboard for causing character size backspace incremental motion relative to said writing sheet, wherein the improvement comprises:

a thin character correction media;

selectively operable positioning means for positioning said correction media adjacent said writing sheet for impact there against by said character defining means;

a selectively operable control means;

means responsive to the operation of said selectively operable control means to disengage said escapement trigger from said escapement torque bar;

means for latching said trigger out of engagement with said torque bar to inhibit letter feed;

mode control means having a primary and secondary position comprising a torque bar interconnected with said trigger for controlling said positioning means, said positioning means responsive to said mode control means being in said secondary position;

linkage means interconnecting said selectively operable control means and said mode control means and responsive to said selectively operable control means for controlling said mode control means; and

means responsive to an operation of said typewriter in response to depression of any character key for returning said mode control means to said primary position and releasing said trigger for reengagement with said escapement torque bar;

whereby operation of said selectively operable control means and depression of a selected keyboard key will impact a selected erroneously typed character onto the positioned correction media and the correction media onto the sheet to obliterate an erroneous character after a depression of said backspace key,

thereby providing for a fully automated and serialized correction mechanism for correcting erroneously typed errors on a writing sheet.

Claims

1. A typewriter having a keyboard, impacting means including character defining means operatively connected with said keyboard and responsive to individual key depression for impacting individual characters on a writing sheet and causing letter feed motion relative to said writing sheet upon each character printed, said impacting means further comprising an escapement trigger operatively engageable with an escapement torque bar for causing said letter feed motion, the typewriter further having backspace operating means responsive to a backspace key at said keyboard for causing character size backspace incremental motion relative to said writing sheet, wherein the improvement comprises: a thin character correction media; selectively operable positioning means for positioning said correction media adjacent said writing sheet for impact there against by said character defining means; a selectively operable control means; means responsive to the operation of said selectively operable control means to disengage said escapement trigger from said escapement torque bar; means for latching said trigger out of engagement with said torque bar to inhibit letter feed; mode control means having a primary and secondary position comprising a torque bar interconnected with said trigger for controlling said positioning means, said positioning means responsive to said mode control means being in said secondary position; linkage means interconnecting said selectively operable control means and said mode control means and responsive to said selectively operable control means for controlling said mode control means; and means responsive to an operation of said typewriter in response to depression of any character key for returning said mode control means to said primary position and releasing said trigger for re-engagement with said escapement torque bar; whereby operation of said selectively operable control means and depression of a selected keyboard key will impact a selected erroneously typed character onto the positioned correction media and the correction media onto the sheet to obliterate an erroneous character after a depression of said backspace key, thereby providing for a fully automated and serialized correction mechanism for correcting erroneously typed errors on a writing sheet.