CA1211064A

CA1211064A - Typing and erasing device for printing machines

Info

Publication number: CA1211064A
Application number: CA000448946A
Authority: CA
Inventors: Pietro Musso
Original assignee: Ing C Olivetti and C SpA
Current assignee: Telecom Italia SpA
Priority date: 1983-03-07
Filing date: 1984-03-06
Publication date: 1986-09-09
Also published as: JPS59188479A; EP0118317A3; JPH0517036B2; BR8400987A; AU2534484A; MX158179A; ES8502915A1; DE3480184D1; ES530322A0; IT1158827B; US4601596A; IT8367255A0; EP0118317B1; AU577278B2; EP0118317A2

Abstract

ABSTRACT (Fig 3) TYPING AND ERASING DEVICE FOR PRINTING MACHINES

The typing and erasing device is applied to a printer of the daisywheel type and comprises a carrier (84, 86) for a typing ribbon (32) having a plurality of transverse tracks which can be selected for the printing operation and a carrier for an erasing ribbon which is disposed parallel to but at a different height from the typing ribbon. The typing ribbon is contained in a cartridge on which two typing ribbon carrier arms (41) are pivoted.
The carriers oscillate vertically in order to render visible the typed characters and for the operations of typing or erasing the characters at the typing point (12). A cam (81) for actuating the typing ribbon, which is controlled by a control shaft (56) selectively and successively positions the various tracks of the typing ribbon, and a second actuating cam (61) positions the correction ribbon independently of the position of the typing ribbon by way of a cam-follower pin ( 126) and a lever (127) which actuates the correction ribbon carrier and also the correction ribbon feed mechanism. The second cam (61) has interconnected tracks (122, 123, 124) such that selection of the correction ribbon is effected only in response to one direction of movement of the control shaft. The second cam (61) also actuates a lever (63) of the typing ribbon-feed mechanism. The cam (81) is three-lobed and rotates 120° for each complete rotation of the control shaft (56) and second cam (61) fixed thereto.

Description

TYPING AND ERASING DEVICE FOR PRINTING MACHINES
The present invention relates to a typing and erasing device for printing machines, in particular of electronic type.
A typing and erasing device in electronic typewriters is known wherein a Casey is disposed on a drive shaft and has fur grooved 5 profiles which are disposed symmetrically in pairs and which are capable of operating on a pin on a cam follower lever which positions a typing ribbon of the machine, at the point of typing.
I A second lever is arranged to be vied by the cam follower lever and ¦ guides the erasing ribbon towards the point of typing. The typing 10 ribbon has two typing regions or tracks in order to make use of the entire height of the ribbon. If the cam with its grooved profiles is rotated in an anti clockwise direction, the cam follower lever - is alternately guided by the first or the second grooved profile and lifts the typing ribbon, positioning the first or the second track lo of the ribbon in front of the point of typing, without altering the position of the correction ribbon. If an erasing cycle is to be performed, the cam is rotated in the clockwise direction and the pin lifts both the cam follower lever which guides the typing ribbon Z and the erasing ribbon guide lever, positioning the erasing ribbon in 20 front of the point of typing and the typing ribbon well above the j point of typing That arrangement is reliable but it is not able to position more than two regions of the typing ribbon since, for a ! greater number of such regions, the even greater lift required in respect of the erasing ribbon would be found to be unacceptable.
I The.:o~ject of thepresP~t invention is therefore to provide a typing . and erasing device which is of moderate cost, reliable and very easy to use and which makes it possible to employ a typing ribbon having more than two tracks which can be selected for the typing operation.

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This object is achieved by the device according to the present invention, which is characterized by the kirk-tensing portion of the main claim.

A preferred embodiment of the invention is set forth in the following description which is given by way of non-limiting example and with reference to the accompanying drawings in which:
Figure 1 shows a first partial longitudinal section of a typewriter, Figure 2 shows a second partial longitudinal section of the machine shown in Figure 1, on an enlarged scale, Figure 3 shows a third partial longitudinal section of the machine shown in Figure 1, on an enlarged scale, Figure 4 shows a plan view of par-t of the machine shown in Figures 1, 2 and 3, on an enlarged scale, Figure 5 shows a fourth partial longitudinal section of the machine shown in Figure 1, on an enlarged scalpel Figure 6 shows a plan view of part of the mechanism for forward feed movement of the typing ribbon of the machine shown in Figure 1, on an enlarged scale, Figure 7 shows a plan view of part of the mechanism for forward feed movement of the erasing ribbon of the machine shown in Figure 1, on an enlarged scale, and Figure 8 shows a logic block circuit diagram of a control and regulating unit of the machine shown in Figures 1, 2 and 3.

In the embodiment described hereinafter, the typing and erasing device for printing or typing machines comprises a platen roller 11 (see Figure 1) on which the point of typing or printing is indicated by reference numeral 12, and a carriage which is indicated generally by reverence numeral 13 and which is movable transversely to the platen roller 11 along a guide 14. The carriage 13 is slid able on the guide 14 in both directions, -for example by means of a reversible electrical stepping motor which is not shown in the drawings and which is as described in the present applicants Italian patent No. 864 395 issued on end May 1970. The carriage 13 comprises a base portion 16 having a bottom plate 17 connected by means of side portions 18 (only one of which is shown in the drawings) to the base portion 16. A solenoid 19 carries a hammer 21 for co-operating with a character carrying disc indicated generally at 22. The character carrying disc or daisywheel 22 is fixed to a flange 23 on a disc selector shaft 24 and is rotatable by means ox an electric motor 26 which is fixed to an upright 27 of the carriage 13. The character carrying disc 22 comprises a slotted peripheral rim portion providing flexible blades 28.
Each blade 28 carries at one end thereof a corresponding typing or printing character 29. The characters 29 are selected by means of the motor 26 in known manner, for example as described in the present applicants' Italian patent No 986 534 issued on Thea January 1975.

The carriage 13 carries a cartridge 31 for a printing or typing ribbon 32, by means of lateral guides 33, and two spools on which a correction or erasing ribbon 34 is wound (only one spool 36 can be seen in the drawings in Figure 7).
The typing ribbon 32 (see Figure I has a plurality of transverse tracks which can be selected for the typing or printing operation, thereby to use the entire height of the ribbon In Figure 1, the ribbon 32 is shown entirely in the rest position and with only the upper edge in the three operating positions which are respectively indicated by 37, 38 and I The cartridge 31 is of the type having two lateral arms, each having an arm 41 movable from a rest position shown in Figure 3 to three successive operating positions, as described hereinafter, for positioning the ribbon 32 (see Figure I in -the three operating positions 37, 38 and 39. The erasing ribbon 34 is movable from a rest position in which it is parallel to the ribbon 32 and permits the point of typing 12 to be viewed, to an operating position indicated at 42, in which it is in front of the point of typing 12.

An electric motor 51 which is designed to rotate selectively in -the clockwise and the anti clockwise directions comprises a shaft 52 on which a pinion 53 is fixed. The pinion 53 is always in mesh with a gear 54 on a shaft 56.
the transmission ratio between the pinion 53 and the gear 54 is 3 to 1. The gear 54 (see Figure 5) is fixed by means of the shaft 56 to a pinion 57 which in turn is engaged with a gear 58 on a shaft 59. In that connection also, the transmission ratio between the pinion 57 and the gear 58 is 3 to 1, whereby a rotary movement of 360 of the shaft 56 corresponds to a rotary movement of the shaft 59 through 12G.

cam 61 is fixed on the shaft 56 and co-operates with a projecting lug 62 (see Figure 1) on a lever 63 for controlling the forward feed movement of the ribbon 32.

In particular, the lever 63 is pivotal mounted on the shaft 59 and, under the force of a spring 64, is normally rotated in a clockwise direction with the projecting lug 62 bearing against the cam 610 The lever 63 has an end 66 which is housed in a seat 67 in a lever 68 (see Figure 6) of a paw mechanism generally indicated by reference numeral 69, for the forward feed movement of the ribbon 32. The paw mechanism I comprises the lever 68 which is rotatable on a shaft 71 and having a pin 72 on which a paw 73 is pivotal mounted. A spring 74 holds the paw 73 rotated in a clockwise direction and in enjoyment with a sawtooth wheel 76. The sawtooth wheel 76 is rotatable with a shaft 77 for controlling the forward feed movement of the typing ribbon 32 of the cartridge 31 in per so known manner which is not shown in the drawings. A spring 78 holds a reverse motion paw 79 normally engaged with the teeth of the sawtooth wheel 76 to prevent rotary movement of the wheel 76 in the reverse direction, which is therefore undesired.
Fixed on the shaft 5q See Figure 1) is a member for actuating the -typing ribbon, comprising a cam 81 having three lobes which have three different lifts and which are disposed at 120 relative to each other and which are arranged to co-operate with a pin 82 on a carrier frame for the typing ribbon, as generally indicated by reference numeral 83. The frame 83 comprises two arms 84 and 86 which are fixed with respect to each other by means of a shaft 87 and which are rotatable on a shaft 88. The lever 34 has an arm 89 to which the pin 82 is fixed. Each lever 84 and 86 has an end 91 capable of co-operating with a shoulder 92 (see Figure 3) on the respective arm 41. A spring 93 holds the respective arm 41 normally engaged with the shoulder 92 against the corresponding end 91. The cam 81 also has three zones of minimum lift, which are disposed I adjacent to the lobes and which define three corresponding rest positions, or positions in which the ribbon 32 permits typing to be seen.

In each typing or printing cycle, as described hereinafter, the three-lobe cam 81 positions the carrier frame 83 with the respective ends 91 from the rest position which is shown in solid lines in Figure 1 and in which the point of typing 12 can be seen, to the successive operating positions 94, 96 and 97 corresponding to lifting and , .

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operational positioning of the ribbon 32 in the positions 37, 38 and 39 respectively. For that purpose, the two movable arms 41 of the cartridge 31 oscillate vertically by means of pins 98 pivoted on fixed carriers 99 of the cartridge 31.

The three-lobe cam 81 see Figure 51 is fixed with respect to the gear 58 which also carries three sector portions 101 which are disposed at 120~ relative to each other. A transducer 102 comprising a photodetector 103 and a lighting means 104 which are disposed on opposite sides with respect to the path of movement of the sector portions 101 signals the passage of the sector portions 101, to an input-output unit 106 (see Figure I and the positions reached by the three-lobe cam 81 see Figure I

The typing and correction device is applied to a machine of the type described in the present applicants British patent No. 2 031 626 comprising the input-output unit 106 see Figure 8j controlled by a central unit 107 connected to memories 108 and to a keyboard 10~, The input-output unit 106 controls clockwise and anti clockwise rotation and stopping ox the motor 51 by means of three lines 111, 112 and 113 and an amplifier 114 and receives information in respect of the angular positions of the three-lobe cam 81 from the transducer 102 by way of the lines 116~ 117 and 118. In particular, when the typing ribbon is in the viewing position, one of the sector portions 101 screens the photo detector 102 from the light produced by the lighting means lQ4.

The cam 61 is fixed with respect to the gear 54 and a control member 121 (see Figure 21, which is substantially similar to that described in our published patent application EN 0 038 215, and is therefore not described in detail herein, comprising a common profile 122 connected to a circular profile 123 and to an eccentric profile 124 in such a way as to form two grooved profiles which are interconnected to each other. The profiles 123 and 124 are arranged to receive a pin 126 on an actuating lever 127. The profiles 123 and 124 are delimited by a step and an inclined surface portion, whereby one of the two profiles 123 and 124 can be engaged by the pin 1.26, in dependence on the direction of rotation of the shaft 56.

The actuating lever 127 comprises two appendages 128 and 129 which are received in suitable seats in lug portions 131 and 132 respectively of a frame structure 133. The frame structure 133 comprises two levers 134 and 136 which are fixed relative to each other by means of a shaft 137 and are rotatable on the shaft 88. The lever 136 comprises the two portions 131 and 132 and an arm 138 having a projecting lug portion 139 co-operable with a U-shaped fork portion 141 of a lever 42 of a paw mechanism generally indicated by reference numeral 143 (see Figure 7) for the forward feed movement of the erasing ribbon 34. The lever 136 also comprises a lug portion 140 housed in a slot 145 in the lever 127. The levers 134 (see Figure I and 136 terminate with U-shaped fork portions 144 and 146 respectively which are cQ-operable with respective lug portions 147 and 148 on two correction ribbon guide elements 149 and 151 respectively (see Figure 4). Each element 149 and 151 comprises a T-shaped slot 152 or housing a fixed guide 153 on the base portion 16 (see Figure l) and a C shaped fork 30 portion 154 which projects towards one side, or guiding the erasing ribbon 34 parallel to the roller 11~

The paw mechanism 143 (see Figllre I comprises the lever 142 which is rotatable on a shaft 156, having a pin 157 on which a paw 158 is pivotal mounted. spring 159 urges the paw 158 in an anti clockwise direction and holds it engaged with a sawtooth wheel 161 on which the spool 36 of the erasing ribbon 34 is mounted. The wheel 161 is rotatable on a shaft 162. A spring 163 holds a reverse motion paw 1~4 normally engaged with the teeth of the sawtooth wheel 161 to prevent rotation in the reverse direction, which is thus undesired, of the wheel 161.

If the motor 51 (see Figure I causes the control member 121 (see Figure I to rotate in a clockwise direction through a cycle of 360, the pin 126 is guided first by the side walls of the common profile 122 and subsequently by the side walls of the circular profile 123, while it cannot enter the profile 124 because it is separated by the step. The angular position of the lever 13~ does not vary and therefore also the actuating lever 127 remains in its rest position together with the frame structure 133 and the 2Q erasing ribbon 34~

If the motor 51 (see Figure I causes the control member 121 (see Figure 2) to rotate in an anti clockwise direction through a cycle of 360, the pin 126 is guided firstly by thy side wall portions of the common profile 122 and subsequently by the wall portions of the eccentric profile 124, while it cannot enter the profile 123 because of the corresponding step. The profile 124 now moves the actuating lever 127 which consequently causes the frame structure 133 to rotate in a clockwise direction about the shaft 88, and the shopped fork portions 144 and 1~6 cause the respective correction ribbon guide elements 14~ and 151 i :

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g (see Figure 41 to slide in the corresponding mixed guides 153 to position the erasing ribbon 34 in front of the point ox typing 12 (see Figure 1) in the position 42 shown in Figure 1.

The pin 126 (see Figure 21, sliding from the rest position in which it is disposed, moves tile frame structure 133 in an anti clockwise direction, to the maximum extent when the member 121 has rotated through 180. The erasing ribbon 34 goes from the rest position in which the point of typing 12 can be viewed, to the raised position 42 (see Figure I in front of the point of typing 12. That fact is also signaled by the photodetector 102 which is no longer screened by the sector portion 101.

During that lifting movement, the paw mechanism 143 (see Figure I is actuated by the arm 138. In fact, the arm 138 with the lug portion 139 causes the lever 142 to rotate in the anticlcckwise direction and the paw 158 moves over thy teeth of the wheel 161, engaging a space following that in wish it was previously engaged. When the erasing ribbon 34 is positioned in front of the point of typing 12 (see Figure I the control member 121 is arrested and the correction strike is made. The control member 121 is then rotated from 180 to 0, moving the pin 126 into a position of engaging the common profile 122. I-t will be clear that the grooved profiles 122 and 124 always positively control the pin 126 to prevent oscillatory movement during correction ox the characters, with respect to the point ox typing 12 During that movement of the member 121 prom the 180~ position to the 0 position, the control lever 127 causes the carrier frame structure 133 to rotate in an anti clockwise direction, whereby the erasing ribbon I goes from the raised position 42 (see Figure 1) to the down position. At the same time, the arm 138 see I

Figure I with the lug portion 139 causes the lever 142 to rotate in the clockwise direction, which lever 142, with the paw mechanism 158, causes anti clockwise rotation of the wheel 161 together with the spool 36, causing the erasing ribbon 34 to advance by a step which is equal to or greater than the space intended for a character. The three-lobe cam 81 (see Figure 1) can assume three angular positions 0 - 120 - 24Q and printing or typing is effected by sequentially using three tracks 37, 38 and 39 disposed at three different levels on the ribbon 32. After each character has been printed, the ribbon 32 is advanced over a length equal to one third of the space intended for a single character, by means of the paw mechanism 69 (see Figure I If the motor 51 (see Figure 1) rotates the control member 121 (see Figure I in a clockwise direction through 360, the three-lobe cam 81 (see Figure 1) is rotated in an anti clockwise direction through 120, being connected to the control member 121 by means of the gear 58 (see Figure 5) and the pinion 57. As described herein before, the pin 126 see Figure I is guided by the circular profile 123 so that its angular position does not change and, with the control lever 127, it remains in its rest position. The cam 61 (see Figure 1) which is fixed with respect to the shaft 56 will be rotated through 360 whereby, after about 135, it permits the lever 63 to rotate in the clockwise direction, due to the force of the spring 64, thereby moving the end 66 from the position shown in solid line to the position shown in broken line. With that movement, the end 66 (see Figure I causes the lever 68 to rotate in the clockwise direction, moving the paw '73 over the teeth of the wheel 76.

The cam 61 see Figure I continues to rotate and from about 225 to about 315, moves the lever 63 see Figure 1) I I

back into its rest position. During that movement, the lever 68 (see Figure 6) rotates in the anti clockwise direction with the paw 73 which, being engaged with a tooth on the wheel 76, rotates the wheel 76 and advances the ribbon 32.
At the same time, the three-lobe cam 81 (see Figure 1), after 35 of rotation, rotates the carrier frame structure 83 in a clockwise direction, whereby the ends 91 of the levers 84 and 86 engage the shoulders 92 (see Figure I lifting the arms 41 against the force of the springs 93. The ends 91 move into the position 94 see Figure 1) and thus the typing ribbon is positioned in position 37 in front of the point of typing 12. The three lobe cam 81 remains, from 35 to 85, in the position in which the ribbon 32 is in position 37. That situation is signaled to -the unit 107 by the photodetector 102. it about 60 of rotation of the three-lobe cam 81, the motor 51 is temporarily stopped and the character to be printed is struck by means of the hammer 21 and the solenoid 19. After about 10.4 my from the strike, the unit 107 reactivates the motor 51 which rotates the cam 81 from 85 to 112 approximately and permits the carrier frame structure 83 to return to the rest condition. The typing ribbon 32 is lowered and again permits the typed character to become visible. The three-lobe cam 81 is now in the rotated position. Printing of another character causes the cam to rotate through a further 120 whereby the ribbon 32 is moved into position 38 for a cycle similar to that described her~inbefore, still to return to the rest position, and then goes to the 360-0 position whereby the typing ribbon 32 is moved into position I and is then returned yet again to the rest position.

Since the three-lobe cam 81 has three angular rest positions at 0, 120 and 240, each corresponding to a zero position of the member 121, each of those angular positions of the three-lobe cam 81 can be a starting position for an erasing cycle.

If the motor 51 rotates the actuating merger 121 see Figure 2) in an anti clockwise direction through a 360 cycle, at the same time as the correction ribbon 32 is raised and advanced, the three-lobe cam 31 (see Figure 1) also rotates in an anti clockwise direction through a 120 cycle, being connected to the control member 121 by means of the gear I (Figure I and the pinion 57 with a transmission ratio of 3 to 1. Therefore, if the three-lobe cam 81 is in the 0 position, it goes to the 240 position, if it is in the 240 piston, it goes to the 120 position and if it is in the 120 position, it goes to the 0 position, and so on.

As described herein before with the rotary movement of the three-lobe cam 81, the frame structure 83 is rotated in the clockwise direction to move the typing ribbon into the positions I 38 and 37, in dependence on the angular positions of the three-lobe cam 81.

Therefore, the typing ribbon 32 being behind the erasing ribbon 34, the hammer 21, when it strikes a blade I -to strike the character 29 against the platen roller 11, causes the character to be removed from the paper rather than causing it to be typed, while the character to be erased is typed on the back of the erasing ribbon 34.

During each erasing cycle, the paw mechanism 69 (see Figure I advances the typing ribbon 32 by one third of the space allocated to the character and the paw mechanism 143 see Figure 7) advances the erasing ribbon 34 by a complete 3Q space. Erasure of a character is programmed by the memories I

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1~8 and the central unit 107 of the machine in such a way as to provide two repeated cycles of erasure of the same character, in the manner already described above, for more complete removal from the paper of the character to be erased.

In order to relocate a fresh portion of ribbon 32 in front of the point of typing 12, in the two erasing cycles, with a striking action, the machine causes a further rotary movement through 360 in the anti clockwise direction of the member 121, without activation of the hammer 21. After those cycles, the ribbon 32 will be advanced by a full space plus one third, while the last track previously used will be selected again.

It will be clear that the actuating member 121 (see Figure I by rotating in the clockwise direction, engages the pin 126 with the circular profile 123, positively leaves the control lever 127 in the rest position, and prevents actuation of the erasing ribbon carrier frame structure 133, while the three-lobe cam 81 (see Figure 1) selectively positions the typing ribbon in one of the three operating positions 37, 38 and OWE

If the actuating member 121 (see Figure 2) rotates in an anti clockwise direction, the pin 126 engages the eccentric profile 124, and the control lever 127 causes rotary movement of the frame structure 133 to position the erasing ribbon 34 in the operating position 42, independently of the track selected on the ribbon 32.

C A N A D A

APPLICANT: In. C. 01ivetti & C., Spy TITLE: Typing and erasing device for printing machines

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A typing and erasing device for printing machines comprising a carrier for a typing ribbon having a plurality of tracks which can be selected for the printing operation, a carrier for a correction ribbon, and a control member which produces oscillating movements of the carriers to permit viewing and typing or correction of characters and wherein selection of the typing ribbon or the correction ribbon is effected by the direction of movement of the control member, characterised by an actuating member for the correction ribbon which member is controlled by the control member and which moves the carrier of the correction ribbon so as to move the correction ribbon in front of the point of typing independently of the position of the typing ribbon.

2. A device according to Claim 1, characterised by an actuating member for the typing ribbon which is controlled by the control member and in that the actuating member for the correction ribbon and that for the typing ribbon are each rotatable about an axis and are interconnected to each other in such a way that a rotary movement through 360°
of the actuating member for the typing ribbon corresponds to three revolutions of the actuating member for the correction ribbon.

3. A device according to Claim 2, characterised in that the actuating member for the typing ribbon comprises a cam having three lobes disposed at 120° to each other and capable of selectively positioning a track of the said plurality in front of the point of typing.

4. device according to Claim 3, characterised in that the three-lobe cam controls a cycle of oscillation of the carrier of the typing ribbon every 120° of the actuating member of the typing ribbon and in that the control member can actuate an erasing cycle before and after each typing cycle.

5. A device according to Claim 1, characterised in that the actuating member for the correction ribbon comprises a common cam profile and two separate profiles, one of which is of constant lift and the other is eccentric with respect to the common profile and which are connected together so as to form two interconnected groove profiles permanently connected to the control member and a cam follower element connected to the carrier of the correction ribbon and in which the constant-lift profile or the eccentric profile are selectively operable in dependence on the direction of rotation of the control member.

6. A device according to Claim 5, characterised by an electric motor for selectively rotating the control member in a clockwise direction and in an anticlockwise direction, to select one of the grooved profiles.

7. A device according to Claim 5, characterised in that the cam follower element comprises a pin fixed to a control lever for lifting the carrier of the correction ribbon to position the correction ribbon when the pin passes through the eccentric profile and preventing lifting movement of the correction ribbon when the pin passes through the constant-lift profile.

8. A device according to Claim 7, characterised in that the pin is always positively controlled by the two grooved profiles.

9. A device according to Claim 1, characterised in that the correction ribbon is disposed on two rotatable spools on a common base portion, the carrier for the correction ribbon controls two ribbon guides movable vertically relative to the base portion and the actuating member of the correction ribbon is connected to a pawl mechanism for controlling one of the two spools for the advance movement of the correction ribbon when the actuating member moves the carrier for the correction ribbon.

10. A device according to Claim 1, characterised in that the typing ribbon is disposed in a cartridge which is removably fixed on to the base portion and in that the carrier for the ribbon comprises two vertically movable arms controlled by the control member and acting on a portion of ribbon outside the cartridge.

11. A device according to Claim 10, characterised in that said control member activates a cam for controlling a pawl mechanism for the forward feed movement of the typing ribbon.

12. A device according to Claim 1, characterised in that the device is applied to a typewriter having a typing member of the type comprising a character carrying disc with flexible blades.

13. A device according to Claim 1, characterised in that a central unit controls an input-output unit for controlling the clockwise and anticlockwise rotation of an electric motor connected to the control member.

14. A device according to Claims 3 and 13, characterised by a transducer for feeding to the input-output unit signals relating to the annular position of the three-lobe cam.

15. A typing and erasing device for printing machines comprising a carrier for a typing ribbon having a plurality of tracks which can be selected for the printing operation, a carrier for a correction ribbon and a control member which produces oscillatory movements of the carriers to permit viewing and typing or correction of characters and wherein selection of the typing ribbon or the correction ribbon is effected by the direction of movement of the control member characterised by an actuating member for the correction ribbon which is controlled by the control member and which moves the correction ribbon carrier so as to move the correction ribbon in front of the point of typing and by an actuating member for the typing ribbon which is interconnected with the actuating member for the correction ribbon with a transmission ratio equal to the number of tracks of the typing ribbon, and in that the actuating member of the correction ribbon effects the forward feed movement of the typing ribbon.

16. A device according to Claim 15, characterised in that the operation of erasing the character provides at least two correction cycles which are repeated in succession and wherein there is provided a forward feed cycle without strike, of the typing ribbon, after the correction cycles.