EP0042949B1 - Positive indexing mechanism for typewriter platen with improved detenting - Google Patents
Positive indexing mechanism for typewriter platen with improved detenting Download PDFInfo
- Publication number
- EP0042949B1 EP0042949B1 EP19810103619 EP81103619A EP0042949B1 EP 0042949 B1 EP0042949 B1 EP 0042949B1 EP 19810103619 EP19810103619 EP 19810103619 EP 81103619 A EP81103619 A EP 81103619A EP 0042949 B1 EP0042949 B1 EP 0042949B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- pawl
- platen
- typewriter
- ratchet
- ratchet wheel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J19/00—Character- or line-spacing mechanisms
- B41J19/76—Line-spacing mechanisms
- B41J19/78—Positive-feed mechanisms
- B41J19/80—Pawl-and-ratchet mechanisms
- B41J19/82—Pawl-and-ratchet mechanisms moving a paper or like carriage
- B41J19/84—Pawl-and-ratchet mechanisms moving a paper or like carriage in the form of a roller rotated for line spacing
- B41J19/86—Pawl-and-ratchet mechanisms moving a paper or like carriage in the form of a roller rotated for line spacing the pawl being normally in engagement with the ratchet
Definitions
- the invention relates to typewriters and, more particularly, to platen indexing mechanisms therefor.
- Typewriters have platens against which the typing occurs and around which a sheet of paper is transported to effect line by line movement of the paper for printing on subsequent print lines.
- the detenting In order to retain the platen in a stationary position during typing, a detenting arrangement is generally utilized.
- the detenting generally takes the form of a roller or detenting bar being spring biased into the index ratchet of the typewriter platen. As the detenting roller or detent member forces its way under spring bias into engagement with the teeth of the platen, it will act to position the platen in a consistent manner from line to line.
- Line feed is accomplished in most typewriters by a pawl driven into the ratchet teeth and causing movement in a rotating motion about the axis of the ratchet, forcing the ratchet to rotate the platen.
- a fixed solid abutment member or pawl stop is mounted on the frame of the typewriter. The index pawl is thus physically jammed into the pawl stop.
- a typewriter platen indexing mechanism of the type comprising a platen rotatably supported by the typewriter frame, a ratchet wheel drivingly associated with said platen, a pawl for driving said ratchet, a pawl stop mounted on said typewriter frame and a detent means yieldably engaged with said ratchet and pivotally supported on said typewriter frame, said typewriter platen indexing mechanism being characterized in that: said pawl stop is associated with said detent means to pivot the latter wheel into forcible engagement with said ratchet wheel into forcible engagement with said ratchet wheel, said pawl stop being engageable by said pawl, at the completion of the driving movement of said pawl to cause said detent means to forcibly engage said ratchet wheel, whereby the force exerted by said pawl against said pawl stop acts to prevent said detent means from being forced out of said ratchet wheel and prevent overthrow of said rat
- indexing of a typewriter platen 10 may be accomplished by a pawl and ratchet drive.
- the platen 10 is supported rotationally in typewriter frame 12.
- Frame 12 also supports a multitude of other assemblies and parts for accomplishing the indexing, as will be explained below.
- Indexing ratchet 14 is drivingly attached to platen 10 most commonly by a shaft (not shown).
- Supported on the shaft may be a line feed selection cam 16 which controls the point of entry into ratchet 14 of indexing pawl 18.
- Indexing pawl 18 has a tip 20 formed to engage ratchet 14.
- the positioning of cam 16 is controlled by a line feed selection lever 22 which is pivotally mounted on frame 12 by pivot member 24.
- Lever 22 extends into engagement with control arm 26 of cam 16 (see Fig. 4).
- cam 16 may be rotated about the axis of platen 10 to shift the cam profile controlling the entry of pawl tip 20 into ratchet 14.
- Pawl 18 is pivotally mounted on pivot member 30 to move into and out of engagement with ratchet 14.
- pivot member 30 is fixedly attached to pawl support bracket 32, one end of which is pivotally supported by the platen shaft and the other end of which carries a pin 34 for rotatably supporting a pulley 36.
- Pulley 36 is engaged about its periphery by carriage return cord 38 one end of which is grounded to the frame 12, the opposite end being controlled by a carriage return mechanism.
- a link 40 is pivotally supported on a pivot pin 42 which is, in turn, attached to frame 12. This link is spring biased by a spring 44 attached to frame 12, to cause restoration of pulley 36 when the tension in cord 38 is relaxed. Link 40 engages pin 34 with a lost motion slot 46.
- detent roller 50 is rotationally supported in detent bracket 52.
- Detent bracket 52 is pivotally supported on member 54 which extends outwardly from frame 12 and provides an axis of rotation for detent bracket 52.
- Pawl stop 56 is rigidly attached by conventional means such as screw 58 to detent bracket 52.
- Detent bracket 52 is also spring biased by spring 60 illustrated in FIG. 4 to effect a movement of detent bracket 52 about its axis of rotation 54 and to engage detent roller 50 with the teeth of ratchet 14.
- Cam 16 provides a plurality of notches 62 representing different degrees of rotation of the platen during an indexing phase.
- spring 60 while acting as a detenting member on cam 16 also provides a biasing force against detent bracket 52 to force the detent member 50 into engagement with ratchet teeth 14.
- Fig. 3 it will be seen that as cord 38 is pulled, pulley 36 pulls on pivot member 34 drawing member 32 downward. As member 32 is pulled downward, pivot member 30 and pawl 18 are also pulled downward and with the tip 20 of pawl 18 engaged in ratchet 14, the continued tension on cord 38 and movement of the linkage described immediately above will cause the rotation of bracket 32 about the axis of platen 10.
- pawl 18 will drive ratchet 14 to rotate platen 10.
- pawl 18 reaches the end of travel to position platen 10 at the next writing line, its stop surface 70 will engage the end 72 of pawl stop 56.
- surface 70 will engage, with increasing force surface 72 of pawl stop 56, effecting a rotation of detent bracket 52 about pivot 54.
- the rotation of detent bracket 52 about pivot 54 will physically jam detent roller 50 into the associated tooth of ratchet 14.
- the tension increases in cord 38, the forces throughout the mechanical chain will likewise increase further preventing the movement of ratchet 14 and platen 10. With the additional force of detent 50 against ratchet 14, it becomes exceedingly difficult for platen 10 to overthrow due to momentum.
- return spring 44 acts to pull link 40 upward which, in turn, will act to restore member 32 and pawl 18 to a raised and disengaged position such that ratchet 14 may be either manually turned or pawl 1 8 is in position for a subsequent index cycle.
Landscapes
- Character Spaces And Line Spaces In Printers (AREA)
- Handling Of Sheets (AREA)
Description
- The invention relates to typewriters and, more particularly, to platen indexing mechanisms therefor.
- Typewriters have platens against which the typing occurs and around which a sheet of paper is transported to effect line by line movement of the paper for printing on subsequent print lines.
- In order to retain the platen in a stationary position during typing, a detenting arrangement is generally utilized. The detenting generally takes the form of a roller or detenting bar being spring biased into the index ratchet of the typewriter platen. As the detenting roller or detent member forces its way under spring bias into engagement with the teeth of the platen, it will act to position the platen in a consistent manner from line to line.
- Line feed is accomplished in most typewriters by a pawl driven into the ratchet teeth and causing movement in a rotating motion about the axis of the ratchet, forcing the ratchet to rotate the platen. In order to stop the platen at the desired point, a fixed solid abutment member or pawl stop is mounted on the frame of the typewriter. The index pawl is thus physically jammed into the pawl stop. If the ratchet and platen are rapidly rotating and the pawl is forced into the pawl stop, the momentum of the platen and ratchet may cause the parts to deflect and cam the pawl out of engagement with the ratchet teeth sufficiently to allow an additional ratchet tooth to pass, thus misaligning the platen for the next print line. An additional potential problem is when the momentum will carry the platen only partially to the next print line position and the detent member may not have sufficient force exerted against it and the ratchet tooth to cause the platen and the ratchet to move back to its desired position. Adjustable pawl stops and other solutions have been attempted. None of the solutions appear to be fully satisfactory inasmuch as parts must be maintained in as small a configuration and as light a weight as possible which tends to permit deflection and therefore prevent totally reliable performance.
- Accordingly, it is an object of this invention to prevent overthrow of the platen during an indexing operation.
- It is another object of the invention to insure the forcible engagement of the detent member with the platen ratchet wheel.
- It is a further object of the invention to insure the proper alignment of the platen for the next printing line operation after an indexing function.
- The objects of the invention are accomplished and the shortcomings of the prior art overcome by a typewriter platen indexing mechanism of the type comprising a platen rotatably supported by the typewriter frame, a ratchet wheel drivingly associated with said platen, a pawl for driving said ratchet, a pawl stop mounted on said typewriter frame and a detent means yieldably engaged with said ratchet and pivotally supported on said typewriter frame, said typewriter platen indexing mechanism being characterized in that: said pawl stop is associated with said detent means to pivot the latter wheel into forcible engagement with said ratchet wheel into forcible engagement with said ratchet wheel, said pawl stop being engageable by said pawl, at the completion of the driving movement of said pawl to cause said detent means to forcibly engage said ratchet wheel, whereby the force exerted by said pawl against said pawl stop acts to prevent said detent means from being forced out of said ratchet wheel and prevent overthrow of said ratchet wheel and said platen.
- A better understanding of the invention may be had by referring to the drawings and the following detailed description.
- In the drawings:
- FIG. 1 illustrates a platen indexing system including a platen, ratchet and pawl arrangement.
- FIG. 2 shows the indexing ratchet and detent roller and mounting brackets.
- FIG. 3 is an end view of the platen, ratchet, detent and indexing pawl, together with the pawl stop.
- FIG. 4 illustrates the technique utilized for selecting the increment of feed of the platen by controlling the point of engagement of the pawl with the ratchet.
- Referring to FIG. 1, indexing of a
typewriter platen 10 may be accomplished by a pawl and ratchet drive. Theplaten 10 is supported rotationally intypewriter frame 12.Frame 12 also supports a multitude of other assemblies and parts for accomplishing the indexing, as will be explained below. Indexingratchet 14 is drivingly attached toplaten 10 most commonly by a shaft (not shown). Supported on the shaft may be a linefeed selection cam 16 which controls the point of entry intoratchet 14 of indexingpawl 18. Indexingpawl 18 has atip 20 formed to engageratchet 14. The positioning ofcam 16 is controlled by a linefeed selection lever 22 which is pivotally mounted onframe 12 bypivot member 24.Lever 22 extends into engagement withcontrol arm 26 of cam 16 (see Fig. 4). Thus,cam 16 may be rotated about the axis ofplaten 10 to shift the cam profile controlling the entry ofpawl tip 20 intoratchet 14. Pawl 18 is pivotally mounted onpivot member 30 to move into and out of engagement withratchet 14. Additionally,pivot member 30 is fixedly attached topawl support bracket 32, one end of which is pivotally supported by the platen shaft and the other end of which carries apin 34 for rotatably supporting apulley 36. Pulley 36 is engaged about its periphery bycarriage return cord 38 one end of which is grounded to theframe 12, the opposite end being controlled by a carriage return mechanism. - Any known technique for placing tension upon the carriage return cord to effect index is satisfactory.
- A
link 40 is pivotally supported on apivot pin 42 which is, in turn, attached toframe 12. This link is spring biased by aspring 44 attached toframe 12, to cause restoration ofpulley 36 when the tension incord 38 is relaxed.Link 40 engagespin 34 with a lostmotion slot 46. - Referring to FIG. 2,
detent roller 50 is rotationally supported indetent bracket 52.Detent bracket 52, in turn, is pivotally supported onmember 54 which extends outwardly fromframe 12 and provides an axis of rotation fordetent bracket 52.Pawl stop 56 is rigidly attached by conventional means such asscrew 58 to detentbracket 52.Detent bracket 52 is also spring biased byspring 60 illustrated in FIG. 4 to effect a movement ofdetent bracket 52 about its axis ofrotation 54 and to engagedetent roller 50 with the teeth ofratchet 14. Cam 16 provides a plurality ofnotches 62 representing different degrees of rotation of the platen during an indexing phase. The engagement ofspring 60 with one of thenotches 62 determines the cam profile against whichindex pawl 18 rides and which controls the entry point of thepawl tip 20 into theratchet teeth 14.Spring 60, while acting as a detenting member oncam 16 also provides a biasing force againstdetent bracket 52 to force thedetent member 50 into engagement withratchet teeth 14. Referring to Fig. 3, it will be seen that ascord 38 is pulled,pulley 36 pulls onpivot member 34drawing member 32 downward. Asmember 32 is pulled downward,pivot member 30 andpawl 18 are also pulled downward and with thetip 20 ofpawl 18 engaged inratchet 14, the continued tension oncord 38 and movement of the linkage described immediately above will cause the rotation ofbracket 32 about the axis ofplaten 10. - As this occurs,
pawl 18 will driveratchet 14 to rotateplaten 10. Whenpawl 18 reaches the end of travel to positionplaten 10 at the next writing line, itsstop surface 70 will engage theend 72 ofpawl stop 56. As additional force is exerted oncord 38 with that force being transmitted topawl 18,surface 70 will engage, with increasingforce surface 72 ofpawl stop 56, effecting a rotation ofdetent bracket 52 aboutpivot 54. The rotation ofdetent bracket 52 aboutpivot 54 will physically jamdetent roller 50 into the associated tooth ofratchet 14. As the tension increases incord 38, the forces throughout the mechanical chain will likewise increase further preventing the movement ofratchet 14 andplaten 10. With the additional force of detent 50 againstratchet 14, it becomes exceedingly difficult forplaten 10 to overthrow due to momentum. - As cord tension is relieved on 38, return
spring 44 acts to pulllink 40 upward which, in turn, will act to restoremember 32 andpawl 18 to a raised and disengaged position such thatratchet 14 may be either manually turned or pawl 1 8 is in position for a subsequent index cycle.
Claims (4)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US16471280A | 1980-06-30 | 1980-06-30 | |
US164712 | 1993-12-10 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0042949A1 EP0042949A1 (en) | 1982-01-06 |
EP0042949B1 true EP0042949B1 (en) | 1983-11-02 |
Family
ID=22595749
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19810103619 Expired EP0042949B1 (en) | 1980-06-30 | 1981-05-12 | Positive indexing mechanism for typewriter platen with improved detenting |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0042949B1 (en) |
JP (1) | JPS5718284A (en) |
DE (1) | DE3161316D1 (en) |
MX (1) | MX154051A (en) |
-
1981
- 1981-05-12 EP EP19810103619 patent/EP0042949B1/en not_active Expired
- 1981-05-12 DE DE8181103619T patent/DE3161316D1/en not_active Expired
- 1981-05-20 JP JP7507381A patent/JPS5718284A/en active Granted
- 1981-06-26 MX MX18801581A patent/MX154051A/en unknown
Also Published As
Publication number | Publication date |
---|---|
MX154051A (en) | 1987-04-13 |
JPS6116633B2 (en) | 1986-05-01 |
EP0042949A1 (en) | 1982-01-06 |
JPS5718284A (en) | 1982-01-30 |
DE3161316D1 (en) | 1983-12-08 |
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