GB2026950A - Paper feed mechanism for a printer - Google Patents

Abstract

Paper is fed by a pair of sprocket wheels with teeth 17 mounted on a shaft 19 driven by a ratchet wheel 61 which is rotated by a pawl 62. The pawl 62 is pivotally mounted on the armature of an electromagnet 64 and is biassed by a spring 65 which holds the pawl against the ratchet wheel and also actuates the paw to advance the ratchet wheel after the pawl has been disengaged by the electromagnet. An arm 70 attached to the armature of the electromagnet allows manual advance of the paper by actuation of the ratchet wheel. <IMAGE>

Description

SPECIFICATION Paper feed mechanism for a printer The present invention relates to a media advancement mechanism of printers and more par ticularlyto a manual advance thereof.

U.S. Patent No. 3,986,594, entitled Serial Impact Calculator Printer, issued to Nicholas Kondur, Jr. on October 19, 1976, teaches a serial impact printer of the type utilizing a dot matrix print head that is specifically adaptable for use as a calculator or adding machine and that is characterized by utilizing a common drive source to advance the print head across the paper, advance the paper between printing operations, and selectively advance the inked ribbon between the ribbon supply spool and takeup spool. An improved paper-advancing apparatus has been devised which operates in close correlation with the print head drive member to provide a relatively high speed, simplified and inexpensive printer unit.The ribbon supply spools are so constructed and arranged as to be interchangeable and to permit direct drive through a spool-engaging member on the print head whereby to advance the inked ribbon in direct response to print head travel.

Paper-advancing rolls, including a platen and pressure roll are arranged in closely spaced, parallel relation to the cylindrical drive member for the print head, one of the rolls being incrementally driven by a drive pawl eccentrically mounted on the print head drive whereby to index the recording medium atthe end of each printing cycle of the print head. The drive pawl selectively interengages with a ratchet on one of the paper-advancing rolls to overcome a detent which releasably engages one of the paperadvancing rolls to station the recording medium securely in position during the printing operation. In turn, the detent as well as the paper-advancing rolls are manually releasably to permit manual positioning or adjustment of the recording medium.The recording medium, i.e. paper, advances between the paper-advancing rolls along a resilient guide path which is so arranged as to accurately guide the paper between the rolls and to firmly support it in an upright position during the printing operation.

In order to advance or rotate the platen, a ratchet wheel is keyed to one of the platen with ratchet teeth on the external surface disposed in the path of movement of a drive pawl arm. The arm has a circular end journaled for rotation at one end on the eccentric sleeve at the end of the drive cam for rearward generally horizontal extension of the arm therefrom. A pin projects outwardly in a lateral direction from the side of the arm for insertion in a slot in the side frame and the arm terminates in a pawl or catch for selective engagement with one of the ratchet teeth on the gear.The free end or pawl of the arm will describe a generally oval-shaped path of movement into and away from engagement with one of the ratchet teeth in following the rotational movement of the opposite end about the eccentric and which is translated into a more nearly linear movement by the pin riding in the angular, generally V-shaped slot. Movement in the manner shown and described will cause the pawl to swing upwardly into engagement with one of the teeth to carry the platen in a clockwise direction over a limited distance to advance or index the paper one line or space; and thereafter to swing downwardly to return to its orig inal position in response to rotation of the drive cam.

In advancing the platen through the interaction of the pawl and ratchet gear, the pawl arm will overcome the holding action of a detent which includes an inner arm portion having a downwardly directed finger, a protuberance extending in a direction opposite to that of the finger and an outer distal end portion. A handle is affixed to the arm by a common boss. The boss has flatted surfaces to permit insertion of the boss through a keyhole shaped slot in the rearward lower end of the frame. The slot includes an enlarged circular portion at its inner closed end so that the boss can be inserted by aligning the flatted surfaces with the open slotted entrance until it reaches the enlarged circuit portion at which point it will become locked in the slot while free to undergo limited rotation.The detent is aligned in the slot such that the finger projects downwardly into the channel with the oppositely directed protuberance or catch extending upwardlyto make engagement with one of the grooves formed in the outer peripheral surfaces of a circular stop element mounted on the end of the platen opposite to that of the ratchet gear. A coil spring encircles the finger and abuts the bottom of the channel so as to yieldingly urge the detent arm in a direction forcing the proturberance or catch into one of the grooves. The handle portion projects upwardly and somewhat forwardly along the outside of the frame and includes an offset portion provided with a knurled end surface which is accessible for manual engagement externally of the casing of the printer.

When the handle is manually depressed in a downward direction it will cause the finger to overcome the urging of the spring and release the catch from engagement with the groove. Simultaneously the finger abutment will engage one of the wings of the support block to cause the pressure roll to be depressed away from the platen surface whereby to permit manual adjustment or positioning of the paper when desired. When the handle is relased, the catch will automatically return underthe urging of the spring behind the finger to a position engaging the stop and the pressure roll will return into engagement with the platen. In this relation, the drive pawl must overcome the detent arm in advancing or indexing the platen.Accordingly, the spacing between grooves on the stop is such that as the drive pawl clears the ratchet gear the catch will move into engagement with the next groove on the stop to accurately index the paper to a predetermined spacing between each line of print. Atwirler or hand wheel is keyed to the reduced end of the platen to permit manual rotation of the platen and indexing of the paper.

U.S. Patent No. 3,787,884, entitled Ink Jet Printer, issued to Frederick M. Demer on January 22, 1974 teaches both a manual paper advance and an automatic paper advance. U.S. Patent No. 3,878,886, entitled Advancing Mechanism for Thermal Print Apparatus, issued to John McCrady on January 22, 1974 teaches an automatic paper advancing mechanism.

U.S. Patent No. 4,070;963, entitled Impact Line Printer, issued to John H. Weaver on January 31, 1978, teaches an apparatus for advancing the paper which includes roller mechanically coupled to a ratchet wheel, a pawl, and a pawl stop which are disposed so that the ratchet wheel will not rotate in either direction. The apparatus also includes a solenoid for disengaging the pawl from the ratchet wheel and a tension spring for turning the disengaged ratchet wheel.

In view of the foregoing factors and conditions characteristic of the prior art, it is a primary object of the present invention to provide a manual advance for the media.

It is another object of the present invention to provide a simple apparatus for use as manual advance for the media that does not require any additional components otherthan a simple lever arm.

It is still another object of the present invention to provide a lever arm which is to be mechanically coupled to the armature of the solenoid of the media advancement mechanism and which does not interfere with the normal operation thereof.

In accordance with an embodiment of the present invention, a manual advance for a media advancement mechanism for use in combination with a printer that includes a frame, a print head mechanically coupled to the frame and a platen mechanically coupled to the frame so that a print media may pass between it and the print head is described. The printer also includes a pair of sprockets which are adapted to support the print media and which are mechanically coupled to the frame by a sprocket shaft. The media advancement mechanism includes a ratchet wheel which is mechanically coupled to the sprocket shaft in order to provide rotational motion thereto in response to an electrical signal from the printer thereby moving the print media incrementally.The media advancement mechanism also includes a plate member which is mechanically coupled to the sidewall of the frame a solenoid with an armature mechanically coupled to the plate member, a pawl which is mechanically coupled to the armature of the solenoid and disposed so that it can mechanically engage the teeth of the ratchet wheel in order to impart rotational motion thereto and a spring which mechanically couples the pawl to the plate member. The manual advance of the media advancement mechanism includes a lever arm which is mechanically coupled to the armature of the solenoid which is adapted to disengage the pawl from a tooth of the ratchet wheel.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims.

Other objects and many of the attendant advantages will be more readily appreciated as the same becomes better understood by reference to the fol lowing detailed description and considered in con nection with the accompanying drawing in which like reference symbols designate like parts through out the figures.

FIG. 1 is a perspective drawing of a printer which includes a frame, a print head and a platen for use in combination with a manual advance of a media advancement mechanism that has been constructed in accordance with the principles of the present invention.

FIG. 2 is a side elevational view of the manual advance of the media advancement mechanism of the printer of FIG. 1 showing it in a first position.

FIG. 3 is a side elevational view of the manual advance of the media advancement mechanism of the printer of FIG. 1 showing it in a second position.

FIG. 4 is a cross-sectional view of the manual advance of the media advancement mechanism of the printer of FIG. 1 showing it in a second position.

FIG. 5 is a partial side elevational view of the printer of FIG. 1 showing the manual advance of the media advancement mechanism.

In order to best understand the present invention it is first necessary to read the foregoing description of a printer which is to be used in combination with the present invention and also to refer to the figures in the accompanying drawing. Referring to FIG. 1 a printer 10 includes a frame 11 having a pair of side plates 12 and a print head 13 which is adapted to travel laterally across the front of the frame 11. The print head 13 is of a type which is taught in U.S.

Patent No.4,004,671, entitled Wire Matrix Print Head, issued to Nicholas Kondur, Jr. on January 25, 1977. Other U.S. Patents that teach similar print heads include: No.4,070,963; No.3,986,594; and No.

4,062,436. The printer 10 also includes an inking apparatus 14 which is mechanically coupled to the print head 13 in order to provide ink for printing onto a print media and a timing shaft 15 which is rotatably coupled to the frame 11 between the pair of side plates 12 and which is mechanically coupled to the print head 13 and the inking apparatus 14 in order to drive them in concert across the front of the frame 11. The print media may be paper with sprocket holes spaced a standardized distance apart along its borders. The printer 10, further includes a pair of sprockets 16, which are disc-shaped members each of which has a plurality of pins 17 which are disposed on its cylindrical wall and are spaced apartthe same distance as are the sprocket holes of the paper and also has a hub 18.A sprocket shaft 19 is rotatably coupled to the frame 11 between the pair of side plates 12 and mechanically couples each of the sprockets 16 adjacent to one of the side plates 12. A media guide 20 is mechanically coupled to the hub 18 of the sprocket 16 so that the print media is disposed between it and the cylindrical wall of the sprocket 16.

Still referring to Fig. 1 the inking apparatus 14 is similartothe one taught in U.S. Patent No.

3,986,594, entitled Serial Impact Calculator Printer, issued to Nicholas Kondur, Jr. on October 1976 and is described in more detail in U.K. application No. (corresponding to U.S. Serial No. 912,090) filed on the same day as the present application.

Referring now to Fig. 2 in conjunction with Fig. 5 a media advancement mechanism for imparting rotational movement to the sprockets 16 mechanically coupled to the sprocket shaft 19 is similar to the mechanism taught in U.S. Patent No. 4,070,963, enti tled Impact Line Printer, issued to John Weaver on January 1978 and reference is made to that Patent for additional description. Parts of the mechanism to be described form the subject of U.K.

application No.7919349 (corresponding to U.S. Ser ial No. 912,089) filed on the same day as the present application. The mechanism includes an adjustment plate 60 which is mechanically coupled to one of the side plates 12 and a ratchet wheel 61 which is mechanically coupled to the sprocket shaft 19, a pawl 62 which engages the ratchet wheel 61 and which is pivotally coupled to the end of an armature 63 of a media feed solenoid 64 and a spring 65 which mechanically couples the adjustment plate 60 to the pawl 62 at a point 66 so located that the line of its force is slightly below the pawl's pivot axis 67 so that a single spring 65 is sufficient in order to both advance the pawl 62 upon release of the armature 63 and apply a clockwise force upon the pawl 62 thereby maintaining the pawl 62 in engagement with the ratchet wheel 61 and a pawl stop 68. Each time a pulse of current is supplied to the media feed solenoid 64, it incrementally rotates the ratchet wheel 61 thereby causing the sprocket 16 and the print media to advance a distance corresponding to the spacing of the teeth on the ratchet wheel 61 and the ratio of the diameter of the sprocket and the ratchet wheel 61.The current pulses are supplied automatically as part of the printing cycle to the media feed solenoid 64.

Referring still to FIG. 2 in conjunction to FIG. the media drive mechanism also includes a manual advance which includes a lever arm 70 that is pivotally coupled to the armature 63 of the media feed solenoid 64. There is a slot 71 in the side plate 12 so that the lever arm 70 may project through and so that it may be moved rearward so that the armature 63 moves rearward in orderto disengage the pawl 62 from the teeth of the ratchet wheel 61. A pin 72, which couples the armature 63 to the lever arm 70, loosely couples through a hole in the pawl 62 thereto in order to permit the pawl 62 to rotate in manner dictated by the spring 65 and the pawl stop 68 when the armature 63 is actuated by the media feed solenoid 64 or manually by having an operator press the lever arm 70.

The inventor notes that the lever arm 70 may be pivotally coupled to the sprocket shaft 19 in another embodiment and also that the lever arm 70 may be replaced with a button which is mechanically coupled to the armature 63 in the same manner as the lever arm 70 and is loosely coupled to the armature 63 also in the same manner as the lever arm 70. The use of the button rather than the lever arm 70 results in an additional feature in that the operator can incrementally advance the media manually while adjusting the print line of the media with one hand.

The lever arm 70 is also useful as a release in order to remove the media from the printer 10. It should be pointed out that the rotation of the drive mechanism is unidirectional.

Referring now to FIG. 3 in conjunction with FIG. 2 it can be seen that the lever arm 70 has been pulled backward along with the armature 63 of the media feed solenoid 64 thereby pulling the pawl 62 from the teeth of the ratchet wheel 61. It can also be seen that the spring 65 pulls the pawl 62 upward into a tooth of the ratchet wheel 61 which is disposed closer to the armature 63 than is the previously engaged tooth thereby causing the ratchet wheel 61 to rotate by the returning pawl 62 under the action of the spring 65 when the lever arm 70 is released by the operator.

Referring now to FIG. 4 in conjunction with FIG. 2 the pin 72 which connects the lever arm 70 to the armature 63 is shown.

Referring now to FIG. 5 in conjunction with FIG. 2 and FIG. 3 the adjustment plate 60 has the media feed solenoid 64, the spring 65 and the pawl stop 68 fixedly mounted thereon. The pawl 62 is mechanically coupled to the armature 63 of the media feed solenoid 64 and is also resiliently coupled to the teeth of the ratchet wheel 61 by the spring 65. The movement of the pawl 62 is biased by the pawl stop 68. An electrical impulse activates the media feed solenoid 64 causing the armature 63 to move rearward thereby disengaging the pawl 62 from a tooth of the ratchet wheel 61. The spring 65 pulls the rearwardly moved pawl 62 upward into the preceding tooth of the ratchet wheel 61 and forward so that the pawl 62 engages the preceding tooth of the ratchet wheel 61 and rotates it clockwise in order to incrementally advance the media.The improved media advancement mechanism not only includes the incrementing mechanism taught in U.S. Patent No.

4,070,963, but also includes the manual advance.

The operation of the manual advance involves the manual movement by the lever arm 70 of the armature 63 of the media feed solenoid 64 and the pawl 62 from its first position to its second position and then back to its first position as shown in FIG. 2 and FIG.3.

The inventor also notes that either the lever arm 70 or the button allows the pawl 62 to escape from the engaged tooth of the ratchet wheel 61 when the lever arm 70 has been displaced by the operator to its rightmost position as shown in FIG. 3 thereby permitting free rotation of the ratchet wheel 61. The pawl stop 68 is therefore ineffective in jamming the mechanism so as to prevent counterclockwise rotation of the pawl 62 caused by the action of the teeth of the ratchet wheel 61 against the tip of the pawl 62.

When eitherthe button orthe lever arm 70 is pushed rearwardly this operation releases the media from the printer 10 by disengaging the pawl 62 from the teeth of the ratchet wheel 61.

Claims (4)

1. A manual advance for a media advancement mechanism for use in combination with a printer which includes: a. a frame; b. a print head mechanically coupled to said frame; c. a platen which is mechanically coupled to said frame so that a print media may pass between said print head and said platen; and d. supporting means for supporting said print media mechanically coupled to said frame, said manual advance for said media advancement mechanism comprising: a. a ratchet wheel mechanically coupled to said supporting means so that it provides rotational motion thereto in order to move said print media incrementally in response to an electrical signal from said printer; b. a plate member mechanically coupled to a sidewall of said frame; c. a solenoid which receives said electrical signal from said printer and which is mechanically coupled to and disposed on the surface of said plate member; d. a pawl mechanically coupled to the armature of said solenoid and disposed so that it can mechanically engage the teeth of said ratchet wheel in order to impart rotational motion thereto; e. a spring mechanically coupling said pawl to said plate member; and f. a lever arm mechanically coupled to the armature of said solenoid which is adapted to desengage said pawl from a tooth of said ratchet wheel.

2. A manual advance according to claim 1 wherein said lever arm is a button that projects from a slot and is pivotally coupled to said pawl and fixedly coupled to said armature of said solenoid.

3. A manual advance according to claim 2 wherein said button is disposed adjacent to the side of said frame in order to provide a one-handed advance and release mechanism.

4. Paper feed mechanism for a printer comprising supporting means rotatably mounted on a frame for supporting and advancing the paper, a ratchet wheel coupled to rotate the supporting means, a solenoid having an armature with a pawl pivotally connected to the armature, a spring coupled to the pawl to bias the pawl against the ratchet wheel and to cause the pawl to advance the ratchet wheel when the pawl is released by the solenoid and a lever arm coupled to the armature of the solenoid to facilitate manual disengagement of the pawl from the ratchet wheel.