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(11) | EP 0 026 890 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Paper drive mechanism for a printer |
| (57) A printer (8) includes a rotatably driven platen (18) for driving paper across a
print station (12). The paper is driven through the print station (12) by a drive
assembly (14, 16). The assembly (16) includes a pair of pivotably supported arms (42,
44) the ends of which are biased toward the platen (18). The ends of the support arms,
(42, 44) carry rocker arms (72, 74) which support entrance (86) and exit (76) axles
each having fixed thereto associated rollers (78, 80; 82; 88, 90). The end of the
entrance axle (86) has an extension (92) carrying a drive roller (94). The roller
(94) engages the platen (18) beyond the rocker arms (72, 74) and outside of the path
of the maximum width paper the printer will accommodate. The drive roller (94) is
biased along with the entrance rollers (88, 90) toward the platen (18). As the paper
passes through the printer (8), it is driven by the entrance rollers (88, 90) which
are continuously driven by the drive roller (94) through the entrance axle (86). |
TECHNICAL FIELD
[0001] This invention relates to a paper drive mechanism for a printer which will accommodate various modes of paper insertion.
BACKGROUND ART
[0002] The term printer generally identifies an apparatus which responds to incoming data signals by printing alpha-numeric characters upon a sheet of paper as the paper is fed through a print station. Printers often provide alternate modes of paper insertion depending upon the form of the paper being used. For example, in computer printout applications as well as communications service, the paper is supplied as a continuous sheet with consecutive segments joined at a perforation line. The paper is supplied fan-folded in a box which is placed under or to the rear of a pedestal supporting the printer and the paper feeds through the bottom or rear of the printer. Alternately, single sheets may be operator fed into the printer from the top in a manner similar to that used in a conventional typewriter. During single sheet paper feed, the plane of the paper enters the feed mechanism at an angle which is different than the angle of entry when continuous feed is used. In prior printers, the paper drive mechanism generally consists of a motor driven platen with a plurality of guide rollers spring biased against the platen. The guide rollers are positioned along the path of the paper through the printer. As the paper is initially fed manually into the mechanism, the leading edge of the paper passes between the platen and the rollers. Paper advance is then solely dependent upon frictional drive from the platen. The initial angle which the plane of the paper makes with respect to a tangent to the surface of the platen at the point of initial contact is dependent on the mode of paper feed. It has been found that the reliability of initial paper feed varies with this angle. Prior drive mechanisms optimized for feed from the rear of the printer will often exhibit erratic feed when paper is fed from the top of the printer with the converse also being true.
[0003] The hereinafter described embodiment provides a paper drive mechanism for a printer which exhibits reliable paper feed for all paper widths which the printer will accommodate regardless of the mode of paper entry.
SUMMARY OF THE INVENTION
[0004] In accordance with this invention, a printer, including a rotatably driven platen, is provided with a mechanism for advancing paper sheets through the printer. An entrance axle has firmly affixed thereto an entrance roller. The entrance axle is biased toward the platen with the entrance roller positioned in the path of the paper through the printer. A drive roller is affixed to the entrance axle and biased along with the entrance roller toward the surface of the platen. The drive roller serves to rotatably drive the entrance roller through the entrance axle. The drive roller is positioned out of the path of the maximum width paper which the printer will accommodate so that for all paper widths the paper will be advanced through the printer by the platen and the entrance roller, which is driven by the platen through the entrance axle and by the drive roller which is maintained in frictional driving contact with the platen.
[0005] An additional aspect of this invention is that the entrance axle is supported by a pair of spaced pivotably supported support arms. Means are included for biasing the arms about their pivots so as to urge the entrance and drive rollers toward the platen. Means are additionally included for selectively positioning the ends of the pair of support arms away from the platen and against the bias of the biasing means. Further, the ends of the entrance roller axle are rotatably journaled in a pair of elongated rocker arms each of which is rotatably fixed to one of the support arms for rotational movement with respect thereto. An exit axle is rotatably supported by the remaining ends of the rocker arms. The exit axle carries at least one exit .roller for directing the paper to the print station of the printer. More particularly, a positioning means in the form of a shaft having at least one elongated flattened surface is located adjacent the pair of support arms so that when the shaft is rotated, one longitudinal edge of the flattened surface will move the entrance axle away from the platen.
THE DRAWINGS
[0006]
FIG. 1 is a top plan view of a portion of a printer embodying certain features of this invention.
FIG. 2 is an enlarged sectional view taken along the line 2-2 of FIG. 1, and illustrating alternate modes of paper feed.
DETAILED DESCRIPTION
[0007] In FIG. 1, a portion of a printer 8 is illustrated which includes a print mechanism 10 establishing a print station 12 and a pair of paper drive assemblies 14 and 16 cooperating with a platen 18 for driving paper 17 or 19 through the print station 12. The print mechanism 10 includes a print head carriage 20 traversing the paper 17, 19 at the print station 12. For a more detailed description of the carriage 20 and its associated drive mechanism, reference is made to U. S. Patent No. 4,134,695 issued to M. E. Randolph on January 16, 1979 and entitled "Printer Carriage". The printer carriage 20 carries a matrix wire print head 24 which prints alpha-numeric indicia on the paper 17, 19 in accordance with incoming signal commands as the carriage 20 traverses the paper 17, 19. A suitable matrix print head 24 is described in U. S. Patent No. 3,973,661 issued to J. L. DeBoo et al. on August 10, 1976 and entitled "Wire-Matrix Printers, and Electromagnetic Actuator Mechanisms Useful In Such Printers" and in U. S. Patent No. 3,982,622 issued to J. A. Bellino et al. on September 28, 1976 and entitled "Actuator Mechanism For Wire Matrix Printers".
[0008] The printer 8 includes a rectangular paper tray 26 which is concave at one end (FIG. 2) to accommodate the curvature of the platen 18. Serving to guide the paper during the single sheet mode is a paper guide 27. The frame of the printer 8 includes an upwardly projecting wall 28 having four spaced slots 30, 32, 34 and 36 for receiving four drive roller support arms 38, 40, 42 and 44. Each of the support arms 38, 40, 42 and 44 has a notch which seats in its respective slot thus restricting lateral movement of the support arms. The upwardly disposed edge of each slot 30; 32, 34 and 36 serves as a fulcrum for the support arms 38, 40, 42, 44 seated therein. The wall 28 has two right angle bends 46 and 48 and located at the bend 48 are four spaced holes each receiving one end of a coil spring 50, 52 54 and 56. The remaining end of each coil spring 50, 52, 54, 56 is hooked over one end of its respective support arm 38, 40, 42, 44 and biases the support arm in a counter-clockwise direction as viewed in FIG. 2. A drive roller release 60 includes a rod 62 having a square cross-section throughout that portion adjacent the support arms 38, 40, 42 and 44 and the rod is round in cross-section at its ends and center. The ends of the rod are journaled in circular openings defined by end plates 64 and 66 with one end of the rod 62 having secured thereto a lever 68 which facilitates manual rotation of the rod 62. The center of the rod 62 rests against a ledge 70 mounted to the wall 28.
[0009] The support arms 38, 40, 42 and 44 are associated in pairs 38-40 and 42-44. Since the paper drive assemblies 14 and 16 are similarly constructed, only one will be considered in detail with similar components of the remaining assembly designated with the same reference numeral and the subscript "a". The paper drive assembly 16 includes right and left rocker arms 72 and 74. The center of each of the rocker arms 72, 74 is mounted to the end of its respective support arm 42, 44 and freely pivots with respect thereto. Each end of each of the rocker arms 72, 74 is enlarged and defines a circular opening. Rotating within the openings defined by the ends of the rocker arms 72, 74 is an exit roller axle 76 carrying three exit rollers 78, 80, 82 which, under bias, serve to force the paper against the platen 18 as the paper 17, 19 passes through the print station 12. Rotatably journaled into the holes defined by the opposite ends of the rocker arms 72, 74 is an entrance roller axle 86 carrying two entrance rollers 88 and 90, secured to and rotatable with the axle 86.
[0010] As illustrated, the entrance rollers 88 and 90 are slightly larger in diameter than the exit rollers thus providing a relatively large frictional drive coefficient with the paper 19. The entrance roller axle 86 extends beyond the rocker arm as at 92 and outside of the path of the maximum width paper 17, 19 the printer will accommodate as the paper passes through the printer 8. The axle extension 92 has fixed thereto a drive roller 94 constructed of suitable material having a high frictional coefficient with the surface of the platen 18. It should be noted that the drive roller 94 is positioned completely out of the path of the maximum paper width the printer will accommodate so that for all paper widths, the drive roller 94 will be in continuous contact with the platen 18 thus maintaining continuous drive of the entrance rollers 88 and 90 through the axle 86 for all paper widths. The entrance rollers 88 and 90 on the entrance axle 86 will rotate with the drive roller 94 so that the paper is continuously driven not only by the platen 18 but also by the entry rollers 88 and 90. Due to a loose fit at the pivoted supports of the rocker arms 72, 74 to the support arms 42, 44 as well as the relatively loose fit between the entry and exit axles, 76, 86 and the rocker arms 42, 44, the entire roller assembly has a large degree of positional freedom and adjusts to the contour of the platen. This feature assures positive contact of the drive roller 94 with the platen and the entrance rollers 88 and 90 with the paper. As illustrated, the axle 86 supporting the entrance rollers is greater in diameter and heavier than the exit axle 76. Thus, when the platen 18 is removed from the printer 8 for servicing, the rocker arm 72, 74 will rest with the axle extensions 92 abutting the upper edge of the support arm 74. This rest position of the assembly 16 facilitates reinstalla- tion of the platen since the drive assmebly 16 will rest in approximately its assembled position. Further, when the rod 62 is rotated, the support arms 42, 44 move away from the platen withdrawing the rollers 88, 90, 94, 78, 80 and 82 from the platen 18. Due to the weight of the entrance axle 86, the rocker arms pivot about their supports and the exit rollers 78, 80 and 82 rest against the platen. This arrangement assures that the assembly 16 will not interfere with the movement of the carriage 20.
- Operation -
[0011] For purposes of discussion it is assumed that the selected mode of paper entry is along the paper tray as shown by the directional arrow 96. The paper 17 is placed on the tray 26 and manually pushed toward the platen 18 until the edge of the paper 17 strikes the rotating platen 18 and entrance rollers 88 and 90. As the entrance rollers 88 and 90 ride upon the paper 17, prior mechanisms often experience erratic paper feed since the frictional coefficient between the paper 17 and platen 18, which is the main force advancing the paper, is insufficient to achieve reliable paper feed. To improve paper advance during initial paper insertion, the entrance axle 86 as previously mentioned, extends beyond the rocker arm 74 well out of the path of the maximum width paper the printer will accommodate so that the drive roller 94 is always maintained in continuous driving engagement with the platen 18 throughout the paper feed process for all usable paper widths. Thus, when the entrance rollers 88 and 90 are lifted from the platen 18 by the paper 17 they are driven by the drive roller 94 and thus the paper 17 is continuously driven by both the platen 18 and the entrance rollers 88 and 90.
[0012] Alternately, a single sheet of paper 19 may be inserted from the top of the printer 8 along the guide 27 with the leading edge of the paper 19 sliding down the guide 27 in the direction of the arrow 98 and engaging the platen 18 and the entrance rollers 88 and 90. The driving force of the platen 18 on the paper 19 is greater with this mode of entry since the plane of:the paper 19 is approximately along a tangent to the platen 18 at the point of contact therewith. As the paper 19 advances, both the rotating platen 18 and the driven entrance rollers 88 and 90 drive the paper 19. Reliable paper drive for all paper widths is assured in either paper mode selected since both the platen 18 and the-entrance rollers 88, 90 continuously drive the paper 19.
[0013] Once the paper 17 or 19 is fed about the platen 18, the operator may desire to align the paper 17 or 19 at the print station 12. To accomplish this, the operator rotates the handle 16.clockwise in the direction of the arrows 100 of FIG. 2 thus rotating the shaft 62 causing the support arms 38, 40, 42, 44 to deflect downwardly as they ride along the edge of the shaft 62. As the arms 38, 40, 42, 44 move downwardly, the frictional coefficient between the paper 17 or 19 and the drive assembly rollers and the platen is reduced thus allowing convenient manual rep6sitioning of the paper 17 or 19 at the print station 12. Additionally, the weight of the entrance axle 86 pivots the arms 72, 74 so that the rollers 78, 80 and 82 loosely rest against the platen out of the path of the carriage 20. After the paper is repositioned, the handle 68 is returned to its original location and the rollers 78, 80, 82, 88 and 90 again rest against the paper.
CHARACTERIZED IN THAT:
a drive roller (94) is rigidly affixed to said entrance axle (86) and biased along with said entrance roller (88, 90) toward the surface of said platen (18), said drive roller (94) serving to rotatably drive said entrance roller (88, 90) through said entrance axle (86), said drive roller (94) being positioned completely out of the path of the maximum width paper which the printer (8) will accommodate so that for all paper widths the paper will be advanced through the printer by the platen(18)and the entrance roller(88) which is driven by the platen (18) through the drive roller (94) the drive roller (94) being maintained in frictional driving contact with the platen (18) throughout paper advance.
CHARACTERIZED IN THAT:
said entrance axle (86) is positioned by a pair of spaced pivotably mounted support arms (42, 44) and means for biasing said support arms (42, 44) about their pivots so as to urge said entrance and drive roller (88) toward said platen.
CHARACTERIZED IN THAT:
means (62, 68) are included for selectively positioning the ends of said pair of support arms (42, 44) positioning said entrance axle (86) away from the platen (18) and against the force of said biasing means.
CHARACTERIZED IN THAT:
each of the ends of said entrance axle (86) are rotatably journaled in one end of a pair of elongated rocker arms (72, 74) each of which is rotatably fixed to one of said pair of support arms (42, 44)for rotational movement with respect thereto, and an exit axle (76) the ends of which are rotatably supported by the remaining ends of said rocker arms (72, 74); said exit axle (76) carrying at least one exit roller (78, 80, 82) for directing the paper to the print station (12) of the printer (8).
CHARACTERIZED IN THAT:
said positioning means is a shaft (62) having at least one elongated flattened surface located adjacent each of said pair of support arms (42, 44) so that when shaft (62) is rotated one longitudinal edge of said flattened surface will move said entrance axle (86) away from the platen (18).
CHARACTERIZED IN THAT:
said entrance axle (86) is heavier than said exit axle (76 )so that the weight of said entrance axle (86) will bias said exit axle (76) toward said platen.
CHARACTERIZED IN THAT:
each of the ends of said entrance axle (86) are rotatably journaled in one end of a pair of elongated rocker arms (72, 74)each of which is rotatably fixed to one of said pair of support arms (42, 44) for rotational movement with respect thereto, and an exit axle (76) the ends of which are rotatably supported by the remaining ends of said rocker arms (72, 74); said exit axle (76) carries at least one exit roller (80) for directing the paper to the print station (12) of the printer (8).
CHARACTERIZED IN THAT:
means are provided for rotationally biasing the end of said rocker arms (72, 74)supporting said exit axle (76) toward said platen (18).
CHARACTERIZED IN THAT:
said rotational biasing means is provided by the weight of said entrance axle (86) which is greater than the weight of said exit axle (76).
CHARACTERIZED IN THAT:
said means for selectively positioning said pair of support arms includes a shaft (62) displaying a rectangular cross-section and a handle (68) secured to one end of the shaft (62) for manual rotation thereof so that when said shaft (62) is rotated one edge of the shaft (62)serves to move said support arms (42, 44) away from said platen (18) against said biasing means (54, 56).