US3568812A - Holdback devices - Google Patents

Abstract

The specification describes a holdback device for controlling the flow of a web of paper in a high-speed line printer. The device prevents reverse movement of the web, for example when being printed upon, and allows forward movement of it. The backward movement - caused by the web being gripped between the rotating character shaft and the printing hammers - results in the misalignment of printed characters, and may even cause damage to the web. The devices described have a blade or pawl movably mounted in contact with the paper web, and pivotally bearing on a fixed surface. If reverse movement starts to take place the blade or pawl pivots on the fixed surface and grips the web between it and a drum contacting the other side of the web. The drum is free to move only in a sense such as to move the web in the forward direction and it is driven in this sense simultaneously with or immediately prior to movement of the web in the forward direction - when the printing of a line of characters has been completed thus aiding the unlocking of the blade or pawl.

Description

United States Patent Ronald John Frank Eitel Stoke-on-Trent, Staffordshire, England (c/o English Electric Computers, Ltd,

[72] inventor Kidsgrove, England) [21] Appl. No. 731,231 [22] Filed May 22, 1968 [45] Patented Mar. 9, 1971 [3 2] Priority May 24, 1967 [3 3] Great Britain [31 24059/67 [54] HOLDBACK DEVICES FOREIGN PATENTS 1,022,370 3/1966 GreatBritain Primary Examiner-Ernest T. Wright, Jr.

Assistant ExaminerStephen C. Pellegrino Attorneys-Misegades and Douglas, Keith Misegades and George R. Douglas, Jrl;

printing hammers results in the misalignment of printed characters, and may even cause damage to the web. The devices described have a blade or pawl movably mounted in contact with the paper web, and pivotally bearing on a fixed surface. If reverse movement starts to take place the blade or pawl pivots on the fixed surface and grips the web between it and a drum contacting the other side of the web. The drum is free to move only in a sense such as to move the web in the forward direction and it is driven in this sense simultaneously with or immediately prior to movement of the web in the forward direction when the printing of a line of characters has been completed thus aiding the unlocking of the blade or pawl.

HOLDBACK DEVICES This invention relates to holdback devices for controlling the flow of a paper web. I

Such devices find application in for example, high-speed line printers which print output data from digital data processing equipment.

Holdback devices prevent the reverse movement of the paper web due to the impulsive forces produced in the web when printing takes place, the paper web being momentarily gripped between a rotating character shaft and one or more printing hammers.

Alternative types of this device have been proposed. One, that described in British Pat. No. l,022,370,describes a loose cam one end of which engages the paper web at a position opposite the printing table. The other end of the cam bears against a fixed surface. Reverse movement of the web causes the cam to rotate against the fixed surface and clamp the web to the printing table.

The above proposal has a disadvantage which the present invention seeks to overcome, namely the cam having been locked onto the paper web by the action of printing needs to be unlocked to allow the paper web to be moved in the forward direction after printing. In earlier arrangements the paper traction devices have had to perform the unlocking action, and damage to the paper web has sometimes resulted.

According to a feature of the invention a holdback device for permitting movement of a web of paper in a forward direction and preventing reverse movement of the web includes a first member having an operative edge or surface in contact with one side of the paper web, and a reaction member having a reaction surface in contact with the side of the web opposite the operative edge or surface, the operative edge or surface being movable towards the reaction surface in response to a small reverse movement of the paper web whereby the paper web is gripped between the first and reaction members and is thereby prevented from substantial further reverse movement, and both the first member and the reaction member being movable to release the paper web subsequent to such gripping action so as to allow substantially unimpeded forward movement thereof.

Preferably the movement of the reaction member results in the reaction surface moving in the forward direction to release the paper web.

Preferably the reaction member is constrained to prevent movement of the reaction surface in the reverse direction.

According to another feature of theinvention a holdback device includes driving means for driving the reaction member so as to move the reaction surface in the forward direction.

Preferably the driving means is operable to commence the forward movement of the reaction surface a short time before the forward movement of the paper web'commences.

According to another feature of the invention a holdback device includes a reaction surface provided by an arcuate peripheral surface of a member movable about an axis aligned transversely of the paper web.

Preferably the said reaction member is cylindrical, having said axis through its center.

According to another feature of the invention the first member comprises a blade having an operative edge in contact with the paper web and further includes holding means, the holding means including a fixed surface against which the blade pivotally bears, the blade being movably supported to make an obtuse angle to the forward-direction of motion of the paper web so as to effect gripping and releasing of the paper web.

According to another feature of the invention the first member comprises a pawl having radiused opposed ends, one of which provides the operative surface and the other of which bears on a fixed surface generally parallel to the paper web, rocking of the pawl on the fixed surface providing for the gripping and releasing of the paper web.

Two alternative holdback devices according to the invention for incorporation in a high-speed line printer will now be described by way of example, with reference to the accompanying drawing, in which:

FIG. 1 shows in diagrammatic form a side elevation of the relevant parts of a line printer including one of the paper holdback devices;

FIG. 2 shows a vertical cross section of the holdback device shown in FIG. 1;

FIG. 3 shows a vertical cross section of the second holdback device; and

FIG. 4 shows graphs depicting to the base of time the speed of a rotatable drum constituting a part of each of the paper holdback devices and the associated paper web.

Referring to FIG. 1, the printer has an elongated character shaft 5 of which one end is seen. The shaft 5 carries lines of character types 6 which extend along its length, the lines of character types 6 being spaced circumferentially around the shaft 5. A printing ribbon 7 having a width as great as the length of the lines of type 6 is hung below the character shaft 5 and arranged to be wound by means not shown between two ribbon reels 7. A fixed platform 8 is mounted beneath the character shaft 5 and supports a paper web 9 on which printing is to be performed. The paper web 9 is fed from a container 10 by a driven sprocket wheel 11 through a paper reservoir device 12, beneath the character shaft 5, past a holdback device 13, which will be described in detail below, over a further driven sprocket wheel 14 to a container 15. The platform 8 has a central gap 16 through which a series of printing hammers 17 may be separately impulsed to press the paper web 9 against the types 6 on the character shaft 5, the ribbon 7 causing an impression of the character types 6 to be printed on the paper web 9. i

In operation, the paper web 9 is advanced in steps by the sprocket wheels 11 and 14 in the direction of the arrow A. During printing the shaft 5 is rotated continuously in the direction shown by arrow B, and at a given instant a line of particular character types 6 faces the operating ends of the hammers 17, so that selected hammers may be operated to print in line on the paper web 9 impressions of these particular character types 6.'When the shaft has rotated so as to present the next line of character types 6 to the paper web 9 selected other hammers 17 may be operated to print impressions of these further character types 6 on the paper web 9. This process continues until the complete line of characters has been printed. The paper web 9 is then stepped on in the forward direction by the sprocket wheels 11 and 14, the paper reservoir device 12 permitting high acceleration of the paper web 9.

When one or more of the hammers 17 are being operated to press the paper web 9 against the ribbon 7 and into contact with the rotating character shaft 5 there is a tendency for the paper web 9 to be carried in the reverse direction due to the rotation of the character shaft 5. Such reverse movement, if not prevented prevents the printing of a straight line of characters on the paper web 9. The holdback device 13 also reduces the settling time of the paper web 9 after forward movement of it. Torsional deflections in the sprocket wheel connecting shafts (not shown) set up oscillations in the paper web 9 along its length. The holdback device 13 by preventing reverse movement of the web 9 while allowing forward movement heavily damps these oscillations thereby reducing the time in which the web 9 comes to a rest. Such reverse movement is in fact inhibited by the holdback device 13 which extends across the width of the paper web 9 and which will now be described in detail with reference to FIG. 2.

A plurality of blades 23 are supported by pins 22 mounted in a support bar 21. Set in a rod 24 are springs 25 whose ends contact the blades 23 so as to urge the operative edges of the blades 23 into contact with the paper web 9. Opposite the operative edges of the blades 23 and an opening 27 extends across the width of the platform 8 and through this opening a rotatable drum 26 having a rough outer surface contacts the underside of the paper web 9.

The drum 26 is arranged for rotation only in the sense shown by arrow C so that in operation the paper web 9 is allowed to move freely in the forward direction. However, any movement of the paper web 9 in the reverse direction results in the operative edges of the blades 23 applying pressure to the paper web 9. Any further movement in the reverse direction therefore increases greatly the pressure exerted on the web 9 by the operative edges of the blades 23, substantially preventing further movement in the reverse direction.

The rotatable drum 26 is rotated by a motor 28 (FIG. 1), in the direction of the arrow C shortly before the paper web 9 is to be moved on by the sprocket wheels 11 and 14 after the printing of a line of characters, the rotation of the drum 26 being continued until the paper web 9 is moving. The rotation of the drum 26 urges the paper. web 9 at the region in contact with the blades 23 in a forward direction indicated by the arrowA thus over overcoming the tendency of the blades 23 to continue pressing onto the paper web 9 and so minimizing the instantaneous forces acting on the paper web 9 to accelerate it.

The drum 26 may be driven continuously while the paper web9 moves in the forward direction indicated by the arrow A, acting as a further drive means for the web 9.

Referring now to FIG. 3 which shows the second holdback device 30, this device includes an upper bar 33, mounted on a lower bar 34 which has a hole 41 passing through it, the upper bar 33 being substantially parallel to the paper web 9. The bar 34 is slotted at 39 to accommodate a plurality of spaced pawls 35. Each pawl 35 has radiused ends 36 and 37 and is of length greater than the perpendicular distance between the platform 8 and a lower surface 38 of the bar33. The pawl 35 is positioned by a tension spring 31 and surface 40 of the bar 34, with the end 36 in contact with the surfaces 38 and 40 and its end 37 resting on the paper web 9. The tension spring 31 passes through the hole 41 and is attached to a fixed member 32. Opposite the end 37 of the pawl 35 there extends across the width of platform 8 a gap 27 through which the outer surface of the rotatable drum 26 contacts the paper web 9.

As described above the drum 26 is free to rotate in the forward sense only so that in operation the paper web may move freely only in the forward direction indicated by the arrow A. However, movement of the paper web 9 in the reverse direction causes the ends 36 and 37 of the pawl 35 to roll on the surface 38 and the paper web 9 respectively so as to force the pawl towards pawl 35 towards an attitude perpendicular to the paper web 9. The rough outer surface of the drum 26 prevents the paper web 9 from slipping back under the end of the pawl 35. The tendency for the pawl 35 to roll greatly increases the reaction force exerted on the paper web 9 by the pawl 35 and increases the friction force acting on the paper web 9 to such an extent that further reverse movement of the paper web 9 is prevented. The rotatable drum 26 is rotated in the direction of the arrow C shortly before the paper web 9 is to be moved on in the forward direction indicated by the arrow A, the rotation of the drum 26 continuing until the paper web 9 is moving so that any tendency for the pawl 35 to continue to press onto the web 9, so causing large forces to act on the paper web 9 during its acceleration, is overcome. Again the drum 26 may be continuously driven while the paper web 9 is moved.

FIG. 4 shows in a diagrammatic form the relative speeds w and v at which the drum 26 is driven and the paper speeds w and v at which the drum 26 is driven and the paper web 9 is moved respectively, when the paper web 9 is moved on. It will be observed from the upper curve that the rotation of the drum 26 starts prior to the acceleration of the web 9 as shown in the lower curve. The time elapsed between the drum 26 starting to rotate and the paper web 9 being moved is adjusted such that it is sufficient for acceleration of drum 26 to cause the paper web 9 to be freed from the gripping means, i.e. the blades 23 or the pawls 35 before forward movement of the web 9 takes place.

The drum 26 may be free to rotate in the forward sense when not being driven in that sense; if such were the case the drum 26 would rotate for a period longer than that shown in the upper curve of FIG. 4, being caused to rotate by the paper web 9 as it passes the drum 26.

Though the paper holdback devices as described with reference to FIGS. 2 and 3 extend across the full width of the paper web 9 each paper holdback device may consist instead of a pluralityof separate units placed side-by-side across the width of the web 9.

It will be appreciated that other forms of a reaction member, while not as preferable, are possible; and that other types of movement of a reaction member may be used, c. g. the reaction member may move perpendicularly away from the web when forward movement of the web commences.

It will be appreciated also that while the drum 26 has been described as being driven by a motor to release the web 9 this may not necessarily be so; the drum 26 could be freely rotatable, being driven by the paper web 9, though this is not as advantag'eous.

Iclaim:

1. Paper-feeding apparatus including a planar bad for supporting a web of paper to be fed; means for feeding the web in one direction along the bed having a gap therein extending transverse to said one direction; a roller having an axis of rotation mounted in the gap with said axis extending parallel to said planar bed and transversely to said one direction such that a part of the surface of the roller lies in the plane of the bed; a member resiliently mounted relative to said roller such that the web may be fed freely between the member and the roller in said one direction and is gripped between the member and the roller by a wedging action acting substantially along a line parallel to said axis of rotation as a result of movement of the web in a second direction opposite to said one direction; means for rotating the roller about its axis to move said part of the surface of the roller in said one direction to facilitate the release of the web from the wedging action when the web is moved in said one direction aftermovement in the second direction.

2. Apparatus as claimed in Claim 1 wherein the rotating means is operative to rotate the roller intermittently, rotation of the roller being initiated immediately prior to feeding the web in said one direction and continued until the web is moving in said one direction.

Claims (2)

1. Paper-feeding apparatus including a planar bad for supporting a web of paper to be fed; means for feeding the web in one direction along the bed having a gap therein extending transverse to said one direction; a roller having an axis of rotation mounted in the gap with said axis extending parallel to said planar bed and transversely to said one direction such that a part of the surface of the roller lies in the plane of the bed; a member resiliently mounted relative to said roller such that the web may be fed freely between the member and the roller in said one direction and is gripped between the member and the roller by a wedging action acting substantially along a line parallel to said axis of rotation as a result of movement of the web in a second direction opposite to said one direction; means for rotating the roller about its axis to move said part of the surface of the roller in said one direction to facilitate the release of the web from the wedging action when the web is moved in said one direction after movement in the second direction.

2. Apparatus as claimed in Claim 1 wherein the rotating means is operative to rotate the roller intermittently, rotation of the roller being initiated immediately prior to feeding the web in said one direction and continued until the web is moving in said one direction.

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