Retard assembly for use in a separator feeder

Abstract: A retard assembly (20) for use in a friction retard separator feeder has a retard member (22), a support member (21) for supporting the retard member, the retard assembly being mountingly engageable with a pivoting support frame (36) for supporting the retard assembly at a first end (37) of the pivot support frame and having a pivot point (48) at an opposing end which is substantially remote from the first end. The support member has at least one mounting hub (50) as seen in Fig. 4A for mounting a locating pivot pin (41). Opposite ends of the pivot pin is engaged with the first end of the pivoting support frame. The support member includes at least one energy absorbing damping pad (60) on the at least one mounting hub to absorb vibration of the retard pad between the support member and the pivoting support frame. The energy absorbing damping pad has a hardness sufficient to maintain an interference fit between the at least one mounting hub and the pivoting support frame and to resist a permanent set. The retard member having a friction retard surface layer (25) and a vibration absorption layer (26) between the friction retard surface layer and the support member (21), so that a sheet entrance guide (28) is vertically compliant.

Description: The present invention relates generally to a retard member for use in a friction retard sheet separator feeder. The development of electrostatographic printing machines has brought about the need for simple, yet reliable, sheet separator feeder apparatus capable of handling sheets varying in length, thickness, weight and surface conditions. One of the more common arrangements involves friction retard feeders wherein separation and feeding is dependent upon a differential friction principle. In one such type of feeder, a feed roller surface has a relatively high coefficient of friction with paper while the retarding surface which may also be a roller driven in the opposite direction or alternatively a stationary pad having a coefficient of friction with paper less than that of the feed roller, but greater than that between two successive sheets of paper. In these feeders, the coefficient of friction of the feed roller with the paper must exceed the coefficient of friction of the retard member which must always exceed that of the coefficient of friction between two sheets of paper. In these separator feeders the region of contact between the retarding member and the feed roll forms a sheet queuing throat which is able to fan out or queue sheets in the throat for feeding single sheets through the throat. Figure 1 schematically illustrates a typical, prior art, sheet separator feeder apparatus capable of handling sheets varying in length, thickness, weight, and surface conditions which includes a sheet support platform 10 urged upwardly by spring 11 to advance sheets to be separated and fed to the friction retard nip formed between the retard member 12 and feed roll 13. The feed roller surface has a relatively high coefficient friction with the paper while the retard member has a lower coefficient of friction with the paper but its coefficient of friction with the paper is greater than the coefficient of friction between two successive sheets. This relationship and geometry enables the shingling or staggering of individual sheets into the nip between the feed roll and retard pad to the path defined by the sheet guide 15. Typically, the feed roll is made from a silicone rubber or other elastomer having a coefficient of friction greater than about 1.5. While capable of performing satisfactorily, there are problems associated with these types of feeders. One of the more common problems is feeding reliability, that is the feeding of single sheets only from the nip between the feed roller and the retard member rather than a multi-feed of from two up to perhaps six sheets. The multi-feed difficulty can be further appreciated with reference to Figure 2, wherein a friction retard sheet separator feeder is provided which has a rigid and fixed sheet entrance guide to guide sheets into the sheet retard nip area. The multi-sheet feed situation occurs in the entrance guide area A in advance of the retard nip area B by a slug, six or more sheets, entering the entrance guide area which become pinched between the entrance guide 14 and the feed wheel 13. Because the entrance guide is rigid and fixed, an additional normal force N is created between the entrance guide and the feed wheel, which creates an increased driving force to drive the slug through the retard nip creating a situation that overpowers the retard system's ability to frictionally separate the slug. In addition, lead edge damage from sheet stubbing is caused by the relatively large distance between the end of entrance guide area A and the entrance to the retard nip area B. While capable of performing in an acceptable manner this feeder frequently experiences misfeeds and multi-feeds as a result of big changes in the feed angle which result from small changes in the feed roll diameter or the retard pad thickness. Accordingly, it is desirable to provide a greater stability in the feed angle in this retard paper feeder to provide increased stability. US-A-5,163,668 describes a retard pad assembly with a movable compliant entrance guide which addresses these issues. One approach to improving the stability of the feed angle in the system described in US-A-5,163,668 is to relocate the pivot point of the retard pad assembly to a point quite remote from that illustrated, wherein the retard assembly is mounted in a frame which is pivotally mounted to a pivot point on the retard assembly and urged upwardly toward the front edge of the retard assembly against a separator feed roll by a spring. However, with the relocation of the pivot point from the retard assembly mount to a location which is quite remote, additional difficulties are frequently encountered, such as, the creation of highly objectionable noise, which resembles the scratching of chalk or a fingernail on a blackboard, between the retard member support member and the pivoting support frame. Since the friction retarding surface is typically an elastomer to be discussed in greater detail hereinafter, the frictional relationship between the elastomer and the paper tends to stretch the elastomer as the sheets of the paper are fed across the elastomer, until it reaches a limit at which time the coefficient of friction between the paper and the elastomer drops dramatically. If the coefficient of friction decreases with relative velocity, the stretching force will decrease below an equilibrium force when slippage occurs. This causes oscillation of the elastomer known as stick-slip. This oscillation excites the paper like a loudspeaker. One object of the present invention is to provide a retard assembly and a friction sheet separator feeder having high reliability of sheet feeding and, in particular, minimizes difficulties associated with noise during sheet separation. Accordingly, the present invention provides a retard assembly for use in a separator feeder including a support member supporting a retard member and mounting means for pivotally mounting the support member to a pivotal support frame, characterized in that the mounting means includes dampening means located between the support member and the pivotal support frame when they are engaged, said dampening means being of a hardness sufficient to maintain an interference fit between said mounting means and said pivotal support frame and to resist a permanent set. In one embodiment of the invention, a retard assembly for a separator feeder comprises a retard member, a support member for supporting said retard member, said retard assembly being mountingly engageable with a pivoting support frame for supporting said retard assembly at a first end of said pivot support frame, the pivoting support frame having a pivot point at one end which is substantially remote from said first end, said retard member support member having at least one mounting hub for mounting a locating pivot pin, said pivot pin being engageable with the first end of the pivoting support frame, said support member including at least one energy absorbing damping pad on said at least one mounting hub to absorb vibration of the retard member between the support member and the pivoting support frame when they are engaged, said energy absorbing damping pad being of a hardness sufficient to maintain an interference fit between said at least one mounting hub and said pivoting support frame to resist a permanent set. The present invention will be described further, by way of examples, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation in cross section of a prior art friction retard separator and feeder, Figure 2 is a schematic representation of a sheet separator feeder according to prior art practices, Figures 3A and 3B are front and rear isometric views of the retard assembly according to the present invention, Figures 4A and 4B are exploded isometric front and rear views of the retard assembly according to the present invention, Figure 5 is a sectional view illustrating the retard assembly according to the present invention mounted to the pivot support frame, and Figure 6 is a damping profile of a system wherein the coefficient of damping in Curve X is 0 and the coefficient of damping in Curve Y is greater than 0. With reference to Figures 3A, 3B, 4A, 4B and 5 the retard assembly 20 comprises a support member 21 which supports a retard member 22 comprising a top friction retarding surface layer 25 having a stable coefficient of friction and an intermediate vibration absorption layer 26. The vibration absorption layer 26 may be secured to the support member 21 by any suitable means, such as, with a conventional adhesive an example of which is an acrylic adhesive like the cyanoacrylote, Loctite 454®. The friction retarding surface layer 25 is secured to the vibration absorption layer in a similar fashion. The support member 21 also supports a sheet entrance guide 28 which has a surface with a low coefficient of friction and has a substantially vertical portion 29 (Fig. 3A and Fig. 4A) and a substantially horizontal portion 30 which overlies a portion 31 of the friction retard surface layer. The sheet entrance guide 28, which is normally urged upwardly by the vibration absorption layer 26 and the friction retarding surface layer 25 of the retard member 22, is vertically compliant and movable in the support member 21 by suitable mounting means such as tabs 32 on each side of the support member and cooperative mounting means such as coupling 33 having channels to enable the sheet entrance guide to move vertically on the tabs. There is a void between the vertical portion of the sheet entrance guide and the top friction retarding surface layer 25 and the intermediate vibration absorption layer with the void adjacent the vibration absorption layer being larger than that adjacent the retarding surface layer. This void enables the sheet entrance guide 28 to be vertically compliant as indicated by the bidirectional arrow, illustrated in Figure 5, and to also be somewhat flexible in a direction normal to the bidirectional arrow and facilitate a mode of operation which overcomes the multi-sheet feed problem noted above by replacing a high spring rate, fixed rigid guide of Figure 2, zone A, with a compliant movable guide having a low spring rate shown in Figure 5, zone A, which therefore reduces the magnitude of the normal drive force when a slug of sheets 16 enters the entrance guide area. When the slug of sheets force the compliant movable entrance guide down, there is no sudden increase in normal force. As a result, the drive force driving the sheets 16 into the retard nip, as indicated by arrow 18, is low and insufficient to drive the slug of sheets through the nip permitting the retard pad to shingle the sheets in the normal way. In this context by the term spring rate we intend to define the slope of a plot of applied force (y axis) versus displacement (x axis) force per unit of displacement as the spring rate with the fixed rigid entrance guide having a much higher spring rate than the compliant movable guide according to the invention. A significant consequence of the above structure is that the spring rate in the entrance guide area A of Figure 5 is approximately half the magnitude of the spring rate in the retard area B. The retard assembly 20 is mounted on a first end 37 of a pivoting support frame 36 (Fig. 5) which pivots at an end opposite the first end 37 about axis 48. The support member 21 has coaxial mounting hubs 50 with internal coincident passageways 40 for mounting a locating pivot pin 41 which has an axis 42 and a length so that it extends outside the support member hubs and engages the first end 37 of the pivoting support frame 36 at both sides thereof in a grooves (not shown) in the side arms 54 (Fig. 5) of the pivoting support frame. To secure the support member 21 to the pivoting support frame 36, a mounting clip 44 has a lip 46 which clips under the pivoting support frame 36 to hold the support member in place. Referring to Figure 5, the pivoting support frame 36, while it supports the support member 21 for the retard member 22 of the retard assembly 20 at the first end 37,pivots about axis 48 at the opposite end thereof, which is substantially remote from the first end 37. While this geometry has the effect of stabilizing the feed angle of the sheet separator/feeder, it introduces, as discussed above, a vibration and therefore a noise problem between the support member 21 and the pivoting support frame 36. To alleviate this vibration and noise difficulty, an energy absorbing damping pad 60 is mounted on each of the mounting hubs 50 on the support member 21 to maintain an interference fit between the mounting hubs 50 on the support member 21 and the pivoting support frame 36. Damping material is defined by those materials whereby the oscillations in the vibration are progressively reduced or suppressed more quickly than in a non-damping system. This is illustrated graphically in Figure 6 for both a system which has a 0 damping coefficient, Curve X, and a system which has a damping coefficient substantially greater than 0, Curve Y. To achieve the desired reduction in vibration and noise the damping pads are mounted on the mounting hubs to provide an interference fit with a pivoting support frame 36, when it is engaged with a pivoting support frame. As illustrated, this is achieved by providing a damping pad 60 which has an indent 62, generally circular, to mate with the mounting hub 50 and a rear surface 64 to provide the interference fit between the mounting hub and pivoting support frame. Accordingly, the energy absorbing damping pad should be of a hardness sufficient to maintain this interference fit and to resist a permanent set. There is a balance between a hardness and interference in that for harder materials there will be less interference in the fit between the two parts and all the more difficult to maintain the interference fit over time. Accordingly, depending on the geometry of the specific system, the balance between the hardness of the damping material and interference fit must be identified. In the system herein illustrated an interference fit of 1.25 mm ± .25 mm providing a total range of 1.0 to 1.50 mm, has been found to provide suitable dampening characteristics with a damping material having a durometer of from about 50 to about 60 and preferably 55 Shore A. Any suitable damping material may be selected based upon the above considerations. A preferred commercially available damping material is Isodamp C-1002® available from EAR Division of Cabot Corporation, Indianapolis, Indiana, which is believed to be a polyvinylchloride alloy based compound containing antimony trioxide and a small amount of plasticizer dispersing agent. We have found with this damping material that any vibrations or oscillations and any accompanying noise quickly disappear. The friction retarding surface is made from an ethylene propylene diene terpolymer rubber known as EPDM which provides a relatively stable coefficient of friction for the retarding surface and can be selected from those materials described in US-A-4,314,006. Such materials are commercially available from various suppliers such as Exxon Chemical Co., USA, under the trade designation Vistalon 2504-099®, and E.I. Dupont Company under the trade designation Nordell 1440®. It is preferred to cure the EPDM in a free radical crosslinking system comprising a free radical initiator. Exemplary of such a system is a peroxide curing system. Examples of free radical initiators are dicumyl peroxide, benzyl peroxide, and di-t-butyl peroxide. It is also preferred that the ethylene propylene diene terpolymer rubber (EPDM) be cured in a process in which the free radical crosslinking is carried out in the presence of a co-agent which is a reactive monomer itself and which adds to the polymer radical formed by the free radical initiator. This type of coagent promotes trimolecular crosslinking. Triallyl cyanurate and triallyl isocyanurate are examples of such coagents which promote trimolecular crosslinking, that is, which join three, rather than merely two, polymer chains together. When triallyl cyanurate or triallyl isocyanurate is used as the coagent, about 0.5 to 3 parts, and preferably about 2 to 2.5 parts, by weight of the coagent may be used per 100 parts of EPDM. The dicumyl peroxide free radical initiator is present in amounts of about 4 to 12 parts and preferably about 8 parts. In addition, for every 100 parts by weight of EPDM the composition may contain up to 80 parts, preferably 40 to 75 parts of various fillers and/or reinforcing agents such as silica and alumina. A lubricant such as zinc stearate may be present in amounts of from about 0.25 to two parts and preferably one part by weight. A processing aid such as zinc methacryate may be present in an amount of from 0.25 to 5 parts and preferably 1.5 parts by weight. Further 2.5 to 20 parts, preferably 5 to 10 parts, by weight of zinc oxide activator stabilizer are provided in a preferred composition. A colorant such as titanium dioxide is typically present in amounts of from 2 to 20 parts, preferably 5 to 8 parts, by weight and up to 50 parts, preferably about 5 to 10 parts of a plasticizer softener such as paraffinic oil, an example of which is Sunthene 4240 available from Sun Oil Company. Typically, the EPDM friction retarding surface layer has a tensile strength of at least 6.2x10 6 N/ m2 (900 pounds per square inch), an ultimate elongation of 200 per cent ± 50 per cent, a maximum compression set of 9 per cent, a tear strength of at least 65.5x10 4 N/ m2 (95 pounds per square inch), a Shore A Durometer of between 63 and 73 and a specific gravity between 1.19 and 2.25. The above described EPDM composition provides a stable and controllable coefficient of friction for the friction retarding surface layer and in particular one wherein the coefficient of friction is relatively stable at about 1.2 with nominal variation within plus or minus 0.2. In addition, the EPDM terpolymer is resistant to abrasion and surface cracking as well as being resistant to ozone attack and exposure to ultraviolet light. The vibration absorption layer is a closed cell polychloroprene foam which provides sufficient dampening to the retarding surface layer to reduce the noise otherwise generated from the stick slip phenomenon when feeding relatively heavy paper and transparencies. The polychloroprene foam supplies a spring rate or constant that allows the retard member to deflect at a steady rate without vibration. Further the polychoroprene foam tends to isolate any vibration in the retard member so that it is not transmitted to the frame. The polychoroprene is an elastomer made by the vulcanization of 2-chlorol-1,3-butadiene with metal oxides rather than sulfur. The 2 clorol-1,3-butadiene is prepared by the action of hydrogen chloride on monoviny-acetylene. The expanded polychloroprene has a uniform closed cell structure and is free from cracks or tears or other surface defects which will be detrimental to its function. The closed cell nature of the foam enables bonding at the surface of the foam to the mount and the surface layer without adhesive penetrating the surface to affect the properties of the foam. The foam may have a skin on all surfaces or each surface may be free from skin. When the skin is used it is of the same compound and vulcanized intricately with the cellular structure. The foam typically has an apparent density between 58 and 106 kg/m 2 (12 and 22 pounds per cubic foot), a compression force deflection of between 34.5 and 62.1x10 3 N/ m2 (5 and 9 pounds per square inch), a tensile strength of at least 483x10 3 N/ m2 (70 pounds per square inch), an ultimate elongation of at least 130 percent, a maximum compression set, after 24 hours at 23° C, of 25 percent and after 24 hours at 50° C, of 40 percent, and Shore 00 Durometer between 40 and 60. Such a polychloroprene foam enables control of the spring force at a steady rate in response to deflection by the force of the feed roll in the separating feeding nip. Typical commercially available materials includes the polychloroprene foam R-425-N® available from Rubatex Corp.; Bedford, Va. and 4219-N® available from American National Rubber Co., Huntington, W. VA. The retard member may be assembled in any suitable fashion. Typically the vibration absorption layer is glued to the support member with a suitable adhesive, such as the Loctite 454®, previously mentioned, when the support member is a plastic. Similarly, the EPDM friction retarding surface layer may be glued to the polychloroprene foam layer with the same adhesive. Particularly, satisfactory results in reducing the noise created by the stick slip phenomenon have been achieved with a retard member, wherein the vibration absorption layer is from about 4 to about 6 times as thick as the friction retarding surface layer. This provides a retard member having a sufficiently thick foam layer to absorb the vibration and thin enough to control deformation under load. Typically, the friction retarding surface layer is of the order of 0.75 to 1.0 millimeters thick and the vibration absorption layer is of the order of 3 to 6 millimeters thick. In a preferred embodiment the friction retarding surface layer is 0.85 millimeters thick and the vibration absorption layer is from 4 to 4.8 millimeters thick. Thus, a novel retard assembly 20, as well as a sheet separator feeder, has been described, delineating the advantageous effect of a greatly reduced, if not totally eliminated, noise created by the vibration of the support member and the pivoting frame. The noise level is reduced to a level at least acceptable to the human ear, if not completely eliminated. This is accomplished by providing energy absorbing damping pads between the support member and the pivoting support frame of a hardness sufficient to maintain an interference fit between the support frame and the pivoting support frame to resist a permanent set. Furthermore, the present retard assembly and sheet separating and feeding device solves the problem associated with multi-feeds or slug feeds in prior art devices through the use of a vibration absorption layer 26 and overlaying friction retarding surface 25 which are secured to the support member 21.

Claims: A retard assembly (20) for use in a separator feeder including a support member (21) supporting a retard member (22) and mounting means (50) for pivotally mounting the support member to a pivotal support frame (36), characterized in that the mounting means includes dampening means (60) located between the support member (21) and the pivotal support frame (36) when they are engaged, said dampening means being of a hardness sufficient to maintain an interference fit between said mounting means and said pivotal support frame and to resist a permanent set. A retard assembly as claimed in claim 1, wherein said retard assembly is mountingly engageable with the pivoting support frame (36) for supporting said retard assembly at a first end (37) of said pivot support frame, the pivoting support frame having a pivot point (48) at one end which is substantially remote from said first end (37), said retard member support member having at least one mounting hub (50) for mounting a locating pivot pin (41), said pivot pin being engageable with the first end of the pivoting support frame, said dampening means including at least one energy absorbing damping pad (60) on said at least one mounting hub (50) to absorb vibration of the retard member (22) between the support member (21) and the pivoting support frame (36) when they are engaged, said energy absorbing damping pad being of a hardness sufficient to maintain an interference fit between said at least one mounting hub and said pivoting support frame to resist a permanent set. A retard assembly as claimed in claim 2, wherein said pivot pin (41) is retainably engageable with mounting grooves on opposite sides of said first end (37) of the pivoting support frame. A retard assembly as claimed in claim 2 or 3, wherein said pivot pin (41) extends through said support member (21) perpendicular to a sheet feeding direction (18), wherein one mounting hub (50) is at each end of said support member, wherein the locating pivot pin (41) extends through said mounting hubs (50), wherein said energy absorbing damping pads (60) are mounted on said mounting hubs to provide said interference fit with said pivoting support frame (36) when engaged with said pivoting support frame. A retard assembly as claimed in claims 2 to 4, wherein the damping pad (60) provides an interference fit between the mounting hubs (50) and the pivoting support frame (36) of from about 1.0 to 1.50 mm. A retard assembly as claimed in claims 2 to 5, wherein the damping pad has a material with a Shore A durometer of from about 50 to 60. A retard assembly as claimed in any of claims 2 to 6, wherein the retard assembly further includes a sheet entrance guide (28) at the incoming end of the retard assembly having a substantially vertical portion (29) and a substantially horizontal portion (30) overlying a portion (31) of the retard member (22) in advance of a friction retard surface layer (25) of the retard member, said retard member having an intermediate vibration absorption layer (26) between said support member and said friction retard surface layer so that said sheet guide is vertically compliant and movable in said support member to enable reduction in the spring rate of the retard member. A friction retard sheet separator and feeder comprising a sheet support platform for supporting a stack of sheets, sheet feed means mounted for sheet feeding engagement with the top sheet of a stack of sheets when a stack of sheets is on said sheet support platform, characterized by a retard assembly as claimed in any one of claims 1 to 7 mounted for engagement with said sheet feed means to form a separating nip therebetween for separating any overlapped sheets from reaching the nip.

Inventors: BENTON RICHARD C, JOHNSTON DONALD E, WINSHIP BRUCE A, BENTON, RICHARD C., JOHNSTON, DONALD E., WINSHIP, BRUCE A.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1995
Main classification: B65H3
IPC codes: B65H3, G03G15