Torque limiter and sheet separating device having a torque limiter   

This application claims the benefit of U.S. provisional patent application Ser. No. 61/076,838, filed on Jun. 30, 2008, entitled “Torque Limiter And Sheet Separating Device Having A Torque Limiter”.

The invention is related to sheet feeding and separation devices and, more particularly, to a torque limiter and a sheet separating device including a torque limiter.

In general, automatic sheet feeding devices engage and remove sheets of paper or other media from a stack and feed the sheets along a path to, for example, a printing zone, copying zone, scanning zone, or the like. Such feeding assemblies must be able to quickly and efficiently feed each individual sheet in a queue (e.g., a sheet media tray) to the printing, copying or scanning zone without creating a backlog and without jamming. This is particularly important where the sheets to be fed are original documents, e.g., photos, to be copied or scanned and cannot risk being damaged.

Typically, during operation, a sheet picker such as, for example, a roller having an outer surface formed of a high friction material, may engage and remove the uppermost sheet from a stack and feed the sheet along a feed path toward a sheet separator positioned downstream. In the event that multiple sheets are inadvertently picked by the sheet picker and fed along the feed path, the sheet separator may be designed to separate the multiple sheets from one another and thereby ensure that only one sheet is passed along the feed path to the printing zone, copying zone, scanning zone, or the like.

Known sheet separators, however, typically use complex and cumbersome clutch mechanisms such as, for example, spring disk clutches, wire wrap clutches, viscous clutches, or magnetic hysteresis clutches. Although generally effective, each of these clutch mechanisms can be large, expensive, and/or unreliable due to the complexity and number of required parts and can, therefore, be prohibitive in terms of developing and manufacturing compact and/or inexpensive consumer devices such as automatic photo feeders/scanners.

SUMMARY

In an embodiment of the invention, a torque limiter may include a first member configured to rotate about a first axis and having a first contact surface. The torque limiter may include a second member configured to rotate about the first axis and including a first axially extending finger. The first finger may be radially biased so that a second contact surface defined by the first finger may contact the first contact surface with a normal force to define a predetermined torque value between the first and second members. When one of the first and second members is rotatably driven in a first rotational direction, the other of the first and second members may be rotatably driven in the first rotational direction unless a torque load greater than or equal to the predetermined torque value is applied to the other of the first and second members.

Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention will be apparent from the following, more particular description of embodiments of the invention, as illustrated in the accompanying drawings wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. Unless otherwise indicated, the accompanying drawing figures are not to scale.

FIG. 1 depicts an end view of a sheet separating device along a sheet path according to an embodiment of the invention, a torque limiter of the sheet separating device being shown in partial cross-section;

FIG. 2 depicts a cross-sectional view of the torque limiter of the sheet separating device according to the embodiment shown in FIG. 1;

FIG. 3 depicts a schematic and illustrative side view of the sheet separating device in a first state according to the embodiment shown in FIG. 1;

FIG. 4 depicts a schematic and illustrative side view of the sheet separating device in a second state according to the embodiment shown in FIG. 1;

FIG. 5 depicts a schematic and illustrative side view of the sheet separating device in a third state according to the embodiment shown in FIG. 1; and

FIG. 6 depicts a graph showing a relationship between roller normal force and clutch torque in a sheet separating device according to an embodiment of the invention.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below. While specific embodiments are discussed, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected and it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations can be used without parting from the spirit and scope of the invention. Each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.

In the following description of some embodiments of the invention, directional words such as, for example, “top,” “bottom,” “left,” “right,” “upwardly,” and “downwardly,” “clockwise,” “counter-clockwise,” are employed by way of description and not limitation with respect to the orientation of the device and its various components as illustrated in the drawings.

FIG. 1 depicts an end view of a sheet separating device 1 along a sheet path according to an embodiment of the invention. The sheet separating device 1 may be, for example, disposed downstream of a queue or media tray (not shown) configured to hold a stack of sheets and from which sheets can be individually picked by a sheet picker (not shown). The sheet separating device 1 may also be, for example, disposed upstream of a printing zone, copying zone, scanning zone, or the like (not shown) to which the sheets are fed. The sheet separating device 1 may include an advancing (separating) roller assembly 10 which may include a roller body 12 rigidly coupled to, or mounted on, a shaft 16. A friction member or surface 14 may be disposed on the outer periphery of the roller body 12 to contact and grip a sheet picked from the stack of sheets and received in the sheet separating device 1. The advancing roller assembly 10 may be rotatably driven about an axis in a first rotational direction by a driving device 40.

As shown in the embodiment depicted in FIG. 1, the sheet separating device 1 may also include a reversing (counter-rotating) roller assembly 20 positioned adjacent to the advancing roller assembly 10 to define a nip N therebetween. The reversing roller assembly 20 may include a roller body 22. A friction member or surface 24 may be disposed on the outer periphery of the roller body 22 to contact and grip a sheet picked from the stack of sheets and received in the nip N of the sheet separating device 1. The reversing roller assembly 20 may be linearly biased against the advancing roller assembly 10 across the nip N by a normal force F which may be, for example, generated by any number of biasing devices such as, for example but not limited to, extension springs (not shown) coupled to the reversing roller assembly 20. In another embodiment, the advancing roller assembly 10 may be biased against the reversing roller assembly 20, or both roller bodies 12, 22 may be biased against one another. The reversing roller assembly 20 may be rotatably driven about an axis in the first rotational direction by the driving device 40, for example, via a gear arrangement 42. A torque limiter 30 such as, for example, a drag clutch mechanism, may be operatively disposed between the driving device 40 and the roller body 22 to allow bi-directional rotation of the roller body 22 depending on a condition at the nip N as discussed in further detail below.

As shown in the embodiment depicted in FIG. 1, the torque limiter 30 may operatively couple a first shaft portion 26 to a second shaft portion 28. The roller body 22 may be rigidly coupled to or mounted on the first shaft portion 26 and the second shaft portion 28 may be coupled to the driving device 40, for example, via gear arrangement 42. Referring to the embodiment depicted in FIGS. 1 and 2, the torque limiter 30 may include a first member 31 such as, for example, a hollow sleeve having an cylindrical or annular inner contact surface 32 which defines an interior volume or cavity 33. The torque limiter 30 may also include a second member 34 received in the cavity 33 and having, for example, a pair of axially extending fingers 36, 38 spaced from one another radially. A radially-oriented biasing member 39 such as, for example but not limited to, a coiled compression spring, may be disposed between the fingers 36, 38 and may function to bias the fingers 36, 38 radially outward. The fingers 36, 38 may have outer contact surfaces which contact the inner annular contact surface 32 of the first member 31 with a normal force to define a predetermined torque value between the first member 31 and the second member 34.

Although the embodiment shown in FIG. 1 depicts the first member 31 rigidly coupled to the second shaft portion 28 and the second member 34 rigidly coupled to the first shaft portion 26, the relative position of the first and second members 31, 34 could be reversed. That is, the first and second members 31, 34 could be rigidly coupled to the first and second shaft portions 26, 28, respectively. In another embodiment (not shown), the torque limiter 30 could be incorporated within the roller body 22 of the reversing roller assembly 20.

FIG. 3 depicts a schematic and illustrative side view of the sheet separating device 1 in a first state according to the embodiment shown in FIG. 1. In FIG. 3, the roller body 12 of the advancing roller assembly 10 may be rotatably driven in a first rotational direction (shown counter-clockwise). The second shaft portion 28 may also be rotatably driven in the counter-clockwise direction. When, as shown in FIG. 3, no sheet is disposed in the nip N between the roller bodies 12, 22, the torque load imparted to the roller body 22 by the roller body 12 through their respective outer frictional surfaces, 14 and 24 may override the predetermined torque value of the torque limiter 30 and, therefore, cause the roller body 22 to rotate clockwise, i.e., in the same linear direction as the roller body 12 at the nip N. In this case, referring back to FIGS. 1 and 2, the first and second members 31, 34 of the torque limiter 30 may slip relative to one another and rotate in opposite directions.

FIG. 4 depicts a schematic and illustrative side view of the sheet separating device 1 in a second state according to the embodiment shown in FIG. 1. Similar to the first state shown in FIG. 3, in FIG. 4, the roller body 12 and the second shaft portion 28 may be rotatably driven in a counter-clockwise direction. When, as shown in FIG. 4, a single sheet S is disposed in the nip N between the roller bodies 12, 22, the torque load imparted to the roller body 22 by the roller body 12 through the sheet S may override the predetermined torque value of the torque limiter 30 and, therefore, cause the roller body 22 to rotate clockwise, i.e., in the same linear direction as the roller body 12 at the nip N, to advance the sheet along a feed path to the printing zone, copying zone, scanning zone or the like (not shown). In this case, again referring back to FIGS. 1 and 2, the first and second members 31, 34 of the torque limiter 30 may slip relative to one another and rotate in opposite directions.

FIG. 5 depicts a schematic and illustrative side view of the sheet separating device in a third state according to the embodiment shown in FIG. 1. In FIG. 5, the roller body 12 and the second shaft portion 28 may be rotatably driven in a counter-clockwise direction. When, as shown in FIG. 5, multiple sheets S1, S2 are picked and received in the nip N between the roller bodies 12, 22, the torque load imparted to the roller body 22 by the roller body 12 through the sheets S1, S2 may not be sufficient to override the predetermined torque value of the torque limiter 30 due to the relatively small coefficient of friction μss between the sheets S1, S2. Therefore, the roller body 22 is driven via the torque limiter 30 to rotate counter-clockwise, i.e., in the opposite linear direction as the roller body 12 at the nip N, to return the sheet S2 to the media tray (not shown). In this case, again referring back to FIGS. 1 and 2, the first and second members 31, 34 of the torque limiter 30 may rotate together to rotatably drive the roller body 22.

From a general dynamics standpoint, assuming that the reversing roller does not slip against the sheet S, the following relationship must always be true:

(Minimum((Tr/Rr) or (μrs·N)))>(Minimum((Tcr/Rcr) or (μcrs·N)))>(μss·N) Where: Tr=Torque of the Advancing Roller Rr=Radius of the Advancing Roller μrs=coefficient of friction between the Advancing Roller and a sheet Tcr=Torque of the Reversing Roller Rcr=Radius of the Reversing Roller μcrs=coefficient of friction between the Reversing Roller and a sheet N=Normal force between the rollers μss=coefficient of friction between two sheets Therefore, for both rollers of a sheet separating device there may be two limiting conditions: either the sheet is slipping on the roller or it isn\'t. If the sheet is slipping, then the maximum drive force that the respective roller can impart is (μss·N). If the sheet does not slip on the roller, then it can be driven by the full torque (T/R) of the roller. The lesser of these two resultant forces will dominate. Thereafter, the force hierarchy must be such that the advancing roller drive force is greater than the reversing roller drive force which, in turn, is greater than the friction force between the sheets.

FIG. 6 depicts a graph showing a relationship between roller normal force and clutch torque in a sheet separating device 1 according to an example embodiment of the invention. As shown in FIG. 6, the clutch torque, or predetermined torque value of the torque limiter, is directly proportional to the normal force F (see FIG. 1) between the advancing and reversing rollers 12, 22 such that an increase in the clutch torque requires an increase in the range of normal force F, and vice versa. As discussed above with regard to the embodiment depicted in FIG. 1, one or more biasing members such as, e.g., extension springs, may be coupled to one or both of the advancing and reversing roller assemblies 10, 20, to provide the normal force F. This normal force F, the normal force generated by the biasing member 39 inside the torque limiter 30, and the materials used within the torque limiter 30, may be considered as a system so that the resulting values are well within the reliable operating range shown in the graph in FIG. 6.

In an embodiment of the invention, the first and second members 31, 34 of the torque limiter 30 may be formed from, for example, but not limited to, Lubricomp KFL-4034 (POM+20% GF+15% PTFE) and Lubricomp RL-4540 (Nylon 6/6+20% PTFE/Si), respectively. Other suitable plastic materials may also used to form the members of the torque limiter 30 and such materials may be chosen to ensure little wear over the life of the torque limiter 30.

The sheet separating device 1 with torque limiter 30 may offer, for example, the following advantages: relatively small radial/axial size, inexpensive, plastic on plastic contact, and/or bi-directional slipping. The sheet separating device 1 may be incorporated into, for example, consumer electronics products such as, for example, but not limited to, an automatic photo feeder, to ensure effective and efficient separation of multi-picks.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described embodiments, but should instead be defined only in accordance with the following claims and their equivalents.