TITLE OF THE INVENTION TORQUE TRANSFER SYSTEM AND METHOD OF USING THE SAME

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0001] The present invention relates to a torque transfer system and a method of using a torque transfer system, and particularly, to a torque transfer system having restart and a method of using a torque transfer system having restart. DISCUSSION OF THE RELATED ART

[0002] In general, rotational motion and torque can be transmitted between two rotating shafts using a magnetic coupling. The magnetic coupling allows for various operational modes. For example, using the magnetic coupling provides for transmitting the rotational motion and torque from a first shaft to a second shaft by gradual engagement of magnets and/or magnetic materials connected to the first and second shafts. This operational mode allows for the second shaft to come-up to the rotational speed and torque of the first shaft without an abrupt increase in speed and torque. Another example of an operational mode includes a safety mode that allows for the first and second shafts to slip with respect to one another to prevent an over-torque condition. This over-torque condition may be exemplified by a first shaft connected to a drive motor and the second shaft connected to a pump. Accordingly, if the pump becomes inoperable (i.e., internal binding or obstruction), then the ability for the first and second shafts to function in a slip-clutch mode will prevent the motor from becoming damaged. An example of the slip-clutch mode may be found in U.S. Publication No. 2006-0111191, which is hereby incorporated by reference. [0003] However, in gradual engagement mode, the magnets and/or magnetic materials connected to the first and second shafts must be moved from a disengaged position to an engaged coupling position. Accordingly, the movement from the disengage position to the engaged position requires both a mechanical system for the movement and a significant amount of time to achieve the engaged coupling position. [0.004] Moreover, once in the slip-clutch mode, the over-torque condition must be resolved (i.e., revert back to the normal operational torque transfer mode) before the relative rotation of the first and second shafts is resumed. Accordingly, the resumption

of the relative rotation of the first and second shafts may require a significant reduction in the rotational speed and torque of the first and second shafts to allow the magnets and/or magnetic materials to "re-couple" and continue the transmission of the rotational speed and torque. Thus, the performance of any device coupled to the driven shaft, i.e., pump or generator, must be reduced, if not completely turned-off. [0005] Furthermore, torque transfer systems may require a manual resetting process to accomplish the magnetic re-coupling after the over-torque condition is resolved. Accordingly, the resetting process requires additional time during which the system is not completely operational.

[0006] Based upon these various deficiencies, a system is required to provide an immediate and automatic magnetic recoupling between first and second rotational shafts once an over-torque condition exists that will not reduce the performance of any device connected to the driven shaft of the system.

SUMMARY OF THE INVENTION

[0007] Accordingly, the present invention is directed to a torque transfer system and a method of using a torque transfer system that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

[0008] An object of the present invention is to provide a torque transfer system capable of providing for an automatic immediate magnetic recoupling of magnets and/or magnetic materials connected to rotational shafts.

[0009] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. [0010] To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a torque transfer system includes a first housing formed of diamagnetic material, a first plurality of magnets disposed within the first housing along a circumferential direction of the first housing, a first rotational shaft connected to a first housing, a second housing formed of the diamagnetic material, a second plurality of magnets disposed within the second housing along a circumferential direction of the second housing, and a second rotational shaft

connected to a second housing, wherein first faces of the first and second housing are separated by a first gap such that each of the first plurality of magnets are disposed between each of the second plurality of magnets.

[0011] In another aspect, a method for transferring rotational motion and torque from a first rotational shaft to a second rotational shaft includes supplying a first rotational speed and torque to a first rotational shaft connected to a first housing, the first housing comprising diamagnetic material with a first plurality of magnets circumferentially disposed therein, and imparting the first rotational speed and torque to a second housing connected to a second rotational shaft, the second housing comprising the diamagnetic material with a second plurality of magnets circumferentially disposed therein. [0012] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: [0014] FIG. 1 is a perspective view of an exemplary torque transfer system according to the present invention;

[0015] FIG. 2 is an end view of an exemplary rotational member of FIG. 1 according to the present invention;

[0016] FIG. 3 is a cross-sectional view of the exemplary rotational member of FIG. 2 according to the present invention;

[0017] FIG. 4 is an overlapping end view of the exemplary rotational members according to the present invention;

[0018] FIG. 5 is a cross-sectional view of the exemplary rotational members of FIG. 4 along A-A according to the present invention;

[0019] FIG. 6 is a cross-sectional view of the exemplary rotational members of FIG. 4 along B-B according to the present invention.

[0020] FIG. 7 is a schematic view of a first exemplary operational mode of the torque transfer system;

[0021] FIG. 8 is a schematic view of a second exemplary operational mode of the torque transfer system;

[0022] FIG. 9 is a schematic view of a third exemplary operational mode of the torque transfer system;

[0023] FIG. 10 is a cross-sectional view of another exemplary torque transfer system according to the present invention;

[0024] FIG. 11 is a cross-sectional view of another exemplary torque transfer system according to the present invention; and

[0025] FIG. 12 is a cross-sectional view of another exemplary torque transfer system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0026] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. [0027] FIG. 1 is a perspective view of an exemplary torque transfer system according to the present invention. In FIG. 1, a torque transfer system may include first and second rotational members 100 and 200. The first rotational member 100 includes a rotational shaft 110 connected to a mounting plate 120 using a plurality of mounting brackets 113. Here, the rotational shaft 110, the mounting plate 120, and the mounting brackets 113 may be formed from non-magnetic material(s). Specifically, a first end portion of the rotational shaft 110 is connected to a central region of the mounting plate 120, and first side regions 115 of the mounting brackets 113 are connected to radial portions of the mounting plate 120 and second side regions 117 of the mounting brackets 113 are connected to the rotational shaft 110. Similarly, the second rotational member 200 may include substantially the same features of the first rotational member 100, such that detailed explanation is not provided for the sake of brevity. [0028] In FIG. 1, the first rotational member 100 further includes a backing plate 130, which may be made from magnetic material(s), such as steel, and a housing 140, which may be made from diamagnetic material(s), such as aluminum and copper. The backing plate 130 has an outer diameter 132 similar to an outer diameter 124 of the mounting plate 120, and includes an inner diameter 134. The housing 140 includes a first face 142a, a second face 142b, and a circumferential face 142c. The housing 140 further includes an outer diameter 144 that is greater than the outer diameters 124 and

132 of the mounting plate 120 and the backing plate 130. In addition, the housing 140 includes a plurality.of magnets 150 that are inserted into the housing 140 through the second face 142b, such that North magnetic orientations of each of the magnets 150 face outward toward the second rotational member 200.

[0029] The backing plate 130 is formed of a magnetic material in order to displace the North magnetic orientation fields of the magnets 150 closer to the first face of the housing of the second rotational member 200. Accordingly, by displacing the North magnetic orientation fields in both the housing 140 of the first rotational member 100 and the housing of the second rotational member 200, the combined repulsive magnetic forces may be increased.

[0030] In FIG. 1, the mounting plate 120, the backing plate 130, and the housing 140 are connected together using fasteners (not shown) that extend through holes 122 of the mounting plate 120 and holes 136 of the backing plate 130 and into the housing 140. Thus, the first and second rotational members 100 and 200 may be an assembled, as shown, such that the first faces of the first and second rotational members 100 and 200 are spaced apart from each other with the first and second rotational shafts 110 and 210 extending along opposing directions, although not necessarily parallel to each other, as will be explained further below.

[0031] FIG. 2 is an end view of an exemplary rotational member of FIG. 1 according to the present invention. In FIG. 2, each of the mounting brackets 113 are arranged to be disposed between each of the magnets 150. In addition, the inner diameter 134 of the backing plate 130 may correspond to an inner face 152 of the magnets 150, and the outer diameter 132 of the backing plate 130 may extend past an outer face 154 of the magnets. 150.

[0032] As shown in FIG. 2, the housing 140 includes magnet regions 140a and diamagnetic regions 140b. Here, a surface area of each of the diamagnetic regions 140b is dependent upon the geometry of the magnets 150, such that the diamagnetic regions 140b are greater than the magnet regions 140a.

[0033] FIG. 3 is a cross-sectional view of the exemplary rotational member of FIG. 2 along A-A according to the present invention. In FIG. 3, the housing 140 includes a circumferential recessed portion 146 that accommodates the outer diameter 132 of the backing plate 130 and the outer diameter 124 of the mounting plate 120. Although not

shown, a thin layer of relatively pliant non-magnetic material may be placed between the backing plate 130 and first faces 156 of the magnets 150 during assembly of the first rotational assembly 100. In addition, other thin layers of relatively pliant nonmagnetic material may be placed between the faces of the magnets 150 and recess/wall regions of the housing 140 where the magnets 150 may be positioned. Although assembly tolerances between each of the individual components of the first rotational member 100 is relatively high, the pliant non-magnetic material provides a cushioning effect due to the high magnetic forces involved during operation of the exemplary torque transfer system.

[0034] In FIG. 3, second face 158 of the magnets 150 are disposed within the housing 140 such that a first thickness Dl of the housing 140 is between the first face 142a of the housing 140 and the second side 158 of the magnets 150. In addition, the outer faces 154 of the magnets 150 are spaced apart from the circumferential face 142c of the housing 140 by a second thickness D2 of the housing 140. [0035] FIG. 4 is an overlapping end view of the exemplary rotational members according to the present invention. In FIG. 4, the first rotational member 100 is shown disposed behind the second rotational member 200. Specifically, the magnets 150 of the first rotational member 100 are shown behind (i.e., as hidden lines) the second rotational member 200, such that the magnets 150 are equally interdispersed between the magnets 250 of the second rotational member 200. Accordingly, the North magnetic orientations of the magnets 150 and 250 are directly facing each other. [0036] In FIG. 4, each of the magnets 150 and 250 are mutually aligned to the diamagnetic regions of the housings 240 and 140, respectively. As shown, each of the magnets 150 is equally spaced apart from each of the magnets 250. Accordingly, sides of each of the magnets 150 are circumferentially spaced from sides of the diamagnetic regions of the housing 240 and sides of each of the magnets 250 are circumferentially spaced from sides of the diamagnetic regions of the housing 140. [0037] FIG. 5 is a cross-sectional view of the exemplary rotational members of FIG. 4 along A-A according to the present invention. In FIG. 5, the first and second rotational members 100 and 200 are disposed such that the housings 140 and 240 face each other and the North magnetic orientations of the magnets 150 and 250 (in FIG. 4) face each

other in an offset manner. Thus, the magnets 150 impart a repelling magnetic force to the magnets 250 upon rotation of either of the housings 140 or 240. [0038] Specifically, with reference to FIG. 1, as the first housing 140 is rotated by the first rotational shaft 110, the combined repulsive magnetic forces between the magnets 140 and 240 impart rotation and torque to the second rotational shaft 210. However, as the rotational speed and torque supplied by the first rotational shaft 110 increases, the same rotational speed and torque may be supplied to the second rotational shaft 210, as long as the supplied torque is substantially less than the combined repulsive magnetic forces between the magnets 150 and 250. When the supplied torque is greater than the combined repulsive magnetic forces between the magnets 150 and 250, or when the delivered torque on the shaft 210 is greater than the combined repulsive magnetic forces between the magnets 150 and 250, then a slip (over-torque) condition will occur. Then, the magnets 150 and 250 will actually pass over each other until the supplied torque is reduced to less than about the combined repulsive magnetic forces between the magnets 150 and 250, or until the delivered torque on the shaft 210 is reduced to less than the combined repulsive magnetic forces between the magnets 150 and 250. [0039] In FIG. 4, the second surfaces of the magnets 150 and 250 are actually experiencing repulsive magnetic forces along a shear direction. Thus, some amount of axial repulsive magnetic force is generated along a direction parallel to the rotational shaft 110 and a direction parallel to the rotational shaft 210. However, during the moment of slip, the axial repulsive magnetic force lasts for a relatively small amount of time. Of course, during repeated slipping, the axial repulsive magnetic force may resemble periodic impulses along the directions parallel to the rotational shafts 110 and 210 so long as the torque exceeds the combined repulsive magnetic forces between the magnets 150 and 250.

[0040] Magnetic fields are produced by small atomic current loops created by the orbital motion of electrons within a material. In some materials, when an external magnetic field is applied, these current loops align in such a way as to oppose the applied field. Accordingly, somewhat analogous to Lenz's Law,- the induced magnetic fields tend to oppose the change that created them. Materials exhibiting this characteristic are classified as diamagnetic materials, of which aluminum and copper are exemplary members.

[0041] The present invention makes use of this characteristic by forming the housings of the torque transfer system using these diamagnetic materials. Thus, movement of the magnets 150 disposed within the first rotational member 100 moving (slipping) past the diamagnetic regions 240b of the second rotational member 200 results in the generation of directional forces between the moving magnets 150 and the diamagnetic regions 240b along a rotational direction of the first rotational member 100. Likewise, movement of the magnets 150 disposed within the first rotational member 100 moving (slipping) past the diamagnetic regions 240b of the second rotational member 200 also results in relative movement of the magnets 250 disposed within the second rotational member 200 past the diamagnetic regions 140b of the first rotational member 100. [0042] FIG. 5 is a cross-sectional view of the exemplary rotational members of FIG. 4 along A-A according to the present invention, and FIG. 6 is a cross-sectional view of the exemplary rotational members of FIG. 4 along B-B according to the present invention. In FIG. 5, diamagnetic opposition forces DMOl will be formed between the magnets 150 of the first rotational member 100 and the diamagnetic regions 240b of the housing 240 of the second rotational member 200 during the over-torque condition when the magnets 150 move past the diamagnetic regions 240b. Similarly, as shown in FIG. 6, diamagnetic opposition forces DMO2 will be formed between the magnets 250 of the second rotational member 200 and the diamagnetic regions 140b of the housing 140 of the first rotational member 100 during the over-torque condition when the magnets 250 move past the diamagnetic regions 140b.

[0043] As described above, and with reference to FIG. 1, when the over-torque condition, i.e., slip clutch mode, occurs, according to the present invention, then the driving torque of the first shaft 110 will exceed the combined repulsive magnetic forces between the magnets 150 and 250, thereby preventing the driving torque of the first shaft 110 from being transmitted to the second shaft 210 as a driven torque. This over- torque condition will cause the first shaft 110 to continue to rotate, and thus, create the diamagnetic opposition forces DMOl and DMO2 between the housings 140 and 240 and the magnets 250 and 150, respectively. Thus, the diamagnetic opposition forces DMOl and DMO2 will assist with automatic and immediate re-establishment of the synchronous rotation of the first and second rotational members 100 and 200 once the

over-torque condition is reduced to an amount less than the combined repulsive magnetic forces between the magnets 150 and 250.

[0044] FIG. 7 is a schematic view of a first exemplary operational mode of the torque transfer system. In FIG. 7, the magnets 1 are formed within the first housing (i.e., the housing 140 of FIG. 1) and the magnets 2 are formed within the second housing (i.e., the housing 240 of FIG. 1). Accordingly, a first torque Tl is transferred from a first shaft to a second shaft as a second torque T2 due to the magnetic repulsive forces between the magnets 1 and 2 of the first and second housings. Here, the first torque Tl is about equal to the second torque T2, and the rotation may be considered synchronous. Accordingly, the diamagnetic opposition forces DMOl and DMO2 between the first and second housing is at a relative minimum since the magnets 1 of che first housing and the magnets 2 of the second housing are rotating at substantially equal rotational velocities (i.e., synchronous rotation). Moreover, in the first exemplary operational mode, the magnets 1 and 2 remain in a mutually equal spaced relation to each other during this period. Thus, torque is efficiently transmitted between the first and second shafts. [0045] FIG. 8 is a schematic view of a second exemplary operational mode of the torque transfer system. In FIG. 8, at a second time period, the second torque T2 exceeds the first torque Tl, wherein the second torque T2 is greater than the combined magnetic repulsive forces between the magnets 1 and 2. Accordingly, the mutually equal spaced relation between the first and second magnets 1 and 2 is changed to one in which each of the second magnets 2 move closer to corresponding ones of the first magnets 1. However, during this second exemplary operational mode, the diamagnetic opposition forces DMOl and DMO2 between the first and second housings remain fairly low since the magnets 1 and 2 are not in a slip clutch mode. [0046] FIG. 9 is a schematic view of a third exemplary operational mode of the torque transfer system. In FIG. 9, at a third time period, a third torque T3 greater than the second torque T2 is transmitted along the second shaft such that the magnets 2 move

even closer to the magnets 1. Accordingly, the general relationship between each of the first, second, and third torques may be expressed as: T3> T2> Tl. Thus, the third torque T3 is greater than the combined repulsive magnetic forces between the first and second magnets 1 and 2.

[0047] However, during this third exemplary operational mode, the diamagnetic opposition forces DMOl and DMO2 between the first and second housings may increase slightly since the magnets 1 and 2 are moving closer together.

[0048] In FIG. 9, immediately after the third torque T3 exceeds the combined repulsive magnetic forces between the magnets 1 and 2, the magnets 2 actually move past (i.e., slip by) the magnets 1. Accordingly, this slip-clutch (over-torque) condition is created wherein the magnets 2 will continually slip past the magnets 1 , thereby increasing the diamagnetic opposition forces DMOl and DMO2 between the magnets and opposing housings. As the rotations of the housings continue, the diamagnetic opposition forces DMOl and DMO2 between the housings increases due to the interaction between the magnets 1 and 2 and the opposing housings. Specifically, the magnets 1 of the first housing impart diamagnetic opposition forces DMOl upon the diamagnetic regions of the second housing and the magnets 2 of the second housing impart diamagnetic opposition forces DMO2 upon the diamagnetic regions of the first housing. For example, as shown in FIG. 5, the magnets 150 of the first housing 140 impart diamagnetic opposition forces DMOl upon the diamagnetic regions of the second housing 240. Similarly, as shown in FIG. 6, the magnets 250 of the second housing 240 impart diamagnetic opposition forces DMO2 upon the diamagnetic regions of the first housing 140.

[0049] As the magnets 150 pass by the diamagnetic regions of the second housing 240, the diamagnetic opposition forces DMOl exert repulsive magnetic forces upon the diamagnetic regions of the second housing 240 along the rotational direction of the magnets 150. Accordingly, during the over-torque condition, the movement of the magnets 150 actually provides a "push" to the second housing 240 along the rotational direction of the magnets 150. Similarly, as the magnets 250 pass by the diamagnetic regions of the first housing 140, the diamagnetic opposition forces DMO2 exert repulsive magnetic forces upon the diamagnetic regions of the first housing 140 along

the rotational direction of the magnets 250. Accordingly, during the over-torque condition, the movement of the magnets 250 actually provides a "push" to the first housing 140 along the rotational direction of the magnets 250. Thus, according to the present invention, the over-torque condition actually contributes to immediately reestablishing the synchronous rotation of the first and second shafts.

[0050] This over-torque condition will continue until the third torque T3 becomes less than the combined magnetic repulsive forces between the magnets 1 and 2. When the third torque T3 becomes less than the combined magnetic repulsive forces between the magnets 1 and 2, then the magnets 2 will come to be positioned between the magnets 1 (either at the condition of T2 > Tl or at the condition of Tl = T2). Accordingly, both the first and second housings will return to synchronized rotation, or nearly synchronized rotation, and the relative rotation of the first and second housings may be considered restarted.

[0051] According to the present invention, torque may be transferred between the first and second shafts even when the first and second shafts are not disposed along a common rotational axis. For example, when coupling of a driver source and a driven component that may not be along a common linear axis, there exists a need to allow for angular off-axis alignment and still maintain constant torque transfer. Moreover, if the driver source and driven component are axially offset, i.e., the first and second shafts are parallel, the coupling must be able to compensate for the axial offset maintain constant torque transfer. Accordingly, the coupling must be able to perform at an angular off-axis alignment and at an axial offset, wherein the coupling must also allow for over-torque conditions and immediate re-establishment of synchronous rotation. [0052] FIG. 10 is a cross-sectional view of another exemplary torque transfer system according to the present invention. In FIG. 10, the first and second rotational members 100 and 200 may be angularly offset by an offset angle θ formed between opposing faces 142a and 242a of the first and second housings 140 and 240. As shown, the offset angle θ is also present between the axis of rotation ARl of the first rotational member 100 and the axis of rotation AR2 of the second rotational member 200. Here, the first and second rotational member 100 and 200 are shown in cross-section along A- A, as shown in FIG. 5, but may also be shown along B-B, as shown in FIG. 6.

Accordingly, the diamagnetic opposition forces DMOl and DMO2 will still be present during the over-torque condition. However, due to the offset angle θ, the diamagnetic opposition forces DMOl and DMO2 at a position where the distance between the opposing faces 142a and 242a are at a maximum may be less than the diamagnetic opposition forces DMOl and DMO2 at a position where the distance between the opposing faces 142a and 242a are at a minimum. As a result, the re-establishment of synchronous rotation of the first and second rotational members 100 and 200 may take a slightly greater amount of time than when the opposing faces 142a and 242a are parallel.

[0053] FIG. 11 is a cross-sectional view of another exemplary torque transfer system according to the present invention. In FIG. 11, the first and second rotational members 100 and 200 may be axially offset by an axial offset distance X between the first rotational axis RAl of the first rotational member 100 and the second rotational axis RA2 of the second rotational member 200. As shown, the axial offset distance X results in a relative shift of the first and second magnets 150 and 250 within the first and second housings 140 and 240. However, so long as the axial offset distance X does not result in the overlap of the first and second magnets 150 and 250, the torque may be transferred between the first and second rotational members 100 and 200, and still provide for accommodation of the over-torque condition and immediate synchronization. Here, the first and second rotational member 100 and 200 are shown in cross-section along A-A, as shown in FIG. 5, but may also be shown along B-B, as shown in FIG. 6. Accordingly, the diamagnetic opposition forces DMOl and DMO2 will still be present during the over-torque condition.

[0054] FIG. 12 is a cross-sectional view of another exemplary torque transfer system according to the present invention. In FIG. 12, the torque transfer system may include a combination of the angular offset θ, as shown in FIG. 10, and the axial offset, as shown in FIG. 11. Accordingly, both angular offset θ and the axial offset X may be accommodated to transfer torque between the first and second rotational members 100 and 200, and still provide immediate synchronous restart. [0055] According to the present invention, by making use of the diamagnetic characteristics of the housings, an automatic and immediate restart (or re- synchronization) will be established. Thus, there will be no need to provide

mechanisms to reposition the housings to gradually re-establish synchronous rotation, nor will there be a need to significantly reduce the rotation of the housings in order to re-establish synchronous rotation.

[0056] Although creation of the diamagnetic opposition forces also generates eddy currents, and thus, thermal energy within the housings, thermal management may not be necessary do to the high thermal conductivity of the diamagnetic materials. Moreover, by forming the housings to have a relatively large mass, heat dissipation may be relatively large, thereby preventing any physical damage to the housings due to melting. In addition, if desired, thermal management may be accomplished by any one of known temperature controlling means, or by modifying the housings to allow air to efficiently pass through the housings.

[0057] According to the present invention, temperature monitoring of the housings may be desired in order to monitor the operational parameters of the torque transfer system. Moreover, other systems may be implemented in order to maintain efficient transfer of rotational motion and torque in addition to the restart capabilities of the torque transfer system according to the present invention.

[0058] According to the present invention, although the drawings may show that the rotational shafts are substantially parallel, the rotational shaft may also be angularly offset such that the housings maintain a gap therebetween and still function to transfer rotational motion and torque. Moreover, the rotational shafts may be axially offset along a direction perpendicular to the shaft directions such that the housings maintain a gap therebetween and still function to transfer rotational motion and torque. Furthermore, according to the present invention, both angular and axially offset to function to transfer rotational motion and torque.

[0059] It will be apparent to those skilled in the art that various modifications and variations can be made in the torque transfer system having restart capabilities and the method of using a torque transfer system having restart capabilities of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.