GB2502040A

GB2502040A - Differential chuck with magnets

Info

Publication number: GB2502040A
Application number: GB1204582.9A
Authority: GB
Inventors: Keith Fordham
Original assignee: Ashe Controls Ltd
Current assignee: Ashe Controls Ltd
Priority date: 2012-03-15
Filing date: 2012-03-15
Publication date: 2013-11-20
Anticipated expiration: 2032-03-15
Also published as: GB2502040B; GB201204582D0

Abstract

A differential chuck 1 for supporting and driving a winding core 2 has an inner ring 3 for encircling a drive shaft and to which torque can be applied, in use, from a drive shaft, the inner ring having a first magnetic portion or magnet 19, an outer ring 5 encircling the inner ring 3 rotatable relative to the inner ring 3 and having a second magnetic portion or magnet 21 and a core engaging element or ball 9 for engaging, in use, an inner surface of the core 2, rotation of the outer ring 5 relative to the inner ring 3 causing the core-engaging element 9 to project or retract radially, and the first and second magnetic portions 19, 21 interacting to maintain the differential chuck either in an unprimed state or a primed state. The core-engaging element 9 in the unprimed state (fig. 7A) is able to retract further than the core-engaging element in the primed state (figs. 7B and 7C). Ramp 7 causes the core-engaging element 9 to project or retract radially. Magnets 19, 21 may repel one another to maintain the primed and unprimed states (figs. 7A, 7B and 7C).

Description

DIFFERENTIAL CHUCK

This invention relates to a differential chuck and a differential shaft for a winding apparatus suitable for carrying and driving a core onto which material is to be wound orrewound.

A sheet cutting, or slitting, and winding machine has a winding shaft or drive shaft that rotates to allow up-take of sheet material on to a spool or a winding core placed on the shaft. Once sufficient sheet material is wound around the core, the core is removed and a new core can be placed on the shaft A plurality of differential chucks or core holders is typically placed on the winding shaft to engage with the core. When the winding shaft is not rotating, each chuck permits the core to slide onto the shaft, encircling one or more chucks. When the core is positioned on the chuck(s) and the shaft rotates, torque supplied by the drive shaft can cause the chuck(s) to engage with the core so that the torque is transferred through the chuck(s) to the core. Each chuck is configured so that it can be disengaged from the core once sufficient material has been wound, so that removal of the core is possible.

An example of a known differential chuck 1 is shown in figures 1, 2 and 3. An inner ring or collar 3 of the chuck has a plurality of ramps or cam surfaces 7 defined in its cylindrical outer surface. Each ramp is circumferentially-oriented and progressively slopes from a deep end 7a to a shallow end Tb. There are two parallel rows (not shown) of five ramps that extend around the circumference of the inner ring. The ramps in each row are arranged end to end such that within one row, the shallow end of one ramp is adjacent to the deep end of a neighbouring ramp. The ramps in one row are offset or staggered with respect to the ramps in the neighbouring row.

The inner ring 3 is situated inside, and is rotatable relative to, an outer ring 5. The outer ring has apertures or passageways 11 defined through it and each aperture accommodates and retains a single ball 9. Each ball forms a core-engaging element of the chuck which can roll along a corresponding ramp. The outer ring also defines a number of outwardly-facing recesses 13 and each recess contains a captive ball 15 urged radially outwards by a spring 14. The spring urges the ball to piotiude from the outel surface of the outer ring by approximately 1 millimetre (mm).

The inner ring 3 is held within the outer ring 5 between a flanged edge 3a on one side of the inner ring and a retaining ring or circlip 17 engaged with the other edge of the inner ring, but is rotatable relative to the outer ring. The extent of rotation is limited by the length of each ramp 7, as each ball is constrained to roll only between the ends of its corresponding ramp.

In use, a row of differential chucks 1 is placed on a drive shaft (not shown) with the inner surface of the inner ring 3 contacting the drive shaft. The drive shaft typically incorporates friction segments that are pushed radially outwards by air-inflatable tubes. The friction segments act on the inner surface of the inner ring, transmitting torque to the inner ring.

Figures 1 and 3 show the chuck with the inner ring 3 positioned relative to the outer ring 5 such that each ball 9 is located at the deepest end 7a of its corresponding ramp 7. In this position, the balls are fully retracted and only slightly project beyond the outer surface of the outer ring. In this configuration, a winding core (not shown) can slide onto the outside of the chuck and the spring-loaded balls 15 and core-engaging balls 9 are able to rotate to help the core slide on to the chuck. At this stage the chuck 1 is not engaged with the core.

Engagement of the core is initiated by rotation of the drive shaft. Rotation of the drive shaft transmits torque to and causes rotation of the inner ring 3. The spring-loaded balls 15 in the outer ring 5 contact the inner surface of the core and generate friction between the outer ring and the core. Therefore, as the inner ring 3 rotates, rotation of the outer ring is retarded and relative rotation between the inner ring and the outer ring can occur. The relative rotation causes each of the core-engaging balls 9 to move from the deep end 7a to the shallowest end 7b of the ramp 7, and drives the balls outwardly, to project beyond the outer surface of the outer ring. The core-engaging balls thus exert an outward radial pressure against the inner surface of the core, which has the effect of securing the chuck to the core. Further rotation of the drive shaft is transmitted to the outer ring and thus to the core, allowing sheet mateiial, such as plastics film, to be wound around the core.

Rotation of the drive shaft in the opposite direction initiates disengagement with the core. The outer ring 5 then rotates relative to the inner ring 3, urging the core-engaging balls 9 towards the shallower end 7b of the ramp 7. The balls retract within the apertures 11 and no longer press against the inside of the core. The core can then be removed from the chuck 1.

This chuck works particularly well with cores made from softer materials such as paper, cardboard or other such fibrous materials.

However, winding cores made from harder materials such as plastics are bein9 used with increasing frequency. They have the advantages of being longer-lasting and producing less dust. The differential chuck, shown in figures ito 3, has difficulty engaging with plastic cores. The smaller spring-loaded balls often do not engage sufficiently with the core to cause relative rotation of the inner and outer rings when torque is applied to the inner ring of the chuck, so that the larger balls are not driven automatically into engagement with the core.

It is desirable to provide differential chucks that engage more readily with cores, in particular cores made from plastics materials.

SUMMARY OF INVENTION

The invention relates to a differential chuck, a differential winding shaft, a cutting, or slitting, and/or winding apparatus and a method of engaging and disengaging a winding core as defined in the appended independent claims to which reference should now be made. Advantageous or preferred features are set forth in dependent claims.

According to a first aspect, the invention may thus provide a differential chuck (or core holder) receivable on a drive shaft of a winding apparatus for supporting and driving a winding core! comprising: an inner ring for encircling the drive shaft and to which torque can be applied from the drive shaft, having a first magnetic portion; an outer ring encircling the inner ring and rotatable relative to the inner ring, having a second magnetic portion; and a core-engaging element for engaging, in use, an inner surface of the core; wherein rotation of the outer ring relative to the inner ring causes the core-engaging element to extend or retract radially, and wherein the first and second magnetic portions interact to maintain the differential chuck either in an unprimed state or a primed state, the core-engaging element in the unprimed state being able to retract further than the core-engaging element in the primed state.

The outer ring may have an outside diameter less than or equal to the internal diameter of the core.

Radial projection or protrusion of the core-engaging element may allow engagement with the core and retraction of the core-engaging element may allow disengagement from the core, for loading or unloading cores onto or from one or more chucks.

The chuck may advantageously be switched between the primed and unprimed states by rotating the outer ring relative to the inner ring, for example by rotation through a position of magnetic repulsion between the magnetic portions, or through a position of minimum magnetic attraction between the magnetic portions. This may allow the chuck to be switched on or off as follows.

The differential chuck may be pnmed before a core is placed onto the chuck. In the primed, oi pie-loaded state, the interaction of the first and second magnetic portions may limit or impede relative rotation of the inner and outer rings such that the core-engaging element may not be able to retract to the same extent as the core-engaging element in the unprimed state. This may set a minimum extent of projection or protrusion. The minimum extent of protrusion of the core-engaging element in the primed state may! in use, be sufficiently small to allow a core to be loaded onto the chuck but may also be sufficiently large to create sufficient friction between the chuck and the core such that, as the inner ring rotates on a winding shaft, the friction between the core-engaging elements and the core permits sufficient relative movement between the inner ring and the outer ring, to drive the core-engaging element outwards to engage the core.

Torque may then be transferred from the shaft to the core for winding.

When a chuck is in its primed state it may therefore be considered to be switched on, for transmission of torque to an encircling core.

In the unprimed configuration, the core-engaging element may adopt a position, such as a fully-retracted position, in which it does not contact the core or in which it is not able to generate sufficient friction between the chuck and the core to drive the core-engaging element outwards when the shaft turns. In this configuration, the chuck may thus not be able to engage the core.

Therefore, the minimum extent of protrusion of the core-engaging element in the primed state may advantageously be greater (i.e. it protrudes more) than the minimum extent of protrusion in the unprimed state.

When a chuck is in its unprimed state it may therefore be considered to be switched off, so that it cannot transmit torque to an encircling core. Switching some of the chucks within a core on, and others off, may advantageously allow the accurate transmission of low torque from a winding shaft to the core.

In other words, in the unprimed state, the core-engaging element may be urged (as the result of interaction of the magnetic portions) towards a position where it does not project sufficiently and in the primed configuration, the core element may be urged towards a position where it projects sufficiently.

"Sufficient projection" may mean that the core-engaging element projects or extends enough to contact the core and to create friction against the core such that, in use, relative rotation of the inner and outer rings causes projection of the core-engaging element and engagement of the chuck with the core. The extent of projection, which constitutes a sufficient projection, may vary depending on the core material and the internal diameter of the core. For example, harder core materials may require the sufficient projection to be greater than for softer materials, in order to generate the requisite friction against the core surface.

However, in the unprimed state, the core-engaging element may protrude to a limited extent. If the core-engaging element is a ball, a slight protrusion may help in sliding the core on and off the chuck as the core can then slide over the ball.

Advantageously, a partially-projected core-engaging element in the primed configuration may enable better engagement with cores made from plastics material. The minimum extent of projection of the core-engaging element in the primed state may advantageously be greater than the maximum extent of projection of the spring-loaded balls typically used in chucks of the prior art (as described above). The spring-loaded balls are of smaller diameter than the balls of the core-engaging elements because the spring-loaded balls and the springs must be captive within the outer ring. The greater radial projection distance of the core-engaging element balls may permit sufficient friction to be generated between the core-engaging element and cores made from plastics material, to cause engagement of the chuck with the core. It may also accommodate greater manufacturing tolerances in the internal diameter of plastic cores.

Furthermore, the chuck may be easier to engineer as spring-loaded balls may no longer be necessary. Nevertheless, spring-loaded balls or other spring-loaded members, such as plungers may optionally be present in chucks embodying the invention.

Preferably, the chuck is switched between the primed state and the unprimed state by rotating the inner ring relative to the outer ring with a force that is above a pie-determined force. The extent of the required force may depend on the interaction between the magnetic portions. For example, the first and second magnetic portions may repel each other and switching between the primed state and the unprimed state may be achieved by overcoming the force exerted by the repelling magnetic portions. This force may be overcome by a user manually rotating the outer ring relative to the inner ring. The pre-determined force may be adjusted by altering, for example, the number of magnetic portions, the size of the magnetic portions or the positions of the magnetic portions.

In the primed state, limited relative rotation may be permitted between the inner ring and outer ring, without switching to the unprimed state. Thus, relative rotation in the primed configuration may urge the core-engaging element between a minimal, partially-projected state and a maximal, fully-projected state.

In a preferred embodiment, the inner ring has a guide along which the core-engaging element is movable. Preferably, the guide is a sloping guide or a ramp or a cam surface. Most preferably, the outer ring defines an aperture for receiving and retaining the core-engaging element and permitting projection and retraction of the core-engaging element relative to an outer surface of the outer ring.

Rotation of the outer ring relative to the inner ring may cause the core-engaging element to travel along the ramp.

The core-engaging element is preferably a rolling element, most preferably a ball that can roll along the ramp. Preferably, the rolling element is able to rotate when the chuck is in the primed state but the rolling element is not fully projected. This may allow the core to slide onto the chuck more easily. However, the core-engaging element may be, for example, a non-rolling rod or plunger that can slide along the guide and thus be driven to project or retract radially with respect to the outer surface of the outer ring.

Any core-engaging element known in the prior art may be suitable. For example, the outer ring may comprise a pivotable member with a slope or cam surface underneath. In use, a rolling member may roll against the slope or cam surface, causing the pivotable member to project or retract radially. This may mean that the rolling member itself does not project or retract.

In a preferred example, the inner ring comprises a plurality of ramps and the chuck comprises a corresponding plurality of core-engaging elements.

In the primed configuration, the inner and outer ring may be rotatable relative to each other to move the core-engaging element along a partial section of the ramp. This partial section of the ramp may thus include the shallowest part of the ramp but preferably does not include the deepest part of the ramp. Thus, in the primed state, the core-engaging element may be restricted to a shallower part of the ramp, whereas in the unprimed state, the core-engaging element may be restricted to a deeper part of the ramp.

The chuck may be any size to fit inside, and engage with, a core of any diameter.

A typical diameter core is 3 inches (76.2 mm). However, core diameters may range from 1 inch (25.4 mm)to 6 inches (152.4 mm). For a chuck intended to fit within a 3 inch (76.2 mm) diameter core, sufficient projection of the core-engaging element in the primed state may be from 1 to 2 mm beyond the outer surface of the outer ring Preferably, a fully projected core-engaging element projects 2 mm or more beyond the outer surface of the outer ring.

In a preferred example, the first magnetic portion is circumferentially aligned with the second magnetic portion, such that the second magnetic portion moves over the first magnetic potion when switching between the primed state and the unprimed state. This may mean that the first and second magnetic portions are brought into close proximity when relatively rotating the inner and outer rings, thus maximising their interaction.

Switching between the primed and the unprimed states may be configured by rotating the inner and outer rings to offset the position of the first magnetic portion with respect to the position of the second magnetic portion. Each magnetic portion may comprise a magnet. In the primed state, the second magnet may then be positioned to one side of the first magnet, and in the unprimed state, the second magnet may be positioned to an opposite side of the first magnet, the magnets being oriented to repel each other.

In an alternative embodiment, the ramp may have a shallow part at each end and a deep part mid-way between each end. The inner ring may have two first magnetic portions that repel a second magnetic portion in the outer ring. In an unprimed state, the second magnetic portion may be positioned between the corresponding first magnetic portions and is repelled by both of them. This may maintain the core-engaging element at the deepest part of the ramp. Relative rotation of the inner and outer rings in either direction may switch the chuck to a primed state, by moving the second magnetic portions past one of the first magnetic portions. Therefore, there may be two possible primed states. In each primed state, the second magnetic portion may be repelled by only one of the first magnetic portions to maintain the core-engaging element at one or other end of the ramp. A similar geometry may be achieved using one first magnetic portion in the inner ring positionable between or to one or other side of two second magnetic portions in the outer ring.

As an alternative to using magnetic portions that repel each other, the chuck may comprise magnetic portions that attract or may even comprise a combination of attracting and repelling magnetic portions. For example, the inner ring may comprise two magnetic portions. A second magnetic portion on the outer ring may attract each of the first magnetic portions on the inner ring. Rotating the inner ring relative to the outer ring may alter which of the first magnetic portions on the inner ring attracts the magnetic portion on the outer ring by moving the second magnetic portion closer to one or other of the first magnetic portions. For example, in the unprimed state, one magnetic portion on the inner ring attracts a magnetic portion on the outer ring to urge the core-engaging element towards a retracted or receded state. In the primed state, the other magnetic portion on the inner ring attracts the magnetic portion on the outer ring to urge the core-engaging element towards a projected state. An equivalent geometry may be obtained using one second magnetic portion and two first magnetic portions.

Where attracting magnetic portions are used, one or more magnetic portions may be magnets and one or more may be ferromagnetic materials.

In another embodiment, the inner ring may comprise a bar magnet possessing opposite ends which are attractive and repulsive to a magnetic portion in the outer ring (or vice versa). An attractive force between the magnetic portion on the outer ring and the attractive end of the bar magnet may urge the core-engaging element towards a retracted state. A repulsive force between the magnetic portion on the outer ring and the repulsive end of the bar magnet may urge the core-engaging element towards a projected state.

In a preferred example, the chuck comprises a plurality of first magnetic portions on the inner ring and a plurality of corresponding second magnetic portions on the outer ring. In a preferred arrangement, interacting pairs or groups of magnetic portions are circumferentially spaced around the rings.

To avoid undesired magnetic interactions, components of the chuck other than the magnetic portions are advantageously fabricated from non-magnetic materials such as stainless steel.

According to a second aspect, the invention may thus provide a differential winding shaft comprising a central drive shaft and a differential chuck as described in any form above, mounted on the drive shaft. The chuck is preferably releasably securable to the drive shaft. However, the chuck could be integral with the drive shaft.

According to a third aspect, the invention may thus provide a cutting or slitting and/or winding apparatus comprising a differential chuck or a winding shaft as described in any form above.

According to a fourth aspect, the invention may thus provide a method for engaging and disengaging a winding core, comprising: selectively configuring a differential chuck as defined in any form above to a primed state, the chuck being secured to a drive shaft; placing the winding core on the chuck; rotating the drive shaft in a first direction to engage the chuck with the core; and rotating the drive shaft in a second direction to disengage the chuck from the core. Configuring the primed state may occur before or after securing the chuck to the drive shaft.

SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention will now be described, by way of example and by comparison to a device of the prior art, and with reference to the accompanying drawings in which: Figure 1 is a top view, in section, of a differential chuck of the prior art.

Figure 2 is a three dimensional view of the differential chuck of figure 1.

Figure 3 is a three dimensional view of the differential chuck in figures 1 and 2 with a section removed.

Figure 4 is a three dimensional view of inner and outer rings of a differential chuck according to an embodiment of the invention, without any core-engaging elements or magnets.

Figure 5 is a three dimensional view of an inner ring of the differential chuck of figure 4 showing a core-engaging element, and a magnetic portion of the outer ring.

Figure 6 is a top view, in section, of the differential chuck of figures 4 and 5 illustrating, in particular, the positions of the magnetic portions in one possible configuration. For clarity, ramps and core-engaging elements amongst other features, are not shown.

Figure 7A is a top view, in section, of part of the differential chuck of figures 3-6, in an unprimed state.

Figure 7B is a top view, in section of the part of the differential chuck of figure 7A, in a primed state, but not engaged with a core.

Figure 7C is a top view, in section, of the part of the differential chuck in figures 7A and 7B, in a primed state and engaged with the core.

A differential chuck 1 according to an embodiment of the invention is shown in figures 4 to 7C. Similar features to those in figures 1 to 3 have been given like reference numerals. The differential chuck shares many similar features to those in the prior art device of figures 1 to 3. However, the most notable differences are that the chuck in figures 4 to 7C does not possess spring-loaded balls in the outer ring and that the inner and outer rings have a plurality of magnetic portions in the form of magnets 19 and magnets 21 respectively.

On the inner ring 3, each cylindrical magnet 19 is housed within a corresponding cylindrical recess 19a, such that it does not protrude beyond an outer surface of the inner ring and interfere with rotation between the inner ring and the outer ring 5. On the outer ring 5, each cylindrical magnet 21 is also housed within a corresponding cylindrical recess 21a, such that each magnet 21 is circumferentially aligned with and positionable in close proximity to a magnet 19 on the inner ring. Figure 6 shows the positions of the magnets 19 in the inner ring (inner magnets) and the magnets 21 in the outer ring (outer magnets) most clearly.

The inner magnets 19 and outer magnets 21 are circumferentially aligned. This means that rotation of the inner ring 3 relative to the outer ring 5 can cause an outer magnet to move directly over its corresponding inner magnet. This is clearly shown in figure 5, in which the position of a single outer magnet 21 from the outer ring (not shown) is shown adjacent to its corresponding inner magnet 19.

Each inner magnet 19 has a corresponding outer magnet 21 with which it interacts. The corresponding magnets repel each other and the repulsive force increases as their proximity increases.

The parts of the inner ring 3 and outer ring 5 that are not magnetic are manufactured from stainless steel. However, other non-ferromagnetic materials may also be suitable. The inner and outer magnets 19, 21 are neodymium magnets, but any other permanent magnetic material may be used.

In use, the differential chuck 1 is placed on a drive shaft (not shown) with the inner surface of the inner ring 3 contacting the drive shaft. Torque can be transmitted from the drive shaft to the inner ring in a known manner.

Prior to placing a core 2 (shown in phantom in figures 7A-7C) on the chuck 1, if the chuck is to be used to transmit torque from the drive shaft to the core, then the chuck is pre-loaded or primed. This involves manually rotating the inner ring 3 relative to the outer ring 5, which urges the core-engaging balls 9 towards the shallow ends 7a of the ramps 7.

Figures 5 and 7A show the relative positions of one inner magnet 19, one outer magnet 21 and one ball 9 in the unprimed state. Figure 7B shows the relative positions of the same features in the primed state. Configuring the primed state from the unprimed state requires rotating the inner ring relative to the outer ring with sufficient force to overcome repulsion between the inner and outer magnets.

In the primed state, magnetic repulsion between the inner and outer magnets 19, 21 prevents relative rotation of the inner and outer rings 3,5 that would urge the balls 9 to the deep ends 7a of the ramps. Consequently, the balls are maintained in a position closer to the shallowest ends 7b of the ramps. Until drive shaft rotation is initiated, the balls are able to adopt a partially projected state (as shown in Figure 7B). This allows the core 2 to slide onto the chuck, as the maximum diameter of the chuck (measured to the outer extremity of the balls) is either less than internal diameter of the core or is larger than the internal diameter of the core to a sufficiently small extent that placing the core over the chuck does not force the chuck into its unprimed state by forcing the balls inwards.

Nevertheless, contact with the core may urge the balls inwards, causing rotation of the outer ring ielative to the innel ling against the repulsive force between the magnets, as long as the chuck remains in its primed state.

When in the primed state, rotation of the drive shaft initiates engagement of the chuck 1 with the core 2. Rotation of the drive shaft causes rotation of the inner ring 3. The partially-projected balls 9 in the outer ring are able to contact the inner surface of the core, generating friction between the outer ring 5 and the core.

Therefore, as the inner ring rotates, rotation of the outer ring is retarded to the extent that relative rotation between the inner ring and the outer ring is permitted.

The movement of the outer ring relative to the inner ring causes each of the balls 9 to move to the shallowest end 7b of the ramp 7, and drives the balls outwards to project further beyond the outer surface of the inner ring. Figure 7C shows the arrangement of the balls when the chuck is engaged with the core.

Rotation of the drive shaft in the opposite direction can initiate disengagement from the core 2. Rotation of the outer ring 5 relative to the inner ring 3, urges the balls 9 to a deeper part of the ramp 7. However, the repelling inner magnets 19 and outer magnets 21 act to maintain the chuck in the primed position so that the balls are prevented from moving towards the deepest end 7a of the ramp. The balls retract sufficiently within the apertures 11 so that they no longer press against the inside of the core, or so that the pressure between the balls and the core is reduced. The core is then removed from the chuck 1.

If desired, an unprimed state can be configured by manually lotating the outer ring 5 relative to the inner ring 3 with sufficient force to overcome the repulsion between the inner magnets 19 and the outer magnets 21. The unprimed state (as shown in Figure 7A), is characterised by the ball 9 being maintained in a position towards the deepest end la of the ramp 7 and so the ball will not project or protrude significantly from the outer surface of the outer ring. In this state, if the drive shaft is rotated, sufficient friction cannot be generated between the chuck and the core to cause the chuck to engage with the core.

The unprimed state is particularly advantageous if there are a number of chucks positioned adjacent to each other on a drive shaft of a cutting and winding machine. The chucks can be switched so that a pie-selected number of the chucks drives a core, in order to enable a pre-determined range of torque to be applied to the core during winding. This can be achieved without having to remove chucks from the drive shaft.

In the unprimed state, the balls 9 protrude slightly beyond the outer surface of the outer ring 5 and are able to rotate in order to help slide the core 2 on and off the chuck.

Claims

CLAIMS1. A differential chuck for supporting and driving a winding core, comprising: an inner ring for encircling a drive shaft and to which torque can be applied, in use, from a drive shaft, having a first magnetic portion; an outer ring encircling the inner ring and rotatable relative to the inner ring, having a second magnetic portion; and a core-engaging element for, in use, engaging an inner surface of the core; wherein rotation of the outer ring relative to the inner ring causes the core-engaging element to project or retract radially, and wherein the first and second magnetic portions interact to maintain the differential chuck either in an unprimed state or a primed state, the core-engaging element in the unprimed state being able to retract further than the core-engaging element in the primed state.
2. A differential chuck according to claim 1, which can be switched between the primed state and the unprimed state by rotating the inner ring relative to the outer ring with a force that is above a pre-determined force.
3. A differential chuck according to claim 1 or claim 2, in which in the primed state, limited relative rotation is permitted between the inner ring and the outer ring to urge the core-engaging element between a minimal, partially-projected state and a maximal, fully-projected state.
4. A differential chuck according to any preceding claim, in which the inner ring has a ramp along which the core-engaging element can move and the outer ring defines an aperture for receiving the core-engaging element, and in which the rotation of the outer ring relative to the inner ring causes the core-engaging element to move along the ramp and project or retract relative to an outer surface of the outer ring.
5. A differential chuck according to claim 4, in which in the unprimed configuration, the core-engaging element is urged towards a position where it does not sufficiently project beyond the outer surface of the outer ring to cause engagement, in use, with a core.
6. A differential chuck according to claim 4 or claim 5, in which in the primed configuration, the core-engaging element is urged towards a position where it sufficiently projects beyond outer surface of the outer ring to cause engagement, in use, with a core.
7. A differential chuck according to any preceding claim, in which the first magnetic portion repels the second magnetic portion.
8. A differential chuck according to claim 7, in which in the primed state, the second magnetic portion is positioned to one side of the first magnetic portion, and in which in the unprimed state, the second magnetic portion is positioned to an opposite side of the first magnetic portion.
9. A differential chuck according to any preceding claim, in which the first magnetic portion is circumferentially aligned with the second magnetic portion, such that the second magnetic portion is movable over the first magnetic potion when switching between the primed state and the unprimed state.
10. A differential chuck according to any preceding claim, comprising a plurality of ramps and a plurality of corresponding core-engaging elements.
11. A differential chuck according to any preceding claim, in which the inner ring comprises a plurality of first magnetic portions and the outer ring comprises a plurality of second magnetic portions.
12. A winding shaft for use with sheet cutting and winding apparatus, comprising a drive shaft and a plurality of differential chucks as defined in any of claims ito 11, mounted on the drive shaft.
13. A winding shaft according to claim 12, in which the differential chucks are releasably securable to the drive shaft.
14. A roll cutting and/or winding apparatus comprising a differential chuck as defined in any of claims ito ii or a winding shaft as defined in claim 12 or claim 13.
15. A method for engaging and disengaging a winding core, comprising: configuring a differential chuck as defined in any of claims ito 11 to a primed state, the chuck being secured to a drive shaft; placing the winding core on the outside of the chuck; rotating the drive shaft in a first direction to engage the chuck with the core; and rotating the drive shaft in a second direction to disengage the chuck from the core.
16. A differential chuck substantially as hereinbefore described with reference to figures 4 to YC.
17. A differential winding shaft substantially as hereinbefore described with reference to figures 4 to 7C.
18. A roll cutting and/or winding apparatus substantially as hereinbefore described with reference to figures 4 to 7C.