GB2071535A - Radially expandable chuck - Google Patents

Abstract

A chuck for gripping internally a tubular element has a number of displaceable gripper segments (12) having part-cylindrical outer surfaces (18) for engagement with an internal surface of a workpiece and inclined radially inner surfaces which cooperate with cam surfaces (10) on a support member (9) upon which the gripper segments (12) are carried within a housing (1). Upon axial displacements of the support member (9) relative to the housing (1) the gripper segments (12) are first carried axially so as to project outwardly from an open end (2) of the housing, until abutments (19) on the segments come into engagement with stop surfaces (3) on the housing, following which further axial displacement of the support member (9) serves to displace the gripper segments (12) radially outwardly into gripping engagement with a workpiece. <IMAGE>

Description

SPECIFICATION Radially expandable chuck This invention relates to radially expandable chucks, that is, chucks capable of gripping a tubular workpiece, or a hollow end of a workpiece, internally.

The invention finds particular, but not exclusive, application to the gripping of tubular cores to be driven rotatably in winding/rewinding and unwinding apparatus. Such cores, which are generally of thick cardboard or plastics material, may be gripped for rotation on drive chucks of various known types, the simplest of which is in the form of metal discs of stepped diameter which register with the internal diameter of the core at opposite ends of the latter. Axially facing surfaces of the chuck are faced with frictional material, or suitably roughened, so as to transmit the necessary winding or unwinding torque to the core by frictional engagement wih the end faces of the core.This type of known drive chuck is unsatisfactory in practice because it cannot accommodate accurately the wide range of internal diameters of the cores used in conventional winding/rewinding and unwinding machines. Furthermore, such stepped chucks cannot accommodate the change in internal diameter which can be exhibited by cardboard or plastics cores as a roll of web material is wound or unwound. Thus a chuck which fitted closely into a tubular core of a fully wound roll might become a slack fit within the core when the latter had been fully unloaded and the radial compressive load on the core relieved.

The known type of stepped chuck can therefore provide an accurately concentric support for a core only in the final stages of winding of a core, when its internal diameter is at the lowest limit of its tolerance range: with a core of any other internal diameter within the tolerance range, and at any other stage in the winding process, the chuck and the core will not run concentrically. This will give rise to fretting and wear of the core where it is engaged frictionally by the chuck. Not only is this destructive of the core, which in the case of heavy roll applications is expensive and re-usable, but it also generates dust which is unacceptable in many roll handling applications, particularly where rolls of plastics film are concerned. Eccentric running in a winding/rewinding and unwinding machine also gives rise to unwanted vibration and can limit the running speed.

Aside from the undesirable frictional wear caused by conventional stepped drive chucks, the torque which can be transmitted through such chucks to tubular cores is also strictly limited.

There have been various attempts to overcome this problem by transmitting torque to tubular cores in winding/rewinding and unwinding machines through more complicated drive arrangements. For example, one such known arrangement employs inflatable annular rubber air chambers which are pressurised into tight engagement with internal surfaces of a tubular core. Although such arrangements can alleviate the dust problem, they do not overcome the problem of eccentric running under heavy roll loads. Moreover, the sealing and supply of compressed air to the rotational drive is in general unsatisfactory.

Other known arrangements for gripping tubular cores for rotational drive purposes include spring loaded serrated pawls, detents or fingers arranged to engage end faces or internal surfaces of tubular cores. Such arrangements can be of complex construction and also tend to cause damage to the cores and distortion by virtue of their pointengagement with the cores.

The previously known mechanical drive mechanisms for the rotational support and drive of tubular cores which rely on friction with core surfaces in order to achieve accurate location and drive have not in general proved satisfactory in a further important respect, namely in the disengagement and unloading of cores from such drive arrangements. If a pair of rotational drive chucks is frictionally engaged with opposite ends of a tubular core the simultaneous disengagement of the chucks from the opposite ends is difficult to achieve: once one of the chucks has become disengaged from the core the other chuck can remain tightly engaged with the core since there is then no means of gripping the core to pull it away from the other chuck.This a serious disadvantage in practice since the ability of a drive arrangement to disengage completely and cleanly from a core, with absolute reliability, is a prime requirement in any automatic core unloading system for a winding/rewinding machine.

The present invention seeks to provide an improved chuck capable of positive engagement with a tubular core or other tubular workpiece, or tubular end of a workpiece, avoiding the problems of known mechanical chuck arrangements referred to above.

According to the present invention there is provided a radially expandable chuck comprising a housing having an open end and radially inwardly projecting stop surfaces, a number of segments within the housing having abutments which cooperate with the stop surfaces and having workpiece-engaging portions which project axially through the open end of the housing, a support member extending coaxially within the housing and having cam surfaces inclined to the axis of the housing and cooperating with complementary radially inner surfaces of the segments; the housing and the support member being relatively movable axially in a sense to move the workpiece engaging portions of the segments axially outwardly through the open end of the housing until the abutments of the segments engage the stop surfaces, further such relative movement causing, through the cam surfaces, radially outward displacement of the segments.

The chuck according to the invention combines an essential mechanical simplicity with a gripping action which is ideally suited to the accurate location and positive gripping of tubular workpieces such as the cardboard or plastics cores used in winding/rewinding and unwinding machines. The workpiece-engaging portions would have surfaces shaped so as to engage the internal surfaces of a tubular core or other workpiece over an extensive circumferential area, avoiding areas of localised stress when the segments are expanded radially into gripping engagement with the workpiece. When the chuck is operated to grip a workpiece the relative axial displacement of the support member and the housing causes the segments to advance axially into one end of the workpiece before expanding radially into positive engagement with the workpiece.Similarly, upon disengagement, the segments first move radially inwards before being retracted axially, thereby ensuring positive disengagement, which is important where two such chucks have to be disengaged simultaneously from opposite ends of a core in the automatic unloading of a winding/unwinding machine.

The housing is preferably cylindrical, and the stop surfaces are preferably formed by a radially inwardly projecting flange at the open end of the housing. For the gripping of tubular cores or other tubular workpieces the workpiece-engaging portions of the segments may have part-cylindrical outer surfaces which remain coaxial with each other during the displacement of the segments.

The segments are preferably keyed onto the support member for sliding movement longitudinally of the said radially inner surfaces of the segments relative to the cam surfaces of the support member. In order to ensure that the segments move axially with the support member in the initial movement of the latter from its fully retracted position resiliently loaded detent elements may be trapped between the said radially inner surfaces of the segments and the cam surfaces of the support member, to present a frictional resistance to the relative longitudinal sliding movement.

In a preferred embodiment of the invention the support member is formed with longitudinally extending keys inclined at equal angles to the axis of the support member and engaging respective complementary keyway slots in the radially inner surfaces of the segments.

The housing is preferably formed at its open end with a radial external abutment surface which, in use of the chuck, comes into engagement with an end of a workpiece to be gripped. The chuck housing may also have an internal shoulder or shoulders remote from the open end against which the segments abut when fully retracted into the housing, the support member having a radially outwardly projecting end flange which retains the segments on the support member when the latter is fully retracted into the housing.

The present invention also comprehends winding/unwinding and rewinding apparatus comprising two radially expandable chucks as herein defined arranged coaxially with their open ends facing each other, the workpiece-engaging portions of the chucks projecting sufficiently from the open ends of the chuck housings when fully retracted to be engageable in opposite ends of a tubular core, and means for displacing each chuck support member axially relative to the chuck housing to cause sequential axial and radially outward displacement of the chuck segments into gripping engagement with the internal surface of a tubular core loaded in the apparatus.

To facilitate positive disengagement of the chucks from a tubular core the chuck housings may be displaceable axially towards and away from each other by positive actuator means, for example through a cam mechanism. Alternatively, the chuck housings may be spring-loaded axially relative to the support member.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a radially expandable chuck according to one embodiment of the invention in its fully retracted condition; Figure 2 is a longitudinal sectional view of the chuck in its fully retracted condition as shown in Figure 1; Figure 3 is a perspective view corresponding to Figure 1 but showing the chuck in its fully expanded condition; Figure 4 is a longitudinal sectional view of the chuck approaching its fully expanded condition; Figure 5 is an end view of the chuck shown in Figure 4, with its segment keep plate removed; Figure 6 is a persepctive view corresponding to Figures 1 and 3, showing the chuck in an axially extended position, before the radial expansion of its segments:: Figure 7 is a perspective view from one end of the partially expanded chuck, with its keep plate removed, and Figure 8 is a perspective exploded view of the support member and one of the segments of the chuck shown in Figures 1 to 7.

The drawings illustrate a radially expandable chuck for use in supporting and driving rotatable tubular cores in web winding/rewinding and unwinding apparatus. In such apparatus it is common to employ re-usable tubular cores of thick cardboard or plastics material the opposite ends of which are engaged by respective chucks according to the present invention. Each chuck expands radially into gripping engagement with the internal surface of the tubular core, and rotational drive or braking torque is imparted to the core through one or both of the chucks. The construction and operation of one of the chucks will be described with reference to the drawings.

The illustrated chuck has a cylindrical housing 1 having a circular opening 2 at one end bounded by a radially inwardly projecting annular flange 3. At its opposite end the housing 1 is provided with a base wall 4 having a central circular hole 5 in which a shaft 6 is axially slidable but keyed to prevent relative rotational movement. The shaft 6 has a reduced diameter end portion 7 defining an annular shoulder 8, the end portion 7 projecting coaxially into the housing 1.

A support member 9 is mounted on and keyed to the reduced diameter end portion 7 of the shaft 6 and retained, for example by a clamping screw (not shown) against the shoulder 8. The support member 9 is formed with a number of flat cam surfaces 10 inclined radially inwardly towards the axially outer end of the shaft 6 and spaced apart at equal angular intervals about the axis of the member 9. In the illustrated embodiment there are three cam surfaces 10 (Figures 5 and 7) each carried on the radially outer surface of a T-section key 1 1 extending longitudinally of the member 9.

A number of gripper segments 12 - three in the illustrated embodiment - are located within the housing 1, each segment having on its radially inner surface a T-section keyway 13 which is a close sliding fit on a respective one of the keys 11 of the support member 9, as shown in Figures 5 and 7. The base of each segment keyway 13 is a flat surface which cooperates with and is complementary to the respective came surface 10 on the associated key 11 so that in sliding longitudinally along the keyways 13 the segments 12 are displaced radially inwardly or outwardly, according to the direction of longitudinal sliding movement of the support member 9 relative to the segments 12.In the assembled chuck longitudinal sliding movement of the segments 12 beyond the axially outer end of the support member 9 is prevented by a radially outwardly projecting end flange on the support member, formed by a circular keeper plate 14 which is retained on the end of the support member 9 by a clamping screw 1 5.

A frictional resistance to the longitudinal sliding movement of the segments 12 relative to the support member is afforded by spring-loaded balls 16 which are trapped in radial pockets 17 in the member 9 and urged resiliently into contact with the respective surfaces of the segments 1 2 which cooperate with the cam surfaces 10.

Each gripper segment 12 has a workpieceengaging portion formed with a part-cylindrical outer surface 18 which projects axially through the open end of the housing 1. At its inner end within the housing 1 each segment 12 is formed with a radially outwardly projecting circumferentially extending lip 19 and with a circumferentially extending groove 20 interposed between the lip 19 and the respective partcylindrical surface 18.

The housing 1 is provided with an internal annular shoulder 21 against which the lips 19 of the segments 12 abut in the fully retracted condition of the chuck, illustrated in Figures 1 and 2. In this fully retracted condition the support member 9 abuts the end wall 4 of the housing 1 and the part-cylindrical surfaces 1 8 of the gripper segments have a small clearance from the radially inner surface of the flange 3 of the housing and project through the open end of the latter by a short axial distance, typically about 5 mm. In this fully retracted condition, the radially outer surfaces 18 of the segments 12 define a substantially cylindrical surface interrupted by small circumferential gaps, as shown in Figure 1.

In order to expand the chuck the shaft 6 is displaced axially relative to the housing 1 by means of an actuator (not shown) which may be a hydraulic or pneumatic actuator, a screw jack or other convenient means. During the first part of the axial displacement of the shaft 6 the segments 12 are carried on the support member 9 and move axially through the open end of the housing 1, without radial displacement. The limit of this axial displacement of the segments 12 is determined by the engagement of the lips 19 of the segments 12 with the flange 3 of the housing. At this stage the segments 12 will be extended axially to their full extent, as shown in Figure 6.

Further axially outward displacement of the shaft 6 relative to the housing 10 from the position illustrated in Figure 6 will cause the segments 12, which are prevented from further axial movement by the flange 3, to move radially outwardly due to the wedging action of the cam surface 10 on the cooperating radially inner faces of the segments 12. During this purely radial displacement of the segments 12 the flange 3 engages in the grooves 20 of the segments.By regulating the axial displacement of the shaft 6 relative to the housing 1 the radial expansion of the segments 12 can be selected, according to the internal diameter of the tubular core or other workpiece to be gripped, so that the substantially cylindrical surface defined by the surfaces 1 8 of the segments 12 has any desired diameter between the minimum diameter condition illustrated in Figure 6 and the maximum diameter condition, illustrated in Figure 3, in which the support member 9 is fully extended and the flange 2 engages the base of the groove 20 in the segments 12.Since the workpiece-engaging surfaces 1 8 of the segments 12 are always concentric they make surface contact over substantially their entire surface with the internal surface of a tubular core or other workpiece, avoiding severely localised point contact with the internal workpiece surfaces and thereby avoiding the disadvantages of damage and stress distortion which were characteristic of some previously known chucks. The part-cylindrical surfaces 18 of the segments will in practice have a radius corresponding to that of the nominal internal cylindrical surface of the tubular core to be gripped, so that when the segments are expanded radially to engage the said internal cylindrical surface the surfaces 18 together define a cylindrical surface of the same diameter.This occurs in the partially expanded condition illustrated diagrammatically in Figure 7: in the minimum and maximum diameter settings of the chuck, shown in Figures 6 and 3 respectively, the surfaces 18 will not form an accurately cylindrical surface, but the surface they form will nevertheless be substantially cylindrical.

It will be appreciated that engagement of the chuck according to the present invention with a tubular core or other workpiece takes place in two quite distinct consecutive stages: the gripper segments first advance purely axially to their maximum axial extension, and then expand in a purely radial direction into gripping engagement with the internal surface of the workpiece.

Similarly, upon disengagement of the chuck, the gripper segments first move radially inwardly to their minimum diameter positions (Figure 6) and are then retracted axially. This is a considerable practical advantage in the handling of tubular cores in winding/rewinding and unwinding machines having automatic core handling devices, where simultaneous positive disengagement of a core is essential.

In a typical winding/rewinding and unwinding apparatus two radially expandable chucks as herein described and illustrated would be mounted coaxially with their open ends facing each other. The housing 1 of one or both of the chucks would be mounted on a carrier capable of controlled limited axial displacement in both directions to displace the entire chuck assembly axially. Such axial displacement may be effected by any convenient actuator means - for example by applying controlled rotation to a sleeve having a helical groove in which a pin carried by an inner sleeve engages, the inner sleeve being connected to the housing of the chuck so that upon rotation of the outer sleeve relative to the inner sleeve a limited axial displacement of the housing takes place, without rotation.

To load a tubular core onto the two chucks in such a winding/rewinding apparatus the chucks would initially be fully collapsed and retracted, as illustrated in Figures 1 and 2, and would be displaced axially to their maximum separation. The core to be engaged would then be located on the cylindrical "step" formed by the short axial projection of the surfaces 1 8 of the retracted segments 12, the end face of the core abutting the end face of the end flange 3 of the respective housing 1. The entire chuck would then be displaced axially towards the other chuck, engaging the other end of the tubular core on the cylindrical "step" formed by the retracted segments 12, so that the opposite end faces of the core are engaged with the end faces of the respective chuck housings.Both chucks would then be expanded by axial displacement of their shafts 6 towards each other, as described previously, to bring the respective chuck segments 12 into positive engagement with the internal cylindrical surface of the core at opposite ends thereof. The reverse of this sequence of operations would be effected upon unloading a tubular core from the chucks: after fully retracting the segments 12 of the chucks to the positions illustrated in Figures 1 and 2 the core would be supported upon the short axial "steps" defined by the cylindrical surfaces 18 of the retracted segments 12, and once the wound roll and its core has been engaged by the unloading device (for example, lifting straps or an unloading conveyor) the two chuck housings 1 would be retracted axially to their maximum separation, allowing the roll and its core to be removed.

For winding/rewinding and unwinding machines in lighter duty applications axially spring-loaded housings 1 may be employed in place of means for positively displacing the chuck housings. In this case the chuck housings would spring-loaded axially relative to the chuck actuating shaft 6, in a direction away from the opposite chuck. The entire chuck is then advanced into preliminary locating engagement with the tubular core or other workpiece by an initial axial movement of the shaft 6, opposed by the spring loading of the chuck housings 1. After this initial axial movement further axial movement of the shaft 6 would effect the sequential extension and expansion of the chuck as described previously.

It will be appreciated that the entire chuck assembly is of simple construction, involving relatively few moving parts. It will further be appreciated that, although the illustrated chuck is shown as having three gripper segments 12, the chuck may in practice be designed with different numbers of segments according to the intended field of application.

The chuck as illustrated can be easily assembled and disassembled. In order to remove the gripper segment 12 the chuck is fully retracted (Figure 2) and the keeper plate 14 removed by releasing the screw 15.

The chuck according to the invention has distinct practical advantages in its application to the gripping and driving of tubular cores in winding/rewinding and unwinding machines. In the first place, accurate concentricity of the core with the chuck is maintained, for all diameters within the operating range of the chuck, so that manufacturing tolerances in a tubular core of a given nominal size can easily be allowed for.

Furthermore, high torque can be transmitted to the supported tubular core through the tight frictional engagement between the chuck segments and the core, without damage to the core, and without the generation of dust.

Moreover, the chuck, being entirely symmetrical, is capable of transmitting torque to a core in either direction.

An important safety feature is that the chuck segments 12 are automatically locked in the annular housing 1 as soon as the segments 12 begin to expand radially under the camming action of the support member 9, by virtue of the engagement of the flange 3 in the grooves 20 of the segments 12. This means that in the event of a power failure the chuck segments 12 cannot retract axially or radially until the control shaft 6 is actuated.

The locking of the chuck segments 1 2 also ensures that, upon retraction of the chuck, the segments cannot be retracted axially until they have been completely contracted radially (to the position illustrated in Figure 6).

A further important practical advantage of the chuck according to the invention is that the axial forces exerted on the chuck segments are reacted against the housing itself so that no axial loads are transmitted to the core or other workpiece.

The chuck according to the invention can easily be adapted for use with tubular cores or other workpieces of different internal diameters. For example, where the chuck is required to transmit high torques to tubular cores of intrinsically weak material the part-cylindrical outer surfaces 18 of the gripper segments 12 may be faced with friction material or provided with a disturbed or roughened surface finish, thereby reducing the required contact pressure between the gripper segments 12 and the internal surface of the tubular core for any given duty. Alternatively, or in addition, an annular groove, concentric with the chuck axis, may be formed in the part-cylindrical outer surfaces 1 8 of the gripper segments 1 2 and may contain a split spring ring which, when expanded by radially outward displacement of the gripping elements, would distribute the expansion pressure evenly against the internal surface of a tubular core engaged by the gripper elements.

The chuck according to the invention has a wide potential field of application to the engagement and gripping of tubular workpieces generally, including non-tubular workpieces having end cavities. For example, the chuck according to the invention may be adapted for the engagement and lifting of tubular fuel element assemblies in nuclear reactors.

Claims (12)

1. A radially expandable chuck comprising a housing having an open end and radially inwardly projecting stop surfaces, a number of segments within the housing having abutments which cooperate with the stop surfaces and having workpiece-engaging portions which project axially through the open end of the housing, a support member extending coaxially within the housing and having cam surfaces inclined to the axis of the housing and cooperating with complementary radially inner surfaces of the segments; the housing and the support member being relatively movable axially in a sense to move the workpieceengaging portions of the segments axially outwardly through the open end of the housing until the abutments of the segments engage the stop surfaces, further such relative movement causing, through the cam surfaces, radially outward displacement of the segments.

2. A chuck as claimed in Claim 1, in which the housing is cylindrical and the stop surfaces are formed by a radially inwardly projecting flange at the open end of the housing.

3. A chuck as claimed in Claim 1 or Claim 2, in which the workpiece-engaging portions of the segments have part-cylindrical outer surfaces which remain coaxial with each other during the displacement of the segments.

4. A chuck as claimed in any one of Claims 1 to 3, in which the segments are keyed onto the support member for sliding movement longitudinally of the said radially inner surfaces of the segments relative to the cam surfaces of the support member.

5. A chuck as claimed in Claim 4, in which resiliently loaded detent elements are trapped between the said radially inner surfaces of the segments and the cam surfaces of the support member, to present a frictional resistance to the relative longitudinal sliding movement.

6. A chuck as claimed in Claim 4 or Claim 5, in which the support member is formed with longitudinally extending keys inclined at equal angles to the axis of the support member and engaging respective complementary keyway slots in the radially inner surfaces of the segments.

7. A chuck as claimed in any one of the preceding claims, in which the housing is provided at its open end with a radial external abutment surface.

8. A chuck as claimed in any one of the preceding claims, in which the housing has an internal shoulder or shoulders remote from the open end against which the segments abut when fully retracted into the housing, the support member having a radially outwardly projecting end flange which retains the segments on the support member when the latter is fully retracted into the housing.

9. Winding/rewinding apparatus comprising two radially expandable chucks according to any one of the preceding claims arranged coaxially with their open ends facing each other, the workpiece-engaging portions of the chuck projecting sufficiently from the open ends of the chuck housings when fully retracted to be engageable in opposite ends of a tubular core, and means for displacing each chuck support member axially relative to the chuck housing to cause sequential axial and radially outward displacement of the chuck segments into gripping engagement with the internal surface of a tubular core loaded in the apparatus.

10. Apparatus as claimed in Claim 10, in which the housing is spring-loaded axially relative to the support member.

11. Apparatus as claimed in Claim 10, including means for displacing the chuck housings axially towards and away from each other for loading and unloading of cores.

12. A radially expandable chuck substantially as herein described with reference to and as shown in the accompanying drawings.