DRIVE TRANSMITTING DEVICE

Abstract: A method of accoupling a driven member (50) from a driving member (46) used to rotate the driven member is disclosed. The method comprises the step of connecting the driving member to the driven member via a connecting means (38) which is torsionally rigid in a plane generally perpendicular to the axis of rotation of the driven member (50), but is readily deformable in other planes to accommodate misalignment. A drive decoupling means for achieving the method is also provided, wherein the connecting means comprises a laminated device attached to the driving member via at least one off axis connection and to the driven member by at least one other off axis connection, the connections being circularly spaced one from the other. Two such decoupling means may be connected in series to compensate for both offset and misalignment. The method and decoupling means are of particular use in machine tools, such as lathes and grinding machines for transmitting drive to workpieces therein.

Description: Title: Drive transmitting device Field of Invention This invention relates to a drive transmitting device for use in transmitting torque to an article to be rotated. The invention is of particular use in transmitting rotational drive to a workpiece in a lathe or grinding machine or the like. Background to the Invention When machining articles to a desired shape it is often necessary to rotate the article (usually termed the workpiece) so that symmetrical machining can be achieved of a given cross section. This applies to both lathe type devices where cutting tools are used and to grinding machines where a rotating grinding wheel runs against a rotating load or workpiece. Rotation of the workpiece to be machined can be achieved by securing the workpiece into a rotating chuck. However if the workpiece is not centralised correctly within the clamping jaws of the chuck, it will not rotate in a 'true' fashion and machining will be inaccurate. Alternative methods of transmitting rotation involve the use of a tailstock and a headstock to support the article, the headstock transmitting the rotation, directly or indirectly to the workpiece. The interengagement between the workpiece and the headstock or driver may be subject to misalignment and offset, which will introduce errors in the machining. It is one object of the present invention to provide an improved drive transmitting device which will not transmit misalignment or offset to the workpiece. Summary of the Invention According to one aspect of the present invention a method of decoupling a driven member from a driving member used to rotate the driven member comprises the step of connecting the driving member to the driven member via a connecting means which is torsionally rigid in a plane generally perpendicular to the axis of rotation of the driven member, but is readily defor able in other planes to accommodate misalignment. According to another aspect of the invention a drive decoupling means as aforesaid comprises a driving member and a driven member which is attachable to a load so as to rotate the latter and a connecting means for transferring torque therebetween which comprises a laminated device attached to the driving member via at least one off axis connection and to the driven member by at least one other off axis connection, the connections being circularly spaced one from the other. By forming the laminations from flexible thin sheet steel, the connecting means is torsionally rigid in a plane perpendicular to the drive axis so as to ensure rotation is transmitted reliably to the driven member, but the flexibility of the laminations accommodates any eccentricity developed through misalignment of the driving member and driven member. In this way the driven member and therefore the workpiece is decoupled from the driving member. Where the load is a workpiece and is to be mounted between a headstock and tailstock, the components of the drive decoupling means may be centrally apertured to accommodate the headstock, which can thereby extend axially therethrough. The driven member may be provided with radially adjustable means for securing it to the load. Preferably the securing means is arranged symmetrically and allows centering of the member relative to the load. Alternatively the securing means may comprise radially fixed and radially adjustable positioning and holding members. In a further arrangement the securing means may comprise one or more radial members which are securable so as to grip the load, where the load is a workpiece, but are spring loaded in a direction away from the workpiece so as to cause separation from the workpiece to facilitate its demounting after a machining operation. The radial member(s) may be externally adjustable. In a preferred embodiment at least two radial members are provided, in which at least one radial member is adjustable and at least one other radial member is fixed. The adjustment may be provided by pneumatic, electrical or hydraulic means so that release and removal of a workpiece can be performed automatically. In another arrangement three positioning and holding members may be arranged circularly around an annular member, two being fixed thereto and the third being spring loaded in a direction to engage the load when the load comprises a workpiece, such that the latter is positioned between the three members, and displacement of the annular member in a direction parallel to the axis of the sprung member so as to compress the spring results in separation of the sprung and fixed members from the workpiece to facilitate its removal. In a particularly preferred embodiment, two drive decoupling means as aforesaid are connected in series, the driven member of the first being connected to the driving member of the second. Such an arrangement allows even greater decoupling to be achieved than if only a single drive decoupling means is employed and permits offset as well as misalignment to be accommodated. The invention also lies in a lathe having a headstock and tailstock for supporting a workpiece therebetween, wherein rotation of the workpiece is effected through one or more drive decoupling means as aforesaid particularly an arrangement involving two such drive decoupling means connected in series so as to remove errors due to offset as well as misalignment. The invention also lies in a grinding machine having a headstock and tailstock for supporting a workpiece to rotate with a grinding wheel, wherein rotation of the workpiece is effected through one or more drive decoupling means as aforesaid, particularly an arrangement involving one having two such drive decoupling means connected in series, so as to remove errors due to offset as well as misalignment. As applied to a grinding machine, the invention is of value in that it permits an NCR grinding machine to be used to grind off-axis elements of a workpiece by synchronously advancing and retracting the grinding wheel as the workpiece is rotated. This permits for example the crankpins of a crankshaft to be ground. The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is an exploded view of a prior art flexible coupling Figure 2(a) is a perspective view of a drive decoupling means as applied to a grinding machine Figure 2(b) is a sectional view through the grinding wheel and workpiece as shown in Figure 2(a) Figure 3(a) is a perspective view of a drive decoupling means as applied to grinding crankpins Figure 3 (b) is a section through the grinding wheel and crankpin as shown in Figure 3 (a) Figures 4(a) and (b) are views of a clamping ring for clamping a workpiece to the drive decoupling means Figures 5(a) and 5(b) are views of a preferred embodiment for clamping a workpiece within the drive decoupling means Figure 6 in a view of a grinding machine with a housing attached encasing a drive decoupling device, and Figure 7 is a vertical section through the grinding machine housing and housing as shown in Figure 6. Detailed Description of a Preferred Embodiment Referring to Figure 1, a flexible coupling device 10 is shown. The coupling device 10 is shown exploded to illustrate the separate components. The coupling device 10 comprises two identical connecting members 12, 14, two laminated discs 16, 18 each formed from a stack of thin sheet steel rings typically formed from shim steel, and a coupling sleeve 20, all the aforesaid being centrally apertured so as to allow a headstock to extend therethrough. The connecting member 12 further comprises a cylindrical hub 22, and a circular flange 24 which is cutaway at three circumferentially equally spaced positions. The three resulting lobes 26, 28, 30 are apertured. The second connecting member 14 is similar in construction. The coupling sleeve 20 comprises a central cylindrical portion 32 with annular flanges 34, 36 at either end. The flanges 34, 36 are circumferentially cut away to leave lobes in a similar manner as in the flange.24. In use, the coupling device 10 is assembled so that the connecting members 12, 14 and coupling sleeve 20 are interconnected by the laminated discs of thin shim steel rings 16, 18. The lobes of the flange 36 of the coupling sleeve 20 are connected to the disc 16 by three hexagon bolts. One of which is shown at 37. Three spaced apertures of the disc 16 are connected to the flange 36. Similar bolts join the three lobes 26, 28 and 30 of member 12 to the disc 16 at points intermediate the bolts 37. The second connecting disc 18 is similarly connected to the lobes of the flange 34 by means of three bolts one of which is shown at 39 and similarly to the lobes of the flange 14 by similar bolts one of which is shown at 41. The members 12, 14 are thus connected to the coupling sleeve 20 through the laminations of the discs 16, 18. Thus on assembly the interconnection of the individual connecting members 12, 14 and coupling sleeve 20 by use of the flexible laminated thin sheet steel discs 16, 18 ensures a torsionally rigid coupling which may be used in a machine tool to transmit drive to a workpiece. The flexibility of the discs 16, 18 absorbs any misalignment or axial offset of the drive member and workpiece relative to each other. A grinding machine embodying the invention is shown in Figure 2 (a) Here a coupling device such as shown in Figure 1 is encased within a housing 38. The grinding machine comprises a grinding wheel 40, a headstock 42, a tailstock 44 and drive means 46 contained within a housing 48. The headstock 42 is free to pass through the centre of the coupling device 10 contained within the housing 38. The headstock 42 and tailstock 44 support a workpiece 50. The coupling device 10 is connected at one end to the driving means 46 and at the other end is detachably secured to the workpiece 50. Rotation of the drive means 46 by the motor 52 rotates the coupling device 10. The workpiece 50 is supported between the headstock 42 and tailstock 44 and is rotated by rotation of the coupling device 10 by the motor 52. The decoupling of the workpiece 50 from the drive means 46 by the coupling device 10 removes errors due to misalignment and offset of the drive means 46 relative to the workpiece 50. Figure 2 (b) shows the grinding wheel 40 and workpiece 50 during a grinding operation. The grinding wheel 40 contacts the workpiece 50 and grinds the surface to a desired diameter. Figure 3(a) shows how a grinding machine can be used for grinding off-axis elements such as the crankpins of a crankshaft 54. Thus the crankshaft is supported between the headstock 42 and tailstock 44, and includes a number of crankpins one of which is denoted by reference numeral 56. The drive means 46 rotates the crankshaft 54 via the coupling device 10 as discussed in relation to Figure 2 (a). Rotation of the crankshaft 54 results in each off axis crankpin describing a circle centred on the crankshaft axis as shown in Figure 3(b) . The grinding wheel 40 synchronously advances and retracts as the crankshaft 54 rotates and the crankpin 56 describes a circle, this advance and retraction is controlled so that the grinding wheel 40 maintains contact with the crankpin surface at all times during the rotation of the crankshaft 54, thereby grinding a true cylindrical surface on the crankpin 56. As each crankpin is ground to the desired diameter, the grinding wheel 40 is retracted and moved axially along the crankshaft 54 to register with another crankpin. In this way an entire crankshaft can be ground automatically. Attachment of the coupling device 10 to the workpiece 50 or crankshaft 54 is preferably achieved by a clamping ring as shown in Figures 4 (a) and 4 (b) and 5(a) and 5 (b). In Figure 4 (a) a clamping ring 58 is shown having two fixed jaws 60, 62 and an adjustable jaw 64. Figure 4 (b) is a section (not to scale) along line A-A of Figure 4 (a) . In use the crankshaft 54, is inserted between the three jaws 60, 62, 64 and the adjustable jaw 64 is tightened onto the crankshaft 64 by means of a threaded thrust member 66 such as a screw. Adjustment of the threaded member 66 may be by way of by an Allen key spanner 68 so as to cause the jaw 64 to grip the crank 54 against the two fixed jaws 60, 62. Loosening the threaded member 66 allows removal of the crankshaft 64. The headstock 42 passes through the central aperture to contact the crankshaft 54 for support. An alternative clamping device 70 is shown in Figures 5(a) and 5(b). Figure 5 (a) shows a clamping ring 70 having as before two fixed jaws 72, 74 and an adjustable jaw 76. A hydraulic piston and cylinder 78 is provided to facilitate insertion and removal. Figure 5 (b) is a section (not to scale) along line B-B of Figure 5 (a) and illustrates the adjustable jaw 70 in more detail. In the clamped position a flange 55 of the crankshaft is held between the adjustable jaw 70 and the fixed jaws 72, 74. The spring 90 acts to urge the adjustable jaw 70 against the flange 55. As before the headstock 42 passes through central apertures in the drive coupling device 10 and clamping ring 70 to support the crankshaft 54. To release the crankshaft 54, the hydraulic cylinder 78 is actuated to push down on touch pad 77. The spring 90 is sufficiently strong as to initially resist this downward force, which is thus transmitted to the ring 70 and the latter displaces downwards until it hits bed 80. Thereafter continued movement of the piston in the cylinder 78 results in compression of the spring 90 and pivoting of the jaw 76 into the position shown at 76', so all three jaws 72,74, 76 are now clear of the flange 55. The crankshaft 54 is now clear to be removed from the jaws 72, 74 , 76 . The bed 80 is spaced by a running clearance from the clamping ring 70. The interaction of the flange 55, the bed 80 and the spring 90 ensures that all three jaws 72, 74,76 are moved clear of the flange 55. Figure 6 shows a view of a grinding machine housing 92 containing the drive means for operating the grinding machine, with a housing 94 attached, to encase a drive decoupling device such as is shown in Figure 1. The housing 94 encases the drive decoupling device except for a drive plate 96 and jaws 100, 102, 104. An annular attachment 98 fits over the housing 94 and attaches to the grinding machine drive housing 92. This ensures that no gap is left between the housing 94 and the housing 92 so as to improve safety and reduce the entry of dirt and swarf during machining. Jaws 100, 102, 104 are provided for clamping a workpiece. An adjustable jaw 104 grips the workpiece against the two fixed jaws 100, 102. Rotation of the drive plate 96 by the drive means, contained within the housing 92, causes rotation of a clamped workpiece. A headstock 106 passes through the central aperture of the coupling device so as to allow for support of the workpiece during machining. The control panel 106 and bed of the machine 108 are shown. As shown in Figure 7 the headstock 106 passes through the central aperture of the coupling device. The latter comprises connecting members 108, 110 and a coupling sleeve 112 which are interconnected by laminated discs in the form of thin shim- steel rings 114, 116. The coupling device is connected at one end to the driving means and at the other end is detachably securable to the workpiece by means of the jaws 100, 102, 104 (only 102, 104 of which are visible in Figure 7). A faceplate 118 is shown surrounding the headstock 106, with the cover 94 enclosing the entire coupling device shown.

Claims: AMENDED CLAIMS [received by the International Bureau on 25 September 1995 (25.09.95); original claims 1 and 4 cancelled; original claims 2,3 and 5-22 replaced by amended claims 1,2 and 3-20 (4 pages)] 1. A drive decoupling means for use in a machine tool, comprising a driving member, a driven member which is attachable to a workpiece to be machined so as to rotate the latter, the workpiece being mounted between a headstock and a tailstock, and connecting means for transferring torque between the driving and driven members and comprising a laminated device attached to the driving member via at least one off-axis connection and to the driven member by at least one other off-axis connection, the connections being circu ferentially spaced one from the other, so that in use the drive decoupling device decouples the load from the driving member, and wherein the components of the drive decoupling means are centrally apertured to accommodate the headstock, which can thereby extend axially therethrough. 2. A drive decoupling means according to claim 1, wherein the laminated device is formed from a plurality of thin flexible sheet discs, so that in use the connecting means is torsionally rigid in a plane perpendicular to the drive axis to ensure rotation is transmitted to the driven member, with the flexibility of the laminations accommodating any eccentricity developed through misalignment of the driving member and driven member. 3. A drive decoupling means according to claim 1 or claim 2, wherein the driven member is provided with radially adjustable means for securing it to the load. 4. A drive decoupling means according to claim 3, wherein the securing means is arranged symmetrically and allows centering of the driven member relative to the load. 5. A drive decoupling means according to claim 3 or claim 4, wherein the securing means comprises radially fixed and radially adjustable positioning and holding members. 6. A drive decoupling means according to any one of claims 3 to 5, wherein the load is a workpiece and at least one radial member is securable so as to grip the workpiece but is spring loaded in a direction away from the workpiece so as to cause separation from the workpiece to facilitate its demounting after a machining operation. 7. A drive decoupling means according to claim 6, wherein the radial member is externally adjustable. 8. A drive decoupling means according to claim 6 or claim 7 , wherein at least two radial members are provied, at least one radial member is adjustable and at least one other radial member is fixed. 9. A drive decoupling means according to claim 7 or claim 8, wherein the adjustment is provided by pneumatic means so that release and removal of a workpiece can be performed automatically. 10. A drive decoupling means according to claim 7 or claim 8, wherein the adjustment is provided by electrical means so that release and removal of a workpiece can be performed automatically. 11. A drive decoupling means according to claim 7 or claim 8, wherein the adjustment is provided by hydraulic means so that release and removal of a workpiece can be performed automatically. 12. A drive decoupling means according to any one of claims 3 to 11, wherein the securing means comprises three positioning and holding members arranged circularly around an annular member, two being fixed thereto and the third being spring loaded in a direction to engage the workpiece, such that the latter is positioned between the three members, and displacement of the annular member in a direction parallel to the axis of the sprung member so as to compress the spring results in separation of the sprung and fixed members from the workpiece to facilitate its removal. 13. A method of decoupling a driven member from a driving member used to rotate the drive member, wherein two drive decoupling means according to any one of claims 1 to 12 are connected in series, the driven member of the first being connected to the driving member of the second, so as to permit offset and misalignment to be accommodated. 14. A lathe having a headstock and tailstock for supporting a workpiece therebetween wherein rotation of the workpiece is effected through at least one drive decoupling means constructed according to any of claims 1 to 12. 15. A lathe having a headstock and tailstock for supporting a workpiece therebetween, wherein rotation of the workpiece is effected through two drive decoupling means constructed according to any of claims 1 to 12, and connected in series so as to remove errors due to offset and misalignment. 16. A grinding machine having a headstock and tailstock for supporting a workpiece to rotate with a grinding wheel, wherein rotation of the workpiece is effected through at least one drive decoupling means constructed in accordance with any one of claims 1 to 12. 17. A grinding machine having a headstock and tailstock for supporting a workpiece to rotate with a grinding wheel, wherein rotation of the workpiece is effected through two drive decoupling means constructed in accordance with any one of claims 1 to 12, and connected in series so as to remove errors due to offset and misalignment. 18. A method of decoupling a driven member from a driving member used to rotate the driven member substantially as herein described with reference to and as illustrated in the accompanying drawings. 19. A drive decoupling means substantially as herein described with reference to and as illustrated in the accompanying drawings. 20. A machine tool for machining a workpiece wherein drive of the latter is provided by means of at least one drive decoupling means substantially as herein described with reference to and as illustrated in the accompaning drawings.

Inventors: LAYCOCK MICHAEL, LAYCOCK, MICHAEL
Applicants: LAYCOCK MICHAEL, WESTERN ATLAS UK LTD, LAYCOCK, MICHAEL, WESTERN ATLAS U.K. LIMITED
Application year: 1995
Main classification: B23Q3
IPC codes: B23B33, F16D3