Abstract:
An apparatus for, and method of, grinding crankpins of a crankshaft wherein the machine is under computer control and the grinding wheel is advanced and retracted under computer control so as to follow the planetary motion of the crankpin as the crankshaft rotates. This maintains grinding contact between the wheel and the crankpin to allow the grinding of the latter. The crankshaft is mounted between centers and is rotated by a drive unit, drive being transmitted to the end of the crankshaft via a connecting device which is torsionally rigid in a plane perpendicular to the axis of rotation of the crankshaft but which is readily deformable in other planes to accommodate misalingnment and so as to decouple the crankshaft from the drive other than to transmit pure rotation to the crankshaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Division of application U.S. Ser. No. 08/737,974, filed on Feb. 6, 19997 now U.S. Pat. No. 6,145,419. 
    
    
     FIELD OF INVENTION 
     This invention relates to grinding machine. 
     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. 
     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 clamaping 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 between centers, 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. 
     An improved drive transmitting device which will not transmit misalignment or offset to the workpiece is described in U.S. patent application Ser. No. 08/737,974. 
     SUMMARY OF THE INVENTION 
     The invention lies in a method of grinding a crankpin of a crankshaft which latter includes a circular flange at one end, comprising the steps of: 
     mounting the crankshaft between centers; 
     attaching radially outer regions of the flange to a rotational drive to rotate the crankshaft about its main axis, via a coupling which is torsionally rigid in a plane generally perpendicular to the axis of rotation of the crankshaft but which is readily deformable in other planes to accommodate misalignment; 
     advancing the grinding wheel to engage a crankpin region of the crankshaft, and 
     synchronously controlling the position of the grinding wheel whilst the crankshaft is rotated thereby to follow the planetary motion of the crankpin so as to maintain grinding contact between the wheel and the pin. 
     The advancement and retraction of the grinding wheel is preferably under the control of a computer. In a method as aforesaid, the crankshaft is preferably mounted between headstock and tailstock centres for rotation about its main axis. 
     The invention also lies in a machine tool (grinding machine) for machining a crankshaft workpiece wherein drive of the latter is provided by means of at least one drive decoupling means, substantially as described in U.S. patent application Ser. No. 08/737,974. 
     The invention thus provides a grinding machine which is adapted to grind a crankpin region of a crankshaft by synchronously advancing and retracting the grinding wheel as the crankshaft is rotated so the contact is maintained between grinding wheel and crankpin during grinding so as to grind a true cylindrical surface on the crankpin, which includes drive means for rotating the crankshaft, and a coupling means which is torsionally rigid in a plane generally perpendicular to the axis of the crankshaft but is readily deformable in other planes to accommodate misalignment, for correcting the drive means to the crankshaft. 
     Preferably the drive coupling means a driving member and a driven member which is attachable to the crankshaft so as to rotate the latter and a connecting means for transferring torque the driving and driven members; 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. 
     In one embodiment the laminations are formed from flexible thin sheet steel, so that 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, and 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 crankshaft and is to be mounted between a headstock and of the grinding machine, the components of the drive decoupling means may be centrally apertured to accommodate the headstock, which can thereby extend axially therethrough to engage one end of the crankshaft. 
     Preferably 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 crankshaft. 
     The adjustment may be provided by pneumatic, electrical or hydraulic means so that release and removal of a crankshaft can be performed automatically. 
     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 is of value in that it permits an NCR grinding machine to be used to cylindrically grind off-axis crankpins of a crankshaft by synchronously advancing and retracting the grinding wheel as the crankshaft is rotated. 
     Thus the invention provides a method of grinding a crankpin of a crankshaft mounted for rotation between centres and driven during the grinding process so as to rotate true about its main axis, wherein a rotating grinding wheel is advanced and retracted under computer control in synchronism with the planetary rotation of the crankpin caused by the rotation of the crankshaft so as to maintain grinding contact between the wheel and the pin at all times during the grinding of the pin. 
     After grinding a crankpin to a desired diameter, the grinding wheel may be retracted and moved axially so as to register with another crankpin on the crankshaft, to enable the latter to be ground. 
     A grinding machine embodying the invention thus comprises a headstock and tailstock between which a crankshaft can be mounted for true rotation between centres, means for driving the crankshaft, and means for coupling the drive means thereto in a manner so as to remove errors due to offset and misalignment, a grinding wheel which can be advanced and retracted towards and away from a crankshaft when the latter is mounted in the machine and aligned with a crankpin thereof, and a computer for controlling the said advance retraction of the wheel thereby, so as to maintain grinding contact between the wheel and the pin al all times during the grinding of the pin. 
     The invention will now be described by way of example with reference to the accompanying drawings in which: 
     FIG. 1 is an exploded view of a prior art flexible coupling 
     FIG.  2 ( a ) is a perspective view of a drive decoupling means as applied to a grinding machine 
     FIG.  2 ( b ) is a sectional view through the grinding wheel and workpiece as shown in FIG.  2 ( a ) 
     FIG.  3 ( a ) is a perspective view of the drive decoupling means as applied to grinding crankpins 
     FIG.  3 ( b ) is a section through the grinding wheel and crankpin as shown in FIG.  3 ( a ) 
     FIG.  4 ( a ) is an end view a clamping ring for clamping a workpiece to the drive decoupling means 
     FIG.  4 ( b ) is a section (not to scale) along line A—A of FIG.  4 ( a ). 
     FIG.  5 ( a ) is an end view of a preferred embodiment for clamping a workpiece within the drive decoupling means 
     FIG.  5 ( b ) is a section (not to scale) along line B—B of FIG.  5 ( a ) and illustrates an adjustable jaw in more detail. 
     FIG. 6 in a view of a part of a grinding machine with a housing encasing a drive decoupling device, and 
     FIG. 7 is a vertical section through the grinding machine housing as shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Referring to FIG. 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 coup ling 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 an 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. 
     Part of a grinding machine is shown in FIG.  2 ( a ) Here a coupling device such as shown in FIG. 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 . 
     FIG.  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. 
     FIG.  3 ( a ) shows how a grinding machine can be used cylindrically grind off-axis crankpins of a crankshaft  54 . 
     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 FIG.  2 ( a ). 
     Rotation of the crankshaft  54  results in each off axis crankpin describing a circle centered on the crankshaft axis as shown in FIG.  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 . Although not shown the operation of the grinding machine is controlled by a computer. 
     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 crankshaft  54  is preferably achieved by a clamping ring as shown in FIGS.  4 ( a ) and  4 ( b ) and  5 ( a ) and  5 ( b ). 
     In FIG.  4 ( a ) a clamping ring  58  is shown having two fixed jaws  60 ,  62  and an adjustable jaw  64 . 
     FIG.  4 ( b ) is a section (not to scale) along line A—A of FIG.  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  54  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  54 . 
     The headstock  42  passes through the central aperture to contact the crankshaft  54  for support. 
     An alternative clamping device  70  is shown in FIGS.  5 ( a ) and  5 ( b ). 
     FIG.  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. 
     FIG.  5 ( b ) is a section (not to scale) along line B—B of FIG.  5 ( a ) and illustrates the adjustable jaw  76  in more detail. 
     In the clamped position a flange  55  of the crankshaft is held between the adjustable jaw  76  and the fixed jaws  72 ,  74 . The spring  90  acts to urge the adjustable jaw  76  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 and can 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 . 
     FIG. 6 shows a view of a grinding machine housing  92  containing a drive means for operating the grinding machine, with a housing  94  attached, to encase a drive decoupling device such as is shown in FIG.  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 the flanged crankshafts. A headstock  106  passes through the central aperture of the coupling device so as to allow for support of the crankshaft during machining. The control panel  106  and bed of the machine  108  are shown. 
     As shown in FIG. 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 flange of the crankshaft by means of the jaws  100 ,  102 ,  104  (only  102 ,  104  of which are visible in FIG.  7 ). A faceplate  118  is shown surrounding the headstock  106 , with the cover  94  enclosing the entire coupling device shown.