Title: Grinding Machines and Methods of Operation Thereof

Field of the invention

The present invention relates to grinding machines, and in particular, supports for grinding wheels on such machines.

Background to the invention

Many grinding machines of the type capable of machining components of a predominantly cylindrical nature, often but not exclusively in a process of cylindrical grinding, comprise means for holding workpieces rotatably in a workhead. Typically, a single grinding spindle is provided, together with means for engaging the wheel with the workpiece. Relative movement between the wheel and workpiece may by achieved by transportation of the wheel towards the workpiece, or vice versa, or a combination of these two approaches. Movement tends to be along linear axes, orientated to provide motion either radially with respect to the axis of the workpiece (conventionally identified as the X axis), or parallel to the workpiece axis (conventionally referred to as the Z axis).

Summary of the invention

The present invention provides a support assembly for supporting a grinding wheel drive assembly on a grinding machine, the support assembly comprising a support body and a base, with the support body rotatably mounted on the base, and a direct drive motor for rotating the body relative to the base, wherein the motor comprises a rotor carried by the support body and a stator mounted on the base.

Provision of a direct motor drive in this way affords higher angular stiffness and minimal backlash when compared to indirect, geared drive configurations.

Preferably, servo control is provided for the drive motor, to allow for fine control of the support body position, in comparison to discrete positioning, as provided by face tooth coupling type designs, for example.

In a preferred embodiment, the support assembly is configured such that the drive motor stator extends around the outside of the rotor.

The present invention further provides a support assembly for supporting a grinding wheel drive assembly on a grinding machine, comprising a support body rotatably mounted on a base, wherein the body is supportable during rotation by at least one hydrostatic thrust bearing. Hydrostatic bearings may provide higher static and dynamic stiffness than rolling element bearings.

In a preferred embodiment, the support assembly base includes an upstanding post, and at least one hydrostatic journal (radial) bearing is provided between the post and the support body. Furthermore, the base may include a support member which extends radially from the post and supports the motor stator. Preferably, a hydrostatic bearing is provided between the support member and the support body.

A hydrostatic bearing may be provided between the support body and the base, beneath the support body. In use, this bearing may be turned off to enhance the angular and tilt stiffness of the support assembly when in a stationary, fixed position.

According to another aspect of the present invention, a support assembly is provided for supporting a grinding wheel drive assembly on a grinding machine, comprising a support body rotatably mounted on a base, wherein the support body includes a flange which extends around the rotational axis of the support body, and wherein the support assembly includes a clamp assembly operable to grip the flange and thereby hold the support body in a selected rotational position.

Preferably, the clamp assembly is loosely retained within the support assembly to allow movement thereof relative to the support assembly during activation of the clamp assembly.

Preferably, the support body flange extends radially with respect to the rotational axis of the support body.

In a preferred embodiment, the support assembly includes a pair of flexure plates provided on either side of the flange. Preferably the plates are annular. They are preferably mounted on the base in such a way as to restrict radial and angular displacement thereof. They may be formed of spring steel, for example.

In a further embodiment, the support body could be fitted with a grinding spindle at one station, and a tool turret mounting tool, or tools if a turret was fitted, on another station. These tools could be capable of turning the component in either a soft or hard condition, depending on the type of turning tool applied.

Preferably, the support assembly includes a rotary position encoder, for outputting a signal indicative of the rotational position of the support body relative to the base.

The present invention further provides a grinding machine comprising a workholder and drive means for rotating a workpiece mounted in the workholder about an axis, a drive assembly for driving a grinding wheel, and a support assembly as described herein for rotating the drive assembly around an axis perpendicular to the axis of rotation of the workholder.

Preferably, the grinding machine includes means for moving the support assembly along two orthogonal axes parallel and perpendicular to the rotational axis of the workholder, respectively.

In addition, the invention provides a grinding machine comprising a workholder and drive means for rotating a workpiece mounted in the workholder about an axis, a drive assembly for driving a grinding wheel, and a support assembly for rotating the drive assembly around an axis perpendicular to the axis of rotation of the workholder, wherein the support assembly is configurable to carry at least one grinding wheel and at least one turning tool.

Preferably, the grinding machine includes means for moving the support assembly along two orthogonal axes parallel and perpendicular to the rotational axis of the workholder, respectively.

A support assembly as described herein allows more than one wheel to be brought to a workpiece, reducing the processing time and increasing the accuracy of relative positioning of features defined using different wheels. The ready availability of different wheel types also allows features to be machined more efficiently. For example, larger and/or coarser grit wheels may be used to remove the bulk of the stock material from a workpiece prior to a finishing process carried out with a different wheel of smaller diameter and finer grit size, for example.

In another implementation, traverse grinding could be carried out by one wheel, followed by a formed wheel plunge grinding operation by a second wheel and spindle.

In addition, a single wheel could be used to grind two different features, for example parallel diameters and tapers, by changing the support body rotational position.

The configuration described herein also enables the use of a double-ended spindle or spindles, rotating the support body to permit access to the component without causing a foul by the other wheel.

The present invention further provides a method of operating the grinding machine, the grinding machine comprising a workholder and drive means for rotating a workpiece mounted in the workholder about an axis, a wheelhead for supporting a grinding wheel, and a support assembly for rotating the wheelhead about an axis perpendicular to the rotational axis of the workholder, the method comprising a step of rotating the wheelhead about said axis whilst the grinding wheel is in contact with a workpiece mounted in the workholder. Thus, the support assembly enables the angular orientation of a grinding wheel to be altered during grinding, facilitating contour grinding, for example.

Brief description of the drawings

Embodiments of the invention will now be described by way of example and with reference to the accompanying schematic drawings, wherein:

Figure 1 is a perspective view of a grinding machine including a support assembly according to an embodiment of the present invention;

Figure 2 is a cross-sectional side view of the support assembly shown in Figure 1;

Figure 3 is an enlarged portion of the cross-sectional view shown in Figure 2 showing the clamp assembly; and

Figure 4 is a perspective view of the clamp assembly and flexure rings of the support assembly shown in Figure 2.

Detailed description of the drawings

The grinding machine shown in Figure 1 has a machine base 2. A workhead 4 and a footstock 6 are mounted on the base and arranged to rotatably hold a workpiece 8 therebetween.

The machine further includes a rotatable support assembly 8 which carries first and second grinding spindles 10, 12 on opposite sides thereof. Grinding wheels 14 are mounted on and driven by the grinding spindles.

The support assembly 8 is mounted on a slidable platform 16, which is in turn carried by a slidable platform 18, and this in turn rests on the machine base. Platform 18 is slidable relative to the machine base along an axis parallel to the axis rotation of the workpiece, identified as axis Z in Figure 1. Platform 16 is slidable relative to platform 18 along an axis which extends radially with respect to the rotational axis of the workpiece and therefore orthogonally with respect to the Z axis. The axis along which platform 16 is slidable relative to platform 18 is identified as axis X in Figure 1.

The support assembly 8 is rotatable relative to the machine base 2 about an axis perpendicular to the X and Z axes, as indicated by arrow B in Figure 1. This allows selection

of a grinding wheel or tool for engagement with a workpiece from those carried by the support assembly.

The grinding spindle or spindles may have grinding wheels mounted at either, or both ends of the spindle, and can be fitted with any combination of wheel diameters and widths, differing types and grades of abrasives, with either straight side and front faces, or other formed features.

Figure 2 shows a cross-section through the support assembly 8 shown in Figure 1. It has a base 20 for mounting on a grinding machine. The base includes an upstanding, vertical post 22. A support member 24 extends outwardly from the upper end of the post 22. It carries a motor stator 26 below it.

A support body 28 is mounted for rotation about post 22. It comprises an inner rotating component or hub 25 and an outer rotating component 27. The hub 25 carries a motor rotor 30 facing the inside of stator 26.

The support body 28 is rotatable about post 22 by a direct drive high torque motor comprising stator 26 and rotor 30. A signal indicating the rotational position of the support body is generated by an on-axis direct mounted encoder 54.

Rotation of the support body 28 about the post 22 is assisted by two hydrostatic thrust bearings, 32 and 34, defined between the support member 24 and the support body, and the base 20 and the support body, respectively. In addition, hydrostatic radial bearings 36 and 38 are defined between the post 22 and the support body 28.

Means (not shown) are provided for mounting one or more grinding spindles or wheelheads, and/or other components on the outer surface of support body 28.

A clamp assembly is shown in cross-section in Figure 2, and an enlarged view thereof is shown in Figure 3. The clamp assembly is shown in combination with flexure rings 42, 44 in Figure 4.

A flange 40 extends radially outwards from the support body 28. Two flexure plates 42, 44 are mounted on the base 20, adjacent respective upper and lower surfaces of the flange 40.

A flexure spacer 41 is provided between the flexure plates 42 and 44, and an upper flexure clamp 43 is provided over the upper flexure plate 42 to hold the plates in position.

The clamp assembly includes a clamp body 50, which is substantially C-shaped in cross- section. A gripping member or piston 52 is slidably mounted in the clamp 50, and moveable to be brought into engagement with the upper flexure plate 42. This action causes the clamp body 50 to move vertically to allow even force to be applied to the two flexures 42 and 44.

Preferably, clamp assembly 50, 52 is one of two radially opposed clamp assemblies provided within the support assembly. The clamps allow the rotational position of the support body to be temporarily fixed. The clamp assemblies are not rigidly attached to the support assembly, allowing relative movement therebetween. In this way, clamping stresses are restricted to the clamp assemblies, and not transmitted through the support assembly.

The clamps supply their clamping force to the flange 40 via the pair of flexure plates 42, 44, which are attached rigidly to the base 20 so as to restrict both radial and angular movement thereof. The flexure plates are able to flex vertically to transmit clamping force from the clamp assemblies to the flange 40. Applying clamping force via the flexures allows clamping to take place without significantly influencing the support body position relative to the central post in radial or axial directions relative to the workpiece. Accordingly, disturbance of the rotational position of the support body by the clamping operation is minimised. Preferably, clamping force is applied by springs (not shown) within the clamp assembly, with a release force being provided by high pressure hydraulic oil. Thus, the assembly is fail-safe in that a loss of oil pressure causes the clamp to be applied.

Using the arrangement shown in Figure 2, a static holding mode may be achieved by turning off the lower hydrostatic thrust bearing 34, allowing the opposing faces of the support body 28 and base 20 to come into contact. This increases the angular and tilt stiffness of the

assembly when in a fixed position. In this mode, the radial bearings remain floating, and the small axial movement of the support body when the hydrostatic thrust is removed is accommodated by the clamp assembly due to the flexure plate arrangement, which is sufficiently axially compliant to allow this movement.

As the rotational position of the support body is detected by encoder 54, any small positioning error can be assessed for its impact on the positioning of a grinding wheel or tool along the X axis, which would have an effect on the ground diameter of a workpiece, and corrected for.

The torque afforded by the direct drive motor of the support assembly may be sufficient to allow grinding to be carried out without use of the clamp assemblies. Nevertheless, the clamping assemblies can provide a greater degree of stiffness, for example for operations involving a high rate of stock material removal.

A support assembly as described herein may allow the angular orientation of a grinding wheel to be altered during a grinding operation. Thus, contour grinding may be achieved by rotation around the B axis, and/or movement along the X and/or Z axes. In implementing such techniques, the rotational position of the support body may be maintained via servo control of the direct drive motor with the clamp assemblies in the released position.