Background It is known to control the different machining axes of a grinding machine using a computer based control system which is programmable so that the wheelhead and workpiece are moved relatively so as to grind a workpiece in different ways.

Shaft encoders, position and movement sensors and gauges can provide feedback signals to the computer to allow grinding to be controlled.

The present invention seeks to provide an improved grinding machine of the type above described.

Summary of the invention According to one aspect of the present invention a grinding machine comprises:- 1. a base, 2. a wheelhead with grinding wheel and wheel drive mounted thereon, 3. a workholder and drive means for rotating a workpiece mounted therein about at least one axis, 4. wheelhead drive means for moving the wheelhead relative to the machine base, and 5. a programmable computer based control system for independently controlling the drives to perform a grinding operation by engaging the wheel with the workpiece, wherein 6. The wheelhead is movable along two orthogonal X and Z linear axes in a first plane in which movement along the X axis moves the wheel towards or away from the workholder, 7. The workholder is rotatable about a C axis which is parallel to and in the same plane as the axis of rotation of the wheel, the common plane being coincident with or parallel to the said first plane, and 8. During engagement between wheel and workpiece the control system is operable to control the rotational movement of the workpiece about the C axis and the movement of the wheelhead along the X and Z axes, so as to determine how the workpiece is to be ground.

After grinding is completed the control system may be programmed to move the wheelhead along at least one of the X and Z axes to move the wheel into engagement with a wheel-dressing tool, (when a dressable wheel is used).

Where the workpiece requires a slot to be ground in an end face thereof the control means is programmed to:- 1) move the wheelhead so as to engage the wheel with the end face of the workpiece and to advance the wheel along the X axis so as to remove material from the end face over the width of the wheel until the wheel has penetrated the workpiece to a required depth, and thereafter to 2) move the workholder during the grinding so as to rotate it about the C axis in an oscillatory manner in synchronism with an oscillatory linear movement of the wheelhead along the X axis so as to grind the bottom surface of the slot as a flat or a curved surface.

Where the workpiece comprises part of the perimeter of a circular object, the latter is positioned in the workholder so as to be rotatable about its central axis and the control means is programmed to:- 1) move the wheelhead so as to engage the wheel with the said part to grind the latter, and thereafter 2) move the workholder and wheelhead during the grinding so as to rotate the workholder about the C axis and produce an oscillatory linear movement of the wheelhead along the X axis, so as to grind a flat or curved external face on the said part.

The part may be one of a plurality of similar circularly spaced apart regions around the periphery of the circular object or one of a plurality of articles circularly spaced around a circular support such as a circular rotatable workholder, and each preferably protrudes radially beyond the periphery thereof.

Where one or more articles are to be mounted around a circular support or workholder, the latter conveniently comprises a chuck fixture having jaws for gripping the articles at circularly spaced apart points therearound.

Where curvature of the surface is to be centred on an axis which is parallel to or coincident with the central axis of rotation of the circular object or support or workholder, only the workholder needs to be oscillated about its central axis.

In a development of the invention the wheelhead includes a first face on which the grinding wheel is mounted and at least one further face from which at least one further tool such as a further grinding wheel, or a milling or a drilling tool, or any combination thereof, protrudes, and the grinding wheel or the at least one further tool is brought into machining engagement with a workpiece by moving the wheelhead along its Z axis so that when advanced towards the workpiece along the X axis, the grinding wheel or the said further tool will move towards and engage the workpiece.

A dressing tool may be provided for dressing the further tool or tools as required and the control system is programmed to move the wheelhead about X or Z axes to engage the or each further tool with the dressing tool.

A plurality of dressing tools may be provided at different positions relative to the wheelhead to simplify the movement of the wheelhead to engage the wheel or further tool (s) with the dressing tools.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figs 1A-lD illustrate a grinding machine constructed and adapted to operate in accordance with one aspect of the invention, for grinding a single workpiece, Figs 2A-2D illustrate a similar machine set to grind a plurality of workpieces, Figs 3A-3D illustrate a machine similar to that of Fig 1 but having additional machining tooling mounted on the wheelhead, and Figs 4A-4D illustrate a machine similar to that of Fig 2 but having additional machining tooling mounted on the wheelhead.

The machine illustrated in Figs 1A-lD comprises a wheelhead 10 carrying a grinding wheel 12 driven about the S-axis (see Fig 1B) by a motor (not shown) within or on the wheelhead 10. The latter is slidable along a linear track (conveniently referred to as the Z- axis) parallel to the axis of rotation 18 of the wheel 12 and denoted by the dotted line 19.

Adjacent to the wheelhead is a workhead generally designated 20, which includes a drive for rotating a workpiece 22 about a parallel axis 24. This is referred to as the C-axis.

Where the workpiece is an elongate device such as 22 a workholder 23 is mounted on the workhead 20 and the workholder is rotatable about the C-axis by the workhead drive (not shown) The workpiece 22 shown in Fig 1A is a camshaft for an internal combustion engine and the grinding wheel 12 is set to grind a slot in one end of the shaft. To this end the wheelhead is movable along an orthogonal linear track denoted by the dotted line 25, referred to as the X-axis.

The X, Z, C and S axes are also denoted in Figs 1B and 1D.

Wheel dressing tools are denoted at 26,28 and 30. Movement of the wheelhead along the X and Z axes allows the wheel to be brought into dressing engagement with one or the other of the wheel dressing tools 28 and 30. Independent movement of the other tool 26 enables it to perform a wheel dressing function.

Fig 1B is a view of the machine from above in the direction of arrow B of Fig 1A.

Fig 1C is a view of the machine in the direction of arrow C in Fig 1A albeit with the machine rotated through 180° about the axis of the camshaft workpiece.

Fig 1D is a side view of the machine of Fig 1A in which the wheel dressing tool 30 has been omitted.

The slot (not shown) is formed by plunge grinding into the end face of the camshaft 22.

The width of the slot is determined by the width of the wheel 12 and will have parallel sides, but since the wheel is circular, the base of the slot will have a radius of curvature similar to the radius of the wheel. Slots of greater width may be ground by moving the wheel along the Z-axis.

Since it is desirable for the slot to have a flat base, in accordance with the invention the workhead 20 rotates the workholder 23 and the camshaft 22 about the C-axis with an oscillating rocking motion at the same time as the wheelhead is advanced and retracted in a similar oscillatory motion along the X-axis, so that the locus of the point of contact between the wheel 12 and the workpiece 22 is a straight line denoted by 32 in Fig 1D.

As shown the line 32 is orthogonal to the X and Z axes, but if the base of the slot is to be inclined relative to the workpiece axis, so that line 32 would not appear vertical and perpendicular to line 25 (the X-axis) in Fig 1D, but instead would be inclined by an angle of less than 90° to the X-axis, the movement of the wheelhead along the X-axis is adjusted so that the locus of the point of contact between wheel and workpiece describes a straight line such as 34 in Fig I D.

In the machines of Figs 2-4 the same reference numerals are employed to denote parts which are common to those of the machine shown in Fig 1.

In Figs 2A-2D the camshaft workpiece and workholder 22,23 are replaced by a disc workholder 36 around the periphery of which are mounted a plurality of small similar workpieces, one of which is denoted at 38. The wheel 12 is now replaced by wheel 40 which is to grind the outer face 41 of each workpiece such as 38. Where this is to be a flat surface the wheelhead 10 and workholder 36 are moved as before about the X and C axes so that the line of contact between the wheel and workpiece moves in a flat plane similar to that denoted by line 32 in Fig 1D.

If the ground surface is to be other than tangential to the circular workpiece holder 36, then the movements of the wheelhead and workholder are selected accordingly so as to describe a plane at an angle such as line 34 in Fig 1D.

The machines shown in Figs 3 and 4 are similar to those in Figs 1 and 2 respectively except that additional machining tools are provided, denoted by 42,43 and carried by an auxiliary head 45 mounted on the wheelhead 10. Movement of the latter along the Z-axis allows tool 42 or 43 to be aligned with the workpiece and movement along the X-axis allows for machining engagement therebetween.

In any of the machines shown, synchronous movement of the wheelhead 10 and workholder 23 or 36 allows a flat surface to be ground by the curved outer surface of the wheel 12, and as mentioned the ground surface may be inclined or perpendicular to an axis of the workpiece.

If a convexly curved surface is to be ground on the workpiece, the head and workholder are moved relatively in a different manner, so that the locus of the point of contact between wheel and workpiece describes an appropriately curved surface, which will correspond to the final ground surface of the workpiece.

If the surface is to be concavely curved with a radius of curvature R then a wheel 12 must be chosen whose radius is not greater than R, and is preferably somewhat smaller, and the curved surface is again produced by synchronous relative movement between wheelhead and workholder.

Control of the machine, including the oscillatory movements along the X-axis and about the C-axis, is preferably achieved using a computer based programmable control system denoted by 46 in each of the Figures.

The side faces such as 45 (see Figs 2D and 4D) of a workpiece such as 38 may be ground using the side faces of the wheel 40.