Unova UK Limited

Michael George Pierse

Mark Andrew Stocker

Dermot Robert Falkner

Paul Martin Howard Morantz

Paul Martin Morantz

The invention provides a method of reducing thermal distortion in grinding machines. Such machines each comprise a machine base () and a grinding wheel () for grinding components in the machine (). The method includes the steps of: (a) sensing a first temperature at an upper surface of the base () substantially below a position () in the machine () whereat component grinding using the wheel () occurs; (b) sensing a second temperature of an underside surface of the base () substantially below the position () whereat component grinding occurs; (c) determining a relationship between component size drift and changes in a difference between the first and second temperatures; and thereafter (d) correcting a positional offset applied to the wheel () during grinding in accordance with the determined relationship, thereby reducing the component size drift. Preferably, the relationship is substantially a linear function of the form MDS=K(&#x394;T&#x2212;&#x394;T) although higher-order polynom be applied if required. The invention also relates to grinding machines () employing the method of reducing thermal distortion.

Method of reducing thermal distortion in grinding machines

A method of grinding the edge of a disc uses a grinding machine having mounted thereon a grooved grinding wheel, in which the groove is formed in situ using a forming wheel also mounted on the grinding machine. After a workpiece has been ground or after a succession of workpieces have been ground, re-engaging the grinding wheel and the forming wheel with the grinding wheel remaining in situ, to re-form the groove in the grinding wheel to correct for wear. A grinding machine comprises a grinding wheel, drive means therefor, a workhead and workpiece spindle and drive means therefor, a forming wheel and drive means therefor, means for moving the grinding wheel so as to plunge grind the edge of the grinding wheel to form a groove therein of precise cross-section and means for effecting relative movement between the grinding wheel and the forming wheel to enable the grinding wheel to engage with the edge of a circular workpiece component mounted on the workpiece spindle to edge grind the component and wherein the forming wheel is also mounted on the workpiece spindle for rotation therewith, and the grinding wheel is a resin bonded wheel.

Grinding and polishing machines

A machine tool has a carriage, has a workpiece carriage for carrying a workpiece from which material is removed by a tool carried by a tool carriage. A two-axis scale is attached to one of the carriages, and cooperates with a reading head attached to the other carriage. The output from the reading head is processed by signaling processing means to provide an indication of the position and/or movement of the carriages relative to each other and for generating positional data about one or both of the carriages to assist in controlling their movement in order to perform a machine operation. By directly measuring the relative positions of the two carriages, problems arising from, for example, distortions of the machine frame on which the carriages are mounted are at least mitigated. A preferred embodiment of the machine incorporates a second reading head attached to one carriage and incorporating the scale on another carriage so that the outputs from the two reading heads can be used to determine whether there has been any relative angular displacement of the paths followed by the carriages. There is also provided a method of determining the linear movement of one of the carriages relative to the other, and the machining process achieved using the machine tool.

System for monitoring workpiece and tool carriages movement using a two-axis scale attached to a carriage cooperating with a reading head attached to the other carriage

Grinding machines and polishing machines

A workpiece alignment and shifting system for moving circular workpieces from a first inspection station to a second machining station, comprises workpiece holding means for attachment to the face of a disc workpiece to move the latter from one position to another. Robotic means controls the position of the workpiece holding means and is adapted to move in a least two orthogonal directions, both of which are parallel to the plane of the disc when it occupies the first station. The disc is rotated in the inspection station and in the machining station and inspection means determines the position of the geometric center of the disc as it is rotated. Computing means calculates from data delivered by the inspection means the two shifts required along the orthogonal directions of movement of the robotic means, to move the geometric center of the disc to a second desired position whose coordinates are known. The computing means includes memory means for storing the said coordinates. The coordinates are those of the center of rotation of the workpiece holder or chuck in the said second station. The workpiece holding means is vacuum operated. A three axis robot is employed to pick and place disc-like wafers of semi-conductor material for edge grinding, and movement along two of the robot axes, X and Z, is used to control the centering of the wafer on a vacuum chuck in the second grinding station.

Workpiece inspection and handling

A grinding or polishing machine comprises a rigid platform on which a workhead spindle and a grinding wheel spindle are located. The grinding wheel spindle is mounted on a sub-assembly which is attached to the platform by means of flexures which permit limited movement of the sub-assembly in a direction generally parallel to the direction in which the wheel has to advance to achieve grinding or polishing of a workpiece mounted on the workhead spindle. The flexures generally inhibit movement of the sub-assembly in all other directions. Two grinding wheels are mounted on the platform, one on each of two sub-assemblies, and each sub-assembly is attached to the platform by flexures as aforesaid. The flexure mounting points are located generally centrally of the machine and are located on either side of and close to the machine centre line. In a grinding or polishing machine having workpiece spindle means, tool spindle means mounted on sub-assemblies which permit limited relative movement in one direction to effect tool and workpiece engagement cam drive means is provided whereby each sub-assembly is movable to advance or retract each tool spindle towards and away from the workhead spindle.

Grinding machine spindle flexibly attached to platform

A grinding machine for grinding the edge of a disc or wafer comprises a grooved grinding wheel 308, means for transporting the wafers before or after grinding, and a housing 332 in which wafers 340 are parked on a vacuum chuck 336 awaiting inspection. A jet 338 protrudes into the housing and directs water or air towards the face and edge of the wafer on the chuck. The transport means then transfers wafers to an inspection station.

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Bedford, United Kingdom

Michael George Pierse