Device and method for detecting an approach of a tool to a workpiece

A method for determining an approach of a tool to a workpiece in a machine tool, the tool and the workpiece being movable relative to one another, the tool or the workpiece being connected to a shaft in a rotationally fixed manner, the tool having a coolant channel adapted to supply a coolant to a machining area in which machining of the workpiece by the tool is performed, the machine tool including a measurement device, having a measuring graduation arranged in a rotationally fixed manner on the shaft and at least one position sensor arranged in a fixed manner relative to the shaft, and a data processor, comprising:

• scanning the measuring graduation by the position sensor;
• generating, from the scanned measuring graduation, position values that indicate a position of the shaft;
• feeding the position values to the data processor;
• determining, by the data processor, that the tool is located in an approach area relative to the workpiece, in which a displacement of the shaft occurs as a result of dynamic pressure of a coolant flow impinging on the workpiece, by evaluating a trend of the position values as the tool approaches the workpiece;
• and
• outputting an approach signal, by the data processor, when the tool reaches an approach position relative to the workpiece, in which the tool has approached the workpiece without touching the workpiece.

A machine tool, comprising:

• a tool movable relative to a workpiece and including a coolant channel adapted to supply a coolant to a machining area in which machining of the workpiece is performed by the tool;
• a rotatable shaft adapted to connect to the tool or the workpiece in a rotationally fixed manner;
• a device adapted determining an approach of the tool to the workpiece, including:
• a measurement system, including a measuring graduation arranged in a rotationally fixed manner on the shaft and at least one position sensor arranged in a fixed manner relative to the shaft and adapted to scan the measuring graduation and to generate position values from the scanned measuring graduation that indicate a position of the shaft;
• and
• a data processor, the position sensor adapted to feed the position values to the data processor, the data processor adapted to determine that the tool approaches the workpiece by evaluation of a trend of the position values, to determine that the tool is located in an approach area relative to the workpiece, in which a displacement of the shaft, resulting from dynamic pressure of a coolant flow impinging on the workpiece, occurs, and to output an approach signal to signal that the tool reaches an approach position relative to the workpiece, in which the tool has approached the workpiece without touching the workpiece.