Machine Tool Geometric Error Identification in Limited Travel Space
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Solution Overview
Problem
Existing methods for evaluating geometric errors in spindle-moving lathes with limited movable ranges are inadequate, as they cannot perform ball bar or R-test measurements, and no methods have been developed to assess how these errors affect machining accuracy.
Innovation Solution
A method involving a reference sphere positioned to align with the tool spindle center, using a position measuring device to acquire displacement data, and identifying geometric errors through a least squares method with a mathematical expression that accounts for rotation angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ball bar measurement or R-test measurement is used to evaluate geometric errors, then measurement precision is improved, but the method cannot be applied to machine tools with limited movable ranges
Solution Approach 1:
A reference sphere is introduced as an intermediary measurement target. The reference sphere is positioned at a location accessible to the tool spindle within the limited movable range, allowing geometric error measurement without requiring the tool spindle to traverse large distances. The sphere serves as a mediator between the measurement system and the machine tool axes, enabling precision evaluation in constrained spaces.
Solution Approach 2:
The measurement method creates a simplified measurement model by using the reference sphere as a substitute for complex workpiece geometries. Instead of measuring actual workpiece features, the system measures the sphere's surface, which provides consistent geometric references for evaluating axis accuracy without requiring the full range of motion needed for traditional workpiece-based measurements.
2Area of stationary object
If a reference sphere is positioned offset from the rotation centerline, then measurement coverage is improved, but the reference sphere moves significantly with rotation causing measurement complexity
Solution Approach 1:
The reference sphere is positioned on the rotation centerline of the tool spindle, creating an equipotential measurement condition. When the tool spindle rotates, the sphere remains at a constant position relative to the rotation axis, eliminating the need to compensate for positional changes during measurement. This positioning strategy ensures that measurement conditions remain constant throughout the rotation cycle.
3Measurement precision
If multiple measurement steps with different positions and angles are performed, then geometric error identification accuracy is improved, but measurement time and complexity increase
Solution Approach 1:
The reference sphere serves multiple measurement functions simultaneously. By positioning the sphere on the tool spindle centerline and using it as a universal measurement target for all axis evaluations, the system eliminates the need for multiple separate measurement setups. The same sphere and measurement configuration are used to evaluate different geometric errors, reducing measurement time while maintaining comprehensive error identification capability.
Data Source
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AI summary
A method for identifying geometric errors in a machine tool includes the steps of: positioning a reference sphere so as to align its center with a centerline of a tool spindle; attaching a position measuring device having a gauge head to a rotation unit so as to direct the gauge head toward a rotation centerline of the rotation unit; acquiring displacement data relative to the center of the reference sphere by measuring positions of the reference sphere with the gauge head while rotating a rotation target (the swivel unit or the rotation unit) with the gauge head directed toward the center of the reference sphere, the displacement data being dependent on rotation angles of the rotation target; and identifying the geometric errors by least squares method using a mathematical expression having terms containing the geometric errors and representing displacement dependent on the rotation angles, and the displacement data.