Machine Tool Axis Positioning Error Compensation
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Solution Overview
Problem
Existing methods for positioning machine axes in machine tools do not effectively compensate for reproducible errors caused by rotary axes, which complicates machining accuracy due to the dependency of static errors on the position of these axes.
Innovation Solution
The method involves entering error transformation amounts dependent on the axis position into a kinematic table, allowing for interpolation and compensation within the kinematic chain, rather than using a compensation table for setpoint values in workpiece coordinates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a compensation table acting on setpoint values in workpiece coordinates is used, then machining accuracy can be improved, but the method does not effectively compensate for errors dependent on rotary axis positions
Solution Approach 1:
The patent segments the compensation approach by separating linear axis compensation (in workpiece coordinates) from rotary axis compensation (in machine coordinates). The compensation table is divided into different sections: one for linear axes acting on setpoint values, and another for rotary axes acting on transformation amounts in the kinematic table. This segmentation allows each type of error to be compensated using the most appropriate coordinate system and method.
Solution Approach 2:
The patent introduces a new dimension to the compensation approach by adding axis-position-dependent error transformation amounts to the kinematic table. Instead of only compensating in the workpiece coordinate system, the system now compensates in the machine coordinate system as well, by modifying transformation amounts based on actual axis positions. This dimensional extension enables effective compensation for rotary axis errors.
2Ease of manufacture
If error transformation amounts dependent on axis position are entered in the kinematics table, then compensation of reproducible errors is simplified, but the device complexity increases due to additional compensation tables and interpolation mechanisms
Solution Approach 1:
The patent makes the kinematic table multi-functional by enabling it to handle both normal coordinate transformations and error compensation simultaneously. The same kinematic table structure is used for both defining the machine tool's kinematics and storing axis-position-dependent error transformation amounts. This universality avoids the need for separate compensation structures and simplifies the overall system architecture.
Solution Approach 2:
The system performs self-service through automatic interpolation. When the numerical control unit encounters an axis position that is not exactly matched in the compensation table, it automatically interpolates the error transformation amounts between the nearest measured positions. This self-service mechanism eliminates the need for manual interpolation calculations and reduces setup complexity.
3Extent of automation
If automated measurement and conversion methods are used for rotary axis errors, then measurement effort is reduced, but the adjustment complexity increases significantly
Solution Approach 1:
The patent uses copying by measuring actual axis positions and using these measured values as indices to retrieve pre-measured error transformation amounts from the compensation table. Instead of complex real-time calculations or adjustments, the system copies the appropriate error values from the table based on the actual position, enabling automated compensation with minimal adjustment complexity.
Data Source
Figure 1a~1d
Figure 2a~2c
AI summary
The method involves indicating kinematics of a machine tool (3) i.e. five-axis milling machine, that describes entries, and indicating axle direction and an associated transformation amount in each entry. Error transformation amount for a machine axle (X) with an error is registered in a direction other than the axle direction, where the amount is dependent upon an axle position. The error transformation amount depending upon the axle position is presented in the form of an axis specific compensation table, which is referenced in a kinematics table.