Machine Tool NC Compensation for Workpiece Gravitational Deformation
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Solution Overview
Problem
Current numerical control systems for machine tools face challenges in accurately correcting deformation errors caused by workpiece mass and barycentric position, especially when the deformation behavior changes with machine usage and assembly accuracy, making it difficult to maintain high machining accuracy for various workpieces.
Innovation Solution
A numerical control device and method that includes an axis-dependent deformation error estimation unit, gravitational deformation estimation unit, correction value calculation unit, and addition unit, which calculates and corrects deformation errors based on axis-dependent and gravitational deformation parameters, using a touch trigger probe to measure and identify errors, even when the workpiece is loaded, and adjusts for changes in deformation behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the mass of the machine is increased to enhance static rigidity and reduce deformation error, then the deformation error is reduced, but the velocity decreases and material costs increase
Solution Approach 1:
The patent changes the parameter of deformation compensation from static (fixed machine mass) to dynamic (variable workpiece mass). By measuring the actual workpiece mass and barycentric position, the system calculates and applies real-time compensation values to correct deformation errors without physically increasing machine mass, thus maintaining velocity while improving precision.
Solution Approach 2:
The patent replaces the mechanical approach of increasing machine mass to reduce deformation with a computational approach. Using measurement data from the workpiece and gravitational force calculations, the system computes compensation values that are applied to the control system, substituting physical reinforcement with intelligent correction.
2Extent of automation
If a touch trigger probe is used to measure geometric error, then automatic error identification is achieved, but the measurement requires the machine to stop and cannot be performed with workpiece loaded
Solution Approach 1:
The patent introduces a mediator approach by using the workpiece itself (or its geometric model) as the reference for measurement instead of requiring external target balls and probe measurements. The measurement system processes images of the workpiece directly, allowing error identification to proceed without stopping the machine or requiring separate measurement operations.
Solution Approach 2:
The patent performs preliminary measurement and error identification during the setup phase or between machining operations, but crucially enables continuous operation by calculating compensation values that can be applied without interrupting the machining process. The system prepares compensation data in advance that remains valid throughout production.
3Ease of manufacture
If deformation error is corrected based on preliminary measurement with fixed workpiece, then correction is simple, but the correction is inaccurate when deformation behavior changes with machine usage
Solution Approach 1:
The patent transforms the static deformation correction approach into a dynamic one. Instead of using fixed compensation values from preliminary measurements, the system continuously updates compensation values based on actual workpiece mass and barycentric position measurements. This dynamic adaptation ensures accuracy even as machine deformation behavior changes with usage, thermal effects, or different workpieces.
Solution Approach 2:
The patent implements a feedback mechanism where the actual workpiece mass and barycentric position are measured, compared against reference values, and used to calculate updated compensation values. This closed-loop feedback ensures that correction accuracy is maintained despite changes in machine deformation behavior over time or with different workpieces.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables accurate identification and correction of deformation errors, ensuring high machining accuracy for various workpieces by estimating deformation errors based on workpiece mass and barycentric position, even when the deformation behavior changes, and corrects errors that were previously difficult to estimate, improving overall machining precision.
Implementation Method 1
a touch trigger probe is attached to a tool post in a machine, a target ball is installed on a table, the machine automatically performs an index operation of an inclined axis and a rotation axis on a specified index position, a central coordinate of the target ball is measured at each index position
Implementation Method 2
A deformation error caused by an external force, such as a gravity of a jig and a workpiece loaded on the table 3, or by shift in center of gravity of the cradle 4, the trunnion 5, and the like in accordance with operations of the translational axis and the rotation axis
Data Source
AI summary
A numerical control device for a machine tool controls a machine tool having a main spindle for attaching a tool, a table holding a workpiece and a jig, three translational axes, and one or more rotation axis. The numerical control device includes an axis-dependent deformation error estimation unit, an input unit, a gravitational deformation estimation unit, a correction value calculation unit, and an addition unit. The correction value calculation unit calculates a correction value of the translational axes and/or the rotation axis with respect to an error of a position and/or a posture of the tool with respect to the workpiece, based on an estimated value of an axis-dependent deformation error, an estimated value of a gravitational deformation error, and command values. The addition unit adds the correction values to the command values.