Curved Workpiece Fixturing and Coordinate Tracking for Precision Machining
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Solution Overview
Problem
Current CNC and universal operations machines struggle to accurately position and process curved workpieces, particularly in airframe structures, due to limitations in tracking the length coordinate and accommodating dynamic forces and vibrations.
Innovation Solution
A method and system that utilize a feeding fixture to constrain a workpiece in all degrees of freedom except one, allowing it to move linearly along its length. Sensors measure the workpiece's position, and a machine control system transforms processing vectors from a workpiece coordinate system to a machine coordinate system, enabling precise operations along the workpiece's curved surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a 3-2-1 approach with multiple locators and clamps is used to fix six DOFs, then the workpiece can be held in a fixed configuration, but the device complexity and manufacturing effort increase significantly
Solution Approach 1:
The patent applies universality by designing a single locator that can constrain multiple degrees of freedom simultaneously. The locator system uses a minimal set of elements where each element serves multiple functions - for example, one locator may constrain both translation and rotation, reducing the total number of components needed compared to traditional 3-2-1 approach requiring six separate locators and clamps
Solution Approach 2:
The patent merges the functions of multiple traditional fixturing elements into a unified system. Instead of separate locators and clamps acting independently on different planes, the invention combines their constraining functions into an integrated fixture system that achieves six DOF constraint with fewer components, reducing device complexity while maintaining positioning stability
2Manufacturing precision
If additional locators and clamps are used to hold curved flexible bodies in defined geometry, then machining accuracy can be maintained, but the engineering and manufacturing effort and cost increase
Solution Approach 1:
The patent applies dynamics by using a friction-based locator system that adapts to the workpiece geometry rather than requiring precisely machined rigid contact surfaces. The friction locators can accommodate variations in curved part geometry while maintaining positioning accuracy, reducing the manufacturing effort needed for both the fixture and the workpiece preparation
Solution Approach 2:
The patent changes the contact mechanism from rigid geometric matching to friction-based constraint. Instead of requiring accurately machined locators that match the curved surface geometry, the system uses friction to constrain the workpiece, fundamentally changing the parameter of contact interaction from geometric precision to friction coefficient, thereby reducing manufacturing complexity
3Ease of operation
If roller fixtures are used to support straight parts, then the processing area is clear and processing can occur over the entire perimeter, but this method cannot be applied to curved parts
Solution Approach 1:
The patent applies universality by designing a locator system that can handle both straight and curved workpieces with the same fixture configuration. The friction-based locators and selective constraint approach allow the same fixture to adapt to different geometries, making the system versatile for multiple workpiece types while maintaining clear processing access
4Measurement precision
If traditional tracking methods with roller encoders are used, then position can be measured, but accuracy is insufficient for high-precision machining of curved extrusions
Solution Approach 1:
The patent replaces traditional mechanical roller encoder tracking with a vision-based measurement system. The vision system uses cameras and image processing to track workpiece position and orientation, providing higher measurement precision suitable for tight tolerance machining while avoiding the mechanical contact and slippage issues of roller encoders
Data Source
AI summary
According to one or more embodiments, methods and systems for performing operations on a workpiece may be provided. An exemplary method may include holding the workpiece in a feeding fixture so that the workpiece is movable in one degree of freedom. The method may further include feeding the workpiece along the workpiece's length into an operations center and measuring the position of the workpiece in a length direction. A time sequence of processing vectors on the workpiece that are defined in a workpiece coordinate system may be transformed into a calculated time sequence of processing vectors in a machine coordinate system. Using a machine control system a processing end effector may be moved through the calculated time sequence of processing vectors in the machine coordinate system and one or more operations may be performed on the workpiece.