CNC Look-Ahead Tool Retraction Paths to Avoid Workpiece Interference
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Solution Overview
Problem
Numerical controllers face challenges in efficiently retracting and returning tools during machining operations without interfering with the machining path, particularly when using external storage devices, which can lead to tool damage and instability due to slower data transfer speeds and potential tool interference with the workpiece.
Innovation Solution
A numerical controller that automatically calculates and executes tool retraction and return paths by dividing machining blocks and generating arc-shaped or similar paths to minimize interference with the machining path, using a tool operation control unit, block division unit, and tool path generation unit to manage tool movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the machining program is stored in an external storage device and read sequentially, then the cost of the numerical controller is reduced, but the data transfer time increases and transfer speed becomes unstable
Solution Approach 1:
The system performs preliminary actions by predicting future tool positions and pre-calculating retraction/return paths before the tool actually needs to retract. The look-ahead function buffers machining program blocks and predicts tool positions in advance, allowing the control system to prepare retraction commands proactively rather than reactively, thus reducing wait states during data transfer from external storage.
2Productivity
If the tool is retracted using conventional tangent path methods, then the tool can avoid stopping on the machining surface, but the tool may interfere with the workpiece during retraction or return
Solution Approach 1:
The system transitions from two-dimensional tangent path retraction (confined to the machining plane) to three-dimensional retraction by introducing vertical movement (Z-axis). The tool retracts in the radial direction (R-axis) and vertical direction (Z-axis) simultaneously, creating a retraction path that exits the machining plane entirely, thus avoiding interference with the workpiece surface while maintaining continuous machining capability.
Solution Approach 2:
The retraction and return paths are made dynamic by continuously adjusting them based on predicted future tool positions from the look-ahead buffer. Instead of using fixed tangent paths, the system calculates optimal retraction/return paths in real-time considering the upcoming machining geometry, allowing the tool to dynamically adapt its retraction trajectory to avoid workpiece interference.
3Productivity
If the tool retraction and return paths are calculated without considering future machining blocks, then the calculation speed is faster, but the tool may interfere with the workpiece at speed vector change points
Solution Approach 1:
The look-ahead function performs preliminary analysis of upcoming machining program blocks to predict future tool positions before actual machining occurs. This advance prediction allows the control system to identify potential interference points in advance and adjust retraction/return paths proactively, ensuring manufacturing precision is maintained while keeping calculation overhead manageable through buffered processing.
Data Source
AI summary
A numerical controller includes a look-ahead unit configured to look ahead a block in the program into a buffer, a remaining block determination unit configured to determine whether retraction of a tool is needed or return of the tool is needed based on an amount of the block looked ahead in the buffer, a tool operation control unit configured to control retraction and return of the tool when the remaining block determination unit determines that retraction of the tool is needed, a block division unit configured to divide a block to divide at a position apart from both ends of the block according to a command from the tool operation control unit, and a tool path generation unit configured to generate a tool retraction path and a tool return path and insert the generated paths into a divided position in the block divided by the block division unit.