NC Feedrate Control for Curved-Path Machining Precision
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Solution Overview
Problem
Existing numerical control devices for machine tools face challenges in accurately moving tools along curved paths without exceeding acceleration limits, leading to potential decreases in machining precision when attempting to shorten machining time by adjusting deceleration parameter limits.
Innovation Solution
A numerical control device that includes a limit setting storage unit for setting parameter limits, a limit velocity calculation unit, a feedrate determination unit, and a deceleration recording unit to calculate and manage limit velocities and deceleration factors, allowing for efficient shortening of machining time while maintaining precision by defining feedrates and displaying deceleration factors and trajectories.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the acceleration of the tool is increased to shorten machining time, then productivity is improved, but manufacturing precision deteriorates due to errors in tool movement along the curved path
Solution Approach 1:
The system dynamically changes multiple parameters (acceleration, jerk, and velocity) simultaneously based on the curvature radius of the tool path. By calculating the relationship between curvature radius and these parameters, the system determines optimal values that allow higher speeds on straight sections while maintaining precision on curved sections, thus resolving the contradiction between productivity and manufacturing precision.
2Manufacturing precision
If deceleration control is performed to maintain manufacturing precision by limiting acceleration, then tool movement accuracy is improved, but productivity deteriorates due to extended machining time
Solution Approach 1:
The system implements dynamic control where acceleration, jerk, and velocity limits are not fixed but vary continuously according to the local curvature of the tool path. On straight sections, higher parameters are allowed for faster machining, while on curved sections, parameters are reduced to maintain precision. This dynamic adaptation resolves the contradiction by optimizing performance for each specific segment of the path.
Solution Approach 2:
The tool path is effectively segmented into sections with different curvature characteristics. The control system applies different parameter sets to different segments - aggressive parameters for straight sections and conservative parameters for curved sections. This segmentation allows the system to maximize productivity where possible while maintaining precision where required.
3Manufacturing precision
If the limit value of deceleration parameters is reduced to ensure manufacturing precision, then tool movement accuracy is maintained, but productivity deteriorates due to excessive deceleration
Solution Approach 1:
Instead of using fixed conservative limit values for acceleration and jerk, the system dynamically adjusts these parameters based on the actual curvature radius encountered during machining. The limit values are calculated as functions of curvature radius, allowing the system to use higher limits on straight sections and lower limits on curved sections, thus maintaining precision while minimizing unnecessary deceleration.
Data Source
AI summary
A numerical control device for a machine tool which causes a tool to move along a movement path decided according to a machining program, the numerical control device including: a limit setting storage unit in which limit values of a plurality of parameters related to movement of the tool are set; a limit velocity calculation unit which calculates a plurality of limit velocities, which respectively correspond to the limit values at each position of the movement path; a feedrate determination unit which defines a minimum value among an ideal velocity of the tool and the plurality of limit velocities at each position on the movement path as a feedrate of the tool at each position on the movement path; and a deceleration recording unit which stores a type of the parameter corresponding to a case of the feedrate determination unit defining the limit velocity as the feedrate.