Abstract
Computer Numerical Control (CNC) is a technology made up of several blocks. Among these, lies the Trajectory Planning block, responsible for reference profile generation that are fed to position control loops. The need for Trajectory Planning arises from the mechanical constraints inherent to every plant to which CNC technology is applied. The machine’s operational limits myst be respected, in order to avoid several issues, such as: loss of precision, early wear of machine’s parts and excessive vibration. This paper proposes a novel smooth real-time trajectory generation setup based on an embedded system platform. A real-time snap and jerk bounded control algorithm is proposed, to achieve continuous and smooth feed motion in traditional Numeric Control code file, dealing both with straight lines and arcs. A local motion blending algorithm, applicable to the proposed method, is also presented. The developed algorithm was deployed to a BeagleBone Black, an embedded System-on-Chip, single board computer and tested in a prototype router machine. A comparison between the proposed method against the seven segments and trapezoidal acceleration methods is presented, both in terms of performance and of real-time computing viability. Simulation and Experimental results demonstrate the effectiveness of the proposed method to generate velocity, acceleration, jerk and snap bounded three dimensional trajectories, reducing the RMS error in up to 8.2% and 22.38% when compared to the Seven Segments and to Trapezoidal Acceleration methods, respectively. Assessing the error area on straight angles, the proposed method produced error areas 24% and 80% smaller when compared to the Seven Segments and to Trapezoidal Acceleration methods, respectively.
Highlights
Computer Numeric Control (CNC) is a very complex, transversal technology, embracing several knowledge areas, such as control systems, electromechanical systems, mechanics and computer programming
C++ was the programming language used and the solutions were deployed to a BeagleBone Black, an embedded low-cost, community-supported, Single Board Computer (SBC), that runs an embedded Linux environment, running PREEMPT_RT, a real-time Linux Kernel
The proposed algorithm produced error areas 24% and 80% smaller when compared to the Seven Segments and to Trapezoidal Acceleration methods, respectively
Summary
Computer Numeric Control (CNC) is a very complex, transversal technology, embracing several knowledge areas, such as control systems, electromechanical systems, mechanics and computer programming. Numeric Control was first applied in the ’40s to machine airplane’s airfoil when less automated machining methods yielded results no longer compliant to the design requirements [1]. Motion controller systems, which are responsible for driving the whole electromechanical structure are the core of the CNC technology. Such systems have a two basic requirement: real-time performance, as poor real-time performance is likely to result in undesired tracking error [3]; and smooth trajectories, in order to mitigate vibration and to ensure the correct operation of the system’s mechanical components.
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