CNC Motion Plan Rate Control for Smooth Deceleration and Restart
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Solution Overview
Problem
Computer-numerically-controlled (CNC) machines face challenges in smoothly halting and resuming operations, leading to undesired effects on materials due to uncontrolled deceleration and acceleration, particularly in laser cutting and engraving processes where precise speed control is critical to prevent damage or incomplete cuts.
Innovation Solution
A control unit in a CNC machine receives a motion plan from a general-purpose computer and alters the execution rate of operations to achieve controlled deceleration and re-acceleration, using techniques like 'clock stretching' to ensure smooth pauses and resumptions, minimizing material damage and ensuring consistent end products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the CNC machine halts operations suddenly, then the operation can be stopped quickly, but the material suffers damage or incomplete cuts due to uncontrolled deceleration
Solution Approach 1:
The system dynamically adjusts the execution rate of motion plan operations based on real-time conditions. When a halt is requested, the control unit gradually decreases the execution rate rather than stopping abruptly, allowing the movable component to decelerate smoothly while maintaining cut quality. This dynamic adjustment resolves the contradiction by making the halting process adaptive rather than fixed.
Solution Approach 2:
The control unit changes the parameter of execution rate from its normal value to a gradually decreasing value during halting, and then back to normal during resumption. This parameter transformation allows the system to transition between different operational states (normal operation, controlled deceleration, halt, controlled acceleration, normal operation) without causing material damage, thus resolving the contradiction between quick halting and cut quality.
2Productivity
If the CNC machine resumes operations immediately after halting, then productivity is maintained, but the material is damaged due to uncontrolled acceleration
Solution Approach 1:
The system dynamically controls the execution rate during resumption operations. Instead of immediately returning to normal speed, the control unit gradually increases the execution rate from zero or low values, allowing the movable component to accelerate smoothly. This dynamic control maintains productivity by enabling quick resumption while preserving cut quality through controlled acceleration.
Solution Approach 2:
Before resuming normal operations, the control unit performs a preliminary acceleration phase where the execution rate is gradually increased. This preliminary action prepares the system for full-speed operation, preventing sudden acceleration that would damage the material. The preliminary acceleration phase resolves the contradiction by preparing the system in advance rather than jumping directly to full speed.
3Loss of time
If the execution rate is altered rapidly, then the response time is reduced, but the movable component experiences mechanical stress and instability
Solution Approach 1:
The control unit implements dynamic control of the execution rate, adjusting it gradually rather than making abrupt changes. This dynamic approach reduces mechanical stress on the movable component while maintaining reasonable response time. The system adapts the execution rate changes to the mechanical capabilities of the component, resolving the contradiction between fast response and motion stability.
Data Source
AI summary
A method of altering a rate of executing a motion plan by a computer-numerically-controlled machine can include: receiving, at a control unit of a computer-numerically-controlled machine and from a general purpose computer that is housed separately from the computer-numerically-controlled machine, a motion plan defining operations for causing movement of a moveable component of the computer-numerically-controlled machine; and altering, in response to a command received at the computer-numerically-controlled machine, a first execution rate of the operations to a second execution rate of the operations to change a rate of movement of the movable component. Systems and articles of manufacture, including computer program products, are also provided.