Rotary Table Position Control Device for Load-Induced Inertia Variation
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Solution Overview
Problem
Conventional position control devices for numerical control machines face challenges in maintaining controllability and positioning performance due to fluctuations in moment of inertia and center of gravity caused by varying loads on the rotary table, leading to reduced feedback control bandwidth and nonlinear characteristic issues.
Innovation Solution
A position control device that uses an identification model to determine and correct torque command values based on actual angular acceleration and angle of rotation, incorporating terms for angular acceleration and angle of rotation to adapt to changing load conditions, thereby enhancing feedback and feedforward control responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If various types of different jigs/tools and workpieces are placed on the rotary table according to respective machining processes, then the adaptability of the machining system is improved, but the moment of inertia increases and the center of gravity changes, leading to deterioration of controllability
Solution Approach 1:
The control device dynamically adapts to changing load conditions by continuously monitoring actual angular acceleration and angle of rotation, then adjusting the torque command value in real-time. The identification model parameters are updated based on actual system behavior, enabling the controller to maintain optimal performance despite variations in moment of inertia and center of gravity caused by different workpieces and tools.
Solution Approach 2:
The system changes control parameters adaptively by identifying the actual moment of inertia and center of gravity position through the identification model. The torque command value is corrected based on identified parameters including the angle of rotation, allowing the controller to compensate for gravitational effects and inertial variations. This parameter adaptation resolves the contradiction by maintaining controllability across varying load conditions.
2Speed
If feedforward control is added with respect to a nominal linear characteristic to increase the speed of command response, then the response speed is improved, but the feedback control band is reduced and nonlinear characteristic resulting from gravity increases, leading to deterioration of positioning performance
Solution Approach 1:
The system employs feedback control that continuously monitors actual angular acceleration and angle of rotation, then adjusts the torque command value based on the identification model. The feedback mechanism compensates for nonlinear gravitational characteristics by calculating the required torque adjustment based on the identified center of gravity position and current angle of rotation. This ensures positioning accuracy is maintained despite the use of feedforward control for rapid response.
Solution Approach 2:
The identification model performs preliminary characterization of the system dynamics by identifying moment of inertia and center of gravity parameters before control execution. This preliminary action enables the controller to pre-calculate appropriate torque compensation for gravitational effects, allowing feedforward control to operate effectively without compromising positioning precision. The system prepares the necessary compensation data in advance based on identified parameters.
Data Source
AI summary
When performing numerical control of a rotary table, the moment of inertia and the center of gravity of a control target change because of a placed object fixed onto the rotary table. A rotary table to which a placed object has been fixed serves as a target plant, the actual motion of this is compared with motion calculated by an identification model of the target plant, and a torque command value is corrected. The identification model comprises a term pertaining to angular acceleration and a term pertaining to angle of rotation, and by including the term pertaining to angle of rotation, correction of a torque command corresponding to a change in the center of gravity can be performed.