Model Predictive Position Control Beyond Sensor Measurement Range
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Solution Overview
Problem
Existing servo control devices face challenges in effectively damping vibrations when the controlled object's position is measured only within a portion of its movability range, leading to delayed vibration damping and inaccurate tracking of target trajectories due to limited sensor measurement capabilities.
Innovation Solution
The control device employs model predictive control in two modes: one using measured values within the measurable range and another using dynamics model outputs outside this range, with a third mode to smooth transitions between these modes, ensuring robust vibration damping and accurate trajectory tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If vibration detection is performed using torque command value oscillation, then vibration can be detected without additional sensors, but vibration damping control starts delayed because detection occurs after the object stops moving
Solution Approach 1:
The system performs preliminary vibration detection during the positioning movement itself by monitoring torque command value oscillations, rather than waiting until the object stops. This allows vibration characteristics to be identified in advance, enabling timely vibration damping control to be applied before residual vibration affects positioning accuracy.
2Device complexity
If position measurement is limited to a portion of the movability range, then sensor cost and complexity are reduced, but vibration damping performance deteriorates when the controlled object moves outside the measurable range
Solution Approach 1:
The torque command value serves as an intermediary parameter to detect vibration characteristics when the controlled object is outside the sensor's measurable range. By monitoring oscillations in the torque command value, the system can identify vibration frequency and amplitude without requiring direct position measurement, thus maintaining vibration damping reliability while keeping the measurement system simple.
Solution Approach 2:
The system replaces direct mechanical position measurement with electrical signal analysis (torque command value monitoring) to detect vibration. This substitution allows vibration detection throughout the entire movability range without extending the physical measurement range of position sensors, reducing device complexity while maintaining reliability.
3Manufacturing precision
If model predictive control uses measured position values, then control accuracy is improved within the measurable range, but control fails when the controlled object moves outside the sensor's measurement range
Solution Approach 1:
The torque command value monitoring mechanism serves multiple functions: it detects vibration characteristics, provides position information for model predictive control, and operates throughout the entire movability range. This universal approach allows the control system to maintain trajectory tracking accuracy and adaptability across all positions without requiring different measurement systems for different ranges.
Data Source
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AI summary
The controlled device comprises a control unit configured to perform model predictive control in a first mode using a measured value as a controlled variable for the current control period when a controlled object has a position within a predetermined range, and configured to perform model predictive control in a second mode using an output value of a dynamics model as the controlled variable for the current control period when the controlled object has a position outside the predetermined range. Thus, even when the controlled object has its position measured only within a portion of its movability range, it can be positioned while vibration is better damped.