Cable Resistance Control With IMU Feed-Forward Compensation
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Solution Overview
Problem
Existing closed loop force control systems in fitness machines face limitations in controlling inertia and momentum effects due to constraints on gain and compensatory signal accuracy, leading to instability and resistance errors during user exercises.
Innovation Solution
Implementing a feed-forward term in the PID control loop using an inertial measurement unit (IMU) to estimate and scale acceleration, combined with selecting components with low inertia and appropriate motor characteristics, and minimizing slack in the system to reduce inertia-driven force disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gain is increased to reduce error, then control accuracy improves, but system stability deteriorates
Solution Approach 1:
The patent applies feed-forward control by estimating inertial forces before they cause errors. The controller predicts the inertial force based on acceleration measurements and compensates for it proactively, rather than reacting after the error occurs. This allows the system to maintain stability while achieving high accuracy without relying on excessive gain.
Solution Approach 2:
The patent introduces an intermediary compensation mechanism that models the inertial effects as a separate control term. By adding an inertial force compensation term to the control signal, the system can accurately compensate for inertial effects without increasing the feedback gain, thus maintaining stability while improving precision.
2Measurement precision
If compensatory signal accuracy is improved, then error reduction improves, but system complexity increases
Solution Approach 1:
The patent replaces complex mechanical inertia compensation mechanisms with an electronic control solution. Instead of physically balancing inertial effects through mechanical means, the system uses sensors to detect acceleration and electronically compensates for inertial forces through software algorithms, simplifying the overall system while improving accuracy.
Solution Approach 2:
The patent changes the control approach by introducing acceleration as a new measurable parameter. By measuring acceleration and using it to calculate inertial forces, the system can accurately compensate for inertial effects without adding complex mechanical components. This parameter-based approach simplifies the system while improving error reduction.
3Measurement precision
If inertial elements are minimized, then force control accuracy improves, but system capability deteriorates
Solution Approach 1:
The patent uses feedback from acceleration sensors to continuously monitor and compensate for inertial effects. The controller measures actual acceleration, calculates the corresponding inertial force, and adjusts the control signal to maintain accurate force control. This feedback mechanism allows the system to maintain high accuracy even with larger inertial elements.
Solution Approach 2:
The patent changes the approach by measuring acceleration as a key parameter and using it to calculate inertial forces. Instead of minimizing inertial elements, the system measures their actual motion and compensates accordingly. This allows the system to work effectively with various inertial configurations while maintaining force control accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Achieves stable and accurate resistance control by minimizing inertia and maintaining stability margins, ensuring smooth and precise cable resistance during user exercises.
Implementation Method 1
acceleration is estimated and properly scaled and added to the PID signal as a feed-forward term
Implementation Method 2
The acceleration component that is in-line with a motor axis (and other actuator elements) can be determined
Data Source
AI summary
In all applications of force, all components, internal or external, moving or otherwise, have inertia associated with their mass and geometry. The inertia of the components, internal or external, moving or otherwise, is detrimental to the precision and/or accuracy of the force being applied by and/or to the system, whether the force is applied internally or externally to the system. A motorbased system and/or a method involves mitigating and/or reducing force errors caused by the inertia of the components, internal or external to the system, moving or otherwise, in systems built for the application of force, the forces being internal or external to the system. This is achieved, in part, by addressing the inertial effects of components in the load-application path, including a motor and/or other force-generating devices, force transmitting elements, and carriers of force between a motor and those elements that contribute to force error due to inertial effects.