Bowden Cable Force Control with Real-Time Friction Modeling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing cable-driven wearable exoskeleton robots face challenges in force control due to non-linear relations between proximal and distal forces, particularly in time-varying configurations, which are not adequately addressed by existing control methods that rely on fixed position modeling and ignore actual robot motion effects.
Innovation Solution
A magnetorheological damper and force sensor-based method is employed to estimate bending angles in real-time, using a calibrated friction model and inverse control formula to achieve real-time force control by integrating a friction model and optimizing parameters for accurate force prediction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback control is used through a force sensor, then force control accuracy is improved, but cable displacement is limited, affecting flexibility
Solution Approach 1:
The patent introduces a magnetic field as an intermediary to transmit force information without physical contact. Magnetic sensors detect changes in the magnetic field caused by cable tension, allowing force measurement without attaching sensors that would constrain cable movement. This resolves the contradiction by enabling accurate force feedback while maintaining cable flexibility.
2Reliability
If compound control combining feedforward and feedback is used, then force control performance is improved, but device complexity increases due to distal end sensor mounting
Solution Approach 1:
The patent replaces the mechanical sensor mounting system at the distal end with a magnetic field-based detection system. Magnetic sensors are positioned externally near the cable path, detecting magnetic field changes caused by cable tension. This substitution eliminates the need for complex distal end sensor mounting while maintaining compound control performance.
3Ease of manufacture
If fixed position modeling is used for feedforward control, then control implementation is simplified, but accuracy deteriorates due to ignoring actual robot motion effects
Solution Approach 1:
The patent transitions from static fixed-position modeling to dynamic modeling that accounts for actual robot motion. The model incorporates real-time cable configuration changes, robot position, and orientation to predict distal force accurately. This dynamic approach maintains control simplicity while significantly improving accuracy by adapting to actual motion conditions.
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
The method enables real-time force control, improving accuracy and flexibility in cable systems with time-varying configurations, overcoming limitations of traditional control methods.
Implementation Method 1
a magnetorheological damper and force sensor based cable force control method applicable to a time-varying configuration
Implementation Method 2
a friction model, and calibrating parameters, where a quasi-static equilibrium equation of a (s+ds) segment in a cable is indicated as
Data Source
AI summary
A cable force control method includes: establishing a friction model, and calibrating parameters; and calculating the parameters in real time, and controlling a force: identifying the parameters according to the friction model to obtain parameters of an auxiliary cable Bowden system and a power Bowden system: a friction coefficient μa of the auxiliary cable Bowden system, and a friction coefficient μp of the power cable Bowden system; calculating the auxiliary cable Bowden system θa in real time according to the model and a force value of a sensor, and using same as a cable bending angle of the power cable Bowden system θp; and obtaining an inverse control formula Fin=Fout·e−uλθ according to the friction model, and bringing the power cable Bowden system θp into the inverse control formula to serve as a feedforward controller, so as to achieve an effect of real-time force control.