Adaptive Dry Friction Compensation for Precise Motion Control
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Solution Overview
Problem
Existing dry friction compensation methods in mechanical systems are inadequate due to their reliance on non-linear, time-varying friction models that require precise parameter identification, leading to inefficiencies and instability, especially in industrial contexts where real-time adaptation is crucial.
Innovation Solution
An adaptive dry friction compensation method that incorporates an ideal model of the mechanical system and uses an adaptive control law to estimate the Coulomb friction parameter in real-time, allowing for precise compensation of dry friction forces based on measured speed and force/torque signals, thereby improving setpoint tracking and reducing oscillatory phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If complex friction models (e.g., LuGre model with 6 parameters) are used to accurately describe friction phenomena, then manufacturing precision and reliability improve, but device complexity and parameter identification time increase significantly
Solution Approach 1:
The patent transforms the complex 6-parameter LuGre model into a simplified 3-parameter model by changing the mathematical representation of friction. The new model uses parameters S (Coulomb friction coefficient), τ (time constant), and γ (Stribeck velocity) instead of the original complex parameters, maintaining accuracy while reducing identification complexity and time
Solution Approach 2:
The patent extracts and isolates the essential friction characteristics (Coulomb friction, Stribeck effect, and transient behavior) from the complex LuGre model, separating them into distinct compensable components. This allows the control system to address only the critical friction elements without being burdened by unnecessary model complexity
2Manufacturing precision
If friction compensation control laws are based on precisely parameterized models, then manufacturing precision improves, but adaptability deteriorates when friction characteristics change over time due to temperature, wear, or lubrication
Solution Approach 1:
The patent introduces dynamic adaptation mechanisms that allow the friction model parameters (S, τ, γ) to be continuously updated in real-time based on actual system behavior. This transforms the static parameterized model into a dynamic adaptive model that automatically adjusts to changing friction conditions caused by temperature, wear, or lubrication variations
Solution Approach 2:
The patent implements feedback loops that continuously monitor system performance and use the observed motion data to refine friction parameter estimates. This feedback mechanism ensures that the compensation control law remains accurate even as friction characteristics evolve over time, maintaining both precision and adaptability
3Device complexity
If simple friction models (e.g., Coulomb model) are used, then device complexity decreases, but manufacturing precision deteriorates due to high-frequency switching and simulation freezing
Solution Approach 1:
The patent incorporates the Stribeck effect which introduces a velocity-dependent periodic component to the friction model. This periodic action smooths the friction transition near zero velocity, preventing the high-frequency switching that plagues simple Coulomb models and eliminating simulation freezing while maintaining computational simplicity
Solution Approach 2:
The patent anticipates and compensates for friction effects before they cause tracking errors by using a control law that proactively adjusts for predicted friction forces. This preliminary action prevents the need for aggressive high-frequency corrections, maintaining both simplicity and 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
The adaptive compensation method enhances the accuracy and stability of mechanical system control by continuously updating the friction compensation, effectively mitigating the effects of friction-induced oscillations and improving the overall performance of mechanical systems with moving parts.
Implementation Method 1
dry friction compensation control law is adaptive according to a dry friction value parameter S... based on the following friction model: F = S·sgn(V) + (S/τ)·∫(0 to t) e^(-(t-σ)/τ)·V(σ)dσ
Data Source
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AI summary
The invention relates to a system and a method of compensation of dry friction for a mechanical system with a movable mass or inertia controlled by a control signal U and according to the prescriptions of a setpoint signal, the motion of the mass or inertia being characterized by a motion signal. On the one hand, there is defined an ideal model of the closed loop receiving as input the setpoint signal Yr and producing as output an ideal motion signal Ym relating to the motion of the mass or inertia according to the ideal model of the system, on the other hand, there is defined a law of control of compensation of dry friction producing the control signal U and which receives as input the setpoint signal Yr and makes it possible to produce a motion feedback signal Y relating to the real motion of the mass or inertia, the dry friction compensation control law based on the model of Philippe de Larminat being rendered adaptive as a function of a parameter of value of the dry friction S, and the ideal motion signal Ym and the motion measurement signal Y are intercompared to produce an error signal ε( ), and the value of the dry friction S is estimated in an estimator receiving as input the error signal ε( ) and producing as output the estimation S of value of the dry friction, and said estimation S is dispatched as parameter of value of the dry friction in the dry friction compensation control law so as to correct the control signal.