Feedforward Linearization for Wave Gear Actuator Positioning
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Solution Overview
Problem
The positioning control of actuators equipped with wave gear devices faces challenges due to nonlinear spring characteristics, relative rotation-synchronous components, and nonlinear friction, leading to precision loss and vibration in load shaft positioning.
Innovation Solution
A semi-closed loop feedback control system incorporating a feedforward linearization compensator, which uses exact linearization methods to compensate for nonlinear elements, including relative rotation-synchronous components and nonlinear friction, by modeling the nonlinear plant and applying linearization feedback and input conversion to achieve precise positioning control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a semi-closed loop control system is used for positioning control of an actuator with a wave gear device, then the control system structure is simple and does not require a load shaft encoder, but positioning precision deteriorates due to nonlinear spring characteristics, relative rotation-synchronous components, and nonlinear friction of the wave gear device
Solution Approach 1:
The patent applies parameter changes by transforming the control approach from direct position control to control based on motor shaft position and velocity, incorporating compensation for nonlinear parameters (spring characteristics, friction, rotation-synchronous components) through mathematical modeling and feedforward control terms that adjust the control input to account for these nonlinearities
Solution Approach 2:
The patent replaces mechanical direct coupling control with a mathematical model-based control system that uses nonlinear compensation algorithms to account for wave gear device characteristics, substituting physical direct measurement with computational compensation of nonlinear effects
2Measurement precision
If exact linearization method is applied to compensate nonlinear spring characteristics, then positioning precision is improved, but device complexity increases due to the need for nonlinear plant model and feedforward compensator
Solution Approach 1:
The patent implements feedback by using motor shaft position and velocity information (readily available from the motor encoder) to continuously adjust the control input through nonlinear compensation terms, creating a closed-loop control system that compensates for wave gear device nonlinearities without requiring additional sensors on the load shaft
Solution Approach 2:
The patent applies preliminary action by incorporating feedforward compensation terms that anticipate and counteract nonlinear effects (spring characteristics, friction, rotation-synchronous components) before they affect positioning accuracy, using pre-computed compensation based on the current state of the system
3Measurement precision
If nonlinear compensation is implemented for all three nonlinear elements (spring characteristics, rotation-synchronous components, friction), then positioning precision and vibration suppression are significantly improved, but control algorithm complexity and computational load increase
Solution Approach 1:
The patent merges multiple compensation objectives (positioning precision, vibration suppression, nonlinear compensation) into a unified control framework that simultaneously addresses spring characteristics, friction, and rotation-synchronous components through integrated feedforward and feedback control terms, reducing overall system complexity by consolidating multiple control functions
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 solution effectively inhibits overshooting, shortens positioning time, and suppresses vibration and load positioning variation, improving the overall positioning performance of the actuator by accurately compensating for nonlinear characteristics.
Implementation Method 1
a unique structure that uses the elastic deformation of the gear thereof
Implementation Method 2
nonlinear friction that comes with hysteresis due to a unique structure
Data Source
AI summary
A positioning control system for an actuator provided with a strain wave gearing is provided with: a semi-closed feedback controller FB(s) that controls a load shaft position θ1 on the basis of a feedback motor shaft position θm; and a feedforward linearization compensator configured by incorporating a nonlinear plant model for an object to be controlled into a feedback linearization compensator using an exact linearization technique. The feedforward linearization compensator uses a forward-calculated state quantity estimated value x* to calculate a feedforward current instruction i*ref and a feedforward motor position instruction θ*m to be input into the feedback controller FB(s). A positioning error caused by a non-linear element (non-linear spring property, relative rotational synchronization component, and non-linear friction) of the strain wave gearing is compensated for by the feedforward linearization compensator.