Wave Gear Actuator Positioning via Exact Linearization
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Solution Overview
Problem
The non-linear spring characteristics of wave gear devices in actuators lead to reduced accuracy in controlling the positioning of load shafts, as existing control methods fail to account for the elastic deformation caused by load torque, resulting in inaccurate positioning.
Innovation Solution
A processor-based method employing exact linearization techniques to construct a linearized plant model, defining linearization feedback and input conversion, and using a cubic polynomial to model non-linear spring characteristics, which are then input into a semi-closed loop control system for feed-forward compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a wave gear device is used to reduce rotational output of a motor, then the actuator can provide decelerated rotational output from the load shaft, but non-linear elastic deformation occurs between input and output which reduces positioning accuracy of the load shaft
Solution Approach 1:
The patent applies parameter changes by modeling the non-linear spring characteristics of the wave gear device using a cubic polynomial function with three parameters (Kg1, Kg2, Kg3). These parameters are identified through measurement and then used in feed-forward control calculations to pre-compensate for non-linear elastic deformation, thereby maintaining positioning accuracy while utilizing the wave gear's rotational reduction capability
Solution Approach 2:
The patent implements preliminary action through feed-forward control that calculates and applies compensation commands before the positioning operation begins. The non-linear spring compensation command is computed in advance based on the desired trajectory and the identified cubic polynomial model, allowing the system to pre-counteract the non-linear elastic deformation effects before they occur during actual operation
2Device complexity
If semi-closed loop control is used to control positioning based on motor shaft readings, then the control system can operate without direct load shaft sensors, but the non-linear characteristics of the wave gear device greatly influence and degrade the positioning control characteristics
Solution Approach 1:
The patent applies feedback principles by using the identified non-linear spring characteristics to generate compensation commands that are fed forward to counteract the non-linear effects. While the overall system remains semi-closed loop, the compensation mechanism effectively creates a feedback-like correction based on the known non-linear properties of the wave gear device, improving positioning control without requiring direct load shaft sensors
Solution Approach 2:
The patent transforms the control approach by changing the control parameters to account for non-linear effects. The cubic polynomial model parameters (Kg1, Kg2, Kg3) are used to adjust the feed-forward control commands, effectively compensating for the wave gear's non-linear characteristics and improving positioning accuracy while maintaining the semi-closed loop structure
3Manufacturing precision
If exact linearization technique is applied to compensate for non-linear spring characteristics, then positioning accuracy of the load shaft is maintained, but the control system requires construction of plant models and calculation of linearization feedback and input conversion
Solution Approach 1:
The patent simplifies the exact linearization approach by reducing the spring characteristic model to a cubic polynomial with three parameters. This parameterized model makes the plant model construction and linearization feedback calculations more tractable while still accurately representing the non-linear elastic deformation, thus maintaining positioning accuracy without excessive computational complexity
Solution Approach 2:
The patent applies local quality by focusing the compensation effort specifically on the non-linear spring characteristics of the wave gear device. The cubic polynomial model and feed-forward compensation are tailored to address the specific non-linear behavior of this component, rather than attempting to model the entire system in detail, thereby achieving good results with moderate computational requirements
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
This approach reduces overshooting and stabilizes the load shaft accurately at target positions by compensating for non-linear spring characteristics, enhancing the precision of load shaft positioning.
Implementation Method 1
Non-linear elastic deformation occurs between the input and output in the wave gear device when a load torque is applied
Data Source
AI summary
A method for controlling positioning of an actuator having a wave gear device uses an exact linearization technique to compensate effects relative to positioning control of a load shaft caused by the non-linear spring characteristics of the wave gear device. A plant model is constructed from the actuator, and linearized using the exact linearization technique; measurements are taken of non-linear elastic deformation of the wave gear device relative to load torque; the non-linear spring model τg(θtw) is defined using a cubic polynomial with the constant defined as zero to allow the measurement results to be recreated; and the current input into the model and motor position of the model when a load acceleration command is a command value are entered into a processor arranged as a semi-closed loop control system for controlling positioning of the load shaft, as a feed-forward current command and a feed-forward motor position command.