Admittance-Control Drive Unit With Dual Virtual Objects
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Solution Overview
Problem
Conventional admittance control systems face challenges in achieving both high and low backdrivability, leading to unstable position control and difficulty in smoothly responding to external forces due to issues with inertia and friction in transmission devices.
Innovation Solution
A drive unit is designed with dual virtual objects and an admittance model calculation device to simulate the motion of these objects, allowing separate control of inertia and friction, and incorporating a virtual interactive force model to manage interactions between them, enabling flexible and stable force control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the inertia of the virtual object is excessively lowered to realize high backdrivability, then backdrivability is improved, but position control stability deteriorates
Solution Approach 1:
The patent divides the single virtual object into two separate virtual objects: a first virtual object with low inertia for high backdrivability, and a second virtual object with high inertia for stable position control. This segmentation allows each virtual object to independently fulfill different functional requirements that were previously conflicting in a single unified model.
2Stability of the object's composition
If the inertia of the virtual object is set to match the mechanism inertia for stable position control, then position control stability is improved, but backdrivability deteriorates
Solution Approach 1:
The patent segments the virtual object model into two distinct components with different inertia characteristics. The second virtual object is configured with inertia matching the mechanism inertia to ensure stable position control, while the first virtual object maintains low inertia for high backdrivability. This resolves the contradiction by allowing both inertia characteristics to coexist in separate segments.
3Device complexity
If a single virtual object is used for admittance control, then device complexity is reduced, but the ability to achieve both high and low backdrivability deteriorates
Solution Approach 1:
The patent introduces a segmented dual virtual object model where each virtual object serves a specific backdrivability requirement. This segmentation enables the system to adapt to different operational modes (high backdrivability vs. stable position control) by selectively utilizing different virtual objects, thereby enhancing versatility without excessive complexity increase.
Solution Approach 2:
The patent implements dynamic switching or interaction between the two virtual objects based on operational requirements. The admittance model calculation device dynamically determines which virtual object characteristics to apply, allowing the system to adapt its backdrivability characteristics in real-time according to the specific task or environmental conditions.
Data Source
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AI summary
A drive unit 10A is configured to exert a driving force on an environment 50 in accordance with a target driving force command τd, and includes a parameter storage device 30A, a force measuring instrument 35, an admittance model calculation device 31A, and a position control and driving device 33A. The parameter storage device 30A has stored therein dynamics parameters of first and second virtual objects affected by a virtual interactive force λR. The force measuring instrument 35 is configured to output a measurement result for the driving force as a measured driving force value τs. The admittance model calculation device 31A is configured to calculate and output a displacement of the first virtual object. The displacement is obtained by calculations based on the stored dynamics parameters, the target driving force command τd, and the measured driving force value τs. The position control and driving device 33A is configured to operate in accordance with a target position command. The force measuring instrument 35 is disposed between the position control and driving device 33A and the environment 50. The target position command corresponds to the first virtual object's displacement outputted by the admittance model calculation device 31A. The drive unit 10A achieves advantages of both high and low backdrivability.