Continuum Robot Wire Tension Control for Precise Back-Drivable Positioning
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Solution Overview
Problem
Existing continuum robots face challenges in achieving high positioning performance without requiring complex operator interactions, particularly in scenarios involving narrow paths with branches or gentle and steep paths, where back drivability and positioning accuracy are compromised.
Innovation Solution
A control system for a continuum robot that includes a curvable unit driven by a wire and a driving unit, with a position control unit to manage wire tension and a force control unit to compensate for tension errors, forming a double-loop control system for enhanced back drivability and positioning precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-mode control system is used for continuum robots, then the device complexity is reduced, but the positioning precision and back drivability deteriorate in complex operation scenarios
Solution Approach 1:
The control system is segmented into two distinct modes: insertion operation mode and operation control mode. Each mode has its own control algorithm and parameter settings, allowing the system to optimize performance for specific tasks while maintaining overall simplicity. The segmentation enables the robot to switch between passive back-drivable operation during insertion and active force-controlled operation during manipulation.
Solution Approach 2:
The control system dynamically switches between different control modes based on the operational phase. During insertion, the system operates in a passive mode with high back drivability, while during manipulation, it transitions to an active force control mode. This dynamic adaptation allows the system to maintain optimal performance characteristics for each operational stage without requiring a permanently complex control architecture.
2Ease of operation
If back drivability is enhanced for easy insertion, then the ease of operation is improved, but the positioning precision and curving control capability deteriorate
Solution Approach 1:
The operational sequence is segmented into insertion phase and manipulation phase, with each phase having optimized control characteristics. During insertion, the passive control mode provides high back drivability for ease of operation. During manipulation, the active force control mode provides precise positioning and curving control. This segmentation allows each phase to have optimized performance without compromising the other.
Solution Approach 2:
The control system prepares for the transition from insertion to manipulation by pre-configuring the dual-mode architecture. The passive control mode is designed with preliminary considerations for easy insertion, while the active control mode is prepared to take over for precise manipulation. This preliminary arrangement ensures smooth transition and prevents performance degradation at the mode switch point.
3Reliability
If the curving operation is disabled during insertion mode, then the operational safety is improved, but the ease of operation deteriorates due to complicated switching requirements
Solution Approach 1:
The control system dynamically enables or disables curving operation based on the current operational mode. During insertion mode, curving operation is automatically disabled to prevent erroneous movements and ensure safety. During manipulation mode, curving operation is enabled for precise control. This dynamic switching is transparent to the operator, maintaining simplicity while ensuring safety through automated mode-based control.
Solution Approach 2:
The control system uses feedback from the operational phase detection to automatically adjust available functions. When the system detects insertion mode, it provides feedback to disable curving operations. When manipulation mode is detected, it enables curving control. This feedback-based automatic adjustment maintains operational safety without requiring complex manual switching procedures.
4Manufacturing precision
If a rigid link robot structure is used, then the manufacturing precision and structural stability are improved, but the adaptability to narrow spaces and fragile objects deteriorates
Solution Approach 1:
The robot employs a flexible continuum structure with curvable units that can deform to navigate narrow spaces and conform to complex geometries. This flexible architecture replaces traditional rigid links while maintaining structural stability through controlled deformation. The flexible structure allows the robot to adapt to narrow passages and handle fragile objects without the need for rigid mechanical joints.
Solution Approach 2:
The robot changes its structural parameters dynamically by adjusting the curvature and configuration of its flexible segments. This allows the robot to transform from a compact configuration for narrow space navigation to an extended configuration for manipulation tasks. The parameter changes enable adaptability to different operational scenarios while maintaining manufacturing precision through controlled actuation of the flexible structure.
Data Source
AI summary
A control system for a continuum robot including at least one curvable unit driven by a wire and configured to be curvable, and a driving unit driving the wire includes: a position control unit performing control so that an error between a target displacement of push-pull driving of the wire by the driving unit and a displacement of a wire holding mechanism holding the wire obtained from a continuum robot is compensated; a force control unit performing control so that an error between a target generated force corresponding to a target tension of the wire output from the position control unit and a generated force corresponding to a tension of the wire obtained from the continuum robot is compensated; and wherein a first loop control system including the force control unit and a second loop control system including the position control unit.