Continuum Robot Wire-Length Control Under Torsional Twist
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Solution Overview
Problem
Existing continuum robots face challenges in maintaining control performance when their bendable portions twist, leading to inaccuracies in wire length calculation and attitude control due to the assumption of linear wire movement, which does not account for spiral movement along the central axis.
Innovation Solution
The solution involves discretizing the bendable portion into minute sections and approximating wire movement as linear within each section, calculating wire lengths using bending, turning, and torsional angles, and applying rotation matrices to accurately determine wire lengths even when the portion is twisted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the bendable portion diameter is decreased to reach deep body portions, then the robot can access deeper areas, but the rigidity of the bendable portion decreases causing twist about the central axis
Solution Approach 1:
The bendable portion is divided into multiple rigid segments connected by joints, allowing the robot to maintain rigidity in each segment while achieving flexibility and depth through the segmented structure. Each segment can be controlled independently to prevent unwanted twisting.
Solution Approach 2:
The robot dynamically adjusts the rigidity parameter of each segment by controlling the activation state of rigidifying mechanisms (such as shape memory alloys or variable stiffness joints). When a segment needs to maintain its position, rigidity is increased; when flexibility is needed for navigation, rigidity is decreased.
2Device complexity
If the wire moves linearly from proximal end to wire guide as assumed in existing techniques, then the calculation is simplified, but the wire length cannot be accurately calculated when the bendable portion is twisted
Solution Approach 1:
The wire path calculation model transitions from a static linear assumption to a dynamic spiral model that adapts to the actual twisted configuration of the bendable portion. The calculation incorporates real-time torsional angle data to determine the spiral parameters, ensuring accurate wire length computation regardless of the degree of twist.
Solution Approach 2:
The system uses feedback from torsional angle sensors to continuously update the wire path model. The measured torsional angles are fed into the spiral path calculation algorithm, allowing the system to compensate for twists and maintain accurate wire length calculations throughout the robot's operation.
3Device complexity
If control is based on linear wire movement assumption, then the control system is simpler, but the correspondence between wire driving amount and robot attitude deviates from designed values
Solution Approach 1:
The control model incorporates the torsional dimension by integrating torsional angle measurements into the kinematic calculations. Instead of considering only the two-dimensional bending plane, the system now accounts for the third dimension of rotation around the central axis, enabling accurate prediction of robot attitude despite twists.
Solution Approach 2:
The control approach combines multiple measurement data types (bending angles, turning angles, and torsional angles) to create a composite state vector that fully characterizes the robot's configuration. This multi-parameter approach allows the control system to accurately determine wire lengths and predict robot attitude in the presence of twists.
Data Source
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AI summary
A control system for a continuum robot includes a kinematics calculation unit configured to calculate a length of a wire in a bendable portion. The kinematics calculation unit includes a wire length calculation unit configured to calculate, for each of a plurality of minute sections obtained by dividing the bendable portion in a longitudinal direction thereof, a length of the wire in the minute section based on a bending angle, a turning angle, and a torsional angle of the minute section, and an addition unit configured to add the lengths of the wire in the plurality of minute sections obtained by the wire length calculation unit to calculate the length of the wire in the bendable portion.