Robotic Surgical Arm Inverse Kinematics Near RCM Singularities
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Solution Overview
Problem
Robotic surgical systems face challenges in controlling tools as they approach singularities, leading to unpredictable tool operation and loss of degrees of freedom, with existing methods either allowing tools to reach singularities or using speed comparisons that may not be sufficient.
Innovation Solution
The method involves correcting the pose of the robotic system's arm and tool by moving the remote center of motion to a boundary distance while maintaining the jaw axis, rotating the remote center of motion according to rigid body kinematics, and expressing the tool center-point frame in the rotated remote center of motion frame for inverse kinematics calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a robotic arm is designed to be lightweight and flexible for patient safety, then patient safety and ease of sterilization are improved, but the robotic arm cannot effectively counteract gravitational forces and maintain precise positioning
Solution Approach 1:
A counterbalance mechanism acts as an intermediary between the lightweight robotic arm and gravitational forces. The counterbalance arm, connected through a gear system, provides mechanical advantage to offset the weight of the robotic arm without requiring the arm itself to be heavy, thus maintaining patient safety while enabling force counteraction.
Solution Approach 2:
The patent implements a counterbalance arm that functions as a counterweight system. This counterbalance mechanism generates an opposing force to gravitational pull on the robotic arm, allowing the arm to remain lightweight for patient safety while still being able to counteract gravity through the counterbalance system rather than through the arm's own mass.
2Ease of manufacture
If the robotic arm is made lightweight for sterilization purposes, then ease of sterilization is improved, but positioning precision deteriorates due to inability to counteract gravity
Solution Approach 1:
The counterbalance mechanism serves as an intermediary system that handles gravitational compensation separately from the robotic arm. This allows the arm to remain lightweight and sterilizable while the counterbalance system, which provides the force needed for precision positioning, handles the gravitational counteraction through its own mechanical advantage system.
Solution Approach 2:
The system is segmented into two functional parts: the lightweight robotic arm that can be easily sterilized, and the separate counterbalance mechanism that handles gravitational forces. This segmentation allows each component to be optimized for its specific function - the arm for sterilization and the counterbalance for precision positioning.
3Reliability
If the robotic arm is kept lightweight, then patient collision safety is improved, but inverse kinematic computation becomes less accurate due to uncounteracted gravitational effects
Solution Approach 1:
The control system incorporates feedback from position sensors that detect the actual position of the robotic arm. This feedback is used in the inverse kinematic computations to compensate for gravitational effects, allowing accurate position calculation even though the arm itself is lightweight and cannot actively counteract gravity. The feedback loop enables the system to calculate and correct for gravitational influence on arm positioning.
Data Source
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AI summary
A method of using inverse kinematics to control a robotic system includes receiving an input pose from a user interface to move an arm of the robotic system, calculating a remote center of motion for a desired pose from the input pose in a tool center-point frame, checking when the desire pose needs correction, correcting the desired pose of the arm, and moving the arm to the desired pose in response to the input pose. The arm of the robotic system including a tool having a jaw disposed at an end of the arm. Checking when the desired pose needs correction includes verifying that the remote center of motion is at or beyond a boundary distance in the desired pose. Correcting the desired pose of the arm occurs when the remote center of motion is within the boundary distance.