Robotic Wrist Cable Force Estimation for End Effector Tracking Error
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Solution Overview
Problem
Surgical robotic systems face challenges in accurately estimating joint friction and tracking error, which affects the precision of end effector movement, leading to potential inaccuracies in robotic surgeries.
Innovation Solution
A method to estimate joint friction in robotic wrists using cable force measurements, allowing for the calculation of tracking error, and enabling designers to reduce these errors by adjusting transmission stiffness or minimizing friction torques through lubrication or material selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If transmission stiffness is increased to reduce tracking error, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The patent changes the physical parameter of transmission stiffness (k) to directly affect tracking error. By increasing the stiffness parameter of the transmission elements, the system reduces elastic deformation and thereby decreases tracking error between commanded and actual end effector positions.
Solution Approach 2:
The patent replaces direct mechanical measurement of tracking error with a computational model that calculates error based on measured friction torques and known transmission parameters. This substitutes complex mechanical sensing with a mathematical estimation approach.
2Reliability
If friction torques are reduced through lubrication or material selection, then reliability improves, but ease of manufacture worsens
Solution Approach 1:
The patent changes the friction parameter by applying lubrication or selecting low-friction materials for the transmission components. This parameter change directly reduces friction torques, improving the reliability of the friction compensation model and reducing tracking error.
Solution Approach 2:
The system uses the measured cable forces and known transmission parameters to self-compensate for friction effects through computational estimation, rather than requiring perfect mechanical friction reduction.
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 enhances the precision of surgical robotic systems by accurately estimating and reducing tracking errors, thereby improving the accuracy and reliability of robotic surgeries.
Implementation Method 1
mechanical compliance (or equivalently stiffness or elasticity) of the transmission
Implementation Method 2
joint friction that may resist the commanded motion of the end effector
Data Source
AI summary
A computerized method for estimating joint friction in a joint of a robotic wrist of an end effector. Sensor measurements of force or torque in a transmission that mechanically couples a robotic wrist to an actuator, are produced. Joint friction in a joint of the robotic wrist that is driven by the actuator is computed by applying the sensor measurements of force or torque to a closed form mathematical expression that relates transmission force or torque variables to a joint friction variable. A tracking error of the end effector is also computed, using a closed form mathematical expression that relates the joint friction variable to the tracking error. Other aspects are also described and claimed.