Virtual Soft Tissue Control for Prosthetic Joint Simulation
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Solution Overview
Problem
Current prosthetic simulator machines fail to accurately replicate the complex forces and motions of human joints, particularly the knee, due to their reliance on mechanical spring systems that are cumbersome and limited in simulating the nonlinear and asymmetric characteristics of soft tissue forces, leading to inadequate testing of prosthetic implant durability and wear.
Innovation Solution
A virtual soft tissue control system using a computational model that incorporates three-dimensional geometry and mechanical properties of ligaments, with a nested loop design and piecewise cubic spline interpolation algorithm to simulate the elastic restoring forces of soft tissues, allowing for more accurate simulation of joint motions and forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical spring systems are used to simulate soft tissue forces, then the simulator can provide passive forces, but the system becomes cumbersome and limited in simulating nonlinear and asymmetric characteristics
Solution Approach 1:
The patent replaces the mechanical spring system with a computational model that calculates soft tissue forces based on joint position and motion. This substitution eliminates the need for complex mechanical components while enabling accurate simulation of nonlinear and asymmetric force characteristics through mathematical algorithms that compute ligament and soft tissue forces in real-time based on measured joint kinematics.
2Productivity
If displacement controlled machines are used, then the machine can prescribe motions, but it makes little allowance for variations in prosthetic design and provides only rough approximation
Solution Approach 1:
The patent transitions from static displacement control to dynamic force control where the simulator actively adjusts forces and torques in real-time based on the prosthetic's actual motion and the computational soft tissue model. This dynamic approach allows the system to adapt to variations in prosthetic design and accurately replicate the complex, varying forces of natural joint motion throughout the testing cycle.
Solution Approach 2:
The system uses feedback from sensors measuring joint position, velocity, and acceleration to continuously update the computational model and adjust applied forces. This closed-loop control ensures accurate approximation of soft tissue forces while accommodating different prosthetic designs, as the system responds to actual measured motion rather than relying solely on pre-programmed displacement profiles.
3Force
If force control system is used, then the machine can apply forces and torques, but it fails to simulate the natural constraints of soft tissue forces
Solution Approach 1:
The patent implements force control with dynamically changing parameters that reflect soft tissue behavior. The computational model calculates time-varying force and torque profiles based on joint position, velocity, and acceleration, allowing the system to apply forces that accurately mimic the nonlinear, position-dependent characteristics of ligaments and soft tissues rather than using constant or simple periodic force patterns.
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 enables a more realistic simulation of joint mechanics, improving the accuracy of prosthetic testing by closely approximating the forces and motions encountered in the human body, thereby enhancing the reliability of prosthetic device testing and longevity assessment.
Implementation Method 1
A virtual soft tissue control system using a computational model that incorporates three-dimensional geometry and mechanical properties of ligaments, with a nested loop design and piecewise cubic spline interpolation algorithm to simulate the elastic restoring forces of soft tissues
Data Source
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AI summary
A simulator for driving a prosthetic element includes a prosthetic drive mechanism that drive the prosthetic element during an accelerated wear test of the prosthetic element. A simulation input represents the action of the simulator and a sensor mechanism is used to measure the force and torque applied to the prosthetic element. Position and orientation control sensors are further used to measure displacement of the prosthetic element. A closed loop feedback control system, responsive to the sensors, is used to determine a drive signal for the drive mechanism. The control system advantageously adds a computational model that incorporates mechanical representations of ligament fibers. The computational model is a non-human approximation to situations that would be encountered by the prosthesis within the human body and includes dimensional geometry of insertion sites and mechanical properties of ligament fibers. The computational model is responsive to the position and angular displacement sensors to determine constraint forces and torques of ligaments that mitigate action of the control system. The action of the control system may further be mitigated by the measured force and torque.