Passive Capacitive Force Sensor for Surgical Robots
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Solution Overview
Problem
Current force sensing technologies for minimally invasive surgical robots are limited by the inability to accurately sense forces applied during surgery, leading to reliance on visual feedback and the challenges of miniaturization, power requirements, and interference from environmental contaminants, which can result in measurement errors and unsuitable for confined surgical spaces.
Innovation Solution
A deformable passive force sensor that induces a change in an RF signal through capacitance changes, allowing for wireless analog force measurement without the need for a local battery source, using a conductive top and bottom layer with a dielectric middle layer, and a grounded wire, enabling miniaturization and integration with medical tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard strain gauge force sensors are integrated with RF transceivers, then force sensing capability is provided, but power consumption increases due to electronic components
Solution Approach 1:
The patent extracts and removes the power-consuming electronic components (strain gauge sensors, analog to digital converters, RF signal modulators) from the force sensing system. Instead, it uses a passive capacitive sensor that modulates an RF signal without requiring local power sources, thereby eliminating the power consumption issue while maintaining force sensing capability.
Solution Approach 2:
The patent replaces the traditional electronic sensing system (mechanical strain gauges with electronic signal processing) with a capacitive sensing system that directly modulates RF signals. This substitution eliminates the need for power-hungry electronic components while preserving the ability to measure forces.
2Measurement precision
If optical fiber-based force sensors are used, then force sensing along the length of the robot is provided, but cost increases and measurement errors occur due to drift and light intensity loss
Solution Approach 1:
The patent replaces optical fiber-based sensing with a capacitive sensing system that modulates RF signals. This substitution eliminates the problems of optical drift and light intensity loss while maintaining the ability to sense forces along the length of the robotic tool.
Solution Approach 2:
The patent changes the sensing parameter from optical properties (light intensity, phase) to electrical capacitance. By measuring capacitance changes in response to applied forces, the system avoids the drift and intensity loss issues inherent in optical systems.
3Volume of moving object
If minimally invasive surgical tools are made smaller, then invasiveness is reduced, but force sensing capability is compromised due to space constraints
Solution Approach 1:
The patent extracts the power source requirement from the force sensing system, creating a passive sensor that can be integrated into small-scale minimally invasive tools without adding bulk for batteries or power management electronics.
Solution Approach 2:
The patent employs a flexible printed circuit board (FPC) as the substrate for the capacitive sensor, allowing the sensor to be made thin and adaptable to the constrained geometry of minimally invasive surgical tools while maintaining force sensing capability.
4Measurement precision
If environmental contaminants are present, then measurement accuracy decreases due to interference with sensor operation
Solution Approach 1:
The patent uses a flexible encapsulated structure that protects the capacitive sensor elements from environmental contaminants while allowing the sensor to function. The flexible film acts as a barrier that prevents contamination interference.
Solution Approach 2:
The patent replaces contact-based sensing mechanisms that are vulnerable to contamination with a capacitive sensing system that measures forces through electric field interactions, which are less susceptible to environmental interference.
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
The sensor provides accurate force measurement with a sensitivity of 2.51°/N and resolution of 0.4 N, suitable for surgical applications, and is compatible with existing medical tools, reducing the risk of injury and improving surgical efficiency by providing direct force feedback.
Implementation Method 1
A force sensor includes a capacitive sensor that responds to an applied force with a capacitance change
Implementation Method 2
A deformable passive force sensor that induces a change in an RF signal through capacitance changes
Data Source
AI summary
A preferred embodiment provides a deformable passive force sensor that induces a change in an interrogation RF signal present on a conductive connection to produce a changed reflective signal and an ID circuit that responds with an ID and the changed reflective signal.