Robotic Surgical Arm Shape Sensing for Force Inference
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Solution Overview
Problem
Existing systems for robotically assisted surgery struggle to precisely monitor the shape and external forces applied to articulated arms due to mechanical tolerances and friction, leading to inaccuracies in determining the actual shape and external forces.
Innovation Solution
Utilizing fiber optic bend sensors, such as Bragg gratings, to measure both internal actuation forces and external forces on the arm by analyzing the shape data to derive both components independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If cable tension is used to determine arm shape, then the system is simple to implement, but mechanical tolerances, drive train friction, and tendon stretch prevent precise shape determination
Solution Approach 1:
The patent replaces mechanical shape sensing methods (cable tension measurement) with optical sensing methods (fiber optic Bragg grating sensors). The optical fiber with Bragg gratings is embedded in the arm structure, and wavelength shifts in the reflected light directly indicate shape changes, eliminating the influence of mechanical tolerances and friction while providing precise shape determination.
2Measurement precision
If fiber optic bend sensors are used to measure arm shape, then shape measurement precision is improved, but the system complexity increases
Solution Approach 1:
The patent makes the fiber optic sensor serve multiple functions: it simultaneously measures arm shape (through wavelength shift analysis) and arm position (through the known relationship between shape and position in the robotic manipulator). This multi-functionality reduces the need for separate sensing systems, thereby limiting the increase in overall system complexity while maintaining high measurement precision.
3Adaptability or versatility
If separate sensors are used for shape and force measurement, then measurement capabilities are comprehensive, but device complexity and cost increase
Solution Approach 1:
The patent uses the measured shape data from the fiber optic sensors as feedback to the control system. By continuously monitoring shape changes and comparing them with commanded positions, the system can infer forces applied to the arm. This feedback mechanism allows a single sensor type to provide both shape and force information, avoiding the need for separate force sensors and reducing overall system complexity.
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
Enables precise monitoring of arm shape and external forces, facilitating accurate control and manipulation during surgical procedures by providing feedback to the surgeon.
Implementation Method 1
Arrays of Bragg gratings are formed along the core continuously or at spaced-apart locations. Each Bragg grating comprises a series of modulations of the core's refractive index so as to generate a spatial periodicity in the refraction index. When a strain is induced on the fiber core, the spacing of the modulations will change, depending on the amount of strain in the core.
Data Source
AI summary
A robotic surgical system includes a surgical instrument and a processor. The surgical instrument includes an elongate, hollow shaft having a proximal end, a distal end, and a flexible section. The surgical instrument further includes a sensor apparatus configured to generate sensor data about the flexible section and a force transmission mechanism coupled to the proximal end of the shaft. The processor is communicatively coupled to at least the sensor apparatus. The processor is configured to receive the sensor data about the flexible section from the sensor apparatus and to combine the sensor data received from the sensor apparatus with known information regarding stiffness of the surgical instrument to derive an internal actuation force applied by the force transmission mechanism.