Relief-Feature Instrument Shafts for Flexible Bending Without Backlash
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Solution Overview
Problem
Existing instrument shafts face challenges in achieving a balance between flexibility and stiffness, particularly in minimally invasive surgery, where high compliance in bending is desired while maintaining high axial and rotational stiffness to prevent rotational backlash.
Innovation Solution
The instrument shafts incorporate relief features that extend circumferentially along the shaft, defining flexural members on opposing sides that engage and interlock at predetermined bend angles to minimize rotational backlash and maintain axial stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous instrumentation shafts are used to maintain structural integrity and reduce bacterial growth, then reliability and hygiene are improved, but manufacturing complexity and cost increase due to requiring specialized materials and processes
Solution Approach 1:
The shaft is divided into multiple discrete segments that can be manufactured separately using standard processes, then joined together to form a continuous structure. This segmentation allows each segment to be produced with conventional manufacturing methods while the assembled structure provides the needed continuity for structural integrity and bacterial resistance.
Solution Approach 2:
Multiple discrete shaft segments are combined through joining mechanisms (such as interference fits, keyways, or coupling devices) to create a functionally continuous shaft assembly. The merging of these segments achieves the benefits of continuous shafts (structural integrity, reduced bacterial growth areas) while maintaining manufacturing simplicity through modular construction.
2Ease of manufacture
If discrete shaft segments are used to simplify manufacturing, then ease of manufacture is improved, but structural integrity and bacterial growth resistance worsen due to joints and gaps
Solution Approach 1:
The joining regions between discrete segments are designed with enhanced local features such as interference fits, tapered sections, or localized material properties that provide joint strength comparable to or exceeding the base material. This local quality enhancement ensures structural integrity at the critical joint interfaces while maintaining the overall simplicity of discrete segment construction.
Solution Approach 2:
Joining features such as interference fits, keyways, or coupling mechanisms are pre-designed and pre-positioned on the discrete segments during manufacturing. This preliminary action ensures that when segments are assembled, they automatically achieve proper alignment and structural integrity without requiring complex post-assembly operations, thereby maintaining both manufacturing simplicity and structural strength.
3Strength
If relief features are added to shafts to reduce stress concentrations, then strength and reliability are improved, but manufacturing complexity increases
Solution Approach 1:
The shaft geometry is modified by introducing relief features such as gradual transitions, fillets, or tapered sections at locations where stress concentrations occur. These parameter changes in the shaft's dimensional profile redistribute stress more evenly throughout the structure, improving strength and reliability while adding only moderate manufacturing complexity through standard machining or forming operations.
Data Source
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AI summary
An instrument includes a tubular shaft, an end effector coupled to a distal end portion of the tubular shaft, and a relief feature extending circumferentially along a wall of the shaft and along at least a portion of a length of the shaft. The relief feature defines flexural members on opposing sides of the relief feature. The flexural members can move relative to one another in response to bending the shaft. The flexural members can engage one another on one or both of tension and compression sides of the shaft on the condition the shaft is bent to an angle within a predetermined range of bend angles. Systems and methods relate to instruments including such shafts.