Rotary Lever-Capstan Actuation for Compact Surgical Force Transfer
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Solution Overview
Problem
Existing minimally invasive surgical instruments face challenges in efficiently transmitting rotary actuating forces to push-pull rods due to space constraints in the surgical field, necessitating a compact and effective force transmission mechanism.
Innovation Solution
A lever mechanism with capstans and a spring bias is employed to translate rotary inputs into push-pull motions using cables and levers, coupled with an axle and hand wheel, allowing for compact force transmission in surgical instruments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a proximal control mechanism receives multiple rotary inputs (6-8 actuators) to control end effector motions, then the control capability and precision are improved, but the device size and space requirements increase, causing crowding in the surgical field
Solution Approach 1:
The patent combines multiple rotary actuator inputs into a single integrated proximal control mechanism. The capstan assembly with multiple capstans (first capstan, second capstan, third capstan) are merged into one compact unit that receives rotary inputs from multiple actuators and translates them into coordinated cable tensions, thereby controlling multiple end effector motions simultaneously without requiring separate control mechanisms for each actuator.
Solution Approach 2:
The patent employs a nested arrangement where the first cable and second cable are routed through the same elongate tube, and the capstan assembly is integrated within the proximal control mechanism housing. The cables pass through guides and around capstans in a compact nested configuration, allowing multiple force transmission elements to occupy minimal space within the surgical instrument.
2Volume of moving object
If the proximal control mechanism is made compact to avoid crowding in the surgical field, then the space efficiency is improved, but the complexity of translating multiple rotary inputs into appropriate motions increases
Solution Approach 1:
The patent introduces capstans as intermediary elements between the rotary actuators and the cables. Each capstan acts as a mediator that converts rotary motion into linear cable tension. The first capstan receives rotary input from a first actuator and tensions the first cable, while the second capstan receives rotary input from a second actuator and tensions the second cable. This intermediary mechanism simplifies the translation process compared to direct mechanical linkages.
Solution Approach 2:
The patent replaces traditional mechanical linkage systems with a cable-driven mechanism. Instead of using rigid rods and joints to transmit motion from actuators to the end effector, the system uses flexible cables that pass around capstans. This substitution allows for a more compact mechanism with fewer mechanical constraints and greater design flexibility in routing the force transmission elements.
3Reliability
If traditional mechanical actuation systems are used to transmit rotary forces to push-pull rods, then the force transmission is reliable, but the mechanism size increases and causes crowding in the limited surgical space
Solution Approach 1:
The patent employs a cable-driven mechanism that functions similarly to pneumatic or hydraulic systems in that it uses a flexible medium (the cable) to transmit force over a distance. The cable acts as a flexible force transmission element that can be routed through the elongate tube to reach the end effector, providing reliable force transmission while occupying minimal space compared to rigid mechanical linkages.
Solution Approach 2:
The patent uses flexible cables as the force transmission medium instead of rigid rods. The cables are thin and can be routed through the elongate tube in a compact manner, allowing the mechanism to maintain a small footprint while still transmitting the necessary actuation forces to the end effector at the distal end of the instrument.
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 solution provides a compact and efficient means to transmit rotary forces to surgical end effectors, enhancing control and reducing crowding in the surgical field while maintaining precise actuation.
Implementation Method 1
There may be a spring between a support structure and the lever to bias the lever to rotate about the fulcrum position of the lever
Implementation Method 2
A first cable extends from the applied force position of the lever to a first capstan, the first cable wrapping around the first capstan. A second cable extends from the applied force position of the lever to a second capstan, the second cable wrapping around the second capstan
Data Source
AI summary
A medical device includes a lever with an applied force position, a load position, and a fulcrum position. A first cable extends from the applied force position of the lever to a first capstan, the first cable wrapping around the first capstan. A second cable extends from the applied force position of the lever to a second capstan, the second cable wrapping around the second capstan. A rod couples the load position of the lever and a surgical end effector. The first and second capstans may be fixed to an axle. The axle may receive a rotational input from a rotary actuator. A hand wheel may be coupled to the axle. There may be a spring between a support structure and the lever to bias the lever to rotate about the fulcrum position of the lever.