Belt-Driven RCM Mechanism With Reducers for Stiffer Surgical Robots
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Solution Overview
Problem
Traditional belt-type remote center of motion mechanisms in minimally invasive surgical robots face issues with stiffness limitations due to direct torque transfer, actuator size and inertia, and interference between links, particularly when operating on hard tissues like bones and joints.
Innovation Solution
The mechanism incorporates reducers, such as harmonic drives or planetary gear assemblies, to reduce pulley rotational speed and adjust gear ratios, reducing tension on the belt and maintaining remote center of motion constraints while allowing for 2-DOF rotation and insertion motion, minimizing link interference and size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the diameter of the pulleys is increased or the stiffness of the belt is increased to increase the stiffness of the surgical robot, then the stiffness is improved, but the assembly and adjustment of tension becomes difficult and slippage of the wire or rope reduces the accuracy of the operation
Solution Approach 1:
A tensioning mechanism is introduced as an intermediary component between the belt and the pulleys. This mechanism includes a tensioning arm with a spring that automatically adjusts and maintains the optimal tension on the belt, eliminating the need for manual tension adjustment while preventing belt slippage and maintaining surgical robot stiffness.
2Strength
If a wire or rope with higher stiffness than the timing belt is used to increase stiffness, then the stiffness is improved, but the assembly and adjustment of the tension becomes difficult and slippage reduces accuracy
Solution Approach 1:
The tensioning mechanism acts as an intermediary that maintains precise belt tension without requiring stiff wires or ropes. The spring-based system continuously adjusts tension to prevent slippage while preserving the flexibility needed for accurate surgical tool operation.
3Adaptability or versatility
If actuators are mounted on the output link to drive insertion/exit motion and axial rotation motion, then the functionality is improved, but the load and inertia of the robot increases
Solution Approach 1:
The patent combines the insertion/exit motion actuator and axial rotation actuator into a single integrated actuator assembly mounted on the output link. This merged configuration achieves the required functionality while minimizing the total load and inertia compared to having separate actuators for each function.
4Device complexity
If traditional belt-type remote center of motion mechanism is used, then the remote center of motion is achieved with fewer links, but the torque acting on the link is transferred directly to the tension in the belt causing displacement
Solution Approach 1:
The tensioning mechanism serves as an intermediary that decouples the direct torque transfer from the belt tension. By introducing this intermediate system, the patent maintains the simplicity of the link configuration while preventing the displacement caused by direct torque transfer to the belt.
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
Enhances rigidity, reduces mass and size, and maintains remote center of motion constraints, improving surgical robot performance on hard tissues by minimizing deformation and interference.
Implementation Method 1
The mechanism incorporates reducers, such as harmonic drives or planetary gear assemblies, to reduce pulley rotational speed and adjust gear ratios
Implementation Method 2
reduces tension on the belt and maintaining remote center of motion constraints
Implementation Method 3
a power transmission member including a belt transmitting a rotation of the first pulley to the second pulley
Implementation Method 4
reduces tension on the belt
Data Source
AI summary
A belt-type remote center of motion mechanism according to an embodiment of the present disclosure, comprising: an input link; a first pulley positioned toward a first end side of the input link and a second pulley positioned spaced apart from the first pulley; a power transmission member including a belt transmitting a rotation of the first pulley to the second pulley; a first reducer located between the first pulley and the first end side of the input link and configured to reduce a rotational speed of the first pulley and transmit it to the input link; an output link having a first end coupled to the second pulley and receiving a rotation of the second pulley; and a second reducer positioned between the second pulley and the first end of the output link and configured to reduce a rotational speed of the second pulley and transmit it to the output link.