Multi-Motor Surgical Tool Actuation for Cable Torque Resistance
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Solution Overview
Problem
Robotic surgery systems face challenges in overcoming mechanical resistance, such as twisting electrical camera cables, which require sufficient torque and a compact actuator profile, while maintaining reliable and durable electro-mechanical feedback control systems for precise position tracking and disturbance rejection.
Innovation Solution
A multi-motor actuator and controller system with at least two input shafts, where each is actuated by a respective motor subsystem, with a digital controller determining position errors to produce appropriate inputs for both primary and secondary motor subsystems, providing torque assist to overcome resistance and improve tracking performance, and incorporating torque feedforward paths to compensate for friction and backlash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a single motor actuator is used to drive the surgical tool, then the device complexity is reduced, but the torque capacity is insufficient to overcome mechanical resistance such as twisting camera cables
Solution Approach 1:
The actuator is segmented into multiple independent motor subsystems (at least two), each with its own input shaft and control channel. This segmentation allows each motor to contribute to the total torque output, overcoming the torque limitation of a single motor while maintaining a manageable structure through modular design
Solution Approach 2:
Multiple motor subsystems are merged through a transmission mechanism that combines their outputs to a common output shaft. The transmissions from different motor input shafts are coupled to simultaneously drive the output shaft, merging their torque contributions to achieve the required total torque capacity
2Force
If the actuator size is increased to provide sufficient torque, then the torque capacity is improved, but the actuator profile becomes non-compact and cannot be used simultaneously with other tools
Solution Approach 1:
The actuator volume is segmented across multiple smaller motor subsystems rather than requiring one large motor. Each motor can be more compact since they share the torque burden, and their combined output achieves the required torque capacity without increasing the overall actuator envelope volume
Solution Approach 2:
The transmission system utilizes multi-dimensional spatial arrangement to combine the outputs of multiple motors. By arranging the transmission paths and input shafts in three-dimensional space, the system achieves high torque capacity within a compact footprint, allowing simultaneous use with other surgical tools
3Measurement precision
If a digital feedback control system is implemented for precise position tracking, then the position tracking accuracy is improved, but the parameter sensitivity increases reducing system reliability
Solution Approach 1:
A digital feedback control system is implemented that continuously monitors the position of the output shaft and compares it with the commanded position. The controller adjusts the motor inputs based on the position error feedback, achieving accurate position tracking while the control algorithm is designed to minimize sensitivity to parameter variations
Solution Approach 2:
The control system dynamically adjusts control parameters and gain values to optimize performance across different operating conditions. By adapting parameters in real-time, the system maintains high position tracking accuracy while reducing sensitivity to fixed parameter uncertainties, thereby improving reliability
Data Source
AI summary
A first input coupling and a second input coupling are coupled to rotatably drive an output coupling at the same time. In one embodiment, the output coupling rotates a robotic surgery endoscope about a longitudinal axis of the output coupling. A first motor drives the first input coupling while being assisted by a second motor that is driving the second input coupling. A first compensator produces a first motor input based on a position error and in accordance with a position control law, and a second compensator produces a second motor input based on the position error and in accordance with an impedance control law. In another embodiment, the second compensator receives a measured torque of the first motor. Other embodiments are also described and claimed.