Surgical Tool with Hydrodynamic Dissipation Brake

Abstract

Systems and methods are provided for passively dissipating a rotational speed of a fluid-driven rotatable shaft. In particular, a dissipation member is provided for dissipating the rotational speed of a shaft having an end effector formed thereon. As the rotational speed of the shaft increases, the dissipation member will apply a counter-torque to the shaft, thereby limiting the rotational speed of the shaft. In an exemplary embodiment, the counter-torque has a non-linear dependence on the rotational speed of the shaft, such that the counter-torque increases at a rate greater than a rate of increase in the rotational speed.

What is claimed is: 
     
         1 . A method for cutting tissue, comprising:
 delivering a high pressure fluid jet to a surgical cutting tool to fluidly drive a rotatable shaft having an end effector formed on a distal end thereof; and   repeatedly placing the end effector in contact with tissue to cut the tissue such that the tissue applies a working load on the end effector;   wherein a hydrodynamic dissipation member coupled to the rotatable shaft applies a counter-torque to the rotatable shaft to limit a rotational speed of the rotatable shaft as a working load on the end effector is decreased.   
     
     
         2 . The method of  claim 1 , wherein the hydrodynamic dissipation member is fixedly coupled to and rotates with the rotatable shaft. 
     
     
         3 . The method of  claim 2 , wherein the hydrodynamic dissipation member is disposed within a fluid-filled housing such that a frictional force is generated between the hydrodynamic dissipation member and fluid contained within the fluid-filled housing, thereby generating a counter-torque that is applied to the rotatable shaft. 
     
     
         4 . The method of  claim 1 , wherein the rotational speed of the rotatable shaft decreases to a cutting speed when the end effector is placed in contact with tissue, and increases to a free speed controlled by the hydrodynamic dissipation member when the end effector is removed from contact with tissue. 
     
     
         5 . The method of  claim 4 , wherein the counter-torque has a non-linear dependence on the rotational speed of the rotatable shaft such that the counter-torque increases at a rate greater than a rate of increase in the rotational speed.