(A) haptic master with 3-axis gimbal structure for active-steering catheter robot

Abstract

Active-steering catheters and haptic masters are being developed for remote manipulation of catheters to reduce radiation exposure to physicians, and improve the accuracy of interventional procedures using catheters. Conventional master devices manipulate only the bending angle of the catheter. This causes a problem that the manipulation direction of the operator is different from the direction of the motion of the catheter. Intuitive manipulation can be possible by matching the orientation of the tip of the catheter with the orientation of the handle of the haptic master. This thesis proposes a haptic master with 3-axis gimbal structure for active-steering catheter robot. Three-dimensional orientation of a handle of the haptic master is expressed by rotational joints of 2-DOF. A rotational joint of 1-DOF is added for redundancy to evade the operator’s hand. The effect of the procedure can be increased by controlling the force applied by the catheter to the body tissues. A 3-axis force sensor is attached to the handle to receive the force input. The maximum required torques are computed by considering the torque for outputting the force to the operator, the torque for gravity compensation, and the torque for enduring the inertia. The motors are selected to have greater output torques than the computed maximum torques. Topology optimization is performed by static analysis simulation to reduce the manipulation inertia of the haptic interface. The safety factor of the haptic interface is at least 7.1 and the maximum deformation is 1mm. A control method that matches the orientation of the tip of the catheter with the orientation of the handle is proposed using the relation between the orientation of the tip of the catheter, the orientation of the imaging device, and the orientation of the handle of the haptic master. Gravity compensation is conducted to reduce the resistance of the manipulation. The maximum force felt by the operator after gravity compensation is 0.7N. A possibility of collision between the link and the operator’s hand exists. Distance measurement sensor is attached and the artificial potential field is generated to control the rotation of the links to evade the operator’s hand and prevent the collision. The proposed control method is implemented and tested with experiments in the virtual environment. Intuitiveness of the manipulation, helpfulness of the haptic master are verified through a questionnaire survey of experts with the virtual environment.