Research And Development Of Control System For Robot Assisted Ultrasonic Scanning

Ultrasound scanning is a simple and effective means of examination.With people's attention to health,the demand for ultrasound scanning is increasing.However,for doctors,ultrasound scanning is tedious and often requires that ultrasound technicians hold the transducers in awkward positions for prolonged periods of time,sometimes exerting large forces leading to high incidence of musculoskeletal disorders.The automatic scanning robot can solve this problem effectively.Doctors only need to draw the trajectory in the view of the camera in the host computer,and then the scanning process can be completed by robots,which can greatly reduce the workload of doctors,but also can alleviate the shortage of doctors in remote areas.The purpose of ultrasonic robots is mainly to collect clear ultrasound images.The existing ultrasonic robots mainly play an auxiliary and fixed role.Most of the robots do not move in the process of ultrasonic scanning.The probe moves only through the guideway installed at the end of the robot.A few of them use serial robots,but the posture of the robot remains unchanged.For thyroid scanning,the patient's neck is nearly cylindrical,so the trajectory is more complex.At the same time,the posture of the ultrasound probe needs to be constantly adjusted to ensure that the probe is as vertical as possible to the human surface.In addition,in the process of ultrasound scanning,we also need to pay attention to the size of the contact force to prevent patients from being injured by excessive contact force.Aiming at the requirement of tangential trajectory tracking and normal contact force and im-age brightness control,this paper presents a normal and tangential control architecture of tool co-ordinate system.The tangential controller ensures that the deviation between the actual trajectory and interpolation trajectory is only along the normal direction in the process of pose adjustment.At the same time,a normal adaptive impedance controller is designed to adjust the image clarity and contact force protection.The specific process is as follows:Firstly,the position and direction of the desired point are obtained by depth camera,and the control points are equal to the input points by designning modified B-spline curve,combined with quaternion representation,completes C2 continuous multi-point interpolation algorithm for position and posture.Then the tan gential controller is designed based on the x and y axes of the speed frame in the tool coordinate system to realize the tangential displacement tracking.The deviation between the tangential displacement and the interpolation trajectory tends to zero in the tangential component.Then a normal adaptive impedance controller is designed in z:axe of tool coordinate system for contact force and intensity of ultrasound image Control.At the same time,in order to adapt to different environments,the impedance parameters are adapted.By estimating the relationship be-tween brightness of ultrasound image and displacement,and force and displacement,the stiffness parameter of impedance control is designed.At the same time,in online operation,the response process is accelerated by reducing the damping parameter in the transient state,and the vibration is reduced by increasing the damping near the steady state.Based on Universal Robot's UR5E robot combined with four-leaf clover ultrasonic machine and Optoforce force sensor,Linux Preempt RT realtime system,this paper construct an integrated ultrasonic scanning robot system that has ability of whole trajectory scanning and collection of clear ultrasound pictures under contact force control.