THE ROBOTIC LUMBAR SPINE FOR MEDICAL EDUCATION
   


RLS 1
RLS 2

Ernur Karadoğan, Ph.D.

Ohio Universtiy
Mechanical Eng. Dept.
418 Stocker Eng. Bldg.
Athens, OH 45701

ek107003@ohio.edu

 

The role of simulation in medical education is rapidly increasing. Simulations to train nurses, veterinarians and doctors (osteopathic and allopathic) are utilized due to their effectiveness and cost-reducing advantages. These simulations can be computer-based or in the form of mannequins that can simulate some functions of the real human body such as breathing, blood pressure, pulse and temperature, among others. Computer-based haptic simulations require the usage of a haptic interface to interact with virtual objects. That is clearly not the case when humans interact with real objects. Therefore, a system which allows the user to interact with a real object could be a more realistic and effective approach.

This project concentrates on the theoretical framework (kinematics, pseudostatics, dynamics and control) of a novel 15 degree-of-freedom cable-actuated robotic lumbar spine (RLS) which can mimic in vivo human lumbar spine movements to provide better hands-on training for medical students.  The design incorporates five active lumbar vertebrae and the sacrum, with dimensions of an average adult human spine.  It is actuated by 20 cables connected to electric motors. Every vertebra is connected to the neighboring vertebrae by spherical joints. The RLS is designed to be controlled by a force-feedback joystick or an affordable haptic device. By moving the joystick, the angles of rotations are commanded to the RLS, therefore representing a normal lumbar spine movement. A static model of the human lumbar spine was also derived to obtain these normal movement patterns for different types of motion.

RLS 3

The RLS (3D View)

 
 

One of the challenges of designing cable-actuated robots is the fact that the cables must remain in tension (positive) at all times during the operation of a task. The robots with rigid links that are actuated with motors are not subject to this limitation. The RLS, being a fully cable-actuated robot, needs to be supplied with positive cable tensions. Optimization procedures are available to produce point-wise feasible positive cable tensions (equal or higher than pre-specified tension limits) for systems with actuation redundancy. However, these feasible cable tensions may not be guaranteed to be continuous in time during the task. This discontinuity is not desirable since it may cause instability during real-time control of the robot. Therefore, a new optimization algorithm is introduced to obtain positive cable tensions that are both point-wise feasible and continuous in time. The algorithm resides in the "Virtual to Real Calculation" block in the following schematic that displays the RLS controller architecture.

 



RLS Controller Schematic

 

Medical schools can benefit from a system that will help instructors train students and assess their palpatory proficiency throughout their education. The RLS has the potential to support these needs in palpatory diagnosis. Medical students will be given the opportunity to examine their own patient that can be programmed with a variety of dysfunctions related to the lumbar spine before they start their professional lives as doctors. The robotic lumbar spine can be used to teach and test medical students to be able to recognize normal and abnormal movement patterns of the human lumbar spine under flexion, extension, lateral bending and axial torsion.

 
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