Bogdanova

pp. 298-317

pp. 201-220

The mechanical heart support/replacement system - ventricular assist device (VAD) design task is considered in this article. Relevance of research in this area is due to high percentage of people suffering from heart diseases. The cause of every 5th death in the world is heart failure. Currently, a number of VAD models have been created some of which are successfully used in medical practice. Over years of research in this area the general concept of VAD development has been formed: requirements to systems have been established, approaches to the tasks solution have been developed, certain results have been received and existing lacks of VAD systems have been revealed. Rapidly developing technologies give more and more opportunities for solving the existing problems. This work presents an analysis of the problem of VAD systems development today. Biomedical and technical requirements to VAD systems are systematized, classification of the problems arising in the design process is carried out, finally, trends and new developments in this area are discussed.

In this paper a point-to-point motion problem was considered by the example of brain biopsy. It was emphasized that this operation requires exceptional end-effector positioning accuracy to the target point. End-effector motion was considered as point-to-point Cartesian trajectory tracking. The desired trajectory in Cartesian space was transformed to joint coordinate trajectory in joint space through solving the inverse kinematic problem. Computed-torque control was selected as a control scheme. Desired joint positions, velocities and accelerations were input signals for the inverse dynamic problem with the control low to compute joint torques required for implementing the required end-effector motion. Current joint position, velocity and acceleration were computed through solving the direct dynamic problem. High point-to-point motion accuracy indicators prove adequacy of the available robotic manipulator model and suitability of the selected control scheme. The task of numerical simulation was solved with the use of MATLAB^® Robotics Toolbox + Simulink^®.

During surgical operations with the use of a robot–manipulator, control actions are managed by force effects in the area of the surgical operation. The constructional design of the robot is chosen according to the technological requirements for implementation of specific movements. It turns out that when a force is applied to the tool, displacement of the force application point can be non-collinear to the force vector. If interaction between a surgical instrument and the operation object can be reduced to a concentrated force, it is necessary to choose a beneficial robot configuration to avoid lateral offset. In this configuration the force vector must be aimed to the proper direction of the robot compliance matrix in the force application point. The proposed calculation method helps to construct a working configuration of the robot with respect to minimization of possible spurious derivation of the instrument from the requested trajectory.

A description of carrying out brain biopsy was examined. It is emphasized that one of the major problems is to position the instrument precisely and to maintain a safe trajectory while carrying out the operation. A disadvantage of traditional stereotaxic systems, apart from constructive disadvantages (long preparation and repeated operations have to be carried out in case of multi-target procedures), is that it doesn’t have the ability to observe the effectiveness of surgical manipulation in the target object in real time and, therefore, to reveal ongoing intracranial complications. Modern technologies which use robotic-manipulators allow to increase accuracy, speed and safety in high-precision operations simultaneously. The need for accuracy in positioning the instruments and automated support system are discussed in detail.