Modular Design of Surgical Robots

Surgical robots have been introduced in the field of Computer Assisted Surgery to assist the surgeon by providing an accurate link between the computer-based plan and the exact (a) positioning or (b) dynamic path control of an instrument on the operating site respectively.

Whereas initial systems mostly have been based on an active supervisory control scheme of industrial robots with large universal workspaces, later on specialized miniaturized kinematics have been proposed, with restricted workspaces adapted to specific applications in order to ease handling and provide inherent safety properties. However, this specialization resulted in even narrower fields of application, low quantities and higher costs. Modularization seems to be a key factor to combine the benefits of both approaches.

Nevertheless, modularization could complicate the surgery or hygienic procedures, such as sterile reprocessing, if it is applied incorrectly, caused by e.g. higher system complexity or additional mounting tasks. A guideline is needed to help the engineer to design a modular surgical robot that suits all requirements of functionality and usability. By means of a guideline the designer shall be able to decide for or against agglomeration of components into modules by applying so called module drivers.

As a first phase of this research, two modular surgical robots that were developed at our institute, have been analyzed regarding their modularity. The MINARO system is an active robot for dynamic path control of surgical instruments whereas the Smart Screwdriver system represents a semi-active system that provides a static instrument guide. By examining the functional and physical independency of both systems, we decided to divide the latter into spatial and temporal independency. By increasing the functional independency in combination with spatial or temporal independency, the degree of modularity can be increased.

As a result, temporal independency of drive modules becomes attractive if three conditions are met: the „separation of sensitive and expensive parts“ is defined as a module driver, actuation can be sequentially and the number of actuations is low. The adjustment of a static instrument guide for pedicle screw placement serves as an example. For simultaneous actuation, e.g. for guiding a burr on a defined path, temporal independency cannot be applied but spatial independency. By using spatial independency, different kinematic modules could be used in order to provide different workspaces for different applications with a single robotic system.