Page 428 - Biomedical Engineering and Design Handbook Volume 2, Applications

406 SURGERY

the operating room. Redundant sensing and consistency checks are essential for all safety-critical
functions. Reliability experience gained with a particular design or component adapted from indus-
trial applications is useful but not sufficient or even always particularly relevant, since designs must
often be adapted for operating room conditions. It is important to guard against both the effects of
electrical, electronic, or mechanical component failure and the more insidious effects of a perfectly
functioning robot system correctly executing an improper motion command caused by improper reg-
istration between the computer’s model of the patient and the actual patient. Further excellent dis-
cussion may be found in Refs. 22 and 23 and in a number of papers on specific systems.
Sterility is also a crucial concern. Usually, covering most of the robot with a sterile bag or drape
and then separately sterilizing the instruments or end effectors provides sterility. Autoclaving, which
is the most universal and popular sterilization method, can unfortunately be very destructive for
electromechanical components, force sensors, and other components. Other common methods
include gas (slow, but usually kindest to equipment) and soaking.
Manipulator design is very important in medical robots. Several early systems (e.g., Ref. 24) used
essentially unmodified industrial robots. Although this is perhaps marginally acceptable in a research
system that will simply position a guide and then be turned off before any contact is made with a patient,
any use of an unmodified robot capable of high speeds is inherently suspect. Great care needs to be taken
to protect both the patient and operating room personnel from runaway conditions. It is generally better
to make several crucial modifications to any industrial robot that will be used in surgery. These include
• Installation of redundant position sensing
• Changes in gear ratios to slow down maximum end-effector speed
• Thorough evaluation and possible redesign for electrical safety and sterility
Because the speed/work volume design points for industrial and surgical applications are very
different, a more recent trend has emphasized design of custom manipulator kinematic structures for
specific classes of applications. 25–30
Many surgical applications (e.g., in laparoscopy or neuroendoscopy) require surgical instruments
to pass through a narrow opening into the patient’s body. This constraint has led a number of groups
to consider two rather different approaches in designing robots for such applications. The first
approach (e.g., Figs. 14.7b, 14.8, 14.9, and 14.10) 25,26,31,32 uses goniometers, chain drives, parallel

A B
®
FIGURE 14.7 Two robotic assistants for laparoscopic surgery. (a) The AESOP system is a widely deployed commercial system for
manipulating a laparoscopic camera. The robot combines active joints with a 2-degree-of-freedom wrist to achieve four controlled motions
of the endoscope while preventing lateral forces from being exerted at the entry point into the patient’s body. (b) The experimental IBM/JHU
LARS system uses a five-bar linkage to decouple rotational and translational motions at the entry point. Both approaches have been used in
a number of experimental and clinically deployed surgical robots. (AESOP photo courtesy Computer Motion, Inc.)