ACTIVE COMPLIANCE IN ROBOTIC SURGERY - THE USE OF FORCE CONTROL AS A DYNAMIC CONSTRAINT

Robotic surgery can be carried out automatically by using a robot to m ove the cutting tool under position control. However, although the sur geon can observe the procedure on a visual display and has the ability to stop the operation in an emergency, he has little direct contact w ith the task. An alternative approach is to involve the surgeon more d irectly, by his moving a robot using active force control. The robot i s then used to allow motion in preprogrammed regions, by the surgeon b ack-driving the robot motors, while preventing motion in prohibited ar eas. This active constraint robot (or ACROBOT) is described in this pa per applied to knee surgery, in which the knee bones are accurately ma chined to allow the fitting of prosthetic knee implants. The ACROBOT i s, however, ideally suited to a range of surgical procedures, because it allows the surgeon to feel the forces exerted during cutting and ta ke appropriate action. This ability to be in direct control, while bei ng constrained to cut within a permitted region, enhances safety and m akes the system more acceptable to the medical community. The system o f programmable constraint also allows the ACROBOT to provide the tradi tional benefits of robot surgery, namely the ability to machine comple x geometrical surfaces very accurately and to make repetitive motions tirelessly. The system also has a potential for minimally invasive pro cedures. In knee surgery, for example, the robot could operate through a small incision in the skin and excise a volume into which a small, specially designed, unicompartmental prosthesis could fit.