Modern applications in medical robotics, force-reflecting teleoperation, haptic interfaces, virtual simulators, and other demanding industrial applications require high performance actuators, with high force output per unit weight and volume, fast and accurate response, as well as low mechanical impedance. Traditional and modern electrical motors can not provide these characteristics especially in applications that require direct drive and long duration, static high force output. I believe that pneumatic and hydraulic actuators can offer a better alternative to electrical motors in this type of applications, often at a lower cost. However, position and force control of these actuators in applications that require high bandwidth is difficult because of compressibility of air, highly nonlinear flow through system components, time delay and attenuation due to connecting tubes, and inherent uncertainties in modeling of fluid power systems. Due to these difficulties the traditional use of fluid power actuators is limited to relatively simple applications that do not exploit their full potential.
Nevertheless, using detailed nonlinear modeling of the entire fluid power system and advanced digital algorithms based on nonlinear control theory it is possible to design and build actuators that achieve a level of performance well above the traditional range.
Figure 1. Sliding mode force controller applied to pneumatic cylinders produced dynamic forces with magnitudes of 75 N and frequencies up to 50 Hz even in systems with long connecting tubes [ 2 ].
There are numerous areas in which high performance fluid power actuators can be extremely beneficial. My research interest is focused in the field of medical robotics, especially novel robotic applications in Minimally Invasive (MI) and Natural Orifice Surgery (NOS). This new surgical procedures hold tremendous potential: the natural orifices could provide the entry point for surgical interventions in the peritoneal cavity, thereby avoiding abdominal wall incisions, avoiding scars, and more importantly reducing patient’s pain and shortenings post-surgery recovery periods. There are many issues that need to be addressed before these techniques can be introduced into clinical care, and many of these are inherently engineering challenges. Better devices are needed to maintain spatial orientation and provide a stable platform during the procedure, for gastric closure, suturing, tissue grasping and manipulation, and anastomosis.