Pneumatic devices are a lot cheaper than hydraulic ones and we were trying to get hydraulic/electric positioning performance at a lower cost -- what we called a "working man's robot". The compressibility of the working fluid was a major handicap in terms of accurate positioning and dynamic path control though.
There were all sorts of tradeoffs; most factory floors have 7 bar compressed air supplies which meant no dedicated compressors were needed to drive the robot unlike hydraulic devices which would usually require a power pack. Robots in food processing facilities can't use regular hydraulic fluids for fear of contamination and this was one of the target markets for our design; all it needed to drive it was a sterile filtered air source. Not requiring recirculation of working fluid was a big win in terms of plumbing, hoses, leak prevention etc. We were looking at the idea of using pneumatic actuators with a suitable low-pressure hydraulic fluid (7-10 bar) to compensate for the compressibility problem when I left the project.
If you do go to rotary actuators you can buy them off-the-shelf with angular position sensors already fitted and qualified saving you a lot of integration hassle. They can also be sealed better than cylinder actuators since there is only a rotating shaft coming out of the actuator housing rather than a sliding piston rod.
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There were all sorts of tradeoffs; most factory floors have 7 bar compressed air supplies which meant no dedicated compressors were needed to drive the robot unlike hydraulic devices which would usually require a power pack. Robots in food processing facilities can't use regular hydraulic fluids for fear of contamination and this was one of the target markets for our design; all it needed to drive it was a sterile filtered air source. Not requiring recirculation of working fluid was a big win in terms of plumbing, hoses, leak prevention etc. We were looking at the idea of using pneumatic actuators with a suitable low-pressure hydraulic fluid (7-10 bar) to compensate for the compressibility problem when I left the project.
If you do go to rotary actuators you can buy them off-the-shelf with angular position sensors already fitted and qualified saving you a lot of integration hassle. They can also be sealed better than cylinder actuators since there is only a rotating shaft coming out of the actuator housing rather than a sliding piston rod.