Chuck, The overall precision of pneumatic axes is still a concern, the compressibility of air being one variable, but many applications don't require high precision. When there is a need for balance between cost, flexibility and the need for precise movements in the five to ten micron-range is not required, servo pneumatics can fit into that gap. The technology is working to take the best of both worlds, and combine the flexibility and software control of electromechanical systems with the speeds and feed force advantages inherent with pneumatic axes.
Other areas where the technology fits are handling of hazardous products such as explosives where you can't guarantee the surrounding air is clean and there is a need to operate on a low voltage since a servo pneumatic system can operate on a 24 VDC supply. Another is where there are space constraints in the machine design, and no high position accuracy requirements.
Al, I'm curious about the uptake of servopneumatics. Have engineers been able to get past the issue of the compressibility of air? Mathematically, this is a really intimidating subject, which I think desrves more study at the university level.
There is alot of work being done on the controllability of pneumatics using proportional control and more extensive use of sensors in systems. Plus, servo pneumatics is emerging as a technology that offers the flexibility of multi-position and force control with position and velocity monitoring. Positioning and force tasks are linked and sequenced, reducing PLC I/O requirements and programming complexity. There are still many simpler applications where the price points of pneumatic systems make them competitive with other technology alternatives especially in apps that have used pneumatic solutions in the past.
In the '60's and '70's, fluid logic circuits got quite a bit of press but as far as I know the uses these days are few and far between. Why bother with fluid gates when they're available on a chip as electonic components?
The power source has to be compatible with the application. Hydraulics are usually low speed, high torque, and high power. Pneumatics are usually high speed, low torque, and low power. I have seen many machines with pneumatic cylinder actuators. There are also pneumatic logic elements that can be used to control a process without electrical solenoid valves. My Fluid Power courses included both hydraulics and pneumatics.
Jon, I wonder if there is really an advantage to pneumatics. They do have some of the advantages you cite. On the other hand, they are not, I suspect, as controllable as electrical devices. Many years ago my father, who worked at a government lab, thought that hydralics would take over for many applications. They were making the equivalent of control circuits with hydralics. He even broght home some of the machined plates to show me. Well, that never happened. The controllability of electro-mechanical devices will make them a prime contender for some time to come.
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