I've seen some of the robotics competitions use pneumatic actuators for brute force actions ( like a hammer or lift ), but nothing precise. Is it possible to use pneumatics in a more precise scenario?, I'm assuming this is how pneumatic robotic arms operate, but I'm a little unclear on how they operate so precisely.
While pneumatic systems can be controlled in a non-discrete manner as GisMofx mentioned, that is generally not the norm because the control system to achieve that movement is more expensive that comparative electric actuators. The result is still less precise and less responsive. This is the reason that all CNC machines are electric. Pneumatic systems are also much less energy efficient than electrical or even hydraulic power systems.
Pneumatic actuators are very hard to precisely position because air is compressible. The flow has to change with inertia and a varying load adding dependencies to the control logic. Pushing a constant load cart back and forth on a rail is hard enough; dynamically loaded systems would be very difficult and the reaction speed would be much lower than hydraulic or electric actuators. So dollar for dollar, an electric actuator will always be more precise than a pneumatic actuator.
The low-cost pneumatic cylinder is offset by the higher cost associated with more complex programming and the expensive bi-directional proportional valve to control the airflow. Hydraulics also use an expensive bi-directional proportional valve, but are much easier to motion control because the load does not greatly affect the flow.
As a general rule:
- Electronic for highest precision (discrete or motion control)
- Hydraulic for high force (discrete or motion control)
- Pneumatic for cheap (discrete)
Yes, it's possible. See here: Position Control of a Pneumatic Actuator
and this youtube video here: Pneumatic Actuator With Position Control on YouTube
Many solutions use a servo controlled pneumatic valve in conjunction with a position sensor on the actuator to control pressures on both sides of the piston to maintain a specific position or motion profile.