The better solution: Use only compressed air. The way to accomplish this is by using a closed-loop mass flow controller. Due to its ability to respond quickly to inputs, a mass flow controller also allows for speed adjustments while the cylinder is traveling.
How It Works
The mass flow of air leaving the pneumatic cylinder (to atmosphere) is controlled with the combination of an electronic mass flow control valve, a mass flow monitor, traditional four-way/five-port solenoid valve and sometimes an additional electronic pressure regulator. The solenoid valve is used to change the cylinder direction between extend and retract. Regardless of whether the pneumatic cylinder is extending or retracting, the speed of extension or retraction is always being controlled by the electronic flow control package by metering out the exhaust from the pneumatic cylinder.
Because the electronic set point command to the pneumatic cylinder can be varied, the velocity can be varied while the cylinder is moving. A soft start and a soft stop can be programmed into the PLC, which can substantially decrease wear and tear on the pneumatic cylinder.
Air-Only Flow Controller in Action
A customer had a rodless cylinder they wanted to move as fast as physically possible while controlling the deceleration, so that parts didn’t fly off. They used proximity sensors – electronic devices that sense when the piston passed the location of the sensor, sending a message to the computer indicating when to throttle back to half speed, again at quarter speed, and then shut off. Once it gets to those throttle back positions, it repeats each time: The mass flow controller’s response time is fast enough to make those adjustments.
Using compressed air with a closed-loop mass flow controller provided an accurate, clean, responsive solution to the challenge of controlling cylinder speeds.