Festo's Controlled Pneumatics for Closed-Loop Control

In 2012, Automation World published an article looking at the decision factors faced when choosing electric or pneumatic actuators. More than a decade later, manufacturing engineers and OEMs still face this decision on a regular basis when designing production systems or industrial equipment.

While both electric and pneumatic actuators are known for delivering high levels of precision, electric actuators tend to be recognized for their ability to deliver the highest rates of precision. Which brings the discussion around to: How much precision is needed for your application?

Once the level of precision needed is determined, if the parameters still allow a choice between the two actuation types, the choice then involves an evaluation of performance, component costs, system costs and productivity gains.

Festo’s latest release to its pneumatic tech line — Controlled Pneumatics — is particularly interesting considering this ongoing decision for engineers. By adding a digital closed-loop control strategy to its pneumatics for energy efficiency, high dynamic response and higher precision movement, Festo said its Controlled Pneumatics line is well suited for web tensioning, welding, surface processing, flexible gripping, dispensing and pumping, PET bottle blowing and diaphragm pump control applications.

(See sidebar at end of article for an explanation of the difference between closed-loop and open-loop control systems).

Lower energy requirements, less noise and reduced compressed air requirements

The Controlled Pneumatic systems from Festo feature digitally controlled proportional pressure regulators, sensors, high-speed communications and control algorithms.

Reduced energy costs with piezoelectric tech Piezoelectric valves are used in the line’s proportional pressure regulators. According to Festo, piezoelectric valves consume 95% less energy than solenoid valves. Piezoelectric valves open proportionally for precision control of pressure and flow and are reportedly fast acting for highly dynamic applications.

Closed-loop control of these valves ensures an accurate, stable and linear flow rate without hysteresis. Repetition accuracy is rated at +/-0.25% of setpoint. These valves have a peak particle size per switching cycle of 0.1 ?m, which is about five times smaller than proportional pressure regulators that do not use piezoelectric valves.

One issue with pneumatic actuators is that they tend to produce more noise than electric actuators. However, Festo pointed out that the piezoelectric valves operate silently.

A key factor of Festo’s new Controlled Pneumatics tech is that it reportedly lowers compressed air usage by up to 50%. According to Festo, “the reduction in energy improves the sustainability of the operation by lowering carbon dioxide emissions from electricity generation.”

The multi-channel VTEM motion terminal was installed at a tire manufacturing plant to replace small pneumatic cylinders used to apply tread patterns. Festo said these cylinders had to be precisely controlled in a pressure range of 0.05 to 8 bar using a proportional valve for each individual pressure zone. With VTEM, the tire manufacturing plant was able to reduce valve slices by 50%.

Festo's Controlled Pneumatics products

VPPI proportional pressure regulator for high flow rate applications.
VTEM motion terminal for multi-channel control of large and small workpieces. Control algorithm features of the VTEM motion terminal include: flow control, selectable pressure level, positioning over the entire stroke of the cylinder, preset travel time, operating actuators with minimum pressure, leakage diagnostics, soft stop and proportional pressure regulation (which eliminates the need for external sensors). Festo noted that, for its proportional pressure regulation, two pressure regulators per valve slice at the two valve outlets can be used to regulate pressures independently of each other, including vacuum. These algorithms can be downloaded as apps on demand for the VTEM motion terminal.
VEAB low flow rate proportional pressure regulator, for pressure ranges up to 6 bar, is designed for highly precise applications.
VTEP is a compact valve terminal for multi-channel low flow rate pressure control. It features high precision and dynamic response. These proportional pressure regulators can be used in addition with solenoid valves for hybrid functionality.
The VEFC is a compact mass flow controller for inert gasses.

Controlled Pneumatics applications in manufacturing

In its announcement of the Controlled Pneumatics line, Festo highlighted two real-world applications of this new technology.

At a silicon wafer manufacturing plant, Controlled Pneumatics were applied to the company’s nitrogen gas (N2) purge application, cutting the N2 flow rate for oxygen flushing by 75%. This equates to savings of US$163,000 for every 1,000 nitrogen purge systems via lower energy costs. This reduced energy also lowered the plant’s CO2 emissions by 1,045 metric tons.

The multi-channel VTEM motion terminal was installed at a tire manufacturing plant to replace small pneumatic cylinders used to apply tread patterns. Festo said these cylinders had to be precisely controlled in a pressure range of 0.05 to 8 bar using a proportional valve for each individual pressure zone. With VTEM, the tire manufacturing plant was able to reduce valve slices by 50%. For the application’s control algorithm, the plant used model-based control for proportional pressure, which did not require external sensors.

More Automation World coverage of pneumatic use in manufacturing:

What is closed-loop control?

A closed-loop control system is an automated system that continuously monitors and adjusts its performance to achieve a desired output. It uses feedback, typically derived from a sensor, to compare the actual output with the controller’s programmed setpoint. The HVAC thermostat in your home is an example of closed-loop control system.

In an industrial motion control application, for example, sensors monitor an actuator’s position or speed and send those data to a controller. The controller compares this information to the programmed setpoint and sends commands to an actuator to make adjustments as needed.

This differs from an open-loop system in that open-loop systems don’t have monitoring feedback from a sensor to which the controller reacts. A basic example of an open-loop system is an electric fan, which is either on or off based on the supply of electric power to operate.