Pneumatic actuators, often called air cylinders, are an inexpensive and easy-to-use design choice for many industrial applications that require linear motion. While the technology has been around in nearly its current form for more than half a century, there are some interesting trends and design advances that engineers should be aware of.
There have been a lot of changes to pneumatic actuators over the last decade. Jerry Scherzinger, Product Marketing Manager-Pneumatics, Bimba, noted that changes in load bearing components, such as bearings, have allowed manufacturers to incorporate more advanced materials into their products.
“Then the products weigh less, provide higher levels of accuracy and control costs,” he said. “One of the beauties of pneumatics is its ability to manage complex applications with combinations of relatively simple components, each of which can serve as a great starting point for enabling design engineers to develop more intricate devices for complex solutions.”
Michael Guelker, Festo Corp.’s Product Manager explained that CAD and advanced finite element analysis software tools are now used to design cylinder components like extrusions, end caps, seals and elastomeric bumpers.
“This provides very rigid and robust extrusions and end caps which are lightweight and cost less to manufacture, seals that last longer and have less leakage, and bumpers which can absorb greater impact energy,” he said.
Jerry Walling, Marketing and Business Development for Fabco-Air Inc., noted that pneumatic actuators are selected by their ability to perform a specific function—and those functions are literally endless. He said that the development of custom air actuators can often be both expensive and time consuming, but may be the only solution for unique applications.
“In order to properly specify an air actuator for any application, it requires that two main questions be answered before moving into the heart of the design. The first question is: what do I need the cylinder to do (what type of work will it be performing)? The second is: what types of cylinders do I have to select from? If the ideal actuator is not found via the host of standard offerings, then a custom actuator might be the only solution!” Walling said.
Two industries that are pushing the technology forward are packaging and food and beverage. Walling said that the packaging industry has been a catalyst for innovations and seems to have put a major emphasis on designing more aesthetically pleasing equipment. And because air cylinders are typically visible on most packaging equipment, modern designs tend to be prevalent.
“Many felt as if the pneumatic actuator market would have taken a major blow because of the increased popularity of electric actuators,” said Walling. “Because the initial cost of a pneumatic actuator is significantly less than electric actuators, most industries still try first to fill their motion control application pneumatically. Furthermore, due to the fact that air cylinders can operate without electricity, there is no chance of spark generation. This makes pneumatic actuators still ideal for hazardous environment use, i.e., petrochemical applications.”
Guelker pointed to the food and beverage industry as an area of growth.
“Each industry has its own unique environmental conditions and application requirements that may require specialized products, such as cylinders with corrosion resistant and FDA compliant materials for the food and beverage industry,” he said. “This is driving pneumatic actuator manufacturers to offer product families with many different design variants so customers can customize the product to meet their application requirements.”
And Scherzinger agreed, saying that his company is currently seeing the greatest rate of change in the use and evolution of pneumatic actuators in the food and beverage industry.
“These changes are occurring in response to the new rules the FDA issued in November 2015 as part of the Food Safety Modernization Act,” said Scherzinger. “These rules include stringent requirements for sanitization and hygiene that will stimulate suppliers and packagers to intensify their commitment to proper equipment cleaning with the latest advances in cleaning chemicals. At the same time, Bimba and other hydraulic and pneumatic component suppliers will expand their product offerings to enable equipment manufacturers to employ corrosion-resistant construction materials such as stainless steel.”
Beyond specific industries, the IoT is affecting pneumatic actuators. Bimba’s Jeremy King, who is Product Marketing Manager-Sensing Technologies, described how they are seeing a lot of systems for collecting data, but that’s not what their customers necessarily want.
“Customers are asking for actionable insights into their equipment and processes, not more data,” he said. “Bimba has leveraged its half century’s worth of experience with pneumatic actuators to develop the IntelliSense product line, which helps our customer gain these insights into their pneumatic actuators. Using a combination of hardware and software IntelliSense is able to predict when a cylinder will fail and can tell the customer when to change the cylinder to avoid costly downtime.”
Fabco-Air, too, has been steadily moving into IoT territory. Walling said they offer position feedback on a multitude of product lines, including electronic (LED) magnetic piston sensors for both PNP Sourcing and NPN Sinking and conventional Reed Switches.
“For more precise position feedback, we offer a Linear Resistive Transducer (LRT) located inside the actual actuator piston rod,” Walling said. “An additional linear feedback option is a Linear Variable Differential Transformer (LVDT). An LVDT is an electromechanical transducer that can convert the rectilinear motion of an object to which it is coupled mechanically into a corresponding electrical signal. Embedded transducers in pneumatic actuators offer excellent repeatability and hysteresis.”
While pneumatic actuators are a mature technology, that doesn’t mean that they aren’t constantly evolving. King described how his company’s IntelliSense helps customers improve the performance of their pneumatic systems.
“In addition to predicting cylinder life IntelliSense monitors the time for the cylinder to extend, retract and dwell. As the cylinder wears, these values will change, affecting the performance of the machine. Machine builders can use this information to adjust the performance of other components on the machine to maintain exact sequencing and improve product quality,” he said.
Guelker said that in order to achieve higher cylinder speeds, manufacturers have to address the moving mass, internal friction, and impact energy absorption. This means reducing the weight of the piston rod, using low friction grease and seal materials, and optimizing elastomeric and air cushioning.
“Our cylinders use compact lightweight pistons with molded low friction piston seals which have integrated elastomer bumpers, enabling high speed and high frequency operation … the PPS self-adjusting air cushioning is a new innovation to the commonplace needle-valve style manually adjustable air cushioning. Cylinders with larger loads and longer stroke lengths typically require air cushioning to absorb the impact energy at the end position. PPS provides optimal cushioning performance regardless of any changes to the cylinder’s operating pressure, speed, or load,” he said.
According to Guelker, this results in improved machine performance, longer service life of the cylinder, and reduced installation time.
Walling also pointed to the advent of composite materials as an important change for pneumatic actuators. He said that the composite tubing that is standard on Fabco-Air’s Pancake II air cylinder line is highly impact-resistant, self lubricating, has an extremely smooth interior, low coefficient of friction, and minimal heat build up.