By Wayne Labs, Contributing Editor
WHILE LINEAR MOTORS offer greater speed and accuracy than older pneumatic and hydraulic actuators, higher costs are causing users still to favor pneumatics. In fact, a recent market study from IMS Research suggested that cost-conscious European machine builders were not inclined to replace existing pneumatic and hydraulic actuators with linear motors.
But there are issues to consider when sticking with lower-cost pneumatics devices. Fortunately, many of these issues are disappearing as advances in technology make pneumatics practical for various motion and position control applications, especially smaller, gripper applications.
CenterLine Ltd., Windsor, Ont., supplies robotic welding machines to the auto industry. Dr. Julio Villafuerto, corporate product development manager, reports that the hammering impact of conventional pneumatic cylinders affects electrode life, part distortion and equipment durability. Although advances in pneumatic and air-over-oil actuator technology’s soft-touch capabilities help minimize or eliminate those three issues, the fact remains that strokes in pneumatic cylinders are defined by design--by bore diameter and stroke specs. This provides little possibility of force and/or positioning programmability.
“Pneumatic motion systems, including static system control using servo-pneumatic control, have been under development for decades but failed to mature because of the intense computations required to handle the dynamics of a compressible fluid,” says Vince McCarroll, chief engineer of Enfield Technologies. “The good news is that advances in micro-computing technology make it possible for pneumatics to provide performance equal to, and often exceeding, that of comparable electric and hydraulic drives.” McCarroll suggests that precise control of the desired position, pressure, flow and force is getting easier, but these advances are dependent upon parallel advances in actuators, sensors and proportional servo-pneumatic servo valves to create a system superior to the old off-on system most system designers know.
According to Enfield’s president, R. Edwin Howe, the main challenge is perception—moving designers’ attitudes away from thinking of pneumatics as old technology. Proportional servo pneumatics gives control to pneumatic systems, providing the benefits of fluid power with control similar to electric motor systems. While servo-pneumatic systems are not yet as precise as electric systems, there are several implementations where the technology may work—at a cost lower than electric drives.
Modularity is catching on in many areas, including pneumatics. You might be familiar with NeSSI, a Lego-like system for combining actuators, valves, and sensors on a stainless steel substrate. According to Al Turney, Bosch Rexroth automation industry manager, his company’s Easy-2-Combine automation system allows the user to combine individual components from linear motion technology and assembly technology to form a modular system. This modularity is suited for linear motion and pneumatically-driven rotational movements, as well as for gripping functions in assembly technology. The standardized interfaces represent the most common applications in assembly and handling technology: pick-and-place, linear and area portals. The individual pneumatic components are combined with positive locking via centering elements, so the normally complex connector kits become unnecessary.
With online proprietary configuration software, the user can combine complete multi-axis applications easily and rapidly. and come up with a bill of materials or a single, unique part number and CAD drawings in DXF or DWG formats.
Configuration software is as important as pneumatic hardware and can save a lot of time when selecting from the myriad of products in a vendor’s catalog. For example, users of the ever-evolving VM10 pneumatic valve island from Norgren might have a tough go of determining just what they need without software that can make sense of the application. There are as many as seven million configurations for the valve island, which can be used in print, medical, semiconductor, and packaging applications. With 260 valve options available including two to 20 individually wired stations, four to 16 multipole stations, and four to 16 fieldbus stations, seven fieldbus protocols, multi-pressure options, and six port sizes from 3-6 mm, users easily could lose their way without configuration software help.
Work being done at the Institute of Fluid Power Transmission and Control (IFAS) at RWTH in Aachen, Germany, seems to point toward smaller, lower-power and more functional systems. The continuing trend towards smaller pneumatic components is supported by research projects in miniaturization and minimization of the power required for pilot control of valves with special attention to the use of micromechanical components.
