Is pneumatic technology able to meet the demands of modern automation technology, or is it inferior to electrical solutions? Industrial automation calls not only for speed and precision but also flexibility. Thanks to initiatives like the Festo modular mechatronic handling system there is a clear trend towards hybrid systems. The win-win solution to this question is hybrid drives that combine the advantages of both types of drive.
Electric drives are precise and flexible. They are ideal when forces need to be developed quickly and positions need to be approached precisely. Electric drives offer high accuracies, constant speeds, good controllability, defined travel profiles and rigidity under load conditions. However, they do need cooling systems for use with heavy loads and duty cycles.
Large loads are generally not a problem for pneumatic drives, which are inexpensive, unaffected by difficult environmental factors such as dust, oil, water or cleaning agents, long-lasting and easy to install and operate. Used with appropriate sensors and valve technology, pneumatic drives are also freely positionable, but, at best, achieve a precision of 0,1 mm.
Users need to find the right drive technology for each application and the selected components must perform reliably. If all the components of a hybrid system are obtained from a single source and are mechanically compatible, there is no more the question of 'electrics versus pneumatics?' The answer is 'electrics and pneumatics'.
Electrical drives
Festo's system solutions specialists act as partners within this selection process for the design and commissioning of complete handling systems. They combine components from the company's comprehensive product range to meet customers' individual requirements. This helps machine builders save considerable time and money in their planning and design work.
The handling axis HME is one example from Festo's comprehensive modular system. The more delicate the application, the better: This axis offers a repetition accuracy of ±0,015 mm and is thus appropriate for applications such as the precision fitting of sensitive components. German special machine builder, Manfred Merklinger Werkzeug- and Maschinenbau, has integrated this axis into a machine in which tiny springs are fitted to a miniature motor. The HME handling axis combines backlash-free heavy-duty ball-bearing guide, high-precision linear motor drive, displacement encoder and reference sensor, all integrated to save space.
Pneumatic drives
With appropriate sensors, software and valve technology, pneumatics can deliver the free positionability of closed-loop drive technology. Servo pneumatics, as an alternative to the familiar types of pneumatic and electric drives, permits movement of a pneumatic cylinder with closed-loop speed and position control. Servo pneumatic drives are every bit as good as electric drives when it comes to dynamic positioning. The system consists of a pneumatic cylinder with an integrated displacement encoder, a proportional valve in place of a simple switching valve, and a position controller such as the Festo SPC200.
A milking machine built by the Dutch machine builder Lely Industries NV is equipped with a servo pneumatic system. The idea behind this milking robot is that the cows themselves decide whether to be milked or not. If they do wish to be milked, they enter a box in which the milking robot is able by means of a transponder to detect the cow's specific data such as weight and size. It can also detect whether the cow has already been milked a short time before. The robot arm, a kinematic mechanism with three pneumatic cylinders, operates flexibly thanks to servo pneumatics, thus ensuring that the cow is not injured. A laser sensor monitors the movement of the cow so that the robot arm can locate the cow's udder.
Hybrid solutions
The Festo modular handling system allows users to exploit the individual strengths of matched electric and (servo-) pneumatic drives. The trend is moving towards combination drives in which pneumatics and electrics work hand in hand. The drive of the future is a hybrid drive in which a pneumatic drive and electric drive are integrated into a cylinder and work in parallel on the same handling task. This hybrid drive combines the advantages of pneumatics - robustness, durability, low costs and easy installation and operation - with the accuracy and dynamism of electric drives. Together, the two technologies create a high-performance drive that can operate quickly and with high precision in confined spaces while transporting large loads.
For more information contact Joanne Dix, Festo, +27 (0)11 971 5560, [email protected], www.festo.com
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