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Warren Harvard, Product Marketing Manager at Festo, argues the case for a more application-led approach to linear motion, including hybrid solutions which can incorporate the simplicity of pneumatics with the benefits of electric automation.
Many machine builders think they need to make a decision between electric automation and pneumatic drives. Some claim that electric actuation is cheaper, more energy efficient and easier to work with. Others feel pneumatic technology is far more rugged, simpler and has a higher power density. But is this ‘one or the other’ approach always helpful in meeting the needs of the application?
Each industrial application has its specific requirements with regards to technical criteria: such as speed, acceleration, load capacity and force required, cycle time, holding duration, power to weight ratio, accuracy, control behaviour, torsional rigidity, efficiency or robustness. Both pneumatic and electric technologies have specific advantages and disadvantages, but energy efficiency wholly depends on the task at hand.
Let’s take some simple examples. Testing and measurements reveal that, for a simple motion task, an electric drive can be efficient. For a pressing or clamping operation, the level of process force and the duration of the operation decide which technology is more efficient. However, if the application requires a holding force, pneumatics is clearly at an advantage: especially for tasks which require large holding forces for extended periods. Electric drives would require constant electricity consumption to generate the holding force in the same applications.
The following rules of thumb can be applied: the shorter the stroke length, the greater the end position force and the longer the holding duration, the more efficient pneumatic technology is. In contrast, the greater the stroke length, the lower the end position force and the shorter the holding duration, the more efficient electric drive technology is. Of course, a technology cannot be selected based on energy aspects alone; other properties include purchase cost, ruggedness, weight, the environment. Installation costs and operating costs also play a significant part and must be incorporated in the decision-making process. For example, a lighter-weight pneumatic actuator can reduce the moving mass of a handling system, dramatically reducing the overall energy requirements. It’s clearly better to have an efficient overall system rather than to focus on the efficiency of individual components: a principle that is driving new advances in linear motion.
Emerging solutions in simple electric drives
Simple electric drives that integrate the motion and control of electric drives in easy-to-use plug and work packages are a rapidly evolving solution. For example, the Simplified Motion Series (SMS) from Festo offering machine builders and users an affordable solution that is easy to install and operate. There is no need for external servo drives installed in control cabinets because the whole device is mounted directly on the machine.
Comprising different linear and rotary electromechanical components together with a simple and application-optimised combination of motor and servo drives (the integrated drive), the Simplified Motion Series integrates all the elements of an electric drive solution into a single package for simple motion tasks such as repositioning, aligning, feeding, sorting, clamping, ejecting and stopping. Simplified set-up and operation make these electric drives perfect for simple motions between two mechanical end positions, without having to sacrifice electric drive motion characteristics such as pre-defined speed, gently cushioned movement into end positions and selectable force for pressing or clamping functions.
Thanks to the intuitive, quick and easy commissioning directly on the drive, configuration doesn’t require any software or specific know-how. The motion can be simply controlled via digital I/O (DIO), like a pneumatic valve. End position feedback, similar to that from a standard proximity sensor or cylinder switch, is provided on completion of the motion. The parameters for the advancing and retracting speed plus the pressing and clamping force can be set directly on the drive, along with the end position reference and cushioning profile.
Advanced user functions are provided via IO-Link®, including convenient remote control, parameter copy, backup function and read functions for advanced process parameters. IO-Link® enables the drives to communicate intelligently from the controllers all the way to the cloud – for simple motions as well as easy handling, commissioning and actuation. It is also possible to control these drives over IO-Link® for flexible end position adjustment with feedback from the integrated encoder. Their simplified set-up and operation makes SMS electric drives perfect for simple motions between two mechanical end positions, without having to sacrifice electric drive motion characteristics such as pre-defined speed, gently cushioned movement into end positions and selectable force for pressing or clamping functions. They can be simply and securely combined mechanically with other SMS actuators, with more advanced electric axes from Festo, or the vast range of pneumatically-driven guided actuators using standardised interfaces and centring rings for accurate positioning and load transfer.
Usually this works simply using a ‘one-size-down’ principle X to Y to Z – making it easy to select the right drive for the right application. For total accuracy, machine builders and specifiers can use the free sizing tool online, which will advise on correct sizing based on the application requirements for speed and force control.
In summary, there is a place for both pneumatic and electric drives as modern linear motion solutions. The optimum solution can be identified through understanding the application, technologies and the technical product data.
The Simplified Motion Series is an ideal entry point to upgrade to electric drive automation with simple set-up and control. Ready matched motor, drive and axis make selection safe and reliable and clearly show the way ahead for simple yet controlled motion. Festo’s sizing software gives added assurance, not only enabling users to select and size their linear motion solutions quickly and accurately, but also to generate the required documentation and drawings for incorporation in their overall machine design.
Furthermore, because these drives are equipped with IO-Link® as standard they can be integrated seamlessly into fully digitalised environments: supporting predictive maintenance regimes and smart air consumption to make a full contribution to optimising production and energy efficiency.