BEARINGS & LINEAR MOTION FEATURE SKF’s LEMC
TAKING THE electromechanical route
Although they may cost more than their hydraulic counterparts, electromechanical actuators can deliver big savings over the life of a machine. Phil Nicholas, business development manager, linear & actuation technology at SKF, explains why
W
hen designing machines, one of the first decisions to be made is about
power. Where significant linear motion is required, this used to be relatively straightforward – pneumatic power for light loads and high speeds, hydraulic power for large forces. Today, however, there is an important third option: electromechanical actuation. Modern ball or roller screw actuators can
replace hydraulic or pneumatic cylinders across a full range of loads and stroke lengths. The new CASM range from SKF, for example, has been designed for demanding duty cycles in high speed, high volume automated production. CASM electric cylinders use a modular design, available in a wide range of standard sizes, that allow the units to be used as a drop in replacement for pneumatic cylinders on existing production equipment. For higher load applications, the latest
When one Japanese car manufacturer switched to electromechanical welding tongs, the new actuators permitted an increase in throughput of 10%, equivalent to more than 100 body shells every day
LEMC electromechanical cylinders use a planetary roller screw instead of a ball screw design, resulting in an actuator with a higher power density than conventional designs and improving performance in environments where the device is exposed to high levels of external vibration. While precision electromechanical
cylinders cost more per unit than the fluid power alternatives, in many cases electromechanical technology provides additional value over the lifetime of
the machine that more than offsets the extra upfront cost. There are a number of reasons for this:
SIMPLER MACHINE DESIGN Electromechanical actuators are smaller and lighter than their hydraulic counterparts. In addition, since the motor powering the actuator is connected directly, electromechanical systems do away with bulky pumps, accumulators, oil tanks and pipework. There is also no need for separate control valves and associated hardware, making them easier to integrate into a machine’s electronic control system. Together with their fast response,
accuracy and repeatability, that makes it easier to program complex movements, or to build machines that adapt quickly to different process requirements.
HIGHER PERFORMANCE Electromechanical systems work more consistently, and can operate at a wider range of speeds and powers, than hydraulic equipment – the viscosity of hydraulic oils can change with time and temperature, affecting machine performance. Electromechanical systems go on working to precise tolerances, and because their moving parts are based on rolling element bearing technology, it’s possible to predict their operating lifetimes under a given set of operating conditions. Enhanced accuracy and consistency
means electrically driven machines typically offer twice the repeatability of hydraulic alternatives, driving up quality and reducing scrap. Furthermore, since the electric machines deliver consistent performance from the moment they start up, losses after changeovers are reduced and less time is then needed adjusting machine variables to get processes under control. Even in applications producing low precision components, savings from scrap reduction and quality improvements can outweigh the additional actuator cost in two years or less.
electromechanical cylinders
The higher speed and improved
controllability of electromechanical actuators can allow machines to run faster, increasing output. As an example, when one Japanese car manufacturer switched to electromechanical welding tongs, the higher speed of the new actuators, along with the ability to control the tong opening precisely to match the shape of the vehicle structure, permitted an increase in throughput of 10%, equivalent to more than 100 body shells every day.
REDUCED MAINTENANCE Electric machines have few wearing parts, and those are all located within the ball or roller screw mechanism and gearbox. A problem with an electrical actuator can usually be addressed by quickly swapping out the affected device. As a result, uptime and machine availability is typically 2% higher with electromechanical actuators, improving output and reducing per-unit production costs. Electromechanical systems can also be equipped with fully integrated condition monitoring technology, alerting operations and maintenance staff to potential problems before they result in an unscheduled stoppage.
ENVIRONMENTAL BENEFITS The absence of pressurised oil has important safety and environmental benefits, eliminating the risk of fire, pollution or injury associated with leaks and spills. Electrical actuation is quieter than hydraulics too, but perhaps the most important environmental advantage is efficiency. Electromechanical systems only lose energy due to the limits of motor efficiency and via friction in the gearbox and actuator components. Such actuators will typically transfer 80% of their input power to the load. In addition, when stationary, electromechanical actuators consume no power at all. Overall, this means that electric actuators can pay back their initial costs in energy savings alone in just a few months.
SKF (UK) T: 01582 490049
www.skf.co.uk DESIGN SOLUTIONS | SEPTEMBER 2016 29
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