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Discovering the benefits of electromechanical actuation

Discovering the benefits of electromechanical actuation

The many potential advantages of electromechanical actuators – such as higher energy efficiency and reliability – are helping them to oust hydraulic cylinders from a host of traditional applications says Phil Nicholas of SKF

Hydraulic systems are still the go-to resource for machine designers who need to produce large forces or move heavy loads. However, advances in electromechanical actuation have created a viable rival to this traditional approach. The latest electromechanical cylinders can create forces approaching 500kN – meaning they could replace hydraulic actuation in all but the most demanding applications.

Electromechanical actuators replace hydraulic systems with a precision ball or roller screw, which is driven by a locally mounted electric motor and gearbox. They offer several advantages over hydraulic systems: they are smaller and lighter, they have far greater energy efficiency, and they operate at a far wider range of speeds and powers.

Another reason for initially rejecting electromechanical systems is the perceived higher cost. It is true that the ‘ticket price’ of an individual electromechanical actuator is higher than its hydraulic equivalent, but this does not take account of ongoing costs. Viewed from a total cost perspective, over the lifecycle of a machine, electromechanical actuators offer savings that far outweigh their higher initial cost. The overall cost effectiveness arises from six principal factors:

  • Energy efficiency
  • Reduced heat
  • Shorter cycle times
  • Improved material utilisation
  • Increased uptime
  • Simplified maintenance

Energy efficiency: hydraulic systems suffer energy losses at every stage of the process – and are likely to deliver only 44% of its input power to the load. Electromechanical losses are restricted to two main factors: motor efficiency, and friction in the gearbox and actuator components. This means that 80% of input power is typically transferred to the load. At the same time, hydraulic pumps must run continually to ensure adequate response from the machine, while electromechanical actuators may only consume peak power for a tiny fraction of the machine’s operating time. Overall, it means that electric actuators can pay back their initial costs in energy savings alone in just a few months.

Reduced heat: the energy lost in hydraulic machines is converted to heat. In precision applications, such as plastic moulding machines, the heat must be removed using chillers, which further increases overall energy demand. Electrically actuated machines require around one-third of the cooling energy of a hydraulic equivalent.

Shorter cycle times: the higher speed and superior controllability of electromechanical actuators allows machines to run faster, which increases output. An example is robotic spot welding in the automotive industry. Between welds, the tongs on a robot arm must open to allow the arm to access the next weld location. Fluid power systems usually require the tongs to be fully opened after every weld, while electro-mechanical systems can be programmed to open just enough to allow the tongs to be repositioned. One Japanese car manufacturer boosted throughput by 10% – equivalent to more than 100 vehicle body shells every day – by switching to electromechanical welding tongs.

Improved material utilisation: electrically driven machines offer twice the repeatability of hydraulic alternatives, boosting quality and cutting scrap. This consistent performance helps to reduce losses after changeovers, meaning that production teams spend less time adjusting machine variables. Even in applications that make low precision components, savings from scrap reduction and quality improvements can outweigh the additional actuator cost in less than two years.

Increased uptime: hydraulic devices rely on a network of valves, hoses, filters and seals – and a failure in one part of the system can bring the entire machine to a stop. In comparison, a problem with an electrical actuator can usually be fixed by replacing the affected device. Uptime and machine availability is typically 2% higher with electromechanical actuators, improving output and reducing per-unit production costs.

Simplified maintenance: electromechanical systems can be equipped with condition monitoring technology, alerting operations and maintenance staff to potential problems before they lead to unscheduled stoppage. At the same time, electric machines have few recurring expenses such as oil, filters and seals – and will never be subject to oil leaks or spills.

The latest generation of electromechanical actuators are more powerful than their predecessors – and are easier to integrate into machines. The LEMC range of electromechanical cylinders from SKF, for example, is aimed specifically at high load applications. They use a planetary roller screw rather than a ball screw. The result is an actuator with a higher power density than conventional designs, with improved performance in environments with high levels of external vibration. By incorporating near field communication (NFC) capabilities, the controller can be adjusted wirelessly using a smartphone.

Returning to the example of the Japanese car manufacturer, replacing hydraulic with electromechanical actuation has had a number of benefits: less risk of fire – due to the absence of flammable hydraulic fluid; more controllable pressing forces – when pressing multiple sheets of steel together before welding; and longer service life – around three times that of their hydraulic predecessors. It all goes to show that the ticket price is possibly the least important factor when it comes to considering the overall cost of an actuation system.

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