Linear actuators are typically grouped into two principal types: fluid power actuators that operate on differential pressure, and electromechanical actuators driven by an electric motor. Increasingly, electromechanical solutions are providing an attractive alternative to hydraulics in a wide and diverse array of automation systems.
Electromechanical systems offer:
Simpler and smaller installation
Quieter positioning and torque control
Lower energy costs
Potential to provide more ATEX-rated solutions for use in explosive environments
In complex applications, electromechanical solutions can be particularly advantageous as they provide control over the entire motion profile. Moreover, integral encoders accurately control speed and position, while some solutions can also control and monitor torque. Programmability means that motion and force profiles can be changed using software without having to shut down and reconfigure the machine.
In terms of energy consumption, unlike hydraulics, electromechanical solutions use power only when they are performing work, thus contributing to significant savings. Also, due to their minimal impact on the environment, solutions of this type are strongly preferred in applications where clean operation is important or desired.
An example case for electromechanical solutions is put by Industrie Cometto SpA, an Italy-based designer/manufacturer of trailers, semi-trailers and self-propelled vehicles, which wanted to replace hydraulic systems on its EMT (Electric Modular Transporter) to achieve greater flexibility in terms of speed and control, and make it suitable for use in ATEX classified atmospheres.
The traction and steering systems on the EMT are now equipped with Parker electromechanical products. Each transporter can have from four to 16 wheels, all of which have to follow a perfect trajectory to ensure coordinated motion. With this in mind, the drive system has to guarantee precision in terms of speed, position and torque control. An AC, three-phase, 2.3kW electric motor is fitted to the traction system on the EMT.
With regard to the steering system, the position of each wheel axle is controlled electronically using an encoder. Here, each suspension unit is linked to the load platform by a rotation system driven by a 1kw electric motor. The motor is controlled by an absolute encoder and managed by Cometto’s central processing unit.
Parker supplies the complete motor and drives packages for both of Cometto’s non-ATEX and ATEX EMT vehicles. For the latter, Parker provides its EX (explosion-proof) servo-motors with AC890 variable speed drives.
The EX series is a range of permanent magnet explosion-proof brushless servo motors characterised by excellent motion quality, dynamic acceleration/deceleration capabilities and high torque output over a wide speed range. Parker’s AC890 is a compact, modular system variable speed AC drive engineered to control speed and position of open-loop and closed-loop, single- or multi-motor AC induction or PMAC motor applications. The AC890 variable speed drive is compatible with any AC motor and many speed/position feedback options.
Ultimately, electromechanical solutions offer engineers a number of potential benefits over hydraulics that are proving difficult to ignore when it comes to new system designs. These can include one or many of quality, reliability, maintenance, performance, cost, ease-of-use, noise levels and operational response.
Article contributed by Edi Gherbezza, electromechanical, motion & drives
application manager & business development manager for Motion Systems Italy
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