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Electric actuators challenge hydraulics

Edited by the Engineeringtalk editorial team Dec 2, 2003

With the launch of a new electric linear actuator offering thrust forces up to 44,500N, hydraulic cylinders now have direct competition in high power applications.

With the launch of a new electric linear actuator offering thrust forces up to 44,500N, hydraulic cylinders now have direct competition in high power applications.

As Jon Harding from Unimatic Engineers explains, electric drives threatening hydraulics' domain is a claim that has been made many times over the last 10-20 years, each proving to be a small incremental move in the right direction.

But this time it looks as if the dam may have been massively breached.

Choosing the right actuation technology for any given application used to be a very straightforward task.

If you needed high power for heavy loads, hydraulic cylinders were your best choice.

If it was all about speed and repetition, pneumatic cylinders were your favoured option.

And when you needed to combine high levels of functionality with precise positioning and multiple points, you turned to electric actuators.

In recent years the boundaries between the technologies have blurred.

Developments in pneumatics have seen these devices challenge hydraulics in high power tasks; electric actuators are now challenging pneumatics for speed; and servo driven electrohydraulic options have increased the flexibility of hydraulic systems in positioning applications.

The result is that designers can much more closely match the requirements of the application with the specific benefits associated with any given technology.

The arguments in favour of electric actuators in an array of applications are well known: they offer a compact, all-in-one solution; electronic systems are easy to program for complex functionality; they are easy to maintain; and their cost is highly attractive.

The one area where fluid power solutions have enjoyed very little competition from electric alternatives is in the high power market.

But now Unimatic has introduced a high power version of its popular Electro-Thrust electric linear actuators, set to provide a direct challenge to hydraulic actuators in many different applications.

The 125mm frame size version is now available with ballscrew diameters up to 50mm (10mm larger than the standard product), enabling it to produce thrust forces up to 44,500N.

With all this available from a compact electric cylinder, design engineers can now evaluate the electric advantage against some of the key weaknesses of hydraulic technology at the lower power end of the high power market.

For example, hydraulic cylinders need their associated hydraulic power pack, which increases the overall size envelope and the cost.

They have a tendency to leak, which can cause environmental concerns.

If the load requires accurate positioning, then expensive position sensing and servo valve controls have to be factored into the equation.

Introduced as a complete, servo driven, electric cylinder system, the ET actuator can mount directly into existing fluid power cylinder applications.

And the high power available makes it a ready alternative to hydraulic power in a host of tasks where hydraulics have traditionally had very little competition.

In sectors such as bridges, dump trucks and areas of aerospace design currently dominated by hydraulic actuators at the lower end of the hydraulic power capability, the compact size, ease of integration and programmable functionality of the electric actuator are significant advantages.

The ET125 electric cylinder provides stroke lengths from 100 to 2000mm, and can operate at speeds up to 1m/s.

Maximum acceleration is 10mm/s2, and typical positioning accuracy is +/-0.013mm.

Electro-Thrust cylinders are built around high quality C7 class ballscrews, and provide a high mechanical efficiency of up to 90%.

The long cylinder rod bearing allows high side load forces to be applied with low bearing deflection, whilst the angular contact bearings at the drive end are designed to accommodate high axial and radial forces.

A polymer bearing supports the front end of the ballscrew, eliminating vibration and run-out, so improving the positioning accuracy and extending screw life.

A precision anti-rotate mechanism virtually eliminates rod end play and noise, and ensures smooth operation.

All standard Electro-Thrust electric cylinders are equipped with a permanent magnet that is integrated in one of the screw nuts.

The cylinder body features two T-grooves that allow limit and home sensors to be freely positioned along the entire length of the casing.

Both Hall-effect sensors and reed contact switches are available.