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Product category: Electric Linear Actuators
News Release from: Danaher Motion | Subject: Electromechanical actuators
Edited by the Engineeringtalk Editorial Team on 26 January 2005

Control by wire technology comes down to
earth

Anders Trygg discusses the considerations of off-highway design through a range of case studies.

"Control by wire" technology is synonymous with aircraft and weapons systems, at the very forefront of technology In the aerospace industry it often involves computer enhancements that may seem to detach pilots from the outside world

The reality is that their jobs would be a great deal less comfortable, and in the case of high speed aircraft impossible without additional support.

One driver for such technology is that a pilot could not physically control a large aircraft using mechanical levers.

Certainly, in the case of off-highway equipment the level of sophistication is vastly reduced, but the principle is the same and the improvements that can be gained are equally dramatic.

The applications of "control by wire" technology to these vehicles is on the increase as vehicle designers, manufacturers and users across the construction, agricultural, municipal and marine sectors are realising the potential benefits.

The basic principles behind all of these applications are the same.

A machine operator is required to control a piece of equipment that is inaccessible.

This may be due to the ergonomics of the vehicle, the physical strength required to operate a control lever or simply the requirement to operate different parts of the vehicle simultaneously.

The solution is to install an electromechanical actuator close to the part that needs to be moved, then the operator can control the part by means of a simple switch or joystick as appropriate.

The generic term "part" is used above because the potential applications of this technology are extensive, hydraulic valve control, the raising and lowering of equipment, and gear shifting to name a few.

This is not a "solve-all" solution, but when used in conjunction with existing technologies it forms the basis of a number of elegant and cost effective solutions.

The control of hydraulic valves using electromechanical actuators is a relatively new concept, being considered by cautious OEMs.

It replaces the use of solenoid valves can only be switched "on" or "off".

Actuators enable the valve to be positioned infinitely, providing proportional valve control for smoother, more controlled movements.

Swepac is Sweden's market leading manufacturer of soil compactors.

Its designs are innovative and environmentally friendly.

At first impression, their soil compactors appear similar to the "walk behind" compactors seen on most building sites, but Swepac compactors are the product of innovative design.

The basic principle behind the design a large eccentrically mounted weight that is rotated inside the body.

This causes the vibrations that are used to compact the sand, gravel or stone.

Existing designs in the industry rely on hydraulics to change the orientation of the weight as it rotates, which has the effect of controlling the direction of the compactor.

The problem with using hydraulics for this application is that hoses are used to connect the handlebar controls to the body of the machine.

These hoses can be protected with armour but are nevertheless exposed to damage, particularly when the compactor is being loaded or unloaded from transport.

A damaged hydraulic hose cannot be simply patched.

Even at low pressure this would require the replacement of the hose and bleeding of the system, both of which take valuable time and money.

A burst hose is also a potential hazard for the operator, and to the environment, although Swepac are conscious of this and offer machines that are compatible with eco-friendly hydraulic oils.

Swepac decided to develop a more operator friendly and environmentally conscious solution and reduce the costs incurred by their customers from expensive hydraulics and repairs.

The solution was to install a linear actuator inside the body of the machine to adjust the hydraulics, thus controlling the eccentricity of the rotating weight.

Hydraulics are still used to change the eccentricity of the weight because this requires considerable force.

The elegance of the solution employed using the actuator is that the hydraulic hoses are not required from the operator handlebars console to the body of the compactor, they are replaced by electric cables to the operators controls The soil compactor application requires a very robust design.

Danaher Motion's E050 actuator is designed specifically for use in rugged environments, it is IP56 rated and designed to withstand the vibration and contamination associated with construction applications.

The "control by wire" system uses electrical signals to control the compactor direction.

Wiring looms are inherently flexible and re-routable in a way that is impossible with the hydraulic alternative.

The result is a more robust, and simplified design.

When operating a motor craft it is unlikely that the skipper will wish to stay in a single position on the boat throughout the course of the journey.

This applies in particular to small boats such as fishing vessels and small ferries.

For example, Scandinavian fishermen often fish along the coastline for salmon in one man boats with small nets or rods.

By adding an additional control console to the side of the boat it is possible to combine the flexibility of a small boat with the convenience and comfort of a larger vessel.

Similarly, by adding controls to the side of the craft can be guided to dock by eye.

Traditionally, small craft have been controlled from the deck by means of steel cables running the length of the vessel.

The cost and inconvenience of such an arrangement has led to the use of electromechanical actuation.

Specialist engineering company Teleflex Morse designed a system that allows a craft to be controlled from up to three different control stations located about the vessel.

Typical positions could be inside, for bad weather, on deck, or to port side for mooring.

With the new electronic solution, the crew must simply hit a button on the console that they wish to use, and control of the boat is transferred to that location.

For the boat designer, electromechanical actuation makes new designs that were previously restricted by the need to route tensioned cables through the body of the craft possible.

Similar to the compactor, all that is required is an electrical signal to control the actuator.

A Thomson LA-1 one linear actuator was employed to control the throttle of the engine, and a second was used to change gear.

Because the actuator is small enough to be used in a confined space, it is ideal for such an application.

In addition, it is very robust (IP65 rated) and has integrated feedback, that is required for continuous control of equipment such as valves.

LA series actuators are available in typical automotive 12, 24 and 36V models, and 115-380V AC models for heavy duty or industrial applications.

Ball or acme screw designs are available across a range sizes and loads to suit the requirement.

Of course the same technology can be applied wherever throttle or gearshift control is required, across the whole industrial vehicle and off-highway sectors.

Holder manufactures articulated tractor vehicles that are sold internationally.

Its "articulated oscillation" technology enables the vehicles to be used for a wide variety of applications such as cutting grass on slopes or maintaining footpaths.

Because the vehicle is articulated, it is essentially in two parts that have a degree of freedom from each other.

For this application, a linear actuator is again used to control the gear shift.

Holder's design engineers implemented an elegant solution that uses a joystick to control the direction of the tractor.

The operator needs only move a joystick in order to drive the tractor, because all gear changes including the change to reverse are carried out automatically.

The compact Elektrak E050 actuator offers a much cheaper solution than the hydrostatic equivalent.

The linear actuator is located underneath the vehicle and is therefore subjected to a harsh environment, particularly if exposed to salt in snow clearing applications.

Elektrak E, LA and PPA actuators have been developed with many years of agricultural and construction application experience and as such are very robust and therefore ideal for such uses.

Indeed, Thomson's first generation of general purpose actuators were developed for remote push button control of accessory drives on garden tractors and automated farm equipment.

We have seen how the use of electromechanical actuation can be used to complement and enhance off highway vehicle designs.

Actuators with integral position encoders facilitate continuous control of hydraulic valves, allowing smoother operation of equipment.

Vehicle designers can implement improved vehicle control because electromechanical actuators integrate directly into electronic control systems.

The result for the OEM is improved user experience and increased freedom of design from the use in electrical wiring where cables or hydraulics have traditionally been used.

Serving such a wide range of applications demands a broad standard product range with highly flexible design capability.

Often a large degree of customisation is required to meet the unique criteria of each application.

Design modifications such as special electrical connections and mounting methods as well as dimensional and key performance changes are necessary in many cases to provide the OEM with a design that meets their exact requirements.

There is undoubtedly a strong trend towards the increased application of electromechanical automation to off highway vehicle applications.

The liberating influence on OEM design and the benefits of "control by wire" solutions to the end user can be clearly seen.

The use of electromechanical actuation can make elegant and cost effective off highway vehicle designs a reality.

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