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Designs on linear motion: ‘pre-engineered’ is the new ‘standard’

03 June 2010

Integrating linear motion system assemblies and sub-assemblies into machines can be a very time-consuming process, particularly when extensive modifications are necessary. Nowadays, the trend is to engineer these assemblies prior to delivery to ensure that they are fit for purpose, helping OEMs to cut their machine build time and costs, as Phil Burge explains

Linear motion systems are used extensively by OEMs and machine builders, as a primary method of moving, positioning, clamping and handling tool pieces, components and finished products. Typically, linear motion devices are supplied as stand alone units that need to be engineered into machine systems by the OEM, often with specially developed ancillary guide mechanisms – a process that can be relatively time consuming and expensive.

Increasingly, however, machine builders are working more closely with the manufacturers of linear motion systems to develop complete assemblies or sub-assemblies that are pre-configured and tested off-line, to minimise machine build time and costs. Perhaps just as importantly, this process is also helping to improve the performance increase the functionality of linear motion devices and, by default, the performance and functionality of machines into which they are fitted.

With the benefit of years of application experience, the industry can now supply a bewildering variety of linear motion technologies, including linear bearings, profile rail guides, precision rail guides and roller screws. This means that the right product can be found to meet the requirements of any application in terms of load bearing capacity and levels of positional accuracy and repeatability. Moreover, these robust positioning systems can operate in a wide variety of environments, such as on board aircraft or inside hospitals, where, respectively, space and weight saving is at a premium and low noise essential.

Feedback from OEMs has focused manufacturers on the need to combine individual components into pre-engineered sub-systems. These serve as self-contained units that not only deliver enhanced performance in terms of speed, robustness, accuracy and reliability, but also ensure that the OEM’s task is simplified and that he achieves those all-important benefits of reduced machine build time and cost.

Depending on the requirements of the application, manufacturers can incorporate feedback devices into these sub-assemblies to establish speed and position, as well as special configurations to support structural loading. And while some sub-systems can be designed and built to meet the challenges of difficult operating conditions and environments, other systems are also available to suit more universal specifications.

Over and above the trend for pre-engineered sub-assemblies, some manufacturers have moved a step further and are now providing fully integrated mechatronic systems, which respond independently to inputs and offer real-time feedback. Mechatronic assemblies are now widely used by machine builders seeking a ‘plug-and-run’ solution to the problem of complex machine construction.

A good example is the industrial welding robot illustrated on this page. Developed by SKF to provide an energy efficient alternative to the pneumatic actuators traditionally used throughout the automotive industry, this compact electromechanical actuator system requires only a fraction of the energy that would otherwise be needed for compressed air. Indeed, up to 90% savings are possible by taking this alternative approach.

Beyond the welcome energy savings, this system also enables both the speed and quality of the welding operation to be significantly improved, thanks to more precise process control. Noise and maintenance requirements are also considerably reduced.

Continuing the energy theme
SKF has also introduced a unit that enables self-regulating blind systems to keep buildings warm in winter and cool in summer, allowing energy use to be cut by up to 50% in glass-clad buildings. The secondary glass facade is a system of self-regulating glass blinds that automatically capture and deflect heat towards the building in winter and away from it in summer.

Linked to the building management software, a special control and actuator system moves the blinds automatically in response to the sun’s position, as well as other factors such as shadows cast by clouds and neighbouring buildings. The system cuts unwanted solar absorption by a substantial amount – as much as 89% on warm days; it also minimises glare while allowing sufficient natural light into the building.

In another development, the company has designed a novel electronic parking brake for tractors and agricultural vehicles. This new hybrid system is based on a mechanical emergency brake combined with a patented intelligent electromechanical actuator, which operates on a conventional transmission parking brake. As well as improving braking efficiency and operator safety, the device also reduces overall emissions and operating costs.
The electronic parking brake incorporates a geared motor and actuator in a sealed housing, along with an electronic control unit that is interfaced to the in-cab operator controls. It is operated by an electronic signal from the cab, with the motor being used to extend or retract a conventional brake cable by driving the actuator shaft via a simple gearing arrangement. This configuration results in exceptional reliability and, unlike conventional parking brakes where the operator has to engage a manually operated brake, considerable brake force can be applied quickly and simply.

Additionally, the electronic parking brake helps to reduce noise and increases the space available for other equipment. And by improving the efficiency of the braking mechanism, the system helps to reduce wear on brakes and associated parts, the lower frictional losses ensuring improved fuel consumption.

Phil Burge is with SKF (UK)

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