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Linear motion: myth and reality
Phil Burge, Communication Manager at SKF, separates the facts from the fiction, exploring the importance of leading edge developments in linear motion, while debunking the hype surrounding many of the supposed innovations of recent years.
In recent years, manufacturers of linear motion devices, especially profile rail guides, slides and actuators, have expended significant technical effort and marketing budgets in extolling the virtues of leading edge products with ever greater levels of performance and precision.
As a result, there has been considerable interest in innovative methods of minimising friction, noise, heat and energy losses, and in finding ways of reducing errors in repeatability, while reaching submicron levels of accuracy. The upshot has been a plethora of design ideas, ranging from caged balls to the adaptation of specialised X and O geometries, gothic arches, et al. Although these developments are all important in breaking new technological ground they have obscured the fact that, in the majority of applications the capabilities and reliability of standard linear bearings, slides, profile and precision rail guides, and ball and roller screws, are more than adequate to meet both the technical and commercial requirements of most end users.
Indeed, it remains a fact that in most applications standard, existing devices provide the levels of performance, accuracy and reliability required by engineers and they need not be seduced into over specifying or over spending on sexy technology. For example, is there really a need for a car that reaches in excess of 150mph, which is engineered and priced accordingly, when we only ever want to drive at a maximum speed of 70mph?
Linear motion devices have been used extensively throughout industry for many years, to position and move parts, workpieces and tooling in single or multiple axes in a wide range of environments, from aviation systems and medical scanners to high speed factory automation lines. They are therefore a proven technology that offers extremely high levels of performance with, in most instances, a long operating life. They are particularly useful in applications where space and weight savings, together with almost silent operation at high speeds are critical.
With the ability to position even the heaviest loads with exceptional levels of precision and repeatability, standard linear motion devices provide engineers with the opportunity to make considerable improvements in line efficiency, and, as a result, boost profitability. Indeed, while they may not be as sexy as some of the latest all singing, all dancing designs, traditional linear motion technologies continue to achieve excellent levels of accuracy, speed and reliability, enabling businesses to realise significant cuts in operating costs, as these systems require minimal maintenance or manual intervention.
Furthermore, it is becoming increasingly common for leading manufacturers to combine these individual components to deliver subassemblies that serve as self-contained units to provide enhanced performance, in terms of speed, strength, accuracy and reliability, while reducing machine build time and costs.
In particular, ball screws have been widely used throughout industry for many years, but leading manufacturers, such as SKF, have been continuously developing the technology to meet changing market demands. As a result, ball screws continue to be a popular choice in many applications for providing a cost effective combination of reliability, accuracy and robustness.
Moreover, the latest ball screws offer particularly high levels of precision and repeatability, with optimised designs to minimise frictional losses, noise and heat, and advanced materials with excellent mechanical characteristics to reduce size and weight, while improving overall performance. Equally, the latest linear and rotary actuators are capable of high levels of speed, temperature stability, and accuracy, with standard devices being able to accommodate loads as great as 12kN at accuracies of up to 6µm per 1000mm, while achieving speeds of up to 174mm/s and traveling as far as 1,500mm.
There is now such a wide variety of functionality and capabilities available that the right solution can be found to meet the load and speed requirements of any automation application. Furthermore, a growing range of controls and operating devices is expanding the environments in which conventional linear motion devices can be beneficial.
For example, many actuators now feature modular designs that make it easy to interchange critical components such as motors, gears, screws and attachments; previously this ability to construct custom built systems would have been the exclusive preserve of the special systems builder. This ability to custom-build actuators easily and cost effectively from standard parts makes the technology suitable for a diverse array of applications, including many where the use of electromechanical technology has previously been limited. Additionally, it can help to make linear motion systems easier to install and maintain, often with compact dimensions that allow the space required for automation systems to be minimised.
Offering strong load carrying capacities, fast duty cycles and quiet movement, traditional linear motion devices, such as linear actuators, provide designers, system builders and OEMs with a viable alternative to some of the latest novel designs, especially in challenging industrial environments. In addition to providing a cost effective alternative, proven linear motion technology is extremely energy efficient and safe.
Similarly to linear actuators, traditional electromechanical rotary actuators are also compact in size but able to produce high torque. As these actuators can withstand heavy loads, they can be used as an integral load bearing element of an automation system. To save costs, a range of standard rotary actuators is now available in a variety of sizes to suit most applications.
The need for increasing automation and productivity, especially in technically demanding applications that rely heavily on extremes of accuracy, speed and reliability, often under demanding production or environmental conditions, is ever more critical as companies fight to succeed in today's extremely competitive marketplace. In many applications, the key to achieving this success is through the use of proven linear motion technology that delivers the results needed without expensive and specialised development.
Thanks to the recent developments in linear motion technology there is now a product to meet the demands of almost any application, whether it be a ready to install unit or a combination of standardised components that can be used to create a bespoke system. As a result, it is easy to see why there is not always a need for over complex and expensive innovations in the creation of linear motion solutions that provide unparalleled levels of accuracy and reliability, which in turn pays a considerable contribution to improving productivity and, ultimately, profitability.
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