Linear motion: Examples of the technology and its applications

Written by: Paul Fanning | Published:

For high-precision motion control of machine tools and other production machinery, design engineers and end users increasingly require ready-to-fit, complete linear motion systems with integrated features such as sealing, lubrication, measuring and braking.

Schaeffler has developed a comprehensive range of standard, ready-to-fit complete linear guidance systems for machine tools, including profiled rail linear guides, linear actuators, shaft guidance systems, linear recirculating roller bearings and guideway assemblies, as well as a range of accessories such as damping carriages, seals, equipment for long term lubrication, clamping and mounting components.

However, manufacturers and design engineers are demanding higher load-carrying capacities, longer term precision, improved dynamics and higher machine availability. In response to these requirements, Schaeffler's premium quality X-life profiled rail linear guidance systems offer improved performance in terms of higher running speeds (typically 40% higher) with unchanged load carrying capacity and rigidity for highly dynamic machine tools.

Schaeffler's RUE range of roller type profiled rail linear guidance systems have been working reliably for many years in machine tool applications. RUE-profiled rail units provide reliable support for the main axes of machine tools.

For feed and discharge systems, tool changers and handling systems, Schaeffler ready-to-mount linear actuators are the preferred choice. The MKUVS 42 LM, for example, is a linear actuator with a direct drive. This system is suitable for high speed, high-precision positioning applications in machine tools and can also be used as a tool changer. The compact, integrated design of the linear actuator system means it requires less space to install. For extremely high loads that need to be transported in vertical axes, Schaeffler MDKUVE tandem actuator module is ideal.

HepcoMotion's GV3 linear motion system for arduous applications is continuing to develop. Build quality is key to its superior performance and so, too, is its 'V' operating principle.
Continuously developed for more than 50 years, the 'V' concept makes the GV3 linear motion system the perfect choice in tough environments such as offshore engineering. One of the major benefits is the self-cleaning action that eliminates contamination of the slideway.

Also significant is the extent of travel achievable by GV3, fitted with HepcoMotion cap seals, before re-lubrication is required. For most harsh environment applications GV3 is therefore a fit and forget system.

The inherently low friction of the GV3 system means it positively thrives in high-speed conditions, especially in applications which also require prolonged accuracy. In addition to low noise, low friction also allows the system to run dry, if needed.

Low friction also means low energy consumption and long re-lubrication intervals cut maintenance costs. By comparison a recirculating ball monorail is highly susceptible to dirt ingress in the ball track, causing the block to fail catastrophically and permanently damage the rail.

The need for a replacement bearing is the worst that can happen to a GV3 system, a task that can easily be accomplished without affecting the slide. Furthermore, thanks to its adjustable eccentric bearings, GV3 will continue to work even when worn.

If corrosion resistance is needed, the customer can specify the HepcoMotion SL2 range which is directly interchangeable with GV3 and made to the same specifications. Indeed the range offers a choice of materials to achieve the best compromise between corrosion resistance and wearability. Different bearing options complement this flexibility.

Superior surface finish also plays an important part in the longevity of the GV3 system. Quite simply, the better the finish, the less likelihood of surface corrosion and for this purpose HepcoMotion has invested heavily in capital equipment to provide this performance edge.

HepcoMotion harsh environment and corrosion resistant products are not just restricted to basic X-Y-Z linear motion. It also provides complete ring and track systems.

Linear motion is often associated with certain industries, but a very atypical application comes from LG Motion. As an addition to its cutting-edge fluid mechanics research facilities, the Department of Aeronautics at Imperial College London.

The servomotor-driven positioner is based on two parallel LR series linear guides from LG Motion's associate MiniTec UK. The mechanical system is configured as parallel mounted belt-driven and non-driven slides on stainless steel precision shafts, supporting a 600mm x 600mm carriage that transports test models with precisely-defined velocity/time waveform profiles at speeds up to three metres per second over an 8m travel range. The complete system comprises the LH series linear slides driven by a powerful brushless servomotor with resolver feedback and high precision gearhead, plus a cabinet-mounted single axis servo drive and motion controller.

The new 9m water flume has two main modes for fluid mechanics research at the Department of Aeronautics. The first concerns understanding the behaviour of complex structures such as oil platforms in sea state studies by simulating current and tidal conditions to create vortex induced vibrations through turbulence. In the second mode the water tank is used in similar way to a wind tunnel except that water rather than air is used as the forcing medium. An area being studied in this way is flow-induced behaviour of cylindrical models that may represent surface piercing pipelines or marine-based tower structures such as wind turbines, and how different surface features and coatings may influence their prolonged use.

For both of these modes, the positioning system drives the carriage mounted model to follow a precise waveform profile initiated from an analogue demand signal from the flumes' main controller or, for set-up and other assessment purposes, directly from the motion controller via simple BASIC-like PC programming. The waveform simulates the required modelling conditions whilst a series of high precision sensors collect the relevant structural behaviour information with the results presented through a dedicated data acquisition system.

For a system with such high-speed and high acceleration capability, safety was a main concern. The linear slide includes a light curtain operating over the full length of its main working side. Adjustable overtravel limit and datum switches are conveniently mounted on the T-slots of the extruded aluminium profile LH slides. The light guard and limit switches are wired to the cabinet mounted motion controller which includes hardwired and software programmed safety features to ensure safe shutdown under emergency conditions.

LH series linear slides are available for customised travel lengths with belt transmissions and various motor technologies available to suit the application. The addition of double-row angular contact bearings on stainless steel precision shafts increases the load carrying and speed/acceleration performance for the 9m water flume.

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