Miniature slide units offer high load carrying capacity, smooth travel torsional stiffness and superb engineering

Citation

(2002), "Miniature slide units offer high load carrying capacity, smooth travel torsional stiffness and superb engineering", Assembly Automation, Vol. 22 No. 1. https://doi.org/10.1108/aa.2002.03322aaf.009

Miniature slide units offer high load carrying capacity, smooth travel torsional stiffness and superb engineering

Miniature slide units offer high load carrying capacity, smooth travel torsional stiffness and superb engineering

Keyword: Slides

In a world where engineering scientists have created working engines so tiny that you can hardly see them with a powerful magnifying glass, a slide unit whose rail is just 2mm across could be considered gigantic. Maybe so, but in the world of slide units, they are indeed exceptionally tiny.

Unlike the engineering scientists whose usual project aim is conceptual and experimental, the miniature slide units manufactured by IKO Nippon Thompson are superbly engineered products whose purpose is to function in a real working environment with an extended working life (Plate 9).

Plate 9

Slides come in many types and sizes, as do the rails they run on. They serve specific functions with some structural types, able to span considerable distances. In the smallest type such as IKO's recently introduced Linear Way LWL2, which has a track width of just 2mm, the engineering is even more impressive. Due to a wide range of varying applications and design parameters for which these units are specified such as clean rooms, vacuum and high temperatures, there are numerous special specifications in multiple combinations in which the units can be supplied. For example, Clean Room grease, all stainless steel, self lube or Capillary plates, black chromium plating and so on.

Slides generally come in two widths and three lengths. These have different operational characteristics for special applications. Longer slides for example will resist unwanted movement less than short slides and can carry greater loads. Although at first glance the benefit may seem very slight, the result can be dramatic, especially in optical grinding equipment for example, we all remember that the Hubble telescope experienced major problems and had to be optically corrected in space. The different slide lengths are entirely interchangeable as are slides and rails of different materials such as a high carbon steel slide and a stainless steel rail.

Other applications may call for operation within a vacuum sealed environment for example. Design engineers might be interested to know that some products can be ordered with the standard synthetic resin end plate changed for a stainless steel equivalent which also helps to improve heat resistance.

OK, so now we know the common variations and combinations that can be ordered, but what about accuracy? Some applications may require a configuration of two or three rails and slides running parallel to each other to move a platten or table. The manufacturing procedures now in use can offer slides and rails whose depths are accurate to within a micron or two of each other. This degree of accuracy is critical in many applications today and is the norm rather than the exception. Manufacturers are pushed to ensure that they offer products made to tolerances even finer than current market demands expect.

So with manufacturing tolerance taken care of, what is left? Performance in operation. We have already established that today's units are superbly engineered but what are the loads they are likely to experience?

The carriages or slide units can vary in size on an identical rail, this ability specifically overcomes the differing moment loads applied in varying applications. For example, the longer the carriage the less of a tendency to pitch and yaw (movements C & D on the diagram) when axial and side loads are applied. The wide rail versions are designed to withstand higher torsional loads (B) and thus alleviate or decrease the tendency to roll in operation.

The stiffness and performance data of these units is obtained by very accurate machining of close conformity Gothic Arch raceways both on the carriages and rails which produces a four point contact design and has a Coefficient of Friction of less than 0.004. To actually gain an overall conception of this Micro engineering capability, the smallest slide and rail unit presently available comes from IKO nippon Thompson. It is the (LWL2 Size and it contains rolling elements of just 0.6mm diameter.

These miniature products have a phenomenal load carrying capacity, for example the physical dimensions of the LWL2 slide unit are 3.2mm high x 6mm, while the rail is just 2mm wide. Despite its incredibly small size, the LWL2 has a dynamic load carrying capacity of 20Kgs (A) and static ofapproximately 40Kgs. The wider unit LWL4 series is 4mm high, 10mm wide and has a static moment rating in the roll direction (B) of 1.5N.m.

The huge variety of applications and uses to which these units are subjected might see the various forces applied individually or collectively. Regardless, all manufacturers offer guidance and formulae which enable the designer to calculate the optimum type and size of the units and rails for a specific application, in addition to estimating the anticipated working life. Regular maintenance will of course affect unit life.

In taking into consideration any of the combinations in which the units can be supplied, they operate and produce extremely high running accuracy with the Precision class units able to operate and produce a total run-out of less than 8µ over 1500mm.

Although several manufacturers produce slides and rails, only IKO Nippon Thompson offer truly miniature products and the engineering excellence is second-to-none. Endless linear motion is achieved by means of moving recirculating elements inside the slide unit. Typically these can be roller type or ball type elements, though in the smallest sizes they are available in ball type only. In either case they are able to accept physical loading from any direction whether moment or complex loads. Ball type recirculating elements can be of the retained or non- retained ball type.

In some applications, a cylindrical roller would be preferred to a ball roller. Cylindrical rollers benefit from excellent elastic deformation characteristics and thus very high rigidity. When a large number of cylindrical rollers are embedded in a slide unit, the elastic deformation is even smaller. Rails are available as standard or wide rail type. They can be manufactured from high carbon steel or stainless steel depending on application need and can be butted together for longer applications requiring longer travel distances.

Specific applications for the smallest slides and rails have included medical machine manufacture. One major project currently under consideration is the use of the LWL Series miniature products as part of a neutron beam shield which comprises 64 separate leaves of thin steel plate. The ability to move the steel plates using IKO LWL slides and rails enables the beam to be irradiated closer to the patient, focussing the treatment to make it more successful. Another use recently launched to designers is measuring and image processing equipment manufacture. Here again, miniature LWL Series slides and rails are providing smooth motion to produce exceptional operational accuracy.

Contact IKO Nippon Thompson Ltd, www.Iko.co.uk