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Solving the problems of long-stroke motion

10 April, 2013

Avoiding whipping

Using the collapsible support block system and precision-manufactured long screw lengths allows strokes of 10.8m or longer to be achieved. A system with a stroke length of 2–3m would have a maximum speed of around 3–4,000 rpm. Normally, with a longer system, the rotational speed would have to be lowered considerably to avoid whipping, but Thomson has engineered a system using additional supports to maintain stroke lengths of more than 10m at 3–4,000 rpm. This offers the benefits of a stiff screw system, long stoke length and high transportation speeds.

Many existing applications work with screw systems up to 5m or 6m long where the screw is left completely open. There are two common issues with such systems:

•  the system cannot operate at the desired speed; and

•  is difficult to maintain because the open screw attracts dust and debris, requiring regular cleaning to avoid premature failure of the ball nut.

In such applications, the additional supports provided by a stacking bearing block configuration mean that the screw can be operated at much higher speeds. Cleaning and reliability issues can be resolved using a covered, sealed system which protects the screw and cuts maintenance. The enclosed screw (shown above) is protected against the ingress of dust and debris and can maintain optimum performance and reliability, without needing regular cleaning. In such a system, the carriage can be equipped with drilled channels and connected with a grease nipple. This enables lubrication from a single point without having to open the casing, thus allowing rapid and comprehensive maintenance. Because the system never has to be opened, only small amounts of dust or water can penetrate and the system is protected even in the dirtiest environments.

As with any process, specific application requirements dictate which technology is best. Linear motion systems using screws can handle larger loads than non-rigid, polymer belt systems. The screws are robust stainless-steel pieces and, if manufactured to the correct tolerance class, can reach stroke lengths well over 10m. The collapsible bearing block system supports the screw length to avoid whipping and bending while enabling it to operate at the higher speeds usually associated with shorter length systems. Long-stroke linear screw-drive systems offer precise positioning with fast, safe operation. When operating in the sealed enclosure, they are suitable for continued reliable use with minimal maintenance, even in harsh environments. 

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