Linear Units - Thomson - #9

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9 Linear Units www.danahermotion.com Technical Introduction Ball Guides A ball guide consists of a ball rail and a ball bushing. The ball rail is made of hardened steel and runs along the inside of the profile. The ball bushing is attached to the carriage of the unit and contains balls that roll against the rail. The balls in the bushing can be recirculating or have fixed ball positions depending on the type of ball guide. The recirculating type has a longer life and better load capability while the fixed type typically is much smaller. Danaher Motion uses three major types of ball guides in its linear units. Either the compact single rail type with recirculating ball bushing (A), the stronger double rail type also with recirculating ball bushings (B) or the fixed ball position ball bushings type (not shown) which require very little space and are used in the smallest units. Ball guides offer high accuracy, high loads and medium speed. Slide Guides A slide guide consist of a guide attached to the inside of the profile and a slide bushing attached to the carriage. The guide can be made of different materials (e.g. polished hardened steel, anodized aluminium) while the bushing is made of a polymer material. There are two types of bushings, fixed and prism. Prism bushings can move in relation to the guide which results in longer life and higher load capabilities. Slide bushings are silent, simple, reliable and robust and can be used in dirty and dusty environments. They are also resistant to shock loads, have a long life expectancy and require little or no maintenance. Wheel Guides A wheel guide consists of ball bearing wheels that run on a hardened steel rail. Wheel guides are a simple and robust guiding method offering high speeds, high loads and medium accuarcy. Screw Supports Screw supports allow screw driven units to travel at high speed even when stroke becomes longer. The supports reduce the unsupported length of the screw, that otherwise would be subjected to vibrations. Screw supports come in single (one screw support on each side of the carriage) or double (two supports on each side) versions. Screw support units will have a slightly shorter stroke for a given overall length. Ball Screw Units with Double Ball Nuts Using double ball nuts will increase the repeatability of the unit. The ball nuts are installed so that they are pre-tensioned against each other eleminating the play between the nuts and the screw. A double nut unit will have a slightly shorter stroke for a given overall length. A B