Pantograph

Linear current collection is similar to carbon brush collection except that in linear collection the collector is moving rather than the conductor. Current collectors have relative motion along a line instead of around a rotating cylinder; point or line contact is present, as opposed to the area contact of a brush. There is more frequent and more complete rupture of contact with the consequence of sparking and arcing. In addition, linear current collectors are more likely to operate outdoors, subject to the variations of environment and weather. In order to cope with these disadvantages, collector materials have to be much harder, denser and more abrasive than brush materials.