Improvements relating to the provision of electrical connection between relatively movable parts

814,828. Current collectors for dynamoelectric machines. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. July 4, 1957 [July 12, 1956], No. 21596/56. Class 35. [Also in Groups XXX and XXXVI] A current collector for use with a slip ring or commutator comprises a roller 1, Fig. 2, shown engaging a slip ring 2 and having a shaft 26 supported in bearings 5, 6 between side plates 7, 8 said shaft having an extension 25 received in a stationary cup 27 containing mercury and having a connecting cable 28 attached thereto, the shaft and the cup carrying concentric sleeves 30, 31 respectively of steel or other material which is not wetted by the mercury and between which there is a small running clearance to prevent egress of mercury from the cup. The framework of which the side plates 7, 8 form part is spring biased towards the slip ring 2. Fig. 3 shows an alternative construction wherein the roller 11 is hollow and a stationary spindle 39 having the conductor 28 attached thereto passes through a bush 35 closing one face of the hollow roller and has a head 40 located in said hollow which contains the mercury. A steel sealing sleeve 41 is fitted to the rod. To reduce the speed of the contact roller where it engages a large slip ring, an intermediate dumb-bell shaped roller 47, Fig. 5, may be interposed between the slip ring 2 and the contact roller 46, the large diameter portion 48 of the roller 47 engaging the slip ring and the small diameter portion 49 engaging the roller 46. Fig. 7 shows an arrangement wherein two contact rollers 51, 52 constructed according to Figs. 2 or 3 and displaced round the periphery of the slip ring are connected in parallel to reduce sparking in the event of temporary impairment of contact at one of the rollers. A sliding brush may replace one of the rollers (Fig. 8, not shown). Selfcleaning of the contacting surface of the roller and slip ring may be provided for by setting the axis of the roller at a slight angle to the axis of the slip ring so that a small amount of slip occurs, and concentration of the contact pressure may be obtained by crowning the surface of the slip ring and/or the roller. Where the contact roller is used with a commutator, the bars 67, Fig. 11, of the latter may be set at an angle or each bar divided into two circumferentially offset parts 69, 70 as shown in Fig. 12, so as to ensure that the roller engages an oncoming bar before breaking contact with a receding one. Suitable materials for the contact surfaces of the roller