| 摘要 |
A mine roof support has a slidable extension at the front end of an auxiliary roof cap pivoted for swinging up and down on a main cap. To prevent the extension from being extended when the angle of inclination of the auxiliary cap is too high an insulative cylindrical block is fitted to say the auxiliary cap to partially rotate as the auxiliary cap pivots. A flattened region on the block supports a metallic plate and indexes as the auxiliary cap pivots. A resiliently-mounted proximity switch on the main cap senses the presence of the plate and produces a signal to prevent the extension from being extended. |
