Abstract: According to the invention, monitoring the load on hydraulic powered shield supports in underground use is performed by using the controller (13) serving for extraction control, which is equipped with microelectronics for load monitoring and load control, the components of the powered shield support being assigned sensors (14 to 18) whose electric measured values are used by the controller (13) for evaluating the measured signals and for driving the hydraulic rams (6, 7) and/or the angle cylinder (11) assigned to the powered shield support. The load control is preferably designed here in such a way that the critical load situations "one-sided loading" and/or "tip-toeing" are detected as early as during the setting operation, with the aid of appropriate sensors, and are rendered non-damaging in their effect by appropriately driving the hydraulic rams and/or the angle cylinder.

Abstract: A pit prop has a floor-engaging foot, at least one arm pivoted at the rear of this foot and extending forwardly, a roof-engaging shield carried at the front end of this arm, and at least one ram extending vertically between the arm and the foot for pressing the shield against the roof and the foot against the floor. A hydraulic ram has its rear end pivoted at the rear end of the foot and its front end pivoted on the rear end of a rigid link whose front end in turn is pivoted on the face conveyor. The rear end of this link is slidable in and pivoted on the foot. A second link has its front end pivoted on the rear end of the main link and its rear end bearing vertically down against the foot but slidable therealong. A short lifting ram has its rear end pivoted on the rear end of the second link and its front end pivoted on the rear end of the main link above the pivot for the other displacement ram pivoted on this link.