At least one bearing frame can be moved on wheels along a path between two fixed bearing frames of a bearing frame system (A, E) by means of reversible electric motors mounted on the bearing frame (B, C, D) in order to create a passage (G) between the bearing frames. Mounted on each longitudinal side of the bearing frame is a set of switches (LR, LF) which are actuated in each case by a different bearing frame. In order to guarantee that the bearing frame to be moved is moved up entirely, each switch (LR, LF) in each set is assigned to a switch in the other set, so that a pair of switches (LR, LF) is formed in each case. This pair of switches (LR, LF) is assigned to an electric motor (M), so that upon actuation each switch interrupts the circuit to the assigned electric motor (M) in order to stop the section of the bearing frame on which the pair of switches is arranged. IMAGE
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