Toggle type temporary roof support for mining machinery

A temporary roof support for use with mining machines comprising:

• a base structure (10) having a generally vertical axis, said base structure having four pivot pins fixed thereto comprising an inside pair symmetrically spaced on each side of said axis defining inside right (19) and inside left (18) pivot pins and an outside pair of pivot pins symmetrically spaced on each side of said axis defining outside right (17) and outside left (16) pivot pins;
• two pairs of swing arms defining a left swing arm pair (30) and a right swing arm pair (31), each swing arm having inner and outer ends, each swing arm having means for pivotal connection at each end, a line joining the said pivotal connection means at each end of each swing arm defining the axis of the swing arm, and said right pair of swing arms (31) being pivotally connected to said right inside pivot pin (19) at the inner end of said swing arms and said left pair of swing arms (30) being pivotally connected to said left inside pivot pin (18) at the inner end of said swing arms;
• left (46) and right (47) linkage extensions having inner and outer ends, said extensions being pivotally connected (48) to each other at their inner ends and being pivotally connected at their outer ends to the outer ends of the left and right swing arm pairs respectively;
• left and right extensible hydraulic means (60, 61) having inner and outer ends, each extensible means having means for pivotal connection at each end, a line joining said pivotal connection means at each end of each extensible means defining the axis of the extensible means, said right extensible means (61) being pivotally connected at its inner end to said right outside pivot pin on said base structure and connected at its outer end to the right swing arm pair such that the axes of the right extensible hydraulic means and the right swing arms are always crossed;
• said left extensible means (60) being pivotally connected at its inner end to said left outside pivot pin on said base structure and connected at its outer end to the right swing arm pair such that the axes of the left extensible hydraulic means and the left swing arms are always crossed;
• and
• a beam attached to the pivotal joint (48) between the left and right linkage extensions for supporting the roof.