Articulated mine door opening mechanism

A mine door system comprising

• a mine door comprising at least one door leaf adapted to be hinged to a door frame defining an entry, and
• a door-moving mechanism, said door-moving mechanism, when moving said door leaf, is movable between a first configuration in which the mechanism applies a first door-moving force to the at least one door leaf and moves the at least one door leaf at a first speed and a second configuration in which the mechanism applies a second door-moving force larger than the first door-moving force to the at least one door leaf and moves the at least one door leaf at a second speed less than the first speed,
• said door-moving mechanism, when opening said door leaf, is configured to assume said second configuration to move the at least one door leaf through an initial-opening segment of movement against an initial load on the at least one door leaf and to assume said first configuration in response to a decrease in said initial load on the door leaf as the door leaf continues to open,
• said door-moving mechanism comprising:
• a variable-length crank being in a first state having a first length when said door-moving mechanism is in said first configuration and being in a second state having a second length shorter than said first length when said door-moving mechanism is in said second configuration,
• a mechanical link having a first end and a second end, the first end being connected to the at least one door leaf for rotational movement relative to the door leaf about a first generally vertical axis, and the second end being connected to the variable-length crank for rotational movement of the crank relative to the mechanical link about a second generally vertical axis spaced from said first axis, wherein said mechanical link is positioned intermediate the door leaf and the crank,
• an actuator for rotating the variable-length crank about a third general vertical axis spaced from the second axis,
• said variable-length crank comprising first and second crank arms connected to one another for rotational movement relative to one another about a fourth generally vertical axis spaced from the third axis, said first and second crank arms rotating relative to one another about the fourth axis as the variable-length crank moves between said first and second states, and
• a holding device for holding the variable-length crank in said first state while allowing the variable-length crank to move to said second state in response to the initial load on the door leaf as said door leaf is opened by said door-moving mechanism whereby said variable-length crank assumes said second state as the door leaf is opened by said door-moving mechanism against said initial load and assumes said first state as said load on said door leaf decreases and the door leaf continues to open.