Sliding security door with passive deadlock prevention

In a high-security sliding-door apparatus for closing and opening a passage in a wall, a door having:

• (a) a door frame having a door-supporting track and a bi-directional effector;
• (b) a carriage secured to a door top edge and having track-engaging rollers;
• (c) a slide plate (i) slidably secured to the carriage, (ii) driven by the effector, and (iii) having two end sections;
• and (d) a controller controlling slide-plate movement and configured to enable the door to be continuously closed but not locked when a continuously-closed signal is received by the controller, the improvement comprising mechanical centering apparatus for relative positioning of the slide plate and carriage, the centering apparatus including:
• a yoke pivotably attached to the slide plate at a yoke pivot and having a yoke cam surface thereabove;
• a yoke-cam follower attached to the carriage and following the cam surface;
• and
• a pair of springs having proximal ends attached to the yoke spaced above the yoke pivot and distal ends each attached to the carriage at points offset from the yoke pivot in opposite lateral directions,
• whereby the door is kept substantially centered on the slide plate unless a slide-plate end section is driven to a locked-open or locked-closed position.