text: The present invention concerns an articulated overhead door with very little overhead space between the top of the door opening and a ceiling or similar surface. The door comprises several panels linked together one after another in the direction of motion. The panels are guided by rollers at each end traveling in two sets of lateral tracks. The first set of tracks has a more or less vertical section that merges into a curved section and then into a horizontal section. The second set of tracks has a horizontal section and, at the door case, a terminating section. The terminating section has two subsidiary sections. The first subsidiary section slants slightly down from the horizontal. The second subsidiary section is bent down toward the floor just slightly more than 90.degree. to the horizontal. All the panels except the one that is uppermost when the door is closed are guided by rollers that travel in the first set of tracks. The panel that is uppermost when the door is closed is guided by rollers at the upper edge that travel in the second set of tracks. Such doors are preferably balanced by spring assemblies mounted inside the door opening and preferably at the associated ends of the horizontal sections.
  The lack of sufficient space above such doors means that the rollers in the uppermost panel must travel such as to ensure that the panel will properly assume its closure position with the rest of the door properly aligned below it. It is accordingly impossible to entirely eliminate a slight slope on the part of the second set of tracks associated with the pair of rollers in the uppermost panel at one side of the door case. Since the doors are intended to be opened and closed manually as well as by a preferably motorized mechanism it must be possible to vary the position of the panel's upper rollers. It must, however, be impossible to raise the door from outside once the rollers associated with the uppermost panel have been moved down in relation to that panel to facilitate manual operation. Yet, when the door is to be opened manually, it must be possible to shift the rollers associated with the uppermost panel into the horizontal sections as smoothly as possible just by raising the door by means of handles attached to it. The motor-powered mechanism generally includes a traction slide that travels straight and is articulated to the uppermost panel. In a position that has been shifted up in relation to the uppermost panel to allow motor-powered operation, it must further be impossible to improperly shift the uppermost panel out of its closure position by forcing the mechanism while an opening motion is being initiated out of the horizontal.
  To satisfy the aforesaid requirements, the end of the second set of tracks is specially shaped with respect to the roller positioning surfaces. The horizontal section of the second set of tracks is followed by a subsidiary section that slants slightly down from the horizontal. This is followed in turn by another subsidiary section that is bent down toward the floor just slightly more than 90 .degree. to the horizontal.
  Accordingly designed terminating sections are easy to handle with a motor-powered mechanism. The pair of rollers shifted up will remain in a practical position at the transition between the two sections as long as the door remains closed, and a motion initiated from the horizontal will easily transfer them into the horizontal sections of the second set of tracks. When the door is closed on the other hand, the motorized mechanism will force the rollers associated with the uppermost panel toward the outer corner of track between the subsidiary sections of the terminating section.
  A problem will be encountered on the other hand during manual operation when the motion is initiated from the lowermost panel. Since the first section of the second set of tracks is straight, the vertical motion can produce only a weak horizontal force on the rollers associated with the uppermost panel, and a considerable threshold of force will have to be overcome beyond the associated hard impact on these rollers as the door begins to open. As the door begins to close on the other hand, the motion of the uppermost panel's rollers entering the bend between the subsidiary sections will be accelerated before they drop into the vertical second subsidiary section, and the resulting impact will be very noisy.