The traditional kind of tilting umbrella has a shaft at whose upper end is a so-called notch on which are pivoted the ribs which support the cover. The ribs themselves are held up, in the erected position of the umbrella, by a corresponding number of stretchers attached pivotally at one end to the ribs and at the other, again pivotally, to a runner which can slide along the shaft in order to fold and unfold the umbrella. In the upper position of the runner, with the umbrella unfolded, the runner is held in place by a catch. In order to provide the required tilting facility for the umbrella, a joint is provided in the shaft at a point below the upper position of the runner.
While this arrangement does allow the head of the umbrella to tilt with respect to the shaft, it has a number of disadvantages, most notably that, during folding and unfolding of the umbrella, the runner tends to catch on the joint. The presence of a tilting joint in the shaft also allows play in the umbrella, and the fact that the entire head of the umbrella, from the tilting joint upwards, is inclined when the tilt facility is used, means that the centre of gravity of the umbrella is displaced some way off the shaft axis, leading to instability and difficulties in handling especially in windy conditions. Further, the joint itself must fit within the confines of the shaft diameter, since the runner has to pass over it to fold and unfold the umbrella. This limits both the strength and the configuration of the joint.
An umbrella frame overcoming these disadvantages has been proposed in EP-A1-368539 U.S. Pat. No. 5,086,797. In this frame, known as the "head-tilt" frame, the tilting joint is located at a position between the top of the shaft and the runner. This means among other things that the joint can be much more robust than previously, and also that various kinds of joints, which otherwise would be unsuitable for umbrella frames, are now available for use. In particular EP 368539 envisages the use of a special design of ball-and-socket joint.
While the frame of EP 368539 has proven highly successful, it still has a minor weakness in that the tilt joint can be activated unintentionally by strong winds, even if the ball-and-socket joint has retaining lugs to keep the shaft straight.