Rapid advancing and retracting mechanism for clamping device

Claim 1

A rapid mechanism for selectively engaging or disengaging with a screw spindle, which, when turned an angle, in a first angular direction that leads to the axial retraction of the screw spindle, is disengaged from its engaged state and becomes axially slidable along its whole threaded length, and when turned in a second angular direction opposite to said first angular direction, is re-engaged from its disengaged state and can be continuously turned in said second direction to convert the rotation in the first angular direction into axial advancing of the screw spindle; said mechanism comprising a hollow housing, of which the inner wall defines a substantially cylindrical cavity, in which are received a pair of semi-annular split nuts, each formed with threads and cooperatively complementary to the threads of said spindle; said housing being so structured that when said screw spindle is received therein, the spindle is always retained in alignment with the axis of said cavity; said cavity having a diameter greater than the outer diameter of said split nuts; resilient means in said cavity for biasing said nuts, which resilient means is positioned between said inner wall of said housing and said split nuts, and is corotatably mounted with said split nuts; said split nuts having at least a portion in contact with said screw spindle in its fully disengaged state and can be frictionally driven by said screw spindle to co-rotate an angle with said spindle in said second angular direction until reaching a first position where the two split nuts are fully engaged with said spindle and prevented from further corotating with the spindle in the second angular direction; and said split nuts in their fully engaged state can be driven by said screw spindle to co-rotate in said first angular direction until reaching a second position where the split nuts are fully disengaged with said screw spindle and prevented from further corotation with said screw spindle in the second angular direction; the first angular end and second angular end of a split nut exactly meeting the second angular end and first angular end of the other split nut when they are in said first, fully engaged position, thus cooperatively forming a complete nut; the mechanism being characterized in that there are provided two opposite projections extending radially from the inner wall of said housing, the length of the radial extension of each projection corresponding to the difference between the radius of said cylindrical cavity and the outer radius of said split nuts; each of split nuts being externally provided with a stop member, said stop member being in form of a flat piece which is fixed to the external semicircular side of a split nut and co-rotate with said split nut, and is provided with an elongate slot, said slot extending a length in the direction of said external semicircular side of said split nut, the width of said slot is not less than the thickness of said projection, the first and second ends of said slot being respectively in the vicinity of the first angular end of a split nut and the middle point of its semicircular side; said resilient means comprising two springs; each of said springs being in the form of an elongate structure of metallic material bent to surround the circumference of said split nut, wherein one end of the first spring is fixed to said first angular end of the first split nut, and the other end of the first spring is fixed to the first angular end of the second split nut, whereas one end of the second spring is fixed to said first angular end of the first split nut, and the other end of the second spring is fixed to the first angular end of the second split nut, the two springs being located at the two opposite sides of the resulting nut formed by said split nuts on their mounting.