In an apparatus known from U.S. Pat. No. 3,995,824, a gripper device has an inclined surface which slides over a mating surface with the same angle of inclination, that is, about 5.degree.. When this gripper device is displaced approximately parallel to the column or leg by means of a tensioning bolt, the gripping surface of the gripper device nearest the column either approaches closer to the column or recedes from it. As a result, the column can be held tightly but releasably, in a bore of the securing device or in the hub of the securing device containing this bore. In principle, a securing device of this kind is easily accessible for adjustment and provides an absolutely reliable mount for the column, especially in the case of columns which are entirely cylindrical in the area where they are gripped. However, the manufacture of this device, particularly due to the inclined surfaces, is relatively expensive; furthermore, in order to execute a purely radial gripping effect, the device also makes axial movements in relationship to the column. Finally, the application or release of the gripping action is made by means of tensioning bolt and requires a relatively high amount of labor.
U.S. Pat. No. 3,790,119, describes the formation of a fastening cone at the upper end of a gas spring which is adjustable in length and forms part of the column and which has an upper valve arrangement and a valve rod protruding at the top. The cone is inserted into a corresponding conical bore of a securing element attached to the chair or table surface. Conical connections of this kind demand extremely high manufacturing precision, because, if the opening angles of the two cones do not coincide exactly, the connection will wobble; at the same time, if the seat fits exactly, the connection will after some time, become very difficult to release. Because the opening angles of these cones are very small, diametrical tolerances in the range of a few hundredths or a millimeter result in relative displacements between the column and the securing element which are in the millimeter range. When an operating lever is provided for the valves on the securing device, such displacements can cause the valve to be under continuous stress due to the operating lever, and fail to close tightly. In other words, very small diametrical variations of the cone and the conical bore can make the lengthwise adjustment capacity useless in order to prevent this or compensate for it, every operating lever must be adjusted by hand. It is also conceivable to compensate for such disadvantages by means of an overly large amount of play in the operating lever; however, the operating lever will then be free to wobble below the chair seat, table top or the like.
USPTO Backgrounds
USPTO Backgrounds