| 摘要 |
An elongated frame has a head section, a foot section and a center section. Hinges connect the center section with the head section and with the foot section, respectively. The head section is pivoted to a support in the region where it is connected to the center section, so it can tilt about a first axis which extends transversely of the elongation of the frame. Below the center section the support is provided with pivots which define a second axis extending parallel to the first axis; on these pivots, tiltable elements are pivotably mounted. Each of the tiltable elements is formed with a guide passage extending normal to the second axis and through which an elongated guide member mounted on a lower side of the center section extends in slidable relationship. A disengageable arresting device is provided on the center and head sections and normally serves to block all of the sections against movement relative to one another and to the support; when the device is disengaged the head section can pivot about the first axis and the center section can pivot about the second axis and can also slide, together with the foot section, because the guide members can perform sliding movements in the guide passages of the tiltable elements. |
