| 摘要 |
<p>A parallel support arm 2 is attached to a fixed structure 1. At the other end of the arm 2 there is a vertically sliding hook 6 which slides within a vertical end bar 3. The end bar remains vertical throughout the range of movement of the support arm 2 about the two fixed pivot points. The hook is held in place by a spring 7, attached to the end bar 3. One end of a zero-free-length spring 4 is attached to the underside of the support arm 2, and the other end of the zero-free-length spring 4 is attached to the sliding hook 6. With no supported mass attached, the spring 7 will fully retract the sliding hook 6, and the vertical attachment point of the zero-free-length spring 4 will be raised and the support arm 2 will be in balance. On picking up an object, the weight of the object will proportionally stretch the spring 7, which will, in turn, lower the effective vertical attachment point 5 of the zero-free-length spring 4 to maintain balance.</p> |
