| 摘要 |
<p>An apparatus is disclosed for maintaining a predetermined mast-boom working angle of a pendant supported boom substantially constant during extension and retraction of the boom. One embodiment of the invention includes control means connected between the boom and the mast for detecting slight angular changes and actuating power means for paying out or drawing in sufficient pendant to return the mast-boom angle to a predetermined angle. Another embodiment utilizes electrical controls having a first potentiometer capable of detecting linear changes in the effective boom supporting length of the pendant and another potentiometer for detecting linear changes in the length of the pendent and another potentiometer for detecting linear changes in the length of the boom, said potentiometer sending output signal ratios which vary from a predetermined output signal ratio for actuating power means that takes up or pays out sufficient pendant to return the boom to the predetermined mast-boom working angle and returns the output signal ratio to said predetermined ratio.</p> |
