Boom structure.

摘要

A boom (11) which is pivotally mounted for swinging movement about a horizontal axis (X) has a pivotally connected depending leg (15) at one end. The boom is constructed in the form of a parallelogram linkage having a counterbalance weight (16) on the side of the axis opposite the leg such that changes in balance from swinging of the leg in the plane of the boom are compensated by corresponding swinging movements of the counterbalance weight.