A lifting device such as a mobile crane having a main body and a boom,
such as a lattice boom, for supporting a pile lead for, e.g., pile
driving or continuous flight auger drilling, and a method of using same.
A hydraulically operated mechanical spotter arm may be attached between
the device body and the pile lead. Electronic position sensors on the
spotter arm may be used to measure angular relationships between the pile
lead and the spotter arm. Position sensors on a boom box on the boom may
also be used. When the pile lead is swung, information from the sensors
may be used by an electronic control system to automatically maintain the
pile lead in a desirable position, limiting torque induced in the boom.
The boom box position sensors may be used to counter-steer the spotter
arm to further limit torque. The boom box may also be fitted with rubber
springs to permit controlled pile lead deflection while limiting load
transmitted to the boom. Other aspects of the invention will become
apparent from the disclosure.