Wide speed range and torque control of new contactorless precision D-C hoist

THE PERFORMANCE required of new cranes and hoists is becoming regularly more demanding; specifications now call for capabilities not previously available. Safety and dependability have always been of primary importance in hoisting work, and to these requirements are now often added a wide speed range for the rapid movement of light loads or the empty hook; quick, smooth acceleration and deceleration of all loads with regenerative braking to reduce service on the mechanical brake; effective torque limitation, both steady-state and transient, to limit the mechanical strains on the entire structure as well as to prevent excessive overloading; controlled slow speeds essentially independent of load; and load suspension or extremely fine inching for the positioning of sensitive loads. All these characteristics and more must be furnished within the framework of a rugged, simple system requiring little or no maintenance.