Industrial Automation Services

The objective was to update three 1970 vintage high speed bucket cranes utilized as ore un-loaders at a major steel mill port. The existing cranes utilized obsolete medium voltage MG sets and magnetic amplifier regulators as a control scheme. Maintaining these obsolete systems was both difficult and costly.

Since the price of replacing the cranes would have been cost prohibitive, and since the cranes were mechanically and structurally sound, it made sense to investigate a controls retrofit.

First Ai Control Systems was contracted to complete a study and write a proposed specification for the controls retrofit. This study fully defined the existing controls and mechanics of the crane and specified the requirements for the new equipment. The study emphasized the need to minimize the changes to the crane by reusing all of the existing mechanical drive components, the existing electrical enclosures, operator controls and fitting isolation transformers in the space formally utilized by the MG set.

New digital DC drives rated for the 250/400HP bucket hold & close lines and 125/200HP rack drive were provided. These were custom programmed for the load sharing and speed matching requirements of bucket crane operation. A PLC control system and HMI was included to interface the drives to the existing operator devices and other ancillary systems and to allow easy monitoring and troubleshooting of the system.

The new control systems have proven to be very reliable and cost justified. Down time has been drastically reduced. Continuation of the retrofit projects is underway to include the AC gantry travel drives.