Patent ID: 6968963

Claim:
A process for controlling motion of a grappler of a gantry crane to lift an object, the grappler including plurality of latching mechanisms to engage the object, the process comprising: providing a center height sensor mounted to the grappler at a generally central position, a front height sensor mounted to the grappler at a generally frontward position, and a rear height sensor mounted to the grappler at a generally rearward position; determining if the center height sensor is less than a predetermined distance above a top of the object; automatically reducing a maximum speed of the grappler if the center height sensor is less than a predetermined distance from the top of the object; determining if the front height sensor has reached a minimum distance from a top of the object, less than said predetermined distance, such that the grappler is capable of engaging the front of the object; automatically cease lowering the front end of the grappler if the front sensor has reached the minimum distance; determining if the rear height sensor has reached the minimum distance from a top of the object; automatically cease lowering the rear end of the grappler if the rear sensor has reached the minimum distance; detecting whether the latching mechanism is fully latched; and permitting the grappler to move at a normal speed if all of the latching mechanisms are fully latched.