Harrison's electrically powered crane latches are designed to connect the runway flange of a single beam travelling crane to the running flange of a runway / runways or between two crane beams in order that a monorail hoist may be transferred between the beams. There is no maximum restriction on beam size or crane capacity as these units are built individually to suit site conditions and environment.
The latch consists of an operating half, normally to be mounted on the crane beam, and a non-operating half. It is supplied with limit switches and with either its own dedicated control panel or with a complete control panel for the crane long travel. Low voltage pendant mounted controls are supplied. Optional indicator lamps for mounting on end carriages are available if appropriate.
Additional halves may be supplied for latching of one crane with several runways.
Method of operation of the latch mechanism
Upon alignment as detailed below, the operation of pendant button raises the removable hoist end stops on both crane beam and runway to allow the passage of the hoist along the now continuous beam. When the crane latch is open, the crane beam is physically latched to the runway end and the long travel motion is also electrically disabled to prevent any movement.
When the crane beam and runway are unlatched, the lock between the two halves is cleared and the removable end stops are reinstated. Only when the end stops are fully home is the crane long travel function again operable and the crane bridge is free to travel along its downshop structure.
Method of indication of proximity for latching
The crane beam is travelling to the vicinity of the runway beam and operates a limit switch illuminating one warning lamp. The operation then moves the crane on slow (creep) speed to line up the crane and runway. When the crane and runway are aligned to within +/- 1.5 mm a second indicator light illuminates. If the crane beam overshoots the alignment position, the first light is extinguished, the second remaining illuminated whilst the crane beam remains in proximity. This system enables accurate indication of proximity to be achieved and also informs the operator the direction necessary for alignment of the crane beam. It does not prevent normal operation of the crane when travelling through the latch position.
The indicator lamps can be mounted in the pendant or on the end of the end carriage to suit site requirements.
Safety features
1. If the hoist is run into the movable end stops whilst the crane and hoist are unlatched, the end stops are pushed further home.
2. If the hoist is in close proximity and fouls the movable end stops whilst the latch is being operated, the latch motor circuit is protected by a torque limiter which in turn is protected by a timer. Limit switches and mechanical mechanism prevents the crane travelling unless the latch has fully disengaged and the movable end stops have returned fully to close off the ends of the beams.
3. Close alignment of the crane beam and runway (+/- 1.5 mm) keeps wheel wear to a minimum and eliminates jarring of the hoist and resultant load swing as the hoist unit travels across the joint.
4. It is impossible to operate the movable stops into the 'open' position without the two halves of the latch being in proximity even if both limit switches fail. All features of the limit 'fail safe' both electrically and mechanically.
