Heavy-lift gantry hoists rely on encoders to provide the operator with the drive and control feedback needed to move cargoes safely and efficiently. Typical feedback points are on the lift motor and horizontal drive gearmotors. Also, an encoder with a wheel or a gear and rack system can be used for speed and position tracking along the gantry rail.
In some applications, a draw wire may be employed to provide positive positional feedback on the horizontal axis. If contaminants are present, a draw wire and encoder with tolerance to dust and debris should be considered, along with a brush system for the draw wire itself.
Due to the potential safety hazards that could arise from an unintentional power-off scenario, a multi-turn absolute encoder may be preferred for gantries. With a properly designed encoder, should the gantry continue moving due to inertia after power loss, any motion would be registered and accounted for upon power up.
Draw wires may have advantages over wheeled encoders or linear scales for some applications, especially when paired with an absolute encoder.
Large A-frame port cranes are heavy lift workhorses that usually operate in outdoor conditions. In addition to their namesake maritime operations, port cranes are also found in timber, metal and mining facilities. Essentially a mobile gantry system, port cranes often transit the workyard on a rail system and have motors on both the overhead hoist and the drive wheels at the base.
Due to their inherently harsh operating conditions, encoders for port crane applications should be tolerant of environmental contaminants, dust, debris, shock, and vibration. Shaft mount encoders should have the highest bearing loads available and through-bore types should be adequately sealed to IP66 or better. Stainless steel housings or corrosion resistant coatings may extend operating life as well.
Four 75 HP motors drive this crane, which performs all the heavy lifting at this lumber mill.
Watch | A P&H Portal Crane performs demanding tasks at a large lumber mill with motor feedback from a Model 25T encoder.
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