Anti-crab: Protect equipment and increase efficiency and crane service life.

The ATV 71’s anti-crab function is an automatic realignment system that helps prevent crane skew and crab drift related to cranes with long spans. It maintains the path and the track parallel between the two bogies independent of load position or initial crane assembly.

Operating Principle

Anti-skew

When the crane is perfectly aligned with the track, both sensors have a similar output value because they are at the same distance. When the crane starts moving, its crosses the track and detects output with different values. With these new values and movement direction, the system determines which drive must be reduced in speed. The speed is reduced until both sensors have the same value and the system recognises the crane path is now parallel to the track.

Anti-drift

Some drift incidences can arise from bad sensor mounting, a badly adjusted detector resulting from a collision, if a screw weakens, or due to slippage of one or more wheels.  In these cases, the crane may shift laterally, thus increasing both detector values. When this happens the system generates a skew to move crane to correct alignment.

Operation

-A bidirectional regulation master-slave assigns which drive must reduce translation motor speed to maintain the parallelism of the undercarriages on the track rails during bridge translation movement, thus preventing crossover of the crane.

-An intensity control on acceleration and deceleration ramp is performed to reduce the sway of the suspended load.

-This function is based on drive controller or logic controller: Altivar® 71 + integrated machine control (Altivar IMC) used on the hoisting movement or Modicon M238 logic controller managing the complete crane. It communicates with both Altivar drives using a translation bridge via CANopen field-bus.

Benefits

-Increase efficiency and crane service life

-Reduce wear and tear on rollers.

-Reduce mechanical vibrations.

-Helps to prevent ample on plates and damaged welding.

A complete solution for gantry overhead travelling and gantry cranes

-Keep crane axis path in the same direction as the track axis path (anti-skew).

-Helps prevent the crane from moving away from its track (anti-drift).

Consideration of internal and external factors

-Absence of undercarriage motor synchronization on start/stop operations.

-Incorrect initial position of wheel mounting.

-Bridge motion with no centred load.

-Transversal load sway. Easy to install

-Use of only two proximity analogue sensors in one of the bogies and controller card integrated in the drive.

-Encoders or others more sophisticated sensors are not needed.

Go here the the hoisting application white paper “Optimising the productivity of lifting appliances.  Anti-Sway: controlling the swaying of the load”

For more information on Altivar ATV 71 for lifting applications see Part 1 of this article

For availability of ATV 71 and next day delivery  go here