Twistlock sensor solution finally found

Twenty years ago, several spreader makers began looking at ways of using spreader twist locks to assess the weight of containers being handled. However, neither load cell nor strain gauge technology could be made to give accurate readings.

Beat Zwygart, chief executive of Lasstec, which became the first company to successfully introduce the technology in 2007, explains that the initial problem was that twist locks are subjected to so many different stresses that it is not always evident that a true assessment of container weight is being made.

The Lasstec solution has been to deploy fibre optics to allow a small sensor to be installed in the twist locks thereby resulting in a successful load sensor system, which can either be fitted to new spreaders or retrofitted to existing ones. This can accurately identify container weight, out-of-balance containers and those they are snagged prior to the main lift taking place.

Bromma has also entered the fray with a similar system of its own, consisting of a load sensor placed in each of its spreader twist locks. The technology involved is based on strain gauges, which are an integral part of the load cell mounted in the twist lock assembly. These strain gauges are individually calibrated and temperature-compensated to increase the accuracy of their load measurement. Sensor signals identifying weight data from each of the twistlocks are then sent to the crane.

Both companies insist that investment can be recouped by lessening the risk of damage to lifting equipment by eliminating accumulated stress from handling overweight boxes, thereby reducing the spreader replacement cycle. Accidents resulting from overload conditions can lead to property damage and/or staff injury, both of which have financial implications.