By Gerald Dorrington on Monday, May 10, 2004 - 01:51 pm:

There is a big requirement from the market for a "universal" lifter that can handle all the different shapes and sizes of bins. Such designs are possible, but there are compromises in the efficiency of the lifter that must be understood.

For a start, let us simply look at masses to be lifted and lowered to the ground again. For lifting, a lightly filled small 2-wheel bin can weigh as little as 20kg while an overloaded "sprico" (1.1m³ steel 4-wheel) can weigh as much as 750kg. The empty bins, for the lowering cycle, can range from around 12kg to 150kg.

During the lift cycle, we need to lift a bin in a time of 3 to 7 seconds, which is actually quite a narrow band considering that the bin mass may range from 20 to 750 kg! To some extent we are lucky that the heavier bins will go up more slowly and this is good for the safety aspects. However, we normally need to add a manually controlled valve that the operators need to change over from fast to slow, but they have a tendency to leave everything on fast.

Then, during the lowering cycle, we have a particularly difficult requirement: We want the heavier bins to come down slower than the lighter bins (to prevent damage to the castor wheels) - against the laws of nature! Without fancy (electric?) control systems, we have to fix a relatively slow "down" speed that is suitable for a 4-wheel bin, but this does slow down the collection rate of 2-wheel bins.