Basic Crane Design principles
 
Looking first at basic crane design principles, a balanced condition of conventional crane is achieved by equalizing forward and rearward moments. In simple terms, let us assume that the weight of the boom and basic machine equalize each other, and that the center of gravity is above the crane's tipping point. The weight of the load multiplied by its distance forward from the tipping point must be equalized by the weight of the counterweight multiplied by its distance rearward from the tipping point. For example, a one ton load at a twenty foot radius gives a forward load moment of twenty. This load moment would then be equalized or counterbalanced by an 4 ton counterweight at a distance of five feet, having rearward load moment of twenty. (figure 1)

- Figure 1 -  

If the weight of the load were to be doubled, the weight of the counterweight must also be doubled to keep the crane in balance.
(figure 2)

- Figure 2-

Alternatively, instead of doubling the weight of the counterweight, it could be moved further rearward from the center of rotation to compensate for the increase in the load. (figure 3)

- Figure 3 -

Since adding counterweight is often neither practical nor, in some cases, recommended, true balance of a conventional "fixed counterweight" crane can only be achieved at one specific radius. Any variation caused by changing the radius at which the load is lifted destroys this equilibrium.

While a hydraulic machine is commonly thought to be faster and more positive for materials handling, the same condition exists. Like the conventional crane, the ability to achieve true balance is limited to one specific radius. Secondly, the extra weight of the box type boom structures reduces the crane's net capacity by a considerable amount. For example, a lattice boom crane with a two thousand pound capacity might be reduced to as little as a five hundred pound capacity at the same distance on a hydraulic machine. (figure 4)

- Figure 4-

And, thirdly, the present boom designs of excavator based material handlers generally include one or more hydraulic cylinders attaching at boom midpoints. The pressures and reactions exerted by the cylinders and loads at these points accelerate metal fatigue often resulting in premature structural failures of the boom. (figure 5)

- Figure 5 -

Indusign can now offer a unique solution to these problems. Instead of using mid-boom mounted hydraulic cylinders to actuate the arm, a cylinder, mounted low in the boom's base section, is used to move the counterweight. The arm is then actuated by a tie rod which is mechanically linked directly to the moving counterweight. This method provides a "fail-safe" system which never requires adjustment, and guarantees that the crane will always be in balance with itself. As the lifting radius is varied, the change in the load moment is automatically equalized by the moving counterweight.
(figure 6)

- Figure 6-