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Our evaluation approach to conveyors is a little different from most. We identify belt conveyors as complex systems and approach our analysis from a classical system-engineering viewpoint. In short, this means we try to look at a conveyor as a system first, which performs a specific function rather than a compilation of components. This may not sound like a big difference, but the process can produce different results.

Probably the biggest difference in the process is the use of dynamic analysis techniques. CEMA design methodologies are the standard in the USA and many other countries and many engineers use CEMA exclusively. However, CEMA calculations for acceleration and deceleration treat the system as a rigid body. CEMA realizes the potential problem with this approach in a statement on page 140 of the 5th Edition of BELT CONVEYORS FOR BULK MATERIALS. “No further attempt will be made to justify the [rigid body] assumption. However, the belt conveyor designer should be aware that, for conveyor systems with very long center belts, stretch considerations should not be overlooked”. However there is no methodology given which considers belt stretch considerations. When long conveyors are designed with these static models only, potential troubles exist.

The specific attributes of and relationships between the drives, control software, belt and take-up device are definitely not static in nature. As system engineers, we attempt to define these relationships as well as the performance characteristics of the components. We build mass and stiffness matrices, apply the appropriate boundary conditions and solve simultaneously with a time-based finite element methodology. Although this methodology was first published over 20 years ago, it has not been used widely due to the complexity of the analysis. However, recent advances in computer technology have advanced its use. Today, this technology has proven to be much more effective in simulating actual conveyor characteristics during the most critical operating conditions of starting and stopping.

To get more specific, we usually break our work into two parts.

Part 1- Static Analysis

Static analysis is still much easier and quicker to perform and still plays an important role in our overall work. During this phase, we can quickly review many conditions that might exist including changes in load, changes in power requirements and changes in friction.

This process is normally referred to as top-down. We first evaluate the overall system and gradually break it down into sub-systems until we get to logical components. An excellent example of this is the operation of the take-up device. A hydraulic take-up is an extremely important sub-system of the conveyor with a specific function. However, it is also a system in itself, which can be further broken down into its own components. This device can be quite complex in its own right and static analysis can help us bracket performance requirements. By varying individual parameters one at a time, we can eventually bracket the performance requirements of each component. By comparing requirements with actual capabilities, most problems usually come to light.

In many cases, a good belt engineer who has experience with dynamic problems and solutions can identify these potential problems based on past experience without having to actually perform the more complex and time consuming procedures. By identifying these problematic conditions, we evaluate the risks and produce reasonable alternatives prior to the dynamic phase. We consider this a very important step as alternatives can then be reviewed with the client to determine which are feasible and which are not. By the time we move to the dynamic phase, we hope to have the potential solutions narrowed down to one or two of the best alternatives. It is impractical for us to make these decisions without the input of the client.

Part 2- Dynamic Analysis

As opposed to the prior top-down analysis, this phase can be considered bottom-up. We define the characteristics of each component and then each sub-system with symbolic mathematical representations. In other words, we put the system back together from its parts. The term “dynamic analysis” is no more than the summation of all these mathematical pieces tied together in a working simulation of the system. This simulation is the most important tool of the systems engineer. With this functioning simulator which includes the flexible belt that interconnects all, we can easily change external conditions (i.e. material loads) and determine the expected results (system response). Once the simulator is built, we can also make changes to control logic and optimize control parameters. On a long belt conveyor, this evaluation and optimization process may not be possible by any other means (including on the actual conveyor) as it is very difficult to accurately evaluate the interaction of drives and components which may be thousands of feet apart.