Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology
I. Kusumaningtyas Dynamics of Multiple Drive Belt Conveyors During Starting Masters thesis, Report 2005.TL.6970, Transport Engineering and Logistics.
This research deals with the dynamics of a multiple drive belt conveyor. A finite element model of a belt conveyor was built, which uses the structure and properties of the Enerka-Becker System (E-BS). Two sets of simulations were carried out: starting procedures with varying number of drives and starting procedures with motor starting sequence. For each simulation group, the linear offset, linear, and direct-on-line start-up were tested. The simulations focused on the study of the axial elastic response of an empty belt conveyor.
The application of multiple drive belt conveyors is increasing due to the growing demands for systems with higher capacity, higher speed, and longer distance. Multiple drive conveyors bring many beneficial effects, such as the reduce of belt tension, the use of belts with lower strength, the installation of lighter support structure, the application of smaller and standardized motors, and the increase of layout flexibility. However, it requires further study in order to achieve reliable design of such systems, particularly in terms of the coordination and control of the drive units.
The DIN 22101 is the most referred standard for the design of belt conveyor systems. However, it merely deals with single drive belt conveyors. No certain guidelines are available yet for multiple drive belt conveyors. Therefore, this research was carried out to investigate the dynamics of multiple drive belt conveyors during starting, to find out whether a belt section between two drives in a multiple drive belt conveyor can be viewed as a single drive system, and whether the DIN 22101 standard for starting of single drive belt conveyor can be used for the starting of a multiple drive belt conveyor. Additionally, a study was done to see the effect of starting the motors in sequence.
A finite element model of a belt conveyor system was built, consisting of a model of the belt and its support structure, a model of the inverter controlled induction motor and traction, and a model of the bulk solid material flow. The belt conveyor system used the properties and structure of the Enerka-Becker System (E-BS). The differential equations which govern the motion of the belt conveyor and the drive system were solved numerically. In this research, focus was given to the axial response of the belt. The simulations were done only for the case of starting procedures of empty belt conveyors. In the simulations of starting procedures with varying number of drives, the number of drive stations in the belt conveyor was increased from one to four, while the start-up time for each case was reduced. The simulations revealed that by using more drive stations, the maximum belt stress during non-stationary as well as non-stationary conditions decreased. However, negative stresses occur in the system, while speed oscillations as well as overshoots appear in the belt velocity profile. This happens for either linear offset, linear, as well as direct-on-line start-up. However, if the belt is started using a linear start-up procedure with a 45 s start-up time (based on DIN 22101 ), the negative stress does not occur in the belt and the velocity profile builds up without oscillations and overshoots. Compared to the other start-up procedure, the linear start-up gives better results because the maximum belt stress during non-stationary conditions and the maximum nodal acceleration are lower.
The simulations of starting procedures with motor starting sequence were carried out by giving each motor its own switch-on time. Motor 1 is switched-on at the beginning of the simulation, while the other motors are switched-on when the acceleration wave from motor 1 has reached their locations, or a while later after the acceleration wave passes them. The results of the simulations show that by starting the motors in sequence, the negative stress in the system can be reduced or even removed. However, the maximum belt stress in nonstationary conditions is higher than that if all motors are switched on at the same time. In view of the belt velocity profile, overshoot still happen at the end of the start-up time. In the linear offset and linear start-up with motor starting sequence, the last motor experiences regenerative braking for a few seconds before it reaches balanced load distribution with other motors. This happens due to the reflection of the acceleration wave from motor 1 arriving at the node where the last motor is located, causing the nodal velocity to increase higher than the synchronous speed of the motor, bringing the motor into the regenerative mode.
From the simulation results, it was observed that the characteristics of each section between two drive stations in a belt conveyor differ from those of the single drive belt conveyor. The differences were seen in the behaviour of the motors during start-up, the belt stress in the belt sections, and the acceleration waves. It was, thus, concluded that a belt section between two drive stations in a multiple drive belt conveyor cannot be considered as a separate single drive conveyor system. This also leads to the conclusion that the start-up time of the multiple drive system should not be based on the length of the belt section between two drives. And in view of the DIN 22101 standard, the guidelines for the start-up of a single drive belt conveyor are not directly applicable for the start-up of a multiple drive belt conveyor. Finally, the linear start-up procedure is most preferable for the start-up of either single or multiple drive belt conveyors. If the multiple drive belt conveyor is of concern, the linear start-up without a motor switching sequence is suggested because the minimum belt stress can be increased by increasing the tension weight, while the maximum belt stress during non-stationary conditions does not increase as high as that if using a motor switching sequence. Furthermore, the regenerative braking of the last motor does not occur in linear start-up without a motor switching sequence.
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