To meet the increasing demand on control precision in industrial forklifts, physical modelling of the lifting system has been combined with parameter estimations from data. A number of different controllers have been evaluated in terms of their ability to achieve a load independent lifting speed. The model and controller performance as well as stability properties were evaluated in simulations, and the most promising controller was implemented on the real system. Especially the electric motor turned out to be difficult to model, and therefore experimental data was used to approximate some parts of it. This, along with some friction parameters that had to be estimated caused a slight loss in model generality. An observer (Extended Kalman filter) was used to estimate the unknown states, including the velocity of the forks. The simulated performance of the MPC controller was slightly better than the PID controller, except for a bigger overshoot when starting from a turned off motor. The PID controller also handles model errors better, because of its integral action. Due to the simplicity in relation to performance, only the PID controller was implemented on the forklift. The model turned out to perform well, but not well enough to estimate the lifting height accurately. The PID controller worked as intended and it could therefore be concluded that a more advanced control algorithm, such as an MPC controller, is not necessary for this system.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:liu-129398 |
| Date | January 2016 |
| Creators | Bäckman, Henrik, Brändström, Anders |
| Publisher | Linköpings universitet, Reglerteknik, Linköpings universitet, Reglerteknik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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