Active Forwarder Cab Suspension

Sammanfattning: The forest industry plays an important role in Sweden, and forest machine manufactures are underconstant pressure to achieve both high productivity and comfortable operating environment in its products. A forwarder is a forestry vehicle that carries logs which are cut by a harvester. It suffers alot of low frequency and high amplitude vibrations during the operation because of the rough terrainin forests. Therefore, it is necessary and vital to introduce an active cab suspension system in orderto reduce the whole vibrations in the forwarder cab.The main purposes of this thesis are to develop, implement and test a feasible control strategy forthe active cab suspension system as well as verify the controller’s performance in terms of vibrationreduction and power consumption. This project is focused on the available mechanical rig installedat KTH lab hall, instead of a real forwarder.A deep study has been carried out on a new valve prototype. Exhausted tests were made to testthe performance of this valve under different conditions. From the test results, the valve was tunedin order to get the best performance out of it. Once the valve has been well calibrated, a model ofthe whole system was estimated by using Black-box estimation. The model has a 96% of matchingbetween the stimulation data and the validation data. Different controllers were designed with thismodel, and the best one was designed by the gain scheduling method.The system has a delay of 36 ms, therefore, it was studied how the performance of this controllerwould increase if this delay was reduced. The study shows that reducing the delay to around 0-2ms, the suspension system is able to reduce the vibration from 60% to 90%. Smith Predictor wasimplemented into the gain scheduling controller in order to reduce the effect of the delay. The resultsdemonstrated a better and more robust performance of the controller with Smith Predictor.Several test cases were implemented to seek a wide range of possible vibrations that a forwardercould handle in the forest. These tests have been done both in a test rig and in a simulationenvironment. The final test was conducted by using a real track test model obtained from Skogforsk.This track is used for testing different systems in a test forwarder since it simulates the terrain ina forest. Based on the simulation result, the total disturbance reduction percentages of SmithPredictor controller are 75% for heave, 68% for pitch and 73% for roll, which shows the systemreduces the cab vibration. Moreover, the maximum amount of power needed during the forwarderoperation is 11.63 kW which is feasible for implementing this system on the actual forwarder.