Development of Position Controller for Pump Controlled Cylinder
Author
Jørgensen, Christian Black
Term
4. term
Education
Publication year
2018
Submitted on
2018-10-04
Pages
129
Abstract
This master’s thesis develops and experimentally validates position-control strategies for a pump-controlled hydraulic cylinder on a laboratory crane at the University of Agder. The crane can hold loads statically by closing two pilot operated check valves (POCVs), but leakage causes the pump’s high-pressure side to depressurize during holding; reopening the POCVs then leads to a position drop and oscillations. A nonlinear Simulink model of the crane is built, validated against measurements, and linearized, revealing a resonance around 12 rad/s. Based on this, high-pass filtered pressure feedback is introduced to increase damping, together with linear position control and velocity feedforward. To mitigate the position drop, pressure controllers are designed to pre-build pressure before reopening the POCVs; although these reduce the drop, initial results exceeded specified limits. The Simulink model is then refined and used to design switching logic for flow feedforward (FFF) and pressure feedforward (PFF). Implemented on the experimental setup, FFF and PFF significantly reduce the position drop and keep it within the stated limits. Across two test trajectories, experiments show a maximum deviation below 10 mm and an average tracking error below 1 mm; the position drop at POCV reopening is reduced from 2.5 mm to 0.6 mm.
Denne kandidatafhandling udvikler og eksperimentelt validerer positionsstyringsstrategier for en pumpestyret hydraulisk cylinder på en laboratoriekran ved University of Agder. Kranen kan holde last statisk ved at lukke to pilotstyrede kontraventiler (POCV’er), men lækage medfører trykfald på pumpens højtryksside under holdning; når POCV’erne åbnes igen, opstår et positionsfald og svingninger. En ikke-lineær model af kranen opbygges i Simulink, valideres mod målinger og lineariseres, hvilket afslører en resonans omkring 12 rad/s. På den baggrund introduceres højpasfiltreret trykfeedback for at øge dæmpningen, sammen med lineær positionsregulering og hastigheds-feedforward. For at begrænse positionsfaldet designeres trykregulatorer til at opbygge tryk før åbning af POCV’erne; disse reducerer faldet, men de første resultater overskred de opstillede grænser. Simulink-modellen forfines derfor og anvendes til at udvikle skiftelogik for flow-feedforward (FFF) og tryk-feedforward (PFF). Implementeret på forsøgsopstillingen reducerer FFF og PFF positionsfaldet markant og holder det inden for de angivne grænser. På tværs af to testbaner viser forsøg en maksimal afvigelse under 10 mm og en gennemsnitlig sporingsfejl under 1 mm; positionsfaldet ved genåbning af POCV’er reduceres fra 2,5 mm til 0,6 mm.
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