th 11 International Conference on Accomplishments in Electrical and Mechanical Engineering and Information Technology DEMI 2013 University of Banja Luka Faculty of Mechanical Engineering DEMI 2013 DEMI 2013 19 71 19 71 У Т Б Е А Т Њ И З О Р Ј Е Л В У И Ц Н И У • • 1975 th th 30 May ' 1 June 2013 Banja Luka PROCEEDINGS