Computer control of a metal bar bending press

[摘要] ENGLISH ABSTRACT:Mechatronics is an exciting research area that stemmed from huge progress in computertechnology from the 1970s onwards. In such systems, computer controlled electronic and mechanicaldevices interact so intimately that it is impossible to tell where the one ends and the other begins.A mechatronic project aimed at automated manufacturing was undertaken by the Department ofIndustrial Engineering at the University of Stellenbosch as part of their programme in mechatronics.ROYIC was the industrial partner in the joint venture. ROYIC manufactures a front loader that is usedon tractors. The front loader fits on a tractor by means of a kit that has to be manufactured speciallyfor each type of tractor. The design of the kit needed many welding joints, which lead to a difficultand expensive manufacturing process.A bending press that was capable of bending pre-cut steel into a predefined shape was identifiedas a viable solution. The mechanical design for the project was done by ROYIC, while the Universitywas responsible for the electronic control.Bending is carried out by pushing a flat bar over a Y-block into the bending position which can beread from a position encoder. The bending blade then bends the metal until the appropriate angle isreached. It is impossible to predict the resulting angle by means of analytical techniques. This is dueto non-linear behaviour caused by spring-back.The position of the bending blade is read with an incremental encoder. An empirical equation isused to convert the distance read by the sensor into the appropriate angle. The parameters arededuced by means of non-linear regression methods. A mean square error of 0.069 was obtained forthe equation when operating in the linear area of the plastic region of bending. A software applicationwas written to enable ROYIC to deduce the needed parameters of the equation for all types of steel.Pulse control was used to control the bending blade. The blade moves continuously until a pulseband is reached. The blade is pulsed from there into a dead band. Consequently the accuracy of themachine is determined by the width of the dead band. The control program is capable of executingbend sequence files to enable the operator to perform a sequence of bends on a metal bar.Safety was of great importance in the design. The control system was designed to give priority tosafety signals over other control signals. Dangerous situations owing to computer failure are thusprevented.

[发布机构] Stellenbosch University