Computer control of a metal bar bending press

Van der Merwe, Dirk (Dirk Jacobus) (2000-12)

Thesis (MEng)--University of Stellenbosch, 2000.

Thesis

ENGLISH ABSTRACT: Mechatronics is an exciting research area that stemmed from huge progress in computer technology from the 1970s onwards. In such systems, computer controlled electronic and mechanical devices 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 of Industrial 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 used on tractors. The front loader fits on a tractor by means of a kit that has to be manufactured specially for each type of tractor. The design of the kit needed many welding joints, which lead to a difficult and expensive manufacturing process. A bending press that was capable of bending pre-cut steel into a predefined shape was identified as a viable solution. The mechanical design for the project was done by ROYIC, while the University was responsible for the electronic control. Bending is carried out by pushing a flat bar over a Y-block into the bending position which can be read from a position encoder. The bending blade then bends the metal until the appropriate angle is reached. It is impossible to predict the resulting angle by means of analytical techniques. This is due to non-linear behaviour caused by spring-back. The position of the bending blade is read with an incremental encoder. An empirical equation is used to convert the distance read by the sensor into the appropriate angle. The parameters are deduced by means of non-linear regression methods. A mean square error of 0.069 was obtained for the equation when operating in the linear area of the plastic region of bending. A software application was 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 pulse band is reached. The blade is pulsed from there into a dead band. Consequently the accuracy of the machine is determined by the width of the dead band. The control program is capable of executing bend 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 to safety signals over other control signals. Dangerous situations owing to computer failure are thus prevented.

AFRIKAANSE OPSOMMING: Megatronika is 'n opwindende navorsingsarea wat ontstaan het uit groot vooruitgang in rekenaartegnologie vanaf 1970. In megatroniese sisteme werk rekenaar beheerde elektroniese en meganiese toestelle so nou saam dat dit onmoontlik is om agter te kom waar die een begin en die ander eindig. 'n Megatronika projek gerig op vervaardigings outomatisasie is onlangs onderneem deur die Departement van Bedryfsingenieurswese van die Universiteit van Stellenbosch as deel van hul program in megatronika. ROVle was die industriële vennoot in die projek. ROVle vervaardig implemente vir gebruik op plase. Een van hul produkte is 'n laaigraaf wat met 'n hegstuk op 'n trekker pas. Die hegstuk moet spesifiek vir elke tipe trekker ontwerp word wat gelei het tot 'n ontwerp met baie sweislaste wat 'n tydrowende vervaardigingsproses vereis. 'n Staal buigmasjien wat vooraf gesnyde staal in 'n spesifieke vorm kan buig sou hierdie probleem kon oorbrug. Die meganiese ontwerp vir die masjien is gedoen deur ROVle terwyl die Universiteit verantwoordelik was vir die elektroniese beheer. Staal word gebruik deur 'n staalbalk te skuif oor die buigbed tot in die buigposisie wat afgelees word vanaf' n posisie enkodeerder. Die buiglem buig dan die staal in die benodigde hoek. Geen analitiese metodes bestaan om die buighoek te voorspel nie weens terugspringing. Die posisie van die buiglem word ingelees met behulp van 'n inkrementeie enkodeerder. 'n Empiriese vergelyking word gebruik om die afstand beweeg om te skakel in 'n buighoek. Die verskillende parameters word afgelei deur middel van regressie metodes. Die gemiddelde foute kwadraat was 0.069 wat getoets is vir slegs die lineêre area van die plastiese gebied. 'n Program is geskryf wat ROVle instaat stelom die benodigde parameters self af te lei. Puls beheer is gebruik op die beheer van die buiglem. Die lem beweeg kontinu tot binne die puls band en word daarvandaan gepuls tot by die stopband. Die grootte van die stopband bepaal dus die akkuraatheid van die masjien. Die beheerprogram kan ook buig sekwensie lêers uitvoer wat die operateur instaat stelom 'n reeks van buigings op 'n staal balk uit te voer. Veiligheid het deurgaans 'n belangrike rol gespeel in die ontwerp van die masjien. Die stelsel is ontwerp om prioriteit te gee aan veiligheidseine bo enige ander beheersein. Gevaarlike situasies wat mag ontstaan as die rekenaar sou faal, word dus voorkom.

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