C:o pvrig hl © IL 'l. C Robol COlllrol Kdr lsr uh e. FRG. ROBOTIC ARC WELDING - PROGRAMMING AND CONTROL G. S. Bolmsjo DFpar/lllfll/ uf Prurillr/1U1I alld ,\1 a/eria/s EII{5lllferillg. LUlld I II .IIl/lI/e uf Terhllu/ogl, L lIlld. SU'edell Ab s tract. The fU'ndamental paramete rs in high level programming and control of robotic arc \velding are outlined. Of special interest is the pr ogramming of a robot and a positioner as an integrated unit. A hierachical control mod el is therefore pr esented that includes high level commands for robotic arc welding. To integ r ate and plan the movements of the robot and the positioner. a kinematic description is giwn. By using the inwrse kin ematic ,olut ion of the positioner it is pos sible to optimize the \\'dd pa r ameters to obtain proper mowments such as orient ation of the we ld joints and the weld torch. Keywords. Robots: welding : hierarchica l systems: ki nemat ics: programming. I I\ T RO D UCT I OI\ The dewlopme nt of i ndust rial robo t systems has lead to a significa nt u se of robots for arc welding. T he reason to this is a number of impo r tant factors that toget her accel- erate the applicability and the dew lopment of fl exible and automated welding t ech nology. E xamples of such factors are 1. lack of qualified welders 2. unh ealthy wor king s urroundi ngs 3. low product i vity with human welders 4. i ncreased fl ex ibility with new robot systems The cent ral part of the robot welding station is t he robot it se lf. wh ich is used to perform the welding op eration, i.e. hold t he welding to r ch and move it along the weld j oint wit h the right orientation and wlocity the joint . \\' hen welding larger obj ect s or joints with arbitrary orien- tatio ns. the working space of the robot will be a limitation of the station. To soh'e this. \ve ha\'(> to add extra move- ments to the station. T hi s can be accomplished by mO\'ing the robot an d/or the obj ect. Ano t her reason for using extra mO\'em ents is tha t the \veld- ing proces s demands great care in select ing the oripntation between th e welding torch and the weld joint. and the ori- en ta tion of the wC'lding joint relati\'e the horizontal plane in order to produc e optimal welds. T hus. in a flexible robotic \\' elding s tation it is often re- qu ired to mo\'e both the robot and. for example, a posi- tioner at the same time during welding. ,-\ n example of a robo t ic arc welding s tation is shown in Fig. 1. Howe\'er. in today' s robot s ystems a defined mo\'ement of the Tool Center Point ( TC P ) in the working s pace is only performed relatiYE' a fixed frame. Clearl y. this is not th e case when executing integrated mO\'enwnts of both a r obot and a positioner. Programming of combined mo\'ement s th erefore requires a numbpr of point s along the weld path in 5-11 the same way as programming robots in joint coordinates to perform a li near movement. Fig. 1. R obot Sys tem for ,-\rc "'clding with Positione r. Robot :' l anipulator. " 'elding Power Source and Control Cabinet. Therefore , it is important to de\'elop techniques whe re the TCP can be defined re lati\'e a mo\'ing frame. or even be t- ter. to adapt the weld path in adnlIlc e according to spec ifi - cations about the weld to be performed ( Bolmsjo. 1987a). Another probl em that oc c ur in robotic arc welding is the need for correct weld path s due to misalignments of weld joints. Several tpchniques may be applied to soh'e this problem including bE'tter tolerances in parts and sensors for seam follc)\\'ing ( Bolmsjo. 1086a ). HI ERARC HI CAL CO\,TROL An overall goal in designing control and programming st ra- tegies must be to reduc e the pre paration time for a new