Real-time con­trol of a Mit­subishi Elec­tric robot

Exter­nal real-time control

In most appli­ca­tions, an indus­tri­al robot moves repet­i­tive­ly on a fixed path after one-time pro­gram­ming. In order to be able to change the move­ment of the robot even at run­time, the robots from Mit­subishi Elec­tric have a so-called exter­nal real-time mode. In this mode, the robot does not exe­cute a pre­vi­ous­ly cre­at­ed robot pro­gram, but instead receives posi­tion data from an exter­nal source, which it nav­i­gates to one after the oth­er. This type of con­trol is also called mul­ti­point con­trol. Qual­i­ty Automa­tion GmbH has imple­ment­ed and test­ed this type of con­trol in the course of a thesis.

Con­trol configuration

The robot can be con­trolled in real-time mode via a PC appli­ca­tion or via high-lev­el lan­guage con­trollers. In the test­ed appli­ca­tion, a mul­ti-CPU con­trol from Mit­subishi Elec­tric is used, which includes a PLC, a high-lev­el lan­guage con­troller and the robot con­troller itself. The use of a com­mon back­plane bus guar­an­tees syn­chro­niza­tion with­in the indi­vid­ual con­trollers, which is impor­tant for real-time con­trol. In this case, the high-lev­el lan­guage con­trol is the exter­nal source which, in a fixed cycle time, sends the next posi­tions to be approached to the robot. These posi­tions can also be adjust­ed dur­ing the process by apply­ing an off­set, for exam­ple. 

Appli­ca­tions

The exter­nal real-time con­trol is par­tic­u­lar­ly well suit­ed if the appli­ca­tion requires high pre­ci­sion with simul­ta­ne­ous high path com­plex­i­ty. In addi­tion, it has, com­pared to the clas­si­cal pro­gram­ming strate­gies point-to-point and the path con­trol, anoth­er advan­tage: by set­ting the next approached posi­tion in a very short cycle of 3.5 or 7.1 ms the robot fol­lows the path simul­ta­ne­ous­ly with high pre­ci­sion and in a flu­id move­ment. 

In con­trast to the point-to-point strat­e­gy, the course of the path and the speed can be pre­cise­ly con­trolled by the small dis­tance between the points. In addi­tion, unlike the path con­trol, there are no micro stops between the path sec­tions. Qual­i­ty Automa­tion GmbH uses mul­ti­point con­trol in con­junc­tion with Mit­subishi Electric‘s mul­ti-CPU sys­tem to use the robot as a 3D print­er. To achieve a high print qual­i­ty, a uni­form and absolute­ly accu­rate mate­r­i­al appli­ca­tion is nec­es­sary. The real-time con­trol is also suit­able for exam­ple, for the appli­ca­tion of adhe­sive bead­ing, for paint­ing and ero­sive and fin­ish­ing process­es in man­u­fac­tur­ing technology.