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However, before discussing the future of robot controltechnology, some examples of the ongoing major industrialrobot control development will be given。 Then the drivingforces for the robot development will be discussed and based onthis some scenarios about the future will be outlined。2。 Present industrial robot control developmentThere is a tendency of technology fashion in thedevelopment of industrial robots。 This usually originates fromnew production concepts brought forward in the automotiveindustry。 One example of a present popular development isabout multi robot control and different solutions are nowpresented by several robot manufacturers, though a couple ofmanufacturers already have offered this as a product for someyears (Bredin, 2005)。 The main reason for adopting multi robotcontrol in industry is the possibility to reduce production costby having robots working in parallel, especially for low speedprocesses as arc welding。 Other benefits are that several robotscan be controlled from one controller, floor space is saved,collision avoidance performance can be improved and cycletimes can be reduced。 In arc welding, it will moreover bepossible to obtain a symmetrical heat distribution by weldingon the same object from different directions simultaneously。 Acommon set up is to use two or more robots welding on thesame work object, which is rotated by a manipulator of one ortwo degrees of freedom。 For higher flexibility, the work objectcan also be hold by a robot (Fig。 1) and still another robot canhold a component to be welded on the work object。 Automotiveindustry is also interested in reducing the cycle time of spotwelding robots by improved coordination of groups of robotsworking on a common car body。 Examples of difficult controltasks, when developing multi robot control for the manufactur-ing industry, are exact timing of dynamically optimised servoreferences, smooth transitions between coordinated and notcoordinated robot movements, exception handling and failurerecovery。When groups of robots work in a large production linethere is also the problem of how to dynamically split tasksbetween robots and between clusters of robots for optimalproductivity。 Simultaneously, it should be noted that collabor-ating robots are more difficult to program than single robotinstallations and therefore off line programming using robotand cell models is even more motivated。
One problem then isthe accuracy of the collaborating robot installations。 Sinceserially connected kinematic chains have to be controlled,errors in the servo loops and in the models of robot kinematicsand dynamics will give bigger pose deviations between the tooland thework object than in single robot installations。 Therefore,the development of multi robot control will motivate furtherimprovements of the accuracy of the kinematic and dynamicrobot models as well as of the robot servo performance。Related to the need of multi robot control are therequirements to develop robots with very high load capacity(ABB-2, 2001)。 Robots handling loads up to 500 kg have beendeveloped to handle, for example, parts of car bodies。 Then oneheavy load handling robot holds the fixture with the car bodycomponents while other robots make, for example, spot- or arcwelding。 This kind of automation solution is motivated by thehigher flexibility obtained when replacing single purposetransport systems with robots。 Beside the multi robot controlaspect on this, the development towards higher load capabilitiesresult in lower mechanical robot eigenfrequencies, increasingthe difficulties to accurately model and control the robotstructure。Another popular development direction is towards newsafety arrangements in robot installations (ESALAN Systems,2006)。 One short term motivation for this is the possibility toreplace electrical and mechanical working range limits withsafe software limits, which makes it cheaper and faster toconfigure a robot cell。 Moreover, the safety fences of a robotcell can be more efficiently adapted to the work spacelimitations, which will save floor space in the workshop。 Thereare also initiatives to develop new concepts for safe directcollaboration between human and robot (Schraft, Meyer,Parlitz, & Helms, 2005)。 Examples of applications for suchcollaboration are material handling, machine tending, compo-nent transfer and assembly。 In order to increase the safety levelFig。 1。 Multi robot control requires high performance model-based controlconcepts and efficient methods for robot programming。 for human–robot cooperation, the redundancy of the robotsupervision of hard- and software is increased, for example, bytwo channels measurement systems and failsafe bus- and I/Osystems。 The redundancy needed can of course be obtained inmany ways but simultaneously it is important not to increasethe cost of the redundancy functionality more than it can beaccepted by the applications。 One control aspect of new safetyconcepts is how to make use of the robot models alreadyrunning in real time in robot controllers to obtain a faultdetection that is sensitive enough without giving too many falsealarms。