Page - 140 - in Proceedings - OAGM & ARW Joint Workshop 2016 on "Computer Vision and Robotics“

robotic tasks. The domain contains information about all the objects which can appear in the envi- ronment. Further it knows about the skills the robot is able to perform. A skill is defined through its nameandthe itsparameters. Askillhasapreconditionandaneffect. Theprecondition is thestate the environmentneeds tobe inbefore theactioncanbeperformed. Theeffectofa skill is thedescription of theenvironmentafter the skill isperformed. Theproblemdescribes the initial states0 and thegoalg,whichareasetofpropositions [4]. Thegoal state sg is a state, that satisfies g. First object instances are defined, which occur in the environment and their initial properties are stored. The planner takes the domain and the problem description and generates a list of skills, which need to be performed to solve the given problem. We use the planner SGPlan6 [5]. This list of skills is forwarded to theexecutive layerof the3-TIERarchitecture. For solving the order picking task, the following skills are required: moveBoxFromLevelToTray, movBoxFromTrayToLevel and graspItem. Lets assume an environment containing transport boxes BOXA,BOXC and a shelf with levelsLEVEL 1,LEVEL 2 and the goal of picking one item from BOXCplacing it at thedeliveryboxDBOXCandpicking twoitemsfromBOXAplacing it atdeliv- eryboxDBOXA.Theplannercomesupwith the followingplan(seeListing1).Thenameof theskill is the first parameter, followed by the parameters the skill requires. So the first skill, which has to be performed ismoveBoxFromLevelToTray. TheBOXC ismoved fromLEVEL 2 to theTRAY. Listing 1: Outputof planner for exampledomainandproblem. 0 (MOVEBOXFROMLEVELTOTRAY BOX C LEVEL 2 TRAY) 1 (GRASPITEM BOX C DBOX C TRAY) 2 (MOVEBOXFROMTRAYTOLEVEL BOX C LEVEL 2 TRAY) 3 (MOVEBOXFROMLEVELTOTRAY BOX A LEVEL 1 TRAY) 4 (GRASPITEM BOX A DBOX A TRAY) 5 (GRASPITEM BOX A DBOX A TRAY) 6 (MOVEBOXFROMTRAYTOLEVEL BOX A LEVEL 1 TRAY) 4.2. ExecutiveLayer The executive layer receives a list of skills from the planner. The executive layer handles the execu- tion of single skills. Each skill is composed of skill primitives, which are the fundamental building blocks of each skill. The executive layer knows about this decomposition and ensures that primi- tives are executed in right order to guarantee a successful skill execution. This decomposition of the skillsmoveBoxFromLevelToTray,moveBoxFromTrayToLevelandgraspItem is showninTable1. The composition of skill primitives for each skill is intrinsic knowledge of this layer. Further it monitors the outcome of each primitive. This layer has also the opportunity to perform recovery behaviors, if primitives fail. If no recovery can be performed or the recovery fails, this failure is reported to the planning layer. The decomposition of themoveBoxFromLevelToTray and its execution is shown in Figure3. skills moveBoxToRack graspItem moveBoxToLevel skill primi- tives detectHandle detectItem detectHandle graspHandle graspItem graspHandle moveArmToSupportPose deliverItem moveArmToSupportPose pullBox pullBox moveBox moveBox deliverBoxOnTray deliverBoxOnLevel Table1: Within this table the skill primitivecompositionofall skills are listed. 4 140