Page - 228 - in Proceedings - OAGM & ARW Joint Workshop 2016 on "Computer Vision and Robotics“

In this paper the different assemblies are referred to as ’wrist’, ’lower arm’, ’upper arm’and ’base’. The following metaphor is applied to alleviate the comprehension of the system: The robot can be seen likeahumanarm. The ’shoulder joint’ismounted to thesurfaceof the tableandwillbe referred to as the ’base’. Next comes the ’upper arm’, which connects the ’shoulder’to the ’elbow joint’. In this project the assemblies that are equal to the ’upper arm’and the ’elbow joint’are called ’upper arm’and’third joint’. Finally, the ’lowerarmassembly’isconnectedbetween the’elbowjoint’and the ’wrist’. According to this rough concept, a six-axis robot was designed using CAD software that can handle payloads of up to500gmass within a working envelope of700mm in diameter. In order to provide a save to use platform the robot was designed to hide all moving parts such as belts, pulleys and shafts inside the robot. This at the same time allows for an likable design. In contrast to commercial indus- trial robots, there is no need to strictly separate the working range of the robot from human reaching areasbymeansofaclosedassemblycell. Thegoalsofoperator-friendlinessandmaintainabilitywere obtainedbyassemblingallcomponents inenclosed,modularassemblies inorder tobeable tochange each module easily or to adapt just one specific part of the robot. A further important design require- ment was to provide a platform that is decomposable multiple times without relevant part defects as a consequence of the dis- and re-assembly process. Even after multiple assembly loops, the robot must ensure a sufficient level of precision. This was achieved by introducing index pins in order to prevent from inaccurate re-assembly. Comparably, centering pins are used in order to be able to re-establish the exact coaxial position of every joint after reassembly. All parts were designed and optimized for the use of additive manufacturing techniques in order to enable the re-manufacturing of any part quickly, easily and cost-efficient. A further major design objective was to preferably use standardparts insteadofmanufacturingcustomizeditems. Thishelps todecreasemanufacturing-time and -effort and at the same time makes use of the granted precision provided by supplier-dependent tolerances. In order to cut the maintenance effort to a minimum, only encapsulated bearings were used (nogreasingor cleaning). 3. Designof theBase Due to limitations regarding the maximum size of the 3D-manufactured objects, the base was split into two parts which were screwed together to provide a single solid base. Educational institutions that have access to more advanced equipment or are willing to deviate from the pure 3D-printing approach, could easily design their own robot concepts by means of using a one-piece manufactured base as an alternative. The base has two hollow chambers in order to hold all electronic components and the controller boards shielded and space-saving. As these openings contain all electronic and controllercomponents, the robotcanbeused instandalonemodeaswellasconnected toacomputer. A further compartment on the bottom of the base hides the drive belt of the first axis and its motor. This additional opening could as well be used to append extra weight (e.g., heavy steel plates) to prevent the base from moving while the robot is used in a stand-alone mode. Another possible use of the bottom compartment is to hold batteries, in case the robot shall be used in locations without electrical power supply, e.g., on fairs or exhibitions. Besides, the batteries take effect as additional weight. Asshowninfigure2, thebaseconsistsofacylindrical tube,alsocontaining themotor-holder for the motors of the second and third axis. The first axis is moved by simply shifting the whole cylindrical tube together with the rest of the robot. The motors for the second and third axis are connected to the fork by means of two timing belts. The fork consists of a hollow shaft which is directly powered by the timing belt assigned to the motor of the second axis. The timing belt on the 228