Seite - 229 - in Proceedings - OAGM & ARW Joint Workshop 2016 on "Computer Vision and Robotics“

other sideof thehollow shaftdrives a second pulley inside the shaft. Figure2. Explodedviewof thebase 4. Designof theUpperArm To reduce the weight of the arm and to maximize the manipulable payload, the motor of the third axis was relocated from the elbow joint into the base. To be able to transmit the torque of the third axis from the base to the elbow joint an arrangement of rods and cardan joints was used inside the upper arm assembly. The upper arm assembly is composed of two main housing parts. It consists of a timing wheel inside the upper arm assembly, which in turn is connected to the timing wheel inside thehollowforkshaft. Finally the torque is transmittedbyabevelgear to therodassemblyandfurther to the lowerarm assembly. 5. Designof theLowerArm Another huge challenge was the design of the lower arm and the TCP-gearhead due to heavy restric- tions regarding size and weight. Every additional gram that the robot weights implies one gram less that canbemanipulatedby the later robot. Therefore theconstructionmaximwas touseas fewcom- ponents as possible and within as small space as possible. To provide a counterweight to the handled payload and to alleviate the drive train design, the motors for the fourth, fifth and sixth axis were located at the third joint. The challenge was to place three motors next to each other, but still have their drive shafts positioned coaxial since a parallel position of two or more axes would lock at least one of the three axes. This problem was solved by using a spur gear drive with a various amount of gears combined with a hollow shaft which holds another shaft inside. The spur gears bridge the two dimensional displacement of the motor shafts from the coaxial position. Each of the two coincide shafts inside the upper arm assembly drives a bevel gear drive inside the lower arm which subse- quently drives the fifth and sixth axis of the robot using a timing belt connection and another bevel gear box inside the TCP head. The assembly can be seen in figure 3. For the purpose of adjusting 229