ASSEMBLY Robot based system for the automation of flow assembly lines G. Reinhart Æ Jochen Werner Æ F. Lange Received: 24 July 2008 / Accepted: 1 December 2008 / Published online: 16 December 2008 Ó German Academic Society for Production Engineering (WGP) 2008 Abstract In this paper a promising approach to the automation of flow assembly lines is presented. The developed system uses a standard industrial robot and synchronizes it to the product in all degrees of freedom. The synchronization is enabled by dividing the assembly process in different phases and controlling the robot in each phase with an adequate sensor system. Besides that a compliance is integrated into the gripper system in order to reduce high contact forces and tolerate high frequent pose deviations. Main advantages of the synchronized assembly are the avoidance of buffers and the reduction of the throughput time. Keywords Assembly  Robot  Flow lines 1 Introduction Today’s assembly systems have to cope with a high number of variants of the product by realizing competitive quality and costs. Therefore these assembly systems are usually manual or hybrid assembly lines [1]. Especially the German car manufacturers use mostly manual labor in their assembly lines [2]. Automation is hindered by the need for clocked cycles, the lack of flexibility of these systems and the necessary separation of man and robots [3]. The synchronized assembly in motion or assembly on the fly as shown in Fig. 1, is one answer for the economic need for automation in flow assembly lines [4]. Even though this idea is around for about 50 years it still needs further development. The existing approaches to an auto- mated assembly in motion can be differentiated by the principle of synchronization between the conveyor system and the robot. There are approaches using mechanical, guided or controlled synchronizing principles. The mechanical synchronization is the simplest princi- ple of synchronization because it is based on either a force fit or an interlocking joint. Disadvantages are the required mechanical adaptations of the conveyor system and the low accuracies [5]. More promising are the guided and the controlled syn- chronization. Today the guided conveyor tracking is implemented in most robot control systems. Using this method the conveyor speed is measured and the difference of the conveyor to the tool center point (tcp) of the robot is calculated within the interpolation cycle. Then the move- ment of the robot is corrected by the robot control. According to Dirndorfer [5] this system cannot achieve a maximum accuracy in synchronization of less than 1 mm due to vibrations and the following error of the robot. The controlled or feedback systems use either hydraulic or electronic algorithms for synchronization. All these methods have in common a constant measurement of the deviation between the robot and the conveyor system. Hence, the robot speed can be adjusted using a feedback algorithm. So far, all applied synchronized robot systems lack in achieving the accuracy of a stationary robot. One reason is the insufficient speed of control because of long processing times. Furthermore, the synchronization is enabled only in flow direction of the conveyor systems. All other movements and therefore deviations in pose perpendicular G. Reinhart  J. Werner (&) Institute of Machine Tools and Industrial Management, Technische Universita ¨t Mu ¨nchen, Boltzmannstr. 5, 85747 Garching, Germany e-mail: jochen.werner@iwb.tum.de F. Lange Institute for Robotic and Mechatronic, German Aerospace Center (DLR), Oberpfaffenhofen, 82234 Weßling, Germany 123 Prod. Eng. Res. Devel. (2009) 3:121–126 DOI 10.1007/s11740-008-0143-z