The research documented in this thesis investigates vision aided robotic feeding systems, within the context of reconfigurable manufacturing systems. The research is focused on comparing EIH and FC configurations for such a feeding station. The objective of the research was to develop a simulation tool would allow a reasonable prediction of the systems behaviour. The development of the simulation tool included the creation of an agent-based control system for a reconfigurable feeding station.
As a case study for validating the simulation, the control system was implemented on a feeding station of an experimental assembly cell at the University of Stellenbosch. The feeding station assembles components of circuit breaker. In a laboratory implementation used for validating the simulation model, collection platforms on which plats were placed manually, were used to emulate reconfigurable singulation units. The physical implementation further included two pallets to receive parts, a part magazine and a six-degree of freedom robot. The case study implementation was developed for two configurations, namely an EIH and a FC configuration. For the FC configurations, a fixed camera was provided above the collection platform and the pallets. While for the EIH configurations, a camera was attached to the end effector of the robot arm. The implementation fed only two component types, but the addition of new component types would be simple, provided the components can be collected approaching from the top and the current gripper can be used.
A holonic control system was developed for the feeding station controller, with consideration of the six core characteristics of RMSs, i.e. customisability, configurability, scalability, modularity, integrability and diagnosability. The control system included a multi-agent system as the high-level controller, in which an agent was created for each holon, thus reflecting modularity. ADACOR was used as the reference architecture, with holon responsibilities being modified as needed for the application. This resulted in a control system with the responsibilities divided between the coordinator, supervisor, task, subtask and operational holons. Integrability was achieved by interfacing the HLC to numerous LLCs using TCP/IP through Ethernet. The control system was further able to scale the number of pallets or tasks and singulation units in the system, thus demonstrating elements of scalability. This was largely made possible by using agents as HLC and the use of the directory facilitator. Rapid integration of new modules, such as additional SUs, was achieved with the aid of JADE agents as a HLC, the use of a modular communication interface and the placement of base coordinates in the agents' code. Error handling and diagnosability was limited in the present implementation to inspecting (using an EIH or a FC configuration) whether the parts fed by the feeding station were correctly placed. Although the agent platform's communication allows subscribers to be informed of events, which allows diagnostic information to be
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communicated and stored, this was not implemented since it does not affect the FC vs EIH comparison. In addition, ADACORs error handling was not implemented here, as the system does not have sufficient redundancy.
In addition to the physical implementation described above, a simulation was also developed in which the physical components were replaced either by external software packages (e.g. Kuka Sim was used to replace the Kuka robot) or by user written functions. The simulation emulated the singulation rate and successful singulation probability of reconfigurable SUs, yielding reasonable results in sample experiments. The ability of the simulation to compare EIH and FC configurations for a number of cases was demonstrated. The results showed that in the particular cases considered, using typical SU performance parameters, a FC station configuration yields a higher throughput rate and a higher throughput rate per unit cost. However, in many cases the EIH configuration offered competitive performance with lower capital investment.
Although this was not explored fully in the thesis, the experiments conducted showed that the simulation model is a useful tool, not only for simulation, but also for development of a physical station. A CAD environment can be used to build a detailed configuration in KUKA Simpro, where the robot movements and collision detection can be programmed. This is especially useful when developing a FC station, since a robot collision with a vision sensor can be very costly. The experiments also showed how hardware in the loop simulations allow the development or integration of other modules (e.g. replacing the camera with another brand or with simulation object) can be done without full station deployment. The main limitation in the simulation, and therefore an area for further work, is in diagnosing errors and handling those errors. However, the implementation of such measures is highly application-specific. The importance of handling the errors also depends on the frequency and cost of the errors, to that the importance may range from insignificant to critical.
Some functionality offered by EIH configurations and not FC configurations, that should be further investigated, is the use of EIH robots for remote visual monitoring, allowing specialist supervision remotely. This functionality will require many safety measures if implemented using an industrial robot and would require investigation into a means of low-level safety mechanisms involving the robot. In this implementation, low-level robot safety mechanisms are programmed on the robot controller and cannot be edited externally (as with Java or JADE in this implementation).
The use of the smart camera to control a singulation unit should be investigated. This may drive down the cost of FC SU substantially making them more competitive in comparison to EIH SUs
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