On Manufacturing Technology as an Enabler of Flexibility : Affordable Reconfigurable Tooling and Force-Controlled Robotics

Sammanfattning: In order to survive in today’s global market many manufacturing companies seek flexibility to reduce product lead times and meet changing market demands. Manufacturing equipment forms the base of the production system and manufacturing technology with the capability to adapt to any changes in prerequisites is thus a key enabler of flexibility. Industrial robots and fixtures are common in all types of manufacturing. Robots are versatile re-programmable units capable of performing many tasks, such as welding, part transfer, etc. Industrial robots have traditionally been unable to handle disturbances and lack of constraints of input. This has led to manual operations often being preferred to automation when some level of flexibility is needed. One way to enhance manufacturing equipment’s capability to handle unknown events is to integrate different kinds of sensors to gain more knowledge of the manufacturing environment. Force sensors, for example, can be used to close the feedback loop and, together with an adequate control system, enable the robot to react to force stimuli. This is useful in manufacturing applications like assembly and deburring, which have previously been difficult to automate.Fixtures are devices that hold and position parts during a manufacturing process. Traditionally many fixtures have been dedicated, i.e. designed for a specific part and purpose. This means that fixtures have not been able to handle different products in the same unit, thus hindering flexibility. Sensors, like measurement systems, can be used together with fixtures to de-couple the structure of the fixture from the accuracy, which is the traditional approach to fixturing. This reasoning forms the base of the Affordable Reconfigurable Tooling (ART) concept, developed at Linköping University. The ART concept aims at increasing flexibility in manufacturing, while ensuring affordability and efficiency.This thesis explores how common manufacturing equipment, like industrial robots and fixtures, combined with sensor input, can enhance flexibility in manufacturing. The research shows that force-controlled robots, reacting to force stimuli, produce consistent results in assembly of compliant structures and in complex deburring. Force control also makes the system more robust, as it is able to handle variance in the assembled and deburred parts which adds to system flexibility. It also lessens the need for accuracy in other equipment used, such as grippers and fixtures, and makes programming easier and safer. Force control would, however, benefit if parameter tuning was simplified in order to fit an industrial environment and if presented user information is tailored for the intended user.Using measurement sensors to build fixtures, new ART devices aimed at increased flexibility in fixtures have been developed. These devices reduce the resources needed for fixture build and reconfiguring between products and also open up for making fixtures more active in manufacturing and similar to robots, while still being affordable. ART also reduces resources needed for design, as shown by the developed design aid programs. ART also supports concurrent design, as fixture specifications may be finalized before the product specifications are fully set.The overall results indicate that the explored sensors in combination with today’s emerging technologies can give additional benefits for applications like assembly and deburring and for fixtures. Furthermore, it is shown that it is possible to increase flexibility on different levels in a manufacturing system by using sensors in combination with industrial robots and fixtures.