Design of passive compliant end-effectors for robotic and autonomous train fluid servicing

Abstract

Due to the ongoing increase in UK rail traffic, train maintenance automation is becoming essential in meeting the future demands of the industry. The issue is that current industrial robotics are not readily suited for train maintenance in outdoor/unstructured applications. To perform useful work, the robot must interact with the train parts, this can include various tasks such as insertion, latching, griping etc. There will always be some misalignment in the autonomous mating of these parts, using a completely rigid robot will cause failures, especially in tight clearance scenarios. The robot or workpiece must be flexible to facilitate smooth interaction with relaxed contact forces and robot payload, reducing overall cost and safety requirements. Compliant mechanisms and end-effectors are inherently flexible and cheap however, existing literature and solutions are only suitable for robotic tasks with small misalignments (<2mm) and basic mating geometry. Our application of train fluid servicing includes more complicated tasks and geometries with misalignment upto 15 mm and 5 deg. The existing literature uses simplified analytical modelling and trial-and-error design approaches which are outdated and in our case impractical. This thesis uses more modern and practical techniques to structure the design of compliant mechanisms in passive compliance applications with large misalignments and applications of train fluid servicing. We hypothesise that such a design problem is always distinguished by some kind of uncertainty (i.e. misalignments) which manifests itself into loads and displacement. In this manner, Robust Engineering Design (RED) methodologies are formulated to solve the general design issue. The approach includes Pseudo Rigid Body Modelling (PRBM) and Finite Element Analysis (FEA) for large deformation and contact modelling. This was accurate in payload prediction between 5-12% of the physical results. We were successful in enabling a range of largely misaligned automated fluid coupling while significantly reducing robot payload for cam and groove type (CET) fluid couplings. A special mechanism was developed to aid the gripping of fluid port caps with standard grippers. Performance charts were produced to convey design insight. Contributions of this thesis are: 1. A unique outlook and new higher-level framework for passive compliance design with RED methodologies 2. Developing and evaluating design and modelling tools necessary for large misalignment and complex contact scenarios in train fluid servicing tasks 3. Design and parametric insight of new compliant end effectors for train fluid servicing