Development of Mobile Machining Cell

This report covers some initial aspects of development of the mobile InnoMill machining cell. The new machining paradigm where the machine is mounted on the workpiece is compared to the old paradigm where the workpiece is mounted inside the machine, and differences are discussed. Parametric studies of the workpiece case study of the InnoMill project, the Vestas V112-3.0MW wind turbine hub, are performed to supply insight regarding load capacity etc. for the machine designers. The hub finite element model is validated using experimental results from Operational Modal Analysis performed on the hub. Furthermore, the InnoMill concept is described, and work regarding the 6 degree of freedom parallel kinematic manipulator which is present in the concept is performed. A numerical procedure accounting for base deflections due to static loading is proposed and implemented. Additionally, a six degree of freedom spring-mass model vibrational response is compared to vibrational response obtained from experiments on the 6 degree of freedom parallel kinematic manipulator at Aarhus University. The model, which is based on assumptions commonly found in literature, is rejected. Finally, an outlook for the remaining part of the PhD project is presented

Stiffness matrix of manipulators with passive joints: computational aspects

The paper focuses on stiffness matrix computation for manipulators with passive joints, compliant actuators and flexible links. It proposes both explicit analytical expressions and an efficient recursive procedure that are applicable in the general case and allow obtaining the desired matrix either in analytical or numerical form. Advantages of the developed technique and its ability to produce both singular and non-singular stiffness matrices are illustrated by application examples that deal with stiffness modeling of two Stewart-Gough platforms.Comment: arXiv admin note: substantial text overlap with arXiv:1107.449

High performance control of a multiple-DOF motion platform for driver seat vibration test in laboratory

Dynamic testing plays an important part in the vehicle seat suspension study. However, a large amount of research work on vibration control of vehicle seat suspension to date has been limited to simulations because the use of a full-size vehicle to test the device is an expensive and dangerous task. In order to decrease the product development time and cost as well as to improve the design quality, in this research, a vibration generation platform is developed for simulating the road induced vehicle vibration in laboratory. Different from existing driving simulation platforms, this research focuses on the vehicle chassis vibration simulation and the control of motion platform to make sure the platform can more accurately generate the actual vehicle vibration movement. A seven degree-of-freedom (DOF) full-vehicle model with varying road inputs is used to simulate the real vehicle vibration. Moreover, because the output vibration data of the vehicle model is all about the absolute heave, pitch and roll velocities of the sprung mass, in order to simulate the vibration in all dimensions, a Stewart multiple-DOF motion platform is designed to generate the required vibration. As a result, the whole vibration simulator becomes a hardware-in-the-loop (HIL) system. The hardware consists of a computer used to calculate the required vibration signals, a Stewart platform used to generate the real movement, and a controller used to control the movement of the platform and implemented by a National Instruments (NI) CompactRIO board. The data, which is from the vehicle model, can be converted into the length of the six legs of the Stewart platform. Therefore, the platform can transfer into the same posture as the real vehicle chassis at that moment. The success of the developed platform is demonstrated by HIL experiments of actuators. As there are six actuators installed in the motion platform, the signals from six encoders are used as the feedback signals for the control of the length of the actuators, and advanced control strategies are developed to control the movement of the platform to make sure the platform can accurately generate the required motion even in heavy load situations. Theoretical study is conducted on how to generate the reasonable vibration signals suitable for vehicle seat vibration tests in different situations and how to develop advanced control strategies for accurate control of the motion platform. Both simulation and experimental studies are conducted to validate the proposed approaches

A Method for Modeling Analytical Stiffness of a Lower Mobility Parallel Manipulator

International audienceThe H4 robot is a parallel machine with four degrees of freedom. The purpose of this work is to evaluate the H4 stiffness, ie the displacement response of the tool controlled point when it is submitted to a given force using an analytical method. A stiffness analysis based on analytical calculations is performed. It has the advantage to be rather fast and easy to integrate into a design optimization. This method allows to compute stiffness matrix of parallel robots and takes into account particularity of parallel robots with articulated traveling plate. Some numerical results are shown at the end of this paper for the H4 first prototype

Design of a Modified Stewart Platform Manipulator for Misalignment Correction

This thesis work is about the design of a modified Stewart platform manipulator for misalignment correction. The common version of the Stewart platform uses six actuators. The traditional Stewart platform of this kind has a moving top plate and a fixed base plate. However, in this research, the modified design of the traditional Stewart platform is studied. It is designed to be an easy connect-disconnect platform that can wrap around different structures with different cross sections and symmetrically designed. It is able to adjust position easily by using four identical but independent linear actuators populated evenly in two parts fastened to the top and bottom base by ball joints with each part been symmetrical to the other. To design two symmetrical parts and an adjustable clamp are a major objective of the thesis. One symmetrical part flipped upside down produces the other. The adjustable clamp was printed in 3D and can be used to align regular structural shapes especially circle of various diameter. To correct the misalignment, a failure study was carried out to determine the two equal but opposite loads required to correct misalignment in two plastic beams. Five loads were applied which showed that the smaller the load, the better the misalignment. This study showed that it is better to fix the base at a location where it does not move. To investigate that the modified Stewart platform can resist structure stiffness, the actuator assembly was analyzed using ANSYS software. The results showed that the deformation and maximum stress is less that the structure stiffness, which proves why the assembly can resist structural stiffness. The results support that the modified Stewart platform can be used for misalignment correction

Appropriate Design of Parallel Manipulators

International audienceAlthough parallel structures have found a niche market in many applications such as machine tools, telescope positioning or food packaging, they are not as successful as expected. The main reason of this relative lack of success is that the study and hardware of parallel structures have clearly not reached the same level of completeness than the one of serial structures. Among the main issues that have to be addressed, the design problem is crucial. Indeed, the performances that can be expected from a parallel robot are heavily dependent upon the choice of the mechanical structure and even more from its dimensioning. In this chapter, we show that classical design methodologies are not appropriate for such closed-loop mechanism and examine what alternatives are possible

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications