Welge-Lüßen, Tobias C.L.
- Doctoral Thesis
Rights / licenseIn Copyright - Non-Commercial Use Permitted
In this thesis the modelling and design of a passively actuated robeot manipulator is presented. It represents a non-smooth structure-variant mechanical system. The non-smoothness is caused by friction and impacts, the structure variance ty the ability to change the number of the degrees of freedom of the system. The primary purpose of the manipulator is to provide an experimental platform for the exploration of control methods and strategies which have been developed and programmed to handle non-smooth mechanical systems. Regarding industrial applications on can think of fail safe manufacturing robots or the development of walking aids. The manipulator has the shape of a classic two-degree-of-freedom robot arm and contains an actuated first joint with a motor inside and a passively actuated second joint with a brake. With the help of the required mathematical and mechanical concepts which are preliminarily covered in detail, the robot arm is modelled in two stages: first as a simple rigid-body model including the dynamical behavior of the drive being located in the actuated first joint and of the brake being located in the passively actuated second joint. The second stage model takes the elasticities of the shafts inside the joint modules and of the arms connecting the shafts into account. The non-smooth effects which are generated within the brake inside the passively actuated joint are modelled using set-valued force laws. The normal contact between the brake disc and the housing of the brake is described by the Upr-relation applying Signorini's Law, the friction contact by the Sgn-relation applying the law of Amontons-Coulomb. Bilateral constraints are included by implementation of the occurring constraint forces. They vanish for the case of choosing a set of minimal coordinates for the descriptionof the mechanical system. For the simulation of the rigid-body motions and of the elastic vibrations a time-stepping algorithm according to Moreau has been implemented. Within this context the so called "percussion P" enables a formulation of the equations of motion together with the impact equations in a single equation, where P is a sum of the effort of the non-impulsive contact forces and the effort of the atomic impulses stemming from impacts. The mechanical design process covers the conceptual layout, starting from different possibilities of realizing a two-degree-of-freedom manipulator. Using two rotational joints turns out as the best choice among the various design alternatives which have been proposed and evaluated with respect to different criteria. The final layout of the robot is realized as a two-degree-of-freedom manipulator containing a direct drive in the fully acutated joint and a brake in the passively actuated joint. Both joints are modular and inserted into a carrier structure, allowing for an easy and fast exchange of the actuated and passively actuated module. For sensing the motion of the robot two optical angle encoders have been mounted at each axis of rotation. The driven joint contains a direct drive which has the advantage of a simple design and the non-existence of a transmission mechanism. The result is a fricitonless drive without self-locking. The electromagnetically operated disc brake in the passively actuated joint generates a braking torque strong enough to instantaneously block the joint. It is held open when switched off using three retraction springs. Driving the motor and impatively blocking the brake are the two control inputs of the system. In addition to the mechanical hardware the electrical power and software system driving the robot has been designed. The software uses a C++ code for a reliable handling of the hardware and a user friendly graphical user interface programmed with GUIDE from MatLab. The experimental section of this work commences with a thorough parameter identification starting with the determination of the eigenfrequencies and eigenforms of the robot arm. they have beedn evaluated by a fininte element calculation and by measurements using a scanning vibrometer. The inertia of the robot arm has been evaluated with precise data from the CAD software the robot arm has been modelled with. For the identivication of further system parameters various experiments have been performed. The friction of the joint bearings has been evaluated by taking the deceleration during a free motion from deriving the position measurement twice with respect to time together with the inertia. The torques generated by the drive and by the brake were measured by applying strain gauges to the drive shaft. The torque difference between this measurement and the indirect measurement of the deceleration has been interpreted as the friction inherent in the joints. For the validation of the entire system and the model of the robot manipulator bang-bang type of motions, braking actions, and open loop trajectories have been implemented, both by experiments and simulation Show more
ContributorsSupervisor: Glocker, Christoph
Supervisor: Ulbrich, Heinz
SubjectROBOT ARMS; MANIPULATOREN + TELEOPERATOREN + GREIFARME + GELENKARME (ROBOTIK); MANIPULATORS + TELEMANIPULATORS + GRIPPERS (ROBOTICS); ROBOTERARME; MATHEMATICAL MODELING IN ROBOTICS, ROBOTS; KONZEPTION UND ENTWURF (MASCHINENBAU); ROBOTICS; MODELLRECHNUNG/ROBOTIK, ROBOTER; CONCEPTUAL DESIGN AND LAYOUT (MECHANICAL ENGINEERING); ROBOTIK
Organisational unit03581 - Glocker, Christoph
NotesDiss., Eidgenössische Technische Hochschule ETH Zürich, Nr. 17701, 2008.
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