Aging in humans is often associated with reduced muscle strength and difficulty in elevating the arm and sustaining it at a certain position. The aim of this master thesis is to propose a number of technical solutions integrated into a complete electronic system which can be used to support the user's muscle capacity and partially resist gravitational load. An electronic system consisting of sensors, a control unit and an actuator has been developed. The system is able to detect the user's motion intention based on an angle detection algorithm and perform kinematic control over the user's arm by adjusting the level of support at different degrees of elevation. A force control algorithm has been developed for controlling the actuating mechanism, providing the user with a natural and intuitive support during arm elevation. The implemented system is a first step towards the development of a medical assistive device for the elderly or patients with reduced muscle strength allowing them to independently perform a number of personal activities of daily life where active participation of the upper limb is required.

Object manipulation is a complex task for robots. It often implies a compromise between the degrees-of-freedom of hand and its fingers have (dexterity) and its cost and complexity in terms of control. One strategy to increase the dexterity of robotic hands with low dexterity is called extrinsic manipulation and its principle is to exploit additional accelerations on the object caused by the effect of external forces. We propose a force control based method for performing extrinsic in-hand object manipulation, with force-torque feedback. For this purpose, we use a prehensile pushing action, which consists of pushing the object against an external surface, under quasistatic assumptions. By using a control strategy, we also achieve robustness to parameter uncertainty (such as friction) and perturbations, that are not completely captured by mathematical models of the system. The force control strategy is performed in two different ways: the contact force generated by the interaction between the object and the external surface is controlled using an admittance controller, while an additional control of gripping force applied by the gripper on the object is done through a PI controller. A Kalman filter is used for the estimation of the state of the object, based on force-torque measurements of a sensor at the wrist of the robot. We validate our approach by conducting experiments on a PR2 robot, available at the Robotics, Perception, and Learning lab at KTH Royal Institute of Technology. / Att greppa och manipulera objekt är en komplex uppgift för robotar. Det innebär ofta en kompromiss mellan hand och fingrars frihetsgrader (fingerfärdighet) mot reglersystemets kostnad och komplexitet. Extrinsic manipulation är en strategi för att öka fingerfärdigheten hos robothänder, och dess princip är att utnyttja accelerationer på objektet som orsakas av yttre krafter. Vi föreslår en metod baserad på att reglerakraft för hantering av objekt i handen, genom en återkoppling av kraftmomentet. För detta ändamål använder vi en prehensile pushing action, där objektet puttas mot en yta, under kvasistiska antaganden. Genom att använda en reglerstrategi får vi en robusthet mot parametrars osäkerhet (som friktion) och störningar, vilka inte beskrivs av systemets model. Kraftkontrollstrategin utförs på två olika sätt: kraften mellan objektet och den yttre ytan styrs med en admittance controller medan en ytterligare styrning av applicerad gripkraft på objektet görs med en PI-reglerare. Ett Kalman filter används för att estimera objektets tillstånd, baserat på mätningar av kraftmoment via en sensor vid robotens handled. Vi utvärderar vårt tillvägagångssätt genom att utföraexperiment på en PR2-robot vid KTHs Robotics, Perception och Learning Lab.

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This thesis focuses on the detailed design, implementation, and testing of a unique high performance rotary actuator for use in a custom haptic force feedback device. This six degree of freedom (DoF) position input and three DoF force output haptic device is specifically designed to recreate force sensations with the goal of improving operator performance in remote or simulated environments. By upholding the strict design principles of an ideal force-source actuator, the developed actuator and consequently the haptic controller can successfully replicate forces accurately and realistically. In the comprehensive presentation of this design, numerous analytical tools are also developed and presented with the intention of them being resourceful in the design or improvement of other haptic actuators, specifically cable-driven force feedback designs. These tools which include a linear system model can be valuable not only in the development but in the control of cable-driven actuators. Due to the imposed design criteria, the developed 1.045 Nm (1.359 Nm peak) cable-driven sectorial rotary actuator exhibits numerous properties that are desired in an open-loop force controlled actuator. These properties include low inertia (6.53e-04 kgm^2), low perceived mass (0.102 kg), small torque resolution (3.84e-04 Nm), small position resolution (21.5 arcsec), and high bandwidth (300 Hz). Due to the efficient cable transmission the design is also backdrivable, isotropic, low friction, and zero backlash. As a result of these numerous intrinsic properties, a high fidelity force feedback haptic actuator was conceived and is presented in this thesis. / Master of Science

In order to function safely in a dynamic environment with humans and obstacles, robots require active compliance control with force feedback. In these applications the control law typically includes full dynamics compensation to decouple the joints and cancel out nonlinearities, for which a high-fidelity model of the robot is required. In the case of a 3D-printed robot, components cannot be easily modeled due non-uniform densities, inconsistencies among the 3D printers used in manufacturing, and the use of different plastics with mechanical properties that are not widely known. To address this issue, this thesis presents an adaptive control framework which modifies the model parameters online in order to achieve satisfactory tracking performance. The inertial properties are estimated by adapting with respect to functions of the unknown parameters. This is achieved by rewriting the robot dynamics equations as the product of a matrix of known nonlinear functions of the joint states and a vector of constant unknowns. The result is a nonlinear system linearly parameterized in terms of the of the unknowns, which can be estimated using adaptation laws derived from Lyapunov stability theory. The proposed control system consists of an outer-loop impedance controller to regulate deviations from the nominal trajectory in the presence of disturbances, and an inner-loop force controller to track the joint torques commanded by the outer-loop. The proposed system is evaluated on an early prototype consisting of a 3DOF leg, and two actuator test setups for the low-level controller. / Master of Science / In order to function safely in a dynamic environment with humans and obstacles, a robot must be able to actively control its interaction forces with the outside environment. In these applications a high-fidelity model of the robot is required. In the case of a 3D-printed robot, the components in the robot cannot be easily modeled due non-uniform densities, inconsistencies among the 3D printers used in manufacturing, and the use of different plastics with mechanical properties that are not widely known. To address this issue, this thesis presents an adaptive control framework which actively modifies the model parameters in order to achieve satisfactory tracking performance. In this work, the equations of motion of the robot are manipulated in such a way that the unknown quantities are separated from the known quantities. The unknowns are updated in real time using adaptive laws derived from Lyapunov stability theory. The proposed control system consists of a high-level torque controller to regulate deviations from the nominal trajectory, and a low-level force controller to track the joint torques commanded at the high-level. The proposed system is evaluated on an early prototype of the robot consisting of a 3 degree of freedom leg, and two actuator test setups for the low-level controller.

This study discusses the design of a force control strategy for reducing force disturbances in the Virginia Tech – Federal Railroad Administration (VT-FRA) Roller Rig. The VT-FRA Roller Rig is a state-of-the-art roller Rig for studying contact mechanics. It consists of a 0.2m diameter wheel and a 1m diameter roller in vertical configuration, which replicates the wheel-rail contact in a 1/4th scale. The Rig has two 19.4 kW servo motors for powering the rotational bodies and six heavy-duty servo linear actuators that control other boundary conditions. The Rig was operationalized successfully with all degrees of freedom working in the default position feedback control. During the Rig's commissioning, this approach was found to result in vertical force fluctuations that are larger than desired. Since the vertical force affects the longitudinal and lateral traction between the wheel and roller, keeping the fluctuations to a minimum provides a better test condition. Testing and data analysis revealed the issue to be in the control method. The relative position of the wheel and roller was being controlled instead of controlling the forces between them. The latter is a far more challenging control setup because it requires a faster dynamic response and full knowledge of forces at the interface. Additionally, force control could result in dynamic instability more readily than position control. Multiple methods for force control are explored and documented. The most satisfactory solution is found in a cascaded loop force/position controller. The closed loop system is tested for stability and performance at various load, speed, and creepage conditions. The results indicate that the controller is able to reduce the standard deviation of vertical force fluctuations at the wheel-rail contact by a factor of four. In terms of power of the vertical force fluctuations, this corresponds to a 12 dB reduction with the force control when compared with the previous control method. This study also explores the possibility of automating the tests in order to enable running a larger number of tests in a shorter period of time. A multi-thread software is developed in C++ for executing a user-defined position, velocity, or force vs. time trajectory, and for recording the data automatically. The software also provides continuous monitoring, and performs a safe shutdown if a fault is detected. An intuitive GUI is provided for constant data polling and ease of user operation. The code is modular in order to accommodate future modifications and additions for various testing needs. The engineering upgrades included in this study, together with the baseline testing, complete the commissioning of the VT-FRA Roller Rig. With unparalleled parameter control and testing repeatability, the VT-FRA Roller Rig holds the promise of being used successfully for various contact mechanics needs that may arise in the railroad industry. / MS / Roller Rigs have seen widespread use around the world for research and development of railway vehicles. These test rigs are specialized machinery that provide the means to test a particular aspect of railroading in a controlled environment, allowing for thorough parametric analyses which aid in the design and development of railroad vehicles. One such test rig is the Virginia Tech – Federal Railroad Administration (VT-FRA) Roller Rig, located at the Railway Technologies Laboratory in Blacksburg, Virginia. It is a state-of-the-art test rig which is developed with the objective of providing a controlled test environment for studying railway contact mechanics. A good understanding of the wheel/rail contact is critical to railroad engineering, and this problem has been the subject of research for about a century now. Several compelling mathematical models have been proposed, but the experimental verification of those theories has proven to be difficult. Traditionally, field testing data has been utilized for comparison with prediction from the models. However, field tests are plagued by a low level of noise control and the inability to carry out sophisticated parametric analyses. VT-FRA Roller Rig holds the promise to fill this gap with its sophisticated electro-mechanical design and high precision instrumentation. The VT-FRA Roller Rig replicates the wheel-rail contact in a 1 /4 th scale by utilizing the INRETS scaling strategy. The locomotive wheel is replicated by a 0.2m diameter wheel and the tangent track is replicated by a 1m diameter roller. The relative size difference ensures that the contact distortion effects from the use of roller are kept to a minimum. The wheel and the roller are arranged in a vertical configuration, and are independently powered by two 19.4 kW servo motors. This enables the VT-FRA Roller Rig to achieve a precise creepage control of up to 0.1%. VT-FRA Roller Rig also has six heavy-duty servo linear actuators which are responsible for controlling four boundary conditions: cant angle, angle of attack, lateral displacement and vertical load. A sophisticated six-axis contact force-moment measurement system allows for precise measurements with a high dynamic bandwidth. The Rig was operationalized successfully with all degrees of freedom working in the default position feedback control. During the Rig’s commissioning, this approach was found to result in force fluctuations that were larger than desired. Since the vertical force affects the longitudinal and lateral traction between the wheel and roller, keeping the fluctuations to a minimum provides a better test condition. Testing and data analysis revealed the issue to be in the control method. The relative position of the wheel and roller was being controlled instead of controlling the forces between them. This study documents the development process of a reliable force control methodology for the VTFRA Roller Rig. Force control is a far more challenging control problem when compared to position control because it requires a faster dynamic response and full knowledge of forces at the interface. Additionally, force control could result in dynamic instability more readily than position control. Multiple methods for force control were implemented on the VT-FRA Roller Rig. Satisfactory solution is achieved with the complicated cascaded loop force/position controller, and the stability and performance of the control system is ensured by a slew of tests at various operating conditions. This study also explores the possibility of automating the tests in order to enable running a larger number of tests in a shorter period of time. A multi-thread software is developed in C++ for executing a user-defined position, velocity, or force vs. time trajectory, and for recording the data automatically. The software also provides continuous monitoring, and performs a safe shutdown if a fault is detected. An intuitive GUI is provided for constant data polling and ease of user operation. The code is modular in order to accommodate future modifications and additions for various testing needs. The engineering upgrades included in this study, together with the baseline testing, complete the commissioning of the VT-FRA Roller Rig. With unparalleled parameter control and testing repeatability, the VT-FRA Roller Rig holds the promise of being used successfully for various contact mechanics needs that may arise in the railroad industry.

This dissertation focuses on improving the capabilities of an assistive robotic exoskeleton glove designed for patients with Brachial Plexus Injuries (BPI). The aim of this research is to develop a force control method, an automatic force planning method, and a Human-Machine Interface (HMI) to refine the grasping functionalities of the exoskeleton glove, thus helping rehabilitation and independent living for individuals with BPI. The exoskeleton glove is a useful tool in post-surgery therapy for patients with BPI, as it helps counteract hand muscle atrophy by allowing controlled and assisted hand movements. This study introduces an assistive exoskeleton glove with rigid side-mounted linkages driven by Series Elastic Actuators (SEAs) to perform five different types of grasps. In the aspect of force control, data-driven SEA fingertip force prediction methods were developed to assist force control with the Linear Series Elastic Actuators (LSEAs). This data-driven force prediction method can provide precise prediction of SEA fingertip force taking into account the deformation and friction force on the exoskeleton glove. In the aspect of force planning, a slip-grasp force planning method with hybrid slip detection is implemented. This method incorporates a vision-based approach to estimate object properties to refine grasp force predictions, thus mimicking human grasping processes and reducing the trial-and-error iterations required for the slip- grasp method, increasing the grasp success rate from 71.9% to 87.5%. In terms of HMI, the Configurable Voice Activation and Speaker Verification (CVASV) system was developed to control the proposed exoskeleton glove, which was then complemented by an innovative one-shot learning-based alternative, which proved to be more effective than CVASV in terms of training time and connectivity requirements. Clinical trials were conducted successfully in patients with BPI, demonstrating the effectiveness of the exoskeleton glove. / Doctor of Philosophy / This dissertation focuses on improving the capabilities of a robotic exoskeleton glove designed to assist individuals with Brachial Plexus Injuries (BPI). The goal is to enhance the glove's ability to grasp and manipulate objects, which can help in the recovery process and enable patients with BPI to live more independently. The exoskeleton glove is a tool for patients with BPI to used after surgery to prevent the muscles of the hand from weakening due to lack of use. This research introduces an exoskeleton glove that utilizes special mechanisms to perform various types of grasp. The study has three main components. First, it focuses on ensuring that the glove can accurately control its grip strength. This is achieved through a special method that takes into account factors such as how the materials in the glove change when it moves and the amount of friction present. Second, the study works on a method for planning how much force the glove should use to hold objects without letting them slip. This method combines a camera-based object and material detection to estimate the weight and size of the target object, making the glove better at holding things without dropping them. The third part involves designing how people can instruct the glove what to do. The command can be sent to the robot by voice. This study proposed a new method that quickly learns how you talk and recognizes your voice. The exoskeleton glove was tested on patients with BPI and the results showed that it is successful in helping them. This study enhances assistive technology, especially in the field of assistive exoskeleton glove, making it more effective and beneficial for individuals with hand disabilities.

The Friction Stir Welding (FSW) process has been under constant developmentsince its invention, more than 20 years ago. Whereas most industrial applicationsuse a gantry machine to weld linear joints, there are applications which consistof complex three-dimensional joints, requiring more degrees of freedom fromthe machines. The use of industrial robots allows FSW of materials alongcomplex joint lines. There is however one major drawback when using robotsfor FSW: the robot compliance. This results in vibrations and insufficient pathaccuracy. For FSW, path accuracy is important as it can cause the welding toolto miss the joint line and thereby cause welding defects.The first part of this research is focused on understanding how welding forcesaffect the FSW robot accuracy. This was first studied by measuring pathdeviation post-welded and later by using a computer vision system and laserdistance sensor to measure deviations online. Based on that knowledge, a robotdeflection model has been developed. The model is able to estimate thedeviation of the tool from the programmed path during welding, based on thelocation and measured tool forces. This model can be used for online pathcompensation, improving path accuracy and reducing welding defects.A second challenge related to robotic FSW on complex geometries is thevariable heat dissipation in the workpiece, causing great variations in the weldingtemperature. Especially for force-controlled robots, this can lead to severewelding defects, fixture- and machine damage when the material overheats.First, a new temperature method was developed which measures thetemperature at the interface of the tool and the workpiece, based on the thermoelectriceffect. The temperature information is used as input to a closed-looptemperature controller. This modifies primarily the rotational speed of the tooland secondarily the axial force. The controller is able to maintain a stablewelding temperature and thereby improve the weld quality and allow joining ofgeometries which were impossible to weld without temperature control.Implementation of the deflection model and temperature controller are twoimportant additions to a FSW system, improving the process robustness,reducing the risk of welding defects and allowing FSW of parts with highlyvarying heat dissipation.

In order to operate safely and naturally in human-centered environments, robots need to respond compliantly to force and contact interactions. While advanced robotic torsos and arms have been built that successfully achieve this, a somewhat neglected research area is the construction of compliant wheeled mobile bases. This thesis describes the mechatronics behind Trikey, a holonomic wheeled mobile base employing torque sensing at each of its three omni wheels so that it can detect and respond gracefully to force interactions. Trikey's mechanical design, kinematic and dynamic models, and control architecture are described, as well as simple experiments demonstrating compliant control. Trikey is designed to support a force-controlled humanoid upper body, and eventually, the two will be controlled together using whole-body control algorithms that utilize the external and internal dynamics of the entire system. / text

Research and development leading to the realisation of a fully autonomous and robust multi-fingered hand has been going on for three decades. Yet none can be found in an industrial application. This is largely because we do not fully understand the fundamental mechanics of multi-finger grasping. / This thesis is a study of the mechanics of multi-finger grasping, with particular attention being paid to applying the analysis to experimental co-operative motion tasks between a hand-arm system and grasped object. / Fine manipulation with multi-fingered robot hands is critically influenced by the capacity to achieve stable grasps. By exploring the fundamental mechanics involved, a method for establishing the stability of spatial four finger-contact grasps is obtained. This work examines both frictionless and frictional grasps in two and three dimensions and develops the stability requirements for grasping. The conditions for a stable grasp are expressed as simple equations relating the line coordinates of (i) transitory sliding actuator and (ii) the normal to the tangent plane at every contact location. This is achieved by using the principle of virtual work and a branch of statics known as astatics. / After specifying a grasp in terms of its contact locations and forces the object can be grasped. However, in general the configuration of the hand-arm combination will not be unique, as such a manipulator system has more than six degrees of freedom and is said to be super-abundant. The choice of appropriate shares taken by the arm and hand in delivering the manipulation task needs to be resolved. This can be done making use of a kinematic performance measure based on aligning the grip triangle with the hand line of symmetry and maximising the available manipulation range. The hand-arm combination can then be driven to this desired grasp enabling the manipulator to carry out the specified task effectively. A Salisbury hand and PUMA 760 robot arm are used to demonstrate these co-operative motion tasks. / All the experimental results are presented along with a detailed description of the implementation of a hierarchical robot controller system which incorporates force control of the PUMA 760.