Modellbasierte Kraftregelung einer mit pneumatischen Muskeln angetriebenen Parallelplatform

In the present work, a force and torque controlled Gough-Stewart type parallel platform driven by six actuator legs was developed and evaluated. Each actuator consists of a fluidic muscle which is combined with a prestressed coil spring in order to produce compressive as well as tensile forces. The platform shall be controlled such that arbitrary force functions can be simulated. Through geometric limit analyses, it was verified that the workspace of the mobile platform suffices to the required motion range. The model-based force control of each actuator uses an exponential approximation of the transient pressure responses. The six actuator control loops are embedded into the force and torque control of the parallel manipulator. The platform-control algorithm includes a kinetostatic platform model, which com-putes the corresponding required leg forces in order to achieve the target forces and torques at the end effector of the platform. It was shown that the target end-effector forces and torques, which do not pursue rapid changes, can be produced effectively with the developed parallel manipulator and the established platform control. The steady-state performance of the developed control algorithm sufficed to the requirements of a fine-tuned force and torque control. The manipulator was designed for its future application as a physical simulator of cervical spine motion for assessing effects of, e.g., implants, surgical treatments, etc.Die vorliegende Arbeit befasst sich mit der Entwicklung und Evaluierung einer kraftgeregelten Gough-Stewart Parallelplattform, die von sechs Aktoren angetrieben wird. Die Aktoren bestehen jeweils aus einem pneumatischen Muskel und einer vorgespannten Druckfeder. Die Plattform wird so geregelt, dass beliebige Kraft- und Momentenverläufe erstellt werden können. Durch die geometrische Analyse der Endlagen wurde verifiziert, dass der geforderte Arbeitsraum durch die Plattform erreicht werden kann. Jeder einzelne Aktor wird durch eine modellbasierte Kraftregelung kontrolliert, die unter anderem die Druckbeaufschlagung eines pneumatischen Muskels durch exponentielle Funktionen annähert. Die sechs Regelschleifen der Aktoren sind der Kraft- und Momentenregelung der Parallelplattform untergeordnet. Die Plattformregelung benutzt das kinetostatische Modell der Plattform und berechnet die jeweiligen Aktorkräfte, die zum Erreichen der aktuellen Sollkraft und Sollmomentes an der Plattform notwendig sind. Es wurde gezeigt, dass die geforderten Zielkräfte und Momente effektiv mit der kraftgeregelten Plattform produziert werden können und im stationären Bereich der Sprungantworten eine genaue Kraftregelung möglich ist. Die Parallelplattform wurde konzipiert für ihre zukünftige Anwendung als physikalischer Simulator der menschlichen Halswirbelsäule, unter anderem für die präoperative Analyse chirurgischer Eingriffe, Implantate etc

Design Feasibility of an Active Ankle-Foot Stabilizer

Walking is the most common form of mobility in humans. For lower limb mobility impairments, a common treatment is to prescribe an ankle-foot orthosis (AFO) or brace, which is a passive device designed to resist undesired ankle-foot motion. Recent advances in actuator technology have led to the development of active AFOs (AAFOs). However, these devices are generally too bulky for everyday use and are limited to applications such as gait training for rehabilitation. The aim of this research was to investigate the feasibility of developing a novel Active Ankle-Foot Stabilizer (AAFS). The design criteria were mainly based on the strengths and limitations of existing AFOs. The sagittal plane functional requirements were determined using simulated gait data for elderly individuals and drop foot patients; however, it is intended that the device would be suitable for a wider range of disabilities including ankle sprains. A model of the foot was introduced to modify the moment of a deficient ankle where young healthy adult kinematics and kinetics were assumed. A moment deficit analysis was performed for different gait periods resulting in an AAFS model with two components: a linear rotational spring to modify the ankle joint rotational stiffness, and a torque source. The frontal plane functional requirements for the AAFS were modeled as a linear rotational spring which responded to particular gait events. A novel Variable Rotational Stiffness Actuator (VSRA) AFO was also investigated. It consisted of an actuated spring medial and lateral to the ankle to control sagittal plane ankle stiffness and a passive leafspring posterior to the ankle to control frontal plane ankle stiffness. Due to high forces and profile limitations, a spring and rotation actuator that satisfied the design criteria could not be developed, resulting in an infeasible design. Considering the high forces and moments required by the AAFS, a pneumatic approach was adopted. A novel Airbeam AFO, which consisted of a shank cuff and a foot plate to which airbeams were attached proximally and distally to the ankle, was examined. The joint rotational stiffness of the ankle would be controlled by the inflation of these individual cylindrical airbeams. To satisfy the functional requirements, the airbeam diameters and pressures were too large to meet the design criteria and were unrealistic for a portable device. Finally, a Pneumatic Sock AFO, which proved to best satisfy the functional requirements within the design criteria, was examined. The design consisted of an inner sock worn on the ankle, surrounded by anterior, posterior, medial, and lateral bladders which inflate against outer fabric shells. Although promising, the Pneumatic Sock AFO requires further investigation in regards to manufacturing and behaviour characterization before a functional prototype can be developed. Mechanical test methods to characterize the behaviour of the Pneumatic Sock AFO in the sagittal and frontal planes were developed including the control components required, the configuration of a test rig, and test procedures.1 yea

Modelling and Evaluation of Piezoelectric Actuators for Wearable Neck Rehabilitation Devices

Neck pain is the most common neck musculoskeletal disorder, and the fourth leading cause of healthy years lost due to disability in the world. Due to the need of hands-on physical therapy and Canada’s aging population, access to treatment will become highly constrained. Wearable devices that allow at-home rehabilitation address this future limitation. However, few have emerged from the laboratory setting because they are limited by the use of conventional actuators. An overlooked type of actuation technology is that of piezoelectric actuators, more specifically, travelling wave ultrasonic motors (TWUM). In this work, a clear procedure that outlines how the required parameters within the hybrid TWUM model can be identified, as well as an assessment of the use of TWUMs within wearable devices for the neck, is presented. The procedure includes custom testing setups that were designed to identify the stator motion parameters, and the Coulomb coefficient of friction. The accuracy of the determined parameters were confirmed when the angular velocity of the hybrid model at different duty cycles was compared to the real TWUM being modelled, producing a coefficient of determination of 0.974. The model was then used to create a position control system that controlled the joints of a virtual robotic manipulator that modelled the neck. The manipulator exhibited a maximum absolute mean error of only 0.0289 m when simulating the required trajectories of range of motion exercises. This performance, in addition to the exemplary traits TWUMs express, demonstrate their potential to advance the field of wearable mechatronic devices

7-degree-of-freedom hybrid-manipulator exoskeleton for lower-limb motion capture

Lower-limb exoskeletons are wearable robotic systems with a kinematic structure closely matching that of the human leg. In part, this technology can be used to provide clinical assessment and improved independent-walking competency for people living with the effects of stroke, spinal cord injury, Parkinson’s disease, multiple sclerosis, and sarcopenia. Individually, these demographics represent approximately: 405 thousand, 100 thousand, 67.5 thousand, 100 thousand, and 5.9 million Canadians, respectively. Key shortcomings in the current state-of-the-art are: restriction on several of the human leg’s primary joint movements, coaxial joint alignments at the exoskeleton-human interface, and exclusion of well-suited parallel manipulator components. A novel exoskeleton design is thus formulated to address these issues while maintaining large ranges of joint motion. Ultimately, a single-leg unactuated prototype is constructed for seven degree-of-freedom joint angle measurements; it achieves an extent of motion-capture accuracy comparable to a commercial inertial-based system during three levels of human mobility testing

Progenitor cells in auricular cartilage demonstrate promising cartilage regenerative potential in 3D hydrogel culture

The reconstruction of auricular deformities is a very challenging surgical procedure that could benefit from a tissue engineering approach. Nevertheless, a major obstacle is presented by the acquisition of sufficient amounts of autologous cells to create a cartilage construct the size of the human ear. Extensively expanded chondrocytes are unable to retain their phenotype, while bone marrow-derived mesenchymal stromal cells (MSC) show endochondral terminal differentiation by formation of a calcified matrix. The identification of tissue-specific progenitor cells in auricular cartilage, which can be expanded to high numbers without loss of cartilage phenotype, has great prospects for cartilage regeneration of larger constructs. This study investigates the largely unexplored potential of auricular progenitor cells for cartilage tissue engineering in 3D hydrogels