Design, Material and Surgical Assembly Effects on Fretting Corrosion Behavior of Modular Tapers in Orthopedic Implants

Mechanically assisted crevice corrosion (MACC) has become a significant problem in the orthopedic device industry, particularly in modular devices with metal-on-metal (MoM) tapered interfaces. Oxide film abrasion, leading to fretting corrosion in the presence of a crevice, accelerates the corrosion process and in some instances may lead to failure of the implant. Failure is defined as the need for revision surgery. The basic processes of oxide film abrasion and repassivation, and the associated effects (chemical, transport, mechanical and electrical) of these processes have been well described and studied over time. Despite these advancements, there is much that is still not well understood about modular taper performance and the role of design, materials, surgical techniques and biological factors, and their effects on MACC performance. For example, the load-displacement behavior of taper junctions during seating, the effect of seating load magnitude, rate of loading and loading orientation, and the role of taper contamination on seating mechanics, pull-off mechanics and MACC behavior remain to be well understood. In addition, few studies have been carried out to improve the understanding of the relationship between MACC, local tissue reaction, taper design and material combination. Thus, with continued concerns surrounding fretting corrosion and MACC of modular taper junctions there is a continuing need to develop appropriate in vitro tests to evaluate the roles of specific design, material and surgical techniques. These concepts are complex, interdependent and need to be clearly understood for effective design of, and surgical practice using modular taper junctions. Therefore, the goals of this dissertation are to systematically assess the effects of seating mechanics in terms of load magnitude, load rate and load orientation, contamination, taper design and material combination on the MACC behavior of head-neck taper junctions and taper locking stability (pull-off behavior) for commercially-used total hip replacements. The information provided from these studies offers a more detailed understanding of the interactions that arise between taper design and material combination based on surgical techniques and taper contamination in reference to taper fretting motions and corrosion. Preliminary testing consisted of a novel test protocol in which the seating (load-displacement) behavior and taper pull-off load were monitored in 12/14 Ti6Al4V/CoCrMo modular taper junctions. The seating behavior for four load magnitudes, three load orientations and five contamination groups was reported. The results showed an increase in seating load magnitude increased seating displacement, work of seating and the taper pull-off load while an increase in load orientation (to 20°) had no significant effect. Taper contamination testing presented findings which suggest the inclusion of lipids into the junction resulted in increased taper stability. The presence of contaminants increased seating displacement and work of seating compared to a control (dry) taper. Fretting corrosion testing incorporated identical taper testing conditions (load magnitude, orientation and contamination) and underwent incremental cyclic fretting corrosion testing. The goal was to investigate the effects of taper seating conditions on fretting motions and fretting corrosion. The outcome of testing highlighted the significant effects of taper seating conditions on each sample group. In the seating load magnitude groups, a correlation between subsidence and current at the end of testing was reported. An increased seating load orientation reduced micromotion throughout testing and the average onset load but had no effect on subsidence, current at the end of testing or taper pull-off. And the introduction of lipid contaminants into the taper junction reduced fretting corrosion currents. Lastly, the effects of taper geometry (C taper vs. V40 taper) and material combination (Ti-6Al-4V/CoCrMo vs. TMZF (Ti-Mo-Zr-Fe)/CoCrMo) as well as load rate and compliance were investigated using novel methodologies. The findings from these studies showed changes in the taper geometry affected the stiffness of the construct, fretting motions and the fretting corrosion performance while material combination had no significant effect. In terms of load rate and compliance, the study presented evidence to suggest load rate and system compliance had no significant effect on work of seating or taper locking stability

Space shuttle pogo studies

Topics covered include: (1) pogo suppression for main propulsion subsystem operation; (2) application of quarter-scale low pressure oxidizer turbopump transfer functions; (3) pogo stability during orbital maneuvering subsystem operation; and (4) errors in frequency response measurements

On the Use of Magnets to Robustify the Motion Control of Soft Hands

In this letter, we propose a physics-based framework to exploit magnets in robotic manipulation. More specifically, we suggest equipping soft and underactuated hands with magnetic elements, which can generate a magnetic actuation able to synergistically interact with tendon-driven and pneumatic actuations, engendering a complementarity that enriches the capabilities of the actuation system. Magnetic elements can act as additional Degrees of Actuation (DoAs), robustifying the motion control of the device and augmenting the hand manipulation capabilities. We investigate the interaction of a soft hand with itself for enriching possible hand shaping, and the interaction of the hand with the environment for enriching possible grasping capabilities. Physics laws and notions reported in the manuscript can be used as a guidance for DoAs augmentation and can provide tools for the design of novel soft hands

Cognitive Reasoning for Compliant Robot Manipulation

Physically compliant contact is a major element for many tasks in everyday environments. A universal service robot that is utilized to collect leaves in a park, polish a workpiece, or clean solar panels requires the cognition and manipulation capabilities to facilitate such compliant interaction. Evolution equipped humans with advanced mental abilities to envision physical contact situations and their resulting outcome, dexterous motor skills to perform the actions accordingly, as well as a sense of quality to rate the outcome of the task. In order to achieve human-like performance, a robot must provide the necessary methods to represent, plan, execute, and interpret compliant manipulation tasks. This dissertation covers those four steps of reasoning in the concept of intelligent physical compliance. The contributions advance the capabilities of service robots by combining artificial intelligence reasoning methods and control strategies for compliant manipulation. A classification of manipulation tasks is conducted to identify the central research questions of the addressed topic. Novel representations are derived to describe the properties of physical interaction. Special attention is given to wiping tasks which are predominant in everyday environments. It is investigated how symbolic task descriptions can be translated into meaningful robot commands. A particle distribution model is used to plan goal-oriented wiping actions and predict the quality according to the anticipated result. The planned tool motions are converted into the joint space of the humanoid robot Rollin' Justin to perform the tasks in the real world. In order to execute the motions in a physically compliant fashion, a hierarchical whole-body impedance controller is integrated into the framework. The controller is automatically parameterized with respect to the requirements of the particular task. Haptic feedback is utilized to infer contact and interpret the performance semantically. Finally, the robot is able to compensate for possible disturbances as it plans additional recovery motions while effectively closing the cognitive control loop. Among others, the developed concept is applied in an actual space robotics mission, in which an astronaut aboard the International Space Station (ISS) commands Rollin' Justin to maintain a Martian solar panel farm in a mock-up environment. This application demonstrates the far-reaching impact of the proposed approach and the associated opportunities that emerge with the availability of cognition-enabled service robots

Cyber-Physical Manufacturing Metrology Model (CPM3) - Big Data Analytics Issue

Internet of Things (IoT) is changing the world, and therefore the application of ICT (Information and Communication Technology) in manufacturing. As a paradigm based on the Internet, IoT utilizes the benefits of interrelated technologies/smart devices such as RFID (Radio Frequency Identification) and WSAN (Wireless Sensor and Actuator Networks) for the retrieval and exchange of information thus opening up new possibilities for integration of manufacturing system and its cyber representation through Cyber-Physical Manufacturing (CPM) model. On the other hand, CPM and digital manufacturing represent the key elements for implementation of Industry 4.0 and backbone for "smart factory" generation. Interconnected smart devices generate huge databases (big data), so that Cloud computing becomes indispensable tool to support the CPM. In addition, CPM has an extremely expressed requirement for better control, monitoring and data management. Limitations still exist in storages, networks and computers, as well as in the tools for complex data analysis, detection of its structure and retrieval of useful information. Products, resources, and processes within smart factory are realized and controlled through CPM model. In this context, our recent research efforts in the field of quality control and manufacturing metrology are directed to the development of framework for Cyber-Physical Manufacturing Metrology Model (CPM3). CPM3 framework will be based on: 1) integration of digital product metrology information obtained from big data using BDA (big data analytics) through metrology features recognition, and 2) generation of global/local inspection plan for CMM (Coordinate Measuring Machine) from extracted information. This paper will present recent results of our research on CPM3 - big data analytics issue

Teleprogramming: Overcoming Communication Delays in Remote Manipulation (Dissertation Proposal)

Modern industrial processes (nuclear, chemical industry), public service needs (firefighting, rescuing), and research interests (undersea, outer space exploration) have established a clear need to perform work remotely. Whereas a purely autonomous manipulative capability would solve the problem, its realization is beyond the state of the art in robotics [Stark et al.,1988]. Some of the problems plaguing the development of autonomous systems are: a) anticipation, detection, and correction of the multitude of possible error conditions arising during task execution, b) development of general strategy planning techniques transcending any particular limited task domain, c) providing the robot system with real-time adaptive behavior to accommodate changes in the remote environment, d) allowing for on-line learning and performance improvement through experience , etc. The classical approach to tackle some of these problems has been to introduce problem solvers and expert systems as part of the remote robot workcell control system. However, such systems tend to be limited in scope (to remain intellectually and implementationally manageable), too slow to be useful in real-time robot task execution, and generally fail to adequately represent and model the complexities of the real world environment. These problems become particularly severe when only partial information about the remote environment is available

Hybrid Open-Loop Closed-Loop Control of Coupled Human-Robot Balance During Assisted Stance Transition with Extra Robotic Legs

A new approach to the human-robot shared control of the Extra Robotic Legs (XRL) wearable augmentation system is presented. The XRL system consists of two extra legs that bear the entirety of its backpack payload, as well as some of the human operator's weight. The XRL System must support its own balance and assist the operator stably while allowing them to move in selected directions. In some directions of the task space the XRL must constrain the human motion with position feedback for balance, while in other directions the XRL must have no position feedback, so that the human can move freely. Here, we present Hybrid Open-Loop / Closed-Loop Control Architecture for mixing the two control modes in a systematic manner. The system is reduced to individual joint feedback control that is simple to implement and reliable against failure. The method is applied to the XRL system that assists a human in conducting a nuclear waste decommissioning task. A prototype XRL system has been developed and demonstrated with a simulated human performing the transition from standing to crawling and back again while coupled to the prototype XRL system

Component-Level Electronic-Assembly Repair (CLEAR) System Architecture

This document captures the system architecture for a Component-Level Electronic-Assembly Repair (CLEAR) capability needed for electronics maintenance and repair of the Constellation Program (CxP). CLEAR is intended to improve flight system supportability and reduce the mass of spares required to maintain the electronics of human rated spacecraft on long duration missions. By necessity it allows the crew to make repairs that would otherwise be performed by Earth based repair depots. Because of practical knowledge and skill limitations of small spaceflight crews they must be augmented by Earth based support crews and automated repair equipment. This system architecture covers the complete system from ground-user to flight hardware and flight crew and defines an Earth segment and a Space segment. The Earth Segment involves database management, operational planning, and remote equipment programming and validation processes. The Space Segment involves the automated diagnostic, test and repair equipment required for a complete repair process. This document defines three major subsystems including, tele-operations that links the flight hardware to ground support, highly reconfigurable diagnostics and test instruments, and a CLEAR Repair Apparatus that automates the physical repair process