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Management of socket fit is challenging for people using lower-limb prostheses because of residual limb volume fluctuation throughout the day. Releasing socket pressures during sitting (partial doffing) may help users increase their limb volume after they have undergone volume loss earlier in the day. The purpose of this research was to develop and evaluate a system to allow for quick and easy locking pin and socket panel release during sitting and relock upon standing. The system was to allow the partial doff tether length to be custom set for each user, accomplish release and relock in less than 2.0 s each, require only one hand, and require a finger push force comparable to a push button on a phone. A motor-driven release/relock system (240 g build weight) housed within the socket adjusts locking pin tether length, and an instrumented ratcheting dial adjusts socket panel position. Three participants with a trans-tibial amputation operated the system properly using one hand. For a partial doff, users preferred a tether length between 5 and 6 cm. All users executed release within 1.5 s and relock within 1.5 s.

A novel method is described to connect a prosthetic liner to the panels of an adjustable socket to facilitate limb fluid volume stabilization in prosthesis users. Magnets are placed in the socket panels, and iron powder is embedded in the user's prosthetic liner. When the magnet is in close proximity to the liner, a firm connection is formed. The system's capability to execute panel pull on transtibial prosthesis users was tested. The backs of the panels were supported by a bracket mounted to the external surface of the socket that allowed the radial position of the panels to be adjusted. Bench testing demonstrated an optimized strength-to-weight ratio using 1.27-cm thick annular-shaped magnets supported by 0.32-cm thick backplates. Testing on four people with transtibial amputation showed that the maximum socket increase achieved using magnetic panel pull ranged from 5.3% to 13.8% of the initial (panels flush) socket volume. The results indicate that magnetic panel pull induces a meaningful increase in socket volume during sitting. The clinical relevance is a novel strategy that may help stabilize prosthesis users' limb fluid volume over the day.

Confined space manufacturing tasks, such as cleaning pilot holes prior to installing fasteners during aircraft wing assembly, currently require human experts to be inside ergonomically-challenging environments. Small rapidly deployable robots can substantially improve manufacturing safety and productivity. However, relatively rapid full automation remains elusive due to high-level of uncertainty in the environment, lack of cost-effective programming for low volume production, and difficulty of deploying adequate number of sensors in the confined space. Moreover, currently, teleoperation (remote human control of a robot via a force-reflection device) with typical levels of training and limited transparency of hardware is too slow for manufacturing applications, requiring experts to spend more time for each task to achieve the same cleaning quality. In this context, the main contribution of this article is to reduce cycle times for remote manufacturing by learning statistical dynamic autonomy from higher quality expert demonstrations in an ideal offline scenario. During the task, to keep cycle times low, the dynamic autonomy imitates the faster expert demonstrations when certain, and employs the slower human teleoperation when uncertain. A user study (n = 8) with an experimental robot platform shows that for the same cleaning quality, the dynamic autonomy reduces process completion time by 54.0% and human operator energy expenditure by 80.5% as compared with teleoperation without dynamic autonomy.

Introduction The purpose of this study was to test a novel activity monitor that tracks the time a prosthesis is worn, and the nature of the ambulatory activity conducted with the prosthesis. These capabilities allow prosthesis users’ wear and accommodation practices (e.g., temporary doffing) to be monitored, and the intensity of their activities to be assessed. Methods A portable limb-socket motion sensing system was used to monitor doffs, walk bouts (≥5 steps), low locomotion (2–4 steps), stationary positions, and weight shifts in a group of transtibial prosthesis users. The relationship between doff time and active motion time was investigated, and durations of low and high intensity active motions were compared. Results For the 14 participants tested, the median prosthesis day duration ranged from 12.8–18.8 h. Eleven participants typically doffed five or fewer times per day, and three participants typically doffed 10 or more times per day. Nine participants demonstrated a positive correlation between daily doff duration and active motion duration. Six participants spent more time in weight shifts than walk bouts, while eight participants spent more time in walk bouts than weight shifts. Conclusion Capturing don time and temporary doffs and distinguishing weight shifts from walks may provide insight relevant to patient care. Longer-term monitoring studies should be conducted, and the clinical utility of the data evaluated.

The purpose of this research was to pursue an innovative cyclic panel-pull strategy during ambulation to minimize limb fluid volume loss in transtibial prosthesis users. Participants' traditional socket shapes were duplicated, and test sockets prepared with three adjustable motor-driven panels that were controlled by a microprocessor. After donning the prosthesis, participants' liners were fastened to the panels. During a 40 min test session, participants conducted three cycles of sitting (5 min) and walking (8 min). During the 5th and 6th min of each cycle of walking, the panels were cyclically pulled outward in late stance phase, decreasing pressure on the residual limb. Panels were returned to their original position in swing phase. Eight of twelve participants gained more fluid volume while walking when panel-pull was added than when it was removed. When the liner was uncoupled from the panels and panel-pull was executed, eight of twelve participants gained less fluid volume compared to when the liner was fastened to the panels. Panel-pull may facilitate limb fluid volume retention in transtibial prosthesis users. Efforts to simplify the design so that it can be implemented in long-term testing during at-home use should be considered.

Step activity monitors provide insight into the amount of physical activity prosthesis users conduct but not how they use their prosthesis. The purpose of this research was to help fill this void by developing and testing a technology to monitor bodily position and type of activity.Thin inductive distance sensors were adhered to the insides of sockets of a small group of transtibial prosthesis users, two at proximal locations and two at distal locations. An in-lab structured protocol and a semi-structured out-of-lab protocol were video recorded, and then participants wore the sensing system for up to 7 days. A data processing algorithm was developed to identify sit, seated shift, stand, standing weight-shift, walk, partial doff, and non-use. Sensed distance data from the structured and semi-structured protocols were compared against the video data to characterize accuracy. Bodily positions and activities during take-home testing were tabulated to characterize participants' use of the prosthesis.Sit and walk detection accuracies were above 95% for all four participants tested. Stand detection accuracy was above 90% for three participants and 62.5% for one participant. The reduced accuracy may have been due to limited stand data from that participant. Step count was not proportional to active use time (sum of stand, walk, and standing weight-shift times).Step count may provide an incomplete picture of prosthesis use. Larger studies should be pursued to investigate how bodily position and type of activity may facilitate clinical decision-making and improve the lives of people with lower limb amputation.

Strategies to maintain prosthesis users' daily limb volume are needed.Test how intermittent incremental socket volume adjustments affect limb fluid volume and limb-socket distance.Repeated measures.People with transtibial limb loss walked on an outdoor trail wearing a motor-driven adjustable socket that they adjusted a small amount, approximately 0.3% socket volume, every 2 min using a mobile phone app. Limb fluid volume and sensed distance between the socket and a target in their elastomeric liner were monitored. A gradual socket enlargement phase was followed by a gradual socket reduction phase.An incremental socket enlargement significantly increased limb fluid volume (Participants' residual limb fluid volume increases during ambulation compensated for incremental socket volume increases. For incremental socket volume decreases, residual limb fluid volume decreases did not compensate and the socket fit became tighter.Results support the hypothesis that for people without co-morbidities, intermittent incremental socket volume enlargements are an effective accommodation strategy to increase limb fluid volume while maintaining socket fit. Intermittent incremental socket volume reductions decreased limb fluid volume but also made the socket fit tighter.

Sockets that allow incremental size adjustment during ambulation may help prosthesis users improve management of their changes in limb volume and the quality of their prosthetic fit. A platform system was developed that allowed people with trans-tibial limb loss to adjust the radial positions of socket panels during ambulation in small increments via a motor mounted beneath the socket. The motor altered the length of a cable running through the socket panels according to commands communicated from a mobile phone. A proportional–integral–derivative controller adjusted the voltage applied to the motor via pulse-width modulation to achieve target settings. Bench test results showed that when the system was subjected to loads comparable to those expected during clinical use, maximum absolute steady state error was 0.036 mm. Treadmill testing on 16 people with trans-tibial limb amputation demonstrated that the range of cable lengths over which participants deemed fit clinically acceptable varied between 24 mm and 114 mm depending on the user. In field testing 11 of 13 participants were comfortable making socket size adjustments while walking. The developed system achieves incremental socket size adjustments appropriate for research and development of ambulatory adjustable sockets.

Background Small intermittent adjustments of socket size using adjustable sockets may be a means for people with transtibial amputation to better maintain residual limb fluid volume and limb position while using a prosthesis. Methods Socket size, limb fluid volume, and distance from the limb to the socket, termed “sensed distance,” were recorded while participants with transtibial amputation walked on a treadmill wearing a motor-driven, cabled-panel, adjustable socket. Researchers made frequent socket size adjustments using a mobile phone app to identify participants' acceptable socket size range. Limb fluid volume and sensed distance were then monitored as incremental adjustments were made to the socket. Findings Prosthesis users in this study (n = 10) accepted socket sizes between −5% and +5% of their neutral socket volume. There was a rapid increase in limb fluid volume and sensed distance upon socket enlargement, and a rapid decrease upon reduction. Subsequently, there were gradual changes in fluid volume and sensed distance. While visually monitoring limb fluid volume data in real time, researchers were able to adjust socket size to maintain consistent limb fluid volume within a −0.7% to +0.9% volume change for 24 min. Interpretation Participant residual limbs compensated to socket size adjustment. Using socket-mounted sensors to monitor limb-socket mechanics, an automatic adjustable socket that maintains limb fluid volume may be possible and may improve socket fit in instances where fit deteriorates during use.

This work aims to facilitate robotic-assisted limited-access manufacturing, where a mechanic manually performs work in an enclosed space while a robot guides a camera to allow the mechanic to observe visually-occluded operations. Gesture control allows the mechanic to adjust their camera view without requiring contact-based interaction through button presses or manual positioning of the robot, which would require setting down tools or exiting the enclosed space. Because the only input to the robotic platform’s gesture recognition system is a continuously tracked hand, there is potential for confusion between the motions of work and motions intended to communicate control. The main contribution of this article is to develop a separability metric Ψ for systematically selecting a set of control gestures that can be easily distinguished from a given set of work gestures. The context-specific control gesture selection process is implemented on a benchmark dataset to validate the method. The process is then implemented on a hand-following robot, and experimental results show that the proposed metric-based selection of the control gesture set results in the improvement of online gesture recognition across eight subjects even in the presence of application-specific distortions in the gestures.

During manufacturing, minor flaws in the surface of commercial airplane interior panels are often corrected using hand sanding, sometimes leading to repetitive stress injuries. Robotic sanding is an attractive option to mitigate these injuries. However, in preprogrammed automated sanding, both the sander path and the speed along that path are predetermined. Such fixed automation has limited effectiveness due to the part-to-part variability of surface condition. In addition, in typical fixed automation, a constant contact force and path speed are used to maintain constant material removal depth. Teleoperated robotic sanding allows a skilled operator to monitor the process and the condition of the surface in real time to correct the individual flaws. However, during teleoperated sanding, the path and speed along the path are inherently both time-varying and unknown a priori. The principal contribution of this work is to facilitate precision teleoperated sanding by developing a process model and control strategy that ensures constant material removal depth along the sanding path. Experimental results, with and without the proposed contact-force adjustments, for the same variable speed motion of the sander, shows 65% improvement in spatial variation of material removal with the proposed approach.

Objective: The purpose was to design, implement, and test a control system for a motor-actuated, cable-panel prosthetic socket that automatically maintains socket fit by continuous adjustment of the socket size. Methods: Sockets with motor-driven adjustable panels were fabricated for participants with transtibial amputation. A proportional-integral control system was implemented to adjust socket size based on Socket Fit Metric (SFM) data collected by an inductive sensor embedded within the socket wall. The sensed distance was representative of limb-to-socket distance. Testing was conducted with participants walking on a treadmill to characterize the system's capability to maintain a set point and to respond to a change in the set point. Results: Test results from 10 participants with transtibial amputation showed that the Integral of Absolute Error (IAE) to maintain a set point ranged from 0.001 to 0.046 mm with a median of 0.003 mm. When the set point was changed, IAE errors ranged from 0.001 to 0.005 mm, with a median of 0.003 mm. An IAE of 0.003 mm corresponded to approximately a 0.08% socket volume error, which was considered clinically acceptable. Conclusion: The capability of the control system to maintain and respond to a change in set point indicates that it is ready for evaluation outside of the laboratory. Significance: Integration of the developed control system into everyday prostheses may improve quality of life of prosthesis users by relieving them of the burden of continually adjusting socket size to maintain fit.

IntroductionA challenge in the engineering of auto-adjusting prosthetic sockets is to maintain stable operation of the control system while users change their bodily position and activity. The purpose of this study was to test the stability of a socket that automatically adjusted socket size to maintain fit. Socket release during sitting was conducted between bouts of walking.MethodsAdjustable sockets with sensors that monitored distance between the liner and socket were fabricated. Motor-driven panels and a microprocessor-based control system adjusted socket size during walking to maintain a target sensed distance. Limb fluid volume was recorded continuously. During eight sit/walk cycles, the socket panels were released upon sitting and then returned to position for walking, either the size at the end of the prior bout or a size 1.0% larger in volume.ResultsIn six transtibial prosthesis users, the control system maintained stable operation and did not saturate (move to and remain at the end of the actuator’s range) during 98% of the walking bouts. Limb fluid volume changes generally matched the panel position changes executed by the control system.ConclusionsStable operation of the control system suggests that the auto-adjusting socket is ready for testing in users’ at-home settings.

This work improves the positioning precision of lightweight robots with series elastic actuators (SEAs). Lightweight SEA robots, along with low-impedance control, can maneuver without causing damage in uncertain, confined spaces such as inside an aircraft wing during aircraft assembly. Nevertheless, substantial modeling uncertainties in SEA robots reduce the precision achieved by model-based approaches such as inversion-based feedforward . Therefore, this article improves the precision of SEA robots around specified operating points, through a multi-input multi-output (MIMO), iterative learning control (ILC) approach. The main contributions of this article are to (i) introduce an input-weighted complex kernel to estimate local MIMO models using complex Gaussian process regression (c-GPR); (ii) develop Gersgorin-theorem-based conditions on the iteration gains for ensuring ILC convergence to precision within noise-related limits, even with errors in the estimated model; and (iii) demonstrate precision positioning with an experimental SEA robot. Comparative experimental results, with and without ILC, show around 90% improvement in the positioning precision (close to the repeatability limit of the robot) and a 10-times increase in the SEA robot’s operating speed with the use of the MIMO ILC.

BACKGROUND Management of fluid in the limbs is a challenge faced by people with disabilities. In prosthetics, a means for transtibial prosthesis users to stabilize their residual limb fluid volume during the day may improve socket fit. OBJECTIVE To determine if releasing the panels and locking pin of a cabled-panel adjustable socket during socket release significantly improved limb fluid volume recovery and retention over releasing the panels alone. DESIGN Repeated-measures experiment to assess the effects on limb fluid volume retention. SETTING Participants were tested in a laboratory setting while walking on a treadmill. INTERVENTION Release of a locking pin tether during sitting as a limb volume accommodation strategy. MAIN OUTCOME MEASURE Percent limb fluid volume retention for panel and pin release compared with panel release alone at 2 minutes (short term) and 50 minutes (long term) after subsequent activity. Limb fluid volume was monitored using bioimpedance analysis. RESULTS Median percent limb fluid volume retention for the panel and pin release was significantly greater than panel release alone for both anterior and posterior regions for the long term (P = .0499 and .0096, respectively) but not the short term (P = .0712 and .1580, respectively). CONCLUSION Augmenting panel release with pin release may be an effective accommodation strategy for prosthesis users with transtibial amputation to better retain limb fluid volume.

Liner-to-socket distance measurement using inductive sensing may be an effective means to continuously monitor socket fit in people using trans-tibial prostheses. A practical limitation, however, is a means to incorporate a thin uniform-thickness layer of conductive or magnetically permeable target material into the wide range of prosthetic liner products that people with limb amputation commonly use. In this paper, a method is presented whereby a 0.50-mm thickness ferrous polymer made from a SEEPS polymer and iron powder that is formed adjacent to a 0.25-mm thick non-ferrous layer of SEEPS polymer is assembled between two sheets of elastic fabric material. Bench testing showed that the fabrication procedure achieved a root-mean-square error in the thickness of this construct of 58 &mu, m, helping to create a consistent calibration result over the entire surface. The original fabric backing of an off-the-shelf prosthetic liner was removed and replaced with the developed construct. When worn in the shoe of an able-bodied participant for 7.5 h per day for 28 days, the sensor well maintained the shape of its calibration curve at the start of wear, but a distance offset (shifting of the y-intercept) was introduced that increased during the initial approximately 12 days of wear. When the distance offset was corrected, for the primary distance range of clinical interest for this application (0.00&ndash, 5.00 mm), the sensor maintained its calibration within 4.4%. Before being used in clinical application for liner-to-socket distance monitoring, new ferrous liners may need to be pre-worn so as to achieve a consistent distance reference.

Background Residual limb volume loss is a source of prosthetic socket fit problems in people with lower-limb amputation. The aim of this study was to investigate a novel volume recovery strategy for people with trans-tibial amputation. Methods Test sockets for people with trans-tibial amputation were created that allowed panels of an adjustable socket and the underlying elastomeric liner to be pulled radially outward, using small motors mounted to the socket. One Control and one Intervention session were conducted with each participant. During Intervention sessions, panel-pull was executed during the sits of a multi-cycle sit/walk protocol. No panel-pull was executed during the Control sessions. Residual limb fluid volume was monitored in anterior and posterior regions using bioimpedance analysis. Findings Results from 12 participants demonstrated that short-term (12 min after the intervention was applied) median posterior residual limb fluid volume change for Intervention (0.44%) was higher than that for Control (−0.02%) (P = .015). Long-term (40 min after the intervention was applied) median posterior residual limb fluid volume change for Intervention (0.95%) was higher than that for Control (−0.26%) (P = .002). Interpretation If a panel-pull mechanism that was easy to assemble and operate could be created, then panel-pull may be an effective accommodation strategy to reduce daily limb volume loss in trans-tibial prosthesis users.

This article studies imitation learning policies that encode task compliance to provide teleoperation assistance for remote manufacturing. The central challenge is how to handle off-nominal situations, such as out-of-sequence work or unplanned obstacles, since the assistance has not been trained to handle such scenarios. In such cases, there is potential for the assistance to degrade-rather than improve-operator performance. This work proposes a method that exploits the learned task compliance to classify persistent human actions as off-nominal, and attenuate assistance in these regions. Applied to a hole-cleaning task with $n$ = 11 subjects, the proposed method shows up to 17% reduction in task completion time and up to 68% reduction in forces in off-nominal situations as compared to assistance without the method. Additionally, the method retains the performance improvements of assistance in nominal operating regimes.

We present a framework for modeling the transport of any number of globally conserved quantities in any spatial configuration and apply it to obtain a model of magnetization transport for spin-systems that is valid in new regimes (including high-polarization). The framework allows an entropy function to define a model that explicitly respects the laws of thermodynamics. Three facets of the model are explored. First, it is expressed as nonlinear partial differential equations that are valid for the new regime of high dipole-energy and polarization. Second, the nonlinear model is explored in the limit of low dipole-energy (semi-linear), from which is derived a physical parameter characterizing separative magnetization transport (SMT). It is shown that the necessary and sufficient condition for SMT to occur is that the parameter is spatially inhomogeneous. Third, the high spin-temperature (linear) limit is shown to be equivalent to the model of nuclear spin transport of Genack and Redfield. Differences among the three forms of the model are illustrated by numerical solution with parameters corresponding to a magnetic resonance force microscopy (MRFM) experiment. A family of analytic, steady-state solutions to the nonlinear equation is derived and shown to be the spin-temperature analog of the Langevin paramagnetic equation and Curie's law. Finally, we analyze the separative quality of magnetization transport, and a steady-state solution for the magnetization is shown to be compatible with Fenske's separative mass transport equation., Comment: 14 pages, 10 figures

We report the development of an instrumentation and control system instantiated on a microprocessor-field programmable gate array (FPGA) device for a harmonic oscillator comprising a portion of a magnetic resonance force microscope. The specific advantages of the system are that it minimizes computation, increases maintainability, and reduces the technical barrier required to enter the experimental field of magnetic resonance force microscopy. Heterodyne digital control and measurement yields computational advantages. A single microprocessor-FPGA device improves system maintainability by using a single programming language. The system presented requires significantly less technical expertise to instantiate than the instrumentation of previous systems, yet integrity of performance is retained and demonstrated with experimental data.

When robots operate in unknown environments small errors in postions can lead to large variations in the contact forces, especially with typical high-impedance designs. This can potentially damage the surroundings and/or the robot. Series elastic actuators (SEAs) are a popular way to reduce the output impedance of a robotic arm to improve control authority over the force exerted on the environment. However this increased control over forces with lower impedance comes at the cost of lower positioning precision and bandwidth. This article examines the use of an iteratively-learned feedforward command to improve position tracking when using SEAs. Over each iteration, the output responses of the system to the quantized inputs are used to estimate a linearized local system models. These estimated models are obtained using a complex-valued Gaussian Process Regression (cGPR) technique and then, used to generate a new feedforward input command based on the previous iteration's error. This article illustrates this iterative machine learning (IML) technique for a two degree of freedom (2-DOF) robotic arm, and demonstrates successful convergence of the IML approach to reduce the tracking error., Comment: 9 pages, 16 figure. Submitted to AMC Workshop

Assembly fixtures that are much smaller than the structure being manufactured, such as an aircraft, must routinely be positioned and docked against the structure on which they act. The major contribution of this article is to develop a variable-impedance-based human-machine control for the docking process. The issues investigated are: (i) impedance control to facilitate intuitive human force input; and (ii) utilizing variable damping to aid docking and safeguard both the fixture and structure. A single-degree-of-freedom experimental test bed is used to simulate docking using the proposed controller, and to explore how controller parameter choices impact overall performance.

In this paper we present heterodyne control as a technique for digital feedback control of a high-frequency, narrowband micromechanical oscillator. In this technique, isolated and synchronized hardware downconversion and upconversion components are used in conjunction with digital signal processing (DSP) to control the oscillator. Heterodyne control offers reduced computational effort for the digital control of high-frequency, narrow band system, the reduction of noise outside the pass-band, and the generation of lock-in amplifier signals. We present heterodyne control with design criteria in the context of magnetic resonance force microscopy (MRFM) cantilever control. Finally, we present experimental results of heterodyne control applied to an emulated radio-frequency microcantilever system.

Magnetic resonance force microscopy (MRFM) images the three-dimensional spatial distribution of resonant spins by mechanical force detection. Image reconstruction in MRFM is challenging because the resonance occurs in a strongly curved shell that extends beyond the scan range. In contrast with conventional magnetic resonance imaging, where Fourier techniques work well, the curved-shell resonant geometry inherent to MRFM requires novel reconstruction methods. Here, we show the application of iterative reconstruction in an electron spin resonance imaging experiment with 80 nm voxels. The reconstructed image has a total scan volume of 0.5 cubic micrometers, and was generated by a magnetic resonant shell with a curvature radius of 2.3 μm. The imaged object was a paramagnetically doped solid with an obliquely tilted surface. The reconstructed image correctly identified the location and orientation of the surface, and mapped the spin distribution within the solid. Applications of MRFM include three-dimensional nanometer-scale mapping of dopant distributions in semiconductors, studies of magnetism of thin films, and spin diffusion physics. An ultimate goal of MRFM is the direct observation of molecular structure at the atomic scale.

Thermal fluctuations generate magnetic noise in the vicinity of any conductive and/or magnetically permeable solid. This magnetic noise plays a fundamental role in the design of spintronic devices: namely, it sets the time scale during which electron spins retain their coherence. This paper presents a rigorous classical and quantum analysis of thermal magnetic noise, together with practical engineering examples. Starting with the fluctuation-dissipation theorem and Maxwell's equations, a closed-form expression for the spectral density of thermal magnetic noise is derived. Quantum decoherence, as induced by thermal magnetic noise, is analyzed via the independent oscillator heat bath model of Ford et al. The resulting quantum Langevin equations yield closed-form expressions for the spin relaxation times. For realistic experiments in spintronics, magnetic resonance force microscopy, Bose-Einstein condensates, atomic physics, and solid-state quantum computing, the predicted relaxation rates are rapid enough that substantial experimental care must be taken to minimize them. At zero temperature, the quantum entanglement between a spin state and a thermal reservoir is computed. The same Hamiltonian matrix elements that govern fluctuation and dissipation are shown to also govern entanglement and renormalization, and a specific example of a fluctuation-dissipation-entanglement theorem is constructed. We postulate that this theorem is independent of the detailed structure of thermal reservoirs, and therefore expresses a general thermodynamic principle.

An apparatus was developed to apply user-specified displacements to biomaterial samples in culture. The device allowed cyclic waveforms of bandwidth 0 Hz to 20 Hz to be applied under physiologic thermal (37.5/spl deg/C) and [CO/sub 2/] (5%) conditions. For a 0 Hz to 20 Hz bandwidth signal similar in shape to a ventricular pressure waveform, the mean displacement error was 0.26% of the full-scale output. The maximum overshoot was 0.700%. Environmental system evaluation tests demonstrated a specimen cartridge temperature of 37.20/spl plusmn/0.15/spl deg/C during cyclic loading and 37.23/spl plusmn/0.21/spl deg/C during static conditions, [CO/sub 2/] was 5.29/spl plusmn/0.54% during cyclic loading and 5.25/spl plusmn/0.61% during static conditions. Laminar flow applied at the loading rod entrances to the specimen cartridge ensured the sample remained sterile during testing. As a preliminary evaluation, polyurethane samples were seeded with fetal foreskin fibroblasts and subject to intermittent cyclic displacements. Results demonstrated enhanced cell proliferation and increased [PGE/sub 2/] for samples subjected to 10% strain compared with unstrained controls. A next step will be to evaluate cell response sensitivity to strain magnitude, duration, direction, and frequency. The long-term intent is to establish mechanical loading configurations that induce acceptable or adaptation-inducing responses for use in implant design and tissue engineering applications.

A simple mechanism regulating polymer mobility is demonstrated to determine initial and final growth states of solid-state microcellular foams. This mechanism, governed by the extent of plasticization of the polymer by the dissolved gases, is examined with a mass balance model and results from foam growth experiments. Polycarbonate was exposed to CO2, which acted as both a plasticizing gas and a physical blowing agent driving foam growth. The polycarbonate specimens were saturated to the equilibrium gas concentration at 25 °C for CO2 pressures of 1–6 MPa in 1-MPa increments. Equilibrated specimens were heated in a glycerin bath until thermal equilibrium was reached, and a steady foam structure was attained. Glycerin bath temperatures of 30–150 °C in 10 °C increments were examined. Using knowledge of gas solubility, the equation of state for CO2, the effective glass-transition temperature as a function of gas concentration, and a model for mass balance within a solid-state foam, we demonstrate that foam growth terminates when sufficient gas is driven from the polycarbonate matrix into the foam cells. The foam cell walls freeze at the elevated bath temperature because of gas transport from the polycarbonate matrix and the associated rise in the polymer glass-transition temperature to that of the heated bath. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 868–880, 2001

The mechanism for nucleation phenomenon in solid-state microcellular foams is identified as a solid-state failure process. This process originates at internal flaws within the gas-polymer matrix, where it is induced by the presence of a state of hydrostatic tensile stress within the polymer matrix. The hydrostatic tensile stress is caused by the presence of the saturating gas within the polymer. The nucleation phenomenon is thermally activated at the effective glass transition temperature of the gas-polymer mixture. At this critical temperature, the hydrostatic tensile stress within the gas-polymer mixture is sufficient to cause the polymer matrix to fail, thereby creating a foam cell nucleus. In general, the nucleation sites are observed to be flat, approximately circular, fracture sites. After the appearance of the initial fracture, gas diffuses from the gas-polymer matrix into the fracture. The fracture seam inflates during the growth process, in which growth begins with the appearance of a disk shaped fracture and concludes with an approximately spherical cell. The results and conclusions presented herein suggest a new avenue to explain the cell nucleation phenomena observed in this process.

The goals of optimal control in force microscopy are: (1) to obtain favorable cantilever dynamic properties and (2) to control the cantilever to a desired amplitude, while (3) exerting as little control force as possible, and (4) preserving the force signal-to-noise ratio of the uncontrolled cantilever. This article describes the experimental implementation of an optimal controller that achieves these goals. The application of this controller to an ultrasoft cantilever with spring constant of 110 μN/m at 10 K reduced the resonant quality from 15 000 to 220, reduced the Brownian amplitude from 11.2 A to 1.4 A, used less than 7×10−17 N of control effort, left the force sensitivity unaltered at 9.8×10−18 N/ Hz, and demonstrated feedback control can force cantilever motion to track a reference input.

An important skill for any design engineer is the ability to embed a computational element into a mechanical product or process. A course in embedded computing suitable for senior undergraduates in a mechanical engineering curriculum is described. The course, which includes both lectures and laboratory exercises, has evolved through our experiences in teaching embedded computing during the past decade and a half. In preparing to modernize this course, we have reexamined the academic ideas on which the course is based and the conflicting issues involved in developing a course in embedded computing with a hands-on laboratory. These issues and our expectations for the future of embedded computing instruction in our department are discussed.

Instrumentation was developed to apply controlled biaxial (normal and shear) forces to the skin of a human or animal subject. The instrument mimicked any reference waveform within the constraints of a bandwidth of 15 Hz, a maximum force of 20 N, and displacement ranges of 15 mm for the normal direction and 18 mm for the shear direction. Two shaker motors, positioned with their axes parallel, were used with a low effective mass linkage and small-angle rotational joints to deliver the force. A digital feedback controller independently controlled the instantaneous normal and shear forces and recorded the resultant displacements. Evaluations on human and animal (pig) subjects demonstrated mean absolute errors between the applied and reference waveforms of less than 1.2% full-scale output for both the normal and shear directions. No degradation in performance was apparent over the course of a 1-h loading session. The instrument is to be used for the investigation of skin adaptation to mechanical stress, information that could be used to design new therapeutic methods to encourage skin load-tolerance.

The detailed design of a mechanically detected nuclear magnetic resonance probe using the SPAM (Springiness Preservation by Aligning Magnetization) geometry, operating at 4 K, in vacuum, and a several-Tesla magnetic field is described. The probe head is vibration-isolated well enough from the environment by a three-spring suspension system that the cantilever achieves thermal equilibrium with the environment without the aid of eddy current damping. The probe uses an ultra-soft Si cantilever with a Ni sphere attached to its tip, and magnetic resonance is registered as a change in the resonant frequency of the driven cantilever. The RF system uses frequency sweeps for adiabatic rapid passage using a 500 μm diameter RF coil wound around a sapphire rod. The RF coil and optical fiber of the interferometer used to sense the cantilever's position are both located with respect to the cantilever using a Garbini micropositioner, and the sample stage is mounted on an Attocube nanopositioner.

Parametric coupling has been demonstrated between mechanical vibration modes in a magnet-tipped microcantilever. An external magnetic field, coupled to the magnetic tip, pumps the effective spring constant at a frequency which is either the sum or the difference of the mode resonance frequencies. The presence of the pump field can be detected by driving one mode and observing the parametrically pumped excitation of the other mode, even though the pump frequency is off-resonance with respect to both mechanical modes. In a room temperature experimental realization, the magnetic flux coupling the pump field to the tip was approximately one flux quantum and the dominant noise source was the thermal vibration of the cantilever. Parametric mode coupling is a useful new design option in magnetic resonance force microscopy, whereby modulation is advantageously performed off-resonance to avoid parasitic excitations caused by stray couplings. Parametric coupling also provides a low-noise technique for amplifying mechanical oscillations. The reported experiment completes the set of all possible force microscope interaction Hamiltonians up to third order in time-dependent fields.

In magnetic resonance force microscopy (MRFM) experiments, magnetic forces couple to the motion of microscale cantilever beams. Extension of MRFM to the detection of single electrons will require both unprecedented force sensitivity and motional stability of the cantilever. We describe the principles and performance of optimal cantilever motion control. The method accounts for inherent noise processes and practical application of control forces. We show that active feedback control improves cantilever motional stability, enabling instrument designs of much higher sensitivity and faster imaging than passive designs. Experimental results of implemented cantilever control systems are presented in Part II.

We describe the implementation of optimal controllers for damping the motion of cantilevers used in magnetic resonance force microscopy. We demonstrate that optimal control is achievable and that torsional magnetic coupling provides an effective actuation method. Cantilever Brownian vibrational amplitude was reduced from 2 to 0.16 A and resonant quality was reduced from 2000 to 5. Applied control fields were sufficiently small that they would not affect magnetic resonance phenomena.

This article presents a new modulation technique for noise reduction in magnetic resonance force microscopy. Applied fields are modulated at frequencies that are not rational fractions of the cantilever resonant frequency, thus avoiding overtones that contribute to the noise level. An on‐resonance signal is obtained because the nonlinear sample magnetization acts as a frequency mixer of the two modulation frequencies, producing a net force modulation at the cantilever resonant frequency. These techniques are experimentally demonstrated using electron spin resonance in a

Recent initial experiments in magnetic resonance force microscopy (MRFM) have detected the magnetic force exerted by electrons and nuclei in microscopic samples. The experiments generate a force signal by modulating the sample magnetization with standard magnetic resonance techniques. Sample sizes of a few nanograms generate readily detected force signals of order ${10}^{\ensuremath{-}14}$ to ${10}^{\ensuremath{-}16}$ Newtons. This article describes the present status of MRFM technology, with particular attention to the feasibility of detecting single-electron magnetic moments, and the possible applications of MRFM in biological imaging.

This article describes systems in which the precession of a single particle spin is magnetically coupled to the excitation of an oscillator. The behavior of such systems resembles that of a ‘‘folded’’ Stern–Gerlach experiment, in which the linear spatial trajectory of the original Stern–Gerlach experiment is folded into the cyclic trajectory of an oscillator. Both quantum and semiclassical solutions to the equations of motion are derived. The results encompass any kind of oscillator which couples to a magnetic field. Examples include mechanical cantilevers with a magnetic source affixed to them, as well as inductor‐capacitor resonant circuits. One potential application of oscillator‐coupled magnetic resonance is the imaging of biological molecules. Some design issues relevant to molecular imaging are discussed.

The use of fringe-field capacitive sensing for surface profile measurement during the turning process is described. Measurements of the local surface height are inferred from variations in a fringe electric field induced between the sensing element and the workpiece. The surface profile is determined from high-speed scanning of the sensing element across the surface. The technique is particularly well-suited to the relatively harsh environment of in-process measurement. We have implemented a system in which profile measurements are made continuously, in real-time, and immediately adjacent to the cutting tool. The results of tests conducted to determine the accuracy and sensitivity of this capacitive profilometer are presented. In-process measurements of surfaces generated by turning with roughness in the range of 0.3 to 4.0 μm were made. Comparisons with static profile measurements made using standard stylus instrumentation are presented, and show quantitative agreement.

Machining of graphite/epoxy composite material is investigated by turning (cutoff) tests using different grades of polycrystalline diamond (PCD) inserts. The wear behavior of the PCD cutting edge is characterized by small cracks, rounded edges, and flank wear. The flank wear growth rate was found to depend on the microstructure of the tool and machining time. The coarser the PCD grade was, the better the wear resistance. The machined surface characteristics were evaluated by analyzing the surface roughness data and by scanning electron microscopy inspection of machined surface textures. Surface quality was found to get better with the cutting time.

This paper presents a theoretical analysis of the equilibrium mechanics of bending and twisting fiber geometries in ligaments and tendons. The theory predicts that the bending of loaded fibers is necessarily accompanied by large transverse pressures and pressure gradients. The predicted pressures are especially large at the bone tunnel entries of ligament grafts, where they can equal or exceed the applied tensile loads. Experimental measurements of internal pressures confirm these predictions.

We describe a fiber-optic interferometer that employs wavelength changes to achieve maximum sensitivity. Wavelength changes are induced by adjusting the operating temperature of the laser, eliminating the need for an actuator to vary the spacing between the sensing fiber and the object to be monitored. The instrument and techniques described are suitable for cryogenic, high vacuum applications such as magnetic resonance force microscopy, where space is limited and micromanipulation can be challenging. The noise floor of 1.6×10−3 nm/Hz is adequate for monitoring subangstrom displacement of force microscope cantilevers.

We proposed to complete three tasks in this project. These tasks were MRFM imaging with nanometer-scale resolution end-to-end performance analysis of quantum spin imaging and a reference design for a year-20O6 quantum microscope. At the time of this report, nanometer-scale MRFM imaging has been achieved at 8Onm resolution. A performance analysis was completed, and published as an invited paper in the Proceedings of the IEEE on the Classical and Quantum Theory of Thermal Magnetic Noise. With recent work in spin simulation exactly matching recent experiments performed at IBM, this technical report represents the deliverable of a complete Reference Design and Performance Analysis (RDPA) as originally proposed.

Bearings commonly are modeled as a linear viscous element. This behavior is easily confirmed with a simple, inexpensive experiment using only a wristwatch and a bicycle equipped with a speedometer. With the bicycle inverted so that its rear wheel is free to spin, this experiment involves observing and recording the variation of the angular velocity of the rear wheel as it decelerates from some initial speed. This experiment is a group activity, requiring teamwork to record the data by hand. From the data recorded and an estimate of the moment of inertia of the wheel, students determine the time constant of the system, the degree to which first-order response is exhibited by the system, and the equivalent damping coefficient for the bearings that support the rear wheel. Because of the familiarity of the components of the system being examined, the simplicity of the experiment, the teamwork required in the experiment, and the high degree of agreement between the analytical predictions and the experimental results, this experiment is an excellent experiment in system dynamics.Copyright © 2003 by ASME

As part of the Manufacturing Engineering Educational Partnership (MEEP) design and manufacturing courses have been restructured into a sequence leading to a Program in Products Realization (PPR) in our undergraduate engineering curriculum. The purpose is to provide a broad based, interdisciplinary program for undergraduate students interested in the design and manufacturing of industrial products. Although each school has taken a slightly different approach to the implementation, the students at the three schools experience design and manufacturing activities each semester (or quarter) in residence. The program bridges the gap between engineering science and practice, and allows students to work in teams on real industrial problems. The implementation of the program has required restructuring of existing courses, the addition of new resources, and the creation of Learning Factories at each of the institutions. The Learning Factories provide modern facilities for design, manufacturing, fabrication, and testing of products. In addition, the program has attracted the support of over 100 industrial sponsors, who have helped promote hands-on experience and provided projects and class room support. This paper describes the new program at each of the institutions, the resources required, and operational experiences to date. This project was supported by the ARPA Technology Reinvestment Program and the National Science Foundation.

We report theory and observations of paramagnetic resonance in a measured field gradient of 44,000 T per meter by the technique of magnetic resonance force microscopy (MRFM). Resonance was induced in a dilute solid solution of diphenylpicrylhydrazyl in polystyrene at 77 and 10 K by an amplitude-modulated microwave field. This modulated the force between resonant sample spins and a micrometer-scale SmCo magnetic tip on a force microscope cantilever. The force signals were typically of order 10 fN, and were detected above a thermal noise floor of 80 aN per root hertz at 10 K, equivalent to a magnetic moment noise of 200 μ B per root hertz of bandwidth. Resonance saturation was readily observed. Starting with the Bloch equations, we derived simple analytic expressions for the predicted cantilever signal amplitudes and T 1 -dependent phase lags, valid at low microwave power levels. For power levels below saturation, the data were in good agreement with the Bloch equation predictions, while above saturation the measured force increased more slowly with power than predicted. Several ESR mechanisms which might lead to non-Bloch dynamics in the MRFM environment are reviewed. Spin-relaxation mechanisms are also reviewed. A detailed description of the experimental apparatus is offered.

Capstone design courses in engineering, which provide students the opportunity to tackle open-ended, real-world projects, are generally held in high regard as learning experiences. A relatively new and increasingly important component of engineering is the area of mechatronics. In this paper, we review the goals of capstone design courses and examine how well suited mechatronics projects are for use as projects in capstone design courses. Our experiences in using mechatronics projects in the senior-level capstone design course in the Department of Mechanical Engineering at the University of Washington are presented. From these experiences, we demonstrate that mechatronics projects are particulary well suited for use in capstone design.

Mechatronics is the synergistic combination of mechanical, electrical, and computer technologies in the design of complex products and processes. Recent rapid growth of mechatronics as an area of engineering has given rise to a significant demand for mechatronics engineers. At the university level, engineering programs have emerged that help meet this need by producing engineering graduates who are capable, well-rounded mechatronics designers. One such program is the multi-course guided curriculum in mechatronics that is available to students in their senior year in the Mechanical Engineering Department at the University of Washington. Described in this paper are that mechatronics program as a whole, the curriculum into which it fits, the individual constituent courses, and our observations after offering this program for two years.

Recently the first experiments in magnetic resonance force microscopy (MRFM) have been conducted. In these experiments a force microscope cantilever is used to detect the magnetic force exerted by electrons and nuclei in a sample. The magnetization of the sample is modulated at the resonant frequency of the cantilever, using standard magnetic resonance techniques. The resulting excitation of the cantilever is detected optically. This article reviews the present status of MRFM technology, emphasizing the physical principles involved and the opportunities for further research and development. Particular emphasis is placed on single spin detection by MRFM and potential applications in biomolecular imaging.