Daniel W. Repperger

Modeling the dynamic characteristics of pneumatic muscle.

AbstractA pneumatic muscle (PM) system was studied to determine whether a three-element model could describe its dynamics. As far as the authors are aware, this model has not been used to describe the dynamics of PM. A new phenomenological model consists of a contractile (force-generating) element, spring element, and damping element in parallel. The PM system was investigated using an apparatus that allowed precise and accurate actuation pressure (P) control by a linear servovalve. Length change of the PM was measured by a linear potentiometer. Spring and damping element functions of P were determined by a static perturbation method at several constant P values. These results indicate that at constant P, PM behaves as a spring and damper in parallel. The contractile element function of P was determined by the response to a step input in P, using values of spring and damping elements from the perturbation study. The study showed that the resulting coefficient functions of the three-element model describe the dynamic response to the step input of P accurately, indicating that the static perturbation results can be applied to the dynamic case. This model is further validated by accurately predicting the contraction response to a triangular P waveform. All three elements have pressure-dependent coefficients for pressure P in the range 207 ⩽ P⩽ 621 kPa (30⩽ P⩽ 90 psi). Studies with a step decrease in P (relaxation of the PM) indicate that the damping element coefficient is smaller during relaxation than contraction.© 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8719Ff, 8710+e, 8768+z

The intentional spring : a strategy for modeling systems that learn to perform intentional acts

In motor task learning by instruction, the instructors skill and intention, which, initially, are extrinsic constraints on the learners perceiving and acting, eventually become internalized as intrinsic constraints by the learner. How is this process to be described formally? This process takes place via a forcing function that acts both as an anticipatory (informing) influence and a hereditary (controlling) influence. A mathematical strategy is suggested by which such intentions and skills might be dynamically learned. A hypothetical task is discussed in which a blindfolded learner is motorically instructed to pull a spring to a specific target in a specific manner. The modeling strategy involves generalizing Hookes law to the coupled instructor-spring-Learner system. Specifically, dual Volterra functions express the anticipatory and hereditary influences passed via an instructor-controlled forcing function on the shared spring. Boundary conditions (task goals) on the instructor-spring system, construed as a mathematical (self-adjoint) operator, are passed to the learner-spring system. Psychological interpretation is given to the involved mathematical operations that are passed, and mathematical (Hilbert-Schmidts and Greens function) techniques are used to account for the release of the boundary conditions by the instructor and their absorption by the learner, and an appropriate change of their power spectra.

Fuzzy PD+I learning control for a pneumatic muscle

A fuzzy learning control technique is used for position tracking involving the vertical movement of a mass attached to a pneumatic muscle. Because the pneumatic muscle is nonlinear and time varying, conventional fixed controllers are less effective than the fuzzy controller proposed in this paper. The controller is of a PID type, with an adaptive fuzzy PD part and a nonfuzzy integral branch. A novelty of the controller is that the fuzzy inverse model, which dynamically adjusts the PD part of the controller, incorporates the internal PM pressure as an input. Experimental results are presented from the pneumatic muscle test facility in the Human Effectiveness Laboratory at Wright-Patterson Air Force Base.

A VSC position tracking system involving a large scale pneumatic muscle actuator

A variable structure controller (VSC) is developed to provide position tracking capability for a very large pneumatic muscle actuator, which has inherently nonlinear dynamics. After the controller design is completed, the internal dynamics of the closed-loop system are shown to be stable. Robustness and passivity issues are then discussed. The switching law is modified to account for the different dynamics through the use of a composite Lyapunov function which guarantees asymptotic tracking stability.

Prolongation of simple and choice reaction times in a double-blind comparison of twice-daily hydroxyzine versus terfenadine

Newer, nonsedating antihistamines provide a therapeutic alternative for the patient with allergy whose work is impaired by the side effects of traditional H1 antihistamines. To assess the differential effect of these antihistamines on reaction times and subjective symptoms, we compared terfenadine, 60 mg twice daily, to hydroxyzine, 25 mg twice daily, in a double-blind, placebo-controlled, crossover study of 16 healthy, asymptomatic adults. Simple reaction time and choice reaction time were measured with a computer-based, eye-hand, reaction-time testing apparatus. Reaction times and symptom scores were assessed 90 minutes after the fourth and tenth doses of each drug. Hydroxyzine, but not terfenadine, significantly prolonged both simple and choice reaction time (p less than or equal to 0.0001). However, decision time, the time to process one bit of spatial information, was not prolonged by either antihistamine. Therefore, hydroxyzine prolonged the interpretation and response to stimuli of the central nervous system without increasing single-bit processing time. Although terfenadine was not different from placebo for any symptom assessed, hydroxyzine produced significant drowsiness (p = 0.001), dry mouth (p = 0.022), and irritability (p = 0.021). During the 5 days of hydroxyzine administration, neither objective nor subjective symptoms demonstrated the development of tolerance. No correlation was found between subjective symptoms and prolongation of reaction times by hydroxyzine, suggesting that side effect symptoms of traditional antihistamines are unreliable predictors of objective performance. Terfenadine provides a promising therapeutic alternative to traditional antihistamines for individuals performing critical tasks.

Development of a mobility assist for the paralyzed, amputee, and spastic patient

An exoskeleton system is being developed to aid in the mobilization of walking-impaired patients. New approaches to personal robotic assists have solved many classic problems with weight, power, endurance, and cost. A versatile platform of development allows for many variations and applications including mobility assist for the paralyzed, amputee, and spastic patient (MAPAS). A variety of strap on supports and braces are used, depending on the magnitude of the forces required. The MAPAS system utilizes compressed gas to power the main force producing elements, or muscles. Pneumatic muscles are used to provide controllable joint torque with moderate levels of pressure. These muscles are mounted to the brace, providing pull-only torque to joints. The MAPAS control system features interpreted joint mapping. The function of each leg joint is primarily directed through the output of a finger joint sensor. A six to eight sensor hand goniometer provides the system with user input. Higher control features actuated by on-board intelligent devices enable finger joint inputs to be enhanced providing balance, gait anticipation, fault-recovery, and spasm signature compensation. Ambient pressure levels of on-board reservoirs can be changed to suit changing environments ranging from heavily loaded amputee walking up stairs to the slight correction of a mild spasm. The entire system is portable with on-board batteries, compressed air reservoirs, intelligent algorithms, and goniometric sensors.

On Extending the Wave Variable Method to Multiple-DOF Teleoperation Systems

It is well known that providing a human operator with contact force information can significantly improve task performance in a teleoperation system. Unfortunately, time delay is a serious problem for such systems. Even a small time delay in a bilateral teleoperation system will generally degrade the systems performance and cause instability. Consequently, without some form of compensation for time delay, latencies in a teleoperation system would preclude the use of force feedback. Fortunately, there are approaches based on scattering theory and passivity that can compensate for time delay and allow the use of force feedback in teleoperation systems with latencies. In particular, the wave variable method is a passivity-based approach that guarantees stability for any fixed time delay. Since its introduction, the wave variable method has been augmented with predictors to compensate for variable time delay. The wave variable formalism has also been extended to multiple-DOF systems by replacing scalar damping constants with a family of impedance matrices. In this paper, the authors generalize this last approach to include a larger family of impedance matrices. The paper includes a complete derivation of the extended family of impedance matrices as well as simulation and experimental results to illustrate the approach.

Evaluation of eye metrics as a detector of fatigue.

Objectives: This study evaluated oculometrics as a detector of fatigue in Air Force–relevant tasks after sleep deprivation. Using the metrics of total eye closure duration (PERCLOS) and approximate entropy (ApEn), the relation between these eye metrics and fatigue-induced performance decrements was investigated. Background: One damaging effect to the successful outcome of operational military missions is that attributed to sleep deprivation-induced fatigue. Consequently, there is interest in the development of reliable monitoring devices that can assess when an operator is overly fatigued. Method: Ten civilian participants volunteered to serve in this study. Each was trained on three performance tasks: target identification, unmanned aerial vehicle landing, and the psychomotor vigilance task (PVT). Experimental testing began after 14 hr awake and continued every 2 hr until 28 hr of sleep deprivation was reached. Results: Performance on the PVT and target identification tasks declined significantly as the level of sleep deprivation increased. These performance declines were paralleled more closely by changes in the ApEn compared to the PERCLOS measure. Conclusion: The results provide evidence that the ApEn eye metric can be used to detect fatigue in relevant military aviation tasks. Application: Military and commercial operators could benefit from an alertness monitoring device.

Biomimetic model of skeletal muscle isometric contraction: I. an energetic–viscoelastic model for the skeletal muscle isometric force twitch

This paper describes a revision of the Hill-type muscle model so that it will describe the chemo-mechanical energy conversion process (energetic) and the internal-element stiffness variation (viscoelastic) during a skeletal muscle isometric force twitch contraction. The derivation of this energetic-viscoelastic model is described by a first-order linear ordinary differential equation with constant energetic and viscoelastic coefficients. The model has been implemented as part of a biomimetic model, which describes the excitation-contraction coupling necessary to drive the energetic-viscoelastic model. Finally, the energetic-viscoelastic model is validated by comparing its isometric force-time profile with that of various muscles reported in the literature.

A study of pneumatic muscle technology for possible assistance in mobility

Pneumatic muscles, in an actuation paradigm, provide a new form of technology which can be used to facilitate and provide strength or mobility assistance. This paper concentrates on how such a system as a balloon which expands within an enclosed sheath surface highly compliant in one direction (radial) and highly noncompliant in the orthogonal direction (axial) can be utilized to provide rehabilitation assistance. The actuator described herein has the unique advantages of having the largest ratio of power/weight and power/volume as compared to hydraulic or electric motor analogs which would perform this function. Studies on the nonlinearities of the composite system under consideration are conducted. As a totally integrated assemblage, the approach here is to treat the actuator like any rigid material substance and to determine both the equivalent Youngs modulus and Poissons ratio.