James Shippen

Robust backstepping and neural network control of a low- quality nonholonomic mobile robot

A robust motion controller based on neural network and backstepping technique is proposed for a two-DOF low-quality mobile robot (MR). There are two main components in the motion controller. One is the tracking controller, which guarantees the MR follows the reference trajectory; the other one is the wheel-level inverse NN controller, which compensates the dynamics of the MR. Simulation results are provided to validate the proposed controllers. Experiments with a real low-quality MR, which were built from cheap drivelines, have been used to verify the effectiveness and robustness of the motion controller.

Consistency Among Musculoskeletal Models: Caveat Utilitor

Musculoskeletal simulation software and model repositories have broadened the user base able to perform musculoskeletal analysis and have facilitated in the sharing of models. As the recognition of musculoskeletal modeling continues to grow as an engineering discipline, the consistency in results derived from different models and software is becoming more critical. The purpose of this study was to compare eight models from three software packages and evaluate differences in quadriceps moment arms, predicted muscle forces, and predicted tibiofemoral contact forces for an idealized knee-extension task spanning −125 to +10° of knee extension. Substantial variation among models was observed for the majority of aspects evaluated. Differences among models were influenced by knee angle, with better agreement of moment arms and tibiofemoral joint contact force occurring at low to moderate knee flexion angles. The results suggest a lack of consistency among models and that output differences are not simply an artifact of naturally occurring inter-individual differences. Although generic musculoskeletal models can easily be scaled to consistent limb lengths and use the same muscle recruitment algorithm, the results suggest those are not sufficient conditions to produce consistent muscle or joint contact forces, even for simplified models with no potential of co-contraction.

Can FES-rowing mediate bone mineral density in SCI: a pilot study

Study design:A single case study.Objectives:To compare proximal tibia trabecular bone mineral density (BMD) of a participant with complete spinal cord injury (SCI), long-termed functional electrical stimulation-rowing (FES-R) trained, with previously reported SCI and non-SCI group norms. To estimate lower limb joint contact forces (JCFs) in the FES-R trained participant.Setting:UK University and orthopaedic hospital research centre.Methods:Bilateral proximal tibial trabecular BMD of the FES-R trained participant was measured using peripheral quantitative computerised tomography, and the data were compared with SCI and non-SCI groups. An instrumented four-channel FES-R system was used to measure the lower limb JCFs in the FES-R trained participant.Results:Structurally, proximal tibial trabecular BMD was higher in the FES-R trained participant compared with the SCI group, but was less than the non-SCI group. Furthermore, left (184.7 mg cm−3) and right (160.7 mg cm−3) BMD were well above the threshold associated with non-traumatic fracture. The knee JCFs were above the threshold known to mediate BMD in SCI, but below threshold at the hip and ankle.Conclusion:As pathological fractures predominate in the distal femur and proximal tibia in chronic SCI patients, the fact that the FES-R trained participant’s knee JCFs were above those known to partially prevent bone loss, suggests that FES-R training may provide therapeutic benefit. Although the elevated bilateral proximal tibial BMD of the FES-R participant provides circumstantial evidence of osteogenesis, this single case precludes any statement on the clinical significance. Further investigations are required involving larger numbers and additional channels of FES to increase loading at the hip and ankle.

Assessment of the ultrasonic dental scaler insert

The ultrasonic dental scaler is an invaluable tool in the fight against dental calculus and periodontal disease. The purpose of this study was to assess the natural frequency of the straight internal ultrasonic scaler insert 30K FSI-SLI-10S (Dentsply International, York, USA) and to measure the displacement observed at the tip when operated under different generator settings. Two approaches were used: finite element analysis and scanning laser vibrometry. The Finite Element Analysis method was employed to calculate the expected modes of vibration of the insert. Scanning laser vibrometry was used to measure displacements of the tip during operation. It was found the insert had two modes of vibration around the operating frequency of 30 kHz; these modes were first order bending in two orthogonal planes.

Leg length measurement: clinical versus mathematical modelling

Abstract It has been suggested that leg length measurement is important in gait pathologies and in the surgical dimension, when certain types of procedure are being undertaken, namely total hip arthroplasties. We report on two different methods of measuring leg length difference in a 31-year-old male. A clinical measure was undertaken and compared to a score utilising a functional methodology. Both methods shared similar results, however, the functional method gave the additional benefit by indicating, not just the total length of the leg, but the length of the two long bones involved.

The calculation of a human lumped-mass model from acceleration and force-plate data

Abstract This paper describes a technique for the calculation of a lumped-mass representation of a human based on acceleration of body locations, typically obtained from a three-dimensional motion tracking system, and external forces and torques, typically measured from a force plate. The inverse problem of solving for lumped masses is presented, which results in a mass model of the individual subject via a fast, fully automated approach. This method can be used to obtain the mass model per se for the identification of growth deformities or together with a kinematic model for inverse and forward dynamics. Furthermore the mass model and acceleration trajectories subsequently can be used to calculate the contact forces between the floor and the subject at locations remote to a force plate.

Protective role of cerebrospinal fluid in brain injuries

Editor,—We would like to offer a simple model of brain injury which explains many features of “closed skull” injuries—that is, those where damage results from the action of inertial forces only. The model is easily constructed as follows. Fill a jam jar to the brim with water. Glue two threads to an egg, suspend the egg in the water, and screw the lid on tightly. If the jar is shaken horizontally as vigorously as possible, …

Neural network control strategies for low specification servo actuators

The paper considers neural network based control techniques as a means of obtaining improved dynamic performance from low specification dc motor servo drives. Such motors are low cost but exhibit large torque variations, non-linearity and possess high hysterisis. The use of neural network methods is demonstrated to offer an improvement compared with a conventional approach using a classical PID technique. Low performance motors of the type considered when combined with a neural network controller achieved a level of performance suitable for automatic handling systems and automated guided vehicles (AGV).

The generation of loads in excess of the osteogenic threshold by physical movement

This study investigates the use of physical movement to cause joint and bone loads that stimulate bone growth in order to reduce the adverse effects of osteoporosis. It has been established that stresses in bones in excess of the osteogenic threshold will stimulate bone growth; however, protocols for the generation of these stresses had not been established. Two trial movements were examined in the study: the plié and a movement requiring the subject to move a leg sequentially to 45° displaced positions – the star excursion balance test. Using inverse dynamics and an optimisation approach, the loads in the muscles crossing the hip and knee joints and the corresponding joint contact forces were calculated. It was found that the osteogenic threshold was exceeded in both these trials identifying them as suitable exercises in the maintenance of bone health. In the order of increasing bone load at the hip, and hence increasing bone growth stimulation, are the following demi plié, star excursion balance test with maximum reach criterion, grande plié and star excursion balance test with maximum speed criterion. In the order of increasing bone load at the knee are demi plié, grande plié, star excursion balance test with maximum reach criterion and star excursion balance test with maximum speed criterion. However, due to the high loads encountered, these exercises are not recommended for subjects with advanced osteoporosis although the boundary between therapeutic bone loading leading to increase in bone mineral density and loads capable of causing fracture is unclear.

Shoulder torques resulting from luggage handling tasks in non-inertial frames

BACKGROUND This paper reports on the torques developed in the shoulder joint experienced by occupants of moving vehicles during manual handling tasks. Handling heavy weights can cause musculoskeletal injuries, especially if handling is done with arms extended or at high levels. OBJECTIVE The aim of the study was to measure the longitudinal and lateral accelerations in a variety of passenger vehicles together with the postures of subjects lifting luggage onto storage shelves. This data enabled the application of inverse dynamics methods in a non-inertial reference frame to calculate the shoulder joint torques. METHODS The subjects lifted 3 pieces of luggage of masses of 5 kg, 10 kg and 14 kg onto shelving which were at heights of 1.2 m, 1.6 m and 1.8 m. The movement of subjects was measured using a 12 camera, 3-dimensional optical tracking system. The subjects stood on force plates to measure the ground reaction forces. RESULTS Sixty-three trials were completed, although 9 trials were aborted because subjects felt unable to complete the task. It was found that the shoulder torques exceeded the levels recommend by the UK Health and Safety Executive for manual handling. A lift assistance device is suggested to reduce the shoulder torques required for luggage handling.