Kaspar Leuenberger

Activity classification based on inertial and barometric pressure sensors at different anatomical locations

Miniature, wearable sensor modules are a promising technology to monitor activities of daily living (ADL) over extended periods of time. To assure both user compliance and meaningful results, the selection and placement site of sensors requires careful consideration. We investigated these aspects for the classification of 16 ADL in 6 healthy subjects under laboratory conditions using ReSense, our custom-made inertial measurement unit enhanced with a barometric pressure sensor used to capture activity-related altitude changes. Subjects wore a module on each wrist and ankle, and one on the trunk. Activities comprised whole body movements as well as gross and dextrous upper-limb activities. Wrist-module data outperformed the other locations for the three activity groups. Specifically, overall classification accuracy rates of almost 93% and more than 95% were achieved for the repeated holdout and user-specific validation methods, respectively, for all 16 activities. Including the altitude profile resulted in a considerable improvement of up to 20% in the classification accuracy for stair ascent and descent. The gyroscopes provided no useful information for activity classification under this scheme. The proposed sensor setting could allow for robust long-term activity monitoring with high compliance in different patient populations.

Low-power sensor module for long-term activity monitoring

Wearable sensor modules are a promising approach to collecting data on functional motor activities, both for repeated and long-term assessments, as well as to investigate the transfer of therapy to activities of daily living at home, but have so far either had limited sensing capabilities, or were not laid out for long-term monitoring. This paper presents ReSense, a miniature sensor unit optimized for long-term monitoring of functional activity. Inertial MEMS sensors capture accelerations along six degrees of freedom and a barometric pressure sensor serves as a precise altimeter. Data is written to an integrated memory card. The realized module measures ⊘25×10 mm, weighs 10 g and can record continuously for 27 h at 25 Hz and over 22 h at 100 Hz. The integrated power-management system detects inactivity and extends the operating time by about a factor of two, as shown by initial 24 h recordings on five energetic healthy adults. The integrated barometric pressure sensor allowed to identify activities incorporating a change in altitude, such as going up/down stairs or riding an elevator. By taking into account data from the inertial sensors during the altitude changes, it becomes possible to distinguish between these two activities.

Design and psychophysical evaluation of a tactile pulse display for teleoperated artery palpation

During traditional open procedures, surgeons directly palpate tissues before dissecting them. In this way, they can avoid the accidental damage of hidden arteries that can lead to fatal hemorrhage. New Minimally Invasive Surgical (MIS) techniques progressively decreased the instrument access into the patients body to reduce scars and side effects. The major drawback of these procedures is that they do not permit surgeons to perform direct tactile exploration of internal tissues. Surgeons have to rely on preoperative images and anatomical knowledge to avoid artery locations. However, the exact artery position changes depending on the patient and his posture. Hence, it is of primary importance to assist surgeons with technology that can guide them during the surgical procedure. This paper presents the design and evaluation of a tactile display that reproduces pulse-like feedback on the surgeons fingertip. The display bandwidth and performance of the ad-hoc control unit were assessed with encouraging results. In addition, the outcome of two psychophysical studies carried out in this work validate the usability of the display in terms of user perception.

Physical Student–Robot Interaction With the ETHZ Haptic Paddle

Haptic paddles-low-cost one-degree-of-freedom force feedback devices-have been used with great success at several universities throughout the US to teach the basic concepts of dynamic systems and physical human-robot interaction (pHRI) to students. The ETHZ haptic paddle was developed for a new pHRI course offered in the undergraduate Mechatronics Focus track of the Mechanical Engineering curriculum at ETH Zurich, Switzerland. Twenty students engaged in this 2-h weekly lecture over the 14 weeks of the Autumn 2011 semester, complemented by a weekly 2-h laboratory session with the ETHZ haptic paddle. In pairs, students worked through three common sets of experiments before embarking on a specialization project that investigated one of several advanced topics such as impedance control with force feedback, admittance control, the effect of velocity estimation on stability, or electromyographic control. For these projects, students received additional hardware, including force sensors, electrooptical encoders or high-performance data acquisition cards. The learning objectives were developed in the context of an accompanying faculty development program at ETH Zurich; a set of interactive sequences and the oral exam were explicitly aligned to these learning objectives. The outcomes of the specialization project presentations and oral exams, and a student evaluation of the course, demonstrated that the ETHZ haptic paddle is a valuable tool that allows students to quite literally grasp abstract principles such as mechanical impedance, passivity, and human factors and helps students create a tangible link between theory and practice in the highly interdisciplinary field of pHRI.

Measurement of human rotation behavior for psychological and neuropsychological investigations.

The investigation of rotation behavior in human beings enjoys a longstanding and enduring interest in laterality research. While in animal studies the issue of accurately measuring the number of rotations has been solved and is widely applied in practice, it is still challenging to assess the rotation behavior of humans in daily life. We propose a robust method to assess human rotation behavior based on recordings from a miniature inertial measurement unit that can be worn unobtrusively on a belt. We investigate the effect of different combinations of low-cost sensors—including accelerometers, gyroscopes, and magnetometers—on rotation measurement accuracy, propose a simple calibration procedure, and validate the method on data from a predefined path through and around buildings. Results suggest that a rotation estimation based on the fusion of accelerometer, gyroscope, and magnetometer measurements outperforms methods based solely on earth magnetic field measurements, as proposed in previous studies, by a drop in error rate of up to 32 %. We further show that magnetometer signals do not significantly contribute to measurement accuracy in short-term measurements, and could thus be omitted for improved robustness in environments with magnetic field disturbances. Results also suggest that our simple calibration procedure can compete with more complex approaches and reduce the error rate of the proposed algorithm by up to 38 %.

Dopamine-responsive pattern in tremor patients.

BACKGROUND Diagnosis and treatment of tremor are largely based on clinical assessment. Whereas in some patients tremor may respond to dopaminergic treatment, in general l-Dopa response to tremor varies considerably. The aim of this study was to predict l-Dopa response by accelerometry. METHODS We included 60 tremor patients and measured harmonic oscillations by accelerometry. In addition to neurological assessment, we performed l-Dopa challenge tests and the individual tremor response was compared to the amount of harmonic oscillations. RESULTS We found a strong correlation between harmonic oscillations and clinical l-Dopa response. Similarly, harmonic oscillations were significantly greater in patients with subjective tremor reduction upon l-Dopa administration. CONCLUSIONS We conclude that harmonic oscillations are a measure for l-Dopa response to tremor irrespective of the underlying disease. Because of the observational character of the study, any causal relation remains speculative. Nevertheless, we propose a novel, non-invasive approach to predict l-Dopa response in tremor patients.

Motion-Based Augmented Broadcasting System with Haptic Feedback

This paper introduces a motion-based augmented broadcasting system enabling haptic, auditory, and visual augmentation of conventional television content. An entertainment use case scenario of the proposed system is presented that comprises haptic feedback for playing along with a TV show using virtual musical instruments. In a preliminary study, the influence of providing haptic feedback as well as visual body skeleton augmentation on the performance in selecting an interactive virtual object in the augmented broadcasting system is examined. While the methods of presentation did not show significant improvements, users clearly favored haptic feedback for interaction.

Objective assessment of vibrotactile mislocalization using a Haptic Glove

There is growing evidence for distortions of somatotopic sensory maps of the hand after neurological injuries such as stroke. However, routine somatosensory assessments are administered manually, leading to poor control over stimuli, inability to capture somatotopic mismatches, and generating only qualitative results. To address these limitations, an automated tool was developed to assess vibrotactile mislocalization on the hand. The ReHaptic Glove includes 24 independently controlled vibration motors distributed on the volar side of the hand. The setup allows the development of novel, refined outcome measures based on which objective distortion maps are proposed. To validate these methods, a vibrotactile localization study was conducted with six healthy young subjects. Correct detection rates were 70% for the distal phalanges and 50% for the base of the proximal phalanges (or metacarpal bone for the thumb). These differences were significant for the right hand (p = 0.018) and marginally significant for the left hand (p = 0.052). The detection rates are in accordance with the known densities of rapidly adapting cutaneous mechanoreceptors. Ergonomics of the glove, such as fit and ease of donning and doffing, were well rated despite large variations of hand size across subjects. Such an objective tool has the potential of assessing somatotopic mismatch in neurological patients, providing a basis for deficit-oriented therapies tailored to the individual patient.