Rolf Adelsberger

Practical motion capture in everyday surroundings

Commercial motion-capture systems produce excellent in-studio reconstructions, but offer no comparable solution for acquisition in everyday environments. We present a system for acquiring motions almost anywhere. This wearable system gathers ultrasonic time-of-flight and inertial measurements with a set of inexpensive miniature sensors worn on the garment. After recording, the information is combined using an Extended Kalman Filter to reconstruct joint configurations of a body. Experimental results show that even motions that are traditionally difficult to acquire are recorded with ease within their natural settings. Although our prototype does not reliably recover the global transformation, we show that the resulting motions are visually similar to the original ones, and that the combined acoustic and intertial system reduces the drift commonly observed in purely inertial systems. Our final results suggest that this system could become a versatile input device for a variety of augmented-reality applications.

Time-of-flight sensor and color camera calibration for multi-view acquisition

This paper presents a multi-view acquisition system using multi-modal sensors, composed of time-of-flight (ToF) range sensors and color cameras. Our system captures the multiple pairs of color images and depth maps at multiple viewing directions. In order to ensure the acceptable accuracy of measurements, we compensate errors in sensor measurement and calibrate multi-modal devices. Upon manifold experiments and extensive analysis, we identify the major sources of systematic error in sensor measurement and construct an error model for compensation. As a result, we provide a practical solution for the real-time error compensation of depth measurement. Moreover, we implement the calibration scheme for multi-modal devices, unifying the spatial coordinate for multi-modal sensors.The main contribution of this work is to present the thorough analysis of systematic error in sensor measurement and therefore provide a reliable methodology for robust error compensation. The proposed system offers a real-time multi-modal sensor calibration method and thereby is applicable for the 3D reconstruction of dynamic scenes.

PIMU: A wireless pressure-sensing IMU

Inertial measurement units (IMU) are included in uncountable consumer electronic products, e.g. smart phones. IMUs are state of the art for research in human motion analysis, context and activity recognition. Sensor setups to estimate the activity of a subject, e.g. standing, sitting, walking, climbing stairs etc., typically require a multitude of sensor nodes to provide reliable estimations. In our paper, we present a sensor system for enhanced context and activity recognition while requiring a minimal set of sensor nodes. Our system combines a pressure sensor featuring high spatial resolution (1248 sensitive points) with an IMU. The pressure sensor is typically placed inside a shoe and measures the force exerted on the feet. Our system eases the detection of many situations: differentiating between sitting and standing, walking and climbing stairs etc. It is adjustable to virtually any shoe and therefore could be included in projects requiring specialized footwear (e.g. running, weight lifting or biking shoes). Data can be stored on the sensor node or it can be transferred wirelessly to a remote aggregator device, i.e. a device responsible for data stream reception, sensor control and analysis. The aggregator can be implemented in a smart phone or a PC. Our system can in real-time detect situations of sitting, standing and walking automatically. The systems low-power implementation allows for run-times exceeding 14 hours. In a multi-system setup the systems can be synchronized with a node-to-node offset in the order of 10μs. The pressure can be sampled at a maximum of 120Hz, the inertial data is available at a rate of 512 Hz. Our small-footprint real-time classifier can distinguish between the situations standing, sitting, and walking with an accuracy above 99%.

One IMU is sufficient: A study evaluating effects of dual-tasks on gait in elderly people

In industrialized countries the share of elderly subjects is increasing. Hence, diseases or symptoms associated with aging are more common than they were in the past. As a consequence, more effort is invested into research analyzing the effects of aging on the motion and cognition. However, economical and flexible methods to measure motion and its cross-effects with cognition are still missing. Therefore, we developed a new approach which neither requires a specific location, large infrastructural requirements, nor does it require large investments. We base our setting on match-box sized inertial measurement units (IMUs) attached to the participants’ legs. 47 elderly subjects participated in our study where we analyzed the interplay between cognitive load and gait features. We show that it is feasible to automatically detect episodes of interest, e.g. straight path, during walking periods of a subject only using IMU data. Our approach detects the steps autonomously and calculates gait features without supervision. The results demonstrate that cognitive load induces a significant increase (p = 0.007) in step-duration variability from 16ms (baseline) to 21ms (load). Our findings demonstrate that IMUs are a proved alternative to static setups that usually require a non-trivial infrastructure, e.g. optical movement tracking.

Automated Romberg testing in patients with benign paroxysmal positional vertigo and healthy subjects.

Objective: Benign paroxysmal positional vertigo (BPPV) is the most common cause of dizziness. The underlying pathomechanism responsible for the recurrent vertigo attacks has been elucidated in detail and highly effective treatment strategies (liberation maneuvers) have been developed. However, many BPPV patients complain about problems of balance especially following liberation maneuvers. Aim: To objectively demonstrate differences in balance performance in BPPV patients compared to healthy subjects both prior and after BPPV liberation maneuvers. Methods: Seven patients with BPPV of the posterior semicircular canal and nine healthy subjects participated. To assess balance while standing, we analyzed the location and temporal stability of the center of pressure recorded by pressure-sensitive electronic soles during Romberg testing (on stable ground and on foam) and tandem stand. To assess regularity of gait, we analyzed the step frequency during walking of 50 m. All tests were performed prior and after liberation maneuvers in both groups. Results: Healthy subjects and patients differ significantly in their balance performance and use different stabilization strategies both prior and after liberation maneuvers. Both Romberg tests indicated poorer balance in BPPV patients (mean COP shifted towards toes), especially in posttreatment tests, while tandem stand appeared unaltered. We did not observe differences in escorted (by an experimenter) walking regularities between patients and healthy subjects and between pre- and post-maneuver testing. Conclusion and significance: Our findings confirm the typical clinical observation of a further posttreatment deterioration of already impaired postural performance in BPPV patients. While the etiology and the time course of this peculiar problem warrants further studies, the treating physician should be familiar with this transient side effect of therapeutic maneuvers to provide adequate counseling of patients. Finally, we successfully demonstrated the pressure-sensitive electronic soles as a new and potentially useful tool for both clinical and research purposes.

Capturing human motion one step at a time

The design, construction, and deployment of a pressure-enhanced IMU system that fits in the bottom of your shoe.