Walter Daems

Assistive Pointing Device Based on a Head-Mounted Camera

This paper introduces and validates the performance of an alternative input device for people with limited hand/arm movement and control. A summary is provided of the current state of the art in alternative input devices. Based on this, a low-cost solution is proposed that allows for 1) low latency and high operating speed and accuracy, 2) use from different viewing angles without recalibration, and 3) the ability to seamlessly control multiple devices. A prototype of this system was built and tested to determine the accuracy of the system (using a pan–tilt system), and to analyze the performance of the system compared to the state of the art (through user tests, based on the ISO 9241–411 test). The proposed system allows for great accuracy (

An optical head-pose tracking sensor for pointing devices using IR-LED based markers and a low-cost camera

sigma _X=text{0.28 px}, sigma _Y=text{0.29 px}, sigma _{XY}=text{0.02 px}

An Ultrasonic Six Degrees-of-Freedom Pose Estimation Sensor

), a decent performance compared to the state of the art (throughput = 1.52 bits/s, error rate = 31%), and good results in the ISO 9241-411 independent rating scale. The results from the performed experiments show that the proposed system leads great promise in real-world applications. A low-cost head-mounted camera could be used as an alternative human interface device for people with limited hand/arm movement and control, allowing them to participate in the ongoing trend of computing devices gaining importance in our everyday activities.

Widening the Directivity Patterns of Ultrasound Transducers Using 3-D-Printed Baffles

In this paper, we present a head-mounted pointing device (i.e. Head-mouse) which consists of an optical sensor based on a small CMOS-camera with the IR blocking filter replaced by an IR-bandpass filter and IR LEDs (850nm wavelength) as markers. The advantage of our sensor compared to other head-mouse systems and eye-gaze systems is that the proposed sensor results in an absolute positioning of the mouse cursor and does not require laborious recalibration as the user changes his position. Furthermore, the sensor has a larger operating area and allows seamless control of multiple devices.

A flexible embedded hardware platform supporting low-cost human pose estimation

Motion capture and human body pose estimation systems have become a more common appliance nowadays because of the movie and video game industry. These measurement systems have been proven to be useful for other applications besides entertainment. One of these applications is motion analysis, which can be used for improving the form of athletes or for providing an objective validation tool for rehabilitation treatments. These analyses are done using high-accuracy measurement systems which result in high costs. Although there are some consumer products (e.g. the Microsoft Kinect) that offer movement tracking at a low cost, the accuracy does not suffice for clinical movement analysis applications. This paper therefore focuses on reducing the cost of a human body pose estimation system while retaining the required accuracy. The proposed solution comprises of an embedded ultrasonic transmitter and receiver subsystem. The receiver subsystem consists of multiple mobile nodes that are equipped with a small microphone array (at least three microphones). Each mobile receiver node captures the encoded simultaneously broadcast ultrasonic transmissions from a distributed transmitter array (which consists of at least three elements). Using signal processing, a distance can be calculated between each transmitter and microphone resulting in at least nine distances for each mobile node. Using these distances in combination with the position of the transmitters and the microphone array configuration, the XYZ-position of the mobile node and its rotation about these axes (six degrees-of-freedom) can be estimated. The combination of low-cost embedded and ultrasonics hardware that forms the transducer and receiver subsystem (consisting of multiple mobile receiver nodes) together with powerful signal processing techniques yields a high-accuracy pose estimation system, which can be used as an affordable tool in various fields and applications (e.g., gait analysis for rehabilitation purposes).

Low-cost synchronization of high-speed audio and video recordings in bio-acoustic experiments

Modern localization and/or mapping systems based on ultrasound use multiple types of ultrasound transducers. These transducers are used to scan the environment and create situational awareness so that obstacles are spotted and collisions may be prevented. Most commercially available transducers however have a field of view (FOV) that is too limited for these applications. As a result of this, multiple transducers are necessary to get a decent perceptional coverage of the environment. The signals coming from the different transducers can cause unnecessary complications. In this paper, we propose a method for widening the FOV of off-the-shelf ultrasonic transducers by creating a baffle that fits on these transducers. This will significantly improve the process of mapping the environment for a wide range of applications, such as obstacle avoidance and SLAM. We provide strong experimental evidence for the widening of the directivity patterns by means of various 3-D-printed baffles.

Stable six-DoF head-pose tracking in assistive technology application

Throughout the last decades, human motion capture systems have become an important tool for various sectors. Besides the entertainment sector, which is probably the most known sector to use these systems through popular movies and video games, the medical sector has adopted this technology as an analysis tool. These clinical analyses measure the human body posture and movement for various purposes including rehabilitation and sports, and require high accuracy and precision. Although there is a variety of products that offer these capabilities, there is not yet an affordable system that meets the requirements for medical implementations. We therefore propose using an ultrasonic six degrees-of-freedom sensor system which combines a distributed array of ultrasonic emitters and a small array of ultrasonic receivers. In order to support low-cost human pose estimation, while retaining the possibility for re-use and expandability, the need for a flexible embedded hardware platform naturally emerged. The proposed hardware design supports the requirements of a high accuracy and high precision pose estimation system while keeping its overall system cost low.

Wireless Surface Electromyography

ABSTRACT In this paper, we present a method for synchronizing high-speed audio and video recordings of bio-acoustic experiments. By embedding a random signal into the recorded video and audio data, robust synchronization of a diverse set of sensor streams can be performed without the need to keep detailed records. The synchronization can be performed using recording devices without dedicated synchronization inputs. We demonstrate the efficacy of the approach in two sets of experiments: behavioral experiments on different species of echolocating bats and the recordings of field crickets. We present the general operating principle of the synchronization method, discuss its synchronization strength and provide insights into how to construct such a device using off-the-shelf components. Summary: A low-cost method to reliably synchronize experimental data streams such as audio, video or other inputs using a 1-bit synchronization signal.

Firefly based distributed synchronization in Wireless Sensor Networks for passive acoustic localization

This paper describes an alternative approach to giving people with limited hand and arm movement the ability to select objects on a computing device using head movement (head mouse). To allow for better filtering of unintentional head movement, and to allow for a faster update rate of the head mouse, the full six-DoF pose of the head is estimated using a low-cost camera and IR markers, a 3-axis accelerometer, and a 3-axis magnetometer. The pose estimation problem was cast in a probabilistic fashion in which information from the different sensors is fused into a single a-posteriori distribution for the sensor pose. Simulations were run to analyze the influence of the proposed sensor fusion algorithm on the stability and accuracy of the pose estimation, and thus on the ability to point a mouse cursor to a specified location on a screen. Experiments were then performed validating the results from the simulations on real sensors. The proposed algorithm was shown to give more accurate and stable results than using only a camera to estimate the six-DoF pose.

Human-computer interface using a head mounted camera and IR markers.

Surface Electromyography (sEMG) is used in the evaluation of muscle activation patterns during body movements. Artefacts in sEMG-signals and analysis are caused by the movements of the cables between the sensor and electrode. Hence, there already exist some pre-amplified and wireless sEMG electrodes. These deliver black box devices to end users, for commercial reasons. However, there is a demand for open source devices from a research perspectives. This paper explores the development of an open source wireless sEMG device that distributes the processing of the raw sEMG data between the wireless electrode and the researcher’s computing device. In cooperation with CSEM Landquart (CH) the possibility for the use of electrode-printing technology will be evaluated. We show that Bluetooth Low Energy has a high potential as a low power wireless communication protocol in this application, but that further improvement of the signal-to-noise ratio is necessary.