Simone Benatti

A Versatile Embedded Platform for EMG Acquisition and Gesture Recognition

Wearable devices offer interesting features, such as low cost and user friendliness, but their use for medical applications is an open research topic, given the limited hardware resources they provide. In this paper, we present an embedded solution for real-time EMG-based hand gesture recognition. The work focuses on the multi-level design of the system, integrating the hardware and software components to develop a wearable device capable of acquiring and processing EMG signals for real-time gesture recognition. The system combines the accuracy of a custom analog front end with the flexibility of a low power and high performance microcontroller for on-board processing. Our system achieves the same accuracy of high-end and more expensive active EMG sensors used in applications with strict requirements on signal quality. At the same time, due to its flexible configuration, it can be compared to the few wearable platforms designed for EMG gesture recognition available on market. We demonstrate that we reach similar or better performance while embedding the gesture recognition on board, with the benefit of cost reduction. To validate this approach, we collected a dataset of 7 gestures from 4 users, which were used to evaluate the impact of the number of EMG channels, the number of recognized gestures and the data rate on the recognition accuracy and on the computational demand of the classifier. As a result, we implemented a SVM recognition algorithm capable of real-time performance on the proposed wearable platform, achieving a classification rate of 90%, which is aligned with the state-of-the-art off-line results and a 29.7 mW power consumption, guaranteeing 44 hours of continuous operation with a 400 mAh battery.

Power Line Interference Removal for High-Quality Continuous Biosignal Monitoring With Low-Power Wearable Devices

Mobile and long-term recording of biomedical signals, such as electrocardiogram (ECG), electromyogram (EMG), and EEG, can improve diagnosis and monitor the evolution of several widespread diseases. However, it requires specific solutions, such as wearable devices, that should be particularly comfortable for patients, while at the same time ensuring medical-grade signal acquisition quality, including power line interference (PLI) removal. This paper focuses on the on-board real-time PLI filtering on a low-power biopotential acquisition wearable system. This paper analyzes in depth basic and advanced PLI filtering techniques and evaluates them in a wearable real-time processing scenario, assessing performance on EMG and ECG signals. Our experiments prove that most PLI removal algorithms are not usable in this challenging context, because they lack robustness or they require offline processing and large amounts of available data. On the other hand, adaptive filtering techniques are robust and well suited for lightweight online processing. We substantiate this finding with offline analysis and comparison, as well as with a complete embedded implementation on our low-power low-cost wearable device.

Hyperdimensional biosignal processing: A case study for EMG-based hand gesture recognition

The mathematical properties of high-dimensional spaces seem remarkably suited for describing behaviors produces by brains. Brain-inspired hyperdimensional computing (HDC) explores the emulation of cognition by computing with hypervectors as an alternative to computing with numbers. Hypervectors are high-dimensional, holographic, and (pseudo)random with independent and identically distributed (i.i.d.) components. These features provide an opportunity for energy-efficient computing applied to cyberbiological and cybernetic systems. We describe the use of HDC in a smart prosthetic application, namely hand gesture recognition from a stream of Electromyography (EMG) signals. Our algorithm encodes a stream of analog EMG signals that are simultaneously generated from four channels to a single hypervector. The proposed encoding effectively captures spatial and temporal relations across and within the channels to represent a gesture. This HDC encoder achieves a high level of classification accuracy (97.8%) with only 1/3 the training data required by state-of-the-art SVM on the same task. HDC exhibits fast and accurate learning explicitly allowing online and continuous learning. We further enhance the encoder to adaptively mitigate the effect of gesture-timing uncertainties across different subjects endogenously; further, the encoder inherently maintains the same accuracy when there is up to 30% overlapping between two consecutive gestures in a classification window.

A Prosthetic Hand Body Area Controller Based on Efficient Pattern Recognition Control Strategies

Poliarticulated prosthetic hands represent a powerful tool to restore functionality and improve quality of life for upper limb amputees. Such devices offer, on the same wearable node, sensing and actuation capabilities, which are not equally supported by natural interaction and control strategies. The control in state-of-the-art solutions is still performed mainly through complex encoding of gestures in bursts of contractions of the residual forearm muscles, resulting in a non-intuitive Human-Machine Interface (HMI). Recent research efforts explore the use of myoelectric gesture recognition for innovative interaction solutions, however there persists a considerable gap between research evaluation and implementation into successful complete systems. In this paper, we present the design of a wearable prosthetic hand controller, based on intuitive gesture recognition and a custom control strategy. The wearable node directly actuates a poliarticulated hand and wirelessly interacts with a personal gateway (i.e., a smartphone) for the training and personalization of the recognition algorithm. Through the whole system development, we address the challenge of integrating an efficient embedded gesture classifier with a control strategy tailored for an intuitive interaction between the user and the prosthesis. We demonstrate that this combined approach outperforms systems based on mere pattern recognition, since they target the accuracy of a classification algorithm rather than the control of a gesture. The system was fully implemented, tested on healthy and amputee subjects and compared against benchmark repositories. The proposed approach achieves an error rate of 1.6% in the end-to-end real time control of commonly used hand gestures, while complying with the power and performance budget of a low-cost microcontroller.

Scalable EEG seizure detection on an ultra low power multi-core architecture

Energy efficient processing architectures represent key elements for wearable and implantable medical devices. Signal processing of neural data is a challenge in new designs of Brain Machine Interfaces (BMI). A highly efficient multi-core platform, designed for ultra low power processing allows the execution of complex algorithms complying with real time requirements. This paper describes the implementation and optimization of a seizure detection algorithm on a multi-core digital integrated circuit designed for energy efficient applications. The proposed architecture is able to implement ultra low power parallel processing seizure detection on 23 electrodes within a power budget of 1 mW, outperforming implementations on commercial MCUs by up to 100 times in terms of performance and up to 80 times in terms of energy efficiency still providing high versatility and scalability, opening the way to the development of efficient implantable and wearable smart systems.

Experimental evaluation of a sEMG-based human-robot interface for human-like grasping tasks

In this paper we present a Human-Robot Interface (HRI) to control a robotic hand via myoelectric signals for grasping tasks. The system is composed by the UB Hand IV as robotic device, and by the Cerebro wearable board as acquisition hardware of the signals from surface skin electrodes. The approach implemented for the HRI relies on a pair of antagonistic flexor-extensor muscles that control both the closure and the grasp stiffness of the robotic hand. Humans accomplish a large variety of grasps thanks to precise impedance regulation: the aim of this study is to emulate this capability on a robotic hand using a users muscles driven HRI. Experiments conducted with healty subjects showed a short training time together with high success rate of grasp-related tasks, where the users of the HRI were able to naturally modulate the hands degrees of control by means of forearm muscle contractions. The results show that the system is suitable for further developments for telemanipulation and prosthetic applications.

A sensor fusion approach for drowsiness detection in wearable ultra-low-power systems

A Wearable Drowsiness Detector based on sensor fusion is presented.EEG and IMU sensors are used to detect 5 levels of drowsiness with 95% of accuracy.Efficient HW/FW co-design permits 6 hours of operation with a 200mAh battery.Further energy saving was investigated by porting the FW in a PULP platform.Results shows a 63x gain in energy efficiency extending 7 times battery duration. Drowsiness detection mechanisms have been extensively studied in the last years since they are one of the prevalent causes of accidents within the mining, driving and industrial activities. Many research efforts were done to quantify the drowsiness levels using behavioral analyses based on camera eye tracking systems as well as by analyzing physiological features contained in EEG signals. Detection systems typically use specific drowsiness indicators from only one of these methods, leaving a risk of missed detection since not all the population presents same symptoms of drowsiness. Thus, multi-feature systems are preferable even though most of the current State-of-the-Art (SoA) solutions are based on power-hungry platforms and they have meager chance to be used in embedded wearable applications with long battery lifetime. This work presents a drowsiness detection scheme fusing behavioral information coming from user motion through an IMU sensor and physiological information coming from brain activity through a single EEG electrode. The solution is implemented and tested on a low power programmable platform based on an ARM Cortex-M4 microcontroller, resulting in a wearable device capable to detect 5 different levels of drowsiness with an average accuracy of 95.2% and a battery life of 6 hours, using a 200mAh battery. We also study the energy optimization achievable by accelerating the sensor fusion-based drowsiness detector on a parallel ultra-low power (PULP) platform. Results show that the use of PULP as efficient processing platform provides an energy improvement of 63x with respect to a solution based on a commercial microcontroller. This may extend the battery life of the complete system up to 46h with a 7x improvement, paving the way for a completely wearable, always-on system.

A wearable EEG-based drowsiness detection system with blink duration and alpha waves analysis

Drowsiness is one of the most prevalent causes of accidents in mining, driving and industrial activities carrying high personal risks and economic costs. For this reason, automatic detection of drowsiness is becoming an important application, and it is being integrated in a large variety of wearable and deeply embedded systems. Relevant effort has been spent in the past to quantify the drowsiness level from behavioral features exploiting eye tracking systems, dermal sensors or steering wheel movements. On the other hand, all these approaches lack of generality, they are highly intrusive and can only be applied in specific circumstances. A promising alternative approach is based on the extraction and processing of physiological features from the EEG using Brain Computer Interfaces (BCI). This work describes a wearable system capable of detecting drowsiness conditions and emitting alarms using only EEG signals, with three levels of alarm based on the blink duration and on the spectral power of alpha waves. This implementation aims to replace or complement the use of cameras and other sensors, extracting drowsiness information exploiting both behavioral and physiological features from EEG sensors only. The system was validated with 7 test subjects achieving detection accuracy of 85%, while being much more lightweight and compact than other state of the art methods.

A machine learning approach for automated wide-range frequency tagging analysis in embedded neuromonitoring systems

EEG is a standard non-invasive technique used in neural disease diagnostics and neurosciences. Frequency-tagging is an increasingly popular experimental paradigm that efficiently tests brain function by measuring EEG responses to periodic stimulation. Recently, frequency-tagging paradigms have proven successful with low stimulation frequencies (0.5-6Hz), but the EEG signal is intrinsically noisy in this frequency range, requiring heavy signal processing and significant human intervention for response estimation. This limits the possibility to process the EEG on resource-constrained systems and to design smart EEG based devices for automated diagnostic. We propose an algorithm for artifact removal and automated detection of frequency tagging responses in a wide range of stimulation frequencies, which we test on a visual stimulation protocol. The algorithm is rooted on machine learning based pattern recognition techniques and it is tailored for a new generation parallel ultra low power processing platform (PULP), reaching performance of more that 90% accuracy in the frequency detection even for very low stimulation frequencies (<1Hz) with a power budget of 56mW.

A contactless three-phase autonomous power meter

Electrical energy management is becoming crucial to optimize the generation and usage of power. Therefore, measurement of parameters (such as amplitude and/or phase shift) of electrical systems is of the utmost importance for achieving efficient control on power usage of electric loads in residential and industrial buildings. Most of the existing smart metering devices available on the market need voltage probes which are invasive, because they need a direct connection with the potentials being measured. We present an innovative low-cost clamp-on power meter, designed and optimized for three-phase systems. It can be installed without temporary interruption of the supply directly on the cable insulators and can measure simultaneously both current and voltage of the underneath wires, providing accurate measurements of apparent power, active power, reactive power and power factor. Moreover an energy harvesting unit extracts the necessary energy to supply the meter without electrical contact, permitting to install the device without need of batteries or power plugs. Experimental results show the accuracy of the measurements and the autonomy of the small size and compact power meter.