Bernhard Vodermayer

Assessment of a Wearable Force- and Electromyography Device and Comparison of the Related Signals for Myocontrol

In the frame of assistive robotics, multi-finger prosthetic hand/wrists have recently appeared, offering an increasing level of dexterity; however, in practice their control is limited to a few hand grips and still unreliable, with the effect that pattern recognition has not yet appeared in the clinical environment. According to the scientific community, one of the keys to improve the situation is multi-modal sensing, i.e., using diverse sensor modalities to interpret the subjects intent and improve the reliability and safety of the control system in daily life activities. In this work, we first describe and test a novel wireless, wearable force- and electromyography device; through an experiment conducted on ten intact subjects, we then compare the obtained signals both qualitatively and quantitatively, highlighting their advantages and disadvantages. Our results indicate that force-myography yields signals which are more stable across time during whenever a pattern is held, than those obtained by electromyography. We speculate that fusion of the two modalities might be advantageous to improve the reliability of myocontrol in the near future.

Low-cost wearable multichannel surface EMG acquisition for prosthetic hand control

Prosthetic hand control based on the acquisition and processing of surface electromyography signals (sEMG) is a well-established method that makes use of the electric potentials evoked by the physiological contraction processes of one or more muscles. Furthermore intelligent mobile medical devices are on the brink of introducing safe and highly sophisticated systems to help a broad patient community to regain a considerable amount of life quality. The major challenges which are inherent in such integrated systems design are mainly to be found in obtaining a compact system with a long mobile autonomy, capable of delivering the required signal requirements for EMG based prosthetic control with up to 32 simultaneous acquisition channels and - with an eye on a possible future exploitation as a medical device - a proper perspective on a low priced system. Therefore, according to these requirements we present a wireless, mobile platform for acquisition and communication of sEMG signals embedded into a complete mobile control system structure. This environment further includes a portable device such as a laptop providing the necessary computational power for the control and a commercially available robotic hand-prosthesis. Means of communication among those devices are based on the Bluetooth standard. We show, that the developed low cost mobile device can be used for proper prosthesis control and that the device can rely on a continuous operation for the usual daily life usage of a patient.

Design and simulation of advanced charge recovery piezoactuator drivers

The German Artificial Sphincter System project aims at the development of an implantable sphincter prosthesis driven by a piezoelectrically actuated micropump. The system has been designed to be fully implantable, i.e. the power supply is provided by a rechargeable lithium polymer battery. In order to provide sufficient battery duration and to limit battery dimensions, special effort has to be made to minimize power consumption of the whole system and, in particular, of the piezoactuator driver circuitry. Inductive charge recovery can be used to recover part of the charge stored within the actuator. We are going to present a simplified inductor-based circuit capable of voltage inversion across the actuator without the need of an additional negative voltage source. The dimension of the inductors required for such a concept is nevertheless significant. We therefore present a novel alternative concept, called direct switching, where the equivalent capacitance of the actuator is charged directly by a step-up converter and discharged by a step-down converter. We achieved superior performance compared to a simple inductor-based driver with the advantage of using small-size chip inductors. As a term of comparison, the performance of the aforementioned drivers is compared to a conventional driver that does not implement any charge recovery technique. With our design we have been able to achieve more than 50% reduction in power consumption compared to the simplest conventional driver. The new direct switching driver performs 15% better than an inductor-based driver. A novel, whole-system SPICE simulation is presented, where both the driving circuit and the piezoactuator are modeled making use of advanced nonlinear models. Such a simulation is a precious tool to design and optimize piezoactuator drivers.

An Efficient Low-voltage Micropump For An Implantable Sphincter System

We present our current developments in the GASS project. GASS is an implantable sphincter prosthesis driven by a micropump. The aim of the previous stages of this project was to demonstrate the feasibility of the approach. Currently we focus on the safety and efficiency of the micropump. A low-voltage multilayer actuator was developed to reduce the driving voltage of the micropump from approximately 300 Vpp to 30 Vpp. A miniaturized driving circuit with charge recovery is currently developed. The overall efficiency of the micropump system is in the range of 2% depending on the hydraulic conditions. Different approaches for the energy management of the prosthesis and the resulting size, weight and lifetime are presented.

A high performance bidirectional micropump utilizing advanced low voltage piezo multilayer actuator technology for a novel artificial sphincter system

We present our latest developments for a novel artificial sphincter system. This system had been continuously developed over several years within the GASS project. Main part of the system is a high performance bidirectional silicon micropump driven by piezo actuators. The driving voltage of the newly developed system had been reduced from 300 V to 40 V peak-to-peak by using advanced multilayer piezo actuators. A peak flowrate of 4.36 ml/min had been measured at a driving frequency of 35 Hz. We have measured a maximum backpressure capability of 505 mbar with a square wave driving signal at Vpp=45 V. The whole system is designed to work as a self-sustaining battery driven, remote controlled system.

Low Power Electronics for Square-Wave Piezoactuator Driving

The German Artificial Sphincter System (GASS) project aims at the development of an implantable sphincter prosthesis driven by a micropump. During the last few years the feasibility of the concept has been proven. At present our team’s effort is focused on the compliance to safety regulations and on a very low power consumption of the system as a whole. Therefore a low-voltage multilayer piezoactuator has been developed to reduce the driving voltage of the micropump from approximately 300 Vpp to 40 Vpp. Doing so, the driving voltage is within the limits set by the regulations for active implants. The operation of the micropump at lower voltages, achieved using multilayer piezoactuators, has already resulted in a much better power efficiency. Nevertheless, in order to further reduce power consumption, we have also developed an innovative driving technique that we are going to describe and compare to other driving systems. A direct switching circuit has been developed where the buffer capacitor of the step-up converter has been replaced by the equivalent capacitance of the actuator itself. This avoids the switching of the buffer capacitor to the actuator, which would result in a very low efficiency. Usually, a piezoactuator needs a bipolar voltage drive to achieve maximum displacement. In our concept, the voltage inversion across the actuator is done using an h-bridge circuit, allowing the employment of one step-up converter only. The charge stored in the actuator is then partially recovered by means of a step-down converter which stores back the energy at the battery voltage level. The power consumption measurements of our concept are compared to a conventional driving output stage and also with inductive charge recovery circuits. In particular, the main advantage, compared to the latter systems, consists in the small inductors needed for the power converter. Other charge recovery techniques require very big inductors in order to have a significant power reduction with the capacitive loads we use in our application. With our design we will be able to achieve approximately 55% reduction in power consumption compared to the simplest conventional driver and 15% reduction compared to a charge recovery driver.Copyright