Stephan Rinderknecht

Qanti: a software tool for quick ambiguous non-standard text input

This paper introduces a single-key text entry application for users with severe physical impairments. The tool combines the idea of a scanning ambiguous keyboard (which promises unusually high entry rates) with intentional muscle contractions as input signals (which require much less physical effort compared to key presses). In addition to the program architecture, the paper presents the results of several evaluations with participants with and without disabilities. An entry speed of 6.59 wpm was achieved.

Active lower limb prosthetics: a systematic review of design issues and solutions

This paper presents a review on design issues and solutions found in active lower limb prostheses. This review is based on a systematic literature search with a methodical search strategy. The search was carried out across four major technical databases and the retrieved records were screened for their relevance. A total of 21 different active prostheses, including 8 above-knee, 9 below-knee and 4 combined knee-ankle prostheses were identified. While an active prosthesis may help to restore the functional performance of an amputee, the requirements regarding the actuation unit as well as for the control system are high and the development becomes a challenging task. Regarding mechanical design and the actuation unit high force/torque delivery, high efficiency, low size and low weight are conflicting goals. The actuation principle and variable impedance actuators are discussed. The control system is paramount for a “natural functioning” of the prosthesis. The control system has to enable locomotion and should react to the amputee’s intent. For this, multi-level control approaches are reviewed.

Scanning-Based Human-Computer Interaction Using Intentional Muscle Contractions

It has already been shown in the past that it is possible to leverage tiny muscular contractions produced at will (e.g., by frowning) in order to give someone complete control over a PC [1]. The underlying interaction technique is ideal for persons with severe motor impairments who are in need for an alternative, non-standard way to operate a computer. This paper deals with a scanning-based computer application of that approach to enable its user to control the immediate environment, e.g., by making a phone call, toggling the lights, or sending particular Infra-Red (IR) remote signals. Although the software is primarily targeted at people with disabilities, it is ready --- and (in certain situations) even expected --- to be used by able-bodied individuals as well. A user study evaluating the remote control module of the system has been conducted with twelve non-impaired subjects, and the results are discussed herein.

Power-optimized stiffness and nonlinear position control of an actuator with Variable Torsion Stiffness

Introducing compliant actuation to robotic joints is an approach to ensure safety in closer human-machine interaction. Further, the possibility to adjust stiffness can be beneficial considering energy storage and the power consumption required to track certain trajectories. The subject of this paper is the stiffness and position control of the Variable Torsion Stiffness (VTS) actuator for application in compliant robotic joints. For the realization of a variable rotational stiffness, the active length of a torsional elastic element in serial configuration between drive and link is adjusted in VTS. After the deduction of an extended drive train model, this paper gives an advanced power analysis clarifying power-optimal settings from previous basic models and identifying additional settings that allow for a more versatile operation. Based on these results that can be generalized to other variable elastic actuator concepts, an optimized strategy for setting stiffness is determined considering the whole system dynamics including natural frequencies as well as antiresonance effects. For position control of VTS in a prototypical implementation, a nonlinear position controller is designed by means of feedback linearization. Although the system is modified significantly by changing drive train stiffness, the stiffness adaptation of the controller ensures the required tracking performance.

Design and control of a robot for the assessment of psychological factors in prosthetic development

This paper introduces a robotic concept for the assessment of psychological factors in prosthetic design. Its aim is to imitate the postural movements of the participants while those are conducting squatting movements in order to investigate the integration of artificial limbs to the subjects body scheme. Therefore, the robot mimics the functionality and appearance of the human foot, shank and thigh as well as the ankle and knee joint. To induce a more realistic outer appearance, the hull of a shop-window mannequin is used as cladding. The robot is controlled by a computed torque control combined with a RGB-D sensor for the acquisition of the desired trajectories from the participant. In the test setup one leg of the participant is hidden from his view while the robot stands next to him and imitates the movements of this leg. This paper gives an insight in the theory of body schema integration. The concept of the robot is described and detailed information about the mechanical design and actuator dimensioning in accordance with psychological and biomechanical requirements are given. Furthermore, the concept of the human-machine interface, the control algorithm and simulations based on experimental data from a human subject are presented.

3DScan: an environment control system supporting persons with severe motor impairments

This proposal is about a poster dealing with a scanning-based software system, which aims at giving persons with severe motor impairments a means to interact with their immediate environment by issuing tiny contractions of an arbitrary muscle. The implementation makes use of an extension of row-column scanning, called three-dimensional scanning, which reduces the time required to select a certain item by eliminating the need to scan long rows or columns. A simple experiment comparing the resulting text entry capabilities to conventional row-column scanning shows that the entry rate can be increased by over 30 %.

OnScreenDualScribe: a computer operation tool for users with a neuromuscular disease

We developed a tool based on a modified number pad aimed at empowering persons with neuromuscular diseases to efficiently operate a computer and enter text. As the keypad lies securely in both hands, the system is ideal for someone who has motor problems using a full-size keyboard but cannot use speech recognition as an alternative method, because of dysarthria. The software offers various assistive techniques; for example, text entry is facilitated with the help of word prediction. An ambiguous mode with word-level disambiguation allows text entry with six keys. Initial empirical results with the system --- which is already in regular use --- indicate that it indeed represents a viable alternative, since it decreases effort without increasing the time to operate a computer.

Observer design for unbalance excited rotor systems with gyroscopic effect

In state space control, system states are usually estimated using observers. In active rotor systems, observer design often faces two major problems: unbalances acting on the shaft are never known to full extent and in case of a rotor with large discs, gyroscopic effect results in system variation dependent on rotor rotary frequency. Two observer types accounting for these problems, a disturbance observer and an unknown input observer are applied to a rotor system with piezoelectric active bearings. The two approaches are compared with respect to accuracy of the estimated states, transfer behavior and expense for implementation.

Consideration of Gyroscopic Effect in Fault Detection and Isolation for Unbalance Excited Rotor Systems

Fault detection and isolation (FDI) in rotor systems often faces the problem that the system dynamics is dependent on the rotor rotary frequency because of the gyroscopic effect. In unbalance excited rotor systems, the continuously distributed unbalances are hard to be determined or estimated accurately. The unbalance forces as disturbances make fault detection more complicated. The aim of this paper is to develop linear time invariant (LTI) FDI methods (i.e., with constant parameters) for rotor systems under consideration of gyroscopic effect and disturbances. Two approaches to describe the gyroscopic effect, that is, as unknown inputs and as model uncertainties, are investigated. Based on these two approaches, FDI methods are developed and the results are compared regarding the resulting FDI performances. Results are obtained by the application in a rotor test rig. Restrictions for the application of these methods are discussed.

DualScribe: a keyboard replacement for those with friedreich's ataxia and related diseases

An alternative text composition method is introduced, comprising a small special-purpose keyboard as an input device and software to make text entry fast and easy. The work was inspired by an FA (Friedreichs Ataxia) patient who asked us to develop a viable computer interaction solution --- taking into account the specific symptoms induced by his disease. The outcome makes text entry easier than with the standard keyboard without being slower. It is likely that the system has general use for anyone with a similar condition, and also for able-bodied users looking for a small-size keyboard. We present a usability study with four participants showing the methods effectiveness.