Philipp Beckerle

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.

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.

A human-robot interaction perspective on assistive and rehabilitation robotics

Assistive and rehabilitation devices are a promising and challenging field of recent robotics research. Motivated by societal needs such as aging populations, such devices can support motor functionality and subject training. The design, control, sensing, and assessment of the devices become more sophisticated due to a human in the loop. This paper gives a human–robot interaction perspective on current issues and opportunities in the field. On the topic of control and machine learning, approaches that support but do not distract subjects are reviewed. Options to provide sensory user feedback that are currently missing from robotic devices are outlined. Parallels between device acceptance and affective computing are made. Furthermore, requirements for functional assessment protocols that relate to real-world tasks are discussed. In all topic areas, the design of human-oriented frameworks and methods is dominated by challenges related to the close interaction between the human and robotic device. This paper discusses the aforementioned aspects in order to open up new perspectives for future robotic solutions.

Prosthesis-User-in-the-Loop: A user-specific biomechanical modeling and simulation environment

In this paper, a novel biomechanical modeling and simulation environment with an emphasis on user-specific customization is presented. A modular modeling approach for multi-body systems allows a flexible extension by specific biomechanical modeling elements and enables an efficient application in dynamic simulation and optimization problems. A functional distribution of model description and model parameter data in combination with standardized interfaces enables a simple and reliable replacement or modification of specific functional components. The user-specific customization comprises the identification of anthropometric model parameters as well as the generation of a virtual three-dimensional character. The modeling and simulation environment is associated with Prosthesis-User-in-the-Loop, a hardware simulator concept for the design and optimization of lower limb prosthetic devices based on user experience and assessment. For a demonstration of the flexibility and capability of the modeling and simulation environment, an exemplary application in context of the hardware simulator is given.

Proprioceptive control of an over-actuated hexapod robot in unstructured terrain

Legged robots such as hexapods have the potential to traverse unstructured terrain. This paper introduces a novel hexapod robot (Weaver) using a hierarchical controller, with the ability to efficiently traverse uneven and inclined terrain. The robot has five joints per leg and 30 degrees of freedom overall. The two redundant joints improve the locomotion of the robot by controlling the body pose and the leg orientation with respect to the ground. The impedance controller in Cartesian space reacts to unstructured terrain and thus achieves self-stabilizing behavior without prior profiling of the terrain through exteroceptive sensing. Instead of adding force sensors, the force at the foot tip is calculated by processing the current signals of the actuators. This work experimentally evaluates Weaver with the proposed controller and demonstrates that it can effectively traverse challenging terrains and high gradient slopes, reduce angular movements of the body by more than 55% and reduce the cost of transport (up to 50% on uneven terrain and by 85% on a slope with 20 °). The controller also enables Weaver to walk up inclines of up to 30 °, and remain statically stable on inclines up to 50 °. Furthermore, we present a new metric for legged robot stability performance along with a method for proprioceptive terrain characterization.

The rubber hand illusion: Maintaining factors and a new perspective in rehabilitation and biomedical engineering?

Feelings of unrealistic body parts are related to deficits in human information processing and can occur as a part of phan, tom sensations after amputation [8]. Experimentally induced sensoric illusions like rubber hand illusion (RHI) [1] may help to understand basic information processing and could give new ideas for treatment or the rehabilitation pro, cess. Factors that are related to modulate sensoric illusions during movement may help to develop new intervention strategies in the rehabilitation of illusory symptoms. The goal of this study was to review the factors affecting persis, tence of the RHI effect during movement. We selected 13 keywords and searched in the following www.dimdi.de data bases (CCTR93, CDAR94, CDSR93, DAHTA, DAHTA, EA08, ED93, EM00, EM47, HG05, KP05, KR03, ME00, ME60, PI67, PY81, TV01, TVPP). A total of 160 articles were found. Duplicates were removed and the remaining list was filtered with the objective to explore the influence of active or passive movement during experimentally induced RHI. Then we identified six articles which experimentally examined persistence of RHI during active or passive move, ments. Results indicate that RHI are maintained during active or passive movements due to visual and temporal congru, ency. During active movements the RHI is more stable or global than in passive movements or during tactile stimulation. Factores like visual and temporal congruency are related to maintain RHI and are discussed in the rehabilitation of phan, tom sensations regarding new innovations in the design of prosthetics

Experimental comparison of nonlinear motion control methods for a variable stiffness actuator

Variable compliant actuators play a key role in the development of efficient biomechatronic systems since energy can be stored in the compliant element thus leading to consumption reduction. In this paper, experimental results comparing passivity-based control (PBC) and feedback linearization (FL) for motion control of an actuator with variable torsional stiffness (VTS) aiming at applications like prosthetic knee joints are presented. The concept of VTS and the experimental setup are described and a mathematical model of the latter one is derived. Based on this, a control architecture consisting of an extended Kalman filter (EKF) to estimate the velocities, a friction compensation as well as the mentioned controller types is developed. Both control methods are analyzed in terms of accuracy, dynamics and their control torque. FL and PBC lead to a stable control with high performance whereas the robustness is low by reason of the model-based control design. FL is superior to the PBC in terms of accuracy and control torque, which is mainly due to the high sensitivity of PBC regarding the discrete position signals. In addition, it is shown that FL can be applied for stable operation near the second natural frequency for different stiffness values.

Series and Parallel Elastic Actuation: Influence of Operating Positions on Design and Control

It is well-established that properly tuned elastic elements can make robotic actuators more energy-efficient, especially in cyclic tasks. Considering a drive train topology, two important subcategories of elastic actuators are series elastic actuation (SEA) and parallel elastic actuation (PEA). There is still no definite answer to the fundamental question which topology consumes less energy in a given task. This paper approaches the problem by studying oscillatory motions of a single degree-of-freedom link in a gravitational field. The imposed motion is a sinusoid with a nonzero offset requiring a static torque that needs to be compensated by the actuation system. Simulations and experiments show that the SEA consumes less energy up to certain offset angles. At high offsets, the PEA becomes the more energy-efficient alternative, provided that its no-load angle is properly tuned. Inverse dynamics simulations show how a threshold offset angle can be determined for a given task.

A systematic approach to experimental modeling and assessment of elastic actuators by component-wise parameter identification

This paper presents a systematic approach for experimental identification and assessment of mechanical effects on the dynamics of elastic actuators. The variable torsion stiffness (VTS) actuator is used as an example. As a basis for parameter identification, a flexible joint robot model considering friction and damping is used. To identify and assess occurring effects, a component-wise experimental investigation of the VTS drive train is performed. In this, influences of friction and inertia are examined using numerical least-squares regression to identify link inertia, friction in bearings, stiffness and damping in the elastic element, and the friction of gear box and actuator based on measured data. Comparing simulations to measured data, allows an evaluation of the obtained particular parameters and an assessment of their impact on overall system dynamics. Hence, the component-wise procedure enables to decide if those should be considered. This approach can be generalized to other elastic actuators by adapting model structure and/or performed experiments.