Powered lower limb exoskeletons require high-performance actuator systems, capable of producing zero to high-assistive torque and at the same time yielding to human interaction torques. Such variable impedance can be achieved by the means of compliant actuators. Because of their intrinsic compliance and high force-to-weight ratio pneumatic muscles are a viable option. However, previous pneumatic muscle powered exoskeleton designs either used them as a position source or failed to meet the high-dynamic torque requirements when using them as a torque source. This paper contributes to the improvement of pneumatic muscle-based actuator systems as a torque source for exoskeleton-type robots. The use of pleated pneumatic artificial muscles in a novel actuator system design allows for a higher torque range in a larger range of motion. Performance evaluation results are given for a 1 DOF test setup and a powered knee exoskeleton. The proposed torque controller achieves the dynamic torques required for zero to full assistance at moderate walking speeds.

Until today it is not entirely clear how humans interact with automated gait rehabilitation devices and how we can, based on that interaction, maximize the effectiveness of these exoskeletons. The goal of this study was to gain knowledge on the human-robot interaction, in terms of kinematics and muscle activity, between a healthy human motor system and a powered knee exoskeleton (i.e., KNEXO). Therefore, temporal and spatial gait parameters, human joint kinematics, exoskeleton kinetics and muscle activity during four different walking trials in 10 healthy male subjects were studied. Healthy subjects can walk with KNEXO in patient-in-charge mode with some slight constraints in kinematics and muscle activity primarily due to inertia of the device. Yet, during robot-in-charge walking the muscular constraints are reversed by adding positive power to the leg swing, compensating in part this inertia. Next to that, KNEXO accurately records and replays the right knee kinematics meaning that subject-specific trajectories can be implemented as a target trajectory during assisted walking. No significant differences in the human response to the interaction with KNEXO in low and high compliant assistance could be pointed out. This is in contradiction with our hypothesis that muscle activity would decrease with increasing assistance. It seems that the differences between the parameter settings of low and high compliant control might not be sufficient to observe clear effects in healthy subjects. Moreover, we should take into account that KNEXO is a unilateral, 1 degree-of-freedom device.

OBJECTIVETo provide an overview of robot-assisted rehabilitation devices developed for actuation of the ankle-foot complex and their ability to influence the attributes of normal gait in patients with spinal cord injury.METHODSA search was conducted in MEDLINE, Web of Knowledge, National Academic Research and Collaborations Information System, and Physiotherapy Evidence Data-base (1985-2011), using, "ankle", "foot", "robotics", "orthotics" and "spinal cord injury" as most relevant keywords. Article inclusion was performed in 3 stages; at the level of: (i) title, (ii) abstract and (iii) full text.RESULTSThe actuated ankle-foot orthoses currently available are characterized by several combinations of an actuator and a control mechanism. Both the actuator and the control strategy substantially influence human-machine interaction and therefore the potential of the device to assist in modifying locomotor function and potentially modify the underlying motor control mechanisms.CONCLUSIONDue to small sample sizes, limited studies in patients with spinal cord injury, and limitations in study design, it is difficult to draw firm conclusions on the effect of different types of actuated ankle-foot orthoses. Based on the limited data available, pneumatic artificial muscles in combination with proportional myoelectric control are suggested to have the potential to meet most of the preconditions to restore the attributes of normal gait and therefore facilitate neuroplasticity.

This paper introduces the third generation of Pleated Pneumatic Artificial Muscles (PPAM), which has been developed to simplify the production over the first and second prototype. This type of artificial muscle was developed to overcome dry friction and material deformation, which is present in the widely used McKibben muscle. The essence of the PPAM is its pleated membrane structure which enables the muscle to work at low pressures and at large contractions. In order to validate the new PPAM generation, it has been compared with the mathematical model and the previous generation. The new production process and the use of new materials introduce improvements such as 55% reduction in the actuator's weight, a higher reliability, a 75% reduction in the production time and PPAMs can now be produced in all sizes from 4 to 50 cm. This opens the possibility to commercialize this type of muscles so others can implement it. Furthermore, a comparison with experiments between PPAM and Festo McKibben muscles is discussed. Small PPAMs present similar force ranges and larger contractions than commercially available McKibben-like muscles. The use of series arrangements of PPAMs allows for large strokes and relatively small diameters at the same time and, since PPAM 3.0 is much more lightweight than the commong McKibben models made by Festo, it presents better force-to-mass and energy to mass ratios than Festo models. (C) 2012 Taylor & Francis and The Robotics Society of Japan

1,2 Kristel Knaepen, 1,3 Pieter Beyl, 1,5 Saartje Duerinck, 4 Friso Hagman, 1,4 Jean-Pierre Baeyens, 1,3 Dirk Lefeber, 1,2 Romain Meeusen Vrije Universiteit Brussel, Belgium 1 Advanced Rehabilitation Technology & Science Research Group, 2 Department of Human Physiology & Center for NeurScience, 3 Robotics & Multibody Mechanics Research Group, 4 Department of Biometrics and Biomechanics, 5 Departement of Experimental Anatomy, email: kknaepen@vub.ac.be

Determinants of locomotor training involve taskspecificity, repeatability, variability, intensity and self-initiative. KNEXO, a unilateral knee exoskeleton has been developed to study the effects of compliant assistance during treadmill gait. Overall, walking within KNEXO, leads to asymmetric kinematics (Figure 1) and changes in naturally occurring muscle activity. Walking without KNEXO and with KNEXO in unassisted mode is difficult to compare as the device is unilateral and the pneumatic muscles give, although weight-compensated, a certain amount of inertia to the movement. Walking with KNEXO in high compliance resembles walking with KNEXO in unassisted mode. Overall, kinematic and EMG data show that the device has its shortcomings (unilateral, 1 DoF, 1 joint) when assisting healthy gait, yet it gives opportunities to study the effects of assistanceas-needed on gait biomechanics.

In situations where robots share their workspace with humans, and where physical human-robot interaction is possible or even necessary, safety is of paramount importance. Low weight and passive compliance are often considered important aspects contributing to robot safety. In this paper, the role of passive compliance is investigated with respect to the safety of a 2-DOF pneumatically actuated arm. By combining measurements and impact simulations, the safety of the system is evaluated for a wide range of joint stiffnesses. It turns out that passive compliance plays a double role: it improves safety in some impact situations, but its capacity to store energy can also be dangerous.

In situations where robots share their workspace with humans, and where physical human-robot interaction is possible or even necessary, safety is of paramount importance. This paper presents a study of the safety of a lightweight robot actuated by pneumatic muscles. Due to its low weight, it has excellent hardware safety characteristics. In spite of this, it is shown that the system can be unsafe when under PID control. It is also shown that safety can be greatly increased by using Proxy-Based Sliding Mode Control (PSMC). The role of passive compliance in safety is also investigated. It is argued that passive compliance can have positive as well as negative effects on robot safety, depending on the situation.

Robot-assisted rehabilitation of gait still faces many challenges, one of which is improving physical human-robot interaction. The use of pleated pneumatic artificial muscles to power a step rehabilitation robot has the potential to meet this challenge. This paper reports on the development of a gait rehabilitation exoskeleton with a knee joint powered by pleated pneumatic artificial muscles. It is intended as a platform for the evaluation of design and control concepts in view of improved physical human-robot interaction. The design was focused on the optimal dimensioning of the actuator configuration. Safety being the most important prerequisite, a proxy-based sliding mode controller (PSMC) was implemented as it combines accurate tracking during normal operation with a smooth, slow and safe recovery from large position errors. Treadmill walking experiments of a healthy subject wearing the powered exoskeleton show the potential of PSMC as a safe robot-in-charge control strategy for robot-assisted gait training.

Numerous prosthetic feet are currently on the market for individuals with a transtibial amputation, each device aimed at raising the 3C-level (control, comfort and cosmetics) with slightly different characteristics. In general, prosthetic feet can be classified into three categories. These are, following the time line: conventional feet (CF), energy-storing-and-returning (ESR) feet and the recent so-called 'bionic' feet. Researchers have shown enhanced performance properties of ESR feet compared with early CF. However, even with the advanced technology, none of the ESR feet is capable of significantly reducing energy cost of walking or enhancing prosthetic gait (Nielsen et al. J Prosthet Orthotics 1989;1:24-31; Waters et al. J Bone Joint Surg Am 1976;58:42-46; Torburn et al. J Rehabil Res Dev 1990;27:369-384). From the 1990s, gradually more attention has been paid to the incorporation of active elements in prosthetic feet as the passive devices are not capable of providing the individual with sufficient ankle power during gait. Most part of the 'bionic' devices are still on the research level nowadays but one can expect that they will become available on the market soon. In this article, the evolution of prosthetic feet over the last two decades is reflected. The importance of mimicking human ankle-foot biomechanics with prosthetic feet is briefly discussed. Prior work in both objective and subjective evaluation of prosthetic gait is reported.

Robotic gait rehabilitation faces many challenges regarding ankle assistance, body weight support and physical human-robot interaction. This paper reports on the development of a gait rehabilitation exoskeleton prototype intended as a platform for the evaluation of design and control concepts in view of improved physical human-robot interaction. The performance of proxy-based sliding mode control as a “robot-in-charge” control strategy is evaluat both in simulation and in experiments on a test setup. Compared to PID control, test results indicate good tracking performance and in particular safe system behavior.

theforce exerted byapneumatic muscle actuator bymeasuring itsgaugepressure ischallenging since hysteresis isalmost alwayspresent. Thispaperinvestigates the hysteresis phenomenon inPleated Pneumatic Artificial Muscles, whichisfoundtobelargely independent ofgaugepressure. A Preisach basedhysteresis modelthatcancopewiththespecific shapeoftheforce-contraction characteristic ofpneumatic muscles isproposed, anditsresults arepresented.

Advances in Mobile Robotics, pp. 1216-1224 (2008) No AccessENERGY -EFFICIENT HUMANOID WALKING WITH ANKLE ACTUATION: LEARNING FROM BIOMECHANICSRINO VERSLUYS, BRAM VANDERBORGHT, RONALD VAN HAM, PIETER BEYL, PIERRE CHERELLE, and DIRK LEFEBERRINO VERSLUYSRobotics & Multibody Mechanics Research Group, Vrije Universiteit Brussel, Pleinlaan 2 Brussels, 1050, Belgium, BRAM VANDERBORGHTRobotics & Multibody Mechanics Research Group, Vrije Universiteit Brussel, Pleinlaan 2 Brussels, 1050, BelgiumItalian Institute of Technology, Robotics, Brain and Cognitive Sciences Department, Via Morego 30, Genova 16163, Italy, RONALD VAN HAMRobotics & Multibody Mechanics Research Group, Vrije Universiteit Brussel, Pleinlaan 2 Brussels, 1050, Belgium, PIETER BEYLRobotics & Multibody Mechanics Research Group, Vrije Universiteit Brussel, Pleinlaan 2 Brussels, 1050, Belgium, PIERRE CHERELLERobotics & Multibody Mechanics Research Group, Vrije Universiteit Brussel, Pleinlaan 2 Brussels, 1050, Belgium, and DIRK LEFEBERRobotics & Multibody Mechanics Research Group, Vrije Universiteit Brussel, Pleinlaan 2 Brussels, 1050, Belgiumhttps://doi.org/10.1142/9789812835772_0147Cited by:0 (Source: Crossref) PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: This paper reports on the importance of understanding human walking biomechanics for the design of new robotic and/or prosthetic feet. Based on human ankle behavior, the design specifications for new ankle-foot systems are determined. Three electrically powered ankle-foot design concepts are described. This work is supported by FWO Flanders, Belgium. FiguresReferencesRelatedDetails Recommended Advances in Mobile RoboticsMetrics History PDF download

This paper reports on the development of a powered below-knee (BK) prosthesis. The initial prosthesis prototype is a pneumatically powered system, which serves as test bed for proof-of-concept and evaluating control algorithms in laboratory conditions. The mechatronical design of the prosthesis is described, including the selection, the characteristics and working principle of its actuators. The control approach is discussed. First experimental results with an amputee are presented that demonstrate the promising performance properties of the powered prosthesis in restoring ankle power to the user in level walking.

In this paper a strategy is proposed to combine active trajectory tracking for bipedal robots with exploiting the natural dynamics by simultaneously controlling the torque and stiffness of a compliant actuator. The goal of this research is to preserve the versatility of actively controlled humanoids, while reducing their energy consumption. The biped Lucy, powered by pleated pneumatic artificial muscles, has been built and controlled and is able to walk up to a speed of 0.15 m/s. The pressures inside the muscles are controlled by a joint trajectory tracking controller to track the desired joint trajectories calculated by a trajectory generator. However, the actuators are set to a fixed stiffness value. In this paper a compliance controller is presented to reduce the energy consumption by controlling the stiffness. A mathematical formulation has been developed to find an optimal stiffness setting depending on the desired trajectory and physical properties of the system and the proposed strategy has been validated on a pendulum structure powered by artificial muscles. This strategy has not been implemented on the real robot because the walking speed of the robot is currently too slow to benefit already from compliance control.

In general, prosthetic feet can be classified in three categories. These are, following the time line: Conventional Feet (CF), Energy-Storing-and-Returning (ESR) feet, and recent so-called dasiabionicpsila feet. Research studies have shown enhanced performance properties of ESR feet compared to early CF. However, even with the advanced technology today, none of the ESR feet is capable of significantly reducing energy cost of walking or enhancing amputeepsilas gait pattern. From the 1990s gradually more attention has been paid to the incorporation of active elements in prosthetics as passive devices are not capable of providing the amputee with sufficient ankle power during gait. Most of these bionic devices are still on research level nowadays but one can expect that they will become available on the market soon. In this paper, the evolution of prosthetic feet over the last two decades is reflected. The importance of mimicking human ankle biomechanics in prosthetic foot design is discussed. Prior work on both objective and subjective evaluation of TT (transtibial = through the lower leg) amputee gait when fitted with different prosthetic feet is reported.

The biped Lucy, powered by pleated pneumatic artificial muscles, has been built and controlled and is able to walk up to a speed of 0.15 m/s. The pressures inside the muscles are controlled by a joint trajectory tracking controller to track the desired joint trajectories calculated by a trajectory generator. However, the actuators are set to a fixed stiffness value. In this paper a compliance controller is proposed which can be added in the control architecture to reduce the energy consumption by exploiting the natural dynamics. The goal of this research is to preserve the versatility of actively controlled humanoids, while reducing their energy consumption. A mathematical formulation has been developed to find an optimal stiffness setting depending on the desired trajectory and physical properties of the system and the proposed strategy has been validated on a pendulum structure powered by artificial muscles. This strategy has not been implemented on the real robot because the walking speed of the robot is currently too slow to benefit already from compliance control.