Welcome to our special issue on lower and upper limb exoskeletons. Robotic exoskeletons are a species of Wearable Robots. The distinctive, specific and singular aspect of exoskeletons is that the exoskeleton's kinematic chain maps onto the human limb anatomy. There is a one-to-one correspondence between human anatomical joints and the robot's joints or sets of joints. This kinematic compliance is a key aspect in achieving ergonomic human–robot interfaces. In exoskeletons, there is an effective transfer of power and information between the human and the robot. Humans and exoskeletons are in close physical and cognitive interaction.
In this issue you will find some important articles on this exciting field, addressing both upper and lower limb exoskeletons. We believe that this field overlaps significantly with the intended scope of Applied Bionics and Biomechanics. This issue covers first upper limb exoskeletons, and then it focuses on lower extremity exoskeletons.
First, a number of articles address the topic of rehabilitation through upper limb exoskeletons. In particular, the objective of article ‘Suitability of Hydraulic Disk Brakes for Passive Actuation of Upper-extremity Rehabilitation Exoskeleton’ is to determine if hydraulic disk brakes are suitable to actuate an upper-extremity exoskeleton for application in rehabilitation settings. Next, the article ‘A Force-feedback Exoskeleton for Upper Limb Rehabilitation in Virtual Reality’ focuses on the design and the clinical validation of an upper-limb force-feedback exoskeleton, the L-EXOS, for robotic-assisted rehabilitation in virtual reality (VR). Following with upper limb exoskeletons in rehabilitation scenarios, the article ‘ARMin III - Arm Therapy Exoskeleton with an Ergonomic Shoulder Actuation’ starts with describing a simplified model of the human shoulder; and on the basis of this model, a new ergonomic shoulder actuation principle that provides motion of the humerus head is proposed, and its implementation in the ARMin III arm therapy robot is described. The focus lies on the mechanics and actuation principle.
In the field of robotic exoskeletons, physical Human–Robot (HR) interaction is an issue which involves both kinematics and dynamics aspects. In the article ‘IKO: a Five Actuated DoF Upper Limb Exoskeleton Oriented to Workplace Assistance’ the aim is to find the best compromise between maximum reachable workspace and minimum moving mass, which are the key factors for obtaining ergonomic, wearable exoskeletons. Likewise, the influence of attachment pressure and kinematic compatibility on the physical interaction is thoroughly addressed in the article ‘Influence of Attachment Pressure and Kinematic Configuration on pHRI With Wearable Robots’. Dynamics aspects of the physical HR interactions are addressed in the article ‘Isotropy of an Upper Limb Exoskeleton and the Kinematics and Dynamics of the Human Arm’.
An important aspect in the design of exoskeletons is bioinspiration. Bioinspiration is a source of information for the design of all system's components. In particular, the article ‘Bio-inspired Control of an Arm Exoskeleton Joint with Active-compliant Actuation System’ presents the methodology followed on the design of a multi-contact point haptic interface that uses a bioinspired control approach and a novel actuation system. The combination of these components aims at creating a system that increases the operability of the target, and, simultaneously, it enables an intuitive and safe tele-operation of any complex robotic system of any given morphology.
Bioinspiration is chiefly based on modelling human structures and control. In this regard, the article ‘Exoskeleton-Based Robotic Platform Applied in Biomechanical Modelling of the Human Upper Limb’, first, it describes the design, development and validation of an experimental platform designed to modify or perturb the mechanics of human movement, and simultaneously acquire, process, display and quantify bioelectric and biomechanical signals; and then it characterises the dynamics of the elbow joint during postural control. In a similar way, a system for finger stiffness measurements is presented in article ‘Design of a 2-Finger Hand Exoskeleton for Finger Stiffness Measurements’.
Finally, two lower limb exoskeletons are fully described in this special issue. First, in the article ‘Design and Control of a Lower Limb Exoskeleton for Robot-assisted Gait Training’ the development of a gait rehabilitation exoskeleton with a knee joint powered by pleated pneumatic artificial muscles is introduced. It is intended as a platform for the evaluation of design and control concepts in view of improved physical human–robot interaction. Next, the article ‘Analysis of the Human Interaction in the Design of a Wearable Lower-Limb Exoskeleton’ presents a method to analyse the interaction between the human user and a unilateral, wearable lower-limb exoskeleton. The lower-limb exoskeleton function was to compensate for muscle weakness around the knee joint. It is shown that the cognitive interaction is bidirectional; on the one hand, the robot gathered information from the sensors in order to detect human actions, such as the gait phases, but the subjects also modified their gait patterns to obtain the desired responses from the exoskeleton.
We would like to mention that Applied Bionics and Biomechanics will be publishing in the near future other special issues on: Humanoid Robots; Biologically Inspired Robots and Mechanisms; Robot Assisted Surgery; and on Human–Robot Interface/Interaction. Those special issues will again contain significant contributions on the fields.
Applied Bionics and Biomechanics warmly welcomes past, present and new authors to the regular and special issues of the journal that it is truly international in scope with published manuscripts from all over the world. We hope that the regular issues, this special issue on lower and upper limb exoskeletons, and the upcoming special issues, will continue to be of great interest, use and benefit to you.