https://ris.utwente.nl/ws/files/6520436/pp.pdf

Variable impedance actuators: A review

We describe the design, fabrication, and calibration of a highly compliant artificial skin sensor. The sensor consists of multilayered mircochannels in an elastomer matrix filled with a conductive liquid, capable of detecting multiaxis strains and contact pressure. A novel manufacturing method comprised of layered molding and casting processes is demonstrated to fabricate the multilayered soft sensor circuit. Silicone rubber layers with channel patterns, cast with 3-D printed molds, are bonded to create embedded microchannels, and a conductive liquid is injected into the microchannels. The channel dimensions are 200 μm (width) × 300 μm (height). The size of the sensor is 25 mm × 25 mm, and the thickness is approximately 3.5 mm. The prototype is tested with a materials tester and showed linearity in strain sensing and nonlinearity in pressure sensing. The sensor signal is repeatable in both cases. The characteristic modulus of the skin prototype is approximately 63 kPa. The sensor is functional up to strains of approximately 250%.

Design and Fabrication of Soft Artificial Skin Using Embedded Microchannels and Liquid Conductors

The development of soft pneumatic actuators based on composites consisting of elastomers with embedded sheet or fiber structures (e.g., paper or fabric) that are flexible but not extensible is described. On pneumatic inflation, these actuators move anisotropically, based on the motions accessible by their composite structures. They are inexpensive, simple to fabricate, light in weight, and easy to actuate. This class of structure is versatile: the same principles of design lead to actuators that respond to pressurization with a wide range of motions (bending, extension, contraction, twisting, and others). Paper, when used to introduce anisotropy into elastomers, can be readily folded into 3D structures following the principles of origami; these folded structures increase the stiffness and anisotropy of the elastomeric actuators, while being light in weight. These soft actuators can manipulate objects with moderate performance; for example, they can lift loads up to 120 times their weight. They can also be combined with other components, for example, electrical components, to increase their functionality.

/pdf/elastomeric-origami-programmable-paper-elastomer-composites-1ljwfzw74i.pdf

Elastomeric Origami: Programmable Paper-Elastomer Composites as Pneumatic Actuators

Artificial muscles hold promise for safe and powerful actuation for myriad common machines and robots. However, the design, fabrication, and implementation of artificial muscles are often limited by their material costs, operating principle, scalability, and single-degree-of-freedom contractile actuation motions. Here we propose an architecture for fluid-driven origami-inspired artificial muscles. This concept requires only a compressible skeleton, a flexible skin, and a fluid medium. A mechanical model is developed to explain the interaction of the three components. A fabrication method is introduced to rapidly manufacture low-cost artificial muscles using various materials and at multiple scales. The artificial muscles can be programed to achieve multiaxial motions including contraction, bending, and torsion. These motions can be aggregated into systems with multiple degrees of freedom, which are able to produce controllable motions at different rates. Our artificial muscles can be driven by fluids at negative pressures (relative to ambient). This feature makes actuation safer than most other fluidic artificial muscles that operate with positive pressures. Experiments reveal that these muscles can contract over 90% of their initial lengths, generate stresses of ∼600 kPa, and produce peak power densities over 2 kW/kg-all equal to, or in excess of, natural muscle. This architecture for artificial muscles opens the door to rapid design and low-cost fabrication of actuation systems for numerous applications at multiple scales, ranging from miniature medical devices to wearable robotic exoskeletons to large deployable structures for space exploration.

https://www.pnas.org/content/pnas/114/50/13132.full.pdf

Fluid-driven origami-inspired artificial muscles

We describe the design and control of a wearable robotic device powered by pneumatic artificial muscle actuators for use in ankle–foot rehabilitation. The design is inspired by the biological musculoskeletal system of the human foot and lower leg, mimicking the morphology and the functionality of the biological muscle–tendon–ligament structure. A key feature of the device is its soft structure that provides active assistance without restricting natural degrees of freedom at the ankle joint. Four pneumatic artificial muscles assist dorsiflexion and plantarflexion as well as inversion and eversion. The prototype is also equipped with various embedded sensors for gait pattern analysis. For the subject tested, the prototype is capable of generating an ankle range of motion of 27 ◦ (14 ◦ dorsiflexion and 13 ◦ plantarflexion). The controllability of the system is experimentally demonstrated using a linear time-invariant (LTI) controller. The controller is found using an identified LTI model of the system, resulting from the interaction of the soft orthotic device with a human leg, and model-based classical control design techniques. The suitability of the proposed control strategy is demonstrated with several angle-reference following experiments.

/pdf/design-and-control-of-a-bio-inspired-soft-wearable-robotic-110pb507k2.pdf

Design and control of a bio-inspired soft wearable robotic device for ankle-foot rehabilitation.

The increasing demand for physical interaction between humans and robots has led to an interest in robots that guarantee safe behavior when human contact occurs. However, attaining established levels of performance while ensuring safety creates formidable challenges in mechanical design, actuation, sensing and control. To promote safety without compromising performance, a human-friendly robotic arm has been developed using the concept of hybrid actuation. The new design employs high-power, low-impedance pneumatic artificial muscles augmented with small electrical actuators, distributed compact pressure regulators with proportional valves, and hollow plastic links. The experimental results show that significant performance improvement can be achieved with hybrid actuation over a system with pneumatic muscles alone. In this paper we evaluate the safety of the new robot arm through experiments and simulation, demonstrating that its inertia/power characteristics surpass those of previous human-friendly robots we have developed.

/pdf/design-and-control-of-a-bio-inspired-human-friendly-robot-4a0yhdyvtm.pdf

Design and Control of a Bio-inspired Human-friendly Robot

Safety is a critical characteristic for robots designed to operate in human environments. This paper presents the concept of hybrid actuation for the development of human- friendly robotic systems. The new design employs inherently safe pneumatic artificial muscles augmented with small electrical actuators, human-bone-inspired robotic links, and newly designed distributed compact pressure regulators. The modularization and integration of the robot components enable low complexity in the design and assembly. The hybrid actuation concept has been validated on a two-degree-of-freedom prototype arm. The experimental results show the significant improvement that can be achieved with hybrid actuation over an actuation system with pneumatic artificial muscles alone. Using the manipulator safety index (MSI), the paper discusses the safety of the new prototype and shows the robot arm safety characteristics to be comparable to those of a human arm.

/pdf/a-hybrid-actuation-approach-for-human-friendly-robot-design-4h1auzlu78.pdf

A hybrid actuation approach for human-friendly robot design

Recently, vacuum-based layer jamming mechanisms have been actively researched for safe human–robot interaction. However, most conventional layer jamming mechanisms provide restricted motion in one direction such that their application in wearable robots is significantly limited. To address this problem, we propose a novel, soft, multi-degree of freedom (multi-DoF) layer jamming mechanism that employs a sliding linkage-based layer jamming mechanism (SLLJ). The proposed SLLJ allows movement not only in the linear direction, but also in the pitch and yaw directions. Furthermore, the SLLJ can control its stiffness in multi-directions and generate a large resisting force with small thickness and light weight. Experimental results show that the maximum linear resisting force of SLLJ is 264.8 N, which is comparable to the conventional layer jamming mechanism, and the maximum yaw resisting torque is 1.363 Nm before buckling. In addition, the stiffness of the SLLJ can be increased by 96.6 folds in the linear direction and 60.02 folds in the yaw direction when the SLLJ transforms from soft state to rigid state. Being fabricated in various shapes, the SLLJ can be adapted to a wide range of wearable robots, which require multi-DoF motions with variable stiffness and substantial resisting force.

Soft, Multi-DoF, Variable Stiffness Mechanism Using Layer Jamming for Wearable Robots

This study explores, in the context of automated braking, how a voice alert accompanying the car's autonomous action affects the driver's attitude and driving behaviour To examine the research question we designed an experimental setup in a simulator environment that (1) enabled automatic braking to perform as a vehicle's autonomous longitudinal behaviour and (2) enacted a voice alert system in a timely way to notify the driver of pending brake actions Subjective driving experience and driver responses towards the car were strongly affected by the voice alerts when the car made automated decisions These results have important implications for the design of vehicle-user interfaces, suggesting that, rather than simply developing a car that executes autonomous decisions, car makers should also focus on the human-machine interaction, ie, on how the car announces its 'intentions' to act

Understanding driver responses to voice alerts of autonomous car operations

There is a growing interest in soft actuators for human-friendly robotic applications. However, it is very challenging for conventional soft actuators to achieve both a large working dista...

Dongjun Shin

Papers

Design and Control of a Bio-inspired Human-friendly Robot

A hybrid actuation approach for human-friendly robot design

Soft, Multi-DoF, Variable Stiffness Mechanism Using Layer Jamming for Wearable Robots

Understanding driver responses to voice alerts of autonomous car operations

A Novel Soft Pneumatic Artificial Muscle with High-Contraction Ratio.