The Staircase Drive—A Novel Actuator Design Optimised for Daisy-Chaining and Minimum Stress Load Coupling

This work presents a novel type of actuator that improves over the standard cantilever by permitting daisy-chaining while minimising stress to the joint connecting to the load. A detailed structural and functional comparison of the proposed device against the cantilever actuator as a baseline is given, led by a brief revision of the cantilever actuator as the state-of-the-art that highlights its limitations with respect to daisy-chaining and the stress it inherently creates within the joint connecting to the load when attempting out-of-plane displacement without rotation. Simulations of both devices’ performance confirm that the newly proposed device yields the targeted displacement profile that both enables the daisy-chaining of such a device into a higher-order actuator for increased displacement and reduce stress in the joint with the load. This comes at the cost of reduced maximum displacement compared to the cantilever, which can be overcome by daisy-chaining. The proposed device’s performance is further evaluated on the basis of manufactured prototypes measured by means of a laser scanning vibrometer. The prototype was manufactured on a 150m alumina substrate, and both electrodes and piezoelectric layer were deposited in a thick-film printing process.

Virtual Actuator Design for Uncertain Metzler Systems

The paper presents the design conditions adequate in design of virtual actuators and utilizable by nominal static output control structures in fault-tolerant control for strictly Metzler systems. The positive stabilization with H∞ norm performance is also addressed for virtual actuator design for strictly Metzler systems with interval uncertainty matrix representations of single actuator faults. Taking into account disturbance conditions and changes of values of variables after the virtual actuator activation, the design conditions are outlined in the terms of linear matrix inequalities. The approach provides a way to obtain acceptable dynamics of the closed loop system after virtual actuator activation.

Fourier Analysis Guided Cable Actuator Design for Coordinated Walking Assistance

Cable-driven exoskeletons add minimal inertia and restrictions to the user’s leg while still providing feedback and quantitative measures of the user’s performance. However, cable robots require at least n + 1 cables to control n degrees-of-freedom, i.e., they require more actuators than the leg’s degrees-of-freedom, challenging their widespread adoption as wearable technology. The state-of-the-art in this field aims to reduce the number of actuated motors. In this paper, we design and evaluate a “single motor-driven” leg exoskeleton prototype based on the Cable-driven Active Leg EXoskleton (C-ALEX). The prototype consists of four crank-spring mechanisms and a crankshaft designed using epicycle analysis. The epicycle analysis is performed using discrete Fourier transform (DFT) and sine curve fitting (SCF). While DFT suggests the maximum number of epicycles to imitate the target waveform, a large number of nested epicycles is challenging to design and manufacture for implementation. To validate the epicycle-guided design, we constructed a simple crankshaft model using one epicycle. Our proposed simplified model predicted and produced the joint angles calculated from the inverse and forward kinematics of a cable-driven leg exoskeleton with multiple motors. To our knowledge, this is the first multi-cable driven exoskeleton powered by a single actuator that is designed to provide continuous assistance to the user.

Design of a contactless powered and piezoelectric-actuated tool for non-resonant low-frequency vibration-assisted machining of brittle-hard materials

Ultrasonic-assisted grinding (UAG) is the state-of-the-art process for machining of brittle-hard materials. In comparison to conventional processes, the main advantages lie in the reduction of tool wear and process forces. Such a vibration system is based on a resonant actuator and a power supply unit generating the alternating current. Both units are interconnected by a contactless energy transfer (CET) system. This system configuration shows one optimal working point at the resonant frequency with maximum amplitude, which is significantly depending on the tool shape. In this work, a piezo-activated tool system is designed to realize non-resonant low-frequency vibrations. Major emphasis is put on the thermal behavior of the piezo drive, particularly on the in-process heating depending on the working frequency. In addition, focus lays on the theoretical and numerical design of the radial operating transducer CET system for a previously set actuator design. As a result, this system configuration offers a fully variable adjustment of the amplitude from under 1 to over 50 μm at frequency range. Outside this range, higher amplitudes can be achieved for short periods to the detriment of the fatigue strength according to FKM.

Fully Polymeric Domes as High-Stroke Biasing System for Soft Dielectric Elastomer Actuators

The availability of compliant actuators is essential for the development of soft robotic systems. Dielectric elastomers (DEs) represent a class of smart actuators which has gained a significant popularity in soft robotics, due to their unique mix of large deformation (>100%), lightweight, fast response, and low cost. A DE consists of a thin elastomer membrane coated with flexible electrodes on both sides. When a high voltage is applied to the electrodes, the membrane undergoes a controllable mechanical deformation. In order to produce a significant actuation stroke, a DE membrane must be coupled with a mechanical biasing system. Commonly used spring-like bias elements, however, are generally made of rigid materials such as steel, and thus they do not meet the compliance requirements of soft robotic applications. To overcome this issue, in this paper we propose a novel type of compliant mechanism as biasing elements for DE actuators, namely a three-dimensional polymeric dome. When properly designed, such types of mechanisms exhibit a region of negative stiffness in their force-displacement behavior. This feature, in combination with the intrinsic softness of the polymeric material, ensures large actuation strokes as well as compliance compatibility with soft robots. After presenting the novel biasing concept, the overall soft actuator design, manufacturing, and assembly are discussed. Finally, experimental characterization is conducted, and the suitability for soft robotic applications is assessed.

Design of an Inkjet-Printed Rotary Bellows Actuator and Simulation of its Time-Dependent Deformation Behavior

State-of-the-art Additive Manufacturing processes such as three-dimensional (3D) inkjet printing are capable of producing geometrically complex multi-material components with integrated elastomeric features. Researchers and engineers seeking to exploit these capabilities must handle the complex mechanical behavior of inkjet-printed elastomers and expect a lack of suitable design examples. We address these obstacles using a pneumatic actuator as an application case. First, an inkjet-printable actuator design with elastomeric bellows structures is presented. While soft robotics research has brought forward several examples of inkjet-printed linear and bending bellows actuators, the rotary actuator described here advances into the still unexplored field of additively manufactured pneumatic lightweight robots with articulated joints. Second, we demonstrate that the complex structural behavior of the actuator’s elastomeric bellows structure can be predicted by Finite Element (FE) simulation. To this end, a suitable hyperviscoelastic material model was calibrated and compared to recently published models in a multiaxial-state-of-stress relaxation experiment. To verify the material model, Finite Element simulations of the actuator’s deformation behavior were conducted, and the results compared to those of corresponding experiments. The simulations presented here advance the materials science of inkjet-printed elastomers by demonstrating use of a hyperviscoelastic material model for estimating the deformation behavior of a prototypic robotic component. The results obtained contribute to the long-term goal of additively manufactured and pneumatically actuated lightweight robots.

Design of a Fluidic Actuator with Independent Frequency and Amplitude Modulation for Control of Swirl Flame Dynamics

Fluidic actuators are designed to control the oscillatory helical mode, called a precessing vortex core (PVC), which is often observed in gas turbine combustors. The PVC induces large-scale hydrodynamic coherent structures, which can considerably affect flow and flame dynamics. Therefore, appropriate control of this structure can lead to a more stable and efficient combustion process. Currently available flow control systems are designed to control the PVC in laboratory-scale setups. To further develop these systems and find an approach applicable to the industrial scale, a new actuator design based on fluidic oscillators is presented and studied in this paper. This actuator allows for independently adjusting forcing frequency and amplitude, which is necessary to effectively target the dynamics of the PVC. The functionality and flow control of this actuator design are studied based on numerical simulations and experimental measurements. To verify the flow control authority, the actuator is built into a prototype combustor test rig, which allows for investigating the impact of the actuator’s forcing on the PVC at isothermal conditions. The studies conducted in this work prove the desired functionality and flow control authority of the 3D-printed actuator. Accordingly, a two-part stainless steel design is derived for future test conditions with flame.