A Review of SMA-Based Actuators for Bidirectional Rotational Motion: Application to Origami Robots

Shape memory alloys (SMAs) are a group of metallic alloys capable of sustaining large inelastic strains that can be recovered when subjected to a specific process between two distinct phases. Regarding their unique and outstanding properties, SMAs have drawn considerable attention in various domains and recently became appropriate candidates for origami robots, that require bi-directional rotational motion actuation with limited operational space. However, longitudinal motion-driven actuators are frequently investigated and commonly mentioned, whereas studies in SMA-based rotational motion actuation is still very limited in the literature. This work provides a review of different research efforts related to SMA-based actuators for bi-directional rotational motion (BRM), thus provides a survey and classification of current approaches and design tools that can be applied to origami robots in order to achieve shape-changing. For this purpose, analytical tools for description of actuator behaviour are presented, followed by characterisation and performance prediction. Afterward, the actuators’ design methods, sensing, and controlling strategies are discussed. Finally, open challenges are discussed

A HIGH EFFICIENCY PNEUMATIC DRIVE SYSTEM USING VANE-TYPE SEMI-ROTARY ACTUATORS

A compressed air driven generator is proposed, where the pneumatic energy is converted into mechanical energy using two vane-type rotational actuators. The use of a second actuator with a higher displacement in order to produce a thermodynamic expansion allows to reach a better energetic efficiency in comparison to the classical operation of such actuators. The alternating movement of the angular actuators is transformed into a unidirectional rotational motion with the help of a mechanical motion rectifier. The paper analyses the enhancement of the energetic performance of the system. An experimental set-up is also described. The performance of the new system is described, and the limits of its realization is commented on the base of experimental recordings of the evolution of the pressure in the chambers

Design of a self-tunable, variable-length pendulum for harvesting energy from rotational motion

In this paper, a self-tunable energy harvester based on pendulum oscillations with a mechanical motion rectifier (MMR) system, which can convert vibration into electrical energy, is proposed. The harvester is composed of a pendulum excited by a slider-crank mechanism. The pendulum system is designed to automatically adjust its own natural frequency to match that of the imposed base excitation. Frequency adjustment in a proposed pendulum-type energy harvester is achieved by varying the length of the pendulum rod through changing the position of pendulum mass which mounted at its tip. The pendulum mass is driven by a ball screw through a stepper motor which controls the length of the pendulum automatically in accordance with the frequency of the external motion. The base motion frequency is detected by an infrared sensor. An ultrasonic distance sensor is used to detect the length of the pendulum rod and feeds this information to a microcontroller to obtain the corresponding natural frequency from a lookup table. The microcontroller calculates the frequency difference between natural frequency and excitation frequency and converts this value into a length difference through another lookup table. The microcontroller then gives instructions to drive a stepper motor through a sequence of steps to achieve the target length and keeps the device in resonance state to harvest maximum power during operation. Different time detection intervals were studied to investigate their effect on the tuning process. This study showed that the longer time intervals increase the detection accuracy for the calculation of low excitation frequency. The amount of energy consumed during the tuning process to adjust the pendulum length is presented. In this context, the consumed energy is only needed until the resonance of the device matches the excitation frequency. The harvester system was studied numerically and experimentally. Based on the findings of this work, the natural frequency of the harvester is successfully tuned below 0.7 Hz, when the length of pendulum rod is changed from 550 mm to 900 mm, generating power from 1.78 W to 4.1 W at an optimal load resistance value of 10 Ω and 3 Ω respectively at maximum excitation amplitude of 120 mm. Therefore, the proposed pendulum system can be used as an efficient harvester for producing power in low-frequency applications (< 1 Hz)

Pneumatic Artificial Muscle Driven Trailing Edge Flaps For Active Rotors

This research focuses on the development of an active rotor system capable of primary control and vibration reduction for rotorcraft. The objective is to investigate the feasibility of a novel Trailing Edge Flap (TEF) actuation system driven by Pneumatic Artificial Muscles (PAMs). A significant design effort led to a series of experimental apparatuses which tested various aspects of the performance of the actuators themselves and of TEF systems driven by them. Analytical models were developed in parallel to predict the quasistatic and dynamic behavior of these systems. Initial testing of a prototype blade section with an integrated PAM driven TEF proved the viability of the concept through successful benchtop testing under simulated M = 0.3 loading and open jet wind tunnel tests under airspeeds up to M = 0.13. This prototype showed the ability of PAM actuators to generate significant flap deflections over the bandwidth of interest for primary control and vibration reduction on a rotorcraft. It also identified the importance of high pneumatic system mass flow rate for maintaining performance at higher operating frequencies. Research into the development and improvement of PAM actuators centered around a new manufacturing technique which was invented to directly address the weaknesses of previous designs. Detailed finite element model (FEM) analysis of the design allowed for the mitigation of stress concentrations, leading to increased strength. Tensile testing of the swaged actuators showed a factor of safety over 5, and burst pressure testing showed a factor of safety of 3. Over 120,000,000 load cycles were applied to the actuators without failure. Characterization testing before, during, and after the fatigue tests showed no reduction in PAM performance. Wind tunnel testing of a full scale Bell 407 blade retrofitted with a PAM TEF system showed excellent control authority. At the maximum wind tunnel test speed of M = 0.3 and a derated PAM operating pressure of 28 psi, 18.8° half-peak-to-peak flap deflections were achieved at 1/rev (7 Hz), and 17.1° of half-peak-to-peak flap deflection was still available at 5/rev (35 Hz). A quasistatic system model was developed which combined PAM forces, kinematics and flap aerodynamics to predict flap deflection amplitudes. This model agreed well with experimental data. Whirl testing of a sub-span whirl rig under full scale loading conditions showed the ability of PAM TEF systems to operate under full scale levels of centrifugal (CF), aerodynamic, and inertia loading. A commercial pneumatic rotary union was used to provide air in the rotating frame. Extrapolation of the results to 100% of CF acceleration predicts 15.4° of half-peak-to-peak flap deflection at 1/rev (7 Hz), and 7.7° of half-peak-to-peak flap deflection at 5/rev (35 Hz). A dynamic model was developed which successfully predicted the time domain behavior of the PAM actuators and PAM TEF system. This model includes control valve dynamics, frictional tubing losses, pressure dynamics, PAM forces, mechanism kinematics, aerodynamic hinge moments, system stiffness, damping, and inertia to solve for the rotational dynamics of the flap. Control system development led to a closed loop control system for PAM TEF systems capable of tracking complex, multi-sinusoid flap deflections representative of a combined primary control and vibration reduction flap actuation scheme. This research shows the promise that PAM actuators have as drivers for trailing edge flaps on active helicopter rotors. The robustness, ease of integration, control authority and tracking accuracy of these actuators have been established, thereby motivating further research

Design of a bidirectional rotational motion actuator by SMA with geometrico-static requirements

International audience<div style=""&gt<font face="arial, helvetica"&gt<span style="font-size: 13px;"&gtShape memory alloys (SMAs) are a group of metallic alloys capable of sustaining large inelastic strains that can be recovered when subjected to a specific process between two distinct phases. Advantages of SMAsreasonable strain, high energy density, mechanical simplicity, and long work-life render them ideal for actuator applications. Especially, Self-folding origami requires high angular motion ranges and low-profile actuators within limited space. Current applications demonstrate the capacity of millimeter-sized torsional SMAs (T-SMAs) for bi-directional rotational motion, but no comprehensive design method for such actuators can be found in the existing literature. To broaden applications of actuator designs, we introduce an inverse design model according to a geometrico-static demand. We couple the geometrical and mechanical properties of torsional SMAs considering assembly and working conditions to construct the design model. We also illustrate a comprehensive mechanical performance characterization for millimeter-sized torsional SMAs and BRM actuators.</span&gt</font&gt<br&gt</div&g

Toward actuation of Kresling pattern-based origami robots

International audienceThis work investigates the technical requirement for the actuation of the bi-directional rotational motion (BRM) of engineering-material-based non-rigid origami robots. While the vast majority of previously published results have focused on paper-based origami structures driven by translation-motion, polypropylene (PP) is implemented in this research to investigate its ability to respond to engineering requirements according to BRM. Following this objective, three experiments are proposed to identify the technical performances of PP-based origami and kirigami robots based on Kresling pattern. First, the stabilization test shows that two hundred full folding cycles are required to reach a repeatable mechanical response. Second, the BRM test characterizes the various mechanical performances of both origami and kirigami structure: the polypropylene(PP)-based origami outperforms existing structures in the literature. Third, the actuation test shows that the actuation mechanical requirements can be described using three key parameters: the required torque for folding, the shape-blocking stiffness, and the bistable portion. Finally, in order to support the development of PP-based origami/kirigami robots, a ‘Bar and Hinge’ reduced-order model is implemented for the description of the nonlinearhysteretic behavior and bistability. This method constitutes a useful tool for the designof highly nonlinear/bistable engineering structures based on PP origami and kirigami

Toward actuation of Kresling pattern-based origami robots

International audienceThis work investigates the technical requirement for the actuation of the bi-directional rotational motion (BRM) of engineering-material-based non-rigid origami robots. While the vast majority of previously published results have focused on paper-based origami structures driven by translation-motion, polypropylene (PP) is implemented in this research to investigate its ability to respond to engineering requirements according to BRM. Following this objective, three experiments are proposed to identify the technical performances of PP-based origami and kirigami robots based on Kresling pattern. First, the stabilization test shows that two hundred full folding cycles are required to reach a repeatable mechanical response. Second, the BRM test characterizes the various mechanical performances of both origami and kirigami structure: the polypropylene(PP)-based origami outperforms existing structures in the literature. Third, the actuation test shows that the actuationmechanical requirements can be described using three key parameters: the required torque for folding, the shape-blocking stiffness, and the bistable portion. Finally, in order to support the development of PP-based origami/kirigami robots, a ‘Bar and Hinge’ reduced-order model is implemented for the description of the nonlinear hysteretic behavior and bistability. This method constitutes a useful tool for the design of highly nonlinear/bistable engineering structures based on PP origami and kirigam

Toward actuation of Kresling pattern-based origami robots

International audienceThis work investigates the technical requirement for the actuation of the bi-directional rotational motion (BRM) of engineering-material-based non-rigid origami robots. While the vast majority of previously published results have focused on paper-based origami structures driven by translation-motion, polypropylene (PP) is implemented in this research to investigate its ability to respond to engineering requirements according to BRM. Following this objective, three experiments are proposed to identify the technical performances of PP-based origami and kirigami robots based on Kresling pattern. First, the stabilization test shows that two hundred full folding cycles are required to reach a repeatable mechanical response. Second, the BRM test characterizes the various mechanical performances of both origami and kirigami structure: the polypropylene(PP)-based origami outperforms existing structures in the literature. Third, the actuation test shows that the actuationmechanical requirements can be described using three key parameters: the required torque for folding, the shape-blocking stiffness, and the bistable portion. Finally, in order to support the development of PP-based origami/kirigami robots, a ‘Bar and Hinge’ reduced-order model is implemented for the description of the nonlinear hysteretic behavior and bistability. This method constitutes a useful tool for the design of highly nonlinear/bistable engineering structures based on PP origami and kirigam

Modelling and performance evaluation of an electromagnetic regenerative shock absorber with mechanical motion rectifier

This thesis is mainly concerned with the modelling of an electromagnetic regenerative shock absorber with mechanical motion rectifier (MMR), and its performance evaluation when it is implemented in the suspension of a road vehicle. Unlike a conventional regenerative shock absorber, the inclusion of a sprag-clutch within the MMR module enables the conversion of bi-directional rotational motion into unidirectional rotary input to the coupled electromagnetic generator. Previous studies have shown that the dynamics of a regenerative shock absorber with MMR can be modelled as a piecewise linear system produced by the engagement and disengagement of sprag-clutches within the MMR. It is seen that the MMR based system potentially works as a switchable inerter in parallel with a switchable damper. To characterise the proposed energy harvesting technique, the system is initially discussed when one terminal of the design is blocked, which allows further validations through experiments. In order to comprehensively study dynamics of MMR system, its energy harvesting as well as mechanical power flow performance are evaluated. Additionally, an analogy between the electrical and mechanical active and reactive power flow, using forcecurrent analogy is carried out. This allows better understanding of the power transmission between sub-systems. Moreover, the output of a conventional regenerative shock absorber is generally coupled with an electrical rectifier to convert the AC voltage signal to DC signal for either energy storage or charging electronic devices. In this work, to justify the usage of each rectifier, the electrical rectifier-based regenerative shock absorber is studied in both electrical and mechanical systems. The discussion is further extended to compare performances between electrical rectifiers and MMR in different scenarios. It is shown that MMR is able to offer much superior performance than electrical rectifiers, typically for lower power application. To validate theoretical predictions, the MMR based regenerative shock absorber is tested in a hydraulic Instron machine. A dynamic model of the proposed design is implemented, and its parameters are estimated from the measured data. In order to establish whether MMR allows acceptable energy harvesting performance when incorporated into the suspension of road vehicles, the first step is to investigate the characteristics of the vibration environment. By using the concept of mechanical impedance and mobility, dynamics of the vibration source is studied when the regenerative shock absorber is incorporated into a road vehicle. According to the vibration source characteristic results, the implementation of the MMR based regenerative shock absorber in the suspension system of road vehicles is discussed. The result shows that MMR enables better performance under certain conditions, but it results in a high jerk motion (excessive change of acceleration) as a trade-off. Finally, the procedure for the design of a mechanical motion rectified regenerative shock absorber for a road vehicle suspension system is presented. The proposed design guidelines enable a designer to select desirable parameters for the regenerative shock absorber based on the system constraints and the application environment