Torsional Spring Research Articles

Novel torsional spring with corrugated flexible units for series elastic actuators for cooperative robots

Novel torsional spring with corrugated flexible units for series elastic actuators for cooperative robots

인장스프링을 활용한 모터 직접 구동형 양방향 날갯짓 장치 개발

This paper proposes a direct-driven bi-directional actuation flapping wings system using an extension spring instead of a torsional spring. Then, the proposed flapping-wing system’s mathematical model is derived and analyzed. A prototype is fabricated using a DC motor, an extension spring, pinion gear, spur gear, and a flapping wing. The performance of the proposed wing is measured using an oscilloscope, a load cell, and a high-speed camera. The results demonstrate that the system works well without fatigue failure or the spring’s mechanical deformation. Additionally, it can generate 11.1 g of thrust when 24 Hz driving signal is applied using 12 V PWM, which is sufficient to fly 20 g micro air vehicles using dual flapping-wing systems. The wing flapping system’s energy consumption is 13.95 W, which means that more than a 1-minute flight is possible using a 7.4 V battery with 70 mAh capacity.

Design and evaluation of coconut fiber bionic‐stripping device based on Lucanidae palate frictional characteristics

AbstractManual stripping of coconut fiber has low processing efficiency coupled with difficulty in operation. To overcome these problems, a coconut fiber bionic‐stripping device based on Lucanidae palate frictional characteristics was designed. The device relied on the torsion spring edge hook and brush working principle to strip the coconut fiber. The coconut shell was not damaged during the stripping operation owing to the elasticity and toughness of the bionic torsional spring. The test parameter optimization was carried out using the coconut fiber bionic‐stripping device and analyzed using Design‐Expert.V8.0.6 Software. The results showed that the planting distance between torsion springs had significant effect on stripping coconut fiber (p < .001), but the diameter of torsion spring had the least effect on stripping coconut fiber. Regression analysis of the test data showed that the device had higher processing efficiency at coconut rotation speed of 1200 rad/min, coupled with bionic torsion springs diameter and planting distance of 2.0 and 17 mm, respectively. Under optimal combination of parameters, coconut fiber removal thickness was found to be R△ = 30.9 mm. The data obtained showed high repeatability, thereby indicating that the coconut fiber bionic‐stripping device can meet the technological requirements for coconut fiber removal.Practical ApplicationsThis study focuses on coconut characteristics as well as the process requirements for coconut fiber removal. A mechanism to strip the fiber using bionic torsion springs was proposed, which was designed based on the characteristics of the Lucanidae palate. Including a device for peeling coconut fiber using bionic torsion springs. Furthermore, the structural stress analysis of the device was carried out so as to explore the feasibility of using the bionic torsion spring group to peel coconut fiber. Parameter optimization test, performance analysis, and comparative performance analysis were carried out using the device to analyze the influence of different bionic torsion spring group parameters on the thickness of stripped coconut fiber. This can provide a theoretical and experimental basis for the study of coconut fiber stripping mechanism, and can broaden the existing research methods of coconut fiber stripping.

Determining Entanglement Molar Mass of Glassy Polyphenylenes Using Mechanochromic Molecular Springs.

Molecular force transduction in tough and glassy poly(meta,meta,para-phenylene) (PmmpP) was investigated as a function of Mn using covalently incorporated mechanochromic donor-acceptor torsional springs based on an ortho-substituted diphenyldiketopyrrolopyrrole (oDPP). Blending oDPP-PmmpP probe chains with long PmmpP matrix chains allowed us to investigate molar-mass-dependent mechanochromic properties for a series of specimens having mechanically identical properties. In the strain-hardening regime, the mechanochromic response (Δλmax,em) was found to be a linear function of the acting stress and fully reversible, making oDPP-PmmpP a real-time and quantitative stress sensor. For entangled and nonentangled probe chains, distinctly different values of Δλmax,em were observed, yielding a critical molar mass of Mc ≈ 11 kg mol-1 for PmmpP. Once physical cross-linking of oDPP in the network of PmmpP was ensured, Δλmax,em was found to be independent of Mn. The resulting value of Mc is in very good agreement with results from rheology.

Analysis of thrust blocks systems: Pipeline, soil and foundation interaction

The aim of this study is to evaluate the behavior of a discharge manifold that has space restrictions. These restrictions do not allow a suitable design by the usual practice. Thus, for its evaluation an upgraded methodology was necessary for structural analysis and revision. The upgrade includes the soil-thrust blocks-pipeline interaction and the influence of fittings outside the blocks using a simplified model. The manifold was assumed as a whole structure. The pipeline was modelled with frame elements. The behavior of the thrust blocks was simulated by means of a Winkler-like model with torsional and horizontal springs. Additionally, the influence of reducers and valves lying outside the blocks was included. Two analyses were performed. The first one, the interaction between soil, thrust blocks and pipeline is neglected; the second one includes the interaction among the elements. It is concluded that the overall capacity of the structural system increases when the interaction among elements is considered. The effects due to the interaction and the fittings lying outside the blocks can be estimated with the proposed model. Finally, it is shown that the reducers not embedded in the blocks produce a significant increment (up to 47%) in the pipeline longitudinal stresses. Nevertheless, the manifold resulted suitable for its operation. Thus, to evaluate a manifold that has space restrictions the enhanced methodology described in this paper can be used.

Study of bipedal locomotion considering property of toe mechanism

Walking behaviour of the humanoid robot depends on many parameters of body structure, in which, the foot structure is one of the most important factors since it directly interacts with the environment in the locomotion. In this paper, joint characteristics of the robot’s foot have been investigated for our further understanding of biped motion. These properties are stiffness and damping factor of spring of passive toe joints. The subject of this paper is a small humanoid robot named Kondo KHR-3HV belonging to the Kondo Kagaku company. The foot structure of the robot consists of a big toe and a tiptoe with passive joints using torsion spring. The effect of the structure property is collected and evaluated through dynamic simulation on Adams and analysis of variance (ANOVA).

Torsional and longitudinal vibration analysis of a porous nanorod with arbitrary boundaries

In the present study, free torsional and axial vibrations of porous nanorods with torsional, axial elastic boundary conditions are presented via Eringen’s nonlocal elasticity theory. This theory takes into account the small size effect into the differential formulation due to dealing with nano-sized structures. Even though free axial and torsional vibrations based analysis of nanorod is a widely investigated topic, there are only few researches which exist in the scientific literature pertaining to the vibration analysis of porous nanostructures with nonrigid (deformable) boundary conditions. This study brings a contribution to the literature by presenting both porosity and small size effects with deformable boundary conditions. It is also planned to examine the effects of porosity and small size in detail. A model that allows to examine all of these effects within the framework is created within the scope of this study. To this end two torsional and axial springs are attached to the porous nanorod at both ends separately. Present model bridges the gap between deformable and non-deformable (rigid) boundary conditions. An eigen-value problem is constructed including torsional and axial coefficients by using Stoke transformation and the Fourier sine series. The novelty of this work is that it seeks to construct a general eigen value algorithm for the torsional and axial vibration frequencies of the porous nanorods subjected to the deformable and rigid boundary conditions for the first time. Moreover, the effects of some parameters such as porosity index, axial and torsional restraints on the free vibration frequencies are investigated and some conclusions are drawn.

A novel design of planar high-compliance joint in variable stiffness module with multiple uniform stress leaf branches on rigid-flexible integral linkage

Benefit from the elastic element in the drivetrain, the variable stiffness actuators offer advantages over traditional rigid actuators in security, robustness, energy consumption. However, it is also very bulky due to the integration of the elastic element, especially with large deflection and high load. This article introduces a novel planar high-compliance joint, in which the torsion spring is not an independent part but a synergy result of two adjacent parts developed from the stiffness adjustment linkage mechanism. The flexible element is a cantilever leaf feature belongs to the rigid-flexible integral linkage. The deflection and load ability of the torsion spring can be enhanced by arranging multiple uniform stress leaf branches on the integral linkage without increasing the size. Explicit analytical formulas are derived in a form convenient for leaf parameters design and verified by the finite element simulation and prototype experiments. Finally, the error factors are quantitatively analyzed, which can provide information for the leaf correction design. This kind of planar high-compliance joint is expected to be an ideal choice for the variable stiffness actuators that require stringent axial compactness with large deflection and high load.

A Novel Design of Torsion Spring-Connected Nonlinear Stiffness Actuator Based on Cam Mechanism

Abstract The nonlinear stiffness actuator (NSA) is a type of compliant joint with variable stiffness that is necessary for human–machine collaboration and has been the focus of extensive research attention. This academic work presents the principle of a torsion spring-connected nonlinear stiffness actuator (TSNSA), a NSA suitable for implementing revolute motions, which contrasts with existing NSAs that often have bulky mechanisms and are affected by a limited range of movement. It has a split sleeve, disc springs, and cam mechanisms (CMs) that when correctly configured, can passively and actively adjust stiffness, where the speed of stiffness regulation can be effectively improved. The mathematical model of a split sleeve inserted into a torsion spring is designed to analyze the behavior of mechanical components. Furthermore, a detailed CM profile has been designed to obtain the desired nonlinear stiffness. Its theoretical analysis includes numerical simulations with results consistent with the desired deflection–torque profile.

Three Characteristics of Cheetah Galloping Improve Running Performance Through Spinal Movement: A Modeling Study

Cheetahs are the fastest land animal. Their galloping shows three characteristics: small vertical movement of their center of mass, small whole-body pitching movement, and large spine bending movement. We hypothesize that these characteristics lead to enhanced gait performance in cheetahs, including higher gait speed. In this study, we used a simple model with a spine joint and torsional spring, which emulate the body flexibility, to verify our hypothesis from a dynamic perspective. Specifically, we numerically searched periodic solutions and evaluated what extent each solution shows the three characteristics. We then evaluated the gait performance and found that the solutions with the characteristics achieve high performances. This result supports our hypothesis. Furthermore, we revealed the mechanism for the high performances through the dynamics of the spine movement. These findings extend the current understanding of the dynamic mechanisms underlying high-speed locomotion in cheetahs.

Preliminary Study of End-Effector Compliance for Reducing Insertion Force in Automated Fluid Coupling for Trains

Robotic assembly of mating parts (peg-in-hole (PiH)) inevitably encounters misalignments. Although passive end-effector compliance is key to successful alignment during the assembly, the literature does not propose many solutions for large misalignments, which is relevant to applications such as compliance of a robot end-effector for train fluid servicing. The results from physical experiments indicate insertion forces that are too large for practical applications, even with small misalignments. This preliminary study applies a hybrid approach combining physical experiments and simulation modelling for large motion PiH coupling with end-effector compliance. This provides a platform for investigating insertion force during misaligned coupling. The simulation model contains configurable parameters for robot compliance and PiH friction which are informed by the physical experiment results. The many robot compliances are lumped as two torsional springs on the pitch and yaw motion axis of the robot arm model. The simulation model is then calibrated using the physical results without having to conduct further intensive physical experiments. The calibrated model represents the physical measurements to a satisfactory degree, however its performance can still be improved.

A Polymorphing Wing Capable of Span Extension and Variable Pitch

This paper presents the development of a novel polymorphing wing capable of Active Span morphing And Passive Pitching (ASAPP) for small UAVs. The span of an ASAPP wing can be actively extended by up to 25% to enhance aerodynamic efficiency, whilst its pitch near the wingtip can be passively adjusted to alleviate gust loads. To integrate these two morphing mechanisms into one single wing design, each side of the wing is split into two segments (e.g., inboard and outboard segments). The inboard segment is used for span extension whilst the outboard segment is used for passive pitch. The inboard segment consists of a main spar that can translate in the spanwise direction. Flexible skin is used to cover the inboard segment and maintain its aerodynamic shape. The skin transfers the aerodynamic loads to the main spar through a number of ribs that can slide on the main spar through linear plain bearings. A linear actuator located within the fuselage is used for span morphing. The inboard and outboard segments are connected by an overlapping spar surrounded by a torsional spring. The overlapping spar is located ahead of the aerodynamic center of the outboard segment to facilitate passive pitch. The aero-structural design, analysis, and sizing of the ASAPP wing are detailed here. The study shows that the ASAPP wing can be superior to the baseline wing (without morphing) in terms of aerodynamic efficiency, especially when the deformation of the flexible skin is minimal. Moreover, the passive pitching near the wingtip can reduce the root loads significantly, minimizing the weight penalty usually associated with morphing.

Design and Experimental Validation of a Shock-Absorption Mechanism Inspired From the Frog's Forelimbs

Frogs reveal superior shock-absorption ability, which is mainly brought by the forelimbs. Frogs touch the ground with their forelimbs first in landing, followed by the elbow joints’ compression. In this process, the muscles and tendons of the forelimbs are pulled to store energy. However, muscles and tendons reveal different characteristics in the buffering process. The shock-absorption principle of the frog's forelimbs should be discussed explicitly and systematically on the coordination of muscles and tendons. In this study, we compared the EMG signals of m. anconeus, a primary muscle of frog's forelimb for landing, with the dynamic motions of the forelimb in the landing process. A short muscle potential resting was found around the time of ground touching. Meanwhile, we found that after the frog's toes touched the ground, the movement of the frog went into a buffer stage to absorb impact energy, and the buffering process exhibited different stages, revealing linear and nonlinear characteristics. These results revealed that the forelimb muscles and tendons worked at different times in landing, which formed the different stages. Inspired by the buffering principle of the frog, a bionic shock-absorption mechanism was designed using the torsion springs and dampers. The newly designed mechanism revealed improved buffering performances than the traditional spring-damper devices.

Multi-Frequency Acoustic Levitation and Trapping of Particles in All Degrees of Freedom.

Stabilization of the position and orientation of non-spherical, sub-wavelength particles in mid-air is required for using acoustic levitation forces in applications such as automation of micro manufacturing processes, 3-D scanning, and inspection. Acoustic locking has previously been demonstrated by time-multiplexing of different acoustic traps at the same frequency. In this case, the magnitude of the acoustic levitation forces and the stabilizing torque are coupled by the ratio of the durations during which the different traps are applied and cannot be adjusted independently assuming operation at maximum power. This work presents a compact device that uses a method for independently adjusting the vertical trapping forces and the stabilizing torque using two different ultrasonic frequencies. A 40-kHz vertical standing wave is used to generate levitation forces that counteract the gravitational force. Additionally, a 25-kHz horizontal standing wave is used to generate a tunable stabilizing torque. Using this method, objects made from high-density materials across a wide range of geometries can be locked acoustically with increased stability compared with state-of-the-art methods. This is demonstrated by locking tin cuboids with a density of 7.3 g/cm3 and plastic cuboids with average side lengths between 0.9 and 3.5 mm. The experimental results demonstrate torsional spring constants of up to 50 nN · m/rad and an orientation stability of <7.5°.

Characterization of Soft 3D Printed Actuators for Parallel Networks

Soft pneumatic actuators allow compliant force application and movement for a variety of tasks. While most soft actuators have compliance in directions perpendicular to their direction of force application, they are most often analyzed only in their direction of actuation. In this work, we show a characterization of a soft 3D printed bellows actuator that considers shear and axial deformations, modeling both active and passive degrees of freedom. We build a model based on actuator geometry and a parallel linear and torsional spring system which we fit to experimental data in order to obtain the model constants. We demonstrate this model on a soft delta mechanism and show how this single actuator model can be used to predict parallel structures of actuators with average positional errors of 4.0%. These results verify that the presented model and modeling approach can be used to speed up the design and simulation of more complex soft robot models by characterizing both active and passive forces of their one degree-of-freedom soft actuators.

Effects of Heat-Treatment Condition on Generating Force and Functional Degradation Characteristics of Single Coiled Torsion Springs Made of Shape Memory Alloy Wire

Effects of Heat-Treatment Condition on Generating Force and Functional Degradation Characteristics of Single Coiled Torsion Springs Made of Shape Memory Alloy Wire

Experimental and numerical modeling of a piezoelectric floating system for wave energy harvesting

In this paper, a floating wave energy converter (WEC) employing a piezoelectric power take-off (PTO) for off-grid powering of electronic devices at sea is presented and its electro-mechanical behavior is investigated both experimentally and numerically. The prototype floating structure consists of two box-shaped bodies joined by flexible beam elements. Due to the wave excitation, the floaters experience relative pitch rotations and vertical displacements, which dynamically deform the piezoelectric linking element, producing a superficial charge distribution. A small-scale prototype, built in an innovative way with LEGO™ bricks, is tested under regular wave excitation in a small basin. The recorded relative motion between the floaters is used as input to calculate via multiphysics software the voltage and power output of a piezoelectric device having the same flexibility of the passive element employed in the experiments. As a starting point for more accurate simulations, a 4-dof reduced-order model (ROM) of the floating system, including a simplified piezoelectric model, is developed and the wave induced response is compared with the experimental data. The elastic connection is represented through a torsional spring and potential linear theory is employed to calculate the hydrodynamic loads. Thus, Cummins equations for the floating system are formulated in pure differential form by introducing additional equations for radiation forces. This numerical approach allows for performing in an efficient and robust way the computation of the specific response amplitude operators, characterizing the WEC’s electro-mechanical response. Introducing system modes, the electro-mechanical equations can be further simplified and, by means of their frequency-domain analytical solution, facilitate a sensitivity analysis of the system response, capture-width ratio and power output with respect to relevant parameters, highlighting optimal conditions and performance enhancements by using arrays of piezoelectric elements, both in ideal (regular waves) and realistic (irregular sea) conditions.

Analytical and finite element analyses of flexural and torsional buckling of I-columns with discrete braces

The present study investigates the buckling strength of braced thin-walled columns under bending and torsional modes. Unlike the well-known bending modes, the torsion buckling modes of braced columns are not adequately assessed in design and are often overlooked. In order to control the buckling behaviour, the effects of elastic discrete springs in bending and torsion are taken into account. Analytical solutions are derived for bending and torsion buckling modes in the case of simply supported struts with doubly symmetric cross sections. Further, the threshold bracing stiffness to achieve the higher buckling modes is found in both bending and torsion modes. For more general cases, the finite element approach of the model is implemented and it is able to carry out the buckling modes of columns under compression in the presence of 3D elastic springs and for any arbitrary cross sections. The analytical and the numerical results of the present models are compared to some available solutions in the literature and to finite element simulations of the commercial code Abaqus. The efficiency of the closed-form solutions and the numerical approach is successfully verified. The post-buckling of braced columns is considered at the end in the presence of elastic bending and torsion springs. The effect of braces to enhance the buckling capacity concludes the study.

A magnetically coupled two-degrees-of-freedom piezoelectric energy harvester using torsional spring

Two-degrees-of-freedom magnetically coupled energy harvesters have been presented by several researches to achieve a broader response bandwidth. However, most two-degrees-of-freedom systems are composed of two piezoelectric beams, while in the low frequency operating environment with limited space, the dimension of the piezoelectric beam is limited which leads to high stiffness of the generated beam. Therefore, the output of dual-beam system is relatively low under low frequency and amplitude vibrations. This paper presents a magnetically coupled two-degrees-of-freedom energy harvester by using torsional spring. The proposed harvester consists of a piezoelectric beam with a tip magnet and an interacting magnet mounted on a rotatable bar with a torsional spring. The shape of the potential well changes with the rotation of the bar, facilitating the occurrence of the snap-through motion under low amplitude and wideband vibration excitation. What’s more, the stiffness of the torsional spring can be easily adjusted to make the designed harvester suitable for low frequency vibrations. Compared with the conventional bi-stable harvester, the presented harvester could easily overcome the potential barrier and generate larger power under low excitation intensity. Analytical, simulation, and experimental results demonstrate that the proposed energy harvester is capable of harvesting low frequency wideband vibration energy.

Efficient technique in computational dynamic modeling of a flexible manipulator with large deformation

In the flexible manipulators, the links could be modeled using rigid elements and torsional springs, and similarly, the flexibility in actuators could be represented with the equivalent springs. This study applies the discrete time transfer matrix method for the dynamic analysis of flexible manipulators with large deformations. On a first-priority basis, transfer matrices are determined, including all the flexible link/joint mechanism components. A single transfer matrix is established for prismatic and rotational actuators with equivalent springs to build the robotic transfer matrix library. On the second priority, to reduce the computation time, a novel algorithm is developed. In the proposed flexible link discretization, the first element of the flexible link is considered as a function of other elements. It is designed to build a mathematical model as closely as possible to the realistic model with fewer elements. It is presented that this modeling technique can employ discrete data extracted by the sensors. The simulation primarily focuses on developing flexible beam/joint models validated in ADAMS. Besides, the dynamic behavior of a flexible PR robot with external forces acting on the linkage system is analyzed and examined. The result shows that the proposed modeling method affords a low computational time while the manipulator control needs to manage fast responses.