There is no agreement on the effect that noncircular chainrings have on cyclists when compared with circular ones. In this research, the effect of the use of noncircular chainrings by recreational cyclists is assessed in terms of power delivery indicators. Two complementary approaches based on experimental tests and numerical models are used to study the differences between the results obtained by using circular and noncircular chainrings. The first approach intends to estimate the changes in the transmission system in terms of mechanical advantage when using different chainrings. The model considers that the point of tangency between the chain and the noncircular chainring varies during the rotation. The second approach aims at comparing the power delivery capacity when using different chainrings. A series of constant power tests until exhaustion is performed with each chainring to obtain the power-time relation at different exertion rates. As a result of this work, a refined model for obtaining the mechanical advantage of the transmission of the bicycle was proposed and validated. Additionally, the effects of the change of the chainring on the cyclists were assessed on a pilot test with two recreational cyclists, registering a change in the behavior of the power delivery capacity during intensive efforts for short periods of time.

Thin-walled tubes as energy absorption devices are widely in use for their low cost and high manufacturability. Employing origami technique on a tube enables induction of a predetermined failure mode so as to improve its energy absorption efficiency. Here we study the energy absorption of a hexagonal tubular device named the origami crash box numerically and theoretically. Numerical simulations of the quasi-static axial crushing show that the pattern triggers a diamond-shaped mode, leading to a substantial increase in energy absorption and reduction in initial peak force. The effects of geometric parameters on the performance of the origami crash box are also investigated through a parametric study. Furthermore, a theoretical study on the deformation mode and energy absorption of the origami crash box is carried out, and a good match with numerical results is obtained. The origami crash box shows great promise in the design of energy absorption devices.

For the Delta robot, a high-speed parallel pick-and-place manipulator, base vibrations are a significant problem. Especially since the Delta robot is suspended above its workpiece, it requires a large, stiff, and heavy base frame for fast and accurate motions. Dynamic balancing of the shaking forces and the shaking moments is a known technique to reduce the dynamic loads on the base frame and to the surroundings. In this paper it is investigated how solely with partial force balancing, dynamic loads and pick-and-place accuracy of a Delta robot-like manipulator can be improved, considering also the compliance of the base frame. This is done since partial force balance solutions can be implemented relatively simply in the current Delta robot designs, whereas full force and moment balance solutions are complex to apply in practice. Numerical simulations with a representative planar model of a Delta robot-like manipulator with a compliant base frame show that with an increasing amount of force balance the shaking moments increase up to 16% for full force balance. The floor contact forces first reduce and then increase with increasing force balance. With 43% force balance the floor contact forces are minimal, giving a 63% reduction. The end-effector accuracy slightly improves with increasing force balance until full force balance yields a 31% accuracy improvement. A further increase of the force (over) balance shows a 59% improvement of end-effector accuracy for 350% force balance. These effects are mainly due to the typical design of the Delta robot base frame and the way the robot is mounted to it.

This paper presents the design of a robust sliding mode controller for a six-degree-of-freedom cable-suspended parallel robot under uncertain disturbances. The control of cable-suspended parallel robots is quite challenging due to the unidirectional constraint of cable tensions. With the aid of interval analysis, a set of algebraic inequalities is obtained to establish the relationship between the cables’ tension constraints and the controller parameters. The sufficient conditions of the controller parameters satisfying the constraints are obtained for the set point motion within the robot’s static workspace. Numerical simulations are presented to verify the effectiveness of the proposed approach.

For utilizing robotic tail to stabilize and maneuver a quadruped, it is important to understand the mechanism of how the tail motion influences the quadruped motion which requires obtaining an analytic dynamic model. This paper presents a systematic methodology for modeling the dynamics of a general quadruped (capable of all 6 DOF motions) with a robotic pendulum tail based on the virtual work principle. The formulation of this model is motivated by robotic tail research, it can also be used as an alternative approach to model the quadruped dynamics other than using Lagrangian and Newton-Euler based methods. Numerical simulations are also conducted to verify both the forward and the inverse model.

This paper addresses the assembly strategy capable of deriving a family of over-constrained mechanisms systematically. The modular approach is proposed. It treats the topological synthesis of over-constrained mechanisms as a systematical derivation rather than a random search. The result indicates that a family of over-constrained mechanisms can be constructed by combining legitimate modules. A spatial four-bar linkage containing two revolute joints (R) and two prismatic joints (P) is selected as the source-module for the purpose of demonstration. All mechanisms discovered in this paper were modeled and animated with computer aided design (CAD) software and their mobility were validated with input-output equations as well as computer simulations. The assembly strategy can serve as a self-contained library of over-constrained mechanisms.

The static balancing of mechanical systems is an important issue because it allows significant reduction of torques. However the literature review shows that in many cases the gravity balancing of mechanical systems is carried out by neglecting the masses of auxiliary links associated to the principal mechanism. For many balancing schemes it is the source of errors. This paper deals with an improved solution for gravity compensators based on the inverted slider crank mechanism considering the masses of the rocker and the spring. For this purpose, the torques due to auxiliary links are determined. Then, they are introduced into the balancing equation for minimization of the residual unbalance. In this way, a more accurate balancing of gravity compensators is achieved. The efficiency of the suggested approach is illustrated by numerical simulations.

As the life span increases and the availability of physicians becomes more and more scarce, robotic rehabilitation for post-stroke patients becomes more and more demanding, especially due to the repeatability character of the rehabilitation exercises. Both lower and upper limb rehabilitation using robotic systems have proved to be very successful in different stages of the rehabilitation process, but only a few address the immediate (critical) post-stroke phase, especially when the patient is hemiplegic and is unable to stand. The paper presents the kinematic modelling, singularity analysis and gait simulation for a new 4-DOF parallel robot named RECOVER used for lower limb rehabilitation for bedridden patients. The robotic system has been designed for the mobilization of the lower limb, namely the following motions: the hip and knee flexion and the plantar adduction/abduction and flexion/dorsiflexion. The kinematics has been studied and the singularity configurations have been determined to achieve a failsafe rehabilitation robot. Numerical simulations prove that the system can be used for gait training exercises in safe conditions.

Various modal analysis methods are available for single-rotor wind turbines, but there is no report and guidance on the modal property analysis of multi-rotor wind turbines. This paper presents a dynamic modeling method for the modal response analysis of a wind turbine with two three-bladed isotropic rotors. The equations of motion are derived using Lagrange’s equations and are further linearized at a steady-state equilibrium. To avoid using Floquet Theory to remove the periodic coefficients, multi-blade coordinates are utilized. Comparison between the numerical simulations and a high-fidelity model in HAWC2 shows agreements in terms of modal frequencies. The results shows that the whirling modes splits into symmetric and asymmetric rotor modes.

In this paper a variant nonlinear energy sink (NES) is developed for the purpose of simultaneous vibration suppression and energy harvesting in a broad frequency band. The NES consists of a cantilever beam attached by a mass at its free end and a pair of so-called double-stop blocks. The beam is formed by a piezoelectric energy harvester and a thin steel plate. It is placed between the double-stop blocks. The constraint of the double-stop blocks forces the beam to deflect nonlinearly. First, the developed apparatus is described. Subsequently, system modeling and parameter identification are addressed. The performance of the apparatus under transient responses is examined through both numerical simulation and experimental study. The results show that the proposed apparatus behaves similarly as the NES with the following features: 1:1 resonance, targeted energy transfer, initial energy dependence, etc.

A yarn has a flexible structure whose axial length is very long compared its diameter. When loose yarn twists at its end, the yarn intertwines with itself as shown in Fig. 1 to produce a shape called a snarl shape with motion referred to as snarl motion. The snarl shape sometimes cuts the yarn or reduces the yarn quality, and may reduce the productivity of textile machinery. As a preliminary step of handling snarl motion in the processes of textile machinery, this paper extends functions of a yarn model proposed in our previous study by appending a contact force and implementing a multithread computing method for fast simulation. The paper validates the yarn model by comparing the results of numerical simulation and experiment. Six-threads computing can make calculation at 5 times the rate possible with single-thread computing.

Considerable research attentions have recently been paid toward a mobile manipulator (a robot arm standing on a mobile platform) due to its extended workspace beyond the manipulator reach. Mobile manipulators have a wide range of potential applications where it is desirable to achieve higher degree of flexibility in transport and handling task. However, a vast number of research publications only focus on trajectory planning. This preliminary research work presents dynamic modeling and analysis of a mobile flexible robot arm with aims to provide insights for the design and control of such mobile robot manipulators. In this work, the dynamic model is developed using a computationally efficient method: Discrete Time Transfer Matrix Method (DT-TMM). The concepts and principle of DT-TMM are briefly overviewed, and then are applied to a mobile flexible robot arm for dynamic modeling with the detailed procedure. Numerical simulations and dynamic analyses are performed to illustrate the effectiveness of the proposed dynamic modeling method, and to provide the clues for our ongoing research work in the design and control of mobile robot manipulators.

Casimir effect on superharmonic resonance of electrostatically actuated bio-nano-electro-mechanical system (Bio-NEMS) circular plate resonator sensor is investigated. The plate sensor resonator is clamped at the outer end and suspended over a parallel ground plate. The sensor can be used for detecting human viruses. Superharmonic resonance of the second order, frequency near one-fourth the natural frequency of the resonator, is induced using Alternating Current (AC) voltage. The magnitude of the AC voltage is also large enough to be consider hard excitation acting on the resonator. Beside Casimir effect, other external forces (i.e. electrostatic force and viscous air damping) acting on the MEMS resonator create a nonlinear behaviors such as bifurcation and pull-in instability. Hence, numerical models, such as Method of Multiple Scales (MMS) and Reduced Order Model (ROM), are used to predict the frequency-amplitude response for MEMS resonator. MMS transforms the nonlinear partial differential equation of motion into two simpler problems, namely zero-order and first-order. While, ROM, based on the Galerkin procedure which uses the mode shapes of vibration of the resonator as a basis of functions, transforms the nonlinear partial differential equation of motion into a system of ordinary differential equation with respect to dimensionless time. The frequency-amplitude response allows one to observe the behavior of the system for a range of frequencies near the superharmonic resonance. The effects of parameters such as Casimir effect, voltage, and damping on the frequency-amplitude response are reported.

The miniaturization of an increasing number of complex hybrid micro-products is currently leading the development of several micro-components to manipulate and assemble, meeting various specifications related to the objects properties and the planned task. However, at the micro-scale, further challenges derive from the effects of surface forces between object and micro-gripper that have to be overcome for an effective and successful manipulation. When contact micro-grippers are used, specific solutions to support the release phase are needed. Further developments and novel tools should be developed for vacuum micro-grippers to actively release the components reliably and precisely. In this context, this paper presents a vacuum micro-gripper with an automatic releasing system able to overcome the adhesive forces simply and effectively. The paper reports the results of a preliminary computational fluid dynamics analysis and the development of a numerical model able to represent the main gripper characteristics and derive a first design procedure.

Programmable multistable mechanisms exhibit stability behavior whereby the stiffness and the number of stable states can be controlled via programming inputs. In this paper, we report the zero stiffness behavior of a 2-degree of programming (DOP) T-combined, axially loaded double parallelogram multistable mechanism. We demonstrate zero force monostability, constant force monostability, zero force bistability, constant force bistability and zero force tristability behaviors by tuning the programming input. We derive analytically the reaction force of the mechanism for each configuration and verify our analytical results using numerical simulations and experimental measurements, showing less than 10% discrepancy. The concept of constant-force programming can be extended to N-DOP T-combined, serial combined and parallel combined programmable multistable mechanisms. Finally, we present potential applications of stability programming.

Flexure pivot based oscillators can advantageously replace the hairspring and balance wheel, the time base used in mechanical watches, by drastically reducing friction. However, flexure pivots have drawbacks including gravity sensitivity and restoring torque nonlinearity. In previous work, we introduced a novel gravity insensitive flexure pivot (GIFP) to solve the problem of gravity sensitivty, but no analytical formulation for the restoring torque nonlinearity was found. In this paper, we use numerical simulation to find an empirical expression for restoring torque nonlinearity. We use this expression to find an analytical formula for the rotational stiffness of GIFP. This formula gives an explicit relationship between restoring torque nonlinearity and the isochronism of the corresponding harmonic oscillator. The results also apply to the widely used generalized cross-spring pivot.

This paper presents the development of a framework based on a quasi-statics concept for modeling and analyzing the physical human-robot interaction in soft robotic hand exoskeletons used for rehabilitation and human performance augmentation. This framework provides both forward and inverse quasi-static formulations for the interaction between a soft robotic digit and a human finger which can be used for the calculation of angular motions, interaction forces, actuation torques, and stiffness at human joints. This is achieved by decoupling the dynamics of the soft robotic digit and the human finger with similar interaction forces acting on both sides. The presented theoretical models were validated by a series of numerical simulations based on a finite element model which replicates similar human-robot interaction. The comparison of the results obtained for the angular motion, interaction forces, and the estimated stiffness at the joints indicates the accuracy and effectiveness of the quasi-static models for predicting the human-robot interaction.

This paper presents a novel design of spatial compliant device with variable stiffness. The main concept of the device is to have two elastic trapezoid four-bar linkages arranging in orthogonal. The tool side of the device can switch between totally stiff and compliant by changing the arrangement of leaf springs and passive joints. Based on the principal axes decomposition of structural compliance matrix, the leaf springs are approximated by hyper-redundant linkages with rigid bodies connected by passive elastic joints. Hence, the nonlinear large deflection problems of the leaf springs can be solved efficiently in a mechanism way. In order to demonstrate the compliance of the proposed device, a numerical simulation is provided using the proposed approach. The result shows that the leaf springs in the compliant device are easy to be deformed and can not generate great force. Due to these characteristics, as an end-of-arm tool, the device has the ability to prevent hard collisions under the compliant status and finish precise positioning under the stiff status.

The driveline of many crafts during mooring maneuvers operates in the “trolling” mode, which is characterized by large slippages of the clutch. Sometimes the properties of clutch material and oil lead to the onset of self-excited torsion vibrations and wide fluctuations in torque. To analyze this phenomenon a numerical model of a typical marine driveline is developed, friction characteristics of the clutch are simulated by means of a LuGre model. A parametric stability analysis is carried out to highlight the effect of the parameters of the LuGre friction model on the stability of torsion vibrations. A series of experimental tests is performed on a specific test bench to identify the parameters of the driveline and to validate the numerical model. Results shows that the updated numerical model is able to replicate experimental results.

The possibility of improving the performance of a piezoelectric harvester by means of a cantilever dynamic vibration absorber (CDVA) is investigated. The CDVA cancels the original mode of vibration of the harvester and generates two new modes. Some prototypes are developed using a mathematical model for predicting the natural frequencies of the coupled system. Impulsive tests were performed on prototypes. Experimental results show that a small CDVA can lower the main resonance frequency of an harvester of the same extent as a larger tip mass. The measured voltage shows also an high frequency resonance peak, which can be exploited for collecting energy. A multi-physics numerical model is developed for performing modal analysis and stress analysis. Numerical results show that the stress inside the piezoelectric material of the harvester with CDVA results smaller than the stress inside the harvester with a tip mass tuned to the same frequency.