Bistable mechanisms are prevalent across a broad spectrum of applications due to their ability to maintain two distinct stable states. Their energy consumption is predominantly confined to the process of state transitions, thereby enhancing their efficiency. However, the transition often requires two distinct digital inputs, implicating the requirement of multiple actuators. Here, we propose an elastic and contactless design strategy for inducing state transitions in bistable mechanisms, requiring only a single digital input. The strategy leverages internal information, interpreted as system state, as an extra input to make a weighted decision for transitioning to the subsequent state. We characterize the behavior using a spring-based rigid-body model, consisting of a column near bifurcation, combined with a non-linear spring connected to a bistable element that represents the information state. The results show that a nonlinear spring with a quadratic stiffness function, i.e., representing internal instability, is crucial for regulating state-switching behavior. We then demonstrate this design strategy by developing a monolithic and compliant design embodiment and experimentally evaluate its behavior.

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The ability to convert reciprocating, i.e., alternating, actuation into rotary motion using linkages is hindered fundamentally by their poor torque transmission capability around kinematic singularity configurations. Here, we harness the elastic potential energy of a linear spring attached to the coupler link of four-bar mechanisms to manipulate force transmission around the kinematic singularities. We developed a theoretical model to explore the parameter space for proper force transmission in slider-crank and rocker-crank four-bar kinematics. Finally, we verified the proposed model and methodology by building and testing a macro-scale prototype of a slider-crank mechanism. We expect this approach to enable the development of small-scale rotary engines and robotic devices with closed kinematic chains dealing with serial kinematic singularities, such as linkages and parallel manipulators.

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Compliant mechanisms have been applied successfully in many quasi-static applications. However, the dynamics of these mechanisms remain largely unexplored. In particular, dynamic problems hinder the implementation of compliant mechanisms in the field of power transmission systems. To realize this, here we present theoretical and experimental dynamics of a statically balanced compliant rotational power transmission mechanism, designed based on kinematics of the Oldham coupling. A fast and flexible generic model is proposed based on multi-body dynamics, which facilitates the design and implementation of this compliant transmission couplings in dynamic applications. In order to make the model applicable for the whole design family, the compliant embodiment is parametrized using a minimum set of design parameters. Furthermore, a case study is performed on an existing design and the method is validated experimentally. Predictions can be given of (i) the maximum attainable velocity before instability due to centrifugal forces, (ii) the lower resonance modes, and (iii) the characteristics of the resulting velocity transmission error. The proposed methodology is not only applicable to the compliant transmission couplings between parallel rotational axes but furthermore provides opportunities for the modeling of other compliant mechanisms applied in dynamic environments.@en

Microtransmission mechanisms made of elastic materials present an opportunity for exploring scalable mechanical systems integrated with sophisticated functionalities. This paper shows how the fundamentally limited range of motion in elastic mechanisms can be circumvented to create a frequency doubling functionality analog to angular velocity doubling in classical gears. The proposed mechanism utilizes the elastic deformation of its internal architecture and buckling of microflexures to perform frequency doubling kinematics. We demonstrate this by the fabrication of a microtransmission device for application in mechanical wrist watches. A key benefit of the proposed method is that such a transmission system can be integrated and fabricated as an embedded part of microarchitected materials to boost the frequency characteristics of energy storage, actuators, and inertial sensors to perform adequately for different applications.

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This work presents a novel design, model and prototype of a motion energy harvester based on bi-stability and frequency up-conversion. The Parametric Frequency up-converter Generator (PFupCG). The PFupCG was designed to harvest energy under conditions where the amplitude of the driving motion is larger than the internal displacement limit. Instead of an impact member, the PFupCG uses a compliant suspension mechanism that combines a bi-stable characteristic with a strong stiffening behavior as a result of geometric effects. This resulted in a prototype of the PFupCG with an internal-to-applied motion amplitude ratio of 0.2. A case study was carried out where the PFupCG was analyzed by simulation and experiment for vibration conditions representative of human walking motion (2Hz, 25 mm).

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Folding is a manufacturing method which can create complex 3D geometries from flat materials and can be particularly useful in cost-sensitive or planar-limited fabrication applications. This paper introduces compliant mechanisms that employ folding techniques from origami to evolve from a flat material to deployed state. We present origami-inspired sacrificial joints, joints which have mobility during assembly of the mechanism but are rigid in their final position, to create regions of high and low stiffness and the proper alignment of compliant flexures in folded mechanisms. To demonstrate the method we fold steel sheet to create some well-known and complex compliant mechanisms.

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Classical human-engineered transmission mechanisms such as linkages, gears, and couplings are well established designs which made out of multiple parts and rigid hinges. However, these mechanisms impose disadvantages such as wear, friction, low precision and reliability, need for assembly and lubrications, and difficulty for miniaturization. By employing the natural elasticity of materials, rather than using rigid hinges and connections, sophisticated motions can be realized with minimal mechanical complexity. This relative new paradigmin engineering design, called compliant mechanisms, enables the creation of monolithic mechanisms that are strong, compliant, precise, scalable, and cost-effective. The kinematics of classical gears and couplings impose several limitations to design@en

A method is introduced to design compliant micro transmission mechanisms which double the motion frequency of a cyclic input motion. Compliant embodiments are generated based on exploiting the singularity in a double-slider mechanism, which provides building blocks with a frequency-multiplication factor of two. It is shown that the proposed building blocks can be concatenated for higher frequency-multiplication ratios. To validate the building block approach, a compliant micro transmission mechanism is presented which quadruples the frequency of a cyclic rectilinear input motion.@en

Static balancing is used to reduce the actuation stiffness in a translational stage compliant mechanism. The planar and monolithic compliant mechanism is preloaded using a buckling beam of which the top part is guided by a double folded flexure. Hooks, that lock the top part of the beam in place, ensure a permanent static balancing of the entire device. The preloading action is caused by an external shaking or shock to the device. A theoretical micro electromechanical system (MEMS) model with a radius of 18.6 mm is developed and a scale 6:1 prototype is fabricated and tested for static balancing, first eigenfrequency (EF) and eigenmode (EM). Finite element modelling is used to predict static balancing and EM behaviour. Experiments on two equally fabricated prototypes show a reduction of -123 % and -126% actuation stiffness where -104.5% was predicted. The expected reduction for the designed MEMS device is 98.4^%. The experimental first EF of the prototype is 3.10±0.25 Hz against a theoretical value of 3.09 Hz. The theoretical first EF of the MEMS model is 21.8 HZ. The prototypes are successfully preloaded by applying shaking or shock by hand. The predicted minimal energy requirement for this is found to be 4.9e-3 J, while 6.4e-3 J and 5.9e-3 J were calculated based on experimental results. The expected minimal energy required for preloading the designed MEMS device is 1.0e-5 J.

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This paper presents a method for the design of compliant micro transmission mechanisms which multiply the motion frequency of a cyclic input motion. Compliant embodiments are generated based on exploiting the singularity in a double-slider mechanism, which provides building blocks with a frequency multiplication factor of two. It is shown that the proposed building blocks can be concatenated for higher frequency multiplication ratios, and that the maximum number of blocks is limited by the desired travel range of the output. The input-output kinematics and the different stiffness characteristics of the building blocks are discussed based on pseudo-rigid-body model (PRBM). To validate the building block approach, a compliant micro transmission mechanism is presented which quadruples the frequency of a cyclic rectilinear input motion. Furthermore, a micro scale prototype was dimensioned and fabricated out of silicon using deep reactive ion etching to evaluate the design experimentally and validate the PRBM and finite element models. [2017-0318]@en

This paper presents a fully compliant, potentially monolithic, power transmission mechanism which can rectify a large lateral offset between two parallel rotational axes. The planar nature of the design makes it ideal for manufacturing-limited applications such as micro/meso-scale power transmissions. The proposed compliant transmission is generated based on the Oldham Coupling and its equivalent Pseudo-Rigid-Body Model (PRBM). Normally, a compliant transmission mechanism cannot achieve a high efficiency due to the internal stiffness, i.e. actuation stiffness is not zero. However, in the proposed design, the internal stiffness is removed by static balancing and results in a statically balanced compliant transmission mechanism, i.e. with zero actuation stiffness. Therefore, the monolithic embodiment and static balancing features compensate for backlash, friction, assembly errors and poor mechanical efficiency inherent in conventional Oldham coupling, resulting in a transmission mechanism with high mechanical efficiency. Possible compliant design configurations based on the importance of different design criteria are discussed. Further, a compliant device based on the Paired Double Parallelogram (DP-DP) linear flexure bearing
is designed and dimensioned. Moreover, the transmission stiffness, i.e. input-output rotational stiffness within the maximum allowable stress, and the actuation stiffness, i.e. minimum required actuation torque for certain angular displacement, of the designed device are predicted by the theoretical model and finite element modeling. Besides, the result shows the device is providing a constant transmission stiffness through a full cycle rotation. To prove the concept, a macro scale prototype is constructed and evaluated experimentally.
It is shown that the results from the experiment are in agreement with the
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Vibration energy harvesting can be used as a sustainable power source for various applications. Usually, the generators are designed as devices with a single degree of freedom (SDoF) along the direction of the driving motion. In this research, harvesting from multi-directional (translational) motion sources will be investigated. Three strategies are assessed: a reference SDoF generator, a SDoF generator using an orientation strategy, and a Multi Degree of Freedom (MDoF) system. This led to the development of a design metric by which any 2D design problem can be described by two dimensionless parameters: the relative strength of vibrations, p_v, and the relative dimension of the design space, p_l. It was shown that the relative power density (RPD) of a 2DoF system compared to a reference SDoF system only depends on the product p^∗=p_vp_l, and has a maximum of 1.185 for p^∗=1. The application of powering a hearing aid is investigated as a case study. It was found that the vibrations in the area of the human head while walking can be represented by a two-directional vibration source with p_v=0.55. Three different design spaces are assessed for a miniaturized generator and three different optimal embodiments are found. For one of the considered situations where p^∗=1.1, a 2DoF system was found to have a 16% higher power output compared to a SDoF reference. The aim of future work will be the validation of the developed metric.

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This paper introduces a homokinetic coupling, a constant velocity universal joint (CV joint), which is fully compliant and potentially monolithic. The proposed compliant design can accommodate high misalignment angles between the input and the output rotational axes. Additional kinematic constraints are applied to well-known Double Hooke’s universal joint, to guarantee a one-to-one constant velocity rotation transmission for all different misalignment angles. The influence of the extra constraints on degrees-of-freedom (DOF) of the mechanism is studied using screw theory. Furthermore, it was shown that the mechanism is yet a 1DOF linkage for rotation transmission and a 2DOF rotational joint as all universal joints. The kinematics of the mechanism is studied, and constant velocity conditions are identified. The pseudo-rigid-body model (PRBM) of the new angled arrangement of the Double Hooke’s universal joint is created, and the input–output torque relationship is then studied. The different possible compliant embodiments based on the PRBM model were discussed and illustrated. Moreover, one of the proposed compliant counterparts is dimensioned as a power transmission coupling for a high misalignment angle, up to 45 deg. Further, a prototype was manufactured for the experimental evaluation, and it is shown that the results are consistent with the PRBM
and the finite element model.@en

A new fully compliant rotational power transmission mechanism is presented. The design is based on the Pseudo-Rigid-Body Model (PRBM) of the Oldham constant velocity coupling. It can be fabricated as a single piece device with planar materials which make it suitable for micro scale applications. The internal stiffness of the proposed structure is eliminated by static balancing technique. Therefore, the compliance and zero stiffness behavior compensate for the structural error and poor efficiency inherent in rigid-body Oldham coupling, resulting in high mechanical efficiency power transmission system. The device is designed and its motion, torsional stiffness, and torque-angular displacement relations are predicted by the PRBM and finite element modeling. A large/macro scale prototype was manufactured and measured to evaluate the concept. This high efficient power transmission system can be applied in different applications in precision engineering and the relevant field such as micro power transmission system.

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This paper presents the concept and fabrication of a large deflection compliant Constant Velocity universal joint (CV joint). A novel compliant structure is proposed based on the 6R Hybrid spatial overconstrained linkage. Due to symmetry, its kinematic properties are such that can transfer rotational motion between two angled shafts with true constant velocity. The kinematic of the mechanism and the Pseudo-Rigid-Body model of its compliant configuration are studied and analyzed. A prototype was manufactured and experimentally evaluated. It was verified that the experimental results are consistent with the theoretical expectations.@en