1-DOF Mechanism Research Articles

Novel compliant mechanism-based auxetic metamaterial: Kinematic and experimental analysis

The parametric study of mechanical metamaterials enables the design of structures and components with tailor-made properties. Novel topologies are designed through innovative strategies, such as the kinematic characteristics of linkages and mechanisms. Here, the kinematic analysis of a 10-link, 1-DOF mechanism led to the design of a novel auxetic metamaterial based on its compliant version. Finite element models and laboratory experimentation on additively manufactured samples were conducted to characterize the Poisson’s ratio of these novel kinematically designed metamaterials. By modifying parameters and unit cell arrangements, various magnitudes of auxeticity were observed, demonstrating the tunability of the topology. The findings presented here highlight the design possibilities of novel metamaterials with tailor-made responses, as well as the potential of converging compliant mechanisms and mechanical metamaterials.

Structural–parametric synthesis of single-loop 6R and 7R mechanisms using factorization of motion polynomials and its application in grippers

Abstract In this study, the so-called quasi-spiral motion pattern of a particular 3R (revolute) chain, which could track a quasi-spiral curve, is discovered for application in envelope gripping. Naturally, a novel perspective on the synthesis of 1-DOF (degree of freedom) single-loop 6R and 7R mechanisms is presented to implement the quasi-spiral motion pattern. In these processes, the method of factorization of the motion polynomial is used to synthesize a series of single-loop mechanisms with the motion to generate quasi-spiral curves. By employing the proposed method, numerous innovative 6R and 7R mechanisms have been developed to construct dual layers of grippers based on specific network regulations. Taking a novel 6R mechanism as an example, the forward solution of the mechanism is determined, and the relationship between different rotation angles is obtained. Then, displaying the changes in each angle during the grasping process. Finally, the novel 6R and 7R mechanisms are employed as a unit to determine the networking method and assemble new types of grippers. Grippers formed by the aforementioned 1-DOF mechanisms exhibit the characteristics of envelope grasping.

Multistable compliant linkages with multiple kinematic paths separated by energy barriers

Multistable morphing structures can reconfigure between different stable states that are separated by energy barriers, and one-degree-of-freedom (1-DOF) mechanisms have many merits, like simple actuation. This paper combines the two and proposes a new family of reconfigurable compliant linkages with many (2−6) 1-DOF kinematic paths that are separated by energy barriers. This new type of design is an extension of multistable structures, where each stable state corresponds to not just one configuration but a 1-DOF configuration space, i.e., a kinematic path. Components of the linkages are made elastically compliant, therefore enabling the switch between two isolated compatible paths with multi-stability. A generation-selection hybrid design algorithm to follow prescribed reconfigurable paths is proposed, and a minimum energy path (MEP) finding method to guide actuation to switch between different kinematic paths is developed. Four design examples with 2–3 reconfigurable paths and their experiments are presented, and the effectiveness of this method is verified. This work provides a fresh perspective to design the single-DOF reconfigurable mechanisms with larger design space, more reconfigurable kinematic paths, and easier reconfiguration actuation.

Synthesis of 1-DOF mechanisms for exact regular polygonal path generation based on non-circular gear transmissions

Design of one-degree-of-freedom (1-DOF) mechanisms is of paramount interest. This work deals with the generation of exact regular polygonal paths by using two particular 1-DOF mechanisms. The design of two-bar and three-bar mechanisms including non-circular gears is presented and evaluated. Differences in the kinematics of both mechanisms are discussed. The three-bar mechanism allows derivable velocity and acceleration curves during the whole trajectory, including the polygon vertices, a feature that cannot be achieved with the simpler two-bar mechanism. Hence, the three-bar mechanism makes it possible to generate perfect vertices using non-circular gears. To the best of the authors’ knowledge, this mechanism is the first 1-DOF mechanism with articulated links and a non-circular gear transmission that can generate exact regular polygonal paths. The proposed mechanisms can also be applied to generate two straight lines with a given angle, which is another novel contribution of this work. A prototype of the three-bar mechanism has been developed for experimental validation.

The Aerodynamic Effect of Biomimetic Pigeon Feathered Wing on a 1-DoF Flapping Mechanism.

This study focused on designing a single-degree-of-freedom (1-DoF) mechanism emulating the wings of rock pigeons. Three wing models were created: one with REAL feathers from a pigeon, and the other two models with 3D-printed artificial remiges made using different strengths of material, PLA and PETG. Aerodynamic performance was assessed in a wind tunnel under both stationary (0 m/s) and cruising speed (16 m/s) with flapping frequencies from 3.0 to 6.0 Hz. The stiffness of remiges was examined through three-point bending tests. The artificial feathers made of PLA have greater rigidity than REAL feathers, while PETG, on the other hand, exhibits the weakest strength. At cruising speed, although the artificial feathers exhibit more noticeable feather splitting and more pronounced fluctuations in lift during the flapping process compared to REAL feathers due to the differences in weight and stiffness distribution, the PETG feathered wing showed the highest lift enhancement (28% of pigeon body weight), while the PLA feathered wing had high thrust but doubled drag, making them inefficient in cruising. The PETG feathered wing provided better propulsion efficiency than the REAL feathered wing. Despite their weight, artificial feathered wings outperformed REAL feathers in 1-DoF flapping motion. This study shows the potential for artificial feathers in improving the flight performance of Flapping Wing Micro Air Vehicles (FWMAVs).

An Integrated Kinematic Mapping and Fourier Method to Design Spherical Coupled Serial Chain Mechanisms for Single-Joint Rehabilitation

Abstract Robotic devices are capable of reducing the physical burden on rehabilitation therapists and providing training programs of good repeatability, high efficiency, and high precision. When designing the kinematic structure for rehabilitation robots, there has been a growing interest toward one-degree-of-freedom (DOF) end-effector mechanisms due to their simpler structure and less complicated control algorithms. Compared with current one-DOF mechanism designs that are mainly customized for multi-joint robotic training, spherical coupled serial chain (SCSC) mechanisms are proposed in this paper to specifically deliver the single-joint robotic training, which is of equal importance to the effective physical recovery. Using kinematic mapping theory, the end-effector motion of SCSC mechanisms can be naturally transformed to two trigonometric curves composed of finite Fourier series in two separate planes of the image space. This novel formulation helps to establish an analytical and direct relationship between the design parameters of the SCSC mechanism and the harmonic parameters of the image-space representation of the task rehabilitation motion. The result is a simple and effective method for kinematic synthesis of SCSC mechanisms for generation of single-joint motion with an arbitrary number of spherical poses. An example of designing SCSC mechanisms for shoulder-joint rehabilitation is presented at the end of this paper to illustrate the feasibility of the proposed method.

Mechanism Balancing Taxonomy

The balancing of mechanisms consists in distributing their moving masses, inertias, and elastic components in order to achieve key mechanical properties, such as the elimination of the shaking forces and moments exported onto their supporting structure or the insensitivity of the mechanism to gravity and to the motions of its chassis. This article introduces a new refined systematic taxonomy for the classification of multi-degree-of-freedom (DoF) 3-dimensional passively balanced mechanisms. The taxonomy is composed of 15 distinct types – compared to only 4 types described in the literature. Each type is provided with its definition, the necessary conditions to be satisfied, the list of resulting mechanical properties, and a 1-DoF mechanism example. This taxonomy applies to mechanisms subject to gravity and mounted onto fixed or mobile chassis undergoing linear and angular accelerations, and, newly, also angular velocities. It is represented as a 4-set Venn diagram built on 4 primary balancing types: static, force, moment, and a newly introduced inertial invariance. This theoretical work allows for a refined categorization of the broad spectrum of balanced mechanisms while alleviating some inconsistencies observed in the existing literature.

Data-Driven Design of a Six-Bar Lower-Limb Rehabilitation Mechanism Based on Gait Trajectory Prediction.

For patients who need lower-limb kinetism rehabilitation training, this paper proposes an effective data-driven approach seeking the design of 1-degree-of-freedom (DOF) six-bar rehab mechanism through gait prediction by body parameters. First, gait trajectories from 79 healthy volunteers are collected along with their body parameters. Then, the normalized gait samples are clustered and regressed into a limited number of representative trajectories with K-means algorithm, and the cluster index is recorded as the label for each trajectory. Next, a genetic-algorithm-optimized support vector machine method is adopted to establish a classifier for the trajectories, obtaining the correspondence between body parameters and cluster labels of gait trajectories. As a result, once a group of body parameters are input into the classifier, the suitable gait trajectory can be predicted for the specific patient. A GA-BFGS algorithm is developed for 1-DOF six-bar mechanism synthesis and a GUI design software is presented that shows how the data-driven design process is realized. The novelty of this paper is using clustering and prediction technique to accomplish the patient-mechanism matching, so that simple, low-priced 1-DOF mechanisms could be adopted for large number of various patients without expensive customized design for each individual. In the end, a gait rehab device design example is provided, and a prototype device driven by a constant speed motor is presented, which illustrates the feasibility of the proposed method.

An Interactive Rehabilitation Mechanism Design System for Kinematic and Kinetostatic Synthesis With Expandable Solution Space

Abstract Compared to manual therapy, robot therapy can provide more intensive and accurate rehabilitation training. However, most current devices are built on bulky and complex multi-degree-of-freedom (multi-DOF) mechanisms. Recently, 1-DOF mechanisms have gained popularity due to their portability and simplicity. Existing synthesis methods for 1-DOF mechanisms focus primarily on computing the optimal mechanism dimensions such that kinematic error between the task and the mechanism output is minimized. In cases where the kinematically feasible solutions become impractical under engineering circumstances, designers may need a handle to intervene in the synthesis process; moreover, the force interactions between the mechanism and users should also be considered to encourage the active participation of users for effective physical recovery. In this paper, we combine kinematic and kinetostatic synthesis to develop an interactive rehabilitation mechanism design system, taking into account task specifications on rehabilitation motion and gravity balancing. To enable interactive design, users are invited to manage the task movement via kinematic tolerance-oriented variation, thus providing the flexibility to address practical constraints. To compensate the gravity, torsional springs are attached to the actuated joints of the mechanism and human limb, and designed based on the principle of static balancing. For presenting a systematic, general, and defect-free design methodology for 1-DOF rehabilitation mechanisms, the synthesis model is formulated in a Fourier way to better accommodate different mechanism types and continuous limb motion. Examples of the upper- and lower-limb rehabilitation mechanism design are given in the end to demonstrate the validity of the proposed method.

Residual vibration reduction in back-and-forth moving systems driven by slider-crank mechanisms working through a dead point configuration

This study proposes an algorithm to construct back-and-forth motion profiles to reduce residual vibrations of 1-dof linear oscillatory systems, driven through a transmission chain made up of a 1-dof linkage mechanism. This set can be advantageous for high transmission ratios, when multistage drive trains are discouraged to prevent a build-up of backlash nonlinearities. We assume that the mechanism: i) is moved by a conventional electric actuator and, ii) is working through a dead point configuration. The solution focuses on the continuity degree Cn of the motion profile to guarantee its feasibility by means of the mentioned actuators. We aim to provide an algorithm to design these profiles. The development meshes several conclusions from other studies: the classical strategies of residual vibration reduction together with an analytical solution, with regard to Cn, of the inverse kinematic problem at a dead point configuration. The development includes an analytical approach to some methods of residual vibration reduction, in addition to numerical simulations. Finally, we present experimental results on a slider-crank mechanism test bed, with a pendulum acting as the oscillatory system.

The Parigi Mechanism: A Novel 1-DOF Mechanism and Its Application as a Kinetic Reciprocal System (KRS) Adaptive Facade

The Parigi mechanism, invented by the author, is described and defined rigorously with the use of the kinetic reciprocal system (KRS) algorithm. The mechanism possesses one degree of freedom (DOF) and consists of a network of elements reciprocally connected with pin-slot joints. The network can be extended infinitely and retain one DOF, regardless of the number of elements added. The principle of the KRS algorithm is presented, and the inputs required to generate the Parigi mechanism are described. A KRS adaptive facade based on the Parigi mechanism is proposed. Since the mechanism possesses one DOF, a single actuator can actuate it. Therefore, a facade based on this mechanism can be engineered with a reduced mechanical complexity, while allowing the control of building physics performance (daylight illumination, solar gain, ventilation, acoustics), as well as quantifiable (privacy, view) and unquantifiable (composition, aesthetic sense of the movement) architectural parameters.

Структурный синтез семейства плоских восьмизвенных кинематических цепей рычажных механизмов с многократными шарнирами и наиболее сложным трехшарнирным звеном

Structural synthesis of closed kinematic chains to create various mechanisms is the first and most difficult stage of creative design of complex machines due to the large variance of possible structural solutions. In this paper, the authors examine the problem of structural synthesis of a family of eight-link kinematic chains with multiple joints of various types and the most complex three-joint link in order to create multi-loop multiple-joint mechanisms with one degree of freedom. To solve this problem, a synthesis technique is proposed based on the search for all integer solutions of a generalized structural mathematical model of plane linkage mechanisms and the identification of all structurally nonisomorphic kinematic chains using a two-column P-matrix. As the result of the structural synthesis, a family of eight-link multiple joint kinematic chains is obtained, which contains seven new kinematic structures. Examples of creating 1-DOF mechanisms with multiple joints based on the obtained new structures are presented. They confirm the effectiveness of using the structural synthesis procedure and analysis of complex mechanisms with multiple joints in various areas of modern engineering (precise guiding mechanisms, automatic lines, technological machines, robots, manipulators, etc.).

Experimental implementation of the ‘effective 4-bar method’ on a reconfigurable articulated structure

A structural concept for reconfigurable buildings is considered. Its basic element is the planar n-bar linkage whose joints are equipped with brakes. Stepwise reconfigurations are realized based on the ‘effective 4-bar’ method. During each intermediate step (n-4) joints of the mechanism are selectively locked reducing the system to a 1-DOF mechanism and one joint angle is adjusted. A basic actuation approach requires only one actuated joint. A more involved cable-driven approach employs a system of two actuated cables. Both approaches are examined through simulations and their experimental implementation on a small-scale prototype demonstrates the applicability of the method and highlights practical implementation issues.

A synthesis method for 1-DOF mechanisms with a cusp in the configuration space

Significant progress has been made in the study of singularities of mechanisms. This research has, however, exclusively focused on situations where different motion branches intersect, i.e. bifurcation points of the configuration space (c-space). Other types of singularities have not been studied due to lack of mechanisms examples. In particular, mechanisms exhibiting cusp singularities in their c-space are almost unknown, besides a planar linkage presented by Connelly and Servatius, which served as an example where the common definition of rigidity fails. In this paper, a method for the synthesis of spatial 1-degree-of-freedom (1-DOF) cusp mechanisms is presented. This method consists in synthesizing the mechanical generator of a spatial curve with specific characteristics and then appropriately connecting this module with its mirrored version. Several examples are presented including a kinematotropic linkage, which is characterized by a singularity that is a cusp (1 DOF motion) and a bifurcation of a curve and a surface (2-DOF motion). It is discussed that all available methods for the local analysis of singularities fail at cusp singularities. The presented synthesis method allows for constructing mechanisms that shall initiate the research into the study of cusp singularities.

Design and analysis of a multi-mode mobile robot based on a parallel mechanism with branch variation

In this paper we propose the design idea of branch variation of a mobile parallel mechanism so that it can execute different locomotion modes. A novel robot is presented based on this idea, which can be reconfigured to be different equivalent mobile robots in topological structure.The robot is a four-limbed parallel mechanism in which each limb contains eight revolute joints. Based on the branch variation with topological reconfiguration of the parallel mechanism, the robot has 3 locomotion modes with 7 gaits to reply to different situations by analyzing its topological structure via adjacency matrixes and transformation equations.Tracked locomotion mode is realized by the motion of platforms as a 3-dof (degree of freedom) planar 6R closed-loop mechanism which can operate obstacles. Legged mode is realized by the deforming of four limbs to carry out trot-walking gait with 1-dof mechanism units. Wheeled mode is realized by the relative motion between each limb and platforms as a 4-dof mechanism to carry out fast moving and direction switching in this mode.To verify the locomotion modes and functionality of the robot, we present the results of a series of experiments, performed on a simulation system and a manufactured prototype.

Functional design for customizing sit-to-stand assisting devices

Standing up refers to the transition from the seating to the standing postures to perform a movement that involves several body segments and requires both voluntary action and equilibrium control during an important displacement of the body Centre of Gravity (COG). This task can be considered very important for people with reduced mobility to achieve minimal independence in Activity of Daily Living (ADL). In this paper, we propose solutions for the homecare of persons with reduced mobility, describing a functional design to customize assisting devices for the Sit-to-Stand (STS). In particular, the support mechanism that generates the requested motion and sustains the body of a person can be synthesized ad-hoc according to the experimental data of the subject. Experimental tests carried out during the Sit-To-Stand are used to track and record point trajectories and the orientation of the trunk of an individual, and they are used to design a 1-DOF mechanism able to reproduce the assigned rigid-body motion. A four-bar linkage has been synthesized according to the desired features. Simulation results are reported to illustrate the engineering soundness of the proposed mechatronic solution.

Determination of a fourth-class Assur group position diagram by means of the revision of the linkage condition of a closure link

This paper describes an alternative method for the position analysis of a fourth-class Assur group, obviating the need for solving the system of nonlinear equations obtained using the analytical method. The objective of this study is to develop a methodology to determine the positions of the links and kinematic pairs that form the group, based on the position of the pairs that connect the group to the base mechanism. The proposed method consists in the separation of one of the closure links and the obtaining of the position diagram of the resulting 1-DOF (one degree of freedom) mechanism, using the connecting pairs of the group as a fixed support and considering one of the drag links as a driving link. Different configurations of the mechanism are obtained for different values of the input link´s coordinate. The position diagram of the group is determined when the resulting 1-DOF mechanism satisfies the linkage condition imposed by the removed closure link. Four examples of fourth-class Assur groups are used to validate the proposed method, the feasibility of which is confirmed by the accuracy of the results obtained in the analyzed examples.

A proposal for a convertible stadium roof structure derived from Watt-I linkage

ABSTRACTIn this paper, a novel convertible stadium roof structure is introduced, which has been derived from a special geometric configuration of Watt-I linkage, a 1-DoF mechanism used in robot technologies as anthropomorphic fingers. The proposed structure can offer a wide range of different shape configurations according to the environmental conditions and spatial needs, thus offering several aesthetic and functional advantages over existing solutions. This paper serves as a feasibility investigation of this concept, mainly from geometric and structural point of view. To that affect, first kinematic analysis and geometric design of this linkage are introduced. Then, structural analyses of the proposed structure with realistic dimensions and loading conditions are performed in three different geometric configurations, in order to discuss strength and stiffness limitations. Finally, potential cover materials and actuators are briefly discussed.

Experimental Validation of Jacobian-Based Stiffness Analysis Method for Parallel Manipulators With Nonredundant Legs

A complete stiffness analysis of a parallel manipulator considers the structural compliance of all elements, both in designed degrees-of-freedom (DoFs) and constrained DoFs, and also includes the effect of preloading. This paper presents the experimental validation of a Jacobian-based stiffness analysis method for parallel manipulators with nonredundant legs, which considers all those aspects, and which can be applied to limited-DoF parallel manipulators. The experimental validation was performed by comparing differential wrench measurements with predictions based on stiffness analyses with increasing levels of detail. For this purpose, two passive parallel mechanisms were designed, namely, a planar 3DoF mechanism and a spatial 1DoF mechanism. For these mechanisms, it was shown that a stiffness analysis becomes more accurate if preloading and structural compliance are considered.

Mechanism for active Π-joint as an equivalent to the combination of revolute joint and proximal fixed-length link

The Pa or ?-joint, as a planar parallelogram four-bar linkage, is of particular interest and importance for parallel kinematic mechanisms. With the idea of replacing the combination of an active revolute joint and of a proximal fixed-length link with an active (powered and controlled) ?-joint, a new parallelogram-based one-degree-of-freedom (1-DOF) mechanism has been developed. The paper describes the structure of the mechanism, modeling approach and analysis as well as the developed active ?-joint laboratory prototype. We propose a parallelogram-based 1-DOF complex mechanism for active ? -joint.We describe its structure, advantages and applicability in parallel machines.We present analysis-oriented modeling approach.We develop and investigate initial laboratory prototype.