Single Degree Of Freedom Mechanism Research Articles

Design method of a single degree-of-freedom planar linkage bionic mechanism based on continuous position constraints

Single degree-of-freedom (DOF) planar linkage mechanism has been widely used in bio-inspired robots because of its simple control. However, designing a single DOF mechanism to meet the complex motion law of creatures is difficult, and the multiple variables of six- or eight-bar mechanism further increase the design difficulty. A design method of single DOF planar linkage bionic mechanism is proposed in this paper. Through the continuous constraints on the position of all reference points with constraint descent method, the requirements of the bionic mechanism in shape, motion trajectory, and posture are met. As for the mechanism by which reference point coordinates cannot be expressed as the analytical solution of the driving angle, a single DOF mechanism is equivalent to a double DOF mechanism containing additional optimization variables, which further improves the design efficiency. For example, the design process of six- and eight-bar bionic mechanisms is given, confirming the feasibility of the method. Then, the effects of the constraint conditions on the design process are analyzed in detail. This study provides a reference for the design of bio-inspired robots.

Design and Development of a Folding Mechanism for Bat-like Bioinspired Wing

Bat is the only mammal capable of powered flight. The most distinctive feature of the batwing is the ability to fold and unfold the wing during the upstroke and downstroke respectively, giving them high maneuverability and energy efficiency. We aim to mimic this folding capability of the batwing in a robotic counterpart. In this paper we have presented a novel single degree of freedom mechanism for wing folding and unfolding, taking into account the kinematics of a biological batwing. We discuss the aerodynamic loading and structural integrity analysis of the mechanism and utilize this to design and fabricate a working prototype.

Dimensional Synthesis of Watt-I Metal Mechanism based on Motion Generation

In industrial automation, there is always increasing demand of generating desired motion with accuracy and precision. It is possible when the mechanism generates motion for large number of precision points. Therefore, in present work, the dimensional synthesis of a 6-bar, Watt-I mechanism has been carried for twenty coupler positions. The single degree of freedom mechanism has revolute pairs at each of its joint and is able to generate required motion. All the links of the mechanism are made of metal. The dyad-triad design equations are formed in terms of complex number algebra. To solve these equations, a MATLAB code is generated and utilized to yield the dimensional parameters i.e. lengths and angular orientations of all links of the mechanism. The complete synthesis methodology is modeled and demonstrated on a numerical problem. To verify the outcomes, SAM 7.0 application software has been incorporated and applied on the given example.

Work-Path Approach Seismic Modelling of Hinge-Controlled Masonry Arches

A dynamic analysis procedure for hinge-controlled masonry arches subjected to horizontal acceleration profiles is developed. Constructed from the principle of energy conservation, the establishment of equivalent systems and the path independence of conservative work, a time-incremental analysis structure is established for kinematic propagation. Equivalent systems are defined through combining kinematic equilibrium with static deformations of the single degree of freedom mechanism through parametric plotting. This generates the minimum work required to propagate the arch towards collapse. For a constant acceleration above the static limit, energy conservation requires the transformation of excess work' into kinetic energy. The path independence of work creates a spatial kinetic energy equation that is used to establish the time domain of the system. Knowing the initial position and kinetic energy thus allows the final position and kinetic energy to be determined for the time increment. A new constant acceleration and timestep then propagates the behaviour through the acceleration profile.

Deformation modeling of manipulators for DEMO using artificial neural networks

A hybrid deformation modeling method is proposed to model deformation physics of manipulators used in DEMO. The deformation of joints is modeled by neural networks and the hybrid deformation model is constructed by integrating the joint’s deformation with the kinematics of the manipulator. The Markov Chain Monte Carlo method is employed to identify weight parameters of the artificial neural network. A complex joint assembly of a boom used for JET maintenance is taken as an example of applying the proposed method, which is treated as a single degree of freedom mechanism. The finite element method is used to generate training data for the hybrid model, as well as being used as a benchmark for verifying the trained model. The comparison results indicate that the hybrid modeling method is competent to model the deformation physics of mechanisms assembly, which is kinematically dependent, under force payload.

Synthesis and optimization of modular deployable truss antenna reflector

PurposeThis paper aims to synthesize a modular deployable truss antenna with the lower degree of freedom (DOF) and larger folding ratio. Because of the advantages of this kind of new truss antenna, the modules that make up the antenna can be deployed together by the synchronous motor drivers instead of twist springs to realize the controllable deployment.Design/methodology/approachThe closed-loop branch equivalence method is proposed to synthesize the single DOF module and the large deployable reflector. The complex mechanism can be equivalently replaced by a simpler mechanism based on screw theory. The motion pairs are synthesized and optimized to make the curved surface achieve to the maximum folding ratio when the modular parabolic truss antenna is folded.FindingsThe results show that the 3(3RR-3RRR)-3RRR-3RRR planar module is a single DOF mechanism. Additionally, the adjacent parts of every two modules are connected with universal joints to obtain the new truss antenna when the modules are networked.Practical implicationsThe configuration of this new modular deployable truss antenna can be synthesized to design the structure, and the proposed method can be applied to other space multi-loop coupling mechanism and other spacecraft.Originality/valueThis paper presents an approach to synthesizing the motion pairs, as well as the DOF analysis. The results lay a foundation for the further analysis of the deployable control and dynamics of this kind of antenna. And the new modular truss antenna has a practical application in aerospace engineering.

Singularity Free Revolute–Prismatic–Revolute and Spherical–Prismatic–Spherical Chains for Actuating Planar and Spherical Single Degree of Freedom Mechanisms

Given a single degree of freedom mechanism, a moving reference frame attached to any link has a motion that can be described with a single parameter. A point relative to this moving frame is sought such that it either continually increases or decreases in distance from a point in the fixed frame over the entire motion. These points can be used to define a revolute–prismatic–revolute (RPR) chain for a planar mechanism or a spherical–prismatic–spherical (SPS) chain for a spherical mechanism capable of actuating the device over its entire range of motion. Moreover, the singularities relative to the joints in the original mechanism are not a concern and the dimensional synthesis can focus on creating the set of circuit-defect free solutions. From this analysis, a unique fixed point is determined in the planar case relative to two positions and their velocities with the following characteristic. All points in the moving reference frame that are moving away from it in the first position are approaching it in the second position, and vice versa. This point is as critical to the identification of singularity-free driving chains as the centrodes or the poles.

Coordinated Planar Mechanisms to Approximate the Three Dimensional Motion of the Knee

The motion of the human knee during flexion and extension generates spatial movement. The current designs of many knee braces and prostheses fail to incorporate this complex motion. This paper presents a method for developing mechanisms with which to more accurately approximate the true movement of the human knee joint with an orthosis comprised of single degree of freedom (DoF) mechanisms. Digitized measurements of the relative motion of the tibia and femur were used to determine the design positions of the mechanisms. Analytical strategies were employed to synthesize suitable Stephenson six-bar linkages for the task of motion generation. The more desirable solutions were selected based on their ability to match the measured movement of the knee as well as the size of their operational envelope. Distinct, single DoF linkages were synthesized for the medial and lateral sides of the knee. Coordination, via attachment to the tibial portion of the orthosis, of these linkages provides a single DoF mechanism to approximate the complex motion of the tibia relative to the femur during flexion and extension.

On the Modeling of Passive Motion of the Human Knee Joint by Means of Equivalent Planar and Spatial Parallel Mechanisms

Recent literature in biomechanics has demonstrated that motion of the human knee joint in virtually unloaded conditions is guided in a single and complex path by the passive structures of the joint alone. It has been deduced that the joint behaves as a single degree of freedom mechanism. Early models, dated on beginning of this century, showed this in the sagittal plane only. The three dimensional motion has been recently modelled by means of equivalent parallel mechanisms, based also on experimental observations on knee specimens of two separate frictionless contacts and three isometric ligament fibres. The model of the joint is a key tool for a deeper understanding of the knee motion and the design of reliable and efficient prostheses. It also provides useful information for the planning of surgical intervention on the basic structures of the knee. The progress of this modelling is reported in this paper. A medical and biomechanical rationale for these studies is provided, together with a number of relevant publications. The pioneering planar four-bar linkage has been initially advanced to a single degree of freedom equivalent spatial mechanism characterised by plane-to-sphere contacts. The closure equations for this mechanism have been progressively simplified. Extensions to more complex articular surfaces have been also performed. The results reported for all these models demonstrate that the original model assumptions were valid and that refinements in articular surface descriptions are justified to a certain extent.

Response of single degree of freedom mechanisms to base excitation

Design dynamic analysis for mechanisms is usually done under the assumption that the mechanism is supported on an inertial frame. When the mechanism is mounted on an accelerating base, the previous analysis must be extended to include the dynamic effects of the base acceleration. This paper provides the necessary extension for single degree of freedom (SDOF) mechanisms and also presents an example.

Kinematics of the human ankle complex in passive flexion; a single degree of freedom system

The restoration of original range and pattern of motion is the primary goal of joint replacement and ligament reconstruction. The objective of the present work is to investigate whether or not a preferred path of joint motion at the intact human ankle complex is exhibited during passive flexion. A rig was built to move the ankle complex through its range of flexion while applying only the minimum necessary load to drive ankle flexion. Joint motion was constrained only by the articular surfaces and the ligaments. The movements of the calcaneus, talus and fibula relative to the stationary tibia in seven cadaveric specimens were tracked with a stereophotogrammetric system. It was shown that the calcaneus follows a unique path of unresisted coupled motion relative to the tibia and that most of the motion occurred at the ankle, with little motion at the subtalar level. The calcaneofibular and the tibiocalcaneal ligaments showed near-isometric pattern of rotations. All specimens showed motion of the axis of rotation relative to the bones. Deviations from the unique path due to the application of load involved mostly subtalar motion and were resisted. The ankle complex exhibits one degree of unresisted freedom, the ankle behaving as a single degree of freedom mechanism and the subtalar as a flexible structure. We deduced that the calcaneofibular and tibiocalcaneal ligaments together with the articular surfaces guide ankle passive motion, other ligaments limit but do not guide motion.

Single degree of freedom mechanism vibration near equilibrium

This paper presents a systematic analysis of the linearization of the equation of motion governing the motion of a single degree of freedom mechanism near an equilibrium position. The results show some terms in the system stiffness expression that are not likely to be included with a less systematic development.

The Case for a General Method of Kinematic Analysis of Plane Mechanisms Based on Equations of Constraint

All but the simplest of single degree of freedom mechanisms have a relatively large number of component parts. To analyse the motion of such systems, therefore, one parameter is rarely sufficient. For an adequate description of the motion characteristics of all components, a number of additional coordinates are needed. This paper introduces a clear and logical notation which facilitates the setting up of the required number of constraint equations by simple inspection of clear line diagrams of the mechanism to be analysed. These constraint equations are eminently suitable for the calculation of velocities and accelerations by direct differentiation. The resulting equations are linear in the velocities and accelerations of all component parts. A method based on this approach is presented and applied to a selection of widely different examples.

General Theorems Concerning Full Force Balancing of Planar Linkages by Internal Mass Redistribution

Two basic questions concerning the full force balancing of n-linked planar mechanisms with pinned and sliding joints are resolved. A contour theorem is shown to differentiate between mechanisms which can be fully force-balanced and those which cannot. (Mechanisms with axisymmetric link groupings are excluded.) In addition, a generalization of the Method of Linearly Independent Vectors for single degree of freedom mechanisms is given, and it is proven that the “apparent” minimum number of counterweights producing full force balancing by internal mass redistribution alone equals n/2.