Degree Of Freedom Mechanism Research Articles

CGull: A Non-Flapping Bioinspired Composite Morphing Drone.

Despite the tremendous advances in aircraft design that led to successful powered flights of aircraft as heavy as the Antonov An-225 Mriya, which weighs 640 tons, or as fast as the NASA-X-43A, which reached a record of Mach 9.6, many characteristics of bird flight have yet to be utilized in aircraft designs. These characteristics enable various species of birds to fly efficiently in gusty environments and rapidly change their momentum in flight without having modern thrust vector control (TVC) systems. Vultures and seagulls, as examples of expert gliding birds, can fly for hours, covering more than 100 miles, without a single flap of their wings. Inspired by the Great Black-Backed Gull (GBBG), this paper presents "CGull", a non-flapping unmanned aerial vehicle (UAV) with wing and tail morphing capabilities. A coupled two degree-of-freedom (DOF) morphing mechanism is used in CGull's wings to sweep the middle wing forward and the outer feathered wing backward, replicating the GBBG's wing deformation. A modular two DOF mechanism enables CGull to pitch and tilt its tail. A computational model was first developed in MachUpX to study the effects of wing and tail morphing on the generated forces and moments. Following the biological construction of birds' feathers and bones, CGull's structure is mainly constructed from carbon-fiber composite shells. The successful flight test of the proof-of-concept physical model proved the effectiveness of the proposed morphing mechanisms in controlling the UAV's path.

A six degrees-of-freedom cable-driven robotic platform for head-neck movement.

This paper introduces a novel cable-driven robotic platform that enables six degrees-of-freedom (DoF) natural head-neck movements. Poor postural control of the head-neck can be a debilitating symptom of neurological disorders such as amyotrophic lateral sclerosis and cerebral palsy. Current treatments using static neck collars are inadequate, and there is a need to develop new devices to empower movements and facilitate physical rehabilitation of the head-neck. State-of-the-art neck exoskeletons using lower DoF mechanisms with rigid linkages are limited by their hard motion constraints imposed on head-neck movements. By contrast, the cable-driven robot presented in this paper does not constrain motion and enables wide-range, 6-DoF control of the head-neck. We present the mechatronic design, validation, and control implementations of this robot, as well as a human experiment to demonstrate a potential use case of this versatile robot for rehabilitation. Participants were engaged in a target reaching task while the robot applied both assistive and resistive moments on the head during the task. Our results show that neck muscle activation increased by 19% when moving the head against resistance and decreased by 28-43% when assisted by the robot. Overall, these results provide a scientific justification for further research in enabling movement and identifying personalized rehabilitation for motor training. Beyond rehabilitation, other applications such as applying force perturbations on the head to study sensory integration and applying traction to achieve pain relief may benefit from the innovation of this robotic platform which is capable of applying controlled 6-DoF forces/moments on the head.

О некоторых динамических свойствах механизма параллельной структуры типа «трипод» вблизи особых положений

The paper considers a three degrees of freedom mechanism, which output link is oscillating in vicinity of the singular positions. Various types of the mechanism motion are observed depending on initial conditions, mass of the output link and feedback coefficients of the drives. In particular, transition through a specific position (singularity) could take place. Translational drives of such a mechanism are positioned along the edges of a pyramid formed by the tripod kinematic chains. Axes of the drives converge at one point, i.e. at the output link center. The entire mass is concentrated in the output link (working body). In turn, entire elasticity of this mechanism is determined by the linear actuators. Dependence between the oscillation frequency and the initial conditions could be of interest. By setting the output link initial position closer or farther from the equilibrium point, different laws of the output link motion could be obtained. In particular, the specified link is able to pass through singularity. By changing the output link initial position height, different frequency of the oscillatory process could be received. Thus, there appears a dependence of the oscillation frequency on the amplitude.

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.

Development of a Wearable Finger Exoskeleton for Rehabilitation

This research work shows a new architecture of a novel wearable finger exoskeleton for rehabilitation; the proposed design consists of a one degree of freedom mechanism that generates the flexion and extension movement for the proximal, medial and distal phalange of the fingers to assist patients during the rehabilitation process, after neurological trauma, such as a stroke. The anatomy and anthropometric measures for the hand were used to define the design of the mechanism. In the analytic part, the representative equations for the forward and inverse kinematic analysis of the fingers are obtained, also a dynamic analysis is presented. The position and displacement continued for the structural analysis, were developed by following a static analysis, to know the deformation that the structure links show when an external load is applied in the mechanism. As result, a prototype was manufactured with acrylonitrile butadiene styrene (ABS) using an additive manufacturing machine.

Integrated design of a lower limb rehabilitation mechanism using differential evolution

In the last years, one degree of freedom mechanisms has been incorporated into rehabilitation machines. Their designs usually involve kinematic synthesis leaving aside their complex dynamic nature. An integrated methodology to design a one degree of freedom eight-bar mechanism for lower limb rehabilitation is presented in this paper. The methodology simultaneously considers kinematic synthesis, structure shape design, and dynamic performance. A non-linear constrained dynamic optimization problem is proposed where the design objective relates the accuracy in the prescribed movement and the energy consumption reduction. This problem is solved by using different differential evolution variants for finding the most suitable synergistic solution. The results show that the obtained design can follow the path with 52.13% less energy consumption compared to a design that does not consider such integration. This also results in less control effort, and hence the velocity regulation accuracy is improved. The three-dimensional printed prototype illustrates the obtained solution.

Object tracking using motion flow projection for pan-tilt configuration

We propose a new object tracking model for two degrees of freedom mechanism. Our model uses a reverse projection from a camera plane to a world plane. Here, the model takes advantage of optic flow technique by re-projecting the flow vectors from the image space into world space. A pan-tilt (PT) mounting system is used to verify the performance of our model and maintain the tracked object within a region of interest (ROI). This system contains two servo motors to enable a webcam rotating along PT axes. The PT rotation angles are estimated based on a rigid transformation of the the optic flow vectors in which an idealized translation matrix followed by two rotational matrices around PT axes are used. Our model was tested and evaluated using different objects with different motions. The results reveal that our model can keep the target object within a certain region in the camera view.

Dynamic analysis of elementary differential gear with rigid links

At present the machine dynamics investigations are conducted in the next directions: dynamic processes research in special machines; research of the machines which links are solids; research of mechanisms representing a combinations of a solids and elastic systems. In this paper the elementary differential gear with rigid links dynamics is investigated. A number of dynamic problems can be solved accurately enough without taking into account the loaded element elasticity. Research of dynamic processes of one degree of freedom mechanisms are quite fully published in scientific literature, which cannot be said about mechanisms that have two degrees of freedom. In this paper are compiled and solved the movement equations for differential mechanism with two degrees of freedom. Mechanism has two degrees of mobility, therefore, the position of all its links is determined by two generalized coordinates. The mechanism movement is described by two Lagrange equations of II kind. Rotation angles of the drive and driven shafts are taken as generalized coordinates. System of differential equations of the second order relativ generalized coordinates is compiled. All coefficients of this system can be calculated in advance. Joint solution of equations of the system makes it possible to determine the angular accelerations of the two main links. Equations for determining angular velocities and angular accelerations of drive and driven shafts are recieved.

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.

Masonry structures made of monolithic blocks with an application to spiral stairs

The broad topic of the present work is Statics and Kinematics of masonry structures, made of monolithic blocks, modelled a la Heyman, that is rigid bodies loaded by external forces, submitted to unilateral constraints, and undergoing small displacements, under the simplifying assumption that sliding on rough interfaces is prevented. Specifically, in this work, we study the effect, in terms of internal forces, of specified loads, by using given settlements/eigenstrains to trigger special regimes of the internal forces. Although our scope here is the analysis of masonry structures composed by monolithic pieces, and whose blocks are not likely to break at their inside, the method we propose can also be applied to generic masonry structures, such as those made of bricks or small stones. Heyman’s assumptions translate, for unilateral continua, into a normality assumption which allows to employ the two theorems of Limit Analysis. These continuous structures may actually fracture everywhere at their inside, forming rigid blocks in relative displacement among each other. Such piecewise rigid-body displacements in masonry are physiological, and rather than the result of over-loading, are most likely the direct product of small changes of the displacement type boundary conditions. However, when in a part of the structure a specific piecewise rigid-body displacement nucleates, that part of the structure exhibits a one degree of freedom mechanism, and becomes statically determined. Therefore, the internal forces can be computed, despite the original uncracked structure being abundantly overdetermined, and then admitting infinite many statically admissible stress regimes. With these assumptions, in the present paper we study the equilibrium and the effect of settlements in a masonry structure made of monolithic blocks. In particular, the triple helical stair of the convent of San Domingos de Bonaval, located in the Bonaval district of Santiago de Compostela, is considered as case study.

Modal Measurements and Model Corrections of A Large Stroke Compliant Mechanism

Abstract In modelling flexure based mechanisms, generally flexures are modelled perfectly aligned and nominal values are assumed for the dimensions. To test the validity of these assumptions for a two Degrees Of Freedom (DOF) large stroke compliant mechanism, eigenfrequency and mode shape measurements are compared to results obtained with a flexible multibody model. The mechanism consists of eleven cross flexures and seven interconnecting bodies. From the measurements 30% lower eigenfrequencies are observed than those obtained with the model. With a simplified model, it is demonstrated that these differences can be attributed to wrongly assumed leaf spring thickness and misalignment of the leaf springs in the cross flexures. These manufacturing tolerances thus significantly affect the behaviour of the two DOF mechanism, even though it was designed using the exact constraint design principle. This design principle avoids overconstraints to limit internal stresses due to manufacturing tolerances, yet this paper shows clearly that manufacturing imperfections can still result in significantly different dynamic behaviour.

1P2-M03 超多自由度機構による非協力衛星把持方法に関しての研究(宇宙ロボット)

1P2-M03 超多自由度機構による非協力衛星把持方法に関しての研究(宇宙ロボット)

MECHANICAL STRUCTURE IMPROVEMENT OF AN UPPER LIMB REHABILITATION ROBOT: BASED ON AN EQUIVALENT KINEMATIC MODEL

Several rehabilitation robots for upper limbs have been introduced so far, and clinical effectiveness was reported in several studies for the aged people or patients with stroke. Upper limb motor deficits of the patients have to be identified during the motor training, which requires the flexibility of mechanical structure. However, the users have difficulties in driving the previous robotic arms precisely because of the previous mechanical structure, especially when they are required to track a circle. This article gives a kinematic analysis on the previous mechanical structure of the previous robot, which is a two bar-linkage, two degrees of freedom mechanism, then solves the force on the handle grip during user's operation based on an equivalent kinematic model. The key of the problem is that force directions exerted by the user are not in the correct directions to drive the robot. Therefore, a new mechanical design using parallel robotic arms is suggested. The improvement is justified by comparing results from tracking circles using different robots.

Study on the Trajectory Planning of Hybrid-Driven Planar 3-RRR Mechanism

Hybrid-driven mechanism synthesis the constant speed motor and the servo motor as the power source through a multi degree of freedom mechanism. The text study on the trajectory planning of hybrid-driven planar 3-RRR mechanism. Firstly, based on compatible link combinations, all possible basic configurations of planar 3-dof kinematics chains were derived. Based on the requirements of hybrid-driven mode, the kinematics chains were selected one by one Planar 3-RRR mechanism was determined to be the research object finally. Then, based on the conclusions of inverse kinematics analysis, using the cubic spline function on point to point path planning, the servo motor rotation laws were presented. Comparing the different speed situation of constant motor, the influence trends on planning results were analyzed.

Investigation of Positional Error in Two Degree of Freedom Mechanism With Joint Clearance

Closed chain mechanisms are used as robotic manipulators with special features. A planar two-DOF closed loop mechanism provides desired position of an end effecter in a confined workspace with two input motions. Position of end effecter depends on various factors including joint clearance. Positional accuracy forms important parameter for kinematic analysis of mechanism. This paper presents simple approach for quantifying error due to joint clearance in a two-DOF mechanism. Generalized scheme for positional deviation with and without clearance at joint is presented. Orientation of clearance links for maximum positional error is identified. Error at various positions is quantified in relation with clearance link length. Computer programming is used as a tool to workout positional analysis of mechanism. Results show that error is independent of magnitude of clearance, however, a function of location of end effecter in workspace.

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.

Dynamic Analysis of Self-Energizing Shock Absorber of Suspension for Energy-Regenerative

Design of self-energizing shock absorber of suspension of SVU, a multi degree of freedom mechanism, is a challenge. In order to decay vibration and recycle energy, self-energizing shock absorber was researched. This paper primarily focuses on kinematics and dynamic analysis in multi-body system (MBS) and validation of system. A simulation model for self-energizing shock absorber was built using the software MATLAB, and the establishment of this model was based on the analysis of internal configuration and characteristics of valves. Vehicle simulation model was built using MBS. The assembly between vehicle simulation model and the shock absorber was realized through co-simulation between MBS and MATLAB. The optimal design of suspension is investigated, in order to improve vertical ride and road-friendliness of vehicles, while maintaining enhanced roll stability. A nonlinear vehicle model is developed to study vertical as well as roll dynamics of vehicles. The simulation results shows that suspension with self-energizing shock absorber can partly energy-regenerative which can be used to adjust ride height due to load change of automobile. Self-energizing shock absorber is also improving the ride performance of vehicle.

Optimum Design of a Hybrid-Driven Mechanical Press Based on Inverse Kinematics

A novel hybrid-driven mechanical press for deep drawing is presented. The main feature of hybrid-driven linkage is to combine the motion of a large constant velocity motor with a small servomotor via a two degree of freedom mechanism. The former provides the main power and motion required, while the latter acts as a motion modulation device. Therefore, the hybrid-driven linkage can provide for programmable motion output. In this paper, a mechanical press driven by hybrid mechanism is developed that considers the displacement and velocity requirement of the drawing process. Inverse kinematic analysis and dimension synthesis optimization of this hybrid-driven mechanism is presented, which points out a new way for press research and provides a new method for press application in flexible manufacture.

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.

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.