Bar Linkage Research Articles

Optimum Design Of Elastic And Flexible Linkages For Motion And Path Generation

This paper presents synthesis of rigid and flexible linkages for the purpose of path generation. Optimization technique with DE algorithm is used to minimize the error. Cam-follower mechanism is considered for the synthesis of rigid linkages. Profile of plate cam with offset follower is designed considering no deformation of cam surface. In course of this design fundamental principle of cam motion function is modified and suitable CMF is introduced. An experimental analysis is conducted to verify the theoretical predictions. For flexible linkages, 4-bar with joint clearances and 4-bar linkage with deformation are considered for path generation. In course of analysis the sensitivity to joint clearances are considered.

Type Synthesis of Metamorphic Parallel Mechanism with Spherical Five Bar Linkage

Type Synthesis of Metamorphic Parallel Mechanism with Spherical Five Bar Linkage

Structural and dynamic analysis of optimized four bar mechanism considering counterweight in coupler link

The paper presents the path synthesis of planar four-bar mechanisms with joint clearances and using differential evolution algorithm. The emphasis of the work is to achieve a globally optimal solution under the constraints of a kinematically good mechanism. Differential evolution algorithm is used for the flexible four bar linkage to optimize the link length which minimize the error between the desired and actual path. The structural and dynamic analysis is done by considering external load in the flexible four bar linkage. The shaking force and shaking moment are calculated and analyzed to observe the deflection obtained in the linkage due to the presence of joint clearance, the loading condition and given input motion. To reduce the deflection and vibration, a counterweight is applied in the optimized linkage. The optimized linkage is analyzed dynamically then and compared.

New MEMS Tweezers for the Viscoelastic Characterization of Soft Materials at the Microscale.

As many studies show, there is a relation between the tissue’s mechanical characteristics and some specific diseases. Knowing this relationship would help early diagnosis or microsurgery. In this paper, a new method for measuring the viscoelastic properties of soft materials at the microscale is proposed. This approach is based on the adoption of a microsystem whose mechanical structure can be reduced to a compliant four bar linkage where the connecting rod is substituted by the tissue sample. A procedure to identify both stiffness and damping coefficients of the tissue is then applied to the developed hardware. Particularly, stiffness is calculated solving the static equations of the mechanism in a desired configuration, while the damping coefficient is inferred from the dynamic equations, which are written under the hypothesis that the sample tissue is excited by a variable compression force characterized by a suitable wave form. The whole procedure is implemented by making use of a control system.

A novel gait-based synthesis procedure for the design of 4-bar exoskeleton with natural trajectories

Background/ObjectiveHuman walking involves the coordination of brain, nerves, and muscles. A disturbance in their coordination may result in gait disorder. The gait disorder may be treated through manually assisted gait training or with the aid of assistive devices/robotic devices. These robotic devices involve mechanisms which are synthesized using complex conventional procedures. Therefore, in this study, a new gait-based synthesis procedure is proposed, which simplifies the mechanism synthesis and helps to develop a mechanism which can be used in rehabilitation devices, bipeds, etc. MethodsThis article presents a novel procedure for the synthesis of 4-bar linkage using the natural gait trajectories. As opposed to the conventional synthesis procedures, in this procedure, a global reference frame is considered, which allows the use of hip trajectory while moving. Moreover, this method is divided into two stages, and five precision points are considered on the hip trajectory in each stage. In the first stage, the 4-bar linkage is designed, thereafter, the configurations of the linkage for the remaining precision points are determined in the second stage. The proposed synthesis procedure reduces the complexity involved in the synthesis and helps in the simplification of the problem formulation. A two-stage optimization problem is formulated for minimizing the error between the generated and desired hip trajectories. Two nature-inspired algorithms are used for solving the optimization problem. The obtained best results are presented, and the designed linkage is simulated in MATLAB. ResultsThe best design of the linkage is obtained using particle swarm optimization. The trajectories generated by the designed linkage using the proposed methodology can accurately track the desired path, which indicates that designed linkage can achieve all the orientations required during walking. The positions of a whole lower limb at all the desired precision points are demonstrated by stick diagram for one gait. ConclusionThe proposed methodology has reduced the complexity of synthesis procedures and used optimization techniques to obtain a feasible design of the mechanism. The stick diagram of the designed mechanism obtained using the proposed method indicates that the designed mechanism can walk smoothly. Hence, the designed mechanism can be used in the rehabilitation devices. Furthermore, a conceptual design of an exoskeleton knee is also presented. The Translational Potential of this ArticleMany hospitals and individuals have used the immobile and portable rehabilitation devices. These devices involve mechanisms, and the design of mechanism plays a vital role in the functioning of these devices; therefore, we have developed a new synthesis procedure for the design of the mechanism. Besides synthesis procedure, a mechanism is developed that can be used in the rehabilitation devices, bipeds, exoskeletons, etc., to benefit the society.

Many-to-one form-to-function mapping weakens parallel morphological evolution.

Evolutionary ecologists aim to explain and predict evolutionary change under different selective regimes. Theory suggests that such evolutionary prediction should be more difficult for biomechanical systems in which different trait combinations generate the same functional output: "many-to-one mapping." Many-to-one mapping of phenotype to function enables multiple morphological solutions to meet the same adaptive challenges. Therefore, many-to-one mapping should undermine parallel morphological evolution, and hence evolutionary predictability, even when selection pressures are shared among populations. Studying 16 replicate pairs of lake- and stream-adapted threespine stickleback (Gasterosteus aculeatus), we quantified three parts of the teleost feeding apparatus and used biomechanical models to calculate their expected functional outputs. The three feeding structures differed in their form-to-function relationship from one-to-one (lower jaw lever ratio) to increasingly many-to-one (buccal suction index, opercular 4-bar linkage). We tested for (1) weaker linear correlations between phenotype and calculated function, and (2) less parallel evolution across lake-stream pairs, in the many-to-one systems relative to the one-to-one system. We confirm both predictions, thus supporting the theoretical expectation that increasing many-to-one mapping undermines parallel evolution. Therefore, sole consideration of morphological variation within and among populations might not serve as a proxy for functional variation when multiple adaptive trait combinations exist.

Sessile nanofluid droplet can act like a crane

Interactive droplet systems form the backbone for emerging avenues in droplet based technologies like cell sorting, inkjet printing and digital microfluidics, to name a few. These and their associated fields have gained significant importance in the recent times. Here, we report one such phenomenon wherein a naturally evaporating nanocolloidal sessile droplet interacts with a porous silica gel bead to mimic a macro scale mechanical crane assembly. Precisely, we show a sequence of events displayed by the particle laden aqueous droplet (nanoparticles of silica at different loading rates placed on a hydrophobic substrate) when brought in contact with a meso-porous silica gel bead. First, preferential self-assembly along droplet-bead interface is followed by formation of an adhesive bond. The phenomenon continues until the evaporating droplet naturally lifts the bead. The kinematics of the lift mechanism can be represented by a simple four bar linkage. This work provides insights into interactions between droplets and freely placed porous objects across multiple spatio-temporal scales. Present study should not just motivate researchers to design interactive droplet based systems but also use the same to perform engineering tasks like the crane action.

The kinematics and mechanical advantage of the double-toggle jaw crusher

The purpose of this article is to obtain a comprehensive mathematical description of the kinematics of a double-toggle jaw crusher. The driving mechanism of the crusher is modeled as a planar six bar linkage. Two closed position vector loops that characterize the configuration of the mechanism are used to derive expressions for the angular position, velocity and acceleration of the moveable jaw. Dimensional data of a typical double-toggle jaw crusher are used in the derived mathematical expressions to demonstrate their application. Moreover, starting with the equation for the angular velocity ratio of the moveable jaw, with respect to the input crank, an expression for the ideal mechanical advantage of the crusher is derived. The expressions derived in this paper provide the foundation for further investigations into the mechanics and the design of the double-toggle jaw crusher.

Kinematic analysis of a new five-bar spherical decoupled mechanism with two-degrees of freedom remote center of motion

A new Spherical Decoupled Mechanism is presented in this paper. It can be consider as a new 5-bar spherical linkage or as a parallel mechanism. Indeed, a platform connected to a base by the mean of two serial spherical arms. Its new specific characteristics allow generating a Remote Center of Motion of two angular decoupled Degrees of Freedom. The decoupled motion is proven by its kinematic and velocity models. Both models are simpler than most of the decoupled mechanisms reported in the literature. Their analysis demonstrate a very simple control. It also provides the suppression of the parallel singularity inside its workspace that the original five-bar spherical linkage suffers from and its operational workspace is consequently larger. Its kinematic performance is also improved for the same linkage sizes. Moreover, this new mechanism concept appears to be very simple both in terms of kinematics compared to the original five-bar spherical linkage and in terms of design, compared to other decoupled mechanisms. A mechanism prototype is manufactured to validate the kinematic concept.

Using the Matrix Method to Compute the Degrees of Freedom of Mechanisms

In this paper, some definitions and traditional formulas for calculating the mobility of mechanisms are represented, e.g. Grubler formula, Somov - Malyshev formula, and Buchsbaum - Freudenstei. It is discussed that there are certain cases in which they are too ambiguous and incorrect to use. However, a matrix method is suggested based on the rank of the Jacobian of the mechanism and its application is investigated. It is shown that the matrix method will definitely lead to a correct answer; however, it is lengthy and consumes more computational effort. It is shown that in the cases the traditional formulas give a wrong answer and the matrix method gives the correct mobility. To compare the methods, several examples are given including the four bar planar linkage, the augmented four bar linkage, University of Maryland manipulator, Cartesian parallel manipulator (CPM), delta robot, orthoglide robot, and H4 parallel robot.

Design, Analysis, and Multicriteria Optimization of an Overground Pediatric Robotic Gait Trainer

Robotic gait training has been gathering much attention and has demonstrated potential to improve walking patterns for children with cerebral palsy. This paper proposes a novel pediatric robotic overground gait trainer (Pro-GaiT) based on a nonanthropomorphic linkage design and walking frame. The robot configuration is a 2 degree-of-freedom 5 bar linkage “end effector” and considers the human as part of the kinematic chain. This permits the user to move relative to the robot, inherently handling joint misalignments (unlike exoskeletons), to simplify clinical application while still allowing various gait patterns to be accurately achieved. To successfully achieve this complex motion, the kinematic design is critically analyzed to ensure that desired motion and forces can be imparted on the user. A thorough design analysis is conducted, and a genetic algorithm is used to optimize the robot configuration in terms of workspace, singularities, and physical size of the robot. The device was experimentally validated with four healthy subjects, as well as with clinical data from three children with CP that walk with crouch gait with varying human–robot misalignment and joint spasticity. The results demonstrate that the Pro-GaiT has achieved the desired clinical specifications.

Quantitative evaluation of hand functions using a wearable hand exoskeleton system.

To investigate, improve, and observe the effect of rehabilitation therapy, many studies have been conducted on evaluating the motor function quantitatively by developing various types of robotic systems. Even though the robotic systems have been developed, functional evaluation of the hand has been rarely investigated, because it is difficult to install a number of actuators or sensors to the hand due to limited space around the fingers. Therefore, in this study, a hand exoskeleton was developed to satisfy the required specifications for evaluating the hand functions including spasticity of finger flexors, finger independence, and multi-digit synergy and algorithms to evaluate such functions were proposed. The hand exoskeleton was composed with the four 4-bar linkages, two motors, and three loadcells for each finger, and it was able to flex/extend the metacarpal (MCP) and proximal interphalangeal(PIP) joints independently while measuring the pulling force at each phalanx. Using the hand exoskeleton, the hand functions of the three healthy subject were evaluated and the experimental results were analyzed.

Structure optimal design research on backfill hydraulic support

Backfill hydraulic support is the key equipment in achieving coal mining and solid backfilling simultaneously in solid backfill mining technology. Based on the summary and analysis of main types, basic structural properties and filed application of backfill hydraulic support, this work has firstly proposed the basic principle of backfill hydraulic support optimization design and provided the method of optimal design of key structural components, like four-bar linkage, rear canopy and tamping structure; the method is further elaborated as changing hinging position of upper bar to optimize four-bar linkage, by lengthening or shortening the rear canopy to optimize length ratio of canopy; and by changing length and hinging position of tamping structure as well as suspension height of backfill scrape conveyor to realize optimization of tamping structure. On this basis, the process of optimal design of backfill hydraulic support is built. The optimal design case of ZC5200/14.5/30 six columns-four bar linkage used in 7203W workface of Zhaizhen Coal Mine shows that the backfill properties like horizontal roof gap, vertical horizontal gap, tamping angle and tamping head gap are improved obviously through optimizing four-bar linkage, canopy length and tamping structure according to the optimal design method proposed in this work.

Reliability-based robust design for kinematic accuracy of a mechanism with axiomatic theory

In this paper, a reliability-based robust design approach was proposed on the basis of axiomatic theory, aiming at actualizing a reliability-based robust design framework for mechanism motion. First, reliability constraint functions of the motion output error of mechanisms were established by using cumulative distribution method after an accuracy analysis of mechanism motion. Second, the number of effective design parameters was equated to the number of functional requirements by classifying design parameters using sensitivity analysis or constructing additional objective functions based on axiomatic theory, and then the independence axiom was satisfied by establishing objective functions according to regularity and the semangularity. Third, a reliability-based robust design model of mechanisms was established based on the axiomatic theory according to the above objective functions and constraint functions. Taking a planar four bar linkage as an example, a reliability-based robust design was achieved with the optimization and symbol toolbox in MATLAB. Meanwhile, correctness and effectiveness of the proposed method was verified under the condition that the first and second moments of basic random parameters were available. Finally, the method proposed in this paper was applied to the reliability-based robust design of an initiative lock mechanism in space docking latch system.

剛性可変機構を有する5指ロボットハンドの開発

This study deals with a robot hand based on the original finger mechanism consisting of a planetary gear system and serially connected four bar linkages. It also has a mechanism for adjusting stiffness of fingers (VSM: Variable Stiffness Mechanism), which allows to give passive gripping force to a gripping object according to the object's elasticity. The mechanism is merely driven by mechanical elements without sensory feedback from tactile or force sensors attached to fingertip or sole. The total number of motors for driving the robot hand is six, all of which are equipped in the palm. Rotation angle of motor is detected by optical encoder equipped to each motor. The robot hand achieves soft and adaptive gripping action due to VSM that adjusts the joint stiffness of the fingers by changing tension of the spring attached to the planetary gear system equipped in every finger except the thumb. Driving tests show that it achieves typical gripping and pinching motions of a human hand in daily life without any sensory feedback and also show that the VSM works effectively.

Key Technologies in Large-scale Rescue Robot Wrists

The full-Automatic Quick Hitch Coupling Device (full-AQHCD for short) is used as the starting point, key technologies in a large-scale rescue robot wrist, which is constituted by integrating a quick hitch coupling device, a turning device, and a swaying device together, are reviewed respectively. Firstly, the semi-AQHCD made domestically for the main-Arm Claw Wrist (main-ACW for short) is introduced, and the full-AQHCD imported from Oil Quick company in Sweden for the vice-Arm Cutter Wrist (vice-ACW for short) is presented. Secondly, aiming at three key technologies in the full-AQHCD including rotary joint technology, automatic docking technology and precise docking technology for quick action coupling, are concisely expressed. Thirdly, the hydraulic motor driving gear type slewing bearing technology of the turning device made domestically for the main-ACW is introduced, and the hydraulic motor driving worm type slewing bearing technology of the turning device imported from HKS company in Germany for the vice-ACW is presented, especially, the existing gap in the similar domestic technology is discussed. Subsequently, the hydraulic cylinder driving 4-bar linkage technology of the swaying device made domestically for the main-ACW is introduced, and the hydraulic double spiral swing cylinder technology of the swaying device imported from HKS company in Germany for the vice-ACW is presented, especially, the existing gap in the similar domestic technology is discussed. Finally, it is emphasized that these technological gaps have seriously restricted the ability of the vice-ACW to successfully work in future actual rescue combats, therefore, it must be highly valued in the follow-up research and development (R&D) through cooperating with professional manufacturers in China, thereby making technological advances.

SWINGING LEG CONTROL OF A LOWER LIMB EXOSKELETON VIA A SHOE WITH IN-SOLE SENSING

A lower limb exoskeleton can help in weight-bearing and walking to assist laborers doing heavy work. For exoskeleton-assisted walking, the wearing comfort and walking convenience are important so there must be minimal interference with leg movement. Hence, a peculiar design strategy based on an in-sole sensing shoe is presented to achieve real-time motion detection and follow-up control of the moving leg. Compared to the elastic muscle extension, the sensor must exhibit minimal deflection under load. Therefore, an ultra-thin structure integrating 6 bar linkages and 3 cantilevers has been used in the design of the in-sole sensing shoe which can detect force in two directions and torque in one. A swing phase experiment and a random leg motion test were carried out. Results show validity of human motion detection and follow-up control strategy based on this plantar surface sensor.

KINEMATIC SYNTHESIS OF PLANAR ADJUSTABLE SIX BAR MECHANISM FOR SPECIFIED OUTPUT

A method for the synthesis of planar adjustable six bar mechanism with a slider output is presented. The multi-loop six bar linkage considered here is a series combination of two four link mechanisms with first phase having regular RRRR linkage. The second phase consists of a slider crank with the slider being the output member. An analytical method is presented for the kinematic synthesis of a planar four bar adjustable mechanisms using Chebychev’s accuracy points and Fruedenstein’s equations for three point function generation that satisfy a given input output relationship. The length of the coupler link is taken as the adjustable parameter. An analytical method of computing the value of this variable for a four bar crank rocker mechanism as well as a slider crank mechanism is presented. A numerical example explains the synthesis procedure developed in which a function to be generated is considered. The unknown link lengths of the mechanism are then found for given range of input and output link parameters and assumed link length. The value of the adjustable length of the coupler is then computed and the results are presented numerically as well as graphically. The method adopted is coded using MATLAB for quick computation and ease of use. The motion and the path generated by the designed mechanism is found for different values of the adjusted parameter.

Robotic Total Knee Arthroplasty: Surgical Assistant for a Customized Normal Kinematic Knee

Although current total knee arthroplasty (TKA) is considered a highly successful surgical procedure, patients undergoing TKA can still experience substantial functional impairment and increased revision rates as compared with those undergoing total hip arthroplasty. Robotic-assisted surgery has been available clinically for almost 15 years and was developed, in part, to address these concerns. Robotic-assisted surgery aims to improve TKA by enhancing the surgeon's ability to optimize soft tissue balancing, reproduce alignment, and restore normal knee kinematics. Current systems include a robotic arm with a variety of different navigation systems with active, semi-active, or passive control. Semi-active systems have become the dominant strategy, providing a haptic window through which the surgeon consistently prepares a TKA based on preoperative planning. A review of previous designs and clinical studies demonstrates that these robotic systems decrease variability and increase precision, primarily with the mechanical axis and restoration of the joint line. Future design objectives include precise planning and consistent intraoperative execution. Preoperative planning, intraoperative sensors, augmenting surgical instrumentation, and biomimetic surfaces will be used to re-create the 4-bar linkage system in the knee. Implants will be placed so that the knee functions with a medial pivot, lateral rollback, screw home mechanism, and patellar femoral tracking. Soft tissue balancing will become more than equalizing the flexion and extension gaps and will match the kinematics to a normal knee. Together, coupled with advanced knee designs, they may be the key to a patient stating, "My knee feels like my natural knee." [Orthopedics. 2016; 39(5):e822-e827.].

Motion Control of Five Bar Linkage Manipulator Using Conventional Controllers Under Uncertain Conditions

Robot trajectory tracking has been the core functioning unit in the modern industrial environment wherein the accuracy in the motion control of robotic manipulators is the main area of research. Based on the fact that the working of these automatic robotic machines is highly influenced by the disturbances, this paper constitutes various conventional controllers for the motion control of five bar linkage manipulator. To verify the performance of proposed conventional controllers, these are made to work with two different trajectories. Common disturbances like payload & friction has been incorporated in the five bar linkage manipulator system for validation purpose. Simulation results prove that the performance of SMC based controller is better when compared with other conventional controllers.