Parallelogram Mechanism Research Articles

Research on Cross-scale Micro-gripper Based on Multi-stable Flexible Mechanism

<p>In order to solve the problems of low precision, small stroke, and inabilityto grip objects across scales (um-mm) in traditional micro-gripper, a multi-stable flexible mechanism-based cross-scale micro-gripper structure was proposed. The multi-stable structure is combined with the traditional amplifying mechanism. The leftside of the micro -gripper adopts a lever mechanism and a parallelogram mechanism, and the right side adopts three different bistables in series to achieve eight-stable state. Finally, the parallelogram mechanism ensures the end of the micro-gripper. The output is pure parallel movement. Firstly, the overall structure design of the micro-gripper is introduced; secondly, the displacement amplification ratio and multi -stable characteristics of the amplification mechanism are deduced through theoretical calculation; finally, the performance and reliability of the micro-gripper are verified by the simulation analysis of the model by finite element. The micro-gripper has high magnification, large grippering range, compact structure, and can realize parallel grippering across μm-mm.</p>

Design of a transrectal ultrasonic guided prostate low dose rate brachytherapy robot

Abstract. Transrectal prostate brachytherapy (BT) can effectively treat prostate cancer. During the operation, doctors need to hold the ultrasound probe for repeated adjustments, which makes it difficult to ensure the efficiency, accuracy, and safety of the operation. We designed an 11 DOF (degrees of freedom) active and passive transrectal BT robot, based on the analysis of the transrectal prostate BT process. The posture adjustment module designed, based on the double parallelogram mechanism, realizes the centering function of the ultrasound probe and performs the kinematic analysis. Based on Simscape Multibody, the working posture and centering effect of the ultrasound probe's different feed distances are simulated. A physical prototype of the transrectal BT robot was developed and measured in experiments. The experimental results indicate that the angle rotation error of the joint is controlled to within 1∘. The rotation range of each joint meets the design requirements. The maximum error of the yaw angle's remote center point motion and pitch angle's remote center point motion are 0.5 and 0.4 mm, respectively, which are less than the deformation that can be endured in the anus by 6 mm. The simulation and experimental results and the analysis of measurement errors have verified the effectiveness and stability of the transrectal BT robot.

Optimal Design and Dynamic Analysis of Hydrofoil Mechanism of Wave Glider

A wave glider can convert vertical wave motion into its forward propulsion. There are many factors affecting the propulsion performance of a wave glider. The swing amplitude of hydrofoil can affect the efficiency of hydrofoil to capture wave energy, and the pull direction of an umbilical cable can affect the transmission efficiency of wave energy. In this paper, an optimized hydrofoil mechanism with a self-adjusting lower limit (SALL) was proposed by analyzing the un- synchronized movement between the submerged glider and the surface float. This mechanism was able to transfer the movement of umbilical cable to the hydrofoil swing mechanism through the linkage to control the lower limit of hydrofoil swing (maximum swing angle of hydrofoil in a counterclockwise direction). Firstly, the user-defined function (UDF) was written to control the motion of hydrofoil in the fluid domain. The lower limit swing angle and the heave direction of the hydrofoil were both set in the UDF, and the forward thrust generated by the passive swing of the hydrofoil in the fluid domain was able to be obtained by the simulation. Secondly, the prototype was designed by introducing a parallelogram mechanism on a conventional submerged glider, and a wave simulation test platform was built to verify the propulsive performance of the prototype. The results showed that, in comparison with the conventional submerged glider, the forward thrust of the SALL submerged glider was able to be improved by 1.50%, 17.78%, 7.42%, and 20.70% under the stiffness coefficients of torsion spring set to K = 2, K = 4, K = 6, and K = 8 in the simulation experiment, respectively. The forward thrust of the SALL submerged glider was able to be elevated by 9.99% with torsion spring K = 8 in the tank experiment. The advantage of the SALL mechanism was verified by comparing the results of the simulation and the tank experiment. Finally, the feasibility of the SALL submerged glider was verified in actual sea conditions by a sea trial.

Design and Testing of a New Piezoelectric-Actuated Symmetric Compliant Microgripper

Precise and stable operations in micromanipulation and microassembly require a high-performance microgripper. To improve the predominant static and dynamic characteristics, a novel piezoelectric-actuated compliant microgripper is designed, analyzed, and tested in this paper. The microgripper realizes a large gripping stroke by integrating a compliant bridge mechanism, an L-shaped mechanism, and a levered parallelogram mechanism. Optimization technology based on response surface analysis is applied to demonstrate the influence of structural parameters on the microgripper performance. Simulation results of finite element analysis reveal the superior performance of the designed microgripper in terms of gripping displacement, mechanism stiffness, equivalent stress, and natural frequency. A gripper prototype has been fabricated, and experimental studies have been conducted to test the microgripper’s physical properties. Experimental results show that the microgripper can grasp micro-objects with a maximum jaw motion stroke of 312.8 μm, natural frequency of 786 Hz, motion resolution of ±0.6 μm, and force resolution of ±1.69 mN. The gripping tests of an optical fiber with a diameter of 200 μm and a metal sheet with a thickness of 100 μm have been performed to demonstrate its gripping capability with position and force control.

Design and analysis of a two-degrees-of-freedom monolithic compliant piezoelectric microgripper

This paper presents the design, modeling, and testing of a compliant two-degrees-of-freedom microgripper using a single piezoelectric actuator. It can move along the x- and y-directions by combining double-leaf bridge and parallelogram mechanisms. An analytical model is established using the finite-element method. The displacement amplification ratio, natural frequency, and output coupling ratio are analyzed using ANSYS software. An experimental test system is built to verify the open-loop performances. Experimental results show that the displacement amplification ratios in the x- and y-directions are 30.8 and 8.6. The first resonant frequencies in the x- and y-directions are 123.3 and 546.9 Hz. If an input displacement of 10 μm is applied, the operating ranges in the x- and y-directions are 0–616.6 μm and 0–51.0 μm, and the gripping force range is 0–25.8 mN. Experimental results validate the feasibility of the theoretical model and simulation analysis. Also, closed-loop trajectory control is conducted to reduce the hysteresis nonlinearity and achieve a high control accuracy for the new microgripper.

Theoretical and Experimental Studies of Following the Soil Microrelief Contour by the Seeder Section

The paper presents the results of theoretical and experimental studies of the operating process of the seeder section for the no-till sowing machine. Based on the theoretical studies, the authors derived the dependences allowing one to obtain the motion trajectories of the seeder section elements with a parallelogram mechanism when following (gauging) the microrelief contour of the soil surface, taking into account its design parameters. The obtained theoretical trajectories were used as a basis for identifying rational parameters of the gauge wheel of the section. The results of the theoretical studies were confirmed experimentally by the laboratory experiments on a tillage bin, using the developed prototype of the seeder section when following artificial roughnesses. A comparison of the results of the theoretical and experimental studies demonstrated a sufficient degree of their convergence. The authors also established a regularity of the change in the uniformity of the coulter motion of the seeder section relative to the microrelief of the soil surface, depending on its position relative to the gauge wheel.

Підвищення довговічності трибоспряжень застосуванням полімерних композиційних матеріалів

The purpose of the work is the theoretical substantiation of the operating modes of the parts of a typical parallelogram mechanism, the determination of the magnitude of the initial deformations and the optimal operating modes of the parts made of polymer-composite materials. Changes in the geometric dimensions of parts of the sowing section under the influence of loads during operation are considered. Determination of the load acting in the tribo couplings of the sowing section of the "Turbosem II 19-60" complex. The mathematical model for determining radial, angular displacements and the magnitude of deformations due to design features and loads on movable couplings is substantiated. The methodology for determining the maximum and minimum compensation of installation deformations for parts made of polymer-composite materials is proposed. Experimental studies have established that the rate of wear (0.003 g/h) of PCM parts has a linear dependence on working life, which allows predicting the resource of tribo couplers. Taking into account the geometric dimensions of the PCM part and the limit value of the gap in the tribo-coupling, it is possible to determine the resource of the moving tribo-coupling with high probability. The obtained linear function of the dependence of the amount of wear on the working life is valid for the material UPA-6-30, under the condition of a linear sliding speed of up to 0.1 m/s and a load on the tribo coupler up to 600 N. Experimental studies have determined the optimal values of the load value - 250 N and the gap - 300 μm in the tribo coupling "polymer composite - steel". The obtained results can be used in the modernization of existing or development of new designs of sowing sections.

Motion/structure mode analysis and classification of [formula omitted]-RR planar parallelogram mechanisms

Planar parallelogram mechanisms (PPMs) have been used in many applications either as standalone pieces or as compositional joints of mechanisms, such as parallel mechanisms, remote center mechanisms and variable-DOF mechanisms. An n-RR PPM is composed of congruent base and moving platform connected with n RR links of equal link lengths. Although it is well known that an n-RR PPM has one 1-DOF circular translation mode, whether an n-RR PPM has structure/motion modes in addition to the 1-DOF motion mode and how the link parameters affect the number of extra motion/structure modes of the n-RR PPMs have not been well investigated. This paper is about the motion/structure mode analysis and classification of n-RR PPMs. Firstly, the motion/structure mode analysis of 3-RR PPMs is carried out. Then conditions for an n (n>3)-RR PPM to have the same motion/structure modes as a 3-RR PPM are revealed. Finally, n (n≥3)-RR PPMs are classified into three types. In addition to one 1-DOF motion mode, Types I, II and III PPMs have two, one or zero structure mode respectively. This work provides a foundation for the construction and analysis of several variable-DOF mechanisms composed of PPMs.

Improving stability of movement of machine section for soil preparation and seeding

The subject research is operation of a combined machine for soil preparation and seeding of sunflower and corn seeds. Technological process of machine operation with installed guides, passive rotating flat discs with flanges (which properly ensure movement of soil along the plough share to loosening-separating device), a sowing device, a seed tube, a furrow former, a rotor, a separating grid, a parallelogram mechanism, a spring, a share is described. Dynamic prerequisites for increasing uniformity of depth of groove formation and seed placement in depth in soil are considered. Values of length of links of parallelogram mechanism, initial angle of their installation and stiffness of spring, values of deviations of combined machine section from given depth of movement of plough share are determined. It is proved that with an increase in length of levers of parallelogram mechanism, maximum deviations of section increase. An increase in initial angle of inclination of levers of parallelogram mechanism causes an increase in maximum deflections. As spring stiffness increases, maximum deflections decrease. Relevance of study lies in ensuring stability of copying soil surface by working bodies of combined machine while depth of seeding remains unchanged along entire length of movement, which will make it possible to increase movement speed and unit width. Target group of consumers of information in the article - designers, specialists involved in development of tillage machines.

Kinematics analysis and workspace optimization for a 4-DOF 3T1R parallel manipulator

A four degrees-of-freedom (DOF) Parallel Manipulator (PM) with a 4PPa-2PaR configuration has been proposed to generate 3-DOF Translational and 1-DOF Rotational (3T1R) motions in our early work. It has the advantages of symmetric geometry, simple kinematics and infinite extension of translational workspace along its linear guide direction. However, its V-type assembly mode results in a long distance between its moving platform and the base, which makes its stiffness and accuracy lower. Besides, its the other two translational workspaces are limited due to its kinematic singularities. To overcome such limitations, the PM is modified by utilizing its M-type assembly mode and placing an offset angle to the last parallelogram mechanism. To simplify the displacement analysis, a geometrical projection method is employed, while a closed-loop vector approach is used for its instantaneous kinematic analysis. Both singularity and workspace issues are investigated. An optimization algorithm based on Genetic Algorithm is proposed to maximize the reachable workspace. The optimization result indicates that the workspace is significantly increased. A prototype of the M-type PM is fabricated to validate the effectiveness of the modified design.

Design and Fabrication of 3-DOF Robot Arm Using Parallelogram Mechanisms

This paper focuses on the design, fabrication and control of a 3-DOF robot arm using stepper motors. The robot arm uses three parallelogram mechanisms to position the end-effector of the robot and keep the end-effector always parallel to the horizontal during the robot motion. The robot is designed on the Autodesk Inventor software. Separated parts of the robot are saved in the stereolithography (STL) file format. Then the parts are fabricated by a 3D printer. The movement of the robotic arm is driven by stepper motors and controlled by Arduino. The Arduino board implements kinematics calculation, creates pulses and sends them to three drivers to driven stepper motors. A software is developed to control the robot by sending the command to the Arduino board.

Optimization design of a compliant linear guide for high-precision feed drive mechanisms

This paper presents an optimal design of a compliant linear-guide mechanism for a high-precision feed drive. In this design, semi-circular flexural hinges are integrated with rigid-links to make lever mechanisms and parallelogram mechanisms to produce large amplification, increase structural rigidity, and reduce undesirable parasitic motion. Therefore it enhances the accuracy and enlarge the operational range of the mechanism. The design process includes five steps: (1) design the pseudo-rigid-body diagram, (2) transform it into the compliant mechanism (CM), (3) analyze the mechanical behaviors using FEM, (4) implement multi-objective optimization using NSGA-II with Pareto-optimal front, and (5) seek the global optimum solution by determining Entropy weight with TOPSIS method. Experiments and GA-PID feedback control are carried out to evaluate the performances of the mechanism. The discrepancies of the theoretical, and simulated results benchmarked against the experimental results for the displacement amplification, and natural frequency are 3.67%, and 1.73% respectively. With an integration of a dual parallelogram mechanism to the linear guide, both simulated and experimental results show that the parasitic motion is negligible. The closed-loop control error of the output displacement is smaller than 0.02 µm. These results reconfirm the effectiveness of the proposed optimization method for other kinds of CMs.

Применение параллелограммного механизма с эффектом квазинулевой жесткости в виброзащитных системах кресла оператора строительно-дорожной машины

For vibration protection of operators of construction and road machines, a promising direction is the use of passive vibration protection systems based on mechanisms with quasi-zero rigidity. Passive vibration isolation systems, being less complex than active ones, require less frequent maintenance, are cheaper to manufacture and more reliable than active ones. The problem of selecting the optimal, most reliable and simple design of the mechanism with the effect of quasi-zero rigidity remains urgent. In this case, the most widespread use of elements that create negative stiffness. This requires elements with positive stiffness in the mechanism, which complicates the design. More promising structures of mechanisms, where elements with negative stiffness are not separated into a separate structure. In mechanisms such as the parallelogram, studied in this work, a section with quasi-zero stiffness can be provided with just one tension spring, which simplifies the design and reduces the cost of the entire vibration protection system. By the method of direct analytical inference for the presented diagram of a parallelogram mechanism with one spring, analytical expressions are obtained for the tensile force of the spring necessary to compensate for the force of gravity of the chair with the operator on the height of the chair and the length of the spring. As an example, the graphical dependences of the spring tensile force on the chair lift and on the spring’s own length are given as an example. It was found that the static force characteristic of the spring is a straight line passing through the origin. That is, the zero force corresponds to the zero spring length, which is not technically feasible. It is proposed to use a mechanism that replaces the tension spring, which will provide a given power characteristic.

SCIENTIFIC-TECHNIQUE TO ENSURE THE STABLE MOVEMENT OF WORKING BODIES CONNECTED BY THE RAMA AND PARALLELOGRAMM MECHANISMS OF SOIL TREATMENT MACHINES

The article presents the scientific and technical solutions developed to ensure the stable movement of tillage machines on the working depth of the working bodies of the tiller (hinged) connected by a parallelogram mechanism with a frame. This is based on the fact that the working bodies connected to the frame by means of parallelogram mechanisms sink to a certain working depth and stable movement at this depth is achieved by ensuring that their longitudinal traction operates horizontally or close to it.

Efficient spatial compliance analysis of general initially curved beams for mechanism synthesis and optimization

Compliant Mechanisms (CMs) present several desired properties for mechanical designs. Conventional rigid-body mechanisms composed of rigid links connected at kinematic joints, serve as devices to transfer motion, force and energy by the movements of rigid links whereas CMs are able to present the same function only through deflection of flexible members. Most designs of CMs in the current literature employ straight beams as the elementary flexible members whereas initially curved beams (ICBs) also provide potential advantages for CMs such as large range of motion and small strain range. This paper presents an efficient spatial compliance analysis method of general ICBs. The spatial compliance analysis of different types of ICBs (such as varying-curvature beams and varying-cross-section beams) was conducted, followed by Finite Element Analysis (FEA) verification. Next, the modeling and optimization of two types of CMs including ICB-based parallelogram mechanisms and ICB-based Ortho-planar springs were carried out by applying screw theory under the framework of position space concept and parameter normalization strategy where a class of anti-buckling translational parallelograms with high load-bearing capacity and a type of compact 2R1T (2 rotational DOF and 1 translational DOF) compliant kinematic joints were obtained. The corresponding FEA was conducted to verify the optimal results.

Design and Motion Analysis of Octopod Bionic Robots Based on a Multi-Link Walking Mechanism

In this paper, a bionic robot walking mechanism based on a multi-link mechanism was proposed, which consisted of two crank-rocker mechanisms, one parallelogram mechanism and two tripods, all of which were connected by hinges. An octopod bionic robot was designed by using the multi-link walking mechanism. The kinematics analysis of the robot walking mechanism was carried out by using MATLAB software, and the linear walking gait of the virtual prototype of the robot was simulated by using ADAMS software. The simulation results showed that the octopod bionic robot had good motion stability, strong terrain adaptability, and good practical application and popularization value.

Leg-wheel composite wheelchair based on parallelogram mechanism

with the aging society in China, the demand for wheelchairs is increasing for the elderly with mobility disabilities. At the same time, the number of people with physical disabilities caused by accidents and natural disasters is also rising. This paper designs a kind of electric wheelchair which can adapt to many kinds of terrain, which integrates climbing stairs, crossing obstacle function and safety and comfort to meet the living needs of specific people.

Modeling and analysing of spring-loaded double parallelogram mechanism using moment balance

Double Parallelogram Lifting Mechanism (DPLM) is a multi-linkage mechanism adopted as the lifting mechanism of the designed robot in this paper. DPLM is designed based on Double Parallelogram Mechanism (DPM), making it a compact and stable multi-linkage mechanism with a low retracted height and a great working height. This paper investigates the condition in which DPLM obtains static equilibrium at any height using Hookean springs and the minimization of the motor’s required torque exertion against the gravitational moment of the weight of the mechanism. A mathematical model describing all the factors involved in moment balancing of DPLM is derived and established in MATLAB and is verified through experiments with a virtual prototype conducted in SOLIDWORKS. The obtained results show that the magnitude of the moment exerted by the tension of a spring can be determined not only by its exact installation positions but also by its D value, which is the difference in the distances between the two installation points of a spring and their respective rotation axes. An optimization method based on minimizing the RMSE of the unbalanced moment for DPLM is introduced.

A cable-driven distal end-effector mechanism for single-port robotic surgery

The development of surgery is to be minimally invasive and collaborative with robot systems, which has caught increasing attention in recent years. However, the narrow access routes and confined working spaces in vivo usually make distal end-effectors of surgical systems not easy to operate. To overcome this problem, a novel cable-driven distal end-effector mechanism designed for single-port robotic surgery was proposed. A cable-driven joint structure and the corresponding methods of threading cables were proposed which can maintain the length and even the tension force of cables constant during operation. Based on the proposed joint structure, the cable-driven distal end-effector mechanism consists of a parallelogram mechanism and a snake mechanism. The parallelogram mechanism is used to enlarge its reachable workspace through establishing the triangulation of operation. The snake mechanism is used to achieve the expected pose through providing sufficient bending degrees of freedom. All of the degrees of freedom can be decoupled at the expense of a slightly more tedious process of threading cables. The primary prototype and its miniature assembled and threaded manually performed as expected regardless of bend, translation and their combination. But the inadequate tension force of cables and assembly errors affect the load capacity and accuracy, which need to be improved by automatic assembly. A cable-driven distal end-effector mechanism composed of a parallelogram mechanism, and a snake mechanism used for single-port robotic surgery was proposed. The mechanism adopts a novel cable-driven joint structure and corresponding methods of threading cables to keep the length and even the tension force of cables constant during surgery.

Calibration Method Based on Models and Least-Squares Support Vector Regression Enhancing Robot Position Accuracy

The positioning accuracy of a robot directly affects the quality of its operations. In this study, a calibration method is proposed based on combining a model with least-squares support vector regression (LSSVR) to improve robot positioning accuracy. First, a geometric error model of the robot is established. Second, singular value decomposition (SVD) and physical model analysis method are employed to process the coupling parameters in the error model to improve the accuracy and efficiency of identification. Third, as nongeometric errors hinder the construction of an accurate and complete mathematical model and affect the residual positioning errors of the robot, LSSVR is used to compensate for the residual positioning errors caused by nongeometric errors. The proposed method thus improves the accuracy and robustness of finite sample estimation. Finally, an experiment is performed on an IRB1410 robot with a parallelogram mechanism. The maximum/mean positioning errors of the robot decrease from 2.0348/1.0978 mm to 0.1659/0.0733 mm, and the effectiveness of the proposed method is verified. The proposed method has higher prediction accuracy and stability for small samples than other methods.