Showing papers in "Mechanical Sciences in 2021"

Review article: State-of-the-art trajectory tracking of autonomous vehicles

Abstract: . Air pollution, energy consumption, and human safety issues have aroused people's concern around the world. This phenomenon could be significantly alleviated with the development of automatic driving techniques, artificial intelligence, and computer science. Autonomous vehicles can be generally modularized as environment perception, path planning, and trajectory tracking. Trajectory tracking is a fundamental part of autonomous vehicles which controls the autonomous vehicles effectively and stably to track the reference trajectory that is predetermined by the path planning module. In this paper, a review of the state-of-the-art trajectory tracking of autonomous vehicles is presented. Both the trajectory tracking methods and the most commonly used trajectory tracking controllers of autonomous vehicles, besides state-of-art research studies of these controllers, are described.

A new magnetorheological elastomer torsional vibration absorber: structural design and performance test

Abstract: . The semi-active torsional vibration absorber can effectively reduce the torsional vibration of the power-train system. In this paper, a new type of variable stiffness torsional vibration absorber with a magnetorheological elastomer (MRE) as an intelligent controlling element is designed, and the modal analysis, frequency-tracking scheme, and damping effects have been studied. A transient dynamic simulation is utilized to validate the rationality of the mechanical structure, the magnetic field parameters of the absorber are matched, and the magnetic circuit simulation analysis and the magnetic field supply analysis are carried out to verify the closed magnetic circuit. The principle prototype of the innovative vibration absorber is manufactured, the magnetic field strength of the absorber is tested by a Gauss meter, and the results show the efficacy of magnetizing the vibration absorber with a conductive slip ring by solving the magnetizing problem of the rotating parts of the vibration absorber. A special-purpose test rig with a torsional vibration exciter as a power source has been implemented. A comparative experiment has been carried out to test the frequency shift characteristics and authenticate the vibration-reduction effect of the new MRE torsional vibration absorber.

Design and analysis of a novel deployable hexagonal prism module for parabolic cylinder antenna

Abstract: . This paper presents a novel deployable hexagonal prism module for parabolic cylinder antennas that exhibit characteristics of geometric scalability. The hexagonal prism module consists of six basic rib mechanisms distributed along the axis and parabolic directions of the parabolic cylinder. The basic rib mechanism along the axis direction is designed, and the position of each member in the deployed state is calculated according to the geometric relationships at the folded state. The basic rib mechanism along the parabolic direction is designed to ensure that the mechanism can be fully folded. The degree of freedom of basic loop mechanisms consisting of four basic rib mechanisms due to the splice of multiple modules is analyzed. The degree of freedom of the proposed hexagonal prism module is verified through simulations and experiments of a deployable mechanism composed of three hexagonal prism modules. The simulation and experiment results show that the proposed hexagonal prism module can offer synchronized and coordinated movement during the deployment process.

A modal-based balancing method for a high-speed rotor without trial weights

Abstract: . The unbalance-induced vibration of a high-speed rotor directly affects the manufacturing accuracy. To effectively suppress this undesired vibration and avoid the complicated process of using trial weights during the balancing adjustment, a modal-based balancing method for a high-speed rotor without trial weights is proposed. First, the matrix sweep operation is employed to acquire the unbalance equivalent plane (EP). Next, the equivalent concentration methods, using the vector feedback principle (VFP) and modal equivalent principle (MEP), respectively, are studied and compared, while the equivalent transfer of the continuous unbalance vector to the EP is realized. Then, through modal analysis and the MEP, a balancing method, without trial weights required, is proposed for the high-speed rotor, which only needs to collect vibration data below critical speed. Finally, the rotor model and the presented method are validated on a rotor test platform, where the simulation and experiment results show that the unbalance-induced vibration has been effectively suppressed, ensuring smooth and safe operation of the rotor at high speed.

Investigation on the size effect in micro end milling considering the cutting edge radius and the workpiece material

Abstract: . Previous research has found that the peripheral and end cutting edges of the cutter had different cutting mechanisms in the micro end cutting process considering the size effect. This investigation is a further study on this point considering the cutting edge radius of the cutter and the material of the workpiece based on the methods of finite element simulation and the micro end cutting experiment. This study adopts a combination of simulation and experiment research methods and the cutting edge radius and the workpiece material as two variables. Considering the cutting mechanisms of the peripheral cutting edge and the end cutting edge are different, the peripheral cutting edge and the end cutting edge are studied respectively. Meanwhile, the minimum undeformed chip thickness (MUCT) value is determined in three ways, chip morphology, cutting force, and surface roughness, so the final result obtained by comparing three kinds of results has a very important reference value. Not only are the chip morphology obtained by finite element simulation and the surface roughness obtained by the micro end cutting experiment used to identify the MUCT value, but also the cutting force. The simulation and experimental results show that the cutting force can be used to identify the MUCT value for the peripheral cutting edge, but it cannot be used for the end cutting edge. The MUCT value increases with the increase of the cutting edge radius, no matter which process it is. The material property has some effects on the MUCT value; even the cutting parameters and the cutting edge radius remain unchanged for the peripheral cutting edge. However, the material property has no effect on the MUCT value for the end cutting edge. In this study, the influence of important variables on MUCT is studied as much as possible to reflect a real application situation.

Design and analysis of a light electric vehicle

Abstract: . This paper discusses a systematic vehicle design process in which light weight is taken as the vehicle design objective, and the designed frame is analyzed in detail. The load condition of a vehicle under different circumstances is calculated according to the distances from the front and rear wheels to the centroid position. The stress on the components in the condition is analyzed by finite element analysis, the steering geometry of the vehicle is analyzed, and the vehicle's turning angle and radius are designed. The displacement of the vehicle under a load is calculated by rigidity analysis to determine the stability of the vehicle in motion. The experimental modal analysis of the real frame and the finite element method are verified mutually for the electric vehicle body-in-white (BIW) manufacturing process to determine the consistency of model formation and the real frame. In terms of the circuit design, we used no-fuse switches and fuses to provide overcurrent protection for the main power supply, and the chip is combined with an optically coupled circuit and current sensor, which is driven by a restriction controller for protection. Moreover, a solid-state relay (SSR) is used for current protection and for controlling the forward/reverse rotation of the motor.

Lagrange-method-based dynamic analysis of multi-stage planetary roller screw mechanism

Abstract: . A rigid-body dynamic model of multi-stage planetary roller screw mechanism (multi-stage PRSM) is proposed in this paper. The structure of multi-stage PRSM is introduced and the motion analysis is presented. The total kinetic energy of the mechanism is calculated. The rotation of the screws and carriers is chosen as generalized degrees of freedom. The generalized forces and motion equations of multi-stage PRSM are derived using the Lagrange method. The transient and steady-state behaviours of multi-stage PRSM are simulated, followed by an analysis of the influence of friction coefficients and thread pitches on the motion and forces acting on the multi-stage PRSM. Taking a two-stage PRSM as an example, the simulation results show that the friction coefficient between screw #1 and screw #2 has a slight effect on efficiency and rotational velocity ratios of carriers to screws. When the sum of the pitches of screws is a constant, the axial component of contact force between screw #1 and roller #1 decreases with the increase in the pitch of screw #1.

Dynamic modeling and vibration analysis of a cracked 3K-II planetary gear set for fault detection

Abstract: . The 3K planetary gear system is a basic planetary transmission structure with many advantages over the 2K-H planetary gear system. However, the vibration characteristics will be more complicated due to the increase of central gears meshing with each planet gear simultaneously. In this paper, a lumped-parameter model for a 3K-II planetary gear set was developed to simulate the dynamic response. The time-varying stiffness of each meshing pair for different gear tooth root crack faults is calculated via the finite element method. By considering the effect of time-varying transmission paths, the transverse synthetic vibrations are obtained. Subsequently, the feasibilities of transverse synthetic vibration signals and output torsional vibration signals as reference for fault diagnosis are analyzed by studying the time-domain and frequency-domain characteristics of these two vibration signals. The results indicate that both the transverse synthetic vibration signals and output torsional vibration signals can be used for fault identification and localization of the 3K-II planetary gear train, and yet they both have their limitations. Some results of this paper are available as references for the fault diagnosis of 3K planetary gear trains.

An innovative equivalent kinematic model of the human upper limb to improve the trajectory planning of exoskeleton rehabilitation robots

Abstract: . Upper limb exoskeleton rehabilitation robots have been attracting significant attention by researchers due to their adaptive training, highly repetitive motion, and ability to enhance the self-care capabilities of patients with disabilities. It is a key problem that the existing upper limb exoskeletons cannot stay in line with the corresponding human arm during exercise. The aim is to evaluate whether the existing upper limb exoskeleton movement is in line with the human movement and to provide a design basis for the future exoskeleton. This paper proposes a new equivalent kinematic model for human upper limb, including the shoulder joint, elbow joint, and wrist joint, according to the human anatomical structure and sports biomechanical characteristics. And this paper analyzes the motion space according to the normal range of motion of joints for building the workspace of the proposed model. Then, the trajectory planning for an upper limb exoskeleton is evaluated and improved based on the proposed model. The evaluation results show that there were obvious differences between the exoskeleton prototype and human arm. The deviation between the human body and the exoskeleton of the improved trajectory is decreased to 41.64 %. In conclusion, the new equivalent kinematics model for the human upper limb proposed in this paper can effectively evaluate the existing upper limb exoskeleton and provide suggestions for structural improvements in line with human motion.

Scheme optimization for a turbine blade under multiple working conditions based on the entropy weight vague set

Abstract: . The deformation of blades under complex loads of multiple working conditions will reduce the energy conversion efficiency. To reduce the deviation of the blade shape in practical working conditions, a combination and optimization method of blade design schemes under multiple working conditions, based on the entropy weight vague sets, is proposed. The sensitivity of each working condition index is analyzed based on the information entropy, and the satisfaction degree of the design scheme based on the design requirements and experiences is described with the vague set. The matching degree of different design schemes for multiple working conditions is quantified according to the scoring function. The combination and optimization of the design scheme are verified by numerical simulation analysis. The results show that the proposed design scheme has a smaller blade shape deviation than the traditional design scheme under multiple working conditions.

Prediction of springback in local bending of hull plates using an optimized backpropagation neural network

Abstract: . Springback is an inevitable problem in the local bending process of hull plates, which leads to low processing efficiency and affects the assembly accuracy. Therefore, the prediction of the springback effect, as a result of the local bending of hull plates, bears great significance. This paper proposes a springback prediction model based on a backpropagation neural network (BPNN), considering geometric and process parameters. Genetic algorithm (GA) and improved particle swarm optimization (PSO) algorithms are used to improve the global search capability of BPNN, which tends to fall into local optimal solutions, in order to find the global optimal solution. The result shows that the proposed springback prediction model, based on the BPNN optimized by genetic algorithm, is faster and offers smaller prediction error on the springback due to local bending.

Parameter tuning of robust adaptive fuzzy controller for 3D elliptical vibration-assisted cutting

Abstract: . Elliptical vibration cutting (EVC), as a precision machining technology, is used in many applications. In precision machining, control accuracy plays an essential role in improving the machinability of difficult-to-machine materials. To improve the control accuracy, dynamic and static characteristics of the system need to be tuned to obtain the optimal parameters. In this paper, we use a glowworm algorithm with an improved adaptive step size to tune the parameters of a robust adaptive fuzzy controller. We then obtain the optimal controller parameters through simulation. The optimal solution of the controller parameters is then applied to a 3D EVC system model for simulation and closed-loop testing experiments. The results indicate that a good agreement between the ideal curve and the tracking signal curve verifies the optimality of the controller parameters. Finally, under certain cutting conditions, the workpieces of three different materials are cut with two different cutting methods. The study revealed that the surface roughness value is reduced by 20 %–32 %, which further verifies the effectiveness of the optimal controller's parameters.

Dynamic characterization of controlled multi-channel semi-active magnetorheological fluid mount

Abstract: . In this paper, a novel structure of a controlled multi-channel semi-active magnetorheological (MR) fluid mount is proposed, including four controlled channels and one rate-dip channel. Firstly, the magnetic circuit analysis, rate-dip channel optimization design, and MR fluid mount damping analysis are given. Secondly, the mathematical model of the controlled multi-channel semi-active MR fluid mount is constructed. We analyze the effect of controlled multi-channel closing on the dynamic characteristics of the mounts and the effect of the presence or absence of the rate-dip channel on the low-frequency isolation of the mount. Finally, the controlled multi-channel semi-active MR fluid mount was applied to the 1 / 4 vehicle model (a model consisting of an engine, a single engine mount, a single suspension and a vehicle frame), with the transmissibility of the engine relative to the vehicle frame at low frequency and the transmissibility of the engine reciprocating unbalanced force to the vehicle frame magnitude at high frequency as the evaluation index. Numerical simulation shows the following points. (1) The controllable multi-channel semi-active MR fluid mount can achieve adjustable dynamic stiffness and damping with applied 2 A current to different channels. (2) With known external excitation source, applied currents to different controllable channels can achieve the minimum transmissibility and meet the mount wide-frequency vibration isolation requirement, while adding a rate-dip channel can improve the low-frequency vibration isolation performance of the MR fluid mount. (3) Switching and closing different controllable channels in the 1 / 4 vehicle model can achieve the minimum transmissibility of low-frequency engine vibrations relative to the vehicle frame and high-frequency engine vibrations reciprocating an unbalanced force to the vehicle frame. Therefore, the design of the controllable multi-channel semi-active MR fluid mount can meet the wide-frequency isolation.

Design of a 4-DoF (degree of freedom) hybrid-haptic device for laparoscopic surgery

Abstract: . This paper presents a novel kinematics architecture with 4 DoFs (degrees of freedom) intended to be used as a haptic interface for laparoscopic surgery. The proposed architecture is a result of an association of serial and parallel kinematics chains, with each one handling a part of the whole device DoF. The serial chain allows one to handle the translation and self-rotation and the parallel chain handles the two tilt motions, and this in a disjoint way as the natural gesture of the surgeon. The proposed hybrid-haptic device (HH device) benefits from the split DoF to ensure a good kinematic performance, large workspace, as well as gravity compensation. The kinematics study of the HH device is presented and followed by the optimal dimensional synthesis and the gravity compensation model.

The effect of rubber powder additives on mechanical properties of polypropylene glass-fiber-reinforced composite

Abstract: . Reinforced thermoplastic composites offer considerable advantages in structural and industrial applications in terms of high specific strength, excellent corrosion resistance, high impact toughness, high specific stiffness, recyclability, cost effectiveness, and design flexibility. Glass fibers (GFs) are the reinforcement material used in polypropylene (PP) composites to enhance PP properties with reasonable cost. To obtain better mechanical properties and decrease the overall cost, recycled rubber powder was used as a low-cost additive to PP/GF composites. The PP and GF, with different weight fractions, were mixed mechanically; then, the mixture was fed into injection molding machine. The PP/GF composites with the highest mechanical properties were selected for further improvements using rubber powder. The obtained samples were tested using tension, impact, and wear tests. The results show that tensile strength of PP/GF composite was improved by 17.8 % by adding 15 wt % GF, and there was a huge drop in impact strength by 80 % for the same GF weight fraction (15 wt %) compared to that of pure PP because of existence of GF. Wear properties and impact strength were improved by adding rubber powder to the composite, with a low weight fraction of 5 wt %, due to the shock-absorbing properties of rubber powder. Micrographs of the fractured sample surfaces revealed the good adhesion between the GF, PP, and the rubber particles.

Performance analysis of an electro-hydrostatic actuator with high-pressure load sensing based on fuzzy PID

Abstract: . Electro-hydrostatic actuator (EHA) is an important form of power-by-wire (PBW) technology, which is widely used in aircraft because of the characteristics of small size, high power and light weight. However, the current traditional EHA with fixed pump displacement and variable motor speed (FPVM-EHA) has the problems of high energy consumption and heating of the motor under heavy load. An improved EHA with high-pressure load sensing (HPLS-EHA) is proposed in this paper, which can reduce the pump displacement under heavy load, so as to achieve reducing the torque and heating of the motor, solving the problem of high energy consumption of EHA system and improving the efficiency. The co-simulation model of the FPVM-EHA and the HPLS-EHA was established using the software programs AMESim and MATLAB, and then the simulation results are analysed. The simulation results show that the HPLS-EHA can reduce the torque and heat flow rate of the motor by 23.20 % and 41.02 % under the load of 20.2 MPa , and the fluctuation times and amplitude of output position are also reduced under varying loads at 5 s , but it will slightly reduce the position accuracy of the EHA system. In order to solve this problem, the fuzzy PID control strategy is adopted for the HPLS-EHA. The simulation results show that the position accuracy and response speed of the HPLS-EHA based on fuzzy PID are improved, the output position is improved from 8.93 to 9.25 mm , better than 9.19 mm of the FPVM-EHA, and it also maintains the advantages of low motor torque, heating and output position fluctuation.

Research on the influence of air-gap eccentricity on the temperature field of a motorized spindle

Abstract: . The air-gap state between the stator and rotor is an important indicator to measure the performance of a motorized spindle. It affects the temperature field distribution of the motorized spindle and the machining accuracy of the mechanical parts. Since the accurate thermal model is the basis of the research on the temperature field distribution of the motorized spindle, in this paper, firstly, the mechanical loss, electrical loss and magnetic loss of the motor under different air-gap eccentricities are calculated and the heat-generating power of an angular-contact ball bearing is obtained based on Harries contact theory. Secondly, the thermal model of the motorized spindle is established and the steady-state temperature field of the motorized spindle is simulated by using ANSYS, and the influence of air-gap eccentricity on the temperature field of the motorized spindle is discussed. Finally, the circumferential temperature field distribution of the motorized spindle with the air-gap eccentricity is verified by experiment. The results show that the air-gap eccentricity has a significant influence on the non-uniform temperature field of the motorized spindle.

Analysis of the shift quality of a hydrostatic power split continuously variable cotton picker

Abstract: . In order to improve the ride comfort of a continuously variable cotton picker, the shift quality of the cotton picker is analysed. Firstly, the transmission principle of the hydrostatic power split continuously variable transmission (CVT) with a single planetary gear set is introduced; secondly, the shift dynamic model of the power train is constructed, and the key models are verified by experiments; finally, the influence law and mechanism of various factors in the shift qualities of a cotton picker are analysed. The results show that the increase in main circuit pressure will reduce the shift quality of the cotton picker; the influence of clutch-charging flow and acceleration rate on the shift quality of the cotton picker can be ignored; with the action time of the clutch delayed in a certain range, the shift impact first decreases slightly, then increases, and finally decreases; the increase in the cotton box weight can slightly improve the shift quality of the cotton picker but is at the cost of consuming more clutch-sliding energy. If different factors are evaluated together, the value of the main circuit pressure and charging flow should not be too large or too small. At the same time, the action time of a clutch to be disengaged should be delayed, and the action time of a clutch to be engaged should be advanced. The conclusions of this study can provide theoretical support for the controller development of a continuously variable cotton picker.

Additive manufacturing of a continuum topology-optimized palletizing manipulator arm

Abstract: . In this article, the lightweight design of a palletizing manipulator arm structure is carried out. The optimization target is designed in 3D with Solid Works. To determine the optimization area and the secondary reconstruction model after the structure is optimized, the reliability and cost of the design structure are also considered. The meta-software performs mechanical performance simulation experiments under the corresponding working conditions for the lightweight structural design of the target structure via the topology optimization methods. Finally, with additive manufacturing technology, the design and printing of the filled skeletal Voronoi structure and the nested-external-removal Voronoi structure of the palletizing manipulator arm are performed.

A new method for isomorphism identification of planetary gear trains

Abstract: . Planetary gear trains (PGTs) are widely used in machinery such as vehicles, pulley blocks, wrist watches, machine tools, and robots. During the process of structural synthesis of PGTs using graph theory, isomorphism identification of graphs is an important and complicated problem. The reliability of the isomorphism detection method directly determines the accuracy of the synthesis result. In this paper, a novel isomorphism identification method for PGTs is proposed. First, a new weighted adjacent matrix is presented to describe the topological graph of PGTs, which has is unique in describing the structure of PGTs. Then, the weighted distance matrix is proposed and the sum of the matrix is obtained, which can determine whether the planetary gear trains is isomorphic or not. Eventually, the examples demonstrate that this new method can be accurately and effectively performed.

Design and analysis of an innovative flapping wing micro aerial vehicle with a figure eight wingtip trajectory

Abstract: . A multi-mode flapping wing micro air vehicle (FWMAV) that uses a figure eight wingtip motion trajectory with wing flapping, rotation, and swing motion is presented in this paper. The flapping wing vehicle achieves three active degrees of freedom (DOF) wing movements only with one driving micromotor which has a good balance in the mechanism design (that is inspired by natural fliers) and total weight. Owing to these characteristics being integrated into the simple mechanism design, the aerodynamic force is improved. The aerodynamic performance of the thrust force is improved by 64.3 % compared to one that could only flap up and down with one active DOF under the condition of routine flapping frequency.

Normal contact stiffness model considering 3D surface topography and actual contact status

Abstract: . A normal contact stiffness model considering 3D topography and elastic–plastic contact of rough surfaces is presented in this paper. The asperities are generated from the measured surfaces using the watershed segmentation and a modified nine-point rectangle. The topography parameters, including the asperity locations, heights, and radii of the summit, are obtained. Asperity shoulder–shoulder contact is considered. The relationship of the contact parameters, such as the contact force, the deformation, and the mean separation of two surfaces, is modelled in the three different contact regimes, namely elastic, elastic–plastic and fully plastic. The asperity contact state is determined, and if the contact occurs, the stiffness of the single asperity pair is calculated and summed as the total normal stiffness of two contact surfaces. The developed model is validated using experimental tests conducted on two types of specimens and is compared with published theoretical models.

Contact dynamics analysis of nutation drive with double circular-arc spiral bevel gear based on mathematical modeling and numerical simulation

Abstract: . This paper describes a dynamic mathematical model of a new type two-stage nutation drive system with double circular-arc bevel gears. The dynamic displacement–vibration coupling model takes into account the gyro torque and side clearance of the nutating gear. A numerical analysis geometric model of the nutation drive system is developed. The geometric model considers the time-varying and contact deformation of nutation gear meshing. Subsequently, the model is analyzed using the ANSYS/LS-DYNA software, and the dynamic contact characteristics of the nutation gear are calculated. The simulation results revealed that the nutation transmission of the double circular-arc spiral bevel gear is reliable. Moreover, the mathematical verification showed that the simulation is feasible and accurate. The research has important significance for improving the tooth load capacity and transmission stability of nutation drives.

Structural synthesis of plane kinematic chain inversions without detecting isomorphism

Abstract: . A plane kinematic chain inversion refers to a plane kinematic chain with one link fixed (assigned as the ground link). In the creative design of mechanisms, it is important to select proper ground links. The structural synthesis of plane kinematic chain inversions is helpful for improving the efficiency of mechanism design. However, the existing structural synthesis methods involve isomorphism detection, which is cumbersome. This paper proposes a simple and efficient structural synthesis method for plane kinematic chain inversions without detecting isomorphism. The fifth power of the adjacency matrix is applied to recognize similar vertices, and non-isomorphic kinematic chain inversions are directly derived according to non-similar vertices. This method is used to automatically synthesize 6-link 1-degree-of-freedom (DOF), 8-link 1-DOF, 8-link 3-DOF, 9-link 2-DOF, 9-link 4-DOF, 10-link 1-DOF, 10-link 3-DOF and 10-link 5-DOF plane kinematic chain inversions. All the synthesis results are consistent with those reported in literature. Our method is also suitable for other kinds of kinematic chains.

Study on dynamic load-sharing characteristics of face gear dual-power split transmission system with backlash, support and spline clearance

Abstract: . The dynamic load-sharing characteristics of aircraft face gear dual-power split transmission system (FGDPSTS) are taken as the research object. Considering the factors of time-varying meshing stiffness, comprehensive error, backlash, support clearance, spline clearance, torsional stiffness, and support stiffness, the dynamic load-sharing model was constructed based on the lumped-parameter method. The loaded tooth contact analysis (LTCA) simulation method was used to calculate the time-varying meshing stiffness. The dynamic load-sharing coefficient (DLSC) is obtained by using Runge–Kutta method. The influences of errors, backlash, support clearance, spline clearance, torsional stiffness and support stiffness on DLSC were analyzed, and the biggest factors affecting dynamic load-sharing performance were found out. The results show that the influence of the backlash of the two-stage herringbone gear pair on the DLSC is more sensitive. The influence of support clearance on the DLSC is less. The load-sharing coefficient increases with the increase of the installation error and eccentricity error, and the influence of the error of the two-stage gears on the system load-sharing performance is the most sensitive. The torsional stiffness has little effect on the load-sharing coefficient of one stage but has great effect on the two-stage load-sharing coefficient. The influence of support stiffness on the DLSC of two-stage is stronger. It provided a theoretical basis for the dynamic stability optimization design of the system.

Synthesis method of two translational compliant mechanisms with redundant actuation

Abstract: . In the fields of electronic packaging, micromanipulation, scanning, and two translational (2T) mechanisms are required, especially with high stiffness, for a large workspace, with good driving stability, and other occasions. Redundant actuators are required to improve the performance of the 2T compliant parallel mechanism. The novelty of the work is to propose a new method for the type synthesis of a 2T redundant actuated compliant parallel mechanism based on the freedom and constraint topology (FACT) approach and the atlas approach. The synthesis conditions are given, and the synthesis process is formulated. With this method, new 2T redundant actuated compliant parallel mechanisms are synthesized. Some new mechanisms have been synthesized, which enriches the compliant parallel mechanism configurations. Based on the atlas method, the synthesized mechanism is analyzed. The results verify the correctness and effective of the synthesis method. The method is also suitable for a type of synthesis of redundant actuated compliant parallel mechanisms with 3, 4, 5, and 6 degrees of freedom (DOF), respectively.

Research on a UV-assisted chemical modification strategy for monocrystalline silicon

Abstract: . A novel UV-assisted chemical modification (UVA-CM) strategy is proposed for micro-grinding monocrystalline silicon based on UV photocatalysis theory in order to develop a combined machining technology. Comparative experiments are carried out between a single heating chemical modification (H-CM) strategy and a hybrid UVA-CM strategy. The effects of different modification strategies on modification degree and mechanical properties of a modified layer are evaluated by inductively coupled plasma mass spectrometry (ICP), Raman spectral analysis, nanoindentation test, and scratch test. The experimental results show that silicate substance is generated on the modified layer surface via the UVA-CM technique. The modified layer under UVA-CM is thicker than that under the H-CM strategy, which also presents relatively lower nanohardness. With the same scratch condition, the modified layer under UVA-CM contributes to inhibiting lateral crack propagation. It is demonstrated that the liquid–solid chemical modification effect is obviously enhanced through UV advanced oxidation reaction. The UVA-CM strategy will contribute to developing a novel hybrid chemo-mechanical process for micro-grinding monocrystalline silicon.

Industrial robot-based system design of thickness scanning measurement using ultrasonic

Abstract: . Wall thickness is one of the core indicators for measuring the quality of large thin-walled parts such as rocket siding and aircraft skin. However, the traditional handheld thickness measurement method has high labor intensity, low efficiency and poor accuracy consistency. Therefore, an in situ ultrasonic automatic scanning thickness measurement method for large thin-walled parts based on industrial robots is proposed. This “industrial robot + ultrasound” integrated function is a compact system, and a set of innovative methodological or technical solutions is presented, such as (i) TCP and UDP communication protocols being constructed to realize a high-speed and stable communication relationship between the upper computer, robot motion controller and ultrasonic thickness measurement unit; (ii) a coupling gap adjustment method based on eddy-current sensors being adopted to ensure the adaptability of the ultrasonic probe to surface topography of the measured part during scanning measurement; and (iii) a multi-sensor coordinate unified model and coupling gap state discrimination model being established for robot-aided thickness measurement. To verify the feasibility of the proposed method, a series of calibrations and experiments were designed based on the KUKA robot platform and the developed ultrasonic pulse measurement system. Finally, the industrial robot-based ultrasonic thickness scanning measurement has been built and tested for performing the measurement of a rocket tank wall.

Rattle dynamics of noncircular face gear under multifrequency parametric excitation

Abstract: . A noncircular face gear (NFG) conjugated with a pinion is a new type of face gear which can transmit variable velocity ratio and in which two time-varying excitations exist, namely the meshing stiffness excitation and instantaneous center excitation. Considering the tooth backlash, static transmission error and multifrequency parametric excitation, a nonlinear dynamic model of the NFG pair is presented. Based on the harmonic balance method and discrete Fourier transformation, a semi-analytic approach for the nonlinear dynamic model is given to analyze the dynamic behaviors of the NFG. Results demonstrate that, with increase in the eccentric ratio, input velocity and error amplitude, the NFG will undergo a non-rattle, unilateral rattle and bilateral rattle state in succession, and a jump phenomenon will appear in the dynamic responses when the rattle state of the gears is transformed from unilateral rattle to bilateral rattle.

A novel algorithm by combining nonlinear workspace partition with neural networks for solving the inverse kinematics problem of redundant manipulators

Abstract: . Redundant manipulators (RMs) have been gaining more attention thanks to their excellent merits of operating flexibility and precision. Inverse kinematics (IK) study is critical to the design, trajectory planning, and control of RMs, while it is usually more complicated to solve IK problems which may inherently have innumerable solutions. In this work, a novel approach for solving the IK problems for RMs while retaining the redundancy characteristics has been proposed. By employing a constraint function, the method delicately reduces the infinite IK solutions of a RM to a finite set. Furthermore, the workspace of RMs is divided into nonlinear partitions through diverse joint angle intervals, which have further simplified the mapping correlations between the desired point and manipulators' joint angles. For each partition, a pre-trained neural network (NN) model is established to acquire its IK solutions with high efficiency and precision. After combing all nonlinear partitions, multiple reasonable IK solutions are available. The presented method offers a possible selection of the most appropriate solution for trajectory planning and energy consumption and therefore has the potential for facilitating novel robot development.