This paper presents theoretical consideration of a travel route while turning at an intersection. The curvature distribution of a travel route is an important physical quantity that generates a traveling track. The formulation and characteristics of a transition curve at connection points for a non-interpolation curve, a single clothoid curve, and a multiple clothoid curve are investigated. The physical variable derived from a curvature distribution function is demonstrated, and the features of the three types of transition curves are explained. The integration value of a curvature distribution function represents an azimuthal angle. Therefore, the curvature distribution curve is the velocity of the azimuthal angle. Then, the first-order differential value of the curvature distribution curve is the acceleration of the azimuthal angle, and the second-order differential value of the curvature distribution curve is the jerk of the azimuthal angle. The theoretical equation of a traveling path is derived from the curvature distribution curve of the three types of transition curves, and their characteristics are formulated. Theoretical expressions of a speed profile of a real running vehicle at a traffic intersection are also proposed. The validity of the multiple clothoid curve is discussed analytically as compared with the other two cases where it is interpolated by the non-interpolation curve or the single clothoid curve. It was also found that the influence of the multiple clothoid curve on vehicle movement and ride comfort was superior to those of the non-interpolation and single clothoid curve. Some results are presented in the form of parametric plots.
For Autonomous Driving (AD) system or vehicle behavior control, it is important to know the friction coefficient of the road surface accurately. It is because the lateral and the longitudinal force characteristics of the tire depend on the road surface condition largely. However, even today it is difficult to detect the tire-road friction coefficient before the deterioration of vehicle dynamics in real time. This is because the tire-road friction coefficient estimation is usually conducted by comparing the actual vehicle motion with the reference vehicle model motion. So, such conventional estimators do not perform well if there is no significant difference between the actual vehicle behavior and the model. This paper propose a method for real-time estimate tire-road friction coefficient that changes variously during driving. Using this method, the friction coefficient value for a real road can be determined from relatively simple calculations. Moreover, this method has the advantage of allowing the independent estimation of the friction coefficient value for both the front and rear wheels. In addition, this paper explain how to apply and the effect on the actual vehicle. Furthermore, we demonstrate its effectiveness via online estimation of the road surface friction coefficient based on actual vehicle experiments.
A 6-degree-of-freedom (DOF) model of a pilot's upper limb is established in this study. A kinematics analysis is performed by using the screw theory and the product of exponential formula. Kane's equation in screw form, which is a concise form with a definite physical meaning, is used to analyze the dynamic characteristics of a pilot's upper limb. In the Mathematica environment, the man-machine system consisting of a pilot and a joystick is taken as the analysis object to simulate the joystick pushing and pulling processes of a pilot at the 50th percentile of Chinese body dimensions. The analysis yields the angular velocity and angular acceleration curves of the joint, which indicate that the manipulation comfort is rather good. The actual posture data during the pilot manipulation process are measured. Through a comparison with the output data, the correctness of the simulation analysis is verified. The torque curve reflects that the torque of the shoulder joint is greater than that of the elbow joint, and the changing tendency conforms to the actual motion law. Therefore, the correctness of Kane's equation in screw form is verified. At the same time, the results can serve as a theoretical basis for evaluating a pilot's manipulation comfort and as an important reference for cockpit layout design.
Aiming at that the instability of the loading force in the low-stress cropping causes the poor quality of the bar cross-section, a precision cropping system with hydraulic compensation and variable loading arm is proposed. The working principle of the cropping method is introduced. The stability of the loading force acting on the bar during the blanking process is analyzed, a method for evaluating the stability of the loading force is proposed and on this basis the fixed speed of the main shaft is determined to be 1000r/min. The research results show that the stability of the loading force is improved by applying the reasonable hydraulic compensation force. With the help of stress concentration coefficient and stress intensity factor, the required critical loading force before and after the crack initiation at the V-shaped notch tip is obtained and it is determined that the best loading arm after crack initiation is 24.7mm. Based on it, the abrupt change problem of the critical loading force before and after the crack initiation is further solved. The experimental results also show that the high quality cross-section can be obtained by the proposed cropping method.
The aim of this work is to synthesize a cam mechanism with translating roller follower based on optimization approaches and reliability analysis. The study consists of two parts. At first, this study performs preliminary deterministic optimization to find the optimum size of a cam system and to ensure its high operating performance. For this, an objective function is defined and that takes into account the three major design parameters typically influence the design of this type of mechanism: the base radius of the cam, the radius of the roller and the eccentricity. Also, constraints on performance and resistance indicators such as the acceptable pressure angles, size radius of curvature of directories curves, the efficiency of the transmission and the specific contact pressure between the cam and follower are taken into account in this work. The second part is devoted to a reliability-mechanism study whose system failure probability is estimated by two complementary methods: the approximation methods FORM / SORM and Monte Carlo simulation using the Phimeca reliability engineer Software. Moreover, inverse FORM was used to provide an elasticity factors evaluation in order to carry out possibilities of the cam mechanism design and reliability improvement. The study has shown that the reliability is greatly improved.
In this paper, a potential energy based slice grouping method was proposed to calculate the mesh stiffness for straight beveloid gears with parallel axes. The mathematical mesh stiffness model was derived. The finite element tooth contact model was developed and the loaded tooth contact analysis was conducted to calculate the mesh stiffness. The verification for the mesh stiffness was conducted with the error 3 %, which proves the feasibility and accuracy. Then, the effects of parameters such as pressure angle, pitch cone angle, and profile shift coefficient on the mesh stiffness were investigated. Results show that the normal pressure angle and the tooth width have obvious effects both on the single tooth and synthesized mesh stiffness. When pressure angle is less than 20°, mesh stiffness will be increased with the increase of pressure angle. However, it decreases rapidly when the pressure angle exceeds 20°. Both the single tooth and synthesized mesh stiffness increase obviously as the tooth width increases. The increase of the cone angle and addendum coefficient have a little effect on the single tooth mesh stiffness, but have the obvious incremental effects on the synthesized mesh stiffness. The contact ratio increases obviously with the increase of the addendum coefficient. The profile shift coefficient and the clearance coefficient have unsubstantial effects both on the single and synthesized mesh stiffness.
The impact process of hydraulic drifter is a periodic vibration course with position feedback and piston control by shuttle valve. For the phenomena of secondary or multiple vibrations within one period during cyclic impact process of hydraulic drifter, this study establishes a dynamic model of the system during hydraulic impact and analyzes the vibration behavior of piston in the impact process of hydraulic drifter from the perspectives of velocity recovery coefficient R , acceleration ratio KF , and acceleration switching time Kt . Then, the impact point position for the nonlinear periodic motion of the piston is observed through point transformation and Jacobian technique. Subsequently, a spatial scope defined by correlated system parameters R , KF , and Kt is identified, within this scope, the piston only stably vibrates once within one impact period. Finally, the position of the signal port is redesigned on the basis of the existence scope, and the design parameters for the hydraulic drifter are improved. The correctness of the derivation process and the conclusion of this study are experimentally verified. The present findings provide a basis for reasonably matching the relationships among design parameters and can help improve drifter impact efficiency.
In this paper, we present a robust controller design method for a magnetic-head positioning system in a hard disk drive (HDD) based on the H∞ control theory and the Robust Controller Bode (RCBode) plot. The RCBode plot represents robust performance criteria as allowable and forbidden areas on Bode diagrams for a controller. Using the RCBode plot, we can improve an existing H∞ controller with visualized guidelines in order to compensate for disturbances against plant perturbations. We show utilities of the proposed method by applying it to a popular benchmark problem for the HDDs. Simulation results with the HDD benchmark problem showed that the proposed method enables us to improve positioning accuracy of the magnetic-head position by about 15% without losing stability margins from the original H∞ controller.
This paper analyzes stability and tracking performance of displayed-marker-based position tracking on visual displays, such as an LCD (Liquid Crystal Display), which have been utilized in several studies about computer-human interaction systems. The tracking system dealt in this paper consists of an LCD and a target object with photo sensors that is placed on the display surface. A fiducial marker image is displayed beneath the object and the photo sensors detect the relative displacement between the marker and the object. The detected displacement is fed back to the tracking program and the program updates the marker position such that it will track the object. In general, this kind of tracking methods can suffer from display latency that arises from programs, graphic engines, and internal signal processing circuits of LCDs. This paper investigates the latency characteristics to reveal that the lag is not constant; it fluctuates with time. The paper, then, formulates the tracking system and analyzes how the lag affects the tracking stability. Then, the paper analyzes the tracking performance of two different classes of stable tracking algorithms, which are PD control and lag compensation. Based on the analyses, the paper provides a guideline on the selection of tracking algorithms, as well as tracking parameters. The analyzed results, as well as the guideline, are verified by experiments in 1-DOF horizontal motions.
This paper offers a review of the latest robotic remote control schemes that are based on human motion through the virtual collaboration system. The robotic remote control schemes have been studied and developed to combine the intelligence of humans with the precision and mechanical strength of robots. They have performed an important role in some dangerous environments by replacing humans in many difficult jobs, but the lack of intuitive control interfaces causes decreased efficiency. To address this problem, various approaches have been recently investigated, including human motion-based control, visual feedback systems, tactile or force feedback, and other various haptic systems. This paper describes the tendencies of these efforts and discusses possibilities and limitations in three parts: remote control based on human motion, multimodal feedback schemes for realistic interaction, and virtual collaboration systems.
The torque-split gear transmission has been used in the transmission system of the rotorcraft, which undertaking high torque loads and requiring low weight. A universal mathematical design method of the torque-split gear transmission is proposed in this work. The teeth with the same phase of the two gears on the duplex idler are marked. And the meshing condition is defined by the whole pitch number between the two points along the pitch circle of the output gear. Then the relationship between the tooth number and gear positions is established by using this meshing condition. Unlike other existing design method, this method involves the idlers, input gear and output gear that engaged directly, and it is suitable for the design of multiple types of torque-split gear transmission. This method is validated through numerical examples of the torque-split transmission with symmetrical duplex idler. Moreover, practical applications of the torque-split transmission with planetary duplex idler, coplanar gear and concentric face gear are also studied with this method. A large number of discrete gear position solutions are observed under the same tooth number design. And different gear positions correspond to different dynamic and load sharing characteristics of the torque-split gear transmission.
Dry gas seal (DGS) is an important way for the nuclear reaction seal and the dynamic property of floating ring system (FRS) is the key to the reliability of DGS. In this study, the vibration characteristics of FRS were obtained through the test experiment under the designed multi-stage discretization operation conditions. A new dynamic model of FRS was established based on the finite element method. The dynamic analysis of FRS was achieved by the means of the pre-stressed modal analysis (PSMA). Based on the spectrum analysis of the experimental data, the modal identification was performed by peak picking method, which verified the dynamic analysis result. The results show that the dynamic performance of the FRS was not sufficient to achieve the absolute seal reliability required for nuclear reactions. An integrated structure optimization method based on the PSMA, response surface methodology (RSM) and particle swarm optimization (PSO) was used to optimize the dynamic property of FRS. The RSM and the Box-Behnken (BB) experiment design were combined to construct the complete quadratic polynomial response surface (RS) models of the natural frequency and static deformation in terms of between the optimized variables, including the uniform spring stiffness and three main axial structure sizes. Under the condition that the static deformation was less than the expected value and the natural frequency value was set as the objective function, the natural frequency was increased by 15% through the velocity- position model of PSO. It was indicated that the dynamic property of FRS was significantly improved. The dynamic analysis of FRS enriches the dynamic characteristics study of the whole DGS system and the integrated optimization method achieves the parameters optimization of DGS system applied to the nuclear reaction seal.
ZnDTP antiwear additive for lubricating oil is known to absorb strongly on sliding surfaces in boundary lubricated tribosystems, forming a tribofilm, which is able to reduce the wear of involved surfaces. It is also known to increase the friction coefficient in most DLC/DLC contacts, with the exception of ta-C DLC / ta-C DLC contact, for which the difference in friction behaviors between a base oil + ZnDTP additive lubricated tribosystem and a base oil lubricated tribosystem is not very significant. In this study we investigate a characterization method of the shape of the tribofilm formed on different types of DLC coatings and on the relation between the shape of the tribofilm and the friction behavior of the related DLC coating. Results show that compared to other investigated DLC types, the tribofilm formed on ta-C DLC has some unique characteristic topography features that promote lower friction coefficient.
Many assembly modes exist due to multi-solutions for forward kinematics of 6-UPS parallel robot. However, the existing theoretical research results have not been well applied to the real-time control, because of the complexity of the forward kinematics. This paper proposes an analytic algorithm to establish the forward kinematics model of a 6-UPS parallel robot with an extra displacement sensor mounted on the centers of upper and lower platform ((6+1)-UPS). Based on the unit quaternion method, the improved forward kinematics model of the proposed (6+1)-UPS system is theoretically derived to be four equations about four components of unit quaternion. The whole computation process is analytical. The method of measurement of the 7th link length and the utilization of unit quaternion reduces the complexity of computation process of forward kinematics, avoids the computer memory spillover and increases the computation efficiency to be suitable for the real-time control application. Then, the analytical solution of the position vector and orientation matrix of the (6+1)-UPS parallel robot are obtained. Finally, the correctness and effectiveness of the proposed approach are illustrated with a numerical example.
Thermal errors account for more than 40% of the machining errors in CNC machine tools, and even reach 70% in precision and ultra-precision machine tools. One approach to reducing thermal errors is to build thermal error prediction models by monitoring the temperature field of machine tools with the data-driven modeling approaches. Usually the data-driven approaches have over-fitting and under-fitting problems. The prediction performances of the data-driven models are greatly dependent on the input of the models, namely the number of temperature measuring points (TMPs) and their locations. In this paper, a selection method of key TMPs is presented to improve the accuracy and generalization of predictive models. In this selection method, correlation analysis is used to eliminate the uncorrelated or weakly correlated TMPs to thermal errors at first; then the Minimum Redundancy Maximum Relevance (MRMR) is presented to narrow the searching scope of TMPs; finally Wrapper method is used to test the candidate set of TMPs with cross-validation accuracy to find the key TMPs. To validate this method, a test platform is built on the CNC gantry drilling machine ZK5540A. 56 Fiber Bragg Grating (FBG) temperature sensors are amounted on the body, column, spindle, and base of this machine. 7 key TMPs was selected from the 56 ones with this method. And Multiple linear regression (MLR) approach is used to build the thermal error prediction model with the 7 key TMPs, 56 TMPs and key TMPs selected by Miao's method(Miao et al., 2014) respectively. The result shows that the prediction model built with MLR using the 7 key TMPs is much more accurate and has stronger generalization.