Different from most existing distributed localization approaches in static networks where the agents in a network are static, this paper addresses the distributed localization problem in dynamic ...networks where the positions of the agents are time-varying. Firstly, complex constraints for the positions of the agents are constructed based on local relative position (distance and local bearing) measurements. Secondly, both algebraic condition and graph condition of network localizability in dynamic networks are given. Thirdly, a distributed localization protocol is proposed such that all the agents can cooperatively find their positions by solving the complex constraints in dynamic networks. Fourthly, the proposed method is extended to address the problem of integrated distributed localization and formation control. It is worth mentioning that the proposed algorithm can also be applied in the case that only distance and sign of direction measurements are available, where the sign of direction measurement is a kind of one bit local relative measurement and has less information than local bearing.
•a new 3-D multi-physics coupling model is proposed for lubricated piston-liner systems.•The sub-models for mixed lubrication, spatial multibody dynamics, and heat transfer are fully coupled on a ...unified absolute coordinate frame.•The coupling model is discretized employing unified spatial and temporal discrete methods.•The occurrence of wear and failure on either side of the piston skirt is predicted by the model.
In this paper, a new 3-D multi-physics coupling model is proposed for lubricated piston-liner systems. The sub-models for mixed lubrication, spatial multibody dynamics, and heat transfer are established and fully coupled on a unified absolute coordinate frame. The coupling model is discretized and solved using the unified spatial and temporal discrete methods. Then, an application example of a four-cylinder engine is employed to comprehensively investigate the coupling characteristics in the piston-liner system. The new coupling model reveals the presence of two distinct locations with the lowest local film thickness on either side of the piston's central axis, consequently yielding elevated local oil film pressures. This observation provides a reasonable explanation for the occurrence of wear and failure in the piston skirt on both sides.
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This paper considers the adaptive sliding‐mode control (ASMC) problem of spacecraft relative position tracking with maneuvering target in the presence of external disturbance and unknown mass ...property. Integrated with the spacecraft absolute orbit dynamics, the line‐of‐sight–based relative position motion model is established; further, the problem is formulated in the general mechanical second‐order form with unknown mass parameter and matching disturbance, which makes it convenient to use some useful physical properties in the control law design. As a stepping‐stone, the traditional ASMC law is proposed without prior knowledge of uncertainty/disturbance bound. Then, incorporated with the smooth‐projection algorithm and equivalent‐control‐dependent gain method, the modified control law is proposed, which can force the mass estimate to remain in a desired domain and efficiently overcome the drawback of the overestimation of the disturbance in the traditional ASMC law. Within the Lyapunov frame, the bounded stability is presented in the real case that the sign function is replaced by the hyperbolic tangent function. Finally, three different simulation cases are presented to show fine performance of the modified ASMC law.
In this paper, a global task coordinate frame (GTCF)-based learning adaptive robust contouring controller is proposed for an industrial X-Y linear-motor-driven stage to achieve not only good ...parametric adaptation ability and disturbance robustness, but also excellent contouring accuracy even under high-speed large-curvature contouring tasks. Specifically, the contouring controller employs GTCF to guarantee the multiaxes motion coordination. After transforming the system dynamics of the X-Y linear-motor-driven stage into the GTCF, a learning adaptive robust control (LARC) scheme is developed to deal with the strongly coupled dynamics under parametric uncertainty and uncertain disturbances. During the LARC, adaptive model compensation term, robust feedback term, and iterative learning term are organically integrated in a serial structure. The controller design process with the stability analysis is presented, while the essence of the practical achievable performance is also introduced for the nature of the GTCF-LARC. Comparative experiments are carried out on an industrial linear-motor-driven stage with different cases. The results consistently verify that the proposed GTCF-LARC contouring controller can simultaneously meet the industrial requirements of excellent transient/steady-state contouring accuracy, parametric adaptation ability, external disturbance robustness, and large-curvature high-speed contouring tasks. The proposed GTCF-LARC scheme actually provides a practical high-performance-oriented contouring control framework, and could be extended to other multiaxes applications.
•The automatic non-contact calibration process of dynamic workpiece coordinate frame in the robot grinding system is realized.•The idea of six-point limit is introduced into the dynamic workpiece ...coordinate frame calibration process by using a point laser displacement sensor.•An economical and practical calibration method of the point laser displacement sensor coordinate frame is proposed.•The multi-dimensional minimal optimization algorithm is applied to the blade calibration process and some improvements are implemented.
Automatic robotic grinding and polishing systems have become a developing trend in aerospace parts manufacturing. In a robotic blade grinding and polishing system (RBGPS), the automatic and precise calibration of the dynamic workpiece coordinate frame is the most important process. In this research, a new method that introduces the concept of six-point positioning into the dynamic workpiece coordinate frame calibration process is proposed using a point laser displacement sensor (PLDS). The static coordinate frame calibration process is conducted based on a robot flange and force sensor. The results indicate that the new method can achieve a higher precision calibration result and has improved operational efficiency and cost. Finally, its practicality is verified in the BRGPS, and the results indicate that the polished blade surface after using the new method has good consistency.
•Numerical calculation algorithm is used in the proposed algorithm to obtain accurate contouring error even in the extreme cases with high speed, large curvature and sharp corner.•Based on the ...estimated contouring error, the Accurate Task Coordinate Frame is constructed, in which the contouring error and the related distance error can be decoupled and expressed easily.•Through the gain adjustment for the above two errors, the optimal trajectory compensation is determined and fed back to the position loop to improve contouring performance.•The effectiveness of the proposed ATCF method has been demonstrated by theoretical analysis and a series of experiments.
To achieve excellent contouring motion control without affecting the structure of original closed-loop controller, a modular design of trajectory compensation based on accurate task coordinate frame (ATCF) is proposed in this paper for precision multi-axis systems. Specifically, the contouring error point, i.e., the point located on the reference contour which is closest to the actual one, is obtained by the numerical computation method. Due to the accurate calculation through the above method, the calculated contouring error point can almost overlap with the actual one even under extreme contouring tasks with high speed, large curvature and sharp corner. Based on the estimated contouring error point, actual point and the desired point, ATCF is constructed. The coordinates of the desired point in ATCF represent the distance error and the contouring error, respectively. Through the trajectory compensators with reasonable gains adjustment, these two errors are fed back to the position loop of the system to modify the reference trajectory and to improve contouring control performance. Comparative experiments under various contouring control tasks are conducted to validate the practical effectiveness of the proposed ATCF scheme. The experimental results illustrate that the proposed scheme can achieve not only nearly perfect contouring error estimation but also obvious improvement of contouring accuracy compared with individual axial control and CCC.
This article studies distributed pose (orientation and position) estimation of leader–follower multi-agent systems over κ-layer graphs in 2-D plane. Only the leaders have access to their orientations ...and positions, while the followers can measure the relative bearings or (angular and linear) velocities in their unknown local coordinate frames. For the orientation estimation, the local relative bearings are used to obtain the relative orientations among the agents, based on which a distributed orientation estimation algorithm is proposed for each follower to estimate its orientation. For the position estimation, the local relative bearings are used to obtain the position constraints among the agents, and a distributed position estimation algorithm is proposed for each follower to estimate its position by solving its position constraints. Both the orientation and position estimation errors converge to zero asymptotically. A simulation example is given to verify the theoretical results.
Kinematics play a vital role in answering both clinical and research questions regarding joint biomechanics. Standardisation of kinematic approaches is important; however, the method that is ...currently recommended for building the joint coordinate system (JCS) to measure kinematics of the wrist is difficult to implement in vivo. In this study, a series of JCSs were examined and compared to the International Society of Biomechanics (ISB) recommendations in terms of landmark digitisation repeatability, coordinate frame creation repeatability, and secondary rotations during planar motion. No differences were found between the ISB JCS and 338 of 408 of the JCSs proposed in the study, meaning that the proposed alternative can be used without affecting the measured joint angles or repeatability of the JCS. Forearm frames that used a vector between the epicondyles to define the YZ plane of the forearm were found to create JCSs that produced secondary rotations greater than that which would be clinically detectable and thus, they should be avoided when defining a JCS. The remaining 338 coordinate systems can be used interchangeably; consequently, should there be any clinical limitations that result in missing landmarks, alternative coordinate systems can be used.
A joint coordinate system created using the radial styloid, ulnar styloid, medial epicondyle, lateral epicondyle, the heads of the second and fifth metacarpal, and the base of the third metacarpal is recommended for quantifying kinematics in vivo.
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