查看更多>>摘要：In this paper, we aim to use a continuous formulation to efficiently calculate the well-known wrench-based grasp metric proposed by Ferrari and Canny which is the minimum distance from the wrench space origin to the boundary of the grasp wrench space. Considering the L-infinity metric and the nonlinear friction cone model, the challenge of calculating this metric is to determine the boundary of the grasp wrench space. Instead of relying on convex hull construction, we propose to formulate the boundary of the grasp wrench space as continuous functions. By doing so, the problem of grasp quality calculation can be efficiently solved as typical least-square problems and it can be easily implemented by employing off-the-shelf optimization algorithms. Numerical tests will demonstrate the advantages of the proposed formulation compared to the conventional convex hull-based methods.
查看更多>>摘要：This paper put forward a new geometric modeling method for forward displacement analysis of 3RPR planar parallel mechanisms (PPMs) under the conformal geometric algebra (CGA) framework. A geometric constraint relationship of four lines intersecting at a point is first given. Then, a new coordinate-invariant geometric constraint equation of 3-RPR PPMs is elaborated via CGA operation. Next, an univariate polynomial equation without algebraic elimination is published. At last, the coordinates of three points on the mobile platform are figured out. The best part of this research is that a complete geometric modeling method by geometric constraint relationship of four lines intersecting at a point is formulated under the CGA framework, which has good intuition and offers a novel idea for solving the other complex mechanisms. Three numerical examples are utilized to confirm the effectiveness of the proposed method.
查看更多>>摘要：A novel methodology for the optimal path synthesis of mechanisms, particularly considering a high number of linkages and prescribed timing of the desired path, is presented in this paper. Such mechanisms are attracting increased interest in innovative fields such as surgical and rehabilitation robotics. The approach presented here is focused on optimizing the control effort of an equivalent "shadow robot" and utilizes a two-stage synthesis algorithm that shows promising capabilities. As a case study, the proposed approach is applied in the context of the popular eightbar Jansen mechanism. In the first stage, we explore a typical Jansen mechanism generating only the pure shape of a desired path, without considering its exact scale, orientation or position, and assuming a normalized path and mechanism. In the second stage, the normalized mechanism is resynthesized to match the non-shape relevant characteristics, i.e. scale, orientation, and position. Some numerical examples are also given to show the efficacy of the suggested method.
查看更多>>摘要：In this paper, a framework for relative motion compensation is presented and demonstrated via simulation with kinematic crane-tip control. The method allows for compensation relative to a fixed platform or world-frame (ship-to-shore/platform transfer), a secondary moving body (ship-to-ship transfer), or the host body itself (on-deck operations) without modification. The system utilizes Motion Reference Units (MRUs) which are located on the host ship and the payload/hook. Sensor fusion is performed on the MRU data using real-time complementary filters to estimate the relative motion. The frequency response of the system is investigated, and practical considerations are discussed through a series of case studies, which include time-varying trajectories. Within simulation, the results show that the complementary filter estimates the orientation of the ship and payload under dynamic conditions. The resulting controller provided an improvement of 35 dB attenuation at the natural frequency of the pendulum relative to the uncompensated system. The case study of a pick-and-place operation demonstrates that the proposed system produces an order-of-magnitude reduction in the error metrics for the tracking performance and pendulum suppression. A hardware implementation reduced 83.8% of the motion for the worst-case natural frequency tests and up to 48.3% for the trajectory experiments.
查看更多>>摘要：This contribution examines a variable stiffness mechanism that is intended for the use as a boundary element in vibration tests. The mechanism consists of two antagonistic nonlinear springs guided along the central axis. The axis is axially guided via two bearings. This paper concerns itself with comparing the effects of friction and roller bearings on the frequency response. Further, a comparison of different measurement techniques for the dynamic characterization of the aforementioned mechanism is in focus. An experimental study utilizing a multisine, sine sweep, and impulse excitation signal is conducted. A nonlinear numerical model as well as a linear approximation are presented and compared with the measurement results. The results indicate that friction bearings have a strong influence on the frequency response of the system, especially at low displacement amplitudes. The influence of the friction contact on the results of different measurement methods is shown. The presented variable stiffness mechanism with the roller bearing configuration yielded in a predictable vibration behavior even for high mechanism pretensions.
查看更多>>摘要：For a crossed beveloid gear pair with approximate line contact, the macroscopic geometric parameter is a dominant factor that affects meshing characteristics. However, geometric parameter design and reliability under misalignment are of great difficulty. To deal with these issues, an enhanced design method for a beveloid gear with approximate line contact is firstly proposed. Based on this, a robust optimization model of geometric parameters for crossed beveloid gear pairs with approximate line contact is developed. Three evaluation items are considered, namely the maximum contact pressure, contact trace offset distance and contact ratio. To reduce the calculation time, the influence coefficient method is applied to calculate the contact pressure. Considering the characteristics of installation deviation uncertainty and distribution, the mean maximum contact pressure, contact trace offset distance and ratio are considered as objective functions, formulated as a robust design optimization problem. Finally, robust optimization of a crossed beveloid gear pair based on a fast elitist nondominated sorting genetic algorithm (NSGA-II) is applied to solve the model to obtain the Pareto front of the macroscopic geometric parameters. A numerical example is provided to demonstrate the effectiveness of the proposed method.
Arredondo-Soto, MauricioCuan-Urquizo, EnriqueGomez-Espinosa, Alfonso
24页
查看更多>>摘要：In this paper, we present the mathematical formulation of the Compliance Matrix Method (CMM) for the kinetostatic analysis of Flexure-Based Compliant Mechanisms (FBCM). The formulation is achieved by integrating the different approaches found in literature, as an attempt of unification of the CMM. The CMM is combined with inverse kinematics in an analytical process, to be used in the kinetostatic analysis of Flexure-Based Compliant Parallel Mechanisms (FBCPM) with multiple actuation forces where the output displacements are not coincident, neither are parallel, with the input forces. This analytical process allows the total compliance matrix of the FBCPM to be obtained, which relates the input forces (commonly applied on the legs) with the output displacements (commonly desired in the moving platform). The effectiveness of the analytical process presented here, is validated using two FBCPM with Two Dimensional and Three-Dimensional architectures as examples. Then, the analytical results are validated with Finite Element Analysis by comparing the capability of the FBCPM to follow complex trajectories: circular and angular trajectories for the 2D-FBCPM, and a spherical spiral trajectory for the 3D-FBCPM, showing excellent agreement (less than 5%).
Zhang, XuLiu, YueBranson, David T.Yang, Chenghao...
17页
查看更多>>摘要：Kinematic control for continuum robots usually involves an inverse model to provide actuator positions according to the desired end-tip position, as well as a servo controller at the actuator level. The resulting control performance of a continuum robot is then related to its kinematic characteristics that vary at different configurations. In this paper, a kinematic model for a typical rod-driven continuum robot is presented. Following this, a kinematic parameter, velocity sensitivity, is proposed to evaluate the kinematic characteristics of the continuum robot, indicating the contribution of the individual actuators to the instant movement of the end-tip when tracking a given path. Next, a variable gain control strategy is presented to tune the servo controller with respect to the varying velocity sensitivity along the path, reducing the fluctuation of the tracking errors in real time. The simulated and experimental results show that the presented methods can effectively smooth the movement of the continuum robot over its workspace by considering the coordination between the kinematic and servo controllers.
查看更多>>摘要：Complex linkages refer to the linkages composed of 4-bar or more than 4-bar Assur Groups (AG). This paper presents a hybrid position analysis method for complex AG. Firstly, position solutions of an external link in AG are obtained by solving the position analysis polynomial, then all configurations of the AG corresponding to the solutions can be determined through solving 2-bar AG. Above is the position analysis process at a single input condition. With the increasement of the input angle, a series of discrete position solutions can be obtained. How to connect these solutions to form different branches and circuits, and determine the movement range of the linkage are the other problems to be solved. This paper presents an effective methodology to determine the branches and circuits as well as the movement range of the linkage and gives a novel discriminant for identifying singular configurations of complex AG. Finally, several nu-merical examples are presented to demonstrate the correctness, effectiveness and universality of the proposed methods and the practicability of the program compiled based on the formulations and methodology.
查看更多>>摘要：In this paper, a systematic design approach is presented combining an analytic open-source design method for electrical machines (EM) with a novel transmission design approach tailored for the usage within a holistic powertrain optimisation. This allows a co-optimisation of both the EM and the transmission aiming at a globally optimal powertrain system for battery electric vehicles (BEVs). To systematically synthesise transmissions, basic elements are defined, which can be connected individually. Additionally, a generic transmission loss model is introduced allowing to account for transmission losses based on the design approach. Using this methodology, two one-speed and one two-speed transmission configurations are synthesised and optimised in a case study. Applying a multi-objective genetic algorithm, both EM and transmission parameters are optimised aiming at minimal electrical energy consumption and minimal powertrain cost. The results show that the optimal powertrain configuration is sensitive to both EM and transmission design parameters, demonstrating that a comprehensive co-optimisation is necessary to obtain globally optimal electric powertrain solutions.
NSTL
Elsevier