查看更多>>摘要：It is difficult to apply the inverse kinematics (IK) of the nominal model of robots directly after the error compensation of geometric parameters. This paper proposed an instruction pose-based compensation method to overcome this problem. Its principle is very simple: the pose error between the calibrated model and the nominal model is compensated to the instruction pose, and then the new instruction pose is solved by the IK algorithm of the nominal model, and the above steps are repeated until the termination condition. According to the principle, we obtained the final iterative expression of the pose error and determined its convergence conditions and convergence. Experiments on the calibrated spherical-wrist and non-spherical-wrist robots show that the theoretical analysis is correct. It is concluded that the calibrated robot could be simplified into a structure with an analytic solution. Then, the IK of the original robot can be obtained by nesting the analytic solution into the proposed method. The proposed method can converge the pose error norm to the order of 10?10 in only a finite number of iterations and takes less time than the Newton-Raphson algorithm.
查看更多>>摘要：The Miura-ori pattern exhibits favorable qualities desirable for deployable space arrays — especially achieving a large deployed area from a compact stowed volume. However, implementing the Miura-ori into a finite-thickness, engineered system poses challenges that are not manifest in a zero-thickness model. As such, it is important to understand and address the limitations of the pattern before implementing it into an engineered system. This paper presents the Miura-ori as a favorable, yet challenging, pattern in design of deployable space arrays. Challenges including thickness-accommodation, nesting, grounding and deployment are presented to introduce designers to unapparent complications associated with design of Miura-ori systems. A preliminary set of approaches to address and mitigate design difficulties is then provided.
查看更多>>摘要：The dynamic interaction between the rolling element and cage has a significant effect on the bearing performances. However, there have been few investigations of this interaction. Hence, this study analyzes this interaction based on dynamic simulations. A dynamic model is proposed considering both the cage flexibility and variable pocket clearance. A comparative analysis is implemented of the proposed model and two widely used models, namely the rigid-cage model and flexible-cage model under a clearance-free assumption. This reveals the necessity of considering the cage flexibility and pocket clearance when estimating ball-cage impacts. Then, the transient response of ball-cage contact impacts is investigated under different cage flexibility and initial pocket clearance values. The coupled influences of these two parameters and operating conditions are evaluated and discussed. The results indicate that it is imperative to consider the cage flexibility and pocket clearance simultaneously to obtain an accurate estimate of the ball-cage interaction. The circumferential stiffness of the cage, initial pocket clearance, and speed of the bearing play a dominant role in the ball-cage dynamic interaction.
查看更多>>摘要：Due to the apparent heat generation and the observed multiple thermal effects in the long-term operation of belt drive system, the thermo-mechanical coupled analysis for the flexible multi-body system is necessitated. A previously proposed absolute nodal coordinate formulation solid-beam element is adopted to create its thermal integrated counterpart since its deformation modes are appropriate for capturing the deformation of V-belt geometry. By means of the unified description of the temperature field and displacement field, the analysis for heat transfer and the continuum mechanics could be integrated in the V-belt drive system. The heat generation caused by frictional creep and the hysteresis loss due to the material viscosity, as well as the thermal deformation, are all included in the model. By describing the flange of pulley groove using a parameterized revolving segment centered by the pulley axis, the contact between V-belt and the flange of pulley groove could be implemented efficiently without complex 3D geometric description of the pulley. The contact force is calculated using penalty method, and the frictional force is determined by the Coulomb friction law in integral form. Numerical results demonstrate the feasibility of the proposed analysis method.
查看更多>>摘要：In gear skiving, the infeed planning process for the multiple radial infeed strategy affects cutting efficiency, local cutting features, and cutter life. The maximum uncut chip thickness nonlinearly changes with infeed combinations, making the infeed planning process challenging. Here, we propose a parametric model to achieve fast infeed planning based on the uncut chip thickness in parametric space. First, the relation between the infeed and chip boundary evolution is elucidated; then, the concept of initial uncut chip geometry (iUCG) is established to perform fast infeed planning according to the chip boundary and uncut chip thickness distribution. An industrial case study is presented to validate the method and demonstrate the implementation. As a result, a decision-making principle that includes infeed planning starting from the finishing to the rough stages enables fast planning owning to the invariance of iUCG and lower simulation capacity requirement on the chip boundary. In such case, the infeed of the “previous” skiving pass can be efficiently determined according to the maximum uncut chip thickness criterion with a constraint condition. The proposed parametric model advances the infeed planning process, further contributing to the multivariable optimization of gear skiving.
查看更多>>摘要：This paper proposes a novel hexagon rolling mechanism, which is composed of inner multiple crank links and outer six-bar chain, driven by a center-arranged actuator (CAA). The rolling locomotion of the hexagon rolling mechanism with single degree of freedom (DOF) is realized by the coupling motion of inner and outer mechanisms, and the locomotion direction is determined by the full rotational direction of CAA. The coupling motion is realized through the combinations in multiple crank links of inner mechanism and the connections between the outer and inner mechanisms, and the design process is carried out. The trajectories of vertices and center of mass (CM) are analyzed to realize the continuity of the coupling motion. By setting the CM as coordinate origin and the overconstrained sliders as equivalent frame, the coupling motion is matched and parameters of links are preliminary designed without singular positions. Meanwhile, by setting supporting links as equivalent frame alternately, the fluctuation of the CM is improved based on the parameters modification. Finally, the functionality of the rolling mechanism is verified by a manufactured prototype.
查看更多>>摘要：A new approach that allows to solve the problems of forward and inverse kinematics for robotic manipulators is proposed by the authors. The approach is to represent the kinematic model of a robotic arm with six rotational joints in the form of a vector model. The first 4 vectors make their movements and turn in the same plane, because of the geometric features of the robot. Thus, on the basis of a vector equation, a system of nonlinear algebraic equations was formed, which were solved by the numerical Newton method, at each iteration of which a system of linear algebraic equations was solved by the Seidel method. The algorithm was tested on a trajectory set in the form of an Archimedean spiral approximated by straight line segments. Trajectory was checked by a real robot KUKA KR6 R900 and it was shown that deviation between calculated and real position of flange point was less than 0.005 mm. It is shown that in comparison with the common Denavit–Hartenberg method the method proposed by the authors has an order of magnitude fewer mathematical operations (790 versus 52).
查看更多>>摘要：Intersecting-axis conical twin-screw rotors have shown great potential to further improve the performance of twin-screw machinery. To investigate their unique generation method, this paper established a mathematical model for the conical rotor surface generation by decomposing it into the rotor profile on the sphere and conical helix. The meshing model between the two intersecting-axis rotors was presented based on the separate solution of the conjugate rotor profiles on the sphere. Then, several common rotor curves in screw machinery were extended to the sphere by analogy and their mathematical generation equations were given. The results showed that the proposed method could effectively generate several conical twin-screw rotors with intersecting-axis for typical applications. Finally, the conical rotor was geometrically compared with the traditional cylindrical rotor to reveal its advantages as screw machinery. The results showed that the conical rotor has the potential to improve the suction and discharge process while reducing the leakage and the force of the discharge section. At the same time, some disadvantages such as difficulty in machining and reduction of bearing installation space were discussed with some possible solutions.
查看更多>>摘要：A new method for calculating the parameters of the hypoid pitch cone, which simplifies the calculation process, is proposed. The method can easily obtain the evolution laws of hypoid pitch cones. The evolution limits of the hypoid pitch cone can be obtained by calculation. The pinion pitch cone evolves from cylinder to cone, and the gear pitch cone evolves from plane to cylinder. In the evolution process, all pitch cones can meet the preset values of key parameters. The variation law of the values representing lubrication and contact characteristics on the whole tooth surface during the evolution of pitch cone is studied.
查看更多>>摘要：Tessellation is an efficient and convenient way to construct large mobile mechanisms with less DOF and has been widely adopted in large deployable structures, in which origami/kirigami is usually adopted as units due to its better symmetric properties. However, the existing origami/kirigami units are quite limited because the discovery mainly depends on the inspiration of designers. In this paper, we propose a new way to find units by setting link lengths to be zero with overconstrained linkages. A kirigami pattern is obtained from twofold-symmetric Bricard 6R linkage and two kinds of novel tessellations are subsequently constructed. Kinematic analysis shows that the obtained tessellations can be folded as tubular and eggbox-like structures. Meanwhile, the folding performance of these tessellations on geometric parameters is analysed for potential applications, and the results are validated by fabricating some prototypes. Therefore, the proposed kirigami pattern and the corresponding tessellations extend the family of large deployable structures.
NSTL
Elsevier