查看更多>>摘要：This work addresses the inverse kinematics of serial robots using conformal geometric algebra. Classical approaches include either the use of homogeneous matrices, which entails high computational cost and execution time, or the development of particular geometric strategies that cannot be generalized to arbitrary serial robots. In this work, we present a compact, elegant and intuitive formulation of robot kinematics based on conformal geometric algebra that provides a suitable framework for the closed-form resolution of the inverse kinematic problem for manipulators with a spherical wrist. For serial robots of this kind, the inverse kinematics problem can be split in two subproblems: the position and orientation problems. The latter is solved by appropriately splitting the rotor that defines the target orientation in three simpler rotors, while the former is solved by developing a geometric strategy for each combination of prismatic and revolute joints that forms the position part of the robot. Finally, the inverse kinematics of 7 DoF redundant manipulators with a spherical wrist is solved by extending the geometric solutions obtained in the non-redundant case.
查看更多>>摘要：This paper investigates the rolling dynamics of spherical wheels using the theoretical framework provided by the brush models. The analysis is mainly conducted under the assumption of vanishing sliding inside the contact patch. Different types of kinematics are considered: simply rolling wheels, rolling and tilting, and purely spinning. For the first two cases, a complete solution is derived concerning both the steady-state and transient behaviours. Some qualitative trends for the forces and moments generated inside the contact patch are then provided when accounting for limited friction. For the case of a purely spinning spherical wheel, it is shown that steady-state conditions are never possible owing to the assumption of vanishing sliding. Moreover, it is demonstrated that the shear stresses acting inside the contact patch grow unbounded if the additional contribution relating to the deflection of the bristle is not taken into account when calculating the total sliding velocity. In this case, a stationary solution may be eventually recovered as an asymptotic distribution only by assuming limited friction inside the contact patch.
查看更多>>摘要：Spherical gear couplings are machine elements that enable power transmission between highly misaligned shafts. The highly crowned tooth surfaces and the presence of undercut sections, have been a matter of disagreement between existing geometry generation methods available in the scientific literature. The main reason for this, are the geometry variations which arise in the generated parts, and consequently, the effect of such variations on the contact point location and clearance distribution. In this paper the influence of the main design parameters of spherical gear couplings (namely, the crowning ratio, the pitch diameter, the pressure angle, etc.), on the geometrical properties of the gear tooth surfaces are investigated. An algorithm to calculate the maximum misalignment angle is proposed, which is one of the most crucial design parameters. It shows that the values obtained with models existing in the literature are not applicable to highly crowned spherical gear couplings. Finally, design criteria are described to help the designer choose proper spherical gear coupling tooth geometry parameters to fit in a certain space and achieve a given maximum misalignment angle without further geometrical issues (undercut or pointed teeth).
查看更多>>摘要：This paper presents the computerized generation and surface deviation correction of face gears generated by skiving. Firstly, the mounting relation among the skiving cutter, the virtual shaper, and the being-generated face gear is defined and the velocity relation analyzed. Secondly, the equations for the rake face angle and back flanks of the skiving cutter are defined, and the profile of the cutting blade obtained. Based on the kinematics of the generation movement of the skiving cutter, the surfaces of the face gear teeth are derived. The influence of the parameters of the cutter profile on the face gear surface topology is studied. Thirdly, the correction of the face gear tooth surface deviation has been achieved to some extent by adjusting the cutting depth, the rotation angle of the face gear, and the cutter offset distance during the process of machining. Finally, the simulation of the proposed machining process has been verified with VERICUT. The results show that the deviation of the face gear tooth surface is consistent with that obtained by the computerized generation as proposed in this paper.
查看更多>>摘要：This paper aims to reveal the relationship between the high-speed gear wear and nonlinear dynamics for a wind turbine gearbox considering the tooth contact temperature. The temperature and deformation of the tooth surface are calculated respectively using the Blok's flash temperature theory and thermal deformation formula, and the meshing stiffness caused by the tooth contact temperature is obtained using the Hertz theory. The wear depth and time-varying meshing stiffness of high-speed gears are calculated using the Archard's equation and potential energy method, respectively. The nonlinear dynamic model of the gearbox is established to study the characteristics, and the frequency domain values of gear wear are compared with experimental data. The results show that the tooth contact temperature makes the time-varying meshing stiffness decrease, then affecting the dynamics of the system, the stability decreases with the increase of comprehensive transmission error, and for the gearbox considering the contact temperature, the gear wear makes the chaotic motion occur in advance and its region increase obviously. The research provides a basis for the wear fault diagnosis and detection of gear transmission systems.
查看更多>>摘要：Continuum manipulators with pneumatic actuators are designed for large-scale movements with high dexterity. However, during applications, such manipulators suffer control inaccuracies due to material nonlinearities. Thus, this paper proposes a generalized forward kinematic and forward dynamic model based on Cosserat-rod theory for a pneumatically actuated multi-segment conic manipulator. The model includes the effect of material nonlinearities and reduces the steady-state absolute error. Moreover, the model also considers the self-weight and external loadings to determine the manipulator backbone shape. Explicit fractional-order Bouc-Wen model is used in the constitutive laws to model the effect of material hysteresis in the developed partial differential equations for the manipulator. The developed mathematical model is solved numerically for possible backbone shapes. The results of the model are validated experimentally on the trunk of the Robotino-XT, which is a two-segment pneumatically actuated conic manipulator. The validation results show that the absolute pose error between the experimental and the proposed model for the manipulator tip at steady-state is very small, which is a far superior result to the other existing models for the same system.
查看更多>>摘要：Compliant grippers have been widely used in engineering systems to achieve precision operations. In this paper, a compliant adjustable constant-force gripper based on circular beams is developed for realizing the compatible and stable constant-force operation. In the developed gripper, a stiffness-combination constant-force mechanism (SCCFM) is applied as its basis. A pseudo-rigid-body PPRR model and particle swarm optimization algorithm are utilized for circular-beam modeling and identification of the SCCFM, respectively. A devised preload mechanism realizes the adjustment of the initial preloading state of the SCCFM. A series of experiments are conducted to demonstrate the effectiveness of the developed SCCFM and the gripper.
查看更多>>摘要：Flexural tensegrity is a structural concept according to which the flexural integrity of a chain of segments in unilateral contact is granted by one prestressing tendon (cable), whose elongation is varied by the relative segmental rotations as a function of the shape of the contact profiles. The elastic strain energy of the tendon, which can be tuned by springs added in series, dictates the constitutive response in bending of the flexural-tensegrity assembly. Here, we show that increasing the internal mobility of the tendon inside hollow segments allows for multi-stable equilibrium configurations. In particular, appropriately designed segmental cavities can induce a complex multi-articulated snap-through motion of long chains of segments, consequent to the harnessing of the elastic energy associated with the relative rotation of only one pair of segments. The motion can be reversed by changing the sign of the relative rotation. The dynamical problem is theoretically solved and results are compared with experiments on 3D printed prototypes for a cantilever configuration, which behaves like a tail that flagellates in response to the cyclic rotation of the pair of end segments. This concept design can find applications in collapsible-deployable micro-and macro-structures, robotics, metamaterials with memory.
查看更多>>摘要：In this paper, a geometric construction based means of realizing any specified planar compliance for an object held by a compliant hand is developed. It is shown that the elastic behavior of an object held by a multi-serial parallel mechanism (a multi-finger compliant hand) is more simply and equivalently modeled by a fully-parallel dual elastic mechanism. Synthesis procedures are developed for the realization of an arbitrary compliance with compliant hands using geometric constraints on the fully-parallel elastic dual. Kinematic topologies addressed are those associated with hands having 2 or 3 fingers for which each finger has 2 joints.
查看更多>>摘要：Power skiving is one of the most effective methods for manufacturing high-accuracy gears, especially internal gears. However, the shortened tool life inhibits the large-scale industrialization of the promising technology. The study proposes a novel multi-blade skiving tool consisting of one finishing blade and several roughing blades, which can achieve a higher productivity and a longer tool life. The barrel-shaped cutter is derived based on the analysis of the conjugated surface of the tool for cylindrical gear skiving. By establishing a cutting force model that can accurately predict undeformed chips, the influence of the cutter blade outer diameter on cutting force and the influence of cutting blade crossed angle on chips and tool wear are analysed. The feasibility of the tool is verified by cutting experiments. The proposed multi-blade skiving tool is a promising approach to improve productivity and tool life. It can be applied in gear skiving applications such as the design of skiving tools.
NSTL
Elsevier