Mechanism and Machine Theory最新文献

In this paper, our objectives are to estimate the moments of inertia and reconstruct the inputs of a two-link pendulum that models a human arm. A blind parameter identification routine to determine the inertia properties of human limbs without input data based on a combination of collocation discretization and homotopy optimization is suggested. Without the input data, inertia parameters are structurally unidentifiable. Complementary equations in terms of the ratio of inertia parameters in the cost function and the rate of change of the inputs in the constraints are introduced to make the problem structurally identifiable. Numerous simulations are performed to validate our approach. Experiments to record human upper arm and forearm oscillatory movements were also performed, and moment of inertia terms were evaluated. The significance of the proposed method is that the method can be used to evaluate the moments of inertia of human body segments only from the experimental kinematic data. The advantages of the method are: numerical integration of dynamic and sensitivity equations is avoided and the record of the inputs to the system is not needed.

Two-point contact bearings are widely used in industry. In space applications, where the speed of the mechanisms is low, the main source of friction in the bearings is the one produced at the ball-raceway contact ellipses. This friction affects the motorization margin which is a key aspect of the operational envelope in space mechanisms. The traditional method to estimate this friction works by trying to find the force equilibrium for each ball. For that, an iterative sequence is arranged with six parameters defining the ball kinematics under the action of normal and friction forces assuming a constant friction coefficient. The force equilibrium model is reviewed analyzing the influence of the speed, and the implications of quasi-static assumption are assessed. For this last assumption, an energetic method is proposed established upon the minimization of the friction power generated within the contact patches. This model provides the same results as the force equilibrium model with a stronger convergence and a simple computational implementation. Finally, the two methods are compared obtaining better performances for the power minimization method. This work represents a first step in order to substitute force equilibrium methods with more stable energy based methods in bearing friction calculations.

Cable-driven Continuum Robots (CCRs) represent a subset of flexible robotic systems with diverse applications encompassing medical, quality control, and search and rescue. Multi-segmented CCRs can independently actuate different CCR segments and deform into a series of connected circular arcs. While this method generates constant-curvature profiles, CCRs with varying radial cable offsets can generate shapes with varying curvatures. However, there are no kinematic models for such robots in the literature. This paper introduces optimization-based formulations to accurately estimate the deformed profile of CCRs, considering both variable cable offset and multi-segment configurations. The presented kinematic approach can predict the deformed profiles with an RMS error less than 5% of the total length of the robot. The application of the proposed method to determine the inverse kinematics of multi-segmented CCRs is demonstrated—even considering obstacles in the robot’s workspace. Practical implementation of the formulation is illustrated using a 3-segmented CCR with a cable-driven soft gripper that imitates biological grippers such as an elephant’s trunk or creeper vine to grasp objects.

Vector propulsion systems enhance the limited three-dimensional motion capabilities of conventional systems at low speeds. However, their requirement for multiple prime movers increases the underwater robot’s power capacity, impacts its size and mass and compromises long endurance capabilities. To solve this problem, a compact dual-motor underwater vector propulsion system is proposed in this paper. It employs a nozzle, adjustable in a two-dimensional plane, to produce an adjusting force, and a propeller, perpendicular to this plane, for main thrust, achieving three-dimensional motion. The innovation lies in a dual-shaft motor with each shaft featuring a one-way bearing. The synchronized direction of rotation of the two one-way bearings is opposite. This configuration enables the motor to drive the propeller during forward rotation and the nozzle during reverse rotation, achieving a two-in-one drive motor and reducing prime movers. Additionally, using nozzles for attitude regulation overcomes the limitation of conventional propulsion systems. An analytical model defines mechanical output characteristics. Computational fluid dynamics analyze hydrodynamic characteristics. The prototype’s underwater experiments confirm its ability to generate main thrust and a two-dimensional planar adjusting force, enabling three-dimensional motion.

As a direct response to robot movements and load distributions, the ground reaction force (GRF) is pivotal for heavy-legged robot (HLR) applications. This study presents a technical framework for GRF monitoring in an electric cylinder-driven HLR, eliminating the need for information on body motion, load distributions, and measured servo outputs. Traditional joint space-based dynamics are extended to include servo currents, compensating for the influence of unknown servo outputs. An essential contribution is incorporating the impact of floating bases and unknown loads into a virtual spatial force (VSF) applied to the HLR hip joint. The VSF is obtained through the nonlinear disturbance observer when the HLR is in a stable contact phase. Subsequently, a high-order GRF observer (HOGO), compensated with VSF, enables GRF observations without the pre-acquired body movement and load distribution data. In contrast to conventional GRF observations, the proposed framework could determine virtual payloads acting on the hip joint while ensuring precise GRF monitoring without requiring supplementary sensors. The GRF observations of the proposed framework are experimentally superior to those of the conventional methods with unknown HLR body motion and load information.

This work presents a high-fidelity lubricated transmission model, coupling Flexible MultiBody (FMB) dynamics with ElastoHydrodynamic Lubrication (EHL). The EHL model is discretised with a coupled finite element approach, in contrast with the more iteration-intensive finite difference approach using relaxation schemes. The finite element method yields nonlinear system matrices, requiring matrix reevaluation in each iteration. To mitigate computational overhead, tensorisation replaces integrals to compute the system matrices with tensor-vector multiplications. Furthermore, this work optimises the use of the discretised EHL model by scaling and reusing it across different contact conditions. Coupling of the contact force resulting from the EHL model with the rigid body displacement resulting from the FMB model enables the computation of steady-state equilibrium for a given torque applied to the gear pair. However, local deformations should be excluded from the FMB model to ensure proper coupling with the EHL model, which exclusively computes local deformation within the contact zone. Newly developed global line contact attachment modes allow the FMB model to exclusively calculate global tooth bending in response to a given contact force.

Redundant non-serial compound manipulators with closed kinematic and actuator loops that enhance precision control and load carrying capacity are treated. Generalized coordinates and associated holonomic constraints that account for kinematic and actuator closed loops and singularity free representation of orientation of spatial manipulator bodies augment input and output coordinates in the kinematic formulation. Disjoint assembly components and path connected singularity free assembly components of manipulator configuration space are defined, in which manipulator kinematics and dynamics can be reliably carried out. A set-valued inverse kinematic configuration mapping is derived, with which compound redundant manipulators are shown to be locally cyclic. A new system of manipulator operational coordinates comprised of output and self-motion coordinates are defined and shown to be equivalent to input coordinates in representation of manipulator kinematics and dynamics. Well-posed ordinary differential equations of manipulator dynamics in both input and operational coordinates are presented that require no ad-hoc derivation. Five model manipulators illustrate applications involved and theoretical methods presented.

Remote center motion (RCM) mechanisms play a significant role in minimally invasive surgery (MIS) to provide geometric constraints to the surgical tool motion. To satisfy the rapid diversified development of the surgical robot in various environment, especially in the head coil, MRI room or other enclosed confined space, this paper focuses on the type synthesis of hybrid-RCM mechanisms using the topological arrangement and modular design method (TAMD). Firstly, the concepts of TAMD are proposed systematically for type synthesis of general hybrid mechanisms. Secondly, TAMD is applied towards the type synthesis of RCM mechanisms to generate their topological arrangement and motion characteristic relationships. Thirdly, main module and secondary modules are designed for RCM mechanisms of four different motions (i.e., 1R, 2R, 1R1T, and 2R1T) based on the proposed topological arrangement. Numerous novel 1R, 2R, 1R1T, and 2R1T RCM mechanisms are then proposed by assembling these main and secondary modules. Finally, one typical case for each motion of RCM mechanisms is taken as an example to validate its motion capability.

Human–robot interaction of human augmentation robots presents a considerable challenge in achieving accurate and robust interaction force control. This paper proposes a novel softening nonlinear elastic mechanism with continuous adjustability (SNEMA) to address this challenge. The SNEMA achieves softening stiffness behavior through a nonlinear mapping relationship between the lengths of the diamond diagonals. This unique stiffness profile, featuring high stiffness for low output and low stiffness for high output, strikes a balance between the output force range and force resolution. Moreover, the continuous and convenient adjustment of the stiffness profile is realized by utilizing two antagonistic linear springs, enabling optimal stiffness matching for different output force ranges. Bench tests were conducted to validate the stiffness modeling and evaluate the force tracking and interaction performance of the developed SNEMA. Experimental results demonstrate the capability of the SNEMA to achieve precise force control and good collision safety in human–robot interaction. The proposed SNEMA is finally deployed on the Centaur robot to demonstrate its advantages in practical application.

To achieve high-performance control, the dynamics and control should be closely integrated. This paper focuses on dynamic-based control design for a hybrid painting robot containing parallelogram linkages to improve its tracking accuracy and motion consistency. The study derives the dynamics of the parallelogram component to investigate its distinctive attributes, which include time invariance, joint independence, and linear approximability. Based on these unique characteristics, a novel theory-experiment mixed two-step method for control design is presented. It involves identifying and visualizing an optimized space of control parameters through theoretical deduction, followed by determining the optimal control parameters within this space through experimental trials. Experimental results underscore a substantial improvement in the tracking accuracy and motion consistency of the painting robot.