查看更多>>摘要：This paper presents the dynamic model and analytical modal analysis for robotic manipulators with rigid links and flexible joints. Dynamic equations of general robots with both prismatic and revolute joints are firstly developed using the Lagrangian formulation in minimal joint and motor coordinates. Next, linearized dynamic equations taking into account the influence of gravity forces, external forces, and control parameters are formulated based on the Taylor series. Therefore, the robot's modal parameters can be computed for any configuration based on a state-space matrix derived from the linearization model. To illustrate the proposed method, modal parameters of a flexible joint robot with six degrees of freedom are computed using the analytical method and estimated using the operational modal technique based on the vector autoregression model. Results obtained by both methods agree very well with each other.
查看更多>>摘要：Zero offsets and geometric source errors will significantly degrade the kinematic accuracy of redundantly actuated parallel manipulators (RAPMs). To relieve the influences of these factors, this paper presents a minimal-error-model based two-step kinematic calibration methodology for this type of parallel manipulators. A novel 3-DOF spindle head with a 2UPR&2RPS topology is taken as an example to demonstrate the kinematic calibration methodology. The proposed kinematic calibration methodology includes three critical steps: (1) a set of general principles is proposed to eliminate redundant geometric source errors in the manipulator to derive a minimal error model that includes the least number of geometric source errors; (2) a sensitivity analysis is carried out using the Monte-Carlo simulation to reveal the relative impact of geometric source errors on the terminal accuracy; (3) a hierarchical identification strategy composed of a coarse identification and a fine identification is proposed, based on which a two-step calibration methodology is constructed. Finally, a set of calibration experiments is performed to verify the effectiveness of the proposed calibration methodology.
查看更多>>摘要：The linearized Cartesian elastodynamics model of mechanical systems with flexible links is introduced in this paper to simplify its counterpart. n-dof generalized model. The stiffness is represented by means of Loncaric's 6 x 6 Cartesian stiffness matrix (CSM), the inertia by what von Mises termed the inertia dyad, i.e., the 6 x 6 Cartesian mass matrix (CMM). This model applies to a mechanical system with compliant components. Furthermore, the Cartesian frequency matrix (CFM) is defined as a congruent transformation of its stiffness counterpart, the transformation matrix being the inverse of the square root of the positive-definite CMM. The CFM thus defined is dimensionally-homogeneous, symmetric and at least positive-semidefinite. Upon the eigenvalue decomposition of the same matrix, the natural frequencies and the corresponding natural modes, i.e., the eigenscrews of the system, are obtained. The physical meaning of the CFM, together with that of its eigenvalues and eigenscrews, are given due interpretation in the paper, within the context of screw theory. This matrix is intended to serve as a useful tool for the elastodynamics analysis and design of a large class of multibody systems with flexible components, especially at the early design stages.
Silva, Fabricio LeonardoSilva, Ludmila C. A.Eckert, Jony JavorskiLourenco, Maria A. M....
18页
查看更多>>摘要：Modular design becomes a trend in the automotive industry to increase competitiveness with vehicle platforms that combine multiple modules to provide different applications. This paper presents an optimized Fuzzy Logic Control (FLC) applied to modular all-wheel-drive vehicles, focusing on Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEV) powered configurations. The vehicle behavior is determined by dynamic model simulation, in which the Magic Formula is applied to define the tire slip, associated with the load transfer during curves or drive/break situations. The controller acts as an electronic differential and changes the in-wheel motor torques to correct the vehicle trajectory during a standard maneuver. A multi-objective optimization based on the genetic algorithm determines the FLC configuration. The vehicle parameters (EV and HEV) have been modified to analyze the optimized FLC and, in all cases, the control showed an improvement in behavior to the vehicle without control. Finally, the FLC was implemented in a simple microcontroller and a hardware-in-the-loop simulation was developed to simulate a real vehicle operating condition and analyze this performance.
查看更多>>摘要：It is well-known that there exist rigid frameworks whose physical models can snap between different realizations due to non-destructive elastic deformations of material. We present a method to measure this snapping capability based on the total elastic strain energy density of the framework by using the physical concept of Green-Lagrange strain. As this so-called snappability only depends on the intrinsic framework geometry, it enables a fair comparison of pin-jointed body-bar frameworks, thus it can serve engineers as a criterion within the design process of multistable mechanisms. Moreover, it turns out that the value obtained from this intrinsic pseudometric also gives the distance to the closest shaky configuration in the case of isostatic frameworks. Therefore it is suited for the computation of these singularity-distances for diverse mechanical devices. In more detail we study this problem for parallel manipulators of Stewart-Gough type.
查看更多>>摘要：Dynamic constant-force performance is essential in suspended astronaut micro-gravity simulation systems. Of particular concern is the active constant-force system comprising a low-stiffness mechanism because of its combination of high-speed response and low stiffness. However, existing simulation systems demonstrate limited performance owing to large amounts of additional mass, difficulties in the fine adjustment of setting force, and low bandwidths. Improving on our previous work, we present a cascade constant-force system with an improved lightweight low-stiffness mechanism. In particular, the proposed system employs an innovative setting force adjusting mechanism with low inertia and a large reduction ratio obtained using a reverse drive screw and nut mechanism. An in-depth theoretical analysis is conducted to reveal the disturbance suppression characteristics of the low-stiffness mechanism and actuator at different frequencies. The enhanced performance obtained using the low-stiffness mechanism was verified experimentally. It was shown that the improved mechanism significantly increases the system bandwidth and achieves an enhanced dynamic constant-force performance.
查看更多>>摘要：A new high precision ultra-compact decoupled XYZO motion stage based on flexure hinges is designed and analyzed. The stage mainly consists of three components including serial-parallel dual-stage amplifier, Z-shape motion steering mechanism and motion decoupled mechanism. Compared with the existing stages, the proposed high precision motion stage has many advantages such as extremely compact structure, large output decoupling motion and XYZO four axes output displacement. The function of serial-parallel dual-stage amplifier is to amplify the travel range of nano positioning piezo actuator (PZT) by connecting two parallel bridge type mechanism. The Z-shape mechanism can change the direction of motion transmission to make the stage more compact and form movement in XYZO four directions. The decouple mechanism can reduce the implicative movement of different piezo actuators. Then, kinetostatic analysis of this new XYZO stage is conducted to analyze the stage. Finally, the finite-element analysis (FEA) and prototype experiments are implemented to verify the design objectives.
查看更多>>摘要：Underactuated grippers represent an appealing solution that allows complex objects to be grasped and manipulated via passive adaptation of the hand with objects via simple control inputs. The grasping ability can be further improved in combination with vacuum gripping, i.e., by outfitting the gripper phalanges with suction cups, that remains a largely underinvestigated solution. This paper presents a novel gripper, referred to as POLYPUS, that features underactuation and vacuum grasping to handle uneven and even objects made of different materials, including cardboard, glass, sheet metal, and plastic. Being characterized by a solid frame, POLYPUS does not fall in the soft gripper category, while preserving similar adaptability. It provides unique load lifting capacity that ranges from light to heavy objects, whereas most of the existing grippers are tailored for a specific target payload. Being modular in design, POLYPUS can be easily reconfigured for a wide range of object sizes and applications. Results obtained from an extensive set of simulations are included to evaluate the grasping performance expressed in terms of the minimum suction force to handle objects of varying shape, material, and pose.
查看更多>>摘要：The digital tooth contact analysis (DTCA) of machined gears is an effective way to evaluate both the design and manufacturing before rolling tests. This is very challenging to face gear drives due to two aspects. (1) No measurement standard is available for face gears to obtain an accurate measurement model. (2) The DTCA equation is highly nonlinear related to the complex geometry of face gears. To fulfil those problems, this work presents an accurate measurement model of the face gear tooth surface, wherein the DTCA is implemented with a robust algorithm. An effective measurement strategy based on sensitivity analysis is proposed to establish a measurement coordinate system (MCS), and the relationship between the MCS and the design coordinate system (DCS) is further analyzed to compensate the measurement errors. Subsequently, the B-spline fitting technology is applied to reconstruct the measurement model. Furthermore, the equation of meshing is simplified to reduce its nonlinearity and realize the DTCA. The proposed method is verified by both the finite element analysis (FEA) and a rolling test.
查看更多>>摘要：Cable-Driven Parallel Robots (CDPR) employ extendable cables to control the pose of an end effector (EE). If the number of cables is smaller than the degrees of freedom of the EE, and cables have no special arrangement reducing the EE freedoms, the robot is underactuated, and the EE is underconstrained: as a consequence, the EE preserves some freedoms even when all actuators are locked, which may lead to undesirable free motions. This paper proposes a novel methodology for the identification of the EE inertial parameters of these robots. Inertial parameters are useful, for example, in the application of feedforward control techniques. The main merit of our approach is that it does not require force or torque measurements, and only a subset of the robot kinematic variables needs to be measured. The method consists in the application of the EE internal-dynamics equations along a free-motion trajectory, also referred to as self-motion zero dynamics. This results in an over-determined system of equations that are linear in the EE inertial parameters (the Free-motion Internal-Dynamics Identification Model, FIDIM); the said system is solved according to the Total-Least-Square technique. Free-motion trajectories that are optimal for identification purposes are investigated and experimentally tested on a 4-cable robot. FIDIM is then applied, statistical analysis is performed, and the experimental results are cross-validated against additional free-motion trajectories.
NSTL
Elsevier