Goian – Cerveira Footbridge over the Miño River. Spain - Portugal

<p>The Goián - Cerveira footbridge over the Miño river, result of an international competition held in 2017, will connect the Espazo Fortaleza park in Goián-Tomiño, Spain, and the Castelinho park in Vila Nova de Cerveira, Portugal.</p><p>The proposed footbridge saves a main span of 265m, and is a suspended structure, with two towers located on the riverbanks, avoiding intermediate supports on the riverbed, and only one suspension cable. The towers are located not centered with the axis of the footbridge deck, that adopts a curved layout both in plan and in elevation. The curved layout in plan fits better to the footbridge arrival in both riverbanks, and improves its structural behavior. Indeed, the eccentric location of the suspension cable within the deck generates important horizontal transverse forces, that are supported by the curved deck by behaving as an arch. This configuration is also very convenient for supporting and controlling wind loads. It is a classic bridge type -suspended bridge- but with a singular configuration due to the curved layout of the deck and its arc-like behavior.</p><p>The result is a very subtle and slender structure, a “line over the Miño river”, that highly preserves the environmental values of the river and the landscape.</p>

A regularization method for solving dynamic problems with singular configuration

In the simulation process for multi-body systems, the generated redundant constraints will result in ill-conditioned dynamic equations, which are not good for stable simulations when the system motion proceeds near a singular configuration. In order to overcome the singularity problems, the paper presents a regularization method with an explicit expression based on Gauss principle, which does not need to eliminate the constraint violation after each iteration step compared with the traditional methods. Then the effectiveness and stability are demonstrated through two numerical examples, a slider-crank mechanism and a planar four-bar linkage. Simulation results obtained with the proposed method are analyzed and compared with augmented Lagrangian formulation and the null space formulation in terms of constraints violation, drift mechanical energy and computational efficiency, which shows that the proposed method is suitable to perform efficient and stable dynamic simulations for multi-body systems with singular configurations.

Optimum Seeking of Redundant Actuators for M-RCM 3-UPU Parallel Mechanism

The singularity problem brings troubles to the design and application for the parallel mechanism. Currently, redundant actuation is one of the useful methods to solve this singularity problem. However, faced to the numerous joints in a parallel mechanism, how to make a quantitative criterion of seeking the most efficient joints added actuators for letting the mechanism passes through singularity is a necessarily open issue. This paper focuses on a 2R1T 3-UPU (U for universal joint and P for prismatic joint) parallel mechanism (PM) with two rotational and one translational (2R1T) degrees of freedom (DOFs) and the ability of multiple remote centers of motion (M-RCM). The singularity analysis based on the indexes of motion/force transmissibility and constraint shows that this PM has transmission singularity, constraint singularity, mixed singularity and limb singularity. To solve these singular problems, the quantifiable redundancy transmission index (RTI) and the redundancy constraint index (RCI) are proposed for optimum seeking of redundant actuators for this PM. Then the appropriate redundant actuators are selected and the working scheme for redundant actuators near the corresponding singular configuration are given to help the PM passes through the singularity. This research proposes a quantitative criterion to optimum seeking of redundant actuators for the parallel mechanism to solve its singularity.

Operation Safety of a 2-DoF Planar Mechanism for Arm Rehabilitation

The operation safety of rehabilitation devices must be addressed early in the development process and before being tested on people. In this paper, the operation safety of a 2-DoF (degrees of freedom) planar mechanism for arm rehabilitation is addressed. Then, the safety and efficiency of the device operation is assessed through the Transmission Index (TI) distribution in its workspace. Furthermore, the produced stresses on the human arm are assessed via the FEM (finite element method) when the rehabilitation device reaches five critical positions within its workspace. The TI distribution showed that the proposed design has a proper behaviour from a force transmission point of view, avoiding any singular configuration that might cause a control failure and subsequent risk for the user and supporting the user’s motion with a good efficiency throughout its operational workspace. The FEM analysis showed that Nurse operation is safe for the human arm since a negligible maximum stress of 6.55 × 103 N/m2 is achieved by the human arm when the device is located on the evaluated critical positions.

Analysis of Singular Configuration of Robotic Manipulators

Robotic manipulators inevitably encounter singular configurations in the process of movement, which seriously affects their performance. Therefore, the identification of singular configurations is extremely important. However, serial manipulators that do not meet the Pieper criterion cannot obtain singular configurations through analytical methods. A joint angle parameterization method, used to obtain singular configurations, is here creatively proposed. First, an analytical method based on the Jacobian determinant and the proposed method were utilized to obtain their respective singular configurations of the Stanford manipulator. The singular configurations obtained through the two methods were consistent, which suggests that the proposed method can obtain singular configurations correctly. Then, the proposed method was applied to a seven-degree-of-freedom (7-DOF) serial manipulator and a planar 5R parallel manipulator. Finally, the correctness of the singular configurations of the 7-DOF serial manipulator was verified through the shape of the end-effector velocity ellipsoid, the value of the determinant, the value of the condition number, and the value of the manipulability measure. The correctness of singular configurations of the planar 5R parallel manipulator was verified through the value of the determinant, the value of the condition number, and the value of the manipulability measure.

Classification of 3-DOF 3-UPU Translational Parallel Mechanisms Based on Constraint Singularity Loci Using Gröbner Cover

A 3-UPU translational parallel mechanism (TPM) is one of typical TPMs. Several types of 3-UPU TPMs have been proposed in the literature. Despite comprehensive studies on 3-UPU TPMs in which the joint axes on the base and the moving platform are coplanar, only a few 3-UPU TPMs with a skewed base and moving platform have been proposed. However, the impact of link parameters on singularity loci of such TPMs has not been systematically investigated. The advances in computing CGS (comprehensive Gröbner system) or Gröbner cover of parametric polynomial systems provide an efficient tool for solving this problem. This paper presents a systematic classification of 3-UPU TPMs, especially those with a skewed base and moving platform, based on constraint singularity loci. First, the constraint singularity equation of a 3-UPU TPM is derived. To simplify this equation, the coordinate frame on the base (or moving platform) is set up such that the centers of three U joints are located on different coordinate axes. Using Gröbner Cover, the 3-UPU TPMs are classified into 20 types based on the constraint singularity loci. Finally, a novel 3-UPU TPM is proposed. Unlike most of existing 3-UPU TPMs which can transit to two or more 3-DOF operation modes at a constraint singular configuration, the proposed 3-UPU TPM can only transit to one general 3-DOF operation mode in a constraint singular configuration. The singularity locus divides the workspace of this 3-UPU TPM into two constraint singularity-free regions. This work provides a solid foundation for the design of 3-UPU TPMs and a starting point for the classification of a general 3-UPU parallel mechanism.

Kinematic Analysis of a 3-DOF Screening Parallel Mechanism With Control Decoupling

In order to raise the low efficiency of traditional screening machine, a new parallel mechanism (PM) with two translation and one rotation is proposed. Analyze the composition of each kinematic chain based on topological characteristics of mechanism The analytical method is utilized to simplify three constraint equations of PM respectively and the correctness is verified by Matlab. On the basis of kinematic analysis, the Jacobian matrix of mechanism is solved, and decoupling characteristics of mechanism input-output control modes are evaluated. The mechanism is coupled between translational input Y and translational output x, and three input-output control modes are decoupling. In addition, the singular configuration of PM is also analyzed. The discrete element method was used to simulate material screening, and the influence of DOF on screening efficiency was analyzed by EDEM software and experiment, which result is met with the theoretical analysis

Vision-Based Hybrid Controller to Release a 4-DOF Parallel Robot from a Type II Singularity

The high accuracy and dynamic performance of parallel robots (PRs) make them suitable to ensure safe operation in human–robot interaction. However, these advantages come at the expense of a reduced workspace and the possible appearance of type II singularities. The latter is due to the loss of control of the PR and requires further analysis to keep the stiffness of the PR even after a singular configuration is reached. All or a subset of the limbs could be responsible for a type II singularity, and they can be detected by using the angle between two output twist screws (OTSs). However, this angle has not been applied in control because it requires an accurate measure of the pose of the PR. This paper proposes a new hybrid controller to release a 4-DOF PR from a type II singularity based on a real time vision system. The vision system data are used to automatically readapt the configuration of the PR by moving the limbs identified by the angle between two OTSs. This controller is intended for a knee rehabilitation PR, and the results show how this release is accomplished with smooth controlled movements where the patient’s safety is not compromised.

A Distribution Method of Driving Torque for A Novel 3UPS-RR Redundant Solar Tracker

This paper proposes a novel two-axis solar tracker with redundant parallel mechanism and investigates the distribution method of driving torque. In view of the difference between the singular configuration of the redundant parallel mechanisms and that of the corresponding non-redundant ones, an index related to the minimum singular value of Jacobian matrix is used to indicate the position of the singular configuration relative to the boundaries of the required workspace. The driving torque and energy consumption can be optimized with this index. Based on the fact that the direction of driving torque is opposite to that of rotor in most of the running processes, a distribution method of driving torque with the minimum energy consumption for redundant parallel solar tracker is proposed. The distribution method is compared with the minimum norm solution which is adopted by the conventional redundant parallel mechanism. And the energy consumption can be significantly reduced by adopting this method. In addition, the workspace and energy consumption of the redundant solar tracker and its non-redundant counterpart are compared. The results show that the redundant solar tracker has larger workspace and lower energy consumption.