Redundant Legs Research Articles

Incomplete Caudal Duplication With Correction of Pygomelia in a Dog

Congenital malformations are structural defects that occur in all species during fetal development. Pygomelia is a type of polymelia in which the redundant legs are joined to the pelvis. This abnormality is observed in both human beings and animals. A mixed female (Shih Tzu) puppy with a rigid mass resembling two pelvic hindlimbs was referred to a pet clinic in Mashhad City, Iran. In radiographic assessments, two extra hindlimbs stemmed from malformed pelvic bones and were shorter than normal limbs. Both extra acetabula were detected on the hemipelvis, with two extra coxofemoral joints perpendicular to the regular hip joints in the caudal direction. Also, two vulvas and two anuses were seen, but only one vulva and anus were functional. The additional limbs were amputated by surgery. This case is the first report of a dog with incomplete caudal duplication and successful correction of pygomelia in Iran.

Kinematically redundant (6＋2)-dof HEXA robot for singularity avoidance and workspace augmentation

This paper introduces a novel (6＋2)-degree-of-freedom (dof) kinematically redundant parallel robot. The proposed architecture is based on the 6-dof HEXA parallel robot. The paper applies methodologies for avoiding type II singularities using kinematic redundancy that were originally proposed for robots with prismatic actuators to a new architecture with revolute actuators. The singularities of the HEXA robot are first examined based on previous work, and new instances of singularities are discovered. The singularity locus in the orientational workspace is identified using the Power Inspired Measure. Then, a novel kinematically redundant leg architecture is proposed to allow for the avoidance of these type II singularities. It is shown that the singularities present within the orientational workspace can successfully be avoided if two kinematically redundant legs are included in the robot architecture. The performance of the new architecture is then examined in various trajectories within the orientational workspace. Results show that the attainable orientational workspace is significantly increased with the proposed architecture.

Computer and experimental analysis of a reconfigurable staircase module-based multi-level inverter with fault tolerant capability

In the conventional multilevel inverters, occurrence of a fault in one or more power switches can cause abnormal changes in the output waveforms. Besides, increasing the applied power switches results to an increase in the possibility of fault on the power switches. Accordingly, providing a comprehensive structure with high fault-tolerant capability is one of the vital requirements and critical challenges. To tackle these issues, this study first presents and explores a new basic unit and staircase module (SM) and then extends and optimizes it to yield a reconfigurable multi-level inverter (MLI) with more levels and different goals. The proposed MLI can continue to operate when open-circuit faults in switches. This advantage of the proposed structure is achieved without any redundant legs or switches. For further investigation, a comparison is made in terms of the number of power switches, drivers, dc sources, and reliability between the proposed and similar structures. To control the output voltage levels, the strategy of fundamental frequency switching triggers the configured topology. The carrier signals are reconfigured under fault conditions based on levels to be generated by bypassing the faulted switch. The validity of the established MLI with its fault-tolerant capability is certified through both computer simulations using the MATLAB/Simulink platform and laboratory prototype implementations.

An improved fault tolerant single phase five-level multilevel inverter

ABSTRACT Despite the numerous advantages of multilevel inverters over two-level inverter, their main limitation is the increase in component count as the level increases. The increase in component count and high failure rate of power semiconductor switches and capacitors tend to reduce the reliability of multilevel inverters. Thus, the ability of multilevel inverter to tolerate faults is an important factor to consider when choosing a multilevel inverter topology for safety-critical applications. In this regard, the current study presents a new single-source five-level fault-tolerant inverter based on switched capacitor with self-balancing capability. In the proposed inverter, the fault tolerance is achieved with the help of redundant legs. A simple fault reconfiguration strategy is proposed in the present study for the proposed inverter which can retain the number of levels in the output, power handling capacity and self-balancing of switched capacitor in the event of any single switch fault and the most of multi-switch fault scenarios. The simulation study and experimental results validate the suggested inverter’s fault tolerant capability under various fault scenarios. A comprehensive and detailed comparison study demonstrates the proposed fault resilient inverter’s superiority over the recently proposed fault tolerant multilevel inverter available in the literature.

An Intelligent Electronic Fuse for Selective Isolation of Faulty Switching Cells in Power Electronic Converter Legs to Guarantee Continuous Operation

This article proposes a novel device designated as an intelligent electronic fuse (iFuse) intended to be connected in series with any current-bidirectional voltage-unidirectional active switch present in a power converter. The iFuse duty is to selectively isolate its series-associated switch from the rest of the converter circuit immediately after detecting that this switch has failed in short circuit. Nonetheless, it maintains the reverse (free-wheeling) current path originally offered by the failed switch. The failure detection is typically performed when the failed switch causes a shoot-through event. Therefore, the iFuse is able to block large currents. The iFuse allows increasing the power-converter fault tolerance and reliability with regard to switch short-circuit failures (SCFs), as in converters featuring switches in parallel, redundant legs, and multilevel neutral-point-clamped topologies. The reliability model analysis of a two-level converter leg with two parallel switches per position reveals that its reliability can be increased up to four times when an iFuse is implemented in series with each switch. The iFuse device feasibility and good performance are verified through experimental tests, proving that it can detect and isolate the associated-switch failure in 6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> , while stopping short-circuit currents of up to 1 kA without incurring in harmful di / dt values.

Redundancy in Parallel Mechanisms: A Review

This paper presents a review of the literature related to the use of redundancy in parallel mechanisms. Two types of redundancies are considered, namely, actuation redundancy and kinematic redundancy. The use of these concepts in the literature is highlighted. Each of the concepts is then formulated mathematically in order to clearly expose their characteristics and their properties. Two subclasses of kinematically redundant parallel mechanisms are defined, namely, those with serial redundant legs and those with parallel redundant legs. The force transmission in redundant parallel mechanisms is then discussed. Finally, a summary of the different approaches that can be used to implement redundancy in parallel mechanisms is given in order to identify the most promising synthesis avenues and to provide insight into their potential fields of application.

Unified formulation for the stiffness analysis of spatial mechanisms

This paper presents a complete stiffness analysis of spatial mechanisms. Links flexibility is modeled through structural elements while joints are inherently considered by means of kinematic relations including their degree of freedoms (dofs) and degree of constraints (docs). Actuation stiffness can be included as well as flexibility of some docs can be added in a selective way leaving the remaining rigid. Preloaded joints can be also modeled including joint wrenches. The Condensed Stiffness Matrix (CSM) of an elementary kinematic chain composed of a flexible two-node element and a spatial joint is derived using a robust mathematical formulation based on partitioned matrices and condensation techniques. The CSMs are then combined to find the global stiffness matrix through techniques coming from the structural analysis. The proposed method solves some critical issues of other formulations providing possibility to work with redundant legs (or joints) of fully- and over-constrained PKMs, inherent use of joints without resorting to Lagrangian multipliers, ability to exploit positive-semidefinite joint stiffness matrices without causing a rank-deficient global stiffness matrix; selective inclusion of stiffness in joints along dofs and docs. Finally, three examples to show the potentiality of the method for different applications of robotics are described.

Kinematically Redundant Spatial Parallel Mechanisms for Singularity Avoidance and Large Orientational Workspace

This paper introduces a novel architecture of kinematically redundant parallel mechanisms. This family of mechanisms is similar to the well-known Gough-Stewart platform, and it retains its advantages, i.e., the members connecting the base to the moving platform are only subjected to tensile/compressive loads. The proposed architecture exploits kinematic redundancy to avoid singularities and extend the rotational workspace. The novel kinematic architecture is described, and the associated kinematic relationships are developed. Based on the derivation of the Jacobian matrices, it is shown that the singularities of this type of mechanism are governed by the orientation of passive links connecting the redundant legs to the platform. Grassmann geometry is then used to demonstrate that, given some simple geometric assumptions on the architecture, all singularities can be avoided by exploiting the kinematic redundancy. The orientational workspace is then discussed, and a graphical representation is provided for an example architecture comprising nine actuators, whose orientational workspace is shown to be very large. The translational workspace is also studied. Example trajectories are given in order to illustrate the capabilities of the mechanism to produce very large rotation angles without encountering singularities. Computer animations of the trajectories are provided in a multimedia extension of the paper.

Diagnosis of the Forcing and Structure of the Coastal Jet near Cape Mendocino Using In Situ Observations and Numerical Simulations

Abstract Several flights were conducted by the University of Wyoming King Air near Cape Mendocino, California, during June 2004 to examine finescale features of the coastal low-level jet (CJ) that frequently forms during summer over the ocean off the West Coast of the United States. The primary goal of these flights was to measure the horizontal pressure gradient force (PGF) and hence to determine the forcing of the CJ directly. By flying a series of redundant legs on an isobaric surface, heights of the pressure surface can be obtained from radar altimeter measurements and refined position estimates from an onboard global positioning system receiver. The slope of the isobaric surface height is proportional to the PGF. Results are shown for the 22 June 2004 case study conducted to the south of Cape Mendocino. The forcing of a CJ under weak synoptic forcing and the role of the elevated terrain near Cape Mendocino are explored. Ten isobaric legs approximately 70 km in length and directed east–west were conducted near the level of the maximum CJ wind speed. The vertical structure of the CJ was obtained from sawtooth legs conducted along an east–west flight leg. Numerical simulations have been performed for this case using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) for comparison with in situ measurements. Model simulations show pressure perturbations in the vicinity of the cape as the northerly winds associated with the CJ interact with the coastal topography. Close agreement is found between in situ measurements and MM5 analyses of the various state parameters and the PGF along the east–west flight track in the lee of Cape Mendocino. Strong variation in the PGF is observed along the flight path. Large ageostrophic accelerations are present in response to the adjustment of the CJ with Cape Mendocino, reflecting the force imbalance between the observed PGF and Coriolis force.

Gait control for redundant legged biped robot at constant velocity and constant height of the waist

AbstractIn this paper, we propose a gait control method for redundant legged biped robot based on leg center of mass (COM) position control at constant velocity and constant height of the waist. The developed biped robot has redundant legs, which have four degrees of freedoms (DOFs) on each in the sagittal plane. The redundant DOF enables movement of its leg tip position and its leg COM position independently. Therefore, the proposed robot has structural capability to control the leg COM position for maintaining the projection of the total COM inside the support polygon without upper body motion. Such capability enables the stable static walk in the arbitrarily desired velocity and height of the waist motion. The validity of the proposed method for the static walk at constant velocity and constant height of the waist in the leg COM position control for redundant legged biped robot is confirmed by several results of simulation and experiment. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(4): 51–59, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20357

冗長脚二足歩行ロボットにおける腰の等高等速移動の歩行制御

In this paper, we propose a gait control method for redundant legged biped robot based on leg center of mass (COM) position control at constant velocity and constant height of the waist. The developed biped robot has redundant legs, which have four degrees of freedoms (DOFs) on each in the sagittal plane. The redundant DOF enables movement of its leg tip position and its leg COM position independently. Therefore, the proposed robot has structural capability to control the leg COM position for maintaining the projection of the total COM inside the support polygon without upper body motion. Such capability enables the stable static walk in the arbitrarily desired velocity and height of the waist motion. The validity of the proposed method for the static walk at constant velocity and constant height of the waist in the leg COM position control for redundant legged biped robot is confirmed by several results of simulation and experiment. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(4): 51–59, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20357

C40 冗長な多関節機構を有する車両型ロボットの目標軌道追従制御(OS11-4 車両型ロボット)

C40 冗長な多関節機構を有する車両型ロボットの目標軌道追従制御(OS11-4 車両型ロボット)

Impact Force Suppression for Redundant Legged Biped Robot Based on Unified Decoupling Control Method

A swinging leg of a biped robot landing, impact force usually occurs between the sole and the ground, and then it causes instability of the gait. The paper describes the advantages of adopting redundant legs to the robot in order to conquer the difficulty, and proposes a novel way of the motion control for the redundant legged biped robot.In general, each leg of a conventional biped robot consists of 3 joints, namely, hip, knee and ankle in the sagittal plane. On the other hand, the proposed robot has been added extra joints, and thereby has redundancy in terms of degrees-of-freedom. Since the redundant leg can select its arbitrary posture, regardless of the tip position, the structure enables to move the position of the center of mass (COM) of the leg independently. The impact force is suppressed by controlling the COM acceleration of the landing leg. In order to achieve the decoupled motions between the tip and the COM, the unified decoupling controller is introduced. The controller includes three types of the disturbance observers together, and both desired motions are realized consequently. The validity of the proposed approach is confirmed in physical experimental results.

Impact Force Reduction on Biped Robot with Redundant Legs

The paper reports a structural approach to reduce impact force in landing the swinging leg of biped robot. The robot introduces redundant legs in the sagital plane, which have redundancy in terms of DOF that is, extra joints besides hip, knee and ankle in each leg. The leg independently changes the posture, regardless of the tip position, while the center of mass (COM) of the leg moves to an arbitrary position even if the tip is fixed. Since the position of COM moves in landing the swinging leg toward the ground, therefore the impact force is reduced. The validity of the proposed approach is confirmed in physical experiments.