Performance Analysis of Planar Cable-Based Parallel Manipulators

2010 ◽  
Author(s):  
Damiano Zanotto ◽  
Giulio Rosati ◽  
Aldo Rossi
Keyword(s):  
Weight Ratio ◽  
Mechanical Impedance ◽  
Parallel Manipulators ◽  
Performance Indices ◽  
End Effector ◽  
Parallel Structures ◽  
Dynamic Performances ◽  
High Dynamic ◽  
First Time ◽  
High Payload

In the last two decades, many research works have been published on cable-based systems, reflecting the considerable interest of the scientific community in this area. Cables are used both in serial structures, to remotely actuate rigid links, and in parallel structures, to directly control the motion of a mobile platform or end-effector. The latter subclass is particularly appealing, thanks to ease of design, high payload-to-weight ratio, potentially high dynamic performances and wide workspace. Such devices have also been effectively employed in haptics, since the use of light-weight elements allows to develop structures with low mechanical impedance. Unilateral actuation represents a major issue in the study of cable-based devices, often forcing to adopt specially formulated design tools. This paper presents a set of performance indices, some of which are introduced here for the first time, that can be used for the optimization of the design and for the analysis of cable-based devices. To prove the effectiveness of these tools, a comparison of the kinematic and dynamic performances of three different designs of planar cable-based parallel manipulators is presented.

Dynamics of a Class of Parallel Wrists

2003 ◽  
Vol 126 (3) ◽  
pp. 436-441 ◽  
Author(s):  
Raffaele Di Gregorio ◽  
Vincenzo Parenti-Castelli
Keyword(s):  
Jacobian Matrix ◽  
Dynamic Performance ◽  
Parallel Manipulators ◽  
Dynamic Problems ◽  
Performance Indices ◽  
Inverse Dynamic ◽  
End Effector ◽  
Kinematic Behavior ◽  
Effective Dynamic ◽  
Spherical Motion

This paper presents a dynamic model of parallel wrists with all links constrained to have a spherical motion with the same center. The model can also be applied to serial wrists. The model, based on Lagrangian formulation of dynamics, exploits the feature that all the links have the same fixed point. Three parameters defining the platform orientation are used as generalized coordinates. This choice allows the use of the generalized inertia matrix (GIM) appearing in the model to calculate effective dynamic performance indices proposed in a previous paper. The model can solve both the direct and the inverse dynamic problems. It also contains the Jacobian matrix useful to characterize the kinematic behavior of parallel manipulators. By the model it is shown that the best performances are reached in the workspace regions where the manipulator has a good kinematic and dynamic isotropy, whereas the incidence of nonlinear forces on performances is relevant at high end-effector speed. A numerical example is provided.

Direct position analysis of parallel manipulators which generate SP-2PS structures

Robotica ◽  
2005 ◽  
Vol 23 (4) ◽  
pp. 521-526 ◽  
Author(s):  
Raffaele Di Gregorio
Keyword(s):  
Polynomial Equation ◽  
Analytic Form ◽  
Parallel Manipulators ◽  
Real Case ◽  
End Effector ◽  
Position Analysis ◽  
Parallel Structures ◽  
Univariate Polynomial

The determination of the assembly modes of the parallel structures with three legs of type PS or SP (P and S stand for prismatic pair and spherical pair, respectively) consists of solving the direct position analysis of all the three-legged parallel manipulators which have, in each leg, one not actuated prismatic pair, one not actuated spherical pair and one or two one-dof actuated pairs of any type, placed along the leg in any order. There are two types of such structures: (i) 3PS structures and (ii) SP-2PS structures. The procedure to determine the assembly modes of the SP-2PS structures has not been presented yet, in the literature. This paper presents the analytic form determination of the assembly modes of the SP-2PS structures. In particular, the closure equations of a generic SP-2PS structure will be written and their solution will be reduced to the solution of an eight-degree univariate polynomial equation with real coefficients. Finally, the proposed algorithm will be applied to a real case. The result of this study is that the assembly modes of any SP-2PS structure are at most eight, and the end-effector poses, which solve the direct position analysis of the parallel manipulators that generate those structures, are also eight.

A Kind of Kinematically Redundant Planar Parallel Manipulator for Optimal Output Accuracy

2009 ◽  
Author(s):  
Genliang Chen ◽  
Hao Wang ◽  
Yong Zhao ◽  
Zhongqin Lin
Keyword(s):  
Parallel Manipulator ◽  
Parallel Manipulators ◽  
Redundant Manipulators ◽  
Kinematic Redundancy ◽  
End Effector ◽  
Optimal Output ◽  
Parallel Structures ◽  
Planar Parallel Manipulator ◽  
Redundant Structure ◽  
Active Joints

Theoretically, parallel manipulators perform higher precision than their serial counterparts. However, the output accuracy is sensitive to their configurations and dimensions. This paper presents a kind of parallel manipulator with kinematically redundant structure, which can improve the output accuracy by optimizing the error transmission from the active joints to the end-effector. With the kinematic redundancy, free redundant variables can be defined as second task variables, which provide the possibility to select a proper configuration for least error transmission at any pose (the position and orientation) of the end-effector for a given task. Contrast to non-redundant manipulators, the output errors of the proposed manipulator, caused by the active joints input errors, can be optimized rather than determined. By this goal, new limbs with redundant parallel structures are introduced to non-redundant planar parallel manipulators. Numerical example shows that the new architecture has the potential to enhance the output accuracy for a given pose or prescribed trajectory of the end-effector.

Structure Synthesis of 3-RRS Type Spatial Compliant Parallel Manipulator

2010 ◽  
Vol 44-47 ◽  
pp. 1375-1379
Author(s):  
Da Chang Zhu ◽  
Li Meng ◽  
Tao Jiang
Keyword(s):  
Parallel Manipulator ◽  
Compliant Mechanisms ◽  
Screw Theory ◽  
Weight Ratio ◽  
Parallel Manipulators ◽  
Robot System ◽  
New Approach ◽  
Structure Synthesis ◽  
Rigid Joints ◽  
Type 3

Parallel manipulators has been extensively studied by virtues or its high force-to-weight ratio and widely spread applications such as vehicle or flight simulator, a machine tool and the end effector of robot system. However, as each limb includes several rigid joints, assembling error is demanded strictly, especially in precision measurement and micro-electronics. On the other hand, compliant mechanisms take advantage of recoverable deformation to transfer or transform motion, force, or energy and the benefits of compliant mechanisms mainly come from the elimination of traditional rigid joints, but the traditional displacement method reduce the stiffness of spatial compliant parallel manipulators. In this paper, a new approach of structure synthesis of 3-DoF rotational compliant parallel manipulators is proposed. Based on screw theory, the structures of RRS type 3-DoF rotational spatial compliant parallel manipulator are developed. Experiments via ANSYS are conducted to give some validation of the theoretical analysis.

scholarly journals Nitrogen-phosphate Fertilizers Based on Activation of Phosphorite Powder with Partially Ammoniated Mix of Phosphoric and Sulphuric Acids

2020 ◽  
pp. 1-10
Author(s):  
A. A. Rasulov ◽  
Sh. S. Namazov ◽  
B. E. Sultonov
Keyword(s):  
Citric Acid ◽  
Gross Domestic Product ◽  
Optimal Condition ◽  
Ammonium Sulphate ◽  
Weight Ratio ◽  
High Strength ◽  
Technological Parameters ◽  
Phosphate Fertilizers ◽  
First Time ◽  
Phosphoric Acids

In this article obtaining complex nitrogen-phosphate fertilizers based on activation of phosphorite powder with partially ammoniated mix of phosphoric and sulphuric acids have been studied. In order to reduce the foaming of the process, for the first time a partially ammoniated mix of acids was used. The optimal technological parameters for activation phosphorite powder with partially neutralized mixes of sulphuric and phosphoric acids are the followings: the mix of sulphuric and phosphoric acids with a ratio of SО3:Р2О5 = 1.2; рН of acids – 2.5; weight ratio of ammonium sulphate-phosphate slurry towards phosphorite powder is 100 : 20; temperature is 60°С; duration is 30 min.  The composition nitrogen-phosphate fertilizers obtained in optimal condition contains (wt., %): N – 11.55; Р2О5total -24.61; Р2О5acceptable by citric acid -21.66; Р2О5 acceptable by EDTA -20.24; Р2О5water-soluble  -13.02; CaOtotal -13.59; СаОacceptable by citric acid -11.43. In that condition, granulated products of nitrogen-phosphate can be produced with high strength. The advantage of offered promising technology concludes in reduction two times expenditure of the most expensive ammonia in comparison with ammonium sulphate production and an increase in gross domestic product.

A Statically Balanced Gough/Stewart-Type Platform: Conception, Design, and Simulation

2009 ◽  
Vol 1 (3) ◽  
Author(s):  
Marco Carricato ◽  
Clément Gosselin
Keyword(s):  
Sufficient Conditions ◽  
Parallel Manipulators ◽  
Point Of View ◽  
Theoretical Point ◽  
Constant Force ◽  
Parallel Mechanisms ◽  
End Effector ◽  
Neutral Equilibrium ◽  
The Difference ◽  
Elastic Elements

Gravity compensation of spatial parallel manipulators is a relatively recent topic of investigation. Perfect balancing has been accomplished, so far, only for parallel mechanisms in which the weight of the moving platform is sustained by legs comprising purely rotational joints. Indeed, balancing of parallel mechanisms with translational actuators, which are among the most common ones, has been traditionally thought possible only by resorting to additional legs containing no prismatic joints between the base and the end-effector. This paper presents the conceptual and mechanical designs of a balanced Gough/Stewart-type manipulator, in which the weight of the platform is entirely sustained by the legs comprising the extensible jacks. By the integrated action of both elastic elements and counterweights, each leg is statically balanced and it generates, at its tip, a constant force contributing to maintaining the end-effector in equilibrium in any admissible configuration. If no elastic elements are used, the resulting manipulator is balanced with respect to the shaking force too. The performance of a study prototype is simulated via a model in both static and dynamic conditions, in order to prove the feasibility of the proposed design. The effects of imperfect balancing, due to the difference between the payload inertial characteristics and the theoretical/nominal ones, are investigated. Under a theoretical point of view, formal and novel derivations are provided of the necessary and sufficient conditions allowing (i) a body arbitrarily rotating in space to rest in neutral equilibrium under the action of general constant-force generators, (ii) a body pivoting about a universal joint and acted upon by a number of zero-free-length springs to exhibit constant potential energy, and (iii) a leg of a Gough/Stewart-type manipulator to operate as a constant-force generator.

A New Measurement Device for Kinematic Calibration of Parallel Manipulators

2004 ◽  
Author(s):  
Abdul Rauf ◽  
Sung-Gaun Kim ◽  
Jeha Ryu
Keyword(s):  
Parallel Manipulators ◽  
Measurement Procedure ◽  
Initial Guess ◽  
Measurement Noise ◽  
Kinematic Calibration ◽  
Kinematic Parameters ◽  
End Effector ◽  
Experimental Procedure ◽  
New Device ◽  
Rotation Component

Kinematic calibration is a process that estimates the actual values of geometric parameters to minimize the error in absolute positioning. Measuring all the components of Cartesian posture assure identification of all parameters. However, measuring all components, particularly the orientation, can be difficult and expensive. On the other hand, with partial pose measurements, experimental procedure is simpler. However, all parameters may not be identifiable. This paper proposes a new device that can be used to identify all kinematic parameters with partial pose measurements. Study is performed for a 6 DOF (degree-of-freedom) fully parallel Hexa Slide manipulator. The device, however, is general and can be used for other parallel manipulators. The proposed device consists of a link with U joints on both sides and is equipped with a rotary sensor and a biaxial inclinometer. When attached between the base and the mobile platform, the device restricts the end-effector’s motion to 5 DOF and measures two position components and one rotation component of the end-effector. Numerical analyses of the identification Jacobian reveal that all parameters are identifiable. Computer simulations show that the identification is robust for the errors in the initial guess and the measurement noise. Intrinsic inaccuracies of the device can significantly deteriorate the calibration results. A measurement procedure is proposed and cost functions are discussed to prevent propagation of the inaccuracies to the calibration results.

Is There a Measurable Difference between the Left and Right Modified Myocardial Performance Indices, and Does This Change to Reflect Unilateral Myocardial Dysfunction in Pathology?

2015 ◽  
Vol 38 (4) ◽  
pp. 288-295 ◽  
Author(s):  
Alec W. Welsh ◽  
Amanda Henry ◽  
Neama Meriki ◽  
Aditi Mahajan ◽  
Linda Wu ◽  
...  
Keyword(s):  
Myocardial Dysfunction ◽  
Cross Sectional Study ◽  
Myocardial Performance ◽  
Performance Indices ◽  
Cross Sectional ◽  
Pilot Data ◽  
Design Function ◽  
Left And Right ◽  
First Time ◽  
Twin Pregnancies

Introduction: Fetal cardiac dysfunction may manifest itself unilaterally as right and left ventricles differing in design, function and load, measurable as differing in myocardial performance indices (MPIs). We wished to define this difference (‘delta-MPI' or DMPI), present its normal range and pilot its use in pathological pregnancy. Material and Methods: Prospective cross-sectional study of 324 normal singleton fetuses (16-38 weeks of gestation). Left and right modified MPI (LMPI and RMPI) were performed during a single examination using the ‘peak' valve click technique. Thirty-seven pathological singleton and monochorionic diamniotic twin pregnancies were compared as pilot data. Results: Modified MPIs (mean ± SD) were 0.45 ± 0.06 (LMPI) and 0.47 ± 0.09 (RMPI), being similar at 18 weeks' gestation with DMPI increasing slightly throughout pregnancy (0.02 ± 0.08). Both singleton intrauterine growth restriction (IUGR) and recipient twin-twin transfusion syndrome (TTTS) showed significantly elevated RMPI, LMPI and DMPI, most pronounced for DMPI (450 and 500% increase, respectively; p < 0.01). DMPI acquisition rates were 83.3% normal and 87.0% pathological. Discussion: We demonstrate for the first time differing intrafetal LMPI and RMPI in a large gestational cohort, with this difference increasing with gestational age. Pilot data confirm the potential for DMPI as a tool to assess unilateral myocardial function in singleton IUGR and recipient twins in TTTS, and further studies are under way to evaluate its clinical utility.

Wrench capabilities of planar parallel manipulators. Part I: Wrench polytopes and performance indices

Robotica ◽  
2008 ◽  
Vol 26 (6) ◽  
pp. 791-802 ◽  
Author(s):  
Flavio Firmani ◽  
Alp Zibil ◽  
Scott B. Nokleby ◽  
Ron P. Podhorodeski
Keyword(s):  
Parallel Manipulators ◽  
Joint Space ◽  
Linear Mapping ◽  
Redundant Manipulators ◽  
Task Space ◽  
Performance Indices ◽  
Study Case ◽  
And Performance ◽  
Planar Parallel Manipulators

SUMMARYThis paper is organized in two parts. In Part I, the wrench polytope concept is presented and wrench performance indices are introduced for planar parallel manipulators (PPMs). In Part II, the concept of wrench capabilities is extended to redundant manipulators and the wrench workspace of different PPMs is analyzed. The end-effector of a PPM is subject to the interaction of forces and moments. Wrench capabilities represent the maximum forces and moments that can be applied or sustained by the manipulator. The wrench capabilities of PPMs are determined by a linear mapping of the actuator output capabilities from the joint space to the task space. The analysis is based upon properly adjusting the actuator outputs to their extreme capabilities. The linear mapping results in a wrench polytope. It is shown that for non-redundant PPMs, one actuator output capability constrains the maximum wrench that can be applied (or sustained) with a plane in the wrench space yielding a facet of the polytope. Herein, the determination of wrench performance indices is presented without the expensive task of generating polytopes. Six study cases are presented and performance indices are derived for each study case.

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