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 Statically Balanced Gough/Stewart-Type Platform

2008 ◽  
Author(s):  
Marco Carricato ◽  
Cle´ment Gosselin
Keyword(s):  
Mechanical Design ◽  
Sufficient Conditions ◽  
Parallel Manipulators ◽  
Constant Force ◽  
Parallel Mechanisms ◽  
End Effector ◽  
Neutral Equilibrium ◽  
Prismatic Joints ◽  
Constant Potential ◽  
Elastic Elements

Gravity compensation of spatial parallel manipulators is a relatively recent topic of investigation. Perfect balancing, by either counterweights or elastic elements, 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 and used 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 design 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 balancing the weight of the end-effector in any admissible configuration. If no elastic elements are used, the resulting manipulator is balanced with respect to the shaking force too. Two Appendices are also provided, presenting formal and novel derivations of the necessary and sufficient conditions allowing i) a body arbitrarily rotating in space to rest in a state of 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 regardless of its configuration.

Kinematic Synthesis of a Spatial 3-RPS Parallel Manipulator

2003 ◽  
Vol 125 (1) ◽  
pp. 92-97 ◽  
Author(s):  
Han Sung Kim ◽  
Lung-Wen Tsai
Keyword(s):  
Parallel Manipulator ◽  
Degrees Of Freedom ◽  
Parallel Manipulators ◽  
Point Of View ◽  
Dimensional Synthesis ◽  
Kinematic Synthesis ◽  
End Effector ◽  
Solution Methods ◽  
Moving Platform ◽  
At Will

This paper presents the design of spatial 3-RPS parallel manipulators from dimensional synthesis point of view. Since a spatial 3-RPS manipulator has only 3 degrees of freedom, its end effector cannot be positioned arbitrarily in space. It is shown that at most six positions and orientations of the moving platform can be prescribed at will and, given six prescribed positions, there are at most ten RPS chains that can be used to construct up to 120 manipulators. Further, solution methods for fewer than six prescribed positions are also described.

Sequential decisions in the control of a space-ship (finite fuel)

1967 ◽  
Vol 4 (3) ◽  
pp. 584-604 ◽  
Author(s):  
John Bather ◽  
Herman Chernoff
Keyword(s):  
Optimal Policy ◽  
Point Of View ◽  
Control Procedure ◽  
Theoretical Point ◽  
New Approach ◽  
Final Approach ◽  
The Mean ◽  
The Difference ◽  
Miss Distance ◽  
Quadratic Case

This paper is a sequel to [1] and considers a more realistic formulation of the same question: that of finding an optimal policy for controlling the path of a space-ship as it moves towards its target. The difference here is that we no longer suppose there is an infinite quantity of fuel, always available at a fixed price, for modifying the current direction of motion. This complicates the problem of reducing the final miss distance, by introducing an extra variable. As before, we shall be particularly concerned to find a control procedure which always minimizes the mean square terminal miss. From the theoretical point of view we are also interested to see whether the techniques used to approximate the optimal policy can be extended, and how far we shall be forced to adopt a new approach. Results are derived which provide bounds on the form of the optimal policy. The derivation depends on a comparison technique whose validity is intuitively obvious, but which is still only a conjecture. However, further confirmation is obtained in the quadratic case from asymptotic expansions giving the form of the solution both when the space-ship is far away from its target and during its final approach.

scholarly journals SHELL WORDS IN ANATOMY A CONTRASTIVE STUDY OF BULGARIAN AND ENGLISH ANATOMICAL SYSTEMS

2018 ◽  
Vol 28 (7) ◽  
pp. 2283-2287
Author(s):  
Ivaylo Dagnev ◽  
Mariya Saykova ◽  
Maya Yaneva
Keyword(s):  
Point Of View ◽  
Semantic Features ◽  
Theoretical Point ◽  
Contrastive Study ◽  
Anatomical Terminology ◽  
General Terms ◽  
Reference Potential ◽  
The Difference ◽  
Anatomical Objects ◽  
Shell Nouns

Shell words are a particular category of lexemes that make up an open-ended functionally defined class of abstract nouns having the potential to be as conceptual shells for complex, proposition-like pieces of information. Examples include: “fact”, “case”, “idea”, “problem”, “position”, “cause”, “situation”, “something”, etc. The idea of a particular class of words that group semantic features, but are not related to a referent is also found in many authors. Such words have greater reference potential and thus become useful for naming different referents (onomasiological salience). From a theoretical point of view, the need for a context to determine the meaning of a single lexeme is in fact equivalent to deleting the difference between polysemy and vagueness. Shell nouns are indexical words or "hollow words, envelopes" because their meaning is incomplete; they only point to what can fill the envelope, but still give it some structure. Thus, the meaning associated with these shell units is both context-related and in turn generates a linguistic context. At first glance it seems strange that generalized words such as shells are not hyperonimic, but in connection with the nature of the anatomical terms (physically perceived) it is important to note that it is precisely words from the basic level that are conceptualized as sensory and functional gestalts. The eventual clash between the specificity of the object and the abstract nature of terms causes the conflict in terminology. Once again, the choice of a linguistic rather than a terminological approach to the names of the anatomical objects is argued. The current research assumes that shell function may be applicable to specific nouns, i.e. anatomical terms, the so-called termini generales. In both Bulgarian and English anatomical terminologies, there are about 190 such terms that are head words in anatomical expressions and occur in all parts of anatomy, e.g. terms such as: glava (en – head), greben (en – crest), gynka (en –fold), klon (en – branch), list (en – leaf), plocha (en – plate), sloy (en – layer), tyalo (en – body), vryzka (en – “link”, “connection”), etc. What is special about them is that with their help are formed the names of organs in the different systems. Their semantic value is contextually defined. They "mark” large branches in the anatomical terminology system and are expressions of terminological multiplicity. Obtained through specialization of commonly used nouns, general terms are a manifestation of re-terminologization through metaphorical projection. In our view, termini generales have lost their metaphorical status (if they have one) and some of them serve as shell nouns. We also perform a cross-linguistic Bulgarian – English analysis of shells in both anatomical systems.

scholarly journals Ship waves: The relative efficiency of bow and stern

1935 ◽  
Vol 149 (868) ◽  
pp. 417-426 ◽  
Keyword(s):  
Wave Resistance ◽  
Point Of View ◽  
Experimental Results ◽  
Theoretical Point ◽  
Surrounding Water ◽  
Fluid Friction ◽  
Simple Modification ◽  
Ship Waves ◽  
The Difference ◽  
Asymmetrical Model

It seems fairly certain that one of the main causes of difference between theoretical and experimental results is the neglect of fluid friction in the calculation of ship wave, and further that the influence of fluid friction may be regarded chiefly as one which makes the rear portion of the ship less effective in generating wave than the front portion. The process may be pictured, possibly, in terms of a friction belt or boundary layer whose more important effect is equivalent to smoothing the lines of the model towards the rear. Some calculations were made from this point of view in a previous paper, the purpose then being to show how such an asymmetry, fore and aft, reduced the magnitude of interference effects between how and stern waves. We may also describe the frictional effect as a diminution in the effective relative velocity of the model and the surrounding water as we pass from how to stern. This is not very satisfactory from a theoretical point of view; but, on the other hand, it leads to a comparatively simple modification of expressions for the waves produced by the model. From a formal point of view, we may regard the modification as an empirical introduction of a reducing factor to allow for decrease in efficiency of the element of the ship's surface as we pass from how to stern. There are now available experimental results, for wave profiles as well as for wave resistance, which made it possible to attempt such a comparison. The following work is limited to a few simple cases, and the assumptions are made in as simple a form as possible for the purpose of the calculations; these deal with the wave profile and wave resistance of a model of symmetrical form, and also with the difference between motion how first and motion stern first for a simple asymmetrical model.

Sequential decisions in the control of a space-ship (finite fuel)

1967 ◽  
Vol 4 (03) ◽  
pp. 584-604 ◽  
Author(s):  
John Bather ◽  
Herman Chernoff
Keyword(s):  
Optimal Policy ◽  
Point Of View ◽  
Control Procedure ◽  
Theoretical Point ◽  
New Approach ◽  
Final Approach ◽  
The Mean ◽  
The Difference ◽  
Miss Distance ◽  
Quadratic Case

This paper is a sequel to [1] and considers a more realistic formulation of the same question: that of finding an optimal policy for controlling the path of a space-ship as it moves towards its target. The difference here is that we no longer suppose there is an infinite quantity of fuel, always available at a fixed price, for modifying the current direction of motion. This complicates the problem of reducing the final miss distance, by introducing an extra variable. As before, we shall be particularly concerned to find a control procedure which always minimizes the mean square terminal miss. From the theoretical point of view we are also interested to see whether the techniques used to approximate the optimal policy can be extended, and how far we shall be forced to adopt a new approach. Results are derived which provide bounds on the form of the optimal policy. The derivation depends on a comparison technique whose validity is intuitively obvious, but which is still only a conjecture. However, further confirmation is obtained in the quadratic case from asymptotic expansions giving the form of the solution both when the space-ship is far away from its target and during its final approach.

scholarly journals SHELL WORDS IN ANATOMY A CONTRASTIVE STUDY OF BULGARIAN AND ENGLISH ANATOMICAL SYSTEMS

2018 ◽  
Vol 28 (7) ◽  
pp. 2283-2287
Author(s):  
Ivaylo Dagnev ◽  
Mariya Saykova ◽  
Maya Yaneva
Keyword(s):  
Point Of View ◽  
Semantic Features ◽  
Theoretical Point ◽  
Contrastive Study ◽  
Anatomical Terminology ◽  
General Terms ◽  
Reference Potential ◽  
The Difference ◽  
Anatomical Objects ◽  
Shell Nouns

Shell words are a particular category of lexemes that make up an open-ended functionally defined class of abstract nouns having the potential to be as conceptual shells for complex, proposition-like pieces of information. Examples include: “fact”, “case”, “idea”, “problem”, “position”, “cause”, “situation”, “something”, etc. The idea of a particular class of words that group semantic features, but are not related to a referent is also found in many authors. Such words have greater reference potential and thus become useful for naming different referents (onomasiological salience). From a theoretical point of view, the need for a context to determine the meaning of a single lexeme is in fact equivalent to deleting the difference between polysemy and vagueness. Shell nouns are indexical words or "hollow words, envelopes" because their meaning is incomplete; they only point to what can fill the envelope, but still give it some structure. Thus, the meaning associated with these shell units is both context-related and in turn generates a linguistic context. At first glance it seems strange that generalized words such as shells are not hyperonimic, but in connection with the nature of the anatomical terms (physically perceived) it is important to note that it is precisely words from the basic level that are conceptualized as sensory and functional gestalts. The eventual clash between the specificity of the object and the abstract nature of terms causes the conflict in terminology. Once again, the choice of a linguistic rather than a terminological approach to the names of the anatomical objects is argued. The current research assumes that shell function may be applicable to specific nouns, i.e. anatomical terms, the so-called termini generales. In both Bulgarian and English anatomical terminologies, there are about 190 such terms that are head words in anatomical expressions and occur in all parts of anatomy, e.g. terms such as: glava (en – head), greben (en – crest), gynka (en –fold), klon (en – branch), list (en – leaf), plocha (en – plate), sloy (en – layer), tyalo (en – body), vryzka (en – “link”, “connection”), etc. What is special about them is that with their help are formed the names of organs in the different systems. Their semantic value is contextually defined. They "mark” large branches in the anatomical terminology system and are expressions of terminological multiplicity. Obtained through specialization of commonly used nouns, general terms are a manifestation of re-terminologization through metaphorical projection. In our view, termini generales have lost their metaphorical status (if they have one) and some of them serve as shell nouns. We also perform a cross-linguistic Bulgarian – English analysis of shells in both anatomical systems.

Evaluation of the Position Error of Four Non-Overconstrained Spherical Parallel Manipulators

2012 ◽  
Vol 162 ◽  
pp. 194-203
Author(s):  
A. Chaker ◽  
A. Mlika ◽  
M.A. Laribi ◽  
L. Romdhane ◽  
S. Zeghloul
Keyword(s):  
Parallel Manipulator ◽  
Parallel Manipulators ◽  
Position Error ◽  
Point Of View ◽  
Good Precision ◽  
End Effector ◽  
High Rigidity ◽  
Manufacturing Errors ◽  
Position And Orientation ◽  
Spherical Parallel Manipulator

The 3-RRR spherical parallel manipulator is known to be highly overconstrained, which causes several problems of mounting the mechanism, but has the advantage of having high rigidity thus a good precision. Several works in the literature proposed non-overconstrained versions of this mechanism. However, very few works dealt with the problem of the consequence of modifying an overconstrained mechanism into a non-overconstrained one, mainly from an accuracy point of view. In this work, we present an analysis of the accuracy of four different non-overconstrained SPMs, i.e., 3-RSR, 3-RCC, 3-RRS, and 3-RUU. These four SPM are then evaluated in translational and rotational accuracy due to manufacturing errors. The error on the position and orientation of the end-effector, due to manufacturing errors, are computed in 100 different configurations within their workspace. These SPMs are then compared among each other and we showed that the 3-RRS has the best compromise between the translational and rotational accuracy.

Agents and their Actions

Philosophy ◽  
1998 ◽  
Vol 73 (2) ◽  
pp. 219-245 ◽  
Author(s):  
MARIA ALVAREZ ◽  
JOHN HYMAN
Keyword(s):  
Philosophy Of Mind ◽  
Human Action ◽  
Point Of View ◽  
Philosophy Of Action ◽  
Theoretical Point ◽  
Reference Guide ◽  
The Past ◽  
General Terms ◽  
Significant Events ◽  
The Difference

In the past thirty years or so, the doctrine that actions are events has become an essential, and sometimes unargued, part of the received view in the philosophy of action, despite the efforts of a few philosophers to undermine the consensus. For example, the entry for Agency in a recently published reference guide to the philosophy of mind begins with the following sentence:A central task in the philosophy of action is that of spelling out the differences between events in general and those events that fall squarely into the category of human action.There is no consensus about what events are. But it is generally agreed that, whatever events may prove to be, actions are a species or a class of events. We believe that the received view is mistaken: actions are not events. We concede that for most purposes, the kind of categorial refinement which is involved in either affirming or denying that actions are events is frankly otiose. Our common idiom does not stress the difference between actions and events, at least not in general terms, because it has no need to. Perhaps it sounds a little odd to say that some events are performed; but if we balked at describing, say, the abdication of Edward VIII as one of the politically significant events in Britain in 1936, it could not be for metaphysical reasons. And since actions, like events, are datable — though often, as we shall see, only imprecisely — actions are said to take place and to occur. But an important class of actions consist in moving something; indeed, according to many philosophers, every action consists in moving something. And when we consider actions of this sort from a theoretical point of view it becomes imperative to distinguish between actions and events. Or so we shall argue.

Rings of Morita contexts which are maximal orders

2016 ◽  
Vol 15 (07) ◽  
pp. 1650129 ◽  
Author(s):  
Bülent Saraç ◽  
Evrim Akalan ◽  
Pınar Aydoğdu ◽  
Hidetoshi Marubayashi
Keyword(s):  
Quotient Ring ◽  
Sufficient Conditions ◽  
Point Of View ◽  
Necessary And Sufficient Conditions ◽  
Maximal Order ◽  
Theoretical Point ◽  
Morita Context ◽  
Maximal Orders ◽  
Necessary And Sufficient

Let [Formula: see text] be a ring of Morita context which is a prime Goldie ring with its quotient ring [Formula: see text]. We define the notion of an [Formula: see text]-maximal module in [Formula: see text] and that of an [Formula: see text]-maximal module in [Formula: see text] from order theoretical point of view and give some necessary and sufficient conditions for [Formula: see text] to be a maximal order in terms of [Formula: see text]-module [Formula: see text] and [Formula: see text]-module [Formula: see text]. In case [Formula: see text] is a maximal order, we explicitly describe the structure of [Formula: see text]-[Formula: see text]-ideals. These results are applied to obtain necessary and sufficient conditions for [Formula: see text] to be an Asano order or a Dedekind order.

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