FR2575452A1 - Method and device for preventing an element attached to a movable installation from being affected by the movements of this installation - Google Patents

Abstract

The present invention relates to a method and a device for preventing an element attached to a movable installation from being affected by the movements of this installation. According to the present invention, the characteristic sizes of the device, which comprises at least one jack, at least one accumulator and a number of pulleys, are determined so that the mechanical and pneumo-oil stresses are substantially equal. The present invention may be applied to the field of marine pitch-damping devices.

Description

The present invention relates to a device for subtracting an element attached to a mobile installation to the influence of movements of limited amplitude of this installation.

The device according to the present invention can be used, especially in the marine field, as anti-heave slide, or heave compensator.

Indeed, at sea, the swell causes, among other effect, the heave of the floating machines. When these support rigs, it is necessary to compensate for the heave so that the drill bit is permanently in contact with the bottom of the hole.

To do this, there are three major families of devices, namely - those that are placed in the drill string, - those that are inserted between the packing and the lifting system
drilling rig, - those that are integrated into the lifting system.

The present invention, when applied to the marine domain, includes a particular device of the third family. This device is one of those that solve the problem by making mobile fixed muffle corresponding to the Anglo-Saxon name of "crown block". This muffle will be referred to by the term "first muffle", just as the mittle corresponding to the Anglo-Saxon name of "traveling block" will be designated by the term "second muffle".

The systems directly connected to the lifting device, according to the prior art, generally comprise at least one jack itself connected to pneumatic accumulators. These accumulators occupy a large volume which is penalizing.

The volume of these accumulators is an important parameter in the determination of a lifting system.

Another important quantity is the variation of the effort to be exerted on the second muffle as a function of the stroke of the mobile installation relative to a constant value that this second muffle should bear.

The difference between the actual effort and this constant value will be qualified as error.

The present invention makes it possible to reduce the volume of the accumulators and / or to reduce the error.

Thus, the present invention relates to a device for subtracting an element attached to a mobile installation to the movements of this installation, this device comprising a first and a second muffle, the latter serving to hook said element, said first muffle being connected both to the axis of a first intermediate pulley and the axis of a second intermediate pulley by a first and U | i ;;; second rod respectively, a first pulley and a second pulley Fired relative to the mobile installation the axis of the first fixed pulley, respectively of the second fixed pulley, being connected by a third rod, respectively by a fourth rod, to the axle of the first intermediate pulley, respectively of the second intermediate pulley, a first and a second retaining member, a cable connecting these two retaining members passing, successively, starting from the second retaining member, by the first fixed pulley; the first intermediate pulley, ie the first block and the second block forming at least one loop, the second intermediate block and the second fixed block, at least one jack, one end of which is connected to the first block and the other is connected to the first block. mobile installation and at least one accumulator in oleopneumatic connection with said cylinder, the first and the second rods having an identical length equal to C, likewise, the third and fourth rods have an identical length equal to B, the half distance separating the axis of the first and second fixed pulley being equal to A and the distance separating the axis of the first mittle of the plane joining the axes of the first and second pulleys is equal to G.

The device according to the invention is characterized in that the magnitudes
A, B, C, G and the passage of the cable are determined so that the mechanical forces Fm and oleopneumatic F v are substantially equal over at least a portion of the race.

The device according to the invention may comprise an auxiliary correction jack whose effort is adjustable.

The device according to the invention may comprise a measuring member to know the force exerted by the second muffle and control means of the auxiliary cylinder.

It will not depart from the scope of the present invention if the angle formed by the line joining the axis of the first and second fixed pulley respectively and the first and second intermediate pulley respectively with the straight line containing the portion of the cable. joining these two pulleys is at least equal to 30.

This angle can be at least equal to 45. Good results can be obtained with an angle close to 653 or higher.

et

The first muffle may include weighting means. In the case where the main jack or cylinders are parallel to the stroke of the first muffle, the expression of the mechanical forces Fm and oleopneumatic F v can be given respectively by the expressions

and

<tb> F <SEP> v <SEP> = <SEP> PgSv <SEP>(<SEP> K <SEP> (1 <SEP> - <SEP> Short <SEP> Run) t
<tb> in which
Q = effort from everything that contributes to the tension of the cables,
N = number of strands of the block, p = angle formed by the strand of the cable between the fixed pulley and
the intermediate pulley and the right joining the centers of these
two pulleys,
U = fraction of Fm independent of the tension of the cables, 9 = angle defined by direction of the straight line joining the center of the
first and second fixed pulley and the direction of the right
joining the axes of the first fixed pulley and the first
intermediate pulley,
(= angle formed by the cable strand joining the intermediate pulley
and a mop block pulley and the right joining the centers of these
two pulleys,
9 = angle formed by the direction of the line joining the center of
first and second fixed pulley and the direction of the right
joining the centers of the first muffle and the first pulley
intermediate,
Pg = the precharge pressure of the accumulators,
Sv = the section of the cylinders,
K = Va / Sv Ccdc with
Va = volume of accumulators,
Ccdc = total stroke of first muffle,
Reduced stroke = actual stroke / Ccdc gas expansion coefficient.

We can determine the quantities A, B, C, G and the cable path to make linearized expressions of Fn and Fv identical.
The expression of the oleopneumatic forces can be linearized by considering only the forces given by the mathematical expression of these forces at the two limit positions of the race of the first muffle.

The present invention also relates to a method for determining the geometry of a device for subtracting an element attached to a mobile installation to the movements of this installation, this device comprising a first and a second muffle, the latter serving to hook said element, said first muffle being connected both to the axis of a first intermediate pulley and to the axis of a second intermediate pulley by a first and a second rod respectively, a first pulley and a second pulley fixed relative to the first mobile installation, the axis of the first fixed pulley, respectively of the second fixed pulley, being connected by a third pin, respectively by a fourth pin, to the axis of the first intermediate pulley respectively of the second intermediate pulley, a first and a second retaining member, a cable connecting these two retention members passing, successively, starting from the second retaining member, by the first fixed pulley, the first intermediate pulley, the first block and the second block by forming at least one loop, the second intermediate pulley and the second fixed pulley, at least one jack, one end of which is connected to the first muffle and the other is related to the mobile installation and at least one accumulator in oleopneumatic connection with said cylinder, the first and second rods having an identical length equal to C, likewise, the third and fourth rods have a identical length equal to B, the half distance separating the axis of the first and second fixed pulley being equal to A and the distance separating the axis of the first muffle from the plane joining the axes of the first and second pulleys is equal to G .

According to the method, the quantities A, B, C, G and the passage of the cable are determined so that the mechanical forces Fm and oleopneumatiques F v are substantially equal over at least a portion of the stroke.

According to one variant, the quantities A, B, C, G and the passage of the cable can be determined so that linearized expressions of the mechanical forces Fm and oleopneumatic F v correspond to curves parallel to each other.

According to another variant, the quantities A, B, C, G and the passage of the cabre can be determined so that linearized expressions of the mechanical forces Fn and oleopneumatic Fv correspond to curves having at least one common point
The present invention will be better understood and its advantages will become more clearly apparent from the following description of a particular example, illustrated by the appended figures, in which: FIG. 1 represents a simple device of the following compensator
the prior art, the right and left part of this figure
corresponding to different positions of a mobile installation, - Figures 2 and 3 illustrate different arrangements of pulleys
used to guide the cable (it should be noted that for each of these
figures, the right and left parts represent
different, in reality it is better to carry out
symmetrical configurations), - Figures 4A to 4C show schematically different
positions of the device according to the invention in operation, - Figure 5 allows the definition of certain variables which
characterize the device according to the invention, and - Figure 6 represents the response of the mechanical system and the system
oleo.

The example described below relates to a loop compensation system.

It is recalled that, when the heave of a floating machine 1 is compensated by moving a first muffle 2 relative to the derrick 3 of a drilling rig, for example, it is necessary and sufficient to move the first muffle 2 less than the amplitude of the heave so that the second muffle 4 is stationary relative to the ford.

If, indeed, the distance from the bottom 5 e. to the floating apparatus 1 increases, it is necessary that the distance of the first mute 2 the floating craft 1 decreases.

But, if one reasons to constant cable length 6, since the first muffle approaches the winch / ot fixed point 8, the second muffle 4 moves away from the pre, z, ier. The compensation stroke of the heave is therefore less than the heave.

During this movement, the cable 6 has rolled up and unrolled on the pulleys of both muffles 2 and 4 and this is unacceptable from the point of view of working the cable. On the other hand, the tension in the different portions of the cable remained constant, the movement of the first muffle 2 having only negligible variations in the angle of the dead and fast strands of the cable with the feet of the derrick.

 It is therefore necessary that the displacement of the first muffle 2, that is to say the variation of the distance of the first muffle 2 to the winch 7, does not cause a variation in the length of the cable path 6.

 To do this, it suffices to make, for example, a cable path such that it passes through two ribs of fixed length of a deformable triangle, the third dimension of variable length, which provides the variation in distance of the first muffle. to the floating craft, not being traversed by the cable (Fig. 2).

In fact, the vertices of this triangle correspond to the centers 9, 10 and 11 of the pulleys 12, 13, 14 on which the cable passes. It can be shown that the cable length remains strictly constant if the pulleys have the same diameter.

If the intermediate pulley 13 is located below the fixed pulley 14, the path of the cable intersects the ribs of length fi of the deformable triangle (Fig. 3, left).

If it is located above and if the triangle only has sharp angles, the cable path will cut one side (Fig 2, right).

But if the triangle has an obtuse angle, the path of the cable will remain parallel to the fixed length sides of the triangle (Fig 3, right).

It is also possible to make a cable run with only two pulleys (Fig. 2, left) and which provides a path with a constant length insofar as the distance between the winch 7 and the point of attachment 8 of the dead end 15 in the center 17 of the intermediate pulley 16 can be considered constant. This is achieved when, on the one hand, the average position of the intermediate pulley 6 is located on or in the immediate vicinity of the straight line joining the point of attachment 8 of the dead end 15 or the winch 7 to the articulation point 18 of the rod 19 and the derrick 3 and when, on the other hand, the movement of the intermediate pulley 16 is not too important.

When the variation of the length of the cable path 6 is not compensated, all the suspended load 20 as well as the tension of the fast strand 23 and the dead end 15 are supported by the jacks 21 and 22 before being by the feet of the mast 3. (Fig. 1).

When this variation is compensated, part of the load and the tension of the dead and fast strands 23 is transferred directly to the mast 3 via the arms, or rods 24 and 25 of the device without passing through the jacks (FIG. 2).

This fraction of load not passing through the cylinders 21 and 22 varies as a function of the position of the first block or first pulley 12 and the law according to which this variation is made depends on the geometric characteristics of the compensation device and its relative positioning. at mast 3
If, therefore, the variation in length is not compensated, it is necessary, in order to balance a constant load, whatever the position of the first muffle 2, to maintain constant the pressure in the jacks 21, 23. In the case of FIG. 2, 27 denotes a liquid gas separator.

If the pressure is kept constant using gas accumulators 26, it will be necessary for the volume thereof to be as large as possible so that the pressure variation due to the polytropic expansion of the gas is low. possible.

If, on the other hand, the variation of length is compensated, for a constant suspended load, the apparent load on the jacks is variable.

It is possible, by sizing and positioning the system, that for a constant suspended load, the apparent load variation is greater or smaller.

If this variation is small, one is practically reduced to the preceding problem.

On the other hand, if it is strong, it can still be satisfied, provided that it is substantially identical to the pressure variation that the polytropic expansion of the accumulator gas entails.

This sensitive identity of the apparent variation of the load on the cylinders and the pressure variation due to the polytropic relaxation constitutes the principle of the compensation method proposed.

The compensation system is positioned relative to the lower position of the first muffle 28 once the magnitudes A and G are selected (Fig. 4C).

 t is the distance from the center of the deflection pulley or fixed pulley 29 the axis 30 of the derrick 3 and G the difrerence of the ribs of the center 31 of the pulley 29 and the center 32 of the pulleys of the first muffle 28 when thoseoci are. e. low position (case of Figure 4C).

The system is dimensioned by the lengths B and C of the articulated arms or rods 34 and 3. It is possible, once these quantities are known, to set up the intermediate pulley 33 regardless of the stroke.

The device will be perfectly defined once the path of the cable has been. that is to say when we have defined the direction of passage of the cable on the pulleys and their dimensioning, and the position of the cylinders, in this case their inclination with respect to the stroke.

The law of variation of the apparent load on the cylinders will therefore depend, as regards the geometry of the system and for each race set by the manufacturer's specifications, six independent parameters.

To simplify the description, it will now be considered that the inclination of the cylinders relative to the stroke is zero.

The effort Fm that the system exerts on the top 3 of the derrick generally designated by the Anglo-Saxon term "water-table" can be considered as the resultant of two efforts U and Q, U being defined as the fraction of Fm independent of the cable tension.

U will itself later be considered as the sum of two efforts Uf and Uc, Uc being the fraction of U dependent on the race.

Uf, independent of the race, corresponds to the weights of the movable elements fixed to the support carriage 47 of the first muffle and animated at the same time as him with a linear movement corresponding to the heave (first muffle, rods of cylinders, etc.).

Uc corresponds to the fraction of the weight of the intermediate pulley 33 and rods, arms or rods, which is carried on the carriage of the first muffle. This is a function of the race but also depends on the positioning and size of the system.

The force Q comes from all that contributes to the tension of the cables, that is to say the suspended load W, the weight of the second muffle and the weight of the cables themselves.

It also depends, all things being equal, sizing and positioning of the device, the race, and of course the number of N strands of the hauling.

The most general expression of Fm, as a function of the angles (3, re and which themselves are explained by means of the stroke and the quantities which determine the positioning and the dimensioning, is written:

Figure 5 defines the angles (3, T, Oet #.

In this figure, the reference 30 designates the axis of the derrick, the reference 28 a pulley of the first muffle, the reference 34 an intermediate pulley and the reference 31 a pulley or fixed pulley.

The angle # is the angle formed by the cable strand between the fixed pulley 31 and the intermediate pulley 34 and the straight line 38 joining the center 39 and 40 of these two pulleys. In FIG. 5, two variants of cable passage have been envisaged, one of these
passages, drawn in solid line, is designated by reference 37 and
the other in dashed line denoted by the reference 41, the first defined the angle sse and the second the angle pi.

The angle T is defined by the cable strand joining the pulley
intermediate 34 and a block pulley 28, and the straight line 42 joining
the centers 40 and 43 of these two pulleys.

In Figure 5, there is shown the passage of the strand of the cable 44
passing outside the two pulleys and defining the angle &gamma; e.

The angle # is defined by the horizontal direction 45 and the direction of the line 38. Similarly, the angle θ is defined by the direction of the
right 42 and the horizontal direction.

It is recalled that sset Fi are independent of the race and only
depending on the sizing of the system whereas 9 and Y depend on the dimensioning and the stroke.

 If the intermediate pulley 34 is located below the water-table -46 (Fig. 3, left-hand side) ss and Tne may not be zero and this is the most general formula that applies.

If the intermediate pulley is located above the plate located at
top of the mast or derrick 3 designated by the term anglo-såxon "water-
table ", but beyond the return pulley with respect to the pulleys of the
first muffle, angle &gamma; is zero if the intermediate pulleys and the
first muffle have the same diameter (Fig 2, right side and Fig 5).

The expression of Fm / Q is simplified and becomes

If the intermediate pulley always located above the water-table is also between the return pulley and the crown block pulleys, and if they have the same diameter, then ss is also zero and the Fm expression becomes
Q
Fm = 1 + U (Fig 3 right and Fig 5) (3)
QQ
It is therefore independent of sizing and positioning as well as the race.

This is the case which is to obtain, over the entire course of an oil system, a most constant effort possible is well known from previous air.

 P and V denote the pressure and the gas volume of the accumulators when the stroke of the cylinders is x, between 0 and Ccdc Pg and Va denote the pre-inflation pressure and the volume of the accumulators, that is to say their pressure and volume in gas when the cylinders have completed their entire stroke Ccdc 'and PM the maximum pressure for the service, that is to say that which appears when the jacks are at the origin of their race.

The force Fv supplied by the cylinders according to the race is written:

<tb> F <SEP> v <SEP> = <SEP> 9 <SEP> 1 <SEP> - <SEP> (i <SEP> - <SEP> C <SEP> editedIT1 = <SEP> + <SEP> C <SEP> our <SEP> reduced <SEP> - <SEP>'<SEP> C4)
<tb> 5v <SEP> K <SEP> 1
<tb><SEP> v
<tb> - "Reduced Skim" is the dimensionless expression of the stroke, ie its value divided by the total stroke Ccdc set by
X
the specifications (Reduced race =).

Ccdc - K is also a dimensionless variable. It is equal to
volume Va accumulators divided by the total stroke Ccdc and by
section S, of the cylinders (K = Va / Sv.Ccdc)
In the zone where the polytropic relaxation of the gas will be used, K will be between 5 and 50 (and even generally close to 10) and stroke reduced between 0 and 1.

Fv In this area (Fig. 6), the representation of is practically
Pg.Sv a straight line.

We can, with an accuracy of a few thousandths, linearize this phenomenon using, for example, the method of the minimum quadratic difference and thus write

<tb> Fv
<tb> S <SEP> 9 <SEP> P <SEP> PgC, urse <SEP> reduced <SEP> + <SEP> d <SEP> (5)
<tb> g
<tb><SEP> v
<tb><SEP> M <SEP> [A '(K) .Racing <SEP> reduced <SEP> + <SEP>B'd (K) | <SEP> (6)
<Tb>
K, Ad (k '), Bd (K), A'd (K) and 6'd (K) are values that are determined once only one of them is.

In fact, it will always be possible for all operating pressures P to linearize the polytropic expansion and find a line such that:

<tb> Fv <SEP> ~ <SEP> ad (K) <SEP> Short <SEP> Run <SEP> + <SEP> bd (KJ <SEP> (7)
<tb><SEP> v
<tb> It has been established that the most general expression of the force Fm that the system applies to the cylinders, related to the load Q (that which contributes to the tension of the cables) is written

The angles ss, γ, γ and γ take a well-defined value, on the one hand, for each position of the first muffle and, on the other hand, for each of the values which have been fixed to the five independent geometrical parameters which position and dimension the device.

 It is also possible to linearize this expression, as has been done for the response of the cylinders and always, for example, using the method of the minimum squared deviation.

In fact, if we do it by supposing that U is zero, we can write Fm = Am.Course reduced + Bm (U = O) + U (9)
QQ
The most satisfactory system geometries are those which make the mechanical responses Fm and oleopneumatic F v as close as possible to each other and throughout the race. The efforts Fm and Fv can be expressed by the formulas 1) and (4).

Geometries of the system can be determined by making identical linearized equations simpler, for example for the oleopneumatic system

<tb><SEP> F <SEP> v <SEP> C
<tb> - = <SEP> reduced <SEP> a
<tb><SEP> d <SEP> ourse <SEP> reduced <SEP> + <SEP> bd
<tb><SEP> v
<tb> and for the mechanical system

pour toutes les valeurs de Q inféri-eures à la charge QMAX fixée par le cahier des charges.<tb> Fn <SEP> An <SEP> Short <SEP> Run <SEP> + <SEP> Bm <SEP> U <SEP> (11)
<tb> Q <SEP> Am <SEP> Run <SEP> + <SEP> Bm <SEP> Q
<Tb>
For this it is necessary that

for all Q values below the QMAX load specified in the specifications.

U is here supposed to be independent of the race. This is not strictly accurate, but it greatly simplifies the present description and will simplify it even more in the second part without causing it to be inaccurate. It suffices, in fact, with the notations defined above, to write the most general expression by replacing U with Uf + Uc. Linearization is then written

<tb><SEP> Fn <SEP> = <SEP> As <SEP> C <SEP>, <SEP> ~ <SEP> Uf
<tb> T <SEP> n <SEP> on <SEP> ourse <SEP> reduced <SEP> + <SEP> Bm <SEP> (13)
<tb><SEP> Q
<tb> where A'm, 8, m and Uf are slightly different from Am, Bm and U.

Only the calculation programs will work with A'm 'B' n e t Uf, The description will be made with Am, Bm and U which does not change anything since the expressions of the formulas are identical.

In fact, it is possible to retain the analytic expression of the response of the oleopneumatic system rather than the linearized expression since, as we have seen, the analytic expression is almost perfectly linear.

The values of the pressure at each end of the race will be used and which result from the formulas already given. We will consider the response of this system is linear between these two points.

qui peut s'écrire

3 autre part, la réponse linéarisée du système mecanique représentée par
Fm = Q(AmCourse réduite + Bm) + U (16)
A chaque extrémité de la course, cette expression s'écrit
Fmm = Q(Am + Bm) + U (17)
FmM = Q Bm + U (18) mais Fmm = Pg S, et FmM = p M Sv (19)

Par ailleurs, le cahier des charges fixe toujours les conditions de fonctionnement extrêmes, à savoir la pression maximale PMAX, qui ne doit pas être dépassées dans le circuit et la charge maximale qui dot pouvoir être manoeuvrée, et qui déterminent QMAX
Sachant que, a'une part, le fonctionnement avec la charge maximale entraine l'apparition de la pression la plus importante et que, d'autre part, pour une charge donnée, la pression est maximale quand la course est nulle , il est possible d'écrire
Fm MAX = QMAX-BM + U (21) et
Fm MAX = Sv.PMAX (22)

The initial-al state and the final state of the transformation are linked by relation

which can be written

3 the other hand, the linearized response of the mechanical system represented by
Fm = Q (AmCourse reduced + Bm) + U (16)
At each end of the race, this expression is written
Fmm = Q (Am + Bm) + U (17)
FmM = Q Bm + U (18) but Fmm = Pg S, and FmM = p M Sv (19)

In addition, the specifications always set the extreme operating conditions, namely the maximum pressure PMAX, which must not be exceeded in the circuit and the maximum load that can be manipulated, and which determine QMAX
Knowing that, on the one hand, the operation with the maximum load causes the appearance of the most important pressure and that, on the other hand, for a given load, the pressure is maximum when the stroke is zero, it is possible to describe
Fm MAX = QMAX-BM + U (21) and
Fm MAX = Sv.PMAX (22)

The specifications fixing PMAX and to know QMAX, the design office determining U, the section of the cylinders is known thanks to the preceding formula once the mechanical system sizes and positioned.

It is also possible to determine the air volume of the accumulators, which means that the oleopneumatic and mechanical systems have responses represented by lines with the same slope for a load Q.

This requires that

It remains to be done that the now parallel lines which represent the responses of the mechanical and oleopneumatic systems are combined.

This amounts to setting the operating pressure at a point of the abscissa stroke. Reduced stroke has a value such that at this point
Fm = Fv, that is to say
Q (Am.Course reduced + Bm) + U = P.Sv (25)

<tb><SEP> ourse <SEP> reaui :: e <SEP> r <SEP> 1 <SEP> - <SEP> Short <SEP> RunT1
<tb> but <SEP> P <SEP> Sv <SEP> = <SEP> PMSVZ <SEP> K <SEP> j <SEP>; $ flce} = <SEP> PgS <SEP> I <SEP> - <SEP > K <SEP> (26)
<tb><SEP> Am <SEP> C <SEP> + <SEP> B <SEP> + <SEP> U / Q
<tb><SEP> -trace <SEP> reduced <SEP> m
<tb> so <SEP> = <SEP> = <SEP> Q <SEP> sort <SEP> Q <SEP> F --- <SEP> (27)
<tb><SEP> c <SEP> + <SEP>'ourseio]"'
<tb><SEP> K <SEP> K <SEP> - <SEP> I <SEP> J
<tb><SEP> Am <SEP> Short <SEP> Run <SEP> + <SEP> Bm <SEP> * <SEP> U / Q
<tb> and <SEP> p9 <SEP> = <SEP> S, <SEP> Run <SEP> (28)
<tb><SEP> reduces
<tb><SEP> ~ <SEP> t <SEP> ~
<Tb>
If the point common to the mechanical and hydraulic answers is chosen for Reduced run = the expression of PM is simple and written

If it is chosen for the reduced value of C = 1, it is the expression of g which becomes simple and is written

Thus for a given specification and for a given mechanical system, it is possible to determine an oleopneumatic system
(Cylinder section, accumulator air reserve and inflation pressure) whose response is identical to the linearised response of the mechanical system for any value of the hook load.

As the normal use of the rig requires a range of loads on the hook, it will be necessary to - adapt the oleo-pneumatic system to each load at the hook (in
for example, to vary the volume of the air reserve of the
accumulators by balastage), - adapt the mechanical system to a determined oleopneumatic system
(by doing, for example, artificially varying the weight-U).

Otherwise you will have to admit an error.

It is recalled that - when considering all moving parts,
sum of the weights of those that do not contribute to the tension of
cables,
- Q is, conversely, the sum of the weights of those which contribute to
the tension of the cables,
- After having varied the five independent parameters which
position and dimension each mechanical device, we do not
holds that all those whose answer can be considered as
linear and expressed by
Fm U = Am.Red course + Bm + (31)
QQ
The use of the device in the range of any hook weights will cause Q to vary Qmin to Qmax, and the pressure in the hydraulic system should never exceed a value set by the specification and is called PMAX.

Suppose one of the mechanical devices is retained. An and Bm are then determined by the calculations and U by the study of the manufacturer.

Let Uconst be this value.

The section of the cylinders is therefore known since it is determined by the formula

The volume of the air reserve of the accumulators is then determined when any load Q has been fixed, which will be called Qexact, e for which the responses of the mechanical and oleopneumatic systems are parallel.

This arbitrary value Qexact of the load Q makes it possible, in fact, to determine the air reserve Va of the accumulators (volume occupied by the air in the oleopmeumatic circuit when the reduced stroke is equal to 1) since

Finally, the operating pressure is determined by writing, for any point of the race, that the mechanical and oleopneumatic responses are equal at this point. The two response curves, already parallel, then become merged.

If one chooses to determine the maximum pressure for this load, that is to say the zero-stroke pressure, it comes

It has just been shown that for an arbitrary exact value Q of the charge Q, the intrinsic response of the compensation system, that is to say the difference between the mechanical responses and the oleopneumatics, could practically be reduced to the only one. linearization error of the mechanical system response.

This one, besides generally weak, can be even made extremely reduced by a subjection which will be -exposed further.

It is therefore possible to calculate the volume of the air reserve of the accumulators by successively choosing Qexact equal to Q min then to
QMAX.

According to a first solution, it is then sufficient to -realize the installation with an air reserve volume equal to the greater of the two volumes found and, in use, to reduce the volume of this reserve according to the value of the charge.

This adaptation of the volume of the air reserve of the accumulators to the load can be carried out either in stages by putting out of service some air bottles, or continuously by balastage or even by combination of these two processes.

 It should be noted that the volume of the accumulator air reserve depends on the Q load via the U / Q ratio.

 So, if, despite the variation of Q, the U / Q ratio remains constant, the air reserve itself remains constant. This is a second solution.

Depending on the value chosen for Qexact, the volume of the air reserve will be such that

c'est-à-dire que

The weight Uconst moving parts not contributing to the tension of the cables should, for example by the inaction of an auxiliary correction cylinder or corrective cylinder 49 which provides a force Uv, be artificially modified so that one always has:

which means

If the corrective cylinder must be single-acting, it is obvious that it will be interesting to choose QMAX for Qexact value. Otherwise, it will be interesting to fix exactly somewhere between QMAX and Qmin depending on hydraulic considerations.

However, if one wished that the value Uv, already independent of the race, is also it of the load, one could choose infinitely great Qexact which is perfectly possible, and one would have then Uv = Uconst.

Physically, and considering only the static phenomena, it amounts to saying that the mobile equipment supporting the crown-block is balanced, for example, by counterweights.

Finally, the operating pressure when the stroke is zero remains determined by the formula

It is possible to combine these two solutions. Suppose we have chosen the interesting solution where Qexact = QMAX-
The correction cylinder must be able to develop the maximum effort

et pour le second tel que

In fact, it is possible, using a particular value of Q between QMAX and Qmin and which will be called Qinter, to split the operating interval delimited by QMAX and Qmin into two complementary intervals. The first one will be delimited. by QMAX and Qinter, while the second will be by Tinter and Qmin
The volume of accumulator air reserves is, for the first interval, as

and for the second such as

e dans le second

The ratio U / Q is kept constant, by the action of the corrector cylinder which provides the effort Uv, so that we have in the first interval ::

e in the second

The ratio of these expressions determines Qinter because it gives
Q2inter = QMAX.Qmin

Toutes choses egales par ailleurs, cela permet sur de gros appareils de ganter 20 % sur les performances maximales de ce vérin correcteur
Ceci n est qu'un exemple, et c' est une étude économique qui pourra montrer si l'on n'a pas intérêt à créer plusieurs plages de fonctionnement qui, de préférence, auront un recouvrement.It was established that over the whole QMAX - Qmin interval, and for this favorable case or Qexact = QMAX, we had

All things being equal, this allows large equipment to ganter 20% on the maximum performance of this corrector cylinder
This is only an example, and it is an economic study that will show if it is not beneficial to create several operating ranges which, preferably, will have an overlap.

 So far, only modes of operation have been considered in which the responses of the mechanical and hydraulic systems are parallel.

In the case where the volume of the air reserve is adapted to the maneuvered load, there remained a setting parameter which was used to superimpose the responses which were parallel.

In the case where the volume of the air reserve is set once and for all, the parallel response curves have been superimposed by the action of a second system, called correction, which must provide a load adapted to the load maneuvered, but constant over the entire clearing race. It is also in this respect that this mode of operation is interesting, because this correction, independent of the race and therefore constant for a given load, can be possibly realized by a passive system, that is to say which does not constantly demand energy from the outside.

This mode of operation can also be considered as an operating mode with error in case the correction system is not installed. The error is then equal to the effort required of the correction system.

But one can also in this mode of operation where the reserve of air is constant, abandon the principle of the parallelism of the answers, in favor of a equality of these at any point of the race of compensation.

If we do not intend to correct the value of the race for which the equality of the mechanical and oleopneumatic responses is achieved, will be chosen so that the greatest difference of the responses, ie the error, be minimal.

If we consider the linearized responses, it is obvious that it is at the mid-race that this condition is alised,
This is acquired when the error is, with the sign near, the same at each of the terminals and, if we consider the linearized responses, this occurs when it is at the halfway point that the mechanical and oleopneumatic is performed.

Claims (7)

REVENjÏCATIONS 1. - Device for subtracting an element attached to a mobile installation to movements of this facility, nn having a first and a second muffle, the latter serving to hook said element, said first muffle being connected to both the axis of a first intermediate pulley and the axis of a second intermediate pulley by a first and a second rod respectively, a first pulley and a second fixed pulley with respect to the mobile installation, the axis of the first fixed pulley, respectively of the second fixed pulley, being connected by a third rod, respectively by a fourth rod, to the axis of the first intermediate pulley, respectively of the second intermediate pulley, a first and a second retaining member, a cable connecting these two retaining members passing, successively, starting from the second retaining member, by the first fixed pulley, the first intermediate pulley, the first muffle and the second muffle forming at least one loop, the second intermediate pulley and the second fixed pulley, at least one jack one end of which is connected to the first muffle and the other is related to the mobile installation and at least one accumulator in oleopneumatic connection with said cylinder, the first and second rods having an identical length equal to C, likewise, the third and fourth rods have an identical length equal to B, the half distance separating the axis of the first and the second fixed pulley being equal to A and the distance separating the axis of the first muffle from the plane joining the axes of the first and second pulleys is equal to G, characterized in the quantities A, B, C, G and the passage of the cable are determined so that the mechanical forces Fn and oleopneumatic F v are substantially equal over at least a portion of the stroke. 2. - Device according to claim 1, characterized in that it comprises an auxiliary correction jack whose effort is adjustable.  @. - - Device according to claim 2, characterized in that it comprises a measuring member for knowing the force exerted by the second muffle and control means of the auxiliary cylinder. 4. - Device according to claim 1, characterized in that the angle formed by the line joining the axis of the first, respectively the second, fixed pulley and the first and second respectively intermediate pulley with the right containing the portion. cable joining these two pulleys is at least equal to 30. 5. - Device according to claim 4, characterized in that said angle is at least equal to 45 ". 6. - @ispositif according to one of claims 1 or 2, characterized in that e first muffle comprises weighting means. 7. - Device according to claim 1 wherein said cylinder is parallel to the stroke of the first muffle, characterized in that the expression of the mechanical forces Fn and oleopneunatiques Fv are given respectively by the expressions

 and

<tb> F <SEP> = <SEP> PS <SEP> 1 <SEP> -L (l <SEP> - <SEP> C <tb> <SEP> v <SEP> PgSv <SEP> g <SEP> K <SEP> (<SEP> K <SEP> ourse <SEP> reduced <tb> in which Q = effort from everything that contributes to the tension of the cables, N = number of strands of muffle, U = fraction of Fm independent of the tension of the cables, ss = golden angle by the strand of the cable between the fixed pulley and  the intermediate pulley and the right joining the centers of these  two pulleys, # = definite angle @ direction of the line joining the center of  first and second fixed pulley and the direction of the right  joining the axes of the first fixed pulley and the first  intermediate pulley,  &gamma;; = angle formed by the cable strand joining the intermediate pulley  and a mop block pulley and the right joining the centers of these  two pulleys,  0 = angle formed by the direction of the line joining the center of  first and second fixed pulleys and the direction of the right  joining the centers of the first muffle and the first pulley  intermediate, P = the precharge pressure of the accumulators, y Sv = the section-of the cylinders, K = Va / Sv Ccdc with Va = volume of accumulators, Ccdc = total stroke of first muffle,  Reduced stroke = real stroke / Ccdc &gamma; = coefficient of expansion of gases.  8. - Device according to claim 7, characterized in that one determines the quantities A, B. C G and the path of the cable to make identical linearized expressions of Fm and Fv. 9. - Device according to claim 8, characterized in that one linearizes the expression give the oleopneumatic forces by considering only the oleopneumatic forces given by said expression at the two end points of the race of the first muffle. 10 - Method for determining the geometry of a device for subtracting an element attached to a mobile installation to the movements of this installation, this device comprising a first and a second muffle, the latter serving to hook said element, said first muffle being connected both to the axis of a first intermediate pulley and to the axis of a second intermediate pulley by a first and a second rod respectively, a first pulley and a second fixed pulley relative to the mobile installation, the axis of the first fixed pulley, respectively of the second fixed pulley, being connected by a third rod, respectively by a fourth rod, to the axis of the first intermediate pulley, respectively of the second intermediate pulley, a first and a second retaining member, a cable connecting these two retaining members passing, successively, starting from the second retaining member, by the first fixed pulley, the first intermediate pulley, the first mitten and the second mitten forming at least one loop, the second intermediate pulley and the second fixed pulley, at least one jack whose one end is connected to the first muffle and the other is connected to the mobile installation and at least one accumulator in oleopneumatic connection with said cylinder, the first and the second rods having an identical length equal to C, likewise, the third and fourth rods have an identical length equal to B, the half distance separating the axis of the first and the second fixed pulley being equal to A and the distance separating the axis of the first muffle from the plane joining the axes of the first and second pulleys is equal to G, characterized in the quantities A, B, -C, G and the passage of the cable are determined so that the mechanical forces Fn and oleopneumatic F v are substantially equal over at least a portion of the stroke. A method according to claim 10, characterized in that the quantities A, B, C, G and the passage of the cable are determined so that linearized expressions of the mechanical forces Fm and oleopneumatic Fv are parallel 12 - Method according to claim 10, characterized in that the quantities A, e, C, G, and the passage of the cable are determined so that linearized expressions of the mechanical forces Fm and oleopneumatic F v have at least one common point.