ITPD20070409A1

ITPD20070409A1 - SUPPORT HEAD WITH FALL COUPLE BALANCING DEVICE

Info

Publication number: ITPD20070409A1
Authority: IT
Inventors: Paolo Speggiorin
Original assignee: Manfrotto Lino & C Spa
Priority date: 2007-12-12
Filing date: 2007-12-12
Publication date: 2009-06-13

Description

DESCRIZI ONE DESCRIPTION

Ambito tecnico Technical field

La presente invenzione ha per oggetto una testa di supporto per attrezzature di ripresa video o fotografica del tipo includente le caratteristiche menzionate nel preambolo della rivendicazione principale. Sfondo tecnologico The present invention relates to a support head for video or photographic shooting equipment of the type including the characteristics mentioned in the preamble of the main claim. Technological background

I n tale ambito è noto impiegare teste di supporto comprendenti piattaforme mobili attorno ad almeno un asse di oscillazione, alle quali le sopra citate attrezzature sono rimovibilmente vincolabili. Nelle applicazioni tipiche e di interesse, tale asse di oscillazione è disposto secondo una direzione sostanzialmente orizzontale. In this field it is known to use support heads comprising platforms that are movable around at least one axis of oscillation, to which the aforementioned equipment can be removably constrained. In typical and interesting applications, this axis of oscillation is arranged in a substantially horizontal direction.

I l movimento attorno all’asse di oscillazione consente di regolare l’orientazione dell’attrezzatura in maniera conveniente per la ripresa video o fotografica, secondo un asse cosiddetto di “tilt”. Esso, tuttavia, determina una coppia di caduta alla quale è sottoposto l’assieme di attrezzatura e piattaforma quando il suo baricentro di discosta dal piano verticale comprendente l’asse di oscillazione, il che, particolarmente nel caso di pesanti telecamere, può risultare di difficile e faticoso controllo da parte dell’operatore, con possibili cadute dell’apparecchiatura stessa. Per questo motivo è noto realizzare teste di supporto comprendenti dispositivi di bilanciamento atti a contrastare l’oscillazione incontrollata della piattaforma al fine di impedire urti e conseguenti danneggiamenti dell’attrezzatura ad essa vincolata. The movement around the axis of oscillation allows you to adjust the orientation of the equipment in a convenient way for video or photographic shooting, according to a so-called "tilt" axis. However, it determines a fall torque to which the assembly of equipment and platform is subjected when its center of gravity deviates from the vertical plane including the axis of oscillation, which, particularly in the case of heavy cameras, can be difficult. and laborious control by the operator, with possible fall of the equipment itself. For this reason it is known to produce support heads including balancing devices designed to counteract the uncontrolled oscillation of the platform in order to prevent impacts and consequent damage to the equipment attached to it.

La coppia C di caduta è proporzionale al peso proprio (P) dell’assieme di piattaforma e attrezzatura, alla distanza (H) del baricentro di tale assieme dall’asse di oscillazione e dal seno dell’angolo (a) di oscillazione del suddetto baricentro, secondo la relazione: The fall torque C is proportional to the self-weight (P) of the platform and equipment assembly, to the distance (H) of the center of gravity of this assembly from the axis of oscillation and from the sine of the angle (a) of oscillation of the aforementioned center of gravity , according to the report:

C = P-H-sen(a) . C = P-H-sen (a).

L’angolo di oscillazione è definito come l’angolo compreso tra il piano verticale comprendente l’asse di oscillazione ed il piano comprendente l’asse di oscillazione e passante per il baricentro dell’assieme di piattaforma e attrezzatura. The oscillation angle is defined as the angle between the vertical plane comprising the axis of oscillation and the plane comprising the axis of oscillation and passing through the center of gravity of the platform and equipment assembly.

Tra i dispositivi di bilanciamento sono noti alcuni meccanism i che forniscono una coppia di contrasto, che si oppone a quella di caduta in modo proporzionale all’angolo di oscillazione. Tali meccanism i, ad esempio, possono essere costituiti da una molla di torsione posta tra la piattaforma oscillante e una sua base fissa. La differenza tra il valore del seno dell’angolo di oscillazione ed il valore in radianti dello stesso angolo rende i dispositivi di bilanciamento così concepiti poco efficaci, dal momento che, indipendentemente dalle altre grandezze, non garantiscono l’equilibrio stabile per ampi intervalli dell’angolo di oscillazione. Among the balancing devices, some mechanisms are known that provide a contrast torque, which opposes the fall torque in a manner proportional to the angle of oscillation. Such mechanisms, for example, can consist of a torsion spring placed between the oscillating platform and a fixed base thereof. The difference between the value of the sine of the oscillation angle and the value in radians of the same angle makes the balancing devices thus conceived ineffective, since, independently from the other quantities, they do not guarantee stable equilibrium for large intervals of the swing angle.

Un altro meccanismo di bilanciamento, descritto nel brevetto US 4732357, prevede l’impiego di una testa di supporto comprendente un cinematismo con molle di compressione che consente di ottenere una coppia di contrasto pari alla coppia di caduta per qualsiasi valore dell’angolo di oscillazione. Principale inconveniente di tale soluzione è rappresentato dal fatto che un dispositivo realizzato in accordo con US 4732357 è efficace solo per attrezzature il cui peso proprio sia compreso all’interno di un intervallo prefissato piuttosto ridotto, così che, spesso, attrezzature di peso diverso devono essere montate su teste diverse. Another balancing mechanism, described in US patent 4732357, provides for the use of a support head comprising a kinematics with compression springs which allows to obtain a contrast torque equal to the fall torque for any value of the oscillation angle. The main drawback of this solution is represented by the fact that a device made in accordance with US 4732357 is effective only for equipment whose own weight is included within a rather small predetermined range, so that often equipment of different weights must be mounted on different heads.

Lo scopo principale della presente invenzione è quello di mettere a disposizione una testa di supporto strutturalmente e funzionalmente concepita per ovviare a tutti gli inconvenienti lamentati con riferimento alla tecnica nota citata, mediante un dispositivo di bilanciamento in grado di contrastare la coppia di caduta per ogni valore dell’angolo di oscillazione e per un ampio intervallo di valori di peso dell’attrezzatura di ripresa video o fotografica supportata. The main purpose of the present invention is to provide a support head structurally and functionally conceived to obviate all the drawbacks complained of with reference to the cited prior art, by means of a balancing device capable of counteracting the falling torque for each value. swing angle and for a wide range of weight values of supported video or photo shooting equipment.

Questo scopo ed altri ancora che meglio appariranno nel seguito della descrizione, sono conseguiti dal trovato mediante una testa di supporto realizzata in accordo con le rivendicazioni che seguono. This object and still others which will become clearer in the following description, are achieved by the invention by means of a support head made in accordance with the following claims.

Le caratteristiche ed i vantaggi dell'invenzione meglio risulteranno dalla descrizione dettagliata di una sua forma di realizzazione preferita, illustrata, a titolo indicativo e non lim itativo, con riferimento agli uniti disegni in cui: The characteristics and advantages of the invention will become clearer from the detailed description of a preferred embodiment thereof, illustrated, by way of example and not of limitation, with reference to the accompanying drawings in which:

- la figura 1 è una vista schematica in alzato laterale di una testa di supporto realizzata in accordo con la presente invenzione, oscillata in due posizioni distinte, - figure 1 is a schematic side elevation view of a support head made in accordance with the present invention, oscillated in two distinct positions,

- la figura 2 è una vista schematica parziale in alzato frontale della testa di figura 1 , Figure 2 is a partial schematic front elevation view of the head of Figure 1,

- la figura 3 è una vista schematica in sezione di un particolare della testa di figura 1 . Figure 3 is a schematic sectional view of a detail of the head of Figure 1.

Con riferimento alle sopra indicate figure, con 1 è complessivamente indicata una testa di supporto realizzata in accordo con la presente invenzione. With reference to the above figures, the reference numeral 1 generally indicates a support head made in accordance with the present invention.

La testa 1 comprende una piattaforma 2 articolata in oscillazione, attorno ad un corrispondente asse di oscillazione X, su una base 3. The head 1 comprises a platform 2 articulated in oscillation, around a corresponding axis of oscillation X, on a base 3.

La base 3 è predisposta per essere vincolata su un apposito sostegno, come ad esempio un treppiede 3a (illustrato solo in parte in figura 1 ), mentre sulla piattaforma 2 è rimovibilmente vincolabile una telecamera 2a mediante mezzi di vincolo in sé noti e non rappresentati. La presente invenzione è tuttavia applicabile in generale a una testa di supporto per una qualsiasi apparecchiatura di ripresa video o fotografica. The base 3 is designed to be fastened to a suitable support, such as for example a tripod 3a (shown only in part in Figure 1), while a camera 2a can be detachably fastened to the platform 2 by means of fastening means known per se and not shown. However, the present invention is generally applicable to a support head for any video or photographic recording equipment.

L’asse X è solidale alla base 3 e generalmente orizzontale per consentire il movimento cosiddetto di “tilt” della telecamera 2a, anche se la presente invenzione è comunque applicabile ad una testa di supporto comprendente una piattaforma oscillabile attorno ad un asse orientato secondo una direzione qualsiasi, purché diversa dalla direzione verticale. The X axis is integral with the base 3 and generally horizontal to allow the so-called "tilt" movement of the camera 2a, even if the present invention is in any case applicable to a support head comprising a platform that can be oscillated around an axis oriented according to a direction any, as long as it differs from the vertical direction.

La piattaforma 2 comprende una piastra 4 di fissaggio sulla quale è vincolata la telecamera 2a ed un braccio di supporto 5, solidale alla piastra 4, ed esteso dalla stessa verso la base 3 da parte contrapposta alla telecamera 2a. The platform 2 comprises a fixing plate 4 on which the camera 2a is constrained and a support arm 5, integral with the plate 4, and extended therefrom towards the base 3 on the opposite side to the camera 2a.

Dalla piattaforma 2 è inoltre estesa una leva di manovra 4a per facilitare lo spostamento in oscillazione della piattaforma 2 attorno all’asse X. A maneuvering lever 4a is also extended from the platform 2 to facilitate the movement of the platform 2 in oscillation around the X axis.

Il braccio di supporto 5 è conformato a forcella, comprendendo un corpo 6 adiacente alla piastra 4 e due rebbi 7a,b tra loro paralleli e distanziati. The support arm 5 is fork-shaped, comprising a body 6 adjacent to the plate 4 and two prongs 7a, b parallel to each other and spaced apart.

La base 3 comprende un corpo 9 dal quale si estendono due sporgenze 10a,b, tra loro distanziate e ortogonali all’asse X, su cui sono rispettivamente incernierati i rebbi 7a,b, mediante due perni 1 1 , estesi coassialmente all’asse X. The base 3 comprises a body 9 from which two protrusions 10a, b extend, spaced apart and perpendicular to the X axis, on which the prongs 7a, b are respectively hinged by means of two pins 11, extended coaxially to the X axis .

Sulla piattaforma 2 sono previsti mezzi di regolazione del posizionamento della telecamera 2a, in modo da consentire lo spostamento di quest’ultima lungo la piastra di fissaggio 4 fino ad ottenere che, con la piastra di fissaggio 4 in posizione orizzontale, il baricentro G dell’assieme formato dalla piattaforma 2 e della telecamera 2a, indicato complessivamente con 100, sia posizionato verticalmente sopra l’asse di oscillazione X. On the platform 2 there are means for adjusting the positioning of the camera 2a, so as to allow the latter to be moved along the fixing plate 4 until obtaining that, with the fixing plate 4 in a horizontal position, the center of gravity G of the the assembly formed by the platform 2 and the camera 2a, indicated as a whole with 100, is positioned vertically above the axis of oscillation X.

La testa di supporto 1 comprende inoltre un dispositivo di bilanciamento 1 a della coppia di caduta alla quale è sottoposto l’assieme 100 nel moto di oscillazione attorno all’asse X, quando la verticale passante per il baricentro G si discosta dall’asse X. The support head 1 also includes a balancing device 1 a for the fall torque to which the assembly 100 is subjected in the oscillation motion around the X axis, when the vertical passing through the center of gravity G deviates from the X axis.

Il dispositivo di bilanciamento 1 a comprende una molla pneumatica 12, posta sul corpo 9 della base 3, estesa lungo una direzione Z verticale ed incidente perpendicolarmente con l’asse X. La molla pneumatica 12 include un cilindro 13 ad asse Z, nel quale, attraverso un foro 13a, è impegnato in scorrimento un pistone 15, a sezione cilindrica, formante un’estremità libera 12a della molla 12 estesa tra le sporgenze 10a,b e rivolta verso la piattaforma 2. The balancing device 1 a comprises a pneumatic spring 12, placed on the body 9 of the base 3, extended along a vertical Z direction and incident perpendicular to the X axis. The pneumatic spring 12 includes a cylinder 13 with a Z axis, in which, through a hole 13a, a piston 15 is slidingly engaged, having a cylindrical section, forming a free end 12a of the spring 12 extending between the projections 10a, b and facing the platform 2.

Nel cilindro 13 è contenuto, a tenuta, un gas, ad esempio azoto. Ai fini della presente invenzione, la pressione del gas all’interno del cilindro, in condizioni di riposo della molla e a temperatura ambiente, è preferibilmente compresa tra 50 e 150 bar. A gas, for example nitrogen, is contained in the cylinder 13, sealed. For the purposes of the present invention, the gas pressure inside the cylinder, in conditions of rest of the spring and at room temperature, is preferably between 50 and 150 bar.

Sul pistone 15 è definita una prima superficie 15a libera, esterna al cilindro 13 e sostanzialmente ortogonale all’asse Z, ed una seconda contrapposta superficie 15b, interna al cilindro 13 ed anch’essa sostanzialmente ortogonale all’asse Z. On the piston 15 a first free surface 15a is defined, external to the cylinder 13 and substantially orthogonal to the Z axis, and a second opposing surface 15b, internal to the cylinder 13 and also substantially orthogonal to the Z axis.

Il dispositivo di bilanciamento 1 a comprende mezzi attuatori agenti sul pistone 15 per sollecitare in compressione la molla 12 quando la piattaforma 2 ruota attorno all’asse X. Tali mezzi comprendono un elemento di riscontro 16 vincolato alla piattaforma 2 neN’oscillazione attorno all’asse X ed in attestato contro la prima superficie 15a del pistone 15. L’elemento di riscontro 16 include una forcella 17 comprendente una base 18, affacciata al corpo 6 del braccio di supporto 5 e due rebbi 17a,b i quali sono impegnati in scorrimento all’interno di rispettive guide 18a estese parallelamente all’asse Z e ricavate sui rebbi 7a,b del braccio di supporto 5. The balancing device 1a comprises actuator means acting on the piston 15 to compress the spring 12 when the platform 2 rotates around the X axis. These means comprise a abutment element 16 constrained to the platform 2 in oscillation around the axis X and abutting against the first surface 15a of the piston 15. The abutment element 16 includes a fork 17 comprising a base 18, facing the body 6 of the support arm 5 and two prongs 17a, b which are engaged in sliding on the internal of respective guides 18a extended parallel to axis Z and obtained on the prongs 7a, b of the support arm 5.

Sulla base 18 della forcella 17 è attestato un grano di posizionamento 19 accolto in un foro filettato 20 previsto nel corpo 6, così che avvitando o svitando il medesimo sia regolata la distanza tra l’elemento di riscontro 16 ed il corpo 6. On the base 18 of the fork 17 there is a positioning dowel 19 received in a threaded hole 20 provided in the body 6, so that by screwing or unscrewing the same, the distance between the abutment element 16 and the body 6 is adjusted.

Tra i rebbi 17a,b è fissato un perno 21 , con asse Y parallelo all’asse X, sul quale è calettato l’anello interno di un cuscinetto 22. L’anello esterno 23 del cuscinetto 22 è invece in contatto con la prima superficie 15a del pistone 15, sulla quale rotola. A pin 21 is fixed between the prongs 17a, b, with axis Y parallel to axis X, on which the inner ring of a bearing 22 is keyed. The outer ring 23 of the bearing 22 is instead in contact with the first surface 15a of the piston 15, on which it rolls.

I l funzionamento del dispositivo di bilanciamento 1 a è di seguito descritto. I n primo luogo la telecamera 2a è posizionata sulla piastra di fissaggio 4 in modo tale che, quando la telecamera 2a è disposta orizzontalmente (angolo di oscillazione a nullo), il baricentro G si trovi sulla verticale rispetto all’asse X. Si noti che in questa posizione anche l’asse Y dell’elemento di riscontro 16 è sulla stessa direzione verticale (vedi figura 1 , linea continua). The operation of the balancing device 1 a is described below. Firstly, the camera 2a is positioned on the fixing plate 4 in such a way that, when the camera 2a is arranged horizontally (zero oscillation angle), the center of gravity G is on the vertical axis with respect to the X axis. in this position also the Y axis of the abutment element 16 is in the same vertical direction (see Figure 1, solid line).

Nel momento in cui la telecamera 2a, e con essa la piattaforma 2, viene oscillata di un angolo a attorno all’asse di oscillazione X (vedi figura 1 , linea in tratteggio) , il baricentro G dell’assieme 100 determ ina una coppia di caduta Cd secondo la seguente espressione: When the camera 2a, and with it the platform 2, is oscillated by an angle a around the oscillation axis X (see Figure 1, broken line), the center of gravity G of the assembly 100 determines a pair of Cd fall according to the following expression:

Cd = P-H-sen(a) , Cd = P-H-sen (a),

in cui P è il peso dell’assieme 100, H è la distanza del baricentro G dall’asse X. where P is the weight of the assembly 100, H is the distance of the center of gravity G from the X axis.

L’oscillazione della piattaforma 2 comporta il contestuale spostamento del cuscinetto 22 sulla prima superficie 15a del pistone 15. Per effetto di questo spostamento, la forza esercitata dalla molla pneumatica 12 sull’elemento di riscontro 16 produce sulla piattaforma 2 una coppia Cb di bilanciamento (di verso opposto alla coppia di caduta Cd) esprimibile come segue: The oscillation of the platform 2 involves the simultaneous displacement of the bearing 22 on the first surface 15a of the piston 15. As a result of this displacement, the force exerted by the pneumatic spring 12 on the abutment element 16 produces on the platform 2 a balancing torque Cb ( opposite to the falling torque Cd) expressed as follows:

Cb = p-A-R-sen(a), Cb = p-A-R-sen (a),

in cui p è la pressione del gas interno al cilindro 13, A è la sezione minima del pistone 15 perpendicolare all’asse Z in corrispondenza del foro 13a ed R è la distanza tra gli assi X e Y. where p is the pressure of the gas inside the cylinder 13, A is the minimum section of the piston 15 perpendicular to the Z axis at the hole 13a and R is the distance between the X and Y axes.

Si noti che, convenientemente, quest’ultimo parametro è regolabile agendo sul grano di posizionamento 19. Note that, conveniently, this last parameter is adjustable by acting on the positioning dowel 19.

Lo spostamento del cuscinetto 22 sulla superficie 15a, comporta il conseguente abbassamento del pistone 15 all’interno del cilindro 13. La molla pneumatica 12 è tuttavia dimensionata in maniera tale che il volume generato dalla corsa del pistone 15 all’interno del cilindro 13, ovvero la diminuzione di volume occupato dal gas nel cilindro 13 determinata dallo scorrimento del pistone 15 sia inferiore o uguale al 10% del volume occupato dal gas quando l’angolo a è nullo. Di conseguenza è possibile assumere con buona approssimazione che la pressione p non vari in modo sostanziale per effetto dello spostamento del cuscinetto 22 e che possa quindi, ai nostri fini, essere considerata costante. The displacement of the bearing 22 on the surface 15a causes the consequent lowering of the piston 15 inside the cylinder 13. The pneumatic spring 12 is however dimensioned in such a way that the volume generated by the stroke of the piston 15 inside the cylinder 13, i.e. the decrease in volume occupied by the gas in the cylinder 13 determined by the sliding of the piston 15 is less than or equal to 10% of the volume occupied by the gas when the angle a is zero. Consequently, it is possible to assume with a good approximation that the pressure p does not vary substantially as a result of the displacement of the bearing 22 and that it can therefore, for our purposes, be considered constant.

Le coppie Cd e Cb sono uguali quando è verificata la relazione: The pairs Cd and Cb are equal when the relation is verified:

R = (Ρ·Η)/(ρ·Α) R = (Ρ Η) / (ρ Α)

che, come si vede, è indipendente dall’angolo di oscillazione a. which, as can be seen, is independent of the angle of oscillation a.

Regolando il grano 19 in modo che la distanza tra gli assi X e Y verifichi quest’ultima espressione, si ottiene che la coppia di bilanciamento eguagli la coppia di caduta per qualsiasi valore dell’angolo di oscillazione a, così che l’assieme 100 risulti in equilibrio per qualsiasi posizione angolare ottenuta per oscillazione attorno all’asse X. By adjusting the grain 19 so that the distance between the X and Y axes verifies the latter expression, we obtain that the balancing torque equals the fall torque for any value of the oscillation angle a, so that the assembly 100 is in equilibrium for any angular position obtained by oscillation around the X axis.

Scegliendo opportunamente la corsa massima del grano 19 è inoltre possibile garantire il bilanciamento di apparecchiature diverse sulla stessa testa di supporto 1 , variando di volta in volta la distanza tra gli assi X e Y. Sebbene nel preferito esempio di realizzazione sopra descritto sia previsto che il pistone 15 presenti sezione cilindrica, è previsto che essa possa essere di forma diversa, ad esempio conica, in modo tale da compensare, almeno in parte, la variazione di pressione del gas interno del cilindro 13 causata dall’abbassamento del pistone 15 durante il movimento di oscillazione. È evidente infatti che in questo caso anche il term ine A sarebbe variabile con la corsa del pistone e potrebbe essere opportunamente dimensionato in modo tale che il prodotto tra pressione (p) ed area (A) risulti costante. By appropriately choosing the maximum stroke of the grain 19 it is also possible to ensure the balancing of different devices on the same support head 1, by varying the distance between the X and Y axes each time. piston 15 having a cylindrical section, it is provided that it can be of a different shape, for example conical, in such a way as to compensate, at least in part, the variation in pressure of the internal gas of the cylinder 13 caused by the lowering of the piston 15 during movement of oscillation. In fact, it is evident that in this case also the term A would be variable with the stroke of the piston and could be suitably dimensioned in such a way that the product between pressure (p) and area (A) is constant.

Analogamente, è previsto che la prima superficie 15a del pistone 15 possa non giacere su un piano sostanzialmente perpendicolare all’asse Z. I n particolare essa può convenientemente avere una conformazione convessa in modo tale che a parità di spostamento del cuscinetto 22 su di essa si ottenga un m inore abbassamento del pistone 15. Similarly, it is provided that the first surface 15a of the piston 15 may not lie on a plane substantially perpendicular to the Z axis. obtain a lesser lowering of the piston 15.

Garantendo un posizionamento stabile per l’apparecchiatura supportata dalla piattaforma, indipendentemente dall’angolo di oscillazione, l’invenzione risolve il problema lamentato con riferimento alla tecnica nota citata, conseguendo, al contempo, molteplici vantaggi. Tra questi il fatto di poter realizzare un dispositivo di bilanciamento compatto in grado di fornire forze elevate in uno spazio ristretto, con un numero lim itato di componenti, e realizzabile con un procedimento relativamente semplice. By ensuring a stable positioning for the equipment supported by the platform, regardless of the angle of oscillation, the invention solves the problem complained of with reference to the aforementioned prior art, achieving, at the same time, multiple advantages. These include the fact that a compact balancing device capable of supplying high forces in a confined space, with a limited number of components, can be produced with a relatively simple procedure.

Claims

RI VENDICAZI ONI 1. Support head for video or photographic shooting equipment comprising a base, a platform on which said equipment can be removably constrained and in turn constrained on said base to oscillate around an axis of oscillation, as well as a balancing device adapted to counteract the oscillation of said platform about said axis of oscillation due to the effect of the weight of said equipment and of said platform, characterized in that said balancing device comprises a pneumatic spring associated with said base and actuator means associated with said platform capable of compressing said pneumatic spring as a function of the oscillation of said platform around said axis of oscillation, in such a way as to generate a torque equal to and opposite to that generated by the weight of said equipment and said platform.

2. Head according to claim 1, wherein said pneumatic spring acts in an incident direction substantially perpendicular to said axis of oscillation.

3. Head according to claim 1 or 2, wherein said axis of oscillation is substantially horizontal.

4. Head according to any one of claims 1 to 3, in which said actuator means comprise an abutment element attached to said platform and abutting against a free end of said pneumatic spring.

5. Head according to claim 4, wherein said abutment element is abutting against said free end at a first from the platform, regardless of the angle of oscillation, the invention solves the problem complained of with reference to the cited prior art, achieving, at the same time, multiple advantages. These include the fact that a compact balancing device capable of supplying high forces in a confined space, with a limited number of components, can be produced with a relatively simple procedure. R = (Ρ Η) / (ρ Α) which, as can be seen, is independent of the angle of oscillation a. By adjusting the grain 19 so that the distance between the X and Y axes verifies the latter expression, we obtain that the balancing torque equals the fall torque for any value of the oscillation angle a, so that the assembly 100 is in equilibrium for any angular position obtained by oscillation around the X axis. By appropriately choosing the maximum stroke of the grain 19 it is also possible to ensure the balancing of different devices on the same support head 1, by varying the distance between the X and Y axes each time. piston 15 having a cylindrical section, it is provided that it can be of a different shape, for example conical, in such a way as to compensate, at least in part, the variation in pressure of the internal gas of the cylinder 13 caused by the lowering of the piston 15 during movement of oscillation. In fact, it is evident that in this case also the term A would be variable with the stroke of the piston and could be suitably dimensioned in such a way that the product between pressure (p) and area (A) is constant. Similarly, it is provided that the first surface 15a of the piston 15 may not lie on a plane substantially perpendicular to the Z axis. obtain a lesser lowering of the piston 15. Ensuring a stable positioning for the supported equipment Cd = P-H-sen (a), where P is the weight of the assembly 100, H is the distance of the center of gravity G from the X axis. The oscillation of the platform 2 involves the simultaneous displacement of the bearing 22 on the first surface 15a of the piston 15. As a result of this displacement, the force exerted by the pneumatic spring 12 on the abutment element 16 produces on the platform 2 a balancing torque Cb ( opposite to the falling torque Cd) expressed as follows: Cb = p-A-R-sen (a), where p is the pressure of the gas inside the cylinder 13, A is the minimum section of the piston 15 perpendicular to the Z axis at the hole 13a and R is the distance between the X and Y axes. Note that, conveniently, this last parameter is adjustable by acting on the positioning dowel 19. The displacement of the bearing 22 on the surface 15a causes the consequent lowering of the piston 15 inside the cylinder 13. The pneumatic spring 12 is however dimensioned in such a way that the volume generated by the stroke of the piston 15 inside the cylinder 13, i.e. the decrease in volume occupied by the gas in the cylinder 13 determined by the sliding of the piston 15 is less than or equal to 10% of the volume occupied by the gas when the angle a is zero. Consequently, it is possible to assume with a good approximation that the pressure p does not vary substantially as a result of the displacement of the bearing 22 and that it can therefore, for our purposes, be considered constant. The pairs Cd and Cb are equal when the relation is verified: 2 rotates around the X axis. Said means comprise an abutment element 16 constrained to the platform 2 in oscillation around the X axis and abutting against the first surface 15a of the piston 15. The abutment element 16 includes a fork 17 comprising a base 18, facing the body 6 of the support arm 5 and two prongs 17a, b which are engaged in sliding inside respective guides 18a extending parallel to the axis Z and formed on the prongs 7a, b of the support arm 5 . On the base 18 of the fork 17 there is a positioning dowel 19 received in a threaded hole 20 provided in the body 6, so that by screwing or unscrewing the same, the distance between the abutment element 16 and the body 6 is adjusted. A pin 21 is fixed between the prongs 17a, b, with axis Y parallel to axis X, on which the inner ring of a bearing 22 is keyed. The outer ring 23 of the bearing 22 is instead in contact with the first surface 15a of the piston 15, on which it rolls. The operation of the balancing device 1 a is described below. Firstly, the camera 2a is positioned on the fixing plate 4 in such a way that, when the camera 2a is arranged horizontally (zero oscillation angle), the center of gravity G is on the vertical axis with respect to the X axis. in this position also the Y axis of the abutment element 16 is in the same vertical direction (see Figure 1, solid line). When the camera 2a, and with it the platform 2, is oscillated by an angle a around the oscillation axis X (see Figure 1, broken line), the center of gravity G of the assembly 100 determines a pair of Cd fall according to the following expression: along the fixing plate 4 until obtaining that, with the fixing plate 4 in a horizontal position, the center of gravity G of the assembly formed by the platform 2 and the camera 2a, indicated as a whole with 100, is positioned vertically above the oscillation axis X. The support head 1 also includes a balancing device 1 a for the fall torque to which the assembly 100 is subjected in the oscillation motion around the X axis, when the vertical passing through the center of gravity G deviates from the X axis. The balancing device 1 a comprises a pneumatic spring 12, placed on the body 9 of the base 3, extended along a vertical Z direction and incident perpendicular to the X axis. The pneumatic spring 12 includes a cylinder 13 with a Z axis, in which, through a hole 13a, a piston 15 is slidingly engaged, having a cylindrical section, forming a free end 12a of the spring 12 extending between the projections 10a, b and facing the platform 2. A gas, for example nitrogen, is contained in the cylinder 13, sealed. For the purposes of the present invention, the gas pressure inside the cylinder, in conditions of rest of the spring and at room temperature, is preferably between 50 and 150 bar. On the piston 15 a first free surface 15a is defined, external to the cylinder 13 and substantially orthogonal to the Z axis, and a second opposing surface 15b, internal to the cylinder 13 and also substantially orthogonal to the Z axis. The balancing device 1 a comprises actuator means acting on the piston 15 to compress the spring 12 when the platform. ), while a television camera 2a can be detachably constrained on the platform 2 by means of constraint means known per se and not shown. However, the present invention is generally applicable to a support head for any video or photographic recording equipment. The X axis is integral with the base 3 and generally horizontal to allow the so-called "tilt" movement of the camera 2a, even if the present invention is in any case applicable to a support head comprising a platform that can be oscillated around an axis oriented according to a direction any, as long as it differs from the vertical direction. The platform 2 comprises a fixing plate 4 on which the camera 2a is constrained and a support arm 5, integral with the plate 4, and extended therefrom towards the base 3 on the opposite side to the camera 2a. A maneuvering lever 4a is also extended from the platform 2 to facilitate the movement of the platform 2 in oscillation around the X axis. The support arm 5 is fork-shaped, comprising a body 6 adjacent to the plate 4 and two prongs 7a, b parallel to each other and spaced apart. The base 3 comprises a body 9 from which two protrusions 10a, b extend, spaced apart and perpendicular to the X axis, on which the prongs 7a, b are respectively hinged by means of two pins 11, extended coaxially to the X axis . Means for adjusting the positioning of the camera 2a are provided on the platform 2, so as to allow the movement of the latter. complained with reference to the cited prior art, by means of a balancing device capable of counteracting the falling torque for each value of the oscillation angle and for a wide range of weight values of the supported video or photographic recording equipment. This object and still others which will become clearer in the following description, are achieved by the invention by means of a support head made in accordance with the following claims. The characteristics and advantages of the invention will become clearer from the detailed description of a preferred embodiment thereof, illustrated, by way of example and not of limitation, with reference to the accompanying drawings in which: - figure 1 is a schematic side elevation view of a support head made in accordance with the present invention, oscillated in two distinct positions, Figure 2 is a partial schematic front elevation view of the head of Figure 1, Figure 3 is a schematic sectional view of a detail of the head of Figure 1. With reference to the above figures, the reference numeral 1 generally indicates a support head made in accordance with the present invention. The head 1 comprises a platform 2 articulated in oscillation, around a corresponding axis of oscillation X, on a base 3. from the axis of oscillation and from the sine of the angle (a) of oscillation of the aforementioned center of gravity, according to the relationship: C = P-H-sen (a). The oscillation angle is defined as the angle between the vertical plane comprising the axis of oscillation and the plane comprising the axis of oscillation and passing through the center of gravity of the platform and equipment assembly. Among the balancing devices, some mechanisms are known that provide a contrast torque, which opposes the fall torque in a manner proportional to the angle of oscillation. Such mechanisms, for example, can consist of a torsion spring placed between the oscillating platform and a fixed base thereof. The difference between the value of the sine of the oscillation angle and the value in radians of the same angle makes the balancing devices thus conceived ineffective, since, independently from the other quantities, they do not guarantee stable equilibrium for large intervals of the swing angle. Another balancing mechanism, described in US patent 4732357, provides for the use of a support head comprising a kinematics with compression springs which allows to obtain a contrast torque equal to the fall torque for any value of the oscillation angle. The main drawback of this solution is represented by the fact that a device made in accordance with US 4732357 is effective only for equipment whose own weight is included within a rather small predetermined range, so that often equipment of different weights must be mounted on different heads. DESCRIPTION Technical field The present invention relates to a support head for video or photographic shooting equipment of the type including the characteristics mentioned in the preamble of the main claim. Technological background In this field it is known to use support heads comprising platforms that are movable around at least one axis of oscillation, to which the aforementioned equipment can be removably constrained. In typical and interesting applications, this axis of oscillation is arranged in a substantially horizontal direction. The movement around the axis of oscillation allows you to adjust the orientation of the equipment in a convenient way for video or photographic shooting, according to a so-called "tilt" axis. However, it determines a fall torque to which the assembly of equipment and platform is subjected when its center of gravity deviates from the vertical plane including the axis of oscillation, which, particularly in the case of heavy cameras, can be difficult. and laborious control by the operator, with possible fall of the equipment itself. For this reason it is known to produce support heads including balancing devices designed to counteract the uncontrolled oscillation of the platform in order to prevent impacts and consequent damage to the equipment attached to it. The fall torque C is proportional to the own weight (P) of the platform and equipment assembly, to the distance (H) of the center of gravity of this assembly