LU88093A1 - EXHAUST TYPE RIGHT PIANO MECHANICS - Google Patents

Description

RIGHT PIANO MECHANICS OF EXHAUST TYPE

The present invention relates to an upright piano mechanics of the exhaust type.

It is known that in the escapement type upright piano mechanics, an intermediate piece, called an exhaust tongue, is used for transmitting the movement of a key to a hammer. The tongue actuated by the key, most often via a second intermediate piece called an easel, propels the hammer by pushing it into a fulcrum, the nut trim, secured to the handle of the hammer. At the end of the hammer stroke, more precisely near its point of impact on the string (s), the tongue escapes from the fulcrum, for example by tilting under the effect of a stop, the button d 'exhaust. This escapement of the tongue at the end of the hammer stroke aims to free the hammer before impact with the string (s), to allow the hammer to bounce freely on the string (s). In fact, a blockage of the hammer on the strings struck would dampen the vibration of the latter.

There is also a known repetition mechanism which allows rapid repetition of the strike without having to fully lift the key. In this mechanism, the hammer is immobilized at the start of its return stroke by a counter-catch secured to the hammer which abuts on a catch installed on the bridge.

A nut return spring 86 normally assists the return of the hammer after its impact on the strings in order to avoid an untimely repetition of the strike. The latter could occur during a pianissimo game when the hammer, which rebounds only slightly on the string (s), falls on the string (s) instead of falling towards the catch. Indeed, apart from the treble hammers, the mass distribution in the overall structure of a hammer is such that it is in an unstable equilibrium position, that is to say that its center of gravity is vertical to its articulation, when the hammer head is in an intermediate position between the striking position and the position blocked by the catcher. There is therefore the possibility for the hammer to fall on the ropes instead of falling on the catch. For this reason, the nut return spring is essential in current mechanics.

When the key is raised to perform a repetition of the strike, the catch deviates from the counter-catch and releases the hammer. The exhaust tab loses contact with the exhaust button and tends to return to the propulsion position under the hammer nut lining, by the effect of a return means, for example an exhaust spring installed between a horizontal arm of the exhaust tab and the bridge.

However, one of the main defects of the mechanisms of upright pianos is that a correct return of the exhaust tongue to said propulsion position under the hammer nut lining unfortunately remains uncertain. Indeed, under the effect of its own weight and especially the nut return spring, the hammer tends to fall towards the catcher, that is to say in the opposite direction of the strings. When returning to the catcher, the hammer is thus subjected to significant restoring forces which the tongue must overcome to engage below the hammer nut garnish, which is the cause of the faults. repetitions in the background, known with current upright pianos.

Different solutions have been proposed to improve the return of the exhaust tab of the upright piano mechanics.

Document DE 31 39 404 A1 proposes for example to adapt the bridge and double escapement assembly, known from the grand piano mechanics, to the upright piano mechanics. It is obvious to those skilled in the art that this solution is very complex and costly.

A French manufacturer offers a system which aims to simulate the effects of the double escapement of the grand piano mechanics on the upright piano. To this end, it removes both the traditional coil exhaust spring and the traditional nut return spring, and replaces them with a drop spring, a repeat spring and an easel spring. The drop spring is a leaf spring installed at the front of the hammer handle. It cooperates with a stop to ensure the return back of the hammer after striking and at the same time avoids the fall of the hammer on the strings. The repetition spring is a spring fixed on one side to the hammer nut and on the other side to the upper end of the exhaust tab. It ensures the forceful return of the exhaust tongue to the propulsion position under the hammer nut trim while lifting the hammer slightly to facilitate this movement. The easel return spring is designed to accelerate the descent of the easel at the end of the stroke. It thus compensates for the disappearance of the traditional nut recall spring. This solution is also complex and expensive. In addition, it does not have any adjustment means making it possible to ensure proper operation, without hardening the keyboard at the end of the stroke. Other solutions belonging to the state of the art also provide for a forceful return of the exhaust tongue to the propulsion position under the packing of the hammer nuts. Thus, it is notably known to install a tab on the hammer nut, which only pushes the exhaust tongue into said propulsion position when the hammer falls backwards. In another embodiment respecting the same principle, a lining of the exhaust spring is proposed. A leaf spring fixed at the base of the tongue is supported, during the exhaust, on a stop installed on an exhaust limitation bar and thus adds its effect to that of the traditional coil spring to force the tongue into- below the walnut filling. Remain to note that all these systems, which aim at a forceful return of the exhaust tongue in said propulsion position, are of doubtful effectiveness or then tend to harden the keyboard at the end of the race and more particularly in the phase exhaust. The object of the present invention is to provide an improvement in exhaust return and repetition by modifying the mechanics of the upright piano with exhaust, which is particularly simple in its production and reliable in its operation.

The solution to this problem is obtained by a mechanism according to the present invention essentially characterized in that each hammer is balanced individually so as to have an unstable equilibrium state in the impact position of its head on the string or strings.

In an upright piano mechanic according to the invention, comprising a series of hammers articulated in line on a frame of which the mass of the hammer heads is different and decreases from the hammers of the bass to the treble hammers, each hammer is consequently balanced individually to be in unstable equilibrium on its articulation when the hammer head is in striking position on at least one string.

It results from this balancing that each hammer has, by bouncing on the strings, tendency to move away from the strings and not to fall back on it, but with a minimum moment of recall, which hinders the return of the tongue as little as possible. exhaust under the nut garnish.

This balancing of the hammer in a position of impact on the strings can be done, either by playing on the intrinsic distribution of the masses of the hammer relative to its articulation on the chassis, or by playing on the position of this articulation, or by ballasting the hammer in appropriate places, either by providing the hammer with a balancing spring whose moment exerted on the hammer is adjustable in intensity and preferably in direction.

The solutions proposed by the present invention have the advantage of adapting to existing structures and are of a particularly simple and inexpensive embodiment, while guaranteeing good reliability.

It will be appreciated that the present invention also proposes several solutions which make it possible to eliminate the floating of the keys when the piano is equipped with a soft pedal provided with a hammer rest bar which can pivot towards the strings. The solutions proposed on this subject have the advantage of generally improving the contact and the transmission of movements between the fingerboard and the bridge. Other advantages and characteristics will emerge from the detailed description of several preferred embodiments, which are described, only by way of illustration, with the aid of the appended drawings, of which: - Figure 1 shows in a cross section through a upright piano frame a schematic view of a mechanics known to itself, the hammer being at rest against a rest bar; - Figure 2 shows a view similar to Figure 1, the hammer being pressed against a catch; - Figure 3 shows a view similar to Figure 1, the hammer being shown in a state of unstable equilibrium in impact position on the strings; - Figure 4 shows a hammer nut with a balancing spring according to an alternative embodiment of the present invention; - Figure 5 shows another embodiment of said balancing spring according to the present invention; Figures 6A and 6B show two different attachments of a nut fork strap of Figure 5; - Figures 7 and 7A show an alternative embodiment of the balancing spring of Figure 5; - Figure 8 shows a first embodiment of a ballast of the hammer according to the invention; - Figure 9 shows a second embodiment of ballasting of the hammer according to the invention; - Figure 10 shows a third embodiment of a ballast of the hammer according to the invention; - Figure 11 shows a variant against catch with a mass greater than a conventional counter catch; - Figures 12A and 12B show two treble hammer heads having the same mass but different centers of mass; Figure 13 shows a detail of a modified mechanism according to the invention; - Figure 14 shows a detail of a ballast of a bridge and a key according to the invention; - Figure 15 shows a variant of the ballast of the easel; - Figure 16 shows an execution of a soft pedal mechanism mistletoe is connected to a movable key rest bar according to the invention.

The references of the Figures and the names used for the various pieces known per se are in accordance with the book "Piano Nomenklatur" by Schimmel-Herzog published by "Verlag das Musikinstrument, Frankfurt am Main".

To illustrate the present invention, an upright piano mechanism of current construction is used. It is however specified that the present invention is not limited to a mechanism of the type described below.

Figure 1 shows in a cross section through an upright piano frame, a schematic view of a key equipped with such a mechanism known per se. For simplicity, only the elements of the mechanics are shown which relate directly to the present invention.

We see a key 45 which is in the fully raised position. On its rear end is supported a bridge 60 which is articulated at 62 on a central bar of the mechanics 24 secured to the frame of the piano. On this bar 24 is also articulated at 90, by means of a fork 89, a hammer nut 85 which supports a hammer handle 112 by its lower end. At the other end of the handle 112 is mounted a hammer head which is made of a hammer wood 113 and a hammer felt 114. The hammer nut 85 has at its lower part a nut packing 92 which serves of support to an exhaust tongue 98. The latter has the shape of a bracket made up of a vertical arm, the end of which comes to rest on the nut packing 92, and of a horizontal arm. The tongue 98 is articulated at the intersection of its two arms at 102 on an exhaust fork 101 secured to the bridge 60. Said horizontal arm is subjected to the action of an exhaust spring 100 which is mounted between said arm horizontal and easel 60.

Note that in Figure 1, said hammer is at rest against a stop 115 on which the handle. 112 is supported. This stop 115 is also called hammer rest bar. When the key 45 is pressed, the latter confers an upward pivoting movement on the bridge 60 which communicates this movement to the escapement tongue 98, which pushes against the nut lining 92 to propel the hammer in the direction of the strings 5. Just before the hammer head hits the rope 5, said horizontal arm of the tongue 98 abuts the exhaust button 105. This results in pivoting of the tongue 98 around the articulation 102 in the direction of the arrow 200 in Figure 1. This pivoting disengages the upper end of the vertical arm of the tongue 98 outside the lining 92 of the hammer nut, so that the hammer can freely strike the string 5 and that its rebound on the latter is not hampered.

In order to prevent the hammer from falling a second time on the rope 5 under the effect of its own weight, especially during a gentle strike, the hammer nut is provided, still in a manner known per se, with a nut return spring 86. The latter is articulated at 88 on the nut 85 and is attached to a strap 87 integral with the nut fork 89, so as to communicate to said hammer an elastic return moment which propels the hammer in the opposite direction after striking the rope 5.

In order to allow rapid repetition of a note, the mechanism further described has a repetition system which is also known per se. This system comprises a catch 109 mounted using a catch rod on the easel 60. This catch 109 constitutes a stop for a counter-catch 93 which is integral with the nut 85, so that the hammer is stopped , in an intermediate position, in its return stroke towards the hammer rest bar 115 (see Figure 2).

When, in this position of the hammer, the key 45 is again slightly raised, the tongue .98 pivots in the opposite direction to the arrow 200 of FIG. 1, under the action of the coil spring 100. It thus comes re-engage below the walnut filling, so you can repeat the note. However, when the key 45 is raised slowly after the first strike, the tongue 98 meets the nut 85, released by the catch and in return movement by the effect of gravity and the action of the nut spring. As a result, the engagement of the upper end of the vertical arm of the tongue 98 below the nut trim 92 may not be done properly (see Figure 2). It may even happen that a repetition of the. note is only possible after the key 45 has been completely raised again to correct this faulty engagement of the tongue 98.

It was specified above that the object of the present invention is to remove this randomness from the engagement of the tongue 98 in the event of repetition of a note in pianissimo. It is recalled that this problem is solved, according to the present invention, by individually balancing each hammer to give it a state of unstable equilibrium on its articulation 90 in the impact position of its head on the string or strings 5.

Figure 3 shows a hammer in this unstable equilibrium position. The hammer head is in contact with the string (s) 5, and there is a balance of moments around the articulation 90, that is to say that the moment due to the balancing spring 86 '' is adjusted to be equal and opposite at the moment of the masses with respect to the articulation 90. In this way, the return of the hammer, leaving by rebounding on the string or strings this unstable equilibrium position, is only subject to a moment of extremely weak, minimal reminder, and always in the direction of the rest bar 115. This avoids an untimely repetition of the note while minimizing the re-engagement of the tongue 98 below the nut garnish, an increase of the key for a repetition of a note in pianissimo.

A particular case of this FIG. 3 is that where the moment of the masses with respect to the articulation 90 is by construction zero in this position of the head in contact with the string (s) 5. In this particular case, there is no need the balancing spring 86 "to cancel the mass moment.

It is important to emphasize that, according to the present invention, each hammer is balanced individually to give it its unstable equilibrium position as defined above. Indeed, the center of gravity and the weight of the hammers vary from one hammer to another. In addition, a hammer can strike a rope 5 which is contained, either in a first or in a second plane of strings, which requires each time the definition of another position of unstable equilibrium.

It is interesting to note that the minimum value of the hammer return moment also results in a reduction in the resistance to pressing the key 45. It is thus possible to strengthen the exhaust spring 100 while keeping the resistance to the pressing the key is substantially identical to that in conventional mechanics. In the present invention, this reinforcement of the exhaust spring 100 consequently makes it possible to further improve the return of the tongue 98 under the hammer nut 85 without increasing the resistance to the depression of the key 45.

Figure 4 shows a first embodiment of balancing means according to the invention. The hammer comprises in this embodiment a balancing spring 86 ′, the restoring moment of which is exerted on the hammer is adjustable in intensity and in the direction of action. This spring 86 'is similar to the traditional nut spring 86 but, instead of engaging with its free end in a loop 87 secured to the nut fork 89, its free end ends in a loop 86'a and carries a loop loop 87 '. The latter is put around the head of a fastening screw 87'a which is partially driven into the central bar of the mechanism 24. It is by driving in the fastening screw 87'a more or less deeply that the action of the balancing spring 86 ′ can be adjusted on the hammer nut 85. In fact, when said fastening head of the screw 87 ′ a is in alignment with the loop 86 ′ a and the pivot 90 , the spring is inactive, when said attachment head is above said alignment, the hammer undergoes a moment of return in the opposite direction of the strings; and when said. attachment head is located below said alignment, the hammer undergoes a moment of return towards the strings. As the intensity and the direction of this return movement acting on the hammer can be thus adjusted by driving the fastening screw 87'a more or less deeply into the frame, we manage to balance the moment of the masses of the hammer in a impact position on the strings 5, which thus becomes an unstable equilibrium position. Remain to note that this balance can be achieved as well for the hammers with heavy head, which tend to fall on the cords 5, as for the hammers with light head, which tend to fall towards the bar of rest of the hammers 115.

A similar effect can be obtained with the execution of the spring according to FIG. 5. In this embodiment, the balancing spring 86 '' is retained at its free end by the nut fork loop 87 fixed on the nut fork 89 We obtain an adjustment of the intensity of the return moment by an adjustment screw 86b passing through the hammer nut 85 to come to rest on a shank 86c which extends the spring 86 '' around its articulation 88 in the nut hammer 85. A reversal of the direction of return movement is obtained by choosing the attachment point for the nut fork strap 87. If this attachment point is located above said nut pivot 90 (see FIG. 6A), the return moment tends to pivot the hammer towards the rest bar 115; if it is below (see Figure 6B), the return moment tends to rotate the hammer towards the strings 5.

According to another variant (see Figure 7), the support tail 86'c is folded tangentially to the joint 88 and engages in a cavity arranged axially in one end of a screw 86'b. This cavity can in particular be conical or spherical or with internal sides for the engagement of a mounting tool. The screw 86b can, in this case, be introduced obliquely into the nut 85 while avoiding passing through the hammer handle, which is an advantage for manufacturing.

Practically, given the position of line of articulation of the hammers adopted in the current invoice, all hammers, except those of the extreme acute, require a correction by a light moment of recall towards the bar of rest. A recall moment in this direction can be obtained by fixing the nut fork strap 87 above the nut fork pivot 90, as is the case in current production. The lightest hammers of the extreme treble, on the other hand, require a correction by a slight moment of return to the strings, which is obtained by fixing the nut fork strap 87 under the nut fork pivot 90.

According to another embodiment (see Figures 8, 9, 10), the traditional return spring is either removed or simply immobilized out of service, for example, tied to the hammer handle. The hammer is then ballasted, either on the side of the head of the hammer, or on the side of the counter-catch 93, in order to be in unstable equilibrium in the impact position on the strings 5.

Most of the hammers require ballasting on the side of the counter-catch which is advantageously achieved by adding a small mass 93a, of lead for example, to the counter-catch 93. The fixing of the lead mass can be done by a screw or by gluing (see Figure 8).

According to a variant represented by FIG. 9, the ballasting consists of a jumper 93b placed on the handle of the counter catcher 93. The jumper 93b is adjusted along this handle to achieve the balance of the hammer on impact on the cords 5 and is then held in position by a screw or by gluing.

The hammers of the extreme treble require ballasting on the side of the head, shown in Figure 10. It is for example constituted by a screw 85a with more or less ballasted head, screwed into the hammer nut 85, in opposition to the handle of the counter catch (see Figure 10).

According to another embodiment, said position of unstable equilibrium of the hammers is directly defined by a judicious choice of the shape, the arrangement and / or the distribution of the mass of the constituent elements of the hammer.

Thus, it is for example possible to reduce the importance of the different balancing operations to be carried out on the various hammers by a judicious choice of the distance between the line of articulation of the hammers and the double plane of the crossed strings.

FIG. 11 shows that said unstable equilibrium point of a hammer can be moved in the direction of the strings 5, for example by increasing the height of the counter-catch 93.

On the other hand, it is possible to move said unstable equilibrium point of a treble hammer in the direction of the rest bar moving the center of gravity of the hammer head, with equal mass, in the direction of the strings. This is achieved by thickening the wood profile on the side of felt 114 and by thinning the side of the handle, as shown in Figure 12A. Figure 12B shows, for comparison, a conventional treble hammer head which has * exactly the same weight as the head of Figure 12A, but its center of gravity is located near the handle 112.

It is important to note that the optimal functioning of repetition in an upright piano mechanism modified according to the invention is a function of the mode of adjustment of a return strap 95 of the hammer (see Figure 1 to 3). This strap 95 connects the counter-catch 93 to the easel 60 by means of a strap hook 97 which is integral with the easel 60. When the key 45 is raised, the easel 60 descends and drives the hammer by the strap 95, thus accelerating his return.

For optimal operation, the tension of the strap 95 is adjusted so that the strap 95 pulls on the hammer as soon as the exhaust tab 98 returns under the nut trim 92. Such a precise adjustment of the strap 95 is particularly useful in mechanics modified according to the invention, where the return moment to which the hammer is subjected is reduced to a minimum.

However, in the current manufacture with a soft pedal system provided with a hammer support bar 118 which can pivot towards the strings, the strap is always set fairly relaxed. A relaxed strap 95 is indeed necessary to prevent the bridge 60 from being lifted by the hammer when this soft pedal is put to advance the hammers towards the strings. Indeed, in the usual mechanics, this lifting of the bridge 60 would produce a "fluttering of the keyboard", because the keys 45 would no longer be subject to the weight of the bridge 60 and would by themselves be in strict equilibrium at their rocking point.

Different solutions are proposed according to the invention to allow optimal adjustment of the strap 95, that is to say almost stretched at the time of the return of the exhaust tab 98 under the nut 85, while avoiding said floating of the keyboard when you put the soft pedal.

A first solution consists in reducing the distance 204 between the strap hook 97 and the fork fork pivot 62, and / or in increasing the distance 202 between the attachment point of the strap 97 to the counter-catch nut 93 and the nut fork pivot 90. The movement of the point of attachment of the strap to the bridge 60 is then reduced and the movement of the point of attachment to the backstop 93 is increased. This has the effect of tightening the strap 97 in the depressed key position and of relaxing it in the raised key position.

Figure 13 shows an implementation of this solution. The counter catcher 93 is bevelled on the opposite side of its bearing surface, which increases the distance 202 between the attachment point of the strap 95 and the nut fork pivot 90. The strap hook 97 is folded towards the bridge pivot 62, which decreases the distance 204 between the point of attachment of the strap and the bridge pivot 62 and allows the tension to be adjusted.

Another solution is to unbalance the key rocker by reducing the back seal 49 by a few grams (see Figure 14) or by loading the front of the key with a few grams. This imbalance can then be compensated by an adequate ballasting of the bridge 60 to maintain or increase the resistance of a key 45 to pressing. It can also be more or less compensated by the reinforcement of the exhaust spring 100, as described above, a solution which has the double advantage of not requiring an additional part and of further improving the conditions of return of the exhaust tab 98 under the nut 85.

It will be noted that the unbalanced key 45 will tend to tilt forward. Its rear end consequently follows the movement of the bridge 60, which is itself pulled upwards by the strap 95 when the soft pedal is put on. There is no longer any floating of the keys 45.

This solution has the advantage of significantly improving the continuity of the transmission contact between the key 45 and the bridge 60 and therefore has a favorable influence on the transmission of movements. It is also interesting for all the mechanics of upright pianos comprising a soft pedal of this type, of which it improves the efficiency by the fact that it reduces the stroke of penetration of the keyboard.

Figure 14 shows such an embodiment. A lead plate 49b is fixed by a screw at the front under the button. Another lead mass 49c is fixed, for example by a screw, to the bridge 60. This lead mass 49c can however also be mounted on the catch rod, as shown in FIG. 15. It then has a groove which comes engage around the catch rod 111 to be then closed by pinching.

Another solution consists in producing a key rest bar 44 which is movable vertically, and in coupling the latter to the swivel bar of hammers 118. When the soft pedal is put, the swivel bar of hammers 118 is voted towards strings and the key rest bar 44 is raised, tilting the keys forward and maintaining contact with the bridge.

Figure 16 shows a preferred embodiment of this solution. The rest bar 44 is articulated by flexible blades 44b on the chassis so that it can be lifted vertically. A rod 44c, articulated to the hammer swivel bar 118 and to the key rest bar 44, exerts traction on the latter when the hammer swivel bar 118 is pivoted in the direction of the strings 5, when the soft pedal.

It will be appreciated that the present invention presents an ingenious solution to the problem of exhaust return in upright piano mechanics. It also offers particularly simple and inexpensive alternative embodiments which are distinguished by particularly reliable operation and are easily adaptable to current mechanics. In some variants, it even offers a reduction in the number of parts used in current upright piano mechanics.

Claims (18)

1. Piano mechanics of the exhaust type, intended to be mounted in an upright piano frame opposite at least one plane of strings (5) and to be actuated by a keyboard of keys (45), comprising for each key (45) a hammer composed of a head (113, 114) integral with one end of a handle (112) the other end of which carries a hinge (90) to a frame (24), said hammer bearing close to the articulation a support lining (92) on which an exhaust tongue (98) is supported, said tongue being actuated by depressing the key to propel the hammer in the direction of the strings (5), then escaping from the support lining at the end of the hammer stroke, when the hammer head is near its point of impact on at least one cord (5) and returning under the effect of a return means (100) in support position on the lining (92) when the key is raised, characterized in that each hammer is balanced individually for a state of unstable equilibrium in its articulation (90) in impact position of his head on or ropes (5). 2. Piano mechanics according to claim 1, characterized in that at least one hammer comprises a balancing spring (86 ') provided with means for adjusting the return moment exerted on this hammer by this spring (86') in intensity and sense. 3. Piano mechanics according to claim 2, characterized in that the balancing spring (86 ') has one end secured to the hammer and one end retained by means (87', 87'a) at an attachment point secured to the frame (24) and whose position is adjustable relative to the hammer joint (90) to adjust the direction and intensity of the action of said balancing spring (86 '). 4. Piano mechanics according to claim 2, characterized in that the spring. balancing (86 '') is articulated with a hammer at one end which surrounds a hinge pin (88) and is extended by a support shank (86c) which is supported on an integral adjustment screw (86b) of the hammer, the other end of said balancing spring being retained by means (87) at an attachment point secured to the frame (24) and positioned relative to the articulation (90) of the hammer to give said hammer a moment return setback from the strings (5), towards a hammer support bar (118), said adjustment screw (86b) making it possible to adjust the intensity of the return moment. 5. Piano mechanics according to claim 4, characterized in that the attachment point of the means (87) is positioned relative to the articulation of the hammer (90) so as to give said hammer a moment of return towards the strings ( 5). 6. Piano mechanics according to claim 4 or 5, characterized in that the end of the tail (86c) is folded and engages in a cavity arranged axially in the screw (86b). 7. Piano mechanics according to claim 1, characterized in that at least one hammer is ballasted to have an unstable equilibrium state in the impact position on the strings (5). 8. Piano mechanics according to any one of claims 1 to 7, characterized in that a distribution of the masses in the hammers is carried out so that the said balancing operations to be carried out are reduced to a minimum. 9. Piano mechanics according to any one of claims 1 to 8, characterized in that the distances of the points of articulation of the hammers on the chassis, relative to the planes of the strings, are chosen so that said balancing operations to be carried out are reduced to a minimum. 10. Piano mechanics according to claim 1 further comprising a conventional soft pedal system with a hammer swivel bar (118) which can be pivoted in the direction of the strings (5) in order to limit the stroke of the hammers and a conventional system for recalling the hammer. hammer composed, for each hammer, of a strap (95) connected on one side to a conventional counter-catch (93) secured to a hammer nut (85) and on the other side to a strap hook ( 97) mounted on an easel (60), said hammer nut (85) being articulated on the chassis by a nut fork pivot (90), and said easel (60) being articulated on the chassis by a fork pivot bridge (62), said piano mechanism being characterized in that the movement of the strap (95) at the point of attachment to the counter catch (93) is greater than the movement of the strap (95) at the point of attachment hook strap (95). 11. Piano mechanics according to claim 10, characterized in that the rod hook rod (97) is bent towards the fork fork pivot (62) to reduce the distance of the strap hook (97) from the fork pivot easel (62) and allow a tight adjustment of the strap (95) as soon as the exhaust tongue (98) returns under the nut packing (92). 12. Piano mechanics according to claim 10 or 11, characterized in that the counter-catch (93) is bevelled on the opposite side of its bearing surface and that the strap (95) is fixed on this bevelled surface so as to increase the distance between the strap attachment (95) and the nut fork pivot (90). 13. Piano mechanics according to claim 1 further comprising, for each key (45) an easel (60) which is articulated at one of its ends to the frame and bears on the key (45), characterized in that the keys (45) are ballasted so as to pivot the bridge upwards. 14. Piano mechanics according to claim 1 or 13, characterized in that at least one bridge (60) is weighted so as to increase the resistance to pressing keys (45). 15. Piano mechanics according to any one of claims 1 to 13, characterized in that said tongue return means (100) is reinforced so as to more or less compensate for a loss of resistance to pressing the keys ( 45). 16. Piano mechanics according to claim 1, further comprising a conventional soft pedal system with a hammer swivel bar (118) which can be pivoted in the direction of the strings (5) in order to limit the stroke of the hammers, characterized in that the keys (45) bear with their rear end on a rest bar (44) which is articulated by flexible blades (44b) on the frame so as to be able to be lifted vertically and in that at least one rod (44c ) articulated on the hammer swivel bar (118) and on the key rest bar (44) exerts a traction on the latter to slightly lift said rear end of the key when the soft pedal is depressed. 17. Escapement type piano mechanic intended to be mounted in an upright piano frame provided with keys (45) and comprising a conventional soft pedal system with a swivel hammer bar (118) which can be swiveled in the direction of the strings (5 ) in order to limit the stroke of the hammers and a conventional hammer return system composed, for each hammer, of a strap (95) connected on one side to a counter-catch (93) secured to a hammer and the on the other side to a strap hook (97) mounted on an easel (60), said hammer nut (85) being articulated on the chassis by a nut fork pivot (90) and said easel (60) being articulated on the chassis by a fork pivot of the bridge (62), said piano mechanism being characterized in that the keys (45) are ballasted so as to tilt forward and in that the bridges (60) are ballasted with so as to increase the resistance to pressing the keys (45).