CH634916A5

CH634916A5 - Instrument with handle for measuring internal diameters

Info

Publication number: CH634916A5
Application number: CH105080A
Authority: CH
Inventors: Charles Roch
Original assignee: Roch Pierre S A R L
Priority date: 1980-02-08
Filing date: 1980-02-08
Publication date: 1983-02-28
Also published as: JPS639601B2; JPS56126701A

Abstract

The measurement prods (15) are controlled by moving equipment constituted by an axially moving rod (7a), on which a cylinder (11a) can slide, which cylinder is subjected to the action of a main spring (13) which pushes it towards a position in which it bears against a stop (19) integral with the rod (7a). This rod is furthermore pushed by a second, weaker spring (16) which acts in the opposite direction to the main spring. The trigger (17) which makes it possible to act on the cylinder (11a) can be actuated as far as its end of travel without the rod (6) of the comparator fixed to the body (1, 2) of the instrument ever being subjected to a pressure greater than the force of the second spring (16). This makes it possible to avoid the drawback of direct action of the trigger on the part of the moving equipment which acts on the feeler (10) of the comparator, and which can by virtue of this fact cause sliding of this rod in the tightening bush (4) and consequent reading errors. <IMAGE>

Description

**ATTENTION** debut du champ DESC peut contenir fin de CLMS **. ** ATTENTION ** start of the DESC field may contain end of CLMS **.

REVENDICATION Instrument à poignée pour la mesure de diamètres intérieurs, du type comprenant un corps pourvu de moyens de fixation pour adapter un comparateur sur ce corps, comprenant aussi un équipage mobile axialement dans ce corps et dont une extrémité est agencée pour commander des touches de mesure mobiles radialement par rapport à cet équipage, tandis que l'autre extrémité de cet équipage est prévue pour agir sur la touche de mesure d'un comparateur préalablement adapté audit corps, un ressort principal étant disposé dans ce corps pour tendre à agir sur cet équipage dans le sens pour lequel l'équipage sollicite les touches à faire saillie hors du corps de l'instrument, et un ressort secondaire, plus faible que le ressort principal, étant disposé dans le corps pour agir en sens inverse du ressort principal, afin de faire rétracter ces touches de mesure lorsque le ressort principal est empêché d'agir sur elles, instrument comprenant en outre une gâchette pour agir sur cet équipage pour faire cesser l'action du ressort principal sur les touches de mesure, caractérisé en ce que l'équipage mobile comporte, à l'endroit où la gâchette vient coopérer avec lui, une tige de commande destinée à faire contact par une de ses extrémités avec la touche de mesure du comparateur, et une pièce de butée montée coulissante sur cette tige, le ressort principal agissant constamment par une de ses extrémités sur cette pièce de butée, en prenant appui à son autre extrémité sur une partie fixe du corps de l'instrument, un arrêt étant prévu sur la tige de commande pour limiter le déplacement de la pièce de butée, par rapport à la tige de commande, sous l'action du ressort principal, la gâchette étant disposée de façon à agir sur cette pièce de butée, à l'encontre de l'action du ressort principal, pour soustraire les touches de mesure de l'instrument à l'action de ce ressort, le tout afin que la force exercée par la tige de commande sur le comparateur ne puisse jamais excéder celle du ressort secondaire, quelle que soit la force exercée sur la gâchette. CLAIM Instrument with handle for measuring internal diameters, of the type comprising a body provided with fixing means for adapting a comparator to this body, also comprising an axially movable element in this body and one end of which is arranged to control movable measuring keys radially with respect to this equipment, while the other end of this equipment is designed to act on the measurement button of a comparator previously adapted to said body, a main spring being disposed in this body to tend to act on this equipment in the direction for which the crew requests the keys to protrude outside the body of the instrument, and a secondary spring, weaker than the main spring, being arranged in the body to act in the opposite direction to the main spring, in order to make retract these measurement keys when the main spring is prevented from acting on them, instrument further comprising a trigger to act on this crew to do this sser the action of the main spring on the measuring keys, characterized in that the movable assembly comprises, at the point where the trigger comes to cooperate with it, a control rod intended to make contact by one of its ends with the comparator measurement key, and a stop piece slidingly mounted on this rod, the main spring acting constantly by one of its ends on this stop piece, bearing at its other end on a fixed part of the body of the instrument , a stop being provided on the control rod to limit the displacement of the stop piece, relative to the control rod, under the action of the main spring, the trigger being arranged so as to act on this stop piece, against the action of the main spring, to remove the measuring keys of the instrument from the action of this spring, all so that the force exerted by the control rod on the comparator can never exceed that second spring area, regardless of the force exerted on the trigger.

On connaît déjà des instruments à poignée pour la mesure de diamètres intérieurs qui comprennent un corps pourvu de moyens de fixation pour adapter un comparateur sur ce corps. Ces instruments connus comprennent encore un équipage mobile axialement dans ce corps, dont une extrémité est agencée pour commander des touches de mesure mobiles radialement par rapport à cet équipage, tandis que l'autre extrémité de cet équipage est prévue pour agir sur la touche de mesure d'un comparateur préalablement adapté audit corps. Handle instruments are already known for measuring internal diameters which include a body provided with fixing means to adapt a comparator to this body. These known instruments also include an axially movable element in this body, one end of which is arranged to control measuring keys which can move radially relative to this element, while the other end of this element is designed to act on the measuring key. a comparator previously adapted to said body.

Dans ces instruments connus, un ressort principal est disposé dans ce corps pour tendre à agir sur cet équipage dans le sens pour lequel l'équipage sollicite les touches à faire saillie hors du corps de l'instrument. De plus, il est prévu un ressort secondaire, plus faible que le ressort principal, qui est disposé dans le corps pour agir en sens inverse du ressort principal, afin de faire rétracter ces touches de mesure lorsque le ressort principal est empêché d'agir sur elles. Enfin, ces instruments connus comprennent une gâchette pour agir sur cet équipage pour faire cesser l'action du ressort principal sur les touches de mesure. In these known instruments, a main spring is disposed in this body to tend to act on this equipment in the direction for which the equipment requests the keys to protrude from the body of the instrument. In addition, a secondary spring is provided, weaker than the main spring, which is arranged in the body to act in the opposite direction to the main spring, in order to retract these measurement keys when the main spring is prevented from acting on they. Finally, these known instruments include a trigger for acting on this equipment to stop the action of the main spring on the measurement keys.

Ces instruments connus ont toutefois ce défaut: la position de la gâchette pour laquelle les touches de mesure sont complètement rétractées n'est pas la position de fin de course de cette gâchette. Il en résulte que si l'usager agit trop fortement sur la gâchette il dépasse cette position normale de fin de course, ce qui provoque une pression de la gâchette sur une partie de l'équipage mobile qui la transmet au comparateur. Etant donné qu'on utilise de plus en plus souvent des comparateurs électroniques dont la tige est délicate et qu'on ne peut par conséquent pas bloquer énergiquement sur le corps de l'instrument, cette action trop énergique sur la gâchette provoque un recul de la tige du comparateur à l'intérieur du corps de l'instrument, dont l'opérateur ne s'aperçoit en général pas, mais qui fausse complètement les lectures ultérieures.Ce même défaut peut apparaître lorsqu'on utilise les comparateurs mécaniques, si ces derniers ne sont pas fixes par serrage très énergique sur le corps de l'appareil. However, these known instruments have this defect: the position of the trigger for which the measurement keys are fully retracted is not the end position of this trigger. As a result, if the user acts too strongly on the trigger, it exceeds this normal end-of-travel position, which causes the trigger to be pressed on a part of the moving assembly which transmits it to the comparator. Since electronic comparators are used more and more often with a delicate stem and therefore cannot be strongly blocked on the body of the instrument, this too energetic action on the trigger causes a reduction in the comparator rod inside the instrument body, which the operator does not generally notice, but which completely falsifies subsequent readings. This same defect can appear when using mechanical comparators, if these are not fixed by very strong tightening on the body of the device.

La présente invention remédie à ce défaut. Elle a pour objet un instrument de mesure conforme à la revendication. The present invention remedies this defect. It relates to a measuring instrument according to the claim.

Le dessin annexé représente à titre d'exemple une forme d'exécution de l'instrument selon l'invention. The accompanying drawing shows by way of example an embodiment of the instrument according to the invention.

La fig. 1 est une vue en coupe axiale schématique d'un instrument de type connu, à poignée, pour la mesure de diamètres intérieurs. Fig. 1 is a schematic axial sectional view of an instrument of known type, with a handle, for measuring internal diameters.

La fig. 2 est une vue en coupe axiale de la forme d'exécution de l'instrument selon l'invention, montrant les organes en position normale de mesure. Fig. 2 is an axial sectional view of the embodiment of the instrument according to the invention, showing the members in the normal measurement position.

La fig. 3 est une vue analogue à la fig. 2, mais montrant la position qu'occupent ces organes lorsqu'on agit sur la gâchette pour amener celle-ci à fin de course. Fig. 3 is a view similar to FIG. 2, but showing the position occupied by these organs when the trigger is actuated to bring the latter to the end of its travel.

Sur la fig. 1, le corps de l'instrument est formé d'une pièce 1, d'une pièce 2 vissée sur la pièce 1 et d'une poignée 3 fixée sur la pièce 2. Des moyens de serrage comprenant une douille fendue 4 et un écrou de serrage 5 servent à fixer la tige 6 d'un comparateur à l'intérieur du corps 1, 2, 3. A l'intérieur du corps se trouve un équipage mobile formé d'une tige cylindrique 7 pouvant coulisser axialement à l'intérieur de la pièce 1, d'une autre tige cylindrique 8 disposée pour faire contact avec l'extrémité de droite de la tige 7, cette tige 8 étant coaxiale avec la tige 7. Cette tige 8 est destinée à agir, par son extrémité de droite sur le dessin (désignée par 9), sur la touche de mesure 10 du comparateur 6. Une pièce de butée cylindrique 11 est fixée sur la tige 8 au moyen d'une cheville 12.Un ressort principal 13 est disposé à l'intérieur de la pièce 2, autour de la partie de la tige 8 située à droite de la pièce 1 1 sur laquelle il agit par l'une de ses extrémités, tandis qu'il prend appui par son autre extrémité sur une partie fixe du corps de l'appareil constituée, dans cet exemple, par la douille de serrage 4. In fig. 1, the body of the instrument is formed of a part 1, a part 2 screwed onto the part 1 and a handle 3 fixed to the part 2. Clamping means comprising a split sleeve 4 and a nut clamp 5 are used to fix the rod 6 of a comparator inside the body 1, 2, 3. Inside the body is a movable assembly formed by a cylindrical rod 7 which can slide axially inside of part 1, of another cylindrical rod 8 arranged to make contact with the right end of the rod 7, this rod 8 being coaxial with the rod 7. This rod 8 is intended to act, by its right end in the drawing (designated by 9), on the measuring button 10 of the comparator 6. A cylindrical stopper part 11 is fixed to the rod 8 by means of a dowel 12. A main spring 13 is disposed inside the part 2, around the part of the rod 8 located to the right of the part 1 1 on which it acts by one of its ends, while it is supported pa r its other end on a fixed part of the body of the device constituted, in this example, by the clamping sleeve 4.

A l'extrémité de gauche sur le dessin, à la pièce 1 se trouve fixée une tête de mesure 14 comprenant trois touches telles que 15 servant à la mesure de diamètres intérieurs. L'extrémité de gauche de la tige 7 est en contact avec ces touches que le ressort 13 tend à faire sortir de la tête 14. Un ressort secondaire 16 est disposé dans la pièce 1 pour agir sur la tige 7 en sens inverse du ressort 13. Ce ressort secondaire 16 est sensiblement plus faible que le ressort principal 13, mais sensiblement plus fort que le ressort du comparateur 6 tendant à faire sortir la touche de mesure 10. At the left end in the drawing, to part 1 is attached a measuring head 14 comprising three keys such as 15 used for measuring internal diameters. The left end of the rod 7 is in contact with these keys that the spring 13 tends to force out of the head 14. A secondary spring 16 is placed in the part 1 to act on the rod 7 in the opposite direction to the spring 13 This secondary spring 16 is appreciably weaker than the main spring 13, but appreciably stronger than the comparator spring 6 tending to release the measurement key 10.

Une gâchette 17 est articulée sur la partie 3 et sert à agir sur la pièce 1 1 à l'encontre de l'action du ressort 13, pour soustraire les touches de mesure 15 de l'action de ce ressort. Dans la position représentée en traits ponctués, la gâchette 17 est en position de repos, c'est-à- dire dans sa position extrême de gauche où elle est maintenue par le ressort 13. Les touches de mesure 15 font alors saillie au maximum hors de la tête de mesure 14. Dans la position représentée en traits mixtes, la gâchette 17 occupe la position dans laquelle les touches de mesure 15 sont toutjuste effacées à l'intérieur de la tête 14. La position de la gâchette 17 représentée en traits pleins est la position de fin de course de cette gâchette.En passant dans la position en traits mixtes à la position en traits pleins, la gâchette 17 a donc agi sur la touche de mesure 10 du comparateur 6, par l'intermédiaire de la pièce 11 et de la partie terminale 9 de la tige 8, d'une façon assez énergique pour que cette tige du comparateur 6 ait glissé à l'intérieur de la douille de serrage 4. Dès lors, les indications ultérieures du comparateur seront fausses, ce qui est l'inconvénient que l'invention vise pré cisément à éliminer. A trigger 17 is articulated on the part 3 and is used to act on the part 1 1 against the action of the spring 13, to subtract the measurement keys 15 from the action of this spring. In the position shown in dotted lines, the trigger 17 is in the rest position, that is to say in its extreme left position where it is held by the spring 13. The measurement keys 15 then protrude as far out as possible. of the measuring head 14. In the position shown in dashed lines, the trigger 17 occupies the position in which the measuring keys 15 are just erased inside the head 14. The position of the trigger 17 shown in solid lines is the end position of this trigger. Passing in the position in dashed lines to the position in solid lines, the trigger 17 therefore acted on the measurement button 10 of the comparator 6, via the part 11 and of the terminal part 9 of the rod 8, in a manner sufficiently energetic that this rod of the comparator 6 has slipped inside the clamping sleeve 4. Consequently, the subsequent indications of the comparator will be false, which is the downside that the inventio n is precisely aimed at eliminating.

Les organes étant représentés dans la position extrême de droite de la gâchette, les tiges 7 et 8 ne font plus contact. Bien entendu, lorsqu'on est entre la position représentée en traits ponctués et la position en traits mixtes de la gâchette 17, les tiges 7 et 8 se touchent. La distance dont ces deux tiges se séparent représente précisément le déplacement qui peut être infligé à la tige 6 du comparateur si l'on agit avec une force excessive sur la gâchette 17. The organs being shown in the extreme right position of the trigger, the rods 7 and 8 no longer make contact. Of course, when one is between the position shown in dotted lines and the position in broken lines of the trigger 17, the rods 7 and 8 touch. The distance from which these two rods separate represents precisely the displacement which can be inflicted on rod 6 of the comparator if one acts with excessive force on trigger 17.

Dans la forme d'exécution de l'instrument représentée sur les fig. 2 et 3, on a désigné les parties identiques à celles de la fig. 1 par les In the embodiment of the instrument shown in FIGS. 2 and 3, the parts identical to those of FIG. 1 by

mêmes numéros de référence. Sur la fig. 2, on voit en 15 les touches de mesure faisant saillie d'une certaine distance hors de la tête de mesure 14 et venues en contact avec l'alésage d'une pièce 18 dont il s'agit de mesurer le diamètre intérieur. same reference numbers. In fig. 2, we see at 15 the measuring keys projecting a certain distance outside the measuring head 14 and coming into contact with the bore of a part 18 whose internal diameter is to be measured.

Dans cette exécution, I'équipage mobile est formé simplement d'une tige cylindrique 7a pouvant se déplacer axialement à l'intérieur des parties 1, 2 du corps de l'instrument, cette tige 7a agissant par son extrémité de gauche sur les touches de mesure 15 et étant destinée à faire contact, par son extrémité de droite, avec la touche de mesure 10 du comparateur dont on voit la tige en 6. Cet équipage mobile comprend une pièce 1 la analogue à la pièce 1 1 de la fig. 1, mais montée pour coulisser librement sur la tige 7a. Un circlip 19 est fixé sur la tige 7a pour limiter le déplacement vers la gauche de la pièce 1 la sur la tige 7a sous l'action du ressort principal 13. Le ressort secondaire 16 prend appui sur la pièce 2 et agit sur un circlip 20 fixé sur la tige 7a.La position de la gâchette 17 représentée en traits ponctués est celle de repos. La position représentée en traits pleins est la position de mesure. Si l'on déplace la gâchette plus loin vers la droite, il arrive un moment où les touches de mesure 15 sont complètement rétractées dans la tête 14; si l'on va encore plus loin, jusqu'au moment ou la gâchette 17 bute contre la partie 21 de la poignée, comme on le voit sur la fig. 3, les touches 15 sont complètement rétractées dans la tête 14 et la tige 7a ne fait plus contact avec elle. Cette tige ne peut toutefois pas agir sur la tige 6 du comparateur avec une force suffisante pour le solliciter à glisser à l'intérieur de la douille de serrage 4.En effet, dès l'instant où l'on a dépassé la position complètement rétractée des touches de mesure 15 et que l'on continue d'agir sur la gâchette pour la pousser vers la droite sur le dessin, la gâchette pousse la pièce cylindrique I la vers la droite mais, cette pièce étant libre sur la tige 7a, elle quitte dès la fin de course de la touche de mesure 10 le contact avec le circlip 19 et comprime davantage le ressort 13, ce qui n'a aucun inconvénient. Dès lors, la seule force par laquelle la pièce 7a agit sur la touche de mesure 10 est la force du ressort secondaire 16 qui, elle, est suffisamment faible pour ne pas provoquer l'inconvénient signalé au début. In this embodiment, the moving element is simply formed by a cylindrical rod 7a which can move axially inside the parts 1, 2 of the body of the instrument, this rod 7a acting by its left end on the keys measurement 15 and being intended to make contact, at its right end, with the measurement key 10 of the comparator, the rod of which can be seen at 6. This movable assembly comprises a part 1 analogous to part 1 1 of FIG. 1, but mounted to slide freely on the rod 7a. A circlip 19 is fixed on the rod 7a to limit the movement to the left of the part 1 la on the rod 7a under the action of the main spring 13. The secondary spring 16 bears on the part 2 and acts on a circlip 20 fixed on the rod 7a. The position of the trigger 17 shown in dotted lines is that of rest. The position shown in solid lines is the measurement position. If the trigger is moved further to the right, there comes a point when the measurement keys 15 are completely retracted in the head 14; if we go even further, until the trigger 17 abuts against part 21 of the handle, as seen in FIG. 3, the keys 15 are completely retracted in the head 14 and the rod 7a no longer makes contact with it. This rod cannot, however, act on the rod 6 of the comparator with sufficient force to urge it to slide inside the clamping sleeve 4. Indeed, from the moment we have passed the fully retracted position measurement keys 15 and we continue to act on the trigger to push it to the right in the drawing, the trigger pushes the cylindrical part I to the right but, this part being free on the rod 7a, it leaves contact with the circlip 19 at the end of the travel of the measuring key 10 and further compresses the spring 13, which has no disadvantages. Consequently, the only force by which the part 7a acts on the measuring key 10 is the force of the secondary spring 16 which, for its part, is sufficiently weak not to cause the drawback indicated at the start.

Les forces respectives des ressorts entrant enjeu ici sont par exemple de 1 à 3 kg pour le ressort 13, de 300 g pour le ressort secondaire 16, et de 200 g pour la force de rappel du comparateur agissant sur la touche de mesure 10. Ces indications montrent que le défaut signalé des instruments connus est complètement évité. The respective forces of the springs entering the stake here are for example 1 to 3 kg for the spring 13, 300 g for the secondary spring 16, and 200 g for the return force of the comparator acting on the measurement key 10. These indications show that the reported defect of known instruments is completely avoided.

Bien entendu, la tige 7a pourrait ne pas être faite d'une seule pièce, comme cela est d'ordinaire le cas, notamment dans la fig. 1, mais le fonctionnement resterait essentiellement le même dés lors que la pièce 11 est mobile par rapport à la pièce 7a. Of course, the rod 7a could not be made in one piece, as is usually the case, especially in FIG. 1, but the operation would remain essentially the same as soon as the part 11 is movable relative to the part 7a.

Claims

CLAIM Instrument with handle for measuring internal diameters, of the type comprising a body provided with fixing means for adapting a comparator to this body, also comprising an axially movable element in this body and one end of which is arranged to control movable measuring keys radially with respect to this equipment, while the other end of this equipment is designed to act on the measurement button of a comparator previously adapted to said body, a main spring being disposed in this body to tend to act on this equipment in the direction for which the crew requests the keys to protrude outside the body of the instrument, and a secondary spring, weaker than the main spring, being arranged in the body to act in the opposite direction to the main spring, in order to make retract these measurement keys when the main spring is prevented from acting on them, instrument further comprising a trigger to act on this crew to do this sser the action of the main spring on the measuring keys, characterized in that the movable assembly comprises, at the point where the trigger comes to cooperate with it, a control rod intended to make contact by one of its ends with the comparator measurement key, and a stop piece slidingly mounted on this rod, the main spring acting constantly by one of its ends on this stop piece, bearing at its other end on a fixed part of the body of the instrument , a stop being provided on the control rod to limit the displacement of the stop piece, relative to the control rod, under the action of the main spring, the trigger being arranged so as to act on this stop piece, against the action of the main spring, to remove the measuring keys of the instrument from the action of this spring, all so that the force exerted by the control rod on the comparator can never exceed that second spring area, regardless of the force exerted on the trigger.

Handle instruments are already known for measuring internal diameters which include a body provided with fixing means to adapt a comparator to this body. These known instruments also include an axially movable element in this body, one end of which is arranged to control measuring keys which can move radially relative to this element, while the other end of this element is designed to act on the measuring key. a comparator previously adapted to said body.

In these known instruments, a main spring is disposed in this body to tend to act on this equipment in the direction for which the equipment requests the keys to protrude from the body of the instrument. In addition, a secondary spring is provided, weaker than the main spring, which is arranged in the body to act in the opposite direction to the main spring, in order to retract these measurement keys when the main spring is prevented from acting on they. Finally, these known instruments include a trigger for acting on this equipment to stop the action of the main spring on the measurement keys.

However, these known instruments have this defect: the position of the trigger for which the measurement keys are fully retracted is not the end position of this trigger. As a result, if the user acts too strongly on the trigger, it exceeds this normal end-of-travel position, which causes the trigger to be pressed on a part of the moving assembly which transmits it to the comparator. Since electronic comparators are used more and more often with a delicate stem and therefore cannot be strongly blocked on the body of the instrument, this too energetic action on the trigger causes a reduction in the comparator rod inside the instrument body, which the operator does not generally notice, but which completely falsifies subsequent readings. This same defect can appear when using mechanical comparators, if these are not fixed by very strong tightening on the body of the device.

The present invention remedies this defect. It relates to a measuring instrument according to the claim.

The accompanying drawing shows by way of example an embodiment of the instrument according to the invention.

Fig. 1 is a schematic axial sectional view of an instrument of known type, with a handle, for measuring internal diameters.

Fig. 2 is an axial sectional view of the embodiment of the instrument according to the invention, showing the members in the normal measurement position.

Fig. 3 is a view similar to FIG. 2, but showing the position occupied by these organs when the trigger is actuated to bring the latter to the end of its travel.

In fig. 1, the body of the instrument is formed of a part 1, a part 2 screwed onto the part 1 and a handle 3 fixed to the part

2. Clamping means comprising a split bushing 4 and a clamping nut 5 serve to fix the rod 6 of a comparator inside the body 1, 2,

3. Inside the body is a movable element formed by a cylindrical rod 7 which can slide axially inside the part 1, by another cylindrical rod 8 arranged to make contact with the right end of the rod 7, this rod 8 being coaxial with the rod 7. This rod 8 is intended to act, by its right end on the drawing (designated by 9), on the measurement key 10 of the comparator 6. A stop piece cylindrical 11 is fixed to the rod 8 by means of a dowel 12. A main spring 13 is disposed inside the part 2, around the part of the rod 8 located to the right of the part 1 1 on which it acts by one of its ends, while it bears by its other end on a fixed part of the body of the device constituted, in this example, by the clamping sleeve

4.

At the left end in the drawing, to part 1 is attached a measuring head 14 comprising three keys such as 15 used for measuring internal diameters. The left end of the rod 7 is in contact with these keys that the spring 13 tends to force out of the head 14. A secondary spring 16 is placed in the part 1 to act on the rod 7 in the opposite direction to the spring 13 This secondary spring 16 is appreciably weaker than the main spring 13, but appreciably stronger than the comparator spring 6 tending to release the measurement key 10.

A trigger 17 is articulated on the part 3 and is used to act on the part 1 1 against the action of the spring 13, to subtract the measurement keys 15 from the action of this spring. In the position shown in dotted lines, the trigger 17 is in the rest position, that is to say in its extreme left position where it is held by the spring 13. The measurement keys 15 then protrude as far out as possible. of the measuring head 14. In the position shown in dashed lines, the trigger 17 occupies the position in which the measuring keys 15 are just erased inside the head 14. The position of the trigger 17 shown in solid lines is the end position of this trigger. Passing in the position in dashed lines to the position in solid lines, the trigger 17 has therefore acted on the measurement button 10 of the comparator 6, via the part 11 and of the terminal part 9 of the rod 8, in a manner sufficiently energetic that this rod of the comparator 6 has slipped inside the clamping sleeve 4. Consequently, the subsequent indications of the comparator will be false, which is the downside that the inventio n is precisely aimed at eliminating.

The organs being shown in the extreme right position of the trigger, the rods 7 and 8 no longer make contact. Of course, when one is between the position shown in dotted lines and the position in broken lines of the trigger 17, the rods 7 and 8 touch. The distance from which these two rods separate represents precisely the displacement which can be inflicted on rod 6 of the comparator if one acts with excessive force on trigger 17.

In the embodiment of the instrument shown in FIGS. 2 and 3, the parts identical to those of FIG. 1 by

** ATTENTION ** end of the CLMS field may contain start of DESC **.