Abstract: A micromechanical timepiece, and a method for making the same, having a plurality of mutually secured functional sub-assemblies stacked in a direction (Z) to form a multistage assembly, wherein each functional sub-assembly comprises a single semiconductor material and is secured to another sub-assembly via bridges made of the semiconductor material, and in that at least one sub-assembly comprises at least two portions, the portions being movable relative to each other and relative to another sub-assembly to which at least one of the portions is secured via at least one deformable link integrally formed between the portions.

Abstract: A timepiece escapement comprising: an escapement wheel pivotably mounted about a first axis of rotation and intended to be driven by a power source; a lever pivotably mounted about a second axis of rotation, said lever comprising an entry pallet and an exit pallet, each pallet comprising a rest face arranged to alternately and sequentially lock the escapement wheel, the lever being suitable for transmitting pulses received from the escapement wheel to a regulating member arranged to oscillate, and for releasing the escapement wheel periodically under the control of said regulating member, wherein the rest face of the entry pallet is arranged such that, when it locks a tooth of the escapement wheel, a draw force is generated by the interaction between the rest face and the tooth to apply a torque that tends to retain the lever in the rest position.

Abstract: An escape lever suppresses energy loss and provides strong resistance to external shocks. An escape lever has a pallet fork; a pallet formed in unison with the pallet fork for engaging the escape wheel; and a pallet staff that is a pivot of the pallet fork and passes through the pallet fork. The pallet has a locking surface that the locking corner of the escape wheel contacts in the unlocking period when the escape wheel is released by the pallet and freed to move. The locking surface is shaped so that the draw angle formed by a normal to the contact point with the locking corner of the escape wheel, and a line through the contact point and the axis of the pallet staff, remains constant during the unlocking period.

Abstract: A system including two components intended to be in friction contact with each other in a given direction, wherein the friction occurs in a functional area, wherein the system is at least one of the two components including, on a surface in the functional area, a texture formed of a series of troughs of rounded shape separated by peaks or a series of bumps of rounded shape separated by troughs, the troughs extending parallel in the given direction and allowing for the evacuation of debris produced by friction and serving as a reservoir for a lubricant. A method for manufacturing at least one component or a mold by the DRIE (deep reactive ion etching) process, wherein surface defects on the sidewalls machined by the DRIE process are used to form the troughs.

Abstract: The present invention concerns an assembly for holding or supporting a timepiece balance spring, comprising a balance spring stud and a balance cock on which is fixed a balance spring stud-holder, wherein said stud-holder comprises a holding means provided with a housing for housing the balance spring stud therein and a gripping means, at least said gripping means being movable with respect to the holding means in order to lock the balance spring stud inside its housing.

Abstract: A timepiece pallet fork for a mechanical oscillator including an arbor allowing the timepiece pallet fork to oscillate about a pivot axis, first and second pallets configured to alternatively engage with an escapement wheel when the timepiece pallet fork oscillates, the first pallet being displaceable with respect to the arbor by absorption of energy, the first pallet being displaceable from a first upstream waiting position to a first downstream stopping end position which is offset compared to the first upstream waiting position, and a first arm having an intermediate section including an elastic bend, one end of the arm being fixed with respect to the arbor to form a first fixed end, the intermediate section of the first arm being located between the first fixed end and the first pallet and returning the first pallet towards the first upstream waiting position by the intermediate section being elastically deformable from a first configuration into a second configuration.

Abstract: The invention relates to an assembly system including a member made of a first material including a staff and a shoulder, the staff of the member being received in an aperture of a part made of a second material having little or no plastic domain. According to the invention, the assembly system includes a locking element made of a third material arranged to elastically attach the part between the shoulder of the member and the locking element and the locking element is a conical washer including an internal wall which radially grips the staff of the member, and a peripheral portion of the locking element which exerts an elastic radial force vertical to the shoulder of the member in order to secure the assembly of the member—part—locking element.

Abstract: A timepiece escapement mechanism, including a balance having no roller and an escape wheel, between which impulses are transmitted by a flexible, single-piece mechanism, connected by at least one flexible strip to a fixed structure or to the wheel. Oscillation is maintained by a balance spring ending in a balance spring stud which is mobile during operation, and which is guided by a flexible guide member with flexible strips, and whose center of rotation is coaxial to the balance, the balance spring stud receiving a pin which is mobile in a cam path of the wheel. During the oscillations, the balance spring stud is moved relative to its locking position under action of force exerted by the balance spring, and the pin maintains and regulates the oscillation.

Abstract: A method for manufacturing a component in a substrate including: a) modifying a structure of at least one region of the substrate to make the at least one region more selective; and b) chemically etching the at least one region to selectively manufacture the component.

Abstract: The balance spring stud holder has a housing in the form of a groove arranged to longitudinally receive and position the stud. The housing is at least partially laterally closed by an elastic strip which is arranged to return the stud against the bottom of the groove so that the stud can be locked, when the stud is inserted into the housing between the elastic strip and the bottom of the groove.

Abstract: Timepiece mechanism cassette including at least one bearing surface for positioning the cassette in a movement, a plate and a bar, at least one of which is rigid, between or on which there are arranged functional components at least two of which are movable relative to each other. At least one functional component is pivotally movable and pivoted between the plate and the bar, and forms an inseparable single piece component with the plate and/or with the bar.

Abstract: A detent escapement for a mechanical timepiece includes an escape wheel, a balance mounted for undergoing oscillation movement about a balance staff, a blade and an actuating spring. The balance has an unlocking stone and has an impulse jewel for contacting a wheel tooth of the escape wheel. The blade has a locking stone for contacting the wheel tooth of the escape wheel and is supported for undergoing movement in approaching and separating directions relative to the escape wheel. The actuating spring is configured to contact the unlocking stone and is mounted for undergoing elastic deformation along the approaching and separating directions with respect to the blade. An adjustment mechanism adjusts a projecting amount of a spring tip portion of the actuating spring from a blade tip portion of the blade.

Abstract: A detent escapement for a timepiece has an escape wheel and an actuating lever. A balance is mounted to undergo pivotal movement about a pivot axis and is configured to contact a wheel tooth of the escape wheel and an unlocking stone. The actuating lever has a locking stone configured to contact the wheel tooth of the escape wheel, a locking stone support arm that supports the locking stone, an actuating spring having a contact portion capable of contacting the unlocking stone, and an actuating spring support arm for determining a position of the contact portion of the actuating spring. At least two of the locking stone support arm, the actuating spring, and the actuating spring support arm are formed of the same material and have the same thickness in a direction along the pivot axis of the balance.

Abstract: The escapement comprises an escapement wheel (1) and an anchor (2). In the place of the traditional limiting walls or pins, the escapement comprises, on the anchor (2) and/or the escapement wheel (1), means (17, 18) for limiting the oscillations of the anchor (2) during normal operation of the escapement. In order to prevent contact between the impulse beak (10) of the pallets (6, 7) and the escapement wheel (1) upon impacts, the escapement wheel (1) has protrusions (20, 21, 22) at its periphery.

Abstract: A detent escapement 100 includes an escape wheel 110, a balance 120 which has an impulse pallet 122 and an unlocking stone 124, and a blade 130 which has a locking stone 132. A one side actuating spring 140 which can contact the unlocking stone 124 is provided in the blade 130. When a working reference line 129, which is a line connecting the rotation center of the balance 120 and the rotation center of the blade 130, is set to a reference, the one side actuating spring 140 is disposed at an angle so that a distance of the tip of the one side actuating spring from the working reference line is increased as the tip is separated from the rotation center of the balance 120 in a side opposite to the side at which the escape wheel 110 is present. The one side actuating spring 140 is disposed between the locking stone support arm 131 and the one side actuating spring support arm 133.

Abstract: An escapement (1) comprising: a roller (5), a first mobile escapement part (2) comprising first escapement teeth (22) and a second mobile escapement part (3) comprising second escapement teeth (32), a means (29, 39) for mechanically coupling the first mobile escapement part to the second mobile escapement part, and an anchor (4) carrying a first and second pallet stone (42, 43), the roller comprising a third impulse pallet stone (52) cooperating with the first escapement teeth and a fourth impulse pallet stone (53) cooperating with the second escapement teeth.

Abstract: Anti-trip device (1) for a balance (2) pivoting about an axis (D1) whose position is fixed relative to a plate (3). It includes a banking pin (5) on said plate (3), a bistable assembly (8) including: a rotor (9) which is synchronous with said balance (2) and a lever (11) pivoting about another axis (D2) of said rotor (9) between two extreme positions of indexing means (12) memorizing the position of said balance (2), the trajectory of said lever (11) partially interfering with said banking pin (5) when said balance (2) is pivoting; means (15) for limiting amplitude in the event of a shock, which includes stop means (16) between said lever (11) and said banking pin (5), forming a pivot stop during a normal arc of the balance and which, when pressed, generates a change of position in said indexing means (12) and a stop for said balance (2) in the event of knocking.

Abstract: This Swiss lever escapement comprises an escape wheel having teeth, and a lever having on the one hand an entry pallet and an exit pallet that engage alternately with the teeth of the escape wheel, and on the other hand a fork that engages periodically with an impulse pin on a roller mounted on the staff of a regulator balance wheel. The relative width Lpl of each of said pallets, expressed as a percentage of the sum of the lengths of arc of one of said teeth and one of said pallets, measured at the circumference of the escape wheel is: Lpl = Ls Ls + d ? ? or ? ? Le Le + d ? 60 ? % where Ls and Le are the lengths of arc of the exit pallet and entry pallet, respectively, and d is the length of arc of one escape wheel tooth.

Abstract: A detent escapement for a timepiece capable of decreasing energy loss with respect to a free oscillation of a balance and improving a timekeeping accuracy is provided. In addition, a detent escapement of a timepiece capable of realizing miniaturization and suppressing variations in the accuracy of a finished product due to assembly errors is provided. A one-side actuating spring of a detent 7 is formed so that a maximum stress portion, which is generated at the time of operating due to the contact of an unlocking stone 4 when a balance 5 is return-rotated, is present to be perpendicular to a first straight line L1 which connects the center of the balance staff 9 and a fulcrum 23a of the blade 23, and to be the side opposite to the balance by a second straight line L2 which passes through the fulcrum 23a.

Abstract: The invention relates to a single piece coaxial escape wheel set (100, 100?) including a first toothing (108, 108?) formed at the periphery of a plate (103, 103?) and a second toothing (113, 113?). According to the invention, the second toothing (113, 113?) is formed in a single piece with the plate (103, 103?) of the first toothing (108, 108?) so as to reduce any problems of alignment of one in relation to the other and to decrease the overall mass of the wheel set (100, 100?). The invention concerns the field of timepieces.

Abstract: In a detent escapement 100, a blade 130 includes a plurality of blade components that includes a one side actuating spring 140 which includes a portion capable of contacting the unlocking stone 124, and a one side actuating spring support arm 133 which determines a position of an unlocking stone contact portion 140G which is positioned in a tip of the one side actuating spring 140. At least two of the blade components are formed of the same material as each other, and each thickness is the same as each other.

Abstract: The escapement comprises an escape wheel assembly (1), a balance roller (3) carrying an impulse pin (4) and a first impulse pallet (5). It further comprises a lever (8) provided with a second impulse pallet (11) and with first and second locking pallets (12, 13). The wheel assembly (1) comprises an escape wheel with teeth (6) that mesh directly with the teeth (20) of the last wheel of a gear train (2), the teeth (6) of the wheel (1) engaging with the impulse and locking pallets.

Abstract: A detent escapement 100 includes an escape wheel 110, a balance 120 which has an impulse pallet 122 and an unlocking stone 124, and a blade 130 which has a locking stone 132. A one side actuating spring 140 which can contact the unlocking stone 124 is provided in the blade 130. When a working reference line 129, which is a line connecting the rotation center of the balance 120 and the rotation center of the blade 130, is set to a reference, the one side actuating spring 140 is disposed at an angle so that a distance of the tip of the one side actuating spring from the working reference line is increased as the tip is separated from the rotation center of the balance 120 in a side opposite to the side at which the escape wheel 110 is present. The one side actuating spring 140 is disposed between the locking stone support arm 131 and the one side actuating spring support arm 133.

Abstract: An anchor escapement of a mechanical watch has an escape wheel, a pallet fork engageable with or disengageable from a roller jewel of a pallet shaft having banking pin engaging portions at both sides, and pallet bridges engageable with the banking pin engaging portions at the pallet engaging portions to define the swing range of the pallet fork. One of the pallet shaft and the pallet bridges has elastic arm portions having engaging portions engageable with the engaging portions of the other member of the pallet shaft and the pallet bridge in a state in which the pallet fork fixes the escape wheel at the pallet jewel.

Abstract: This timepiece is furnished with a direct impulse escapement comprising a locking lever (2) for locking the escapement wheel furnished with two locking pallets (2a, 2b), with a fork (2c) and with a guard pin (2d). The guard pin is mounted so as to pivot on the fork about an axis parallel to the pivoting axis of the locking lever (2). It comprises displacement means (2d1, 2d2, 2d3), designed to engage with drive means secured to said frame, so as to amplify the angular displacement of the guard pin (2d), caused by the locking lever (2) passing from one to the other of its two positions. This invention also applies to the guard pin of a pallet assembly of an indirect impulse escapement.

Abstract: This Swiss lever escapement comprises an escape wheel having teeth, and a lever having on the one hand an entry pallet and an exit pallet that engage alternately with the teeth of the escape wheel, and on the other hand a fork that engages periodically with an impulse pin on a roller mounted on the staff of a regulator balance wheel. The relative width Lpl of each of said pallets, expressed as a percentage of the sum of the lengths of arc of one of said teeth and one of said pallets, measured at the circumference of the escape wheel is: Lpl = Ls Ls + d ? ? or ? ? Le Le + d ? 60 ? % where Ls and Le are the lengths of arc of the exit pallet and entry pallet, respectively, and d is the length of arc of one escape wheel tooth.

Abstract: To provide a timepiece bearing, a movement, and a portable timepiece helping to achieve an improvement in terms of time indication accuracy. A timepiece bearing 180 includes: a bearing member 181 provided at at least one end portion 145 of a shaft member 143 rotating around an axis C and regulating movement of the shaft member in axial and radial directions; an elastic member 182 having an force facing in axial direction to the bearing member; and a frame member 166 containing the bearing member, wherein the elastic member is provided so as to establish connection between the bearing member and the frame member; the frame member is supported by and fixed to a support member 167; and the shaft member is rotatable around the axis, with the shaft member and the bearing member being held in contact with each other by the elastic member.

Abstract: This escapement comprises a balance wheel (3), an escape wheel (1), a detent rocker (4) having an arresting element (4a) and an elastic clearance element (4c), means for inserting the arresting element into the path of the teeth of the escape wheel (1), and a clearance pin (7) rotating integrally with the balance wheel (3) in order to engage with the elastic clearance element (4c) of the rocker (4) once per period of oscillation of the balance wheel. The means for inserting the arresting element (4a) into the path of the teeth of the escape wheel (1) comprise a sliding surface (4b) integral with the detent rocker (4) and arranged so as to move into the path of the teeth of the escape wheel (1) when the arresting element (4a) leaves it, this sliding surface being shaped so as to return the arresting element (4a) to the locking position.

Abstract: Disclosed are an integrally molded type pallet fork (incomplete) with a safety pin and a roller table that are formed with high precision by a simple process, a thin escapement governor including the pallet fork (complete) and the roller table, and a method of manufacturing the pallet fork (complete) and the roller table.

Abstract: The escapement comprises an escape wheel assembly (1), a balance roller (3) carrying an impulse pin (4) and a first impulse pallet (5). It further comprises a lever (8) provided with a second impulse pallet (11) and with first and second locking pallets (12, 13). The wheel assembly (1) comprises an escape wheel with teeth (6) that mesh directly with the teeth (20) of the last wheel of a gear train (2), the teeth (6) of the wheel (1) engaging with the impulse and locking pallets.

Abstract: The invention concerns an escapement (1) for a timepiece comprising an anchor (2) articulated on a stem (3) and co-operating with an escapement mobile (4) articulated on an axis (5), said mobile comprising a plurality of teeth (8; 15, 16) uniformly spaced around said mobile, said anchor including an entry pallet (6) and an exit pallet (7) arranged to receive alternately an impulse from one of the teeth borne by the mobile and for acting as rest plane for said tooth. The invention is characterized in that the escapement mobile (4) comprises first and second integral and coaxial wheels (13, 14) including each the same number of teeth (15, 16), in that the entry and exit pallets (6, 7) co-operate respectively with the first and second wheels (13, 14) and in that the peripheral radius (R1) of the first wheel (13) is greater than the peripheral radius (R2) of the second wheel (14).

Abstract: The timepiece escapement includes first (3) and second (4) impulse pallet stones secured to the balance (2) directly cooperating with the teeth of the escape wheel set (1) and a brake lever (5) periodically driven by the balance, the brake lever being provided with first (6) and second (7) locking pallet stones arranged for cooperating with the teeth of the escape wheel set (1).

Abstract: The escapement includes an escape wheel set (1), a balance roller (3) carrying an impulse pin (4) and a first impulse pallet stone (5). It further includes a pallet assembly (8) fitted with a second impulse pallet stone (11) and first and second locking pallet stone (12, 13). The wheel set (1) includes at least one escape wheel fitted with teeth (6) that mesh directly with the teeth (20) of the first wheel of a gear train (2), the teeth (6) of the wheel (1) cooperating with the impulse pallet stones and locking pallet stones.

Abstract: A tourbillon is provided that includes a platform rotatable about a platform axis. In one implementation, the platform carries an escapement including an escape-wheel and pallets, wherein the escape-wheel is rotatable about an escape-wheel staff, the pallets are rotatable about a pallet-staff, and the escape-wheel staff and the pallet-staff are disposed so as to be essentially parallel to the platform axis. The platform also carries a balance-wheel rotatable about a balance-staff, wherein the balance-staff is arranged at an angle of inclination ? with respect to the platform axis.

Abstract: The escapement includes first (1) and second (2) escape wheels each driven by independent gear trains and barrels. The system includes a brake lever (8) cooperating with an impulse pin (7) of the roller (4) and with the escape wheels via locking pallet stones (12, 13). The roller carries pallet stones (10, 11) for receiving impulses from the escape wheels. When the wheels are locked, the brake lever occupies a centred position relative to said wheels. Means (16, 30, 31) for re-engaging the locking pallet stones in the toothing of the wheels are provided to ensure proper operation of the system.

Abstract: The escapement includes two distinct escape wheel sets (1, 2), a roller (3) including a first impulse pallet stone (5) cooperating with the first wheel set (1) and a third impulse pallet stone (12) cooperating with the second wheel set (2). An anchor piece (6) articulated on a pivot (7) cooperates with an impulse pin (4) via a fork (8) fitted to the anchor piece. This anchor piece carries second (9) and fourth (13) impulse pallet stones respectively cooperating with the first (1) and second (2) wheel sets. The same anchor piece carries first (10) and second (11) locking pallet stones cooperating with the second wheel set (2).

Abstract: The tangential impulse escapement includes a lever device (1) including a lever (3) driving a roller (65) and a ring (7) surrounding an escapement wheel set (8), said ring being fitted with pallet-stones (9, 10, 11, 12) for cooperating with the teeth (13, 14, 15, 16) of said wheel set, in order, alternately, to lock the latter then import an impulse to said roller. The escapement wheel set includes at least first (17) and second (18) coaxial secured wheels. The pallet pallet-stones (9, 11, 12) of the ring cooperate with the teeth (13, 15, 16) of the first wheel (17) with the exception of one (10), which is arranged for cooperating with the teeth of the second wheel (18).

Abstract: The invention concerns a device for securing a pallet stone to an escapement pallet including at least one housing for receiving said pallet stone, characterized in that the portion of the pallet including said housing is made of a shape memory alloy able to undergo a reversible transformation from an austenitic crystallographic phase to a martensitic crystallographic phase.

Abstract: The escapement includes a large roller 4 carrying an impulse pallet stone 5 surmounted by a first finger-piece 14 and a small roller 23 in which a notch 22 is made. A blocking member carries, on the one hand, a device 80 for locking the escape wheel 2, and on the other hand, a second finger-piece 11 arranged for cooperating with the first finger-piece 14, the blocking member also including a follower 20 ending in a beak 21 which acts on the small roller and particularly with notch 22 which is made therein. The first and second finger-pieces 14 and 11 are respectively rigidly secured to the table roller and the blocking member.

Abstract: The escapement includes two distinct escape wheel sets (1, 2), a roller (3) including a first impulse pallet stone (5) cooperating with the first wheel set (1) and a third impulse pallet stone (12) cooperating with the second wheel set (2). An anchor piece (6) articulated on a pivot (7) cooperates with an impulse pin (4) via a fork (8) fitted to the anchor piece. This anchor piece carries second (9) and fourth (13) impulse pallet stones respectively cooperating with the first (1) and second (2) wheel sets. The same anchor piece carries first (10) and second (11) locking pallet stones cooperating with the second wheel set (2).

Abstract: The escapement includes an escape wheel set (1), a balance roller (3) carrying an impulse pin (4) and a first impulse pallet stone (5). It further includes a pallet assembly (8) fitted with a second impulse pallet stone (11) and first and second locking pallet stone (12, 13). The wheel set (1) includes at least one escape wheel fitted with teeth (6) that mesh directly with the teeth (20) of the first wheel of a gear train (2), the teeth (6) of the wheel (1) cooperating with the impulse pallet stones and locking pallet stones.

Abstract: The invention concerns an escapement for a mechanical watch comprising: an escapement wheel (10) kinematically connected to a power source, a roller (14) mounted on a balance (16) including, on two different levels, a pin (23) and an impulse pallet (24) co-operating with said wheel (10); a limiting member (26) performing a periodic movement during which it co-operates with said pin (23) to limit the travel of said roller (14); a control member (30) provided with a rest lift (32) performing, from a stable position wherein said wheel (10) is pressed on said rest lift (23), a periodic movement during which said wheel is released and provides an impulse to said impulse pallet (24). The invention is characterized in that the periods of the limiting member (26) and of the control member (30) correspond, respectively, to an alternation and an oscillation of said balance.

Abstract: The lever escapement includes at least one escape wheel (2). The pallet assembly (5) is fitted with locking pallet stones (6, 7) and a first impulse pallet stone (8) cooperating with the teeth of the wheel (2). The pallet assembly (5) drives an auxiliary wheel set (9) carrying a second impulse pallet stone (10) cooperating with the teeth of the wheel (2).

Abstract: The timepiece escapement includes first (3) and second (4) impulse pallet stones secured to the balance (2) directly cooperating with the teeth of the escape wheel set (1) and a brake lever (5) periodically driven by the balance, said brake lever being provided with first (6) and second (7) locking pallet stones arranged for cooperating with the teeth of the escape wheel set (1).

Abstract: An escapement for a timepiece movement includes a toothed escape wheel, a balance and a detent respectively pivoted on rotation axes. The detent supports a pallet lock that interacts with the first tooth of the escape wheel along a certain length of penetration in order to block it in an idle phase during which the balance executes a free arc of oscillation. An impulse pallet rotationally driven by the balance interacts with a second tooth when the detent is pivoted in order to release the escape wheel, this wheel turning by a forward pitch before being blocked again by the pallet lock by interaction with the second tooth. The escapement also includes a limiting plate, which is coaxial and rotationally secured to the balance, has a periphery including a substantially circular main portion and a cutout positioned facing the pallet lock in the release phase.

Abstract: A pallet stone cooperates with the teeth of an escapement wheel of a watch or clock movement, and includes a trailing plane and an impulse plane and at least one capillary channel acting as a tank for a lubricant, characterized in that the capillary channel connects the trailing plane to the impulse plane.

Abstract: The invention concerns a detent escapement for a timepiece including an escape wheel fitted with teeth, a balance onto whose staff there is secured at least one roller 4 including an impulse pallet-stone and in the circular periphery of which a notch is made, and a blocking member in the form of a lever hinged on a pin, said blocking member carrying means for locking the escape wheel, a control finger-piece and a follower ending in a beak arranged for cooperating with the notch of said roller, characterized in that said roller further includes a safety finger-piece arranged for cooperating with the teeth of the escape wheel and locking the latter when the impulse pallet-stone is accidentally unlocked from the toothing of the escape wheel.

Abstract: The blocking member (6) or detent member of the escapement carries a follower (20) which ends in a beak (21) which cooperates with a small roller (23) comprising a notch (22). When the locking pallet-stone (7) of the blocking member releases itself from the teeth of escapement wheel (2), the beak (21) penetrates in the notch (22). The return of the pallet-stone (7) in the locking position is caused by a rising flank (25) of said notch, said rising flank being inclined such that the beak (21) is forced to follow and climb over said flank when the small roller (23) rotates. The arrangement allows the escapement to resist to shocks and consequently to omit the return spring acting on the blocking member.

Abstract: The detent escapement includes a wheel 2 fitted with teeth 3, a roller 4 fitted with an impulse pallet stone 5, a blocking member in the form of a lever 6 hinged on a pin 8. The first and second arms 9 and 10 of the lever respectively carry a locking pallet stone 7 and a first actuating finger 11. An elastic member 12 is mounted on the roller 4, said member carrying a second actuating finger 14 capable of driving the first finger 11 when the roller 4 rotates in a first direction a to actuate the blocking member 6 and to move around said first finger 11 without driving it, when the roller 4 rotates in a second direction b opposite to the first. The elastic member 12 is a spring of great length including a plurality of turns 15 wounded about a centre 16.