阅读说明：本技术 用于对具有体积剂量的液体进行收集和受控输送的装备 (Device for collecting and controlled delivery of a liquid having a volumetric dose ) 是由 马里奥·斯卡蒂茨 于 2020-04-01 设计创作，主要内容包括：一种用于对液体进行受控提取和分配的设备包括具有平台(1)的结构(S),该平台容置第一系列的容器(2)和第二系列的容器(3),第一系列的容器容纳液体物质,第二系列的容器适于对第一系列的容器的物质进行接纳,设备还包括用于从第一系列的容器提取液体并且将这些液体分配到第二系列的容器中的装置。在每个第一系列的容器上插入有半吸移管,该半吸移管包括桶状件(4)、没有致动杆的活塞(5)和针状件(6)。提取和分配装置包括单元(9),该单元设有竖向杆(95、96),该竖向杆用于致动每个半吸移管的活塞,所述单元被约束至托架(10),该托架可以在平台上方移动。单元(9)可以从平台(1)竖向地移动并且朝向该平台竖向地移动。(An apparatus for the controlled extraction and dispensing of liquids comprises a structure (S) having a platform (1) housing a first series of containers (2) containing a liquid substance and a second series of containers (3) suitable for receiving the substance of the first series of containers, the apparatus further comprising means for extracting the liquids from the first series of containers and dispensing them into the second series of containers. On each of the first series of containers, a semipipette is inserted, which comprises a barrel (4), a piston (5) without an actuating rod and a needle (6). The extraction and dispensing device comprises a unit (9) provided with vertical rods (95, 96) for actuating the pistons of each semipipette, said unit being constrained to a carriage (10) movable above the platform. The unit (9) is vertically movable from and towards the platform (1).)

1. A device for the controlled extraction and dispensing of liquids with volumetric doses, comprising a structure (S) on which a platform (1) is arranged, said platform (1) being intended to house a first series of containers (2) and a second series of containers (3), said first series of containers (2) containing a liquid substance to be extracted and metered, said second series of containers (3) being suitable for receiving a predetermined dose of the substance contained in said first series of containers (2), said device further comprising means for extracting said liquid from said first series of containers (2) and dispensing such liquid in a predetermined dose into said second series of containers (3), said device being characterized in that on each first series of containers (2) a semipipette is inserted, comprising a barrel (4), A piston (5) and a needle (6), the barrel (4) defining a volume fillable with the liquid of the respective first series of containers (2), the piston (5) being free of an actuating handle, the liquid being able to be sucked and injected by means of the needle (6), and the apparatus being characterized in that the means for extracting the liquid from the first series of containers (2) and dispensing it into the second series of containers (3) comprise a unit (9), the unit (9) being provided with a vertical rod (95, 96), the vertical rod (95, 96) being adapted to engage and actuate the piston (5) of each semi-pipette (4, 5, 6), the unit (9) being constrained to a carriage (10), the carriage (10) being in turn movable above the platform (1), the unit (9) is vertically movable from the platform (1) and vertically movable towards the platform (1).

2. The apparatus according to claim 1, characterized in that the unit (9) is connected to the carriage (10) by means of a vertical guide (102), the vertical guide (102) being arranged in a corresponding surface (103) of the carriage (10), and in that the unit (9) is connected to an electric actuator (104), the electric actuator (104) controlling the movement (Z) of the unit (9) along the vertical guide (102).

3. The apparatus according to claims 1 to 2, characterized in that said unit (9) comprises a hollow body (90), said hollow body (90) being fixed to said carriage (10) by means of said vertical guide (102), and said rods (95, 96) being positioned inside said hollow body (90) vertically through said hollow body (90), said rods (95, 96) being vertically movable inside said hollow body (90) by means of corresponding actuators (91) having a vertical axis.

4. The apparatus of claim 3, wherein the vertical axis actuator (91) is positioned within the hollow body (90).

5. The apparatus according to claim 1, wherein the rod (95, 96) comprises a first part (95) and a second part, the first part (95) being connected to an actuator (93), the actuator (93) controlling the vertical movement of the rod (95, 96), the second part comprising a tubular body (96), air being introducible in the tubular body (96) for inflating an inflatable cushion (98), the inflatable cushion (98) being adapted to engage with a cavity (52) provided on each piston (5) when the inflatable cushion (98) is inflated due to the introduction of air in the second part (96).

6. The apparatus of claim 5, wherein the tubular body (96) has a tip (99), the tip (99) being disposed below the inflatable cushion (98).

7. The apparatus according to claim 5, characterized in that said pad (98) engages said piston (5) only in the step of lifting the piston itself.

8. The apparatus according to claim 1, wherein the rods (95, 96) have ends adapted to engage with cavities (52) provided on each piston (5).

Technical Field

The present invention relates to a device for the controlled extraction and delivery of liquids having volumetric doses, particularly but not exclusively for the preparation of dyeing solutions for the textile industry.

Background

EP0602737 discloses an apparatus for the controlled extraction and delivery of a liquid with volumetric doses, comprising a structure on which there is a platform, in a first position a plurality of containers containing a liquid substance are placed, and in a second position on the platform there are further containers intended to receive a predetermined dose of liquid contained in the containers of the first station. The extraction of the liquid from the container of the first station and of the dose of the same liquid into the container of the second station is operated by means of an injector connected to a carriage which moves it on the aforementioned platform according to a work program managed by a programmable control unit. This system has the following disadvantages: the syringe needs to be cleaned with a suitable solvent after each use to avoid contamination of the liquid contained in the container of the first station. On the one hand, this system requires an excessively long operating time compared to the current production requirements and, on the other hand, it does not guarantee that, after cleaning, the syringe completely removes the residues of the solvent used for cleaning. In addition, each cleaning is associated with a loss of the liquid contained in the syringe, which has a negative impact on the economics of the process, also because it requires special handling of the substances resulting from repeated cleaning of the syringe.

EP0945728 discloses a device for the controlled extraction and delivery of a liquid with volumetric doses, comprising a support structure suitable for receiving a first series of containers containing a liquid substance and a second series of containers suitable for receiving one or more of said substances in predetermined doses, and automatic means for extracting a substance from a first series of containers and dispensing a predetermined dose of this substance into a second series of containers. The extraction and transport device comprises a plurality of individual extraction and transport members, positioned in correspondence with each of said containers and coupled in a decomposable manner with a unit for activating and moving said members. In the embodiment described in EP0945728, the individual components are syringes, which are each arranged to correspond to a first series of containers, such that each container of the first series is associated with a corresponding syringe. Although this system avoids cleaning each syringe prior to use of the system, it requires a relatively high cost due to the need to prepare a syringe corresponding to each first series of containers.

US6302168B1 discloses an automatic liquid metering device which uses a syringe as the metering means provided. The apparatus essentially comprises a plurality of storage containers which are evenly spaced in a plane in a plurality of rows. Each storage container is sealed with a lid and has a load stone disposed in the storage container. The stirring device is located below the storage vessel to cause the load stone to rotate and thereby uniformly stir the liquid in the storage vessel. The lid of each storage container has at least one syringe extending through the lid. The liquid suction-release means mounted on the moving means may be displaced to be located above the selected storage container under the control of the control means. The liquid suction-release means holds the syringe on the selected storage container when the liquid suction-release means is lowered, and causes the syringe to suck a certain amount of liquid from the selected storage container while withdrawing the syringe from the selected storage container when the liquid suction-release means is raised. Then, the taken-out syringe is moved to a receiver positioned on the electronic balance by the moving means, and the taken-out syringe is caused to release all the liquid previously sucked into the receiver at which the liquid is accurately measured with the electronic balance by the liquid suction-release means.

EP1402952a1 discloses a cartridge for use with an analysis unit for investigating fluids or gases, in particular for medical diagnostic applications, having a cartridge tank with an opening for the fluid/gas which is pumped in and out through a needle by means of a piston provided with an actuating rod. The actuating rod of the piston has a connection for a drive to move the piston back and forth. The connecting element and the drive element are structured such that they are closed during a longitudinal movement along one section of the tank and released upon a reverse movement. The connection remains closed while moving along the second section of the tank.

CN1404908A discloses an apparatus with a combined measuring system for the automated preparation of solutions. Said plant comprises a structure with a worktable on which one or more containers for solid products, one or more bottle containers for liquid products, one or more containers for solutions and one or more empty and clean bottle containers can be placed, the support means being movable on the worktable, and is characterized in that it also comprises means connected to the support means to move and process said bottles and to move, process and actuate at least the containers for solid products, and another apparatus for preparing solutions and/or mixtures by using solid products.

The above-mentioned document discloses an apparatus using a delivery device comprising a pump which is entirely formed in the delivery device, which requires excessive costs with respect to the current production requirements.

Disclosure of Invention

The main object of the present invention is to overcome the above mentioned drawbacks.

According to the present invention, this result is achieved by providing a device having the features indicated in claim 1. Other features of the invention are the subject of the dependent claims.

Thanks to the invention, it is possible to realize a device for the controlled extraction and delivery of a liquid having a volumetric dose, which avoids contamination of the liquid contained in the initial container and, at the same time, has a simplified overall structure and relatively low manufacturing costs.

Drawings

These and further advantages and features of the present invention will be more and better understood by each person skilled in the art in view of the following description and the appended drawings, which are provided by way of example and are not to be considered limiting, in which:

figure 1 shows a side view of the apparatus according to the invention;

figure 2 represents a top view of the plant shown in figure 1;

FIG. 3 shows a vertical schematic section of a useful semipipette in the device according to the invention;

figure 4 shows a partial pipette inserted in a container (2) containing a liquid substance;

FIG. 5 shows only the container (2) with the adapter for positioning the respective micropipette;

figures 6A to 6G schematically show a series of phases relating to the extraction of a dose of liquid substance from the container (2);

figures 7A to 7D schematically represent a series of phases relating to the dosing of the liquid substance in the different containers (3);

figures 8A to 8D schematically represent the repositioning of the micropipette in the respective container (2);

figure 9 is a detail of figure 6A;

FIG. 10 is a detail of FIG. 6D, FIG. 10 showing the expanded configuration of the pad (98) in the piston (5) of the micropipette;

figure 11 shows a vertical schematic section of the piston (5).

Detailed Description

The device for the collection and controlled delivery of a liquid with volumetric doses according to the present invention is simplified to a basic structure and with reference to the attached figures, being of the type comprising a structure (S) on which a platform (1) is arranged, the platform (1) being suitable for housing a first series of containers (2) and a second series of containers (3), the first series of containers (2) housing a liquid substance intended for the preparation of a solution, the second series of containers (3) being suitable for receiving a predetermined dose of the substance housed in the first series of containers (2). The device also comprises means for removing the liquid from the containers (2) of the first series and dispensing a predetermined dose of said liquid into the containers (3) of the second series.

For example, the solutions are intended for the preparation of dyeing liquors of the textile industry or also for the preparation of pharmaceutical, food or cosmetic formulations.

According to the invention, a barrel (4) of a syringe or "pipette" with associated piston (5) and needle (6) is applied on each first series of containers (2). The piston (5) has no actuating lever. The needles (6) have a suitable length to be inserted into the respective container (2) and constitute an element by means of which the liquid coming from the container (2) can be sucked out and injected. The lower part (46) of the barrel (4) defines the connection of the barrel (4) to the needle (6). In fact, the barrel (4), the piston (5) without stem and the needle (6) constitute a syringe or pipette without piston-actuating rod, which is defined as a "semi-pipette" in the context of the present description. Each piston (5) is equipped with an annular rubber gasket (50), said annular rubber gasket (50) being positioned in a corresponding circumferential seat (51), said circumferential seat (51) ensuring a close contact with the inner wall of the respective sheath (4). The needle (6) defines a lower extension of the barrel (4) through which the suction and delivery of the liquid is performed.

Each half-pipette (4, 5, 6) can be reversibly associated with an actuating rod for actuating the piston (5), carried by a unit (9) connected to a carriage (10), the carriage (10) being arranged above the platform (1). The carriage (10) is mounted on a guide (100), which guide (100) extends transversely to the structure (S) and which guide is in turn mounted on two guides (101), said two guides (101) extending along the longitudinal edges of the structure. Furthermore, the carriages (10) are constrained to respective movement means (known per se to the person skilled in the art and therefore not described in further detail) which allow them to be moved along the transverse guides (100) as well as along the longitudinal guides (101). In this way, the unit (9) can be moved horizontally on the structure (S), i.e. above the platform (1), as schematically indicated by the double arrows "X" and "Y". The unit (9) is constrained to the carriage (10) by means of a vertical guide (102), the vertical guide (102) being arranged in a corresponding surface (103) of the carriage (10), and the unit (9) being connected with an electric brake (104), the electric brake (104) controlling the movement (Z) of the unit (9) along said vertical guide (102). Thus, the unit (9) may also be moved vertically from the platform (1) and vertically towards the platform (1). It will be appreciated that the mechanism for moving the unit (9) along said direction (X, Y, Z) may be of any other suitable type.

The unit (9) comprises a main body (90), which main body (90) is connected to the carriage (10) by means of a vertical guide (102). The main body (90) is hollow and a vertical pneumatic actuator (91) is mounted inside the main body (90), the stem of the pneumatic actuator (91) passing through the upper wall (900) of the main body (90). An inverted 'L' -shaped bracket (92) is mounted on the actuator (91) stem, the vertical section of the bracket (92) also passing freely through the upper wall (900) of the body (90). The horizontal section of the bracket (92) serves as a support for a stepping motor (93), the axis of the stepping motor (93) being vertical and oriented downwards. A nut-threaded bushing (94) is applied on the motor (93) and engaged by the upper side of the corresponding threaded rod (95). On the lower side of the rod (95) there is a tubular piece (96), the tubular piece (96) being equipped with a radial hole (97), on which radial hole (97) a flexible duct (not visible in the figures) is inserted to supply the tubular piece (96) with compressed air. The tubular member (96) passes within the body (90) and extends beyond a lower wall (901) of the body (90). A rod (95) associated with the motor (93) passes through the upper wall (900) of the body (90). An inflatable cushion (98) is mounted on the lower side of the tubular member (96), the inflatable cushion (98) being inflated when compressed air is fed into the tubular member (96). The tubular piece (96) is closed at the bottom and ends with a tip (99), which tip (99) is intended to be inserted in each of the pistons (5), as described further below. In practice, when the actuator (104) controls the movement of the body (90) of the unit (9) along the guide (102), the actuator (91) controls the vertical movement of the motor (93) with respect to the body (90), and the motor (93) independently controls the vertical movement of the tubular member (96).

Thus, the vertical movement of the tubular member (96) relative to the container positioned on the platform (1) can be controlled by the combined action of the actuator (104), the actuator (91) and the motor (93).

The assembly comprising the rod (95) and the tubular member (96) constitutes a rod for driving the piston (5) of the micropipette.

In the example shown in the figures, the rod (95) and the tubular member (96) are vertical and coaxial with each other.

The body (90) is provided with a self-centering pneumatic radial grip (P) on the lower side of the body (90), the grip (P) having three radial jaws (RP) intended to engage and respectively release the semipipette, as described further below. The clamp (P) is a component known per se. The jaws (RP) are preferably L-shaped to engage the upper ring (40) of each pipette half, as described further below.

Each piston (5) has a central cavity (52) on the upwardly facing side of the piston (5). Preferably, the cavity (52) has a circular cross-section to facilitate engagement of the cavity (52) with the inflatable cushion (98). Further, preferably, the upper portion (520) of the cavity (52) has a tapered shape that facilitates and guides the tip (99) and pad (98) into the cavity.

The upper part (40) of the barrel (4) of the pipette half (4, 5, 6) is preferably shaped like a ring to facilitate the engagement of this upper part (40) with the jaws (RP) of the gripper (P). The upper portion (40) of the tub (4) can also rest on the upper edge of a tubular piece (T2), which tubular piece (T2) is positioned in each of the containers (2) and which tubular piece (T2) acts as an adapter support for the tub itself when it is not engaged with the clamp (P). In fact, the tubular piece (T2) allows fixing the half pipettes (4, 5, 6) in the respective containers (2) in a vertical condition.

Possible modes of operation of the above-described device are as follows.

The carriage (10), controlled by a programmable electronic unit (not visible in the figures) which moves the carriage (10) according to the dose to be made, is brought above the container (2) containing the required liquid and in this container (2) the respective partial pipettes (4, 5, 6) are inserted. At this point, the actuator (104) commands the unit (9) to descend towards the selected container (2), after which the actuator (91) commands the assembly (92, 93, 95, 96) to descend with respect to the body (90), determining the insertion of the tip (99) and the pad (98) in the cavity (52) of the piston (5) of the semipipette inserted in the selected container (2). Subsequently, the clamp (P) is activated and grips the upper ring (40) of the barrel (4). Compressed air is then fed into the tubular member (96), which determines the expansion of the cushion (98) in the cavity (52). Thus, the piston (5) is associated with the rod (95, 96). Subsequent lifting of the rods (95, 96) by the stepper motor (93) determines the extraction of a predetermined amount of liquid from the container (2). The above operation is schematically illustrated in fig. 6A to 6F. As shown in fig. 6G, at this point the unit (9) is raised in a way that reverses the movement with respect to the previous one, and the carriage (10) carries the same unit (9) corresponding to the container (3) intended to receive the predetermined dose of liquid sucked into the semipipette, with the semipipette (4, 5, 6) hooked by the grip (P), as shown in fig. 7A. Then, as schematically shown in fig. 7B to 7D, the unit (9) is lowered to a predetermined distance from the container (3), the pad (98) is deflated, interrupting the supply of compressed air into the tubular member (96), and the stepper-motor-activated piston (5) is lowered to a value corresponding to the dose of liquid to be dispensed into the container (3). When this operation is completed, the carriage (10) returns the unit (9) with the semipipettes (4, 5, 6) to the starting container (2) and repositions the semipipettes (4, 5, 6) on this container with a movement opposite to the one previously described. Subsequently, the actuator (91) controls the lifting of the assembly (92, 93, 95, 96) and the gripper (P) releases the pipettes (4, 5, 6).

Since a complete pipette is not associated with each container (2), but instead a pipette without piston actuating rods is associated with each container (2) and only one actuating rod is used for collecting and delivering the liquid, the overall cost of the device is reduced compared to the known devices. At the same time, since the rod for actuating the piston housed in the semipipette is not in contact with the liquid, there is no contamination and no intermediate washing is required.

In fact, the present device comprises only one rod, i.e. the rod of the unit (9), which is adapted to engage and brake each piston (5). As mentioned above, the piston (5) is configured to be reversibly engaged by the stem of the unit (9), and vice versa, said stem being configured to reversibly engage the piston (5). According to the example provided above, the cavity (52) of the piston (5) is engaged by a rod provided by the unit (9), which in turn is adapted to engage said cavity (52). More generally, according to the invention, each piston (5) is provided with a surface that can be engaged directly and reversibly by the rod, which is the only actuation rod for actuating each piston (5). It should be noted that the piston (5) forms a pumping means inside the respective barrel (4) only when the piston (5) is engaged by an actuating rod provided by the unit (9).

Preferably, the liquid metering step is performed after the pad (98) is deflated as previously described. Since the elasticity caused by the pneumatic expansion of the pad (98) is eliminated, the pushing action exerted by the rod (96) is not affected by said elasticity, which determines a higher precision in the metering phase.

The activation of the aforementioned carriage (10) and the actuators is controlled by a control unit of a type known to the skilled industrial automation technician. Thus, according to the invention, a device for the controlled extraction and delivery of a liquid with volumetric doses comprises a structure (S) on which is arranged a platform (1) for housing a first series of containers (2) containing a liquid substance to be extracted and metered and a second series of containers (3) suitable for receiving a predetermined dose of the substance contained in the first series of containers (2), means for extracting the liquid from the first series of containers (2) and dispensing it in a predetermined dose into the second series of containers (3), on each of the first series of containers (2) there being inserted a semi-pipette comprising a barrel (4), a piston (5) and a needle (6), the barrel (4) defining the volume that can be filled with the liquid of the respective first series of containers (2), the piston (5) is free of an actuating handle, the device by means of which the needle (6) can aspirate and inject liquid, for extracting liquid from the containers (2) of the first series and dispensing it into the containers (3) of the second series, comprising a unit (9) provided with a vertical rod (95, 96), the vertical rod (95, 96) being adapted to engage and actuate the piston (5) of each half-pipette (4, 5, 6), the unit (9) being constrained to a carriage (10), the carriage (10) in turn being movable above the platform (1), the unit (9) being vertically movable from the platform (1) and towards the platform (1).

Preferably, according to a possible embodiment of the invention, said unit (9) is connected to said carriage (10) by means of a vertical guide (102), the vertical guide (102) being arranged in a corresponding surface (103) of the carriage (10), and said unit (9) is connected to an electric actuator (104), the electric actuator (104) controlling the movement (Z) of said unit (9) along said vertical guide (102).

Furthermore, preferably, the unit (9) comprises a hollow body (90), the hollow body (90) being fixed to the carriage (10) by means of a vertical guide (102), and said rods (95, 96) being positioned inside the hollow body (90) vertically through the hollow body (90), said rods (95, 96) being vertically movable inside the hollow body (90) by means of a corresponding actuator (91) having a vertical axis.

Preferably, the vertical axis actuator (91) is positioned within the hollow body (90).

Preferably, said rod (95, 96) comprises a first part (95) and a second part, the first part (95) being connected to an actuator (93), the actuator (93) controlling the vertical movement of said rod (95, 96), the second part comprising a tubular body (96), air being introducible into the tubular body (96) for inflating an inflatable cushion (98), the inflatable cushion (98) being adapted to engage a cavity (52) provided inside each piston (5) when the inflatable cushion (98) is inflated due to the introduction of air into said second part (96).

Preferably, the tubular body (96) has a tip (99), the tip (99) being disposed below the inflatable cushion (98).

Preferably, the pad (98) engages the piston (5) only during the step of lifting the piston itself.

In practice, however, the details of execution may vary in an equivalent manner with respect to the single elements described and illustrated, without thereby departing from the idea of the solution adopted, and therefore remain within the scope of protection granted to the present patent as defined by the annexed claims.

The claims (modification according to treaty clause 19)

1. Device for the controlled extraction and dispensing of a liquid with volumetric doses, comprising a structure (S) on which a platform (1) is arranged, said platform (1) being intended to house a first series of containers (2) and a second series of containers (3), said first series of containers (2) containing a liquid substance to be extracted and metered, said second series of containers (3) being suitable for receiving a predetermined dose of the substance contained in the first series of containers (2), means for extracting said liquid from the first series of containers (2) and dispensing such liquid in a predetermined dose into the second series of containers (3), wherein on each first series of containers (2) a semipipette is inserted, comprising a barrel (4), A piston (5) and a needle (6), the barrel (4) defining a volume fillable with liquid of the respective first series of containers (2), the piston (5) being free of an actuating handle, the liquid being able to be sucked and injected by means of the needle (6), and wherein the means for extracting the liquid from the first series of containers (2) and dispensing it into the second series of containers (3) comprise a unit (9), the unit (9) being provided with vertical rods (95, 96), the vertical rods (95, 96) being adapted to engage and actuate the piston (5) of each half-pipette (4, 5, 6), the unit (9) being constrained to a carriage (10), the carriage (10) being able to move in turn above the platform (1), the unit (9) being able to move vertically from and towards the platform (1) -said device being characterized in that said rod (95, 96) comprises a first part (95) and a second part, said first part (95) being connected to an actuator (93), said actuator (93) controlling the vertical movement of said rod (95, 96), said second part comprising a tubular body (96), in which tubular body (96) air can be introduced for inflating an inflatable cushion (98), said inflatable cushion (98) being adapted to engage with a cavity (52) provided on each piston (5) when said inflatable cushion (98) is inflated due to the introduction of air in said second part (96).

2. The apparatus according to claim 1, characterized in that the unit (9) is connected to the carriage (10) by means of a vertical guide (102), the vertical guide (102) being arranged in a corresponding surface (103) of the carriage (10), and in that the unit (9) is connected to an electric actuator (104), the electric actuator (104) controlling the movement (Z) of the unit (9) along the vertical guide (102).

3. The apparatus according to claims 1 to 2, characterized in that said unit (9) comprises a hollow body (90), said hollow body (90) being fixed to said carriage (10) by means of said vertical guide (102), and said rods (95, 96) being positioned inside said hollow body (90) vertically through said hollow body (90), said rods (95, 96) being vertically movable inside said hollow body (90) by means of corresponding actuators (91) having a vertical axis.

4. The apparatus of claim 3, wherein the vertical axis actuator (91) is positioned within the hollow body (90).

5. The apparatus of claim 1, wherein the tubular body (96) has a tip (99), the tip (99) being disposed below the inflatable cushion (98).

6. The apparatus according to claim 1, characterized in that said pad (98) engages said piston (5) only in the step of lifting the piston itself.

7. The apparatus according to claim 1, wherein the rods (95, 96) have ends adapted to engage with cavities (52) provided on each piston (5).