Apparatus for clamping a workpiece on a machine tool

Abstract

An apparatus for clamping a workpiece on a machine tool comprises: a base frame securable to a machine tool for machining a workpiece; a clamping unit; a hydraulic actuator comprising a first chamber supplyable with a first pressurised hydraulic fluid and connectable to a first sensing device for sensing a pressure of the first pressurised hydraulic fluid; a sensing channel supplyable with pressurised air and connectable to a sensing sensor for sensing a pressure of the air; wherein the first sensing device and the sensing sensor are connectable to a control system adapted to authorise machining of the workpiece when the pressure of the first pressurised hydraulic fluid and the pressure of the air are simultaneously above their respective threshold values.

Description

Technical Field

[0001] This invention relates to a device for clamping workpieces on a machine tool. Background Technology

[0002] As is well known, highly automated systems are widely used in the mass production of mechanical workpieces that need to be processed on machine tools. In these systems, humanoid robots bring the workpieces to be processed to the machine tool, where hydraulic-type specialized equipment receives the workpieces and clamps them in place to allow for processing.

[0003] When the processing is complete, the device releases the processed workpiece, which is then moved away again by a robot.

[0004] Clamping equipment must be able to apply very high clamping forces to the workpiece being processed.

[0005] This demand is particularly evident in industries such as automotive, where the ongoing need to optimize production cycles has led to the use of tools operating at very high speeds to unload extremely strong forces and vibrations from workpieces that must be counteracted by fastening systems.

[0006] Furthermore, in the automotive industry, particularly lightweight materials (such as aluminum) are being used more and more widely, but during processing, these materials cannot guarantee the same durability as materials such as cast iron and steel.

[0007] Therefore, whenever a new workpiece is mounted on a machine tool, the clamping device, in addition to applying a very large force, needs to hold the workpiece at a predetermined point with very high precision and repeatability; otherwise, the large force applied by the clamping device may cause the workpiece to deform, which will impair the machining quality and lead to the risk of obtaining workpieces that exceed the tolerance.

[0008] In such automated systems, the operational reliability of individual components, including the equipment used to clamp the workpiece, is typically very high.

[0009] However, sometimes the workpiece to be processed is not placed correctly and accurately, so the clamping device cannot clamp the workpiece well (or although it is clamped, the position is incorrect), which may endanger the entire processing and damage the workpiece and / or the machine tool and / or the clamping device.

[0010] A similar problem arises when unloading the workpiece at the end of the machining process; in fact, if the clamping device does not fully and properly release the machined workpiece, the workpiece moving robot may pick up (or attempt to pick up) a workpiece that is not fully released, posing a risk of serious damage to the workpiece and / or the clamping device and / or the robot itself.

[0011] In this context, it is important to emphasize that in highly automated systems, any malfunction that causes a production halt can easily lead to underproduction, or worse, system damage and consequently, significant economic losses. Summary of the Invention

[0012] The main objective of this invention is to design a device for clamping workpieces on a machine tool, allowing for the prevention of machining operations on workpieces that are not properly placed and clamped on the machine tool.

[0013] Another object of the present invention is to design a device for clamping workpieces on a machine tool, which allows for the prevention of machining workpieces that are not fully unloaded and properly released.

[0014] Finally, and equally importantly, the object of this invention is to design a device for clamping workpieces on a machine tool with high reliability and operational accuracy.

[0015] Another object of the present invention is to design a device for clamping workpieces on a machine tool, which allows for the avoidance of undesirable malfunctions and damage to the workpiece being processed and / or the machine tool and / or the workpiece moving robot and / or its clamping device.

[0016] Another object of the present invention is to design a device for clamping workpieces on a machine tool, which allows for overcoming the aforementioned disadvantages of the prior art within the scope of a simple, reasonable, easy, effective, and affordable solution.

[0017] The above objective is achieved by the device for clamping a workpiece on a machine tool, having the features of claim 1. Attached Figure Description

[0018] Other features and advantages of the invention will become more apparent from the description of some preferred but non-exclusive embodiments of a device for clamping a workpiece on a machine tool, which are illustrated in the accompanying drawings by way of illustrative but non-limiting examples, wherein:

[0019] Figure 1 This is an isometric view of a first embodiment of the device according to the present invention;

[0020] Figure 2 yes Figure 1 Exploded view of the equipment in the diagram;

[0021] Figure 3 It is in the clamping position. Figure 1 A sectional view of the equipment in the diagram;

[0022] Figure 4 It is in the middle transition position. Figure 1 A sectional view of the equipment in the diagram;

[0023] Figure 5 It is in the release position. Figure 1 A sectional view of the equipment in the diagram;

[0024] Figure 6 This is a cross-sectional view of a second embodiment of the device according to the present invention;

[0025] Figure 7 This is an exploded view of a third embodiment of the device according to the present invention. Detailed Implementation

[0026] For details, please refer to the following: Figures 1 to 5 The embodiment shown, with reference numeral 1 generally indicating a device for clamping a workpiece on a machine tool.

[0027] Specifically, device 1 is used to clamp workpiece P after it has been placed on the operating table L of machine tool M and before machining begins.

[0028] Preferably, the machine tool M is of a highly automated type, wherein an anthropomorphic robot is dedicated to loading the workpiece P to be processed and unloading the processed workpiece P.

[0029] It should be noted that the machine tool M is equipped with multiple devices 1, which are arranged in appropriate numbers and positions based on the shape of the workpiece P and the type of machining to be performed.

[0030] In the accompanying drawings and the remainder of this disclosure, reference will be made to a single device 1 for simplicity, unless otherwise stated.

[0031] The device 1 includes at least one basic frame 2, which can be fixed to the machine tool M, for example, to its operating table L, its base or any other part thereof.

[0032] The device 1 includes at least one clamping unit 3 associated with the basic frame 2, which is movable between a release position and a clamping position of the workpiece P, passing through a plurality of intermediate transition positions.

[0033] Conveniently, clamping unit 3 includes:

[0034] - At least one support element 4, which is hinged to the movable portion 5 about a first hinge axis A and adapted to contact the workpiece P in the clamped position;

[0035] - At least one hinged link 6, 7, which is hinged to the basic frame 2 about a second hinge axis B and to the support element 4 about a third hinge axis C.

[0036] Advantageously, the hinge axes A, B, and C are substantially parallel to each other.

[0037] Due to the shape of the clamping unit 3, in the release position, the support element 4 is actually placed in an almost vertical position, which allows free access to the operating table L to position and remove the workpiece P; on the other hand, in the clamping position, the support element 4 is in a basically horizontal position and suspended on the operating table, thereby clamping the workpiece P between the support element 4 and the operating table L.

[0038] The hinge between the support element 4 and the movable part 5 about the first hinge axis A is defined by a series of first holes 8 formed on the support element 4 and the movable part 5 and first pins 9 inserted into the first holes 8 aligned with each other.

[0039] For example, the hinged links 6 and 7 include a first connecting rod 6 and a second connecting rod 7, both of which are hinged around the second and third hinge axes B and C.

[0040] Conveniently, connecting rods 6 and 7 are arranged on the symmetrical opposite sides of the hinge portion 10 of the support element 4 and the basic frame 2.

[0041] The hinge between the connecting rods 6 and 7 and the basic frame 2 around the second hinge axis B is defined by a series of second holes 11 formed on the connecting rods 6 and 7 and the hinge portion 10, and second pins 12 inserted into the second holes 11 aligned with each other.

[0042] On the other hand, the hinge between the connecting rods 6, 7 and the support element 4 about the third hinge axis C is defined by a series of third holes 13 formed on the connecting rods 6, 7 and the support element 4 and third pins 14 inserted into the third holes 13 that are aligned with each other.

[0043] The device 1 includes at least one sensing channel 15 formed on at least one of the basic frame 2 or clamping unit 3.

[0044] The sensing channel 15 can be supplied with pressurized air and can be connected to a sensing sensor 16 suitable for sensing the pressure of the pressurized air.

[0045] More specifically, the sensing channel 15 is connected to a first pneumatic circuit 17 suitable for supplying pressurized air.

[0046] The first pneumatic circuit 17 is equipped with a sensing sensor 16 (e.g., a pressure switch) through which the air pressure in the sensing channel 15 can be known.

[0047] When the clamping unit 3 is in the clamping position, the sensing channel 15 is airtight, and at least when the clamping unit 3 is in the intermediate transition position, the sensing channel 15 is open to the outside.

[0048] Therefore, when the clamping unit 3 is in the clamping position, the air supplied to the sensing channel 15 under pressure remains trapped in the sensing channel itself, and its pressure tends to increase; however, in the intermediate transition position, air is allowed to escape, and its pressure tends to decrease.

[0049] Conveniently, the sensing channel 15 is formed on the basic frame 2, and the hinge links 6 and 7 are shaped to open and close the sensing channel 15 based on the position of the hinge links 6 and 7.

[0050] More specifically, the sensing channel 15 appears on the first surface 18 of the basic frame 2, for example, formed on the hinge portion 10.

[0051] The first connecting rod 6 is rotatably rested on the first surface 18 and includes a first ventilation groove 19.

[0052] The first connecting rod 6 is associated with the first preloading devices 20 and 21, which are adapted to maintain the first connecting rod 6 in sealed contact on the first surface 18 and to keep the sensing channel 15 normally closed.

[0053] The first preloading devices 20, 21 include, for example, a set of disc springs 20 and washers 21 mounted on the second pin 12 and the third pin 14, and operate to push the connecting rods 6, 7 against the hinge portion 10 and the support element 4.

[0054] In this way, on the one hand, the existing gaps between the basic frame 2, connecting rods 6 and 7 and support element 4 are reset, thereby achieving a more stable and precise assembly operation; on the other hand, the sensing channel 15 is sealed and closed even without rubber seals or other soft materials.

[0055] In fact, the sensing channel 15 is opened only when the first ventilation groove 19 at least partially overlaps with the sensing channel 15, as described above, which occurs when the clamping unit 3 moves to the intermediate transition position.

[0056] As described and shown, the sensing channel 15 is formed on the basic frame 2, and the hinge links 6 and 7 are shaped to open and close the sensing channel 15; however, alternative embodiments are not excluded, in which the sensing channel 15 is arranged differently and its opening and closing are achieved by means other than the hinge links 6 and 7.

[0057] For the clamping unit to move between a release position and a clamping position, the device 1 includes at least one hydraulic actuator 22, 23, which is provided with a fixed portion 24 associated with the basic frame 2 and a movable portion 5 connected to the clamping unit 3.

[0058] The movable portion 5 of the hydraulic actuators 22 and 23 conveniently coincides with the movable portion of the support element 4 that is hinged about the first hinge axis A.

[0059] For example, hydraulic actuators 22 and 23 include a cylinder 22 that defines a fixed portion 24 and a valve stem 23 provided with a plunger 25, the valve stem extending from the cylinder 22 and defining a movable portion 5.

[0060] The cylinder 22 of the hydraulic actuators 22 and 23 is integrated with the basic frame 2.

[0061] Inside the cylinder, hydraulic actuators 22 and 23 include at least a first chamber 26, which is supplied with a first pressurized hydraulic fluid to move the clamping unit 3 from a released position to a clamped position. In this invention, hydraulic fluid refers to any liquid fluid used as an energy transfer carrier in a hydraulic circuit (and therefore ideally incompressible); preferably, the hydraulic fluid is composed of conventional synthetic oil, but alternative embodiments are not excluded, wherein the hydraulic fluid may be mineral oil, vegetable oil, water, etc.

[0062] The first chamber 26 operates on one side of the plunger 25.

[0063] The first chamber 26 can be connected to the first sensing device 27 for sensing the pressure of the first pressurized hydraulic fluid.

[0064] More specifically, the first chamber 26 is connected to a first conduit 28 formed in the cylinders of the hydraulic actuators 22 and 23, and the first conduit is in turn connected to a first hydraulic circuit 29 adapted to supply first hydraulic fluid.

[0065] The first hydraulic circuit 29 is provided with a first sensing device 27 (e.g., a pressure switch), through which the pressure of the first pressurized hydraulic fluid in the first chamber 26 can be known.

[0066] The first sensing device 27 and the sensing sensor 16 can be connected to a control system adapted to authorize the processing of workpiece P when the pressure of the first hydraulic fluid under the pressure in the first chamber 26 and the air pressure in the sensing channel 15 are both above their respective thresholds.

[0067] The control system, not shown in the figure, includes, for example, a control unit (electronic, hydraulic, or a combination of both) that manages the operation of the machine tool M.

[0068] In fact, in order to agree to begin machining on workpiece P, the control system performs a double check:

[0069] - Check whether the first chamber 26 is pressurized, that is, whether it is supplied with first pressurized hydraulic fluid; and

[0070] - Check if sensing channel 15 is pressurized, i.e., closed and air cannot be discharged outwards.

[0071] If both of these conditions occur simultaneously, the control system senses that the clamping unit is correctly positioned in the clamping position and allows the machine tool M to perform the machining operation; this situation is as follows: Figure 3 As shown.

[0072] on the other hand, Figure 4 A scenario is illustrated where workpiece P is incorrectly positioned on machine tool M, and support element 4 fails to reach the clamping position because support element 4 is in contact with workpiece P while clamping unit 3 is still in one of its intermediate transition positions. In this case, the first hydraulic fluid in the first chamber 26 is pressurized, and the first sensing device 27 senses this pressure; however, on the other hand, the first ventilation groove 19 at least partially overlaps with the sensing channel 15, pressurized air is discharged outward, and sensing sensor 16 senses that the pressure in sensing channel 15 is not higher than a threshold. Therefore, in this situation, the control system knows that clamping unit 3 has not yet reached the clamping position and does not authorize the commencement of machining operations.

[0073] Lack of authorization can protect workpiece P and machine tool M by preventing the execution of operations that could potentially endanger the integrity of workpiece P and machine tool M.

[0074] In response to a lack of authorization, protocols designed to restore normal working conditions can be activated, such as the repositioning of workpiece P and / or operator intervention.

[0075] exist Figure 1-5 In the illustrated embodiment, the hydraulic actuator is double-acting and includes at least one second chamber 30, which can be supplied with a second pressurized hydraulic fluid to move the clamping unit 3 from the clamping position to the release position.

[0076] Preferably, the second hydraulic fluid is the same as the first hydraulic fluid used as a carrier to set the first chamber 26 under pressure; in other words, the same hydraulic fluid can be pumped into the first chamber 26 and the second chamber 30 as needed.

[0077] However, alternative embodiments using two different hydraulic fluids cannot be ruled out.

[0078] The second chamber 30 operates on the side of the plunger 25 opposite to the first chamber 26.

[0079] The second chamber 30 can be connected to a second sensing device 31 for the pressure of the second pressurized hydraulic fluid.

[0080] More specifically, the second chamber 30 is connected to a second conduit 32 formed in the cylinders of the hydraulic actuators 22 and 23, and the second conduit is in turn connected to a second hydraulic circuit 33 suitable for supplying a second hydraulic fluid.

[0081] The second hydraulic circuit 33 is provided with a second sensing device 31 (e.g., a pressure switch), through which the pressure of the second pressurized hydraulic fluid in the second chamber 30 can be known.

[0082] Advantageously, when the clamping unit is in the released position, the sensing channel 15 is airtightly closed, and the second sensing device 31 and the sensing sensor 16 can be connected to a control system adapted to authorize the picking of workpiece P from the machine tool M when the pressure of the second hydraulic fluid in the second chamber 30 and the air pressure in the sensing channel 15 are simultaneously higher than their respective thresholds.

[0083] The control system designed to authorize the picking of workpiece P can be conveniently overlapped with the control system designed to authorize the machining of workpiece P, and includes, for example, a control unit that manages the operation of machine tool M.

[0084] In fact, in order to agree to pick up workpiece P, the control system performs a double check after the machining operation has been completed:

[0085] - Check whether the second chamber 30 is pressurized, that is, whether it is supplied with a second pressurized hydraulic fluid; and

[0086] - Check if sensing channel 15 is pressurized, i.e., closed and air cannot be discharged outwards.

[0087] If both conditions occur simultaneously, the control system senses that the clamping unit is correctly positioned in the release position and allows the moving robot of workpiece P to pick up the workpiece from machine tool M; this situation is as follows: Figure 5 As shown.

[0088] like Figures 1 to 5 As described and shown, device 1 has several workpieces in contact with pressurized hydraulic fluid. Therefore, special seals are provided at different points in device 1. For simplicity, these seals are generally indicated by reference numeral 34 in the figures.

[0089] Figure 6 A second embodiment of the present invention is shown, wherein device 1 and Figures 1 to 5 The embodiments are the same, except that the hydraulic actuators 22 and 23 are single-acting and include at least one spring element 35 to move the clamping unit 3 from the clamping position to the release position.

[0090] The rebound element 35 includes, for example, a helical spring that operates on the plunger 25 on the opposite side relative to the first chamber 26.

[0091] In this embodiment, the device 1 is provided with a first chamber 26 connected to the first sensing device 27, but there is no second chamber 30 and a second sensing device 31.

[0092] Therefore, through Figure 6 Device 1 in the middle cannot be like Figures 1 to 5 As in the embodiment, the release position is definitively identified by the clamping unit 3, but when the pressure of the first hydraulic fluid in the first chamber 26 and the air pressure in the sensing channel 15 are both found to be above their respective thresholds, the clamping position and the start of machining operation may still be definitively identified.

[0093] Figure 7 A third embodiment of the invention is shown, wherein the hydraulic actuators 22 and 23 are still single-acting and are provided with a spring element 35, which allows the clamping unit 3 to move from the clamping position to the releasing position.

[0094] However, with Figure 6 Unlike the embodiments described above, device 1 includes at least one auxiliary channel 36 located on at least one of the basic frame 2 or clamping unit 3.

[0095] The auxiliary channel 36 can be supplied with pressurized air and can be connected to an auxiliary sensor 37 suitable for sensing the pressure of the pressurized air.

[0096] More specifically, the auxiliary channel 36 is connected to a second pneumatic circuit 38 suitable for supplying air at a given pressure.

[0097] The second pneumatic circuit 38 is equipped with an auxiliary sensor 37 (e.g., a pressure switch) through which the air pressure in the auxiliary channel 36 can be determined.

[0098] When the clamping unit 3 is in the released position, the auxiliary channel 36 is airtight, and at least when the clamping unit 3 is in the intermediate transition position, the auxiliary channel is open to the outside.

[0099] Therefore, when the clamping unit 3 is in the released position, the air supplied to the auxiliary channel 36 under pressure remains trapped in the sensing channel itself, and its pressure tends to increase; however, in the intermediate transition position, air is allowed to escape, and its pressure tends to decrease.

[0100] Conveniently, the auxiliary channel 36 is formed on the basic frame 2, and the hinge links 6 and 7 are shaped to open and close the auxiliary channel 36 based on the position of the hinge links 6 and 7.

[0101] More specifically, the auxiliary channel 36 appears on the second surface 39 of the basic frame 2 on the opposite side to the first surface 18, which is formed on the hinge portion 10.

[0102] The second connecting rod 7 is rotatably rested on the second surface 39 and includes a second ventilation groove 40.

[0103] The second preloading device is associated with the second connecting rod 7 and is adapted to maintain the second connecting rod 7 in sealed contact on the second surface 39 and to keep the auxiliary channel 36 normally closed.

[0104] The second preloading device effectively overlaps with the first preloading devices 20 and 21.

[0105] In fact, the disc spring 20 and washer 21 operate to push the connecting rods 6 and 7 against the hinge portion 10 and the bracket element 4.

[0106] In fact, the auxiliary channel 36 is opened only when the second ventilation groove 40 at least partially overlaps with the auxiliary channel 36, as described above, which occurs when the clamping unit 3 moves to the intermediate transition position.

[0107] exist Figure 7 In the illustrated embodiment, the first sensing device 27 and the auxiliary sensor 37 are connected to a control system adapted to authorize the picking of workpiece P from machine tool M when the pressure of the first hydraulic fluid in the first chamber 26 is below a corresponding threshold and the air pressure in the auxiliary channel 36 is above a corresponding threshold.

[0108] Similarly, in Figure 7 In some embodiments, the control system designed to authorize the picking of workpiece P can be conveniently overlapped with the control system designed to authorize the processing of workpiece P, and may include, for example, a control unit that manages the operation of machine tool M.

[0109] In fact, in order to allow the picking of workpiece P after the machining operation has been completed, the control system performs a double check:

[0110] - Check whether the first chamber 26 is not pressurized, that is, whether the first pressurized hydraulic fluid is not supplied; and

[0111] - Check if auxiliary channel 36 is pressurized, i.e., closed and air cannot be discharged outwards.

[0112] If both of these conditions occur simultaneously, the control system senses that the clamping unit 3 is correctly positioned in the release position and allows the mobile robot of workpiece P to pick up the workpiece from the machine tool M.

Claims

1. A device for clamping a workpiece on a machine tool, comprising: - At least one basic frame (2), which can be fixed to a machine tool (M) for machining workpieces (P). - At least one clamping unit (3) associated with the basic frame (2), the clamping unit being movable between the release position and the clamping position of the workpiece (P) and passing through a plurality of intermediate transition positions; - At least one hydraulic actuator having a fixed portion (24) associated with the basic frame (2) and a movable portion (5) connected to the clamping unit (3), the hydraulic actuator including at least a first chamber (26) capable of being supplied with a first pressurized hydraulic fluid to move the clamping unit (3) from the release position to the clamping position, the first chamber (26) being capable of being connected to a first sensing device (27) for sensing the pressure of the first pressurized hydraulic fluid; Its features are: - The device includes at least one sensing channel (15) formed on at least one of the basic frame (2) and the clamping unit (3), the sensing channel being capable of being supplied with pressurized air and being connected to a sensing sensor (16) for sensing the air pressure, wherein the sensing channel (15) is airtight when the clamping unit (3) is in the clamped position, and is open outward at least when the clamping unit (3) is in the intermediate transition position; and - The first sensing device (27) and the sensing sensor (16) are connected to a control system adapted to authorize the processing of the workpiece (P) when the pressure of the first pressurized hydraulic fluid in the first chamber (26) and the pressure of the air in the sensing channel (15) are both higher than their respective thresholds. - The hydraulic actuator is a double-acting type and includes at least a second chamber (30) that is supplied with a second pressurized hydraulic fluid to move the clamping unit (3) from the clamping position to the release position. The second chamber (30) is connected to a second sensing device (31) for the pressure of the second pressurized hydraulic fluid. - When the clamping unit (3) is in the released position, the sensing channel (15) is airtight; and - The second sensing device (31) and the sensing sensor (16) are connected to a control system adapted to authorize the removal of the workpiece (P) from the machine tool (M) when the pressure of the second pressurized hydraulic fluid in the second chamber (30) and the pressure of the air in the sensing channel (15) are both above their respective thresholds.

2. The device according to claim 1, characterized in that, The hydraulic actuator is single-acting and includes at least one spring-loaded element (35) to move the clamping unit (3) from the clamping position to the release position.

3. The device according to claim 2, characterized in that: - The device includes at least one auxiliary channel (36) located on at least one of the basic frame (2) or the clamping unit (3), the auxiliary channel being capable of supplying pressurized air and being connected to an auxiliary sensor (37) adapted to sense the pressure of the air in the auxiliary channel (36), wherein the auxiliary channel (36) is airtight when the clamping unit (3) is in the released position, and the auxiliary channel is open to the outside when the clamping unit (3) is in the intermediate transition position; - The first sensing device (27) and the auxiliary sensor (37) are connected to a control system adapted to authorize the picking of the workpiece (P) from the machine tool (M) when the pressure of the first pressurized hydraulic fluid in the first chamber (26) is lower than a corresponding threshold and the pressure of the air in the auxiliary channel (36) is higher than a corresponding threshold.

4. The device according to claim 1, characterized in that, The hydraulic actuator includes a cylinder (22) defining the fixed portion (24) and a valve stem (23) extending from the cylinder (22) and defining the movable portion (5).

5. The device according to claim 1, characterized in that, The clamping unit (3) includes: - At least one support element (4) is hinged to the movable portion (5) about a first hinge axis (A) and adapted to contact the workpiece (P) in the clamped position; - At least one hinged link, which is hinged to the basic frame (2) about a second hinge axis (B) and to the support element (4) about a third hinge axis (C). The hinge axes (A, B, C) are substantially parallel to each other.

6. The device according to claim 5, characterized in that, The hinged link includes a first connecting rod (6) and a second connecting rod (7), both of which are hinged around the second and third hinge axes (B, C).

7. The device according to claim 5, characterized in that, The sensing channel (15) is formed on the basic frame (2), and the hinge link is shaped to open and close the sensing channel (15) according to the position of the hinge link.

8. The device according to claim 6, characterized in that, The first connecting rod (6) is rotatably rested on the first surface (18) of the basic frame (2), the sensing channel (15) appears on the first surface and includes a first ventilation groove (19), the first connecting rod (6) is associated with a first preloading device (20, 21) adapted to keep the first connecting rod (6) in sealed contact on the first surface (18) to keep the sensing channel (15) normally closed, and to open the sensing channel (15) when the first ventilation groove (19) overlaps at least partially with the sensing channel (15).

9. The device according to claim 6, characterized in that, The device includes at least one auxiliary channel (36) located on at least one of the basic frame (2) or the clamping unit (3), the auxiliary channel being supplied with pressurized air and being connected to an auxiliary sensor (37) adapted to sense the pressure of the air in the auxiliary channel (36), wherein the auxiliary channel (36) is airtight when the clamping unit (3) is in the released position and is open outward when the clamping unit (3) is in the intermediate transition position; a second connecting rod (7) is rotatably resting on a second surface (39) of the basic frame (2), the auxiliary channel (36) appearing on the second surface and including a second ventilation groove (40), the second connecting rod (7) being associated with a second preloading device adapted to keep the second connecting rod (7) in sealed contact on the second surface (39) to keep the auxiliary channel (36) normally closed, and opening the auxiliary channel (36) when the second ventilation groove (40) at least partially overlaps with the auxiliary channel (36).

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