FR2680128A1 - Pneumatic gripper and, more particularly, a pneumatic gripper of the type having fingers with parallel and linear displacement - Google Patents

Abstract

The present invention relates to a pneumatic gripper of the type having fingers with parallel and linear displacement made up of a body, a piston, of two fingers which can move in terms of translation on the said body, and of a yoke including a mechanism for controlling the opening and closing of the said fingers. The said piston, when it slides, can entrain the said yoke in terms of translation so as to control the opening and closing of the said fingers. For each finger (22), the said control mechanism includes a plate (23) which can slide and at the end of which is fixed the said finger (22). The said yoke (12) controls the rotation, in opposite directions, of two wheels (35 and 36), the spindles (29 and 30) of which are secured to the body (1). The said wheels (35 and 36 respectively) include grooves (37 and 39) forming teeth which mesh with respective racks (38 and 40) parallel to the said longitudinal axis of the said plate (23) and mounted secured to the said plate (23) symmetrically on either side of the said axis.

Description

 The present invention relates to a pneumatic gripper and, more particularly, to a pneumatic gripper of the finger type with linear and parallel movement.

 Pneumatic clamps are known, the fingers of which pivot under the action, on the piston of a jack, of the pressurized air introduced into its cylinder. Reference is made, for example, to patent documents FR-A-2,592,827 and EP-A-368,777. The clamp described in this latter document essentially comprises a jack body in which a piston can slide, causing a cylinder rod. The latter carries, at its end opposite to that of the piston, an operating part which is designed to be able to actuate two fingers.

 Attempts have been made, in the present invention, to provide pneumatically driven grippers whose fingers move linearly while remaining parallel to each other.

 The problem posed by this type of pliers relates to the finger control mechanism so that the fingers can, in particular, exert, on the object to be manipulated, clamping forces of the same intensity. A single piston is then used and a mechanism is then provided which transmits the pneumatic force of the piston on each of the fingers of the clamp. Furthermore, provision is made for guiding the fingers in translation, in particular so that they can remain strictly parallel, without becoming biased and possibly jamming under the action of the clamping forces.

 The object of the invention is to solve the problems mentioned above.

 To this end, a clamp according to the invention is characterized in that, for each finger, it comprises a control mechanism which consists of a plate guided in translation so as to be able to slide along its own longitudinal axis and at the end of which is attached the corresponding finger. The clamp comprises a yoke which, by sliding driven by a piston, controls the rotation, in opposite directions, of two wheels whose axes are integral with the body of the clamp, said wheels having grooves forming teeth which mesh respectively with racks parallel to said longitudinal axis of said plate and mounted integral with said plate, on either side of said axis.

 According to another characteristic of the invention, said racks consist of lanterns aligned along the longitudinal axis of the corresponding plate, said lanterns being designed to engage in semicircular grooves at the periphery of said wheels.

 According to another characteristic of the invention, said plates have their rear faces in a common plane and comprise, on these faces, longitudinal grooves forming a common space of rectangular section in which is mounted a guide bar secured to said body.

 According to another characteristic of the invention, the yoke has a cylindrical head intended to slide and be guided in a bore of the same axis as the bore receiving the piston and a coaxial rod at the end of which is mounted, with radial clearance, said piston.

 According to another characteristic of the invention, a face of the cylindrical head forms with the bottom and the side wall of the bore a chamber into which opens a channel for supplying air under pressure.

 According to another characteristic of the invention, on each plate, is mounted a seal which encloses it and whose outer surface is in contact with the walls of a groove of the body in which said mechanisms are mounted.

 According to another characteristic of the invention, the head (13) is provided, projecting from its lateral surface, with a radial rod consisting of a permanent magnet and designed to be housed in a groove on the internal surface of the bore of the yoke and opening into a housing of the body, said rod traversing the entire length of said groove when the yoke and the piston slide in their respective bores, magnetic sensors mounted on a card in said housing being provided, facing the ends of said groove, for directly detecting the magnetic field emanating from said rod.

The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which:
Fig. 1 is a view which represents a clamp according to the invention, the body of which has been cut along its median axis of symmetry, the other elements not being cut so that they appear as in an elevation view,
Fig. 2 is a sectional view of pliers according to the invention, said cut having been made, for the left part of FIG., Along the broken plane IIG / II of FIG. 1 and, for the right part of FIG., According to the plane IID / II of FIG. 1, and
Fig. 3 is a view similar to FIG. 1 but with the fingers of the clamp shown, unlike those of FIG. 1, are in their closed positions.

 The present description is made in relation to FIGS. 1 and 2. The clamp shown in these Figs. essentially comprises a body 1 pierced longitudinally, at its ends, of two blind bores 2 and 3 coaxial connected together, by their respective bottoms, by a third bore 4 coaxial with the first two 2 and 3.

 A piston 5 is provided to slide in the bore 2 thus forming a cylinder for this piston. It has on its periphery an annular seal 6. The bore 2 is closed by a cover 7 provided, on its periphery, with annular seals 8. The internal surface of the bore 2 forms, with the face 5a of the piston 5 on the cover side 7, a first chamber Cf (Fig. 3) and, with the other face 5b of the piston 5, a second chamber Co. The cover 7 is pierced with an air intake channel 9 which opens, by one of its ends, inside the first chamber Cf and, by the other end, into a corresponding channel 10 drilled in the body 1. A second intake channel 11 is drilled in the body 1 to open, through one of its ends, into the second chamber Co.

 A yoke 12 has a cylindrical head 13 provided to be able to slide in the bore 3. An annular seal 14 is provided on the head 13. The yoke 12 also includes a rod 15 in the longitudinal axis of the yoke 12 which is provided for slide in the bore 4. An annular seal 16 is provided in the bore 4 in contact with the periphery of the rod 15.

 The piston 5 is mounted, with radial clearance, at the end of the rod 15 of the yoke 12.

 The head 13 is split by a diametrical groove 17 so as to form two fingers 18 in the cylinder segment each carrying two pins 19 and 20 of axis orthogonal to the longitudinal axis of symmetry of the clamp.

 The yoke 12 is guided in translation by its head 13 and its rod 15 respectively in the bores 3 and 4. As for the piston 5, it does not provide a function for guiding the yoke 12 because it is mounted with radial clearance on the rod 15. With such an assembly, radial forces on the yoke 12, are transferred to the head 13 and the rod 15 but not to the piston 5. It follows that the bore 2, forming a cylinder, and the piston 5 are not damaged by such efforts.

Furthermore, the rod 15 is relieved by the head 13 and does not break under the effect of these radial forces.

 The piston 5 plays its driving role. Indeed, when introducing pressurized air through the channel 10, the chamber Cf has its volume which increases thus pushing the piston 5 towards the bottom of the bore 2. If, on the contrary, it introduces pressurized air through the channel 11, it is the chamber Co which has its volume which increases then pushing the piston 5 towards the cover 7. The piston 5 by sliding in the bore 2 drives the yoke 12 in translation.

 It will be noted that the rod 15 has a length such that, when the piston 5 is in the low position shown in FIG. 1, the yoke 12 is substantially in the bottom of the bore 3.

 The body 1 is split by a groove 21 of rectangular section in which are housed two opening and closing mechanisms of two fingers 22. In FIG. 1, a single finger 22 and a single mechanism are visible, the other finger and the other mechanism mounted symmetrically with respect to the longitudinal axis of the clamp being shown, for reasons of readability of the drawing, only by a dotted finger 22 '.

 Each mechanism consists of a rectangular plate 23 at a) end of which is mounted, on a small side, the corresponding finger 22. The plate 23 is provided with a countersink 24 opening, at one of its ends, on the face of the short side opposite to the finger 22, and having, at the other end a semicircle shape. The plate 23 thus has, in section, a "U" shape lying with two wings 25 and a core 26 (FIG. 2). The plate 23 is pierced right through with two oblong holes 27 and 28 whose longitudinal axes lie in the longitudinal axis of symmetry of the plates 23.

 The plate 23 of a mechanism has the rear face of its core 26 which is in contact with the rear face of the core 26 of the plate 23 of the other mechanism.

 Two axes perpendicular 29 and 30 to the longitudinal axis of symmetry of the clamp are mounted1 by their ends, in the body 1, so as to be orthogonal to the common plane formed by the core 26 of each plate 23.

 The rear face of the core 26 of each plate 23 is provided with a longitudinal groove 31 opening, on one side, by the face of the plate 23 opposite the finger 22, and, on the other side, in the finger 22 himself. The grooves 31 of the two plates 23 form a space of rectangular section in which is mounted a guide bar 32 pierced with bores passing right through and receiving respectively the two axes 29 and 30. As will be seen later, the guide bar 32 is also fixed relative to the body 1, the plates 23 can slide relative to each other in opposite directions and, each, relative to the guide bar 22.

In their sliding movements, the plates 23 are guided in translation by the guide bar 32. The displacement travel of each plate 23 is limited by the length of the oblong holes 27 and 28. Each plate 23 can thus take all the positions included between an extreme position where the corresponding finger 22 is in its closed position and is, therefore, in abutment against the body 1 (see Fig. 3) and another extreme position where the finger 22 is in the fully open position ( Fig. 1). When the finger 22 is in its closed position, the rear edge 33 of the plate 23 is substantially in the plane which contains the lateral face 34 of the body 1 (FIG. 3).

 It will be noted that the length of the guide bar 32 is greater than the width of the body 1 as well as the maximum stroke of each plate 23. This arrangement provides guidance over a greater length and therefore more effective.

 Each mechanism further comprises two wheels 35 and 36 respectively mounted on the axes 29 and 30 so as to be in abutment against the body 1 and to be capped by the corresponding plate 23.

 The wheel 35 has grooves 37, advantageously four in number, designed to be able to mesh with lanterns 38 mounted aligned parallel to the longitudinal axis of symmetry of the plate 23, at the lower part thereof, and orthogonally in its main plane, straddling its wing 25 and its core 26. Likewise, the wheel 36 has grooves 39, advantageously four in number, designed to be able to mesh with lanterns 40 mounted aligned parallel to said axis, with the upper part of the plate 23, on the plate 23 itself and orthogonally to its main plane, straddling its wing 25 and its core 26.

 The two sets of four lanterns 38 and 40 respectively constitute two racks mounted on each plate 23 symmetrically with respect to the longitudinal axis of said plate. Although racks of the conventional type could be mounted, it has been found advantageous to provide lantern racks. They ensure a more efficient transmission of the pneumatic force from the piston 5 to the fingers 22.

 Each wheel 35, 36 of each mechanism also has a radial groove 41 in which is housed, in order to be able to slide therein, the pins 19 and 20 carried by the corresponding finger 18 of the yoke 12.

 The operation of a clamp according to the invention is now described.

 Suppose the fingers 22 of the pliers in their closed positions (Fig. 3). When air is introduced into the channel 11, the volume of the chamber Co increases, which has the effect of causing the piston 5 to slide down (arrow A). I, a yoke 12 also slides downward, causing in its movement, by the internal diary of pins 19 and 20 in the radial grooves 41, the wheels 35 and 36 (arrows B). By turning, these drive, by means of the lanterns 38 and 40 which mesh respectively in the grooves 37 and 39 of the wheels 35 and 36, the plates 23 so that the corresponding fingers 22 move towards their fully open positions ( arrows C). As already mentioned above, the plates 23 are guided in translation, in their movement, by means of the guide bar 32. It will be noted that in operation the plates 23 slide one relative to each other in opposite directions.

 When the fingers 22 are in their fully open positions (Fig. 1), the piston 5 and the head 13 of the yoke 12 are in their low positions.

 When air under pressure is now introduced into the channel 10, the chamber Cf has its volume which increases, the piston 5 and the head 13 of the yoke 12 slide upwards (arrow D).

In the clamp shown, a channel 10 'is provided, one end of which is connected to channel 10 and the other end in a chamber
Cf 'that the face 13a of the head 13 forms with the side wall of the bore 3. The air introduced into the channel 10 is thus applied both to the face 5a of the piston 5 and to the face 13a of the head 13, which makes it possible to increase the force of action of the clamp on closing.

 In its sliding movement, the yoke 12, via pins 19 and 20 in the grooves 41, rotate the wheels 35 and 36 (arrows F) whose grooves 37 and 39 mesh respectively with the lanterns 38 and 40 of the plates 23. These therefore slide so that the fingers 22 move towards their closed positions (arrows G).

 It will be noted that the fact of providing two drive wheels 35 and 36 by an opening and closing control mechanism makes it possible, on the one hand, to increase the efficiency of the transmission of the pneumatic force of the piston 5 on the fingers 22, and, on the other hand, to urge the plates 23 symmetrically with respect to their longitudinal axes, thus avoiding their biasing and their possible jamming.

 Seals 42 are provided which enclose the plates 23 and whose outer surface is constantly in contact with the walls of the housing created by the groove 21. A cover 43 mounted integral with the body 1 covers all the mechanisms of finger control 22. The seals 42 seal the mechanisms against dust.

 Furthermore, the body 1 comprises a longitudinal housing 44 in which is mounted an electronic card 45 for controlling and controlling the clamp. Such a card is, for example, of the type which is described in patent document FR-A-2 651 515. It is connected, by a cable 46, to a control unit (not shown) in which are programmed the various sequences of opening and closing of the fingers 22 of the pliers. On the card 45, two or more linear magnetic sensors 47 and 48 are mounted, for example of the Hall effect type. The sensors 47 and 48 are mounted opposite the ends of a groove 49 parallel to the longitudinal axis of the clamp and opening, on the one hand, inside the bore 3 and, on the other hand, at inside the housing 45. A permanent magnet formed by a rod 50 is mounted radially on the external surface of the head 13 of the yoke 12 and is designed to engage in the groove 49 and travel its entire length when the yoke 12 slides between its two extreme positions. It will be understood that the sensors 47 and 48 deliver an analog signal which is directly a function of the position of the yoke 12 in its bore 3, a position which it is easy to link to the open position of the fingers 22.

 It will be noted that the influence of the magnetic rod 50 on the sensors 47 and 48 takes place directly without any material other than air between them, which has the advantage of increasing the amplitude of the signal delivered by these sensors 47 and 48 and the accuracy of the measurement thus made.

 In known clamps, the magnet on the piston attracts magnetic dust which, agglomerated by magnetism, contributes to the wear of the piston and its bore. This phenomenon cannot take place with the clamps of the invention since the piston 5 does not include a magnet.

 Finally, the fact of mounting a stick 50 instead of a generally used magnetic ring, makes it possible to considerably reduce the amount of magnetic dust which sticks to the external walls of the clamp.

It should be noted that a clamp according to the invention can be fitted with control drawers connected to channels 9, 10, 10 ′ and 11 in order to control the distribution of the pressurized air in the chambers Cf,
Co and Cf '. Such drawers can be of the type described in patent document FR-A-2 638 670. They can be mounted in the cover 7.

 The clamp which has just been described is of the type whose fingers 22 close when the piston 5 rises (arrows D, F, G). By a symmetrical arrangement of the closing / opening mechanisms with respect to that which has just been described, one could produce, according to the same operating principle, a clamp of the type whose closing of the fingers 22 is obtained by lowering the piston in its cylinder. This last point can be of importance when a double action of the air introduced into the channels 10 and 10 ′ and acting on the piston 5 and the head 13 of the yoke 12 is provided.

Claims (7)

 1) Pneumatic gripper of the finger type with linear and parallel movement consisting of a body pierced with a bore forming a cylinder in which can slide, under the action of pressurized air, a piston, of two fingers mounted movable in translation on said body so as to be able to take all the positions comprised between an extreme open position and an extreme closed position, and a yoke comprising a mechanism for controlling the opening and closing of said fingers, said piston, when '' it slides, being able to cause said clevis in translation so as to control the opening and closing of said fingers, characterized in that, for each finger (22), said control mechanism comprises a plate (23) guided in translation to be able slide along its own longitudinal axis and at the end of which is fixed said corresponding finger (22), said yoke (12), by sliding driven by said piston (5), controlling the rotation , in opposite directions, of two wheels (35 and 36) whose axes (29 and 30) are integral with the body (1), said wheels (35 and 36) respectively comprising grooves (37 and 39) forming teeth which mesh with respective racks (38 and 40) parallel to said longitudinal axis of said plate (23) and mounted integral with said plate (23), symmetrically on either side of said axis.  2) pliers according to claim 1, characterized in that said racks consist of lanterns (38 and 40) aligned parallel to the longitudinal axis of the corresponding plate (23), said lanterns (38 and 40) being provided for engage in semicircular grooves (37 and 39) at the periphery of said wheels (35 and 36).  3) Pliers according to claim 1 or 2, characterized in that said plates (23) have their rear faces in a common plane and; comprise, on these faces, longitudinal grooves (31) forming a common space of rectangular section in which is mounted a guide bar (32) integral with said body (1).  4) Pliers according to one of the preceding claims, characterized in that the yoke (12) has a cylindrical head (13) provided for: sliding and being guided in a bore (3) of the same axis as the bore (2) receiving the piston (5) and a coaxial rod (15) at the end of which is mounted, with radial clearance, said piston (5).  5) Pliers according to claim 4, characterized in that a face (13a) of the cylindrical head (13) forms with the bottom and the side wall of the bore (3) a chamber (Cf ') into which opens a supply duct (10 ') for pressurized air.  6) Pliers according to one of the preceding claims, characterized in that, on each plate (23), is mounted a seal (42) which encloses it and whose outer surface is constantly in contact with the walls of a groove (21) of the body (1) in which said mechanisms are mounted.  7) Pliers according to one of claims 4 to 6, characterized in that the head (13) is provided, projecting from its lateral surface, with a magnetized radial rod (50) and designed to be received in a groove (49 ) on the internal surface of the bore (3) of the yoke (12) and opening into a housing (44) of the body (1), said rod (50) traversing the entire length of said groove (49) when the yoke (12) and the piston (5) slide in their respective bores (2 and 3), magnetic sensors (47 and 48) mounted on a card (45) in said housing (44) being provided, facing the ends of said groove (49), for directly detecting the magnetic field emanating from said rod (50).