FR3074077A1 - PASSIVE AUTOMATIC TRIPPING GRIPPING DEVICE - Google Patents

Abstract

The device comprises at least: a mechanical support (21, 22); - a bistable plate (1) fixed under stress on said support; - two blades (3), said clamp blades, mechanically secured to said plate, each forming a jaw of a gripper of said object; - A trigger element (2) projecting from said plate, adapted to come into contact with said object to be grasped, placed between said blades (3) of length less than this and extending in the same direction; In the approach phase of said object (20), the convex face of said plate is oriented towards said object so that said blades are in the open position, bringing said trigger element (2) into contact with said object causing the change of shape. stable state of said plate, the face facing said object passing in the concave position so that said blades (3) are closed on said object.

Description

Gripping device with passive automatic release

The present invention relates to a gripping device with passive automatic triggering. It is in the field of inputting and depositing objects on assembly lines. It applies, for example, to automated operations known as "pick & place" in packaging boxes or on conveyors.

Pick-up and drop-off operations require the use of grippers that are particularly suited to different operational requirements.

There are usually several types of technical problems when entering and dropping an object.

A first problem to be overcome is the positioning accuracy of the gripper relative to the object and the knowledge of the positioning error. The grip guarantee is not optimal unless the gripper and the robot handling it are very precise. This generally leads to significant investment costs.

A second problem is the coordination between the approach phase and the triggering of the object's grip. Poor coordination leads to a large number of wrong catches or deterioration of products and thus reduces the output of a production line.

The great variability of the products to be handled poses another problem. Indeed, it is necessary to adapt to the different rigidities and possible shapes, which imposes significant modifications of the gripper or even a different gripper for each category of object.

Another problem is energy. The robotic manipulator is often limited to fairly low payloads while the gripper is composed of gripping systems but also of actuation systems for each functional unit. This requires an external energy supply (usually compressed air) and the additional weight adds inertia and limits the dynamics of the robot and therefore the efficiency of the production line.

Several gripping solutions are known, but these do not solve all of the problems set out above. Among these solutions of the prior art, we can cite:

- Gripping by pneumatic suction, which offers all-or-nothing systems which apply unknown gripping forces and do not solve the problems of positioning error and picking up of porous objects. The yield is low when picking up an object due to the great variability of the products. A gripper is adapted to a single type of product, each gripper being specific to a product;

- Gripping by simple pliers which requires significant equipment;

- Gripping by flexible elements.

An object of the invention is in particular to allow the manipulation of fragile objects of various shapes, with precision, simple to implement and without the need for external energy input. To this end, the subject of the invention is a device for gripping at least one object, said device comprising at least:

- mechanical support;

- a bistable plate fixed under stress on said support;

- two blades, said clamp blades, mechanically integral with said plate, each forming a jaw of a gripper for gripping said object;

- a trigger element protruding from said plate, capable of coming into contact with said object to be grasped, placed between said blades of length less than this and extending in the same direction;

when approaching said object, the convex face of said plate being oriented towards said object so that said blades are in the open position, bringing said trigger element into contact with said object causing the stable state of said plate to change , the face oriented towards said object passing in a concave position so that said blades close on said object.

In a particular embodiment, said trigger element is composed of a rigid part linked to said plate and of a trigger plate surmounting said part, said plate being able to come into contact with said object.

Said clamp blades extend for example perpendicular to said plate. They are for example flexible.

Said plate is for example composed of a circular central part and flexible blades arranged radially around said central part, said flexible blades being fixed on said support formed by a circular frame, each flexible blade being equipped with a clamp blade . Said central part is for example flat.

In a particular embodiment, said plate comprises at least three flexible blades.

Said trigger element is for example composed of a rod linked to said central part and a circular plate surmounting said rod and able to come into contact with said object.

Said flexible blades arranged radially around said central part are for example embedded in a groove made in said circular frame.

Said circular frame has for example an adjustable diameter, the stress exerted on said flexible blades being a function of said diameter.

In another particular embodiment, among said flexible blades arranged radially around said central part, at least three flexible blades are equipped with rigid blades, for each of said three flexible blades a rigid blade is linked in parallel to the clamp blade, the two blades being parallel in their small dimensions, said rigid blades transmitting to said bistable plate the reaction force produced by a surface with which they come into contact, said reaction force causing a stable change of state of said plate.

Other characteristics and advantages of the invention will become apparent with the aid of the description which follows, made with reference to the appended drawings which represent:

- Figure 1, a first embodiment of a gripping device according to the invention;

- Figures 2a to 2c, an illustration of the operating principle of a device according to the invention;

- Figures 3a and 3b, a second embodiment of a device according to the invention;

- Figure 4, an illustration of a stress connection mode between a bistable plate and a frame;

- Figure 5, another embodiment of a device according to the invention.

FIG. 1 illustrates, in a perspective view, a first possible embodiment of a gripping device according to the invention. The device comprises at least:

- A bistable plate 1, rectangular in the example of Figure 1;

- A trigger 2, having a T profile and extending over the entire width of the plate in this example, thus consisting of a plate 2 "surmounting a plate 2’ mechanically secured to the plate 1;

- Two blades 3 acting as a clamp, extending perpendicularly on either side of the trigger towards the ends 1 ′, 1 ”of the plate, the blades being for example curved and flexible, more particularly having a first flat part 3 'extended by a second part 3 ”folded towards the inside of the clamp in the example of Figure 1. These two blades will be called jaws. The jaws 3 are not necessarily flexible, an advantage of flexibility being notably not to deform the objects seized.

All these parts 1, 2, 3 are for example grouped in a single piece forming a monolithic block.

The bistable plate 1 is fixed at its ends to a support, not shown. This support is movable with the plate. This support and all of the parts 1,2,3 can also form a monolithic block.

Figures 2a, 2b and 2c illustrate the operating principle of a gripping device according to the invention. They show in particular the clever use of the mechanical properties of a bistable plate by the invention. This operating principle is illustrated with the device of Figure 1, shown schematically, in profile.

The bistable plate 1 is fixed to a support of which only the parts 21, 22 mechanically integral with the plate are shown.

The gripping device is shown opposite an object 20 to be grasped.

FIG. 2a illustrates the approach phase of the object 20. The plate is in a first stable state (convex face directed towards the object). The entire device 1, 2, 3, 21, 22 is directed towards the object. In this state, the jaws 3, projecting from the convex face, are spaced apart from one another and form an open clamp.

Figure 2b illustrates the contact of the trigger 2 with the object 20. In the example shown, the contact is made by the plate 2 ". Simultaneously with this contact, a force F is directed towards the convex face of the plate 1. This force is caused by the thrust exerted by the object. It is very weak but sufficient to trigger the change of state of the plate 1, then passing into its second stable state. It is adjustable according to the needs of the applications through the axial mechanical preload of the bistable plate 1.

FIG. 2c illustrates this second stable state corresponding to the grip of the object 20. The face comprising the jaws 3 passing from the convex state to the concave state causes the jaws 3 to come together and therefore to close the clamp. The dimensions and the shape of the jaws 3 are defined so that in the closed state, the clamp grips the object, totally or partially. In all cases, the closure is sufficient to keep the object under the grip of the forceps.

The trigger may have another shape than that shown in Figures 1 and 2. In particular, the plate is not necessary. It suffices with a contact triggering the change of state of the bistable plate 1. For this purpose, the trigger can consist of a simple tip capable of coming into contact with the object to be grasped. However, the 2 ”tray has the advantage of coming into contact with the object more easily, without any problem with positioning accuracy. Furthermore, the tray does not deteriorate soft objects, unlike a projecting part.

In either state, the plate is kept bent under stress. This stress is exerted on the plate 1 and is conventionally regulated by the force F exerted at its fasteners 21, 22 on the support, parallel to the deformation of the plate. This force can be exerted for example by embedding the ends T, 1 ”of the plate in a frame. The trigger sensitivity depends on the stress setting.

The operating principle illustrated in FIGS. 2a to 2c shows that there is no need for energy to close the gripper 3. Advantageously, the closure is simply triggered by bringing the plate 2 "into contact, more generally from the trigger 2, on object 20 which passes the plate into its second state. The gripping solution according to the invention therefore saves an actuator and also an object presence sensor to trigger the taking of it. Trigger 2 performs the function of actuator and sensor. The trigger mode is passive, requiring no external actuation. It is therefore not necessary to embed an actuator in the gripping device. The triggering is done automatically in contact with the object 20 and the trigger 2. In other words, the presence of the trigger 2, kinematically synchronized with the opening movement of the jaws 3, makes it possible to trigger the closing of the clamp around the object, then exert a gripping effort to ensure the grip during transport. The 2 ”tray allows you to center the object in the gripping device. It is also used to correctly deposit the object during removal.

To remove the object, a simple push on the convex face (then oriented upwards as illustrated in FIG. 2c) reverses the state of the bistable plate whose lower face then becomes bistable again, causing the jaws to open. .

Figures 3a and 3b show another possible embodiment of a gripping device according to the invention. Figure 3a shows a perspective view of the device and Figure 3b shows a sectional view, partial and schematic.

The architecture is different from the device in FIG. 1, but the operating principle is the same. In the embodiment of Figures 3a and 3b, the bistable plate has a different shape. The plate 1, rectangular, is replaced by a circular plate composed of a plate 31 and six flexible blades 32 arranged radially around this plate, and preferably regularly. The assembly 31.32 is placed under stress thanks to an open circular frame 33, the diameter of which can be modified to apply a more or less significant force F on the blades, the latter being curved under the effect of the stress . The circular frame 33 serves both as a support for the plate and as a constraint device.

To implement this constraint, the frame is for example formed of two semicircles the ends of which are each extended outwards by a tapped part 331, 332, 33T, 332 ’. The two semicircles are made mechanically integral by means of these parts fixed to each other by a threaded rod whose path makes it possible to bring the two semicircles closer or further apart, thus playing on the stress applied to the blades 32.

To keep the blades integral with the frame, a groove is provided in which the blade ends are engaged, the engaged end being opposite the end linked to the plate 31.

Each blade 32 is extended perpendicularly by another flexible blade 3. The assembly of blades 3 forms a circular clamp and these blades 3 may also be called jaws subsequently. The two blades 32, 3 are not, for example, formed from the same block of material, and constitute the same monolithic part. It is also possible to produce in a single monolithic block the plate 31 and all of the blades 32, 3.

The trigger 2 is fixed under the plate 31. In the embodiment of Figures 3a and 3b, the trigger 2 is composed of a rod 211 and a trigger plate 212 intended to come into contact with the object 20 to seize. The operating mode for gripping this object is identical to that described in FIGS. 2a to 2c, the difference being that the entire device is circular with a larger number of jaws, which makes it possible to better grasp the object.

Like the plate 1 of the device of FIG. 1, the plate 31, 32 of FIGS. 3a and 3b is a bistable system characterized by two stable deformation states, where the passage from one state to the other allows the opening or the closing of the jaws in synchronization with the contacting of trigger 2 on the object to be grasped. This plate 31, 32 can be likened to a shell, bistable, having a particular shape.

The gripping of an object is thus ensured automatically without any other energy input than the approach movement (see Figure 2a). As soon as the object comes into contact with the tray 212, the flexible blades (jaws) close, pass under the object and press it against the tray to keep it trapped and ensure it grips during transport.

A simple push on the convex face of the bistable shell, formed by the plate 31 and the blades 32, then makes it possible to reverse its state and cause the jaws to open and deposit the object.

The plate 31 could be replaced by any other structure making it possible to assemble the blades 32 radially around this structure. A flat shape, however, makes it easier to interface with other organs. Depending on the size of the device and the envisaged application, the number of blades 32 used may vary. At least three flexible blades 32 can be provided which are arranged radially.

The lower blades 3 acting as jaws have been illustrated with a shape analogous to that of FIG. 1. Other shapes are of course possible as long as they make it possible to hold the object when the clamp is closed.

FIG. 4 illustrates more precisely the connection between the blades 32 and the circular frame 33. In this figure, the upper blade 32, extended perpendicularly downwards by the lower blade 3, enters the groove of the frame 33 which loads the blade under the pressure of the force F which has been described above by way of example how it can be exerted. To facilitate the engagement of the blade in the groove, the latter can be terminated by a non-flexible flat 321, this flat being introduced into the groove.

FIG. 5 shows another possible embodiment of a gripping device according to the invention. The latter incorporates the embodiment of Figures 3a and 3b supplemented by a device for removal without external energy supply.

The devices illustrated in FIGS. 1 and 3a, 3b do not require any energy for gripping the object (automatic triggering of the closing of the jaws under the effect of bringing the trigger into contact with the object). On the other hand, an external energy (even a weak one) is necessary for the removal of the object, to bring the bistable shell 1, 31, 32 into the other state corresponding to the separated position of the jaws. The example of embodiment in FIG. 5 saves this supply of external energy.

To allow removal without external energy input, passively therefore, the gripping device of FIG. 5 comprises a set of rigid blades 51 positioned in parallel with the flexible blades 3 of the clamp, outside the clamp. More specifically, a rigid blade 51 is positioned in parallel with the flexible blade 3, forming a jaw, under each upper blade 32. The three blades 32, 3, 51 can form the same monolithic block. The two blades 51, 3 are parallel along their small dimension. The flexible blade 3 and the rigid blade 51 equipping the same upper blade 32 can share the same connection zone on the latter. In other words, they are then connected to the same place of the blade 32.

The external energy is supplied by the reaction force of a flat surface on these rigid blades during the removal operation. When the flexible blades 3 are in the closed position, the rigid blades touch the surface before these flexible blades. Because of their rigidity, the reaction force is transmitted to the upper blades 32 of the bistable shell by creating a pivoting moment around each point of attachment of the blades on the circular constraint frame 33. This change in state of the bistable shell 31, 32 causes the flexible blades 3 to open, allowing the object to be removed.

Simultaneously, when the bistable shell changes state, the rigid blades 51 pivot and are lifted, their movement evolves so that they pass over the flexible blades 3, as illustrated by the left part of FIG. 5. The flexible blades can then pass under the object to take it under the effect of contact with trigger 2.

Advantageously, the setting phase and the removal phase can be linked quickly by passing the bistable shell from a stable convex to concave state simultaneously, and quickly by passing from a triggering by contact of the object on the plate of trigger 31 (closing for grip) on contact with rigid blades 51 on any surface (opening for laying).

The rigid blades have a curved end outward to facilitate their sliding on the flat surface upon contact.

Other embodiments are possible of a device according to the invention are possible, where in particular:

- The clamp is made up of several blades, flexible or not, which close on the object to ensure its grip during transport;

- The object is detected by contact on the trigger element 2 which triggers the gripping;

- The actuation energy is in elastic form, it is in fact directly a robot which already transports the gripper from a point A to a point B which supplies the energy for turning the bistable plate by contact on the object.

The various parts ensuring this combination of functions can be formed in a single monolithic object, for example in polymer material printable in stereolithography therefore easily and quickly manufactured, and at low cost.

The polymer material in which the device is manufactured being flexible, the gripping force exerted on the object to be grasped is then limited, which also makes it possible to grasp flexible and fragile objects, in a delicate manner so as not to degrade the visual quality Objects.

Advantageously, a device according to the invention, whether monolithic or not, is light and provides the robot which guides it with significant dynamics, therefore increased efficiency in a production line.

Inexpensive and robust, the device according to the invention adapts to several shapes and flexibility of objects. It is not specialized for a given type of objects.

Unlike conventional gripping systems comprising a carrying robot embedding an independent actuator (with its own energy) which triggers the setting and removal, with a device according to the invention only the carrying robot is supplied with energy. This energy is used both for positioning the gripping device and for picking up and depositing objects. More generally, given that there is no actuation system or external energy brought in to carry out the gripping, this results in a significant reduction in the mass and the cost of the gripping device.

It should be noted that synchronization between the appropriate position of the gripper and the gripping of the object takes place without the presence of sensors. Triggering is done automatically when the object comes into physical contact with trigger 2. This triggering is also done independently between different gripping devices arranged in parallel, in order to ensure maximum grip of several independent objects.

Finally, the production of monolithic material does not require assembly, is free of fouling, facilitates cleaning, and allows greater precision as well as greater reliability (no play, nor friction). The elasticity of the material, the geometry of the bistable plate (in particular its transverse thickness) and the preload make it possible to know the force necessary for the reversal of the plate (passage from one stable state to another) and the gripping force applied by the blades.

Claims (11)

1. Device for gripping at least one object (20), characterized in that it comprises at least: - a mechanical support (21,22, 33); - a bistable plate (1,31,32) fixed under stress on said support; - two blades (3), said clamp blades, mechanically integral with said plate, each forming a jaw of a gripper for gripping said object; - a trigger element (2) projecting from said plate, capable of coming into contact with said object to be grasped, placed between said blades (3) of length less than this and extending in the same direction; when approaching said object (20) the convex face of said plate being oriented towards said object so that said blades are in the open position, bringing said trigger element (2) into contact with said object causing the change of stable state of said plate, the side facing said object passing into a concave position so that said blades (3) close on said object. 2. Device according to claim 1, characterized in that said triggering element is composed of a rigid part (2 ', 211) linked to said plate and of a triggering plate (2 ”, 212) surmounting said part, said plate (2 ', 212) being able to come into contact with said object. 3. Device according to any one of the preceding claims, characterized in that said clamp blades (3) extend perpendicular to said plate. 4. Device according to any one of the preceding claims, characterized in that said clamp blades (3) are flexible. 5. Device according to any one of the preceding claims, characterized in that said plate is composed of a circular central part (31) and flexible blades (32) arranged radially around said central part, said flexible blades (32) being fixed on said support formed by a circular frame (33), each flexible blade (32) being equipped with a clamp blade (3). 6. Device according to claim 5, characterized in that said central part (31) is planar. 7. Device according to any one of claims 5 or 6, characterized in that said plate comprises at least three flexible blades (32). 8. Device according to any one of claims 5 to 7, characterized in that said triggering element is composed of a rod (211) linked to said central part (31) and of a circular plate (212) surmounting said rod and able to come into contact with said object. 9. Device according to any one of claims 5 to 8, characterized in that said flexible blades (32) arranged radially around said central part (31) are embedded in a groove made in said circular frame (33). 10. Device according to any one of claims 5 to 9, characterized in that said circular frame (33) has an adjustable diameter, the stress exerted on said flexible blades (32) being a function of said diameter. 11. Device according to any one of claims 5 to 10, characterized in that among said flexible blades (32) arranged radially around said central part (31), at least three flexible blades (32) are equipped with rigid blades ( 51), for each of said three flexible blades (32) a rigid blade (51) is linked in parallel to the clamp blade (32), the two blades (51, 32) being parallel in their small dimensions, said rigid blades transmitting to said bistable plate (1) the reaction force produced by a surface with which they come into contact, said reaction force causing a stable change of state of said plate.