FR3119786A1 - SCARA-type robot joint, with smooth shaft - Google Patents

Abstract

The invention relates to a joint (1) for a robotic arm comprising: - a first part (10) receiving a second part (20) of the robotic arm with the ability to rotate around a general axis (0) of the joint by being driven by a first motor (11);- a third part (30) inserted into the second part (20) and driven in translation along the general axis (0) by means of a second motor (21) and a helical link (40); the third part (30) comprising a shaft (32) of which a free end (33) is intended to receive a tool, the shaft (32) being intended to enter and leave the articulation (1) according to the translation between the second and third parts (20, 30). According to the invention, the first part (10) defines a closed internal volume fully receiving the second part (20) and the first and second motors (11, 21), and an external surface of a portion of the shaft (32 ) coming out of the first part (10) is smooth and passes through a seal (14) mounted on the first part (10). Figure for abstract: Fig. 2

Description

SCARA-type robot joint, with smooth shaft

The invention relates to the technical field of robotic arms, and in particular manipulator arms designated by the acronym SCARA meaning in English “Selective Compliance Articulated Robot Arm”.

Prior art

It is known from the prior art to carry out manipulations of objects with robotic arms of the SCARA type, that is to say robotic arms comprising a first arm connected to a support by a pivot connection, a second arm connected to the first arm by a second pivot connection parallel to the first, and a third arm guided in translation relative to the second arm along an axis parallel to the two pivot connections. A tool is then placed at the end of the third arm, depending on the operations to be performed by the robotic arm.

This type of robotic arm is particularly used to perform object placement operations, for example by picking up loose objects in a first container and then depositing them in an orderly manner in a second container.

Conventionally, the translational movement of the third arm is ensured by a helical connection, one screw of which fulfills the role of third arm. This third arm therefore has grooves corresponding to the threads of the helical connection.

Moreover, this same screw is generally used to guide the third part in translation, by means of additional longitudinal grooves which cooperate with a ball socket.

The screws of the prior art having to have good characteristics of hardness or resistance to wear, they generally do not have good characteristics of resistance to oxidation.

In the field of food, pharmaceuticals or nuclear, for example, the robotic arm must be cleanable, generally with a water jet. In other dirty industries, it is also necessary to prevent any insertion of particles or dust inside the robot. The use of SCARA-type robots is therefore complicated, in certain fields of use, by the fact that it is difficult to make such a robotic arm waterproof, in particular at the level of the grooves of the screw.

It is known, in order to protect the robotic insertion arm from dirt that may occur at the level of the grooves of the screw, to conceal the screw by means of a bellows connecting the end of the second arm and the end of the third arm. The bellows also prevent the escape of lubricant or wear dust from the parts into the environment of the robot.

However, the bellows are fragile and have a limited lifespan. In addition, the bellows by nature have many folds that are difficult to clean effectively. In addition, the compression and decompression of the bellows produces a pumping effect which tends to cause dust to enter and exit from the environment in the robotic arm, and vice versa.

Finally, the bellows do not always resist the high-pressure water jets used for cleaning in the food industry. Moreover, they cannot be cleaned by wiping or smearing, as is customary in the nuclear field.

One of the aims of the invention is to overcome the drawbacks of the prior art by proposing an articulation for a robot, in particular of the SCARA type, which resists pollution from its environment, and whose lifespan of the solutions used is improved. .

For this purpose, a joint for a robotic arm comprising:
- a first part receiving a second part of the robotic arm with the ability to rotate around a general axis of the joint while being driven by a first motor;
- a third part inserted in the second part and driven in translation along the general axis by means of a second motor and a helical connection; the third part comprising a shaft, one free end of which is intended to receive a tool, the shaft being intended to enter and exit the articulation according to the translation between the second and third parts.

According to the invention, the first part (10) defines a closed internal volume fully receiving the second part (20) and the first and second motors (11, 21), and an external surface of a portion of the shaft (32 ) coming out of the first part (10) is smooth and passes through a seal (14) mounted on the first part (10).

In this way, the shaft no longer has the screw ridges of the prior art allowing the insertion of materials such as dust or water inside the robotic arm. Also, the absence of grooves prevents the lubricant contained in the joint or particles resulting from the wear of the parts of the joint from circulating via these grooves and falling on the objects handled. In addition, the shaft being smooth, it is possible to use simple sealing solutions such as O-rings or lip seals. Finally, it allows to adapt the choice of the material of the shaft for its stainless or inert properties, and to adapt separately the material of the screw for its properties of hardness and resistance to wear.

According to a preferred embodiment, the helical connection comprises a screw connected to the second part and a nut connected to the third part. In this way, the screw is fixed in height relative to the second part, while the nut is movable in translation with the third part. This makes it possible to limit the height of the joint obtained, and in particular avoids having, as practiced in the prior art, a cover above the joint to protect the screw. In addition, this makes it possible to encapsulate the screw within other mechanical parts in order to constitute a reserve of lubricant and to ensure the lubrication of the screw.

In this mode, the second motor comprises a stator coupled to the first part, and a rotor connected to the screw. This achieves a compact joint, in that the second motor does not rotate with the second part and therefore remains stationary. The shape of a joint cover is also simplified.

In order to obtain a rigid and efficient sliding connection, the shaft and the second part are connected by means of plain rings constituting a bearing whose length is at least equal to the external diameter of the shaft. Such a guide length makes it possible to withstand the forces to which the articulation at the end of the shaft may be subjected.

In order to achieve the locking in rotation of the translation guide in a simple way, the second part has at least one longitudinal groove and parallel to the general axis of the joint, in which a complementary shape of the third part is inserted.

Advantageously, the joint comprises networks, such as a power supply network, a motor control network. The networks cross the joint internally from the first part of the robotic arm to the third part. The networks are thus protected from attacks related to the environment in which the robotic arm operates. Their concealment also represents a reduction in the retention zones in which germs can develop, which is an important point in the field of the food industry.

Preferably, the shaft is crossed by a conduit configured to receive networks, which makes it possible to protect them up to the level of the tool carried by the robotic arm.

In order to allow the free movement and the expansion of the gratings during the relative movements of the first, second and third parts with respect to each other, at least one of the gratings comprises a spiral portion around the second part by passing through a chamber defined between the first part and said second part.

In order to simplify the wiring of the robotic arm, the first part internally comprises at least one electronic card intended to control the first motor and/or the second motor. It is thus possible to avoid running cables back and forth between the motors and an electrical box that would be installed outside the robotic arm. In addition, the electronic cards are protected inside the robot.

In order to be able to provide security functions for the robotic arm, the free end of the shaft includes sensors, such as force sensors and/or presence sensors. Thus, the robotic arm is able to detect a possible collision and to get to safety.

According to the preferred embodiment, the first part defines an internal volume fully receiving the second part, the first and second motors, the networks and the electronic card. The third part is intended to pass through a seal mounted on the first part. The resulting robotic arm is simple, compact and waterproof.

is a block diagram of a prior art SCARA-type robot.

is a section, from the front, of a joint according to the invention in a first position.

is a section, from the front, of such a joint in a second position.

is a section, from above, of such a joint.

Detailed description of the invention

Referring to Figures 2 to 4 which illustrate a preferred embodiment of the joint (1), it can be seen that the latter comprises three kinematic groups, like the SCARA-type robots of the prior art:
- a first part (10), intended to be fixed to the free end of the robotic arm;
- a second part (20) mounted in pivot connection with the first part (10) along a general axis (0) of the joint, and able to pivot on either side of a median position shown ;
- A third part (30) driven in translation along the general axis (0) with respect to the second part (20), and intended to receive at a free end (33) a tool (not shown).

The second part (20) is moved relative to the first part (10) by a system of pulleys and belts driven by a rotor (111) of a first motor (11), a stator (110) of which is fixed to the first part (10).

According to the invention, the first part (10) defines a closed internal volume fully receiving the second part (20) and the first and second motors (11, 21), and the third part (30) comprises a remarkable shaft (32) in that its portion intended to enter and exit the joint (1) has a smooth outer surface. Advantageously, this makes it possible to mount simpler sealing solutions than in the prior art, and in particular simple seals. Preferably, these are lip seals, which behave well when the parts they connect have combined rotational and translational movements.

Moreover, the design of the joint (1) now having a majority of smooth surfaces, its cleaning by wiping, or by smearing, is possible, which makes it compatible with applications in the nuclear field.

In particular, the material of the shaft (32) is chosen for its stainless or inert properties, and may for example be titanium.

The third part (30) is moved relative to the second part (20) by a helical connection (40) comprising a screw (41) and a nut (42), for example a screw (41) and a nut ( 42) with balls. This third part (30) is also remarkable in that, contrary to what is practiced in the prior art, it carries the nut (42) and not the screw (41). This design results in a short third part (30) since the length of the screw (41) stroke overlaps the length of the shaft (32) stroke.

To this end, the screw (41) is fixed in translation and moved in rotation by a second motor (21), of which a stator (210) is fixed on the first part (10) and a rotor (211) drives a system of pulleys and belt connected to the screw (41).

The screw (41) for its part must have a high resistance to wear, which is generally not possible with materials having good stainless properties. The screw (41) is made for example of hardened and tempered steel, such as 100C6.

The kinematic connection between the first part (10) and the second part (20) is achieved by suitable guide means, such as ball bearings or needle bearings.

The kinematic connection between the second part (20) and the third part (30) is achieved by guiding by means of rings (37). These rings (37) are of any suitable type, and are preferably self-lubricating rings, such as made of sintered bronze and loaded with lubricant.

Advantageously, an upper ring (37) is fixed on the shaft (32) and a lower ring (37) is fixed on the second part (20). With reference to the , in order to obtain sufficiently rigid and precise guidance, the minimum length (d) of the bearing surface between the two rings (37), measured between the middles of the rings (37), is greater than or equal to the external diameter (D) of the shaft (32). This minimum length (d) is obtained when the shaft (32) is in the low position, and the length (d) increases when the shaft (32) rises.

Several technical solutions can be envisaged to achieve the rotational blocking of the guide obtained. Preferably, it is a question of providing at least one longitudinal groove (22) parallel to the axis (0) in the second part (20), and in which is inserted a complementary shape (34) of the third part ( 30).

It may for example be a key arranged on the shaft (32), but preferably it is prominences of the shaft (32). In order to guarantee the longevity of this guide, plates not shown are placed at the interface between the complementary shape (34) and the groove (22). These pads are advantageously made of self-lubricating material, and preferably made of sintered bronze loaded with lubricant.

The first and the second motor (10, 20) being each fixed to the first part (10), they are preferably fixed one above the other, which makes it possible to obtain a compact joint (1) , and which also makes it possible to simplify the wiring since a single network bundle (50) arrives in the joint (1) from the robotic arm. Movement interpolation.

The networks (50) include the power supply for the first and second motors (10, 20), the control networks for these motors (10, 20), and power supply and control networks for the tool intended to be carried by the free end (33).

The networks (50) further include the supply and connection of sensors (36) arranged at the free end (33). These sensors (36) are preferably force sensors, such as strain gauges, which make it possible to detect whether the robotic arm has collided with an object or with an operator. These sensors (36) are therefore safety elements complementing the current inrush detections of the motors generally used in robotics.

Some of the networks (50) are connected to one or more electronic cards (13) which are arranged inside the joint (1). Preferably, there is an electronic board (13) for each of the first and second motors (10, 20). These electronic cards can be used to redistribute the power supply and to control the tool intended to be carried by the joint (1), and also to receive and interpret the data coming from the sensors (36).

In order to circulate the networks in a practical way to the free end (33), two characteristics are remarkable:
- an expansion chamber (12) is provided between the first part (10) and the second part (20), so that a spiral portion (51) of networks (50) is wound around the second part (20). Thus, the spiral portion (51) can expand and/or expand freely according to the combined movements of the first, second and third parts (10, 20, 30). This expansion chamber (12) can be contained in a sleeve (15) preventing the cables of the networks (50) from moving in a disorderly manner within the joint (1). It may for example be preferable that the networks (50) do not come into contact with the electronic cards (13) or the motors (10, 20);
- the shaft (32) comprises a duct (35) intended to receive the networks (50) and to hold them up to the level of the free end (33). Preferably, the conduit (35) is a bore passing through the shaft (32) along its length.

The networks (50) may also include a compressed air network to power the tool. In this case, one can imagine that a second conduit (35) is made in the shaft (32), and that a pneumatic connection is arranged at each end of this second conduit (35). Thus, the pneumatic networks (50) could be connected at the top of the shaft (32) to supply it with compressed air, and a secondary pneumatic network (50) would be connected at the bottom of the shaft (32), at the level from its free end (33), in order to supply the tool.

The joint (1) thus designed, and in particular in its preferred embodiment, is compact, sealed, and has no retention zones in which dirt could accumulate or germs develop.

In particular, the shaft (32) has a smooth outer surface and passes through a seal (14) mounted in a bore of the first part (10). So that the seal (14) can fully play its role, the lower guide ring (37) and another ring (38) are arranged close to the seal (14) and perfectly align the bores of the first, second and third games (10, 20, 30).

The first part (10) receives in its interior all the elements of the articulation (1), except the shaft (32) which slides and a possible tool holder which can be arranged at its free end (33). The first part (10) therefore comprises a casing made in several parts, possibly connected by seals.

In particular, the casing of the first part (10) comprises removable covers opposite the electronic cards (13) or the pulley and belt systems of the first and second motors (10, 20). These covers allow easy access to these elements during assembly and also for maintenance of the joint (1).

The joint (1) can be shaped differently from the figures without departing from the scope of the invention, which is defined by the claims. In addition, the technical characteristics of the various embodiments and variants mentioned above can be, in whole or for some of them, combined with each other. Thus, the joint (1) can be adapted in terms of cost, functionality and performance.

Claims (9)

Articulation (1) for robotic arm comprising:
- a first part (10) receiving a second part (20) of the robotic arm with the ability to rotate around a general axis (0) of the joint while being driven by a first motor (11);
- a third part (30) inserted into the second part (20) and driven in translation along the general axis (0) by means of a second motor (21) and a helical connection (40); the third part (30) comprising a shaft (32) of which a free end (33) is intended to receive a tool, the shaft (32) being intended to enter and leave the articulation (1) according to the translation between the second and third parts (20, 30);
characterized in that the first part (10) defines a closed internal volume fully receiving the second part (20) and the first and second motors (11, 21), and in that an outer surface of a portion of the shaft (32) which comes out of the first part (10) is smooth and passes through a seal (14) mounted on the first part (10). Articulation (1) according to Claim 1, characterized in that the helical connection (40) comprises a screw (41) connected to the second part (20) and a nut (42) connected to the third part (30). Articulation (1) according to Claim 2, characterized in that the second motor (21) comprises a stator (210) coupled to the first part (10), and a rotor (211) connected to the screw (41). Articulation (1) according to claim 1, characterized in that the second part (20) has at least one longitudinal groove (22) parallel to the general axis (0) of the articulation, in which a shape is inserted complementary (34) to the third part (30), and in that the shaft (32) and the second part (20) are connected by means of smooth rings (37) constituting a bearing surface, the length of which (d ) is at least equal to the outer diameter (D) of the shaft (32). Articulation (1) according to claim 1, characterized in that the first part (10) internally receives networks (50), such as a power supply network, a motor control network, passing internally through the articulation (1 ) from the first part (10) of the robotic arm to the third part (30). Articulation (1) according to Claim 5, characterized in that the shaft (32) is crossed by a duct (35) configured to receive networks (50). Articulation (1) according to Claim 5, characterized in that at least one of the networks (50) comprises a spiral portion (51) around the second part (20) passing through a chamber (12) defined between the first part (10) and said second part (20), the chamber (12) allowing the expansion of the grating (50) during the relative movements of the first, second and third parts (10, 20, 30) relative to each other others. Articulation (1) according to Claim 5, characterized in that the first part (10) comprises internally at least one electronic card (13) intended to control the first motor (11) and/or the second motor (21). Articulation (1) according to Claim 1, characterized in that the free end (33) of the shaft (32) comprises sensors (36), such as force sensors and/or presence sensors.