FR2696670A1 - Robot joint and robot comprising such joints. - Google Patents

Abstract

Robot articulation for producing a rotation in relation to two arms (1, 2) and characterized in that it comprises a sealed housing composed of two half shells each integral with the end of an arm and rotatably mounted on one another. Said articulation is also characterized in that one of the two half shells contains a dc brushless motor reducer and the other half shell is driven by said motor reducer, the housing being filled with an electrically insulating liquid. Each half shell comprises a connector (5, 6) which receives a coupling cable (7) including supply conductors and a data transmission line and is connected to the adjacent articulation, said housing containing a motor reducer control device which comprises a processor.

Description

 The present invention relates to robots or manipulators and, more particularly, the joints between two arms of such a manipulator.

 We have designed robotic systems comprising one or more central computers and a set of "intelligent" peripherals each having their own function in the system: exteroceptive sensors (proximity sensors, rangefinders, effort sensors, etc.), sensory sensors (vision machines, tactile sensors etc ...), among others. Research has been done on both hardware and software to improve the overall reaction performance of a system.

 If we are particularly interested in the actuator components of a manipulator or a robot, and more particularly in motorized articulations of the electrical "pivot" type, we can see that the number of connecting cables per articulation is very large.

 This of course leads to a large number of constraints as regards both the weight / power ratio and the stability. Advanced connectivity, low level signal interference, line losses on power wires, etc. are all possible causes of malfunction. On the other hand, most joints involve a nested servo system, on the motor current, speed and position on the complete axis and possibly effort.

 As a result, for a system comprising several articulations, the volume of the part relating to piloting and the complexity of the connections becomes very large.

 Another important problem is the presence of numerous parasites in the environment where these manipulators work. To obtain sufficient stability, it is necessary to provide additional circuits, which leads to a problem of cost and size.

 The subject of the present invention is a robot articulation intended to perform a relative rotation of two consecutive robot arms, characterized in that it comprises a sealed enclosure constituted by two half-shells each secured to the end of an arm and rotatably mounted one on the other with the interposition of a dynamic seal, one of the two half-shells contains a brushless direct current electric gearmotor and the other half-shell is driven by said gearmotor, said enclosure is filled with an electrically insulating liquid, each half-shell comprises a connector fixed on one of its external faces and intended to receive a connection cable comprising supply conductors and a data transmission line and connected to the neighboring joint, and said enclosure contains a gearmotor control device which includes a processor and which operates autonomously according to the data received from other joints and from a centralized command via the data transmission lines.

 The invention therefore makes it possible to very greatly reduce the number of connection cables between the various articulations since the connection cable only comprises supply conductors and the data transmission lines, ie for example five conductors.

 The use of a geared motor unit comprising a brushless direct current electric motor also makes it possible to improve the reliability of the device.

 The insulating liquid provides good cooling of the entire joint.

 According to another characteristic of the invention, the data transmission lines are optical fiber lines.

 This eliminates all interference problems on the data transmission lines.

 Advantageously, the optical fibers are made of silica.

 This provides insensitivity to radiation, which is important in the case of manipulators working in radioactive environments.

 In the embodiment of the invention, the data transmission lines connect two neighboring joints and the enclosure contains a data retransmission circuit connected between the two connectors; this retransmission device performs signal regeneration and error management. This arrangement makes it possible to obtain a modular structure for each of the joints.

 According to yet another characteristic of the invention, the enclosure comprises a device for optical coding of the movement of the gearmotor and the insulating liquid is transparent. The use of an optical device also makes it possible to overcome the problems of parasites.

 Advantageously, the processor used in the geared motor control device is a microcoded processor comprising a task scheduler with priorities, a fast memory and four communication systems per link, that is to say a processor of the type designated by "transputer ".

 The use of such a processor makes it possible to control the electric motor directly at the processor.

 The invention also relates to a robot comprising a centralized control unit and a succession of arms connected together by an articulation of the type described above. The last arm has an effector at its end. It can also include a video camera at its end.

 Advantageously, for the operation of this robot, a download is made of the processor of each joint.

Other characteristics and advantages of the invention will emerge from the description which follows, of an exemplary embodiment, made with reference to the appended drawings in which
- Figure 1 is a side view of two consecutive arms of a robot comprising a hinge according to the invention;
- Figure 2 is a top view corresponding to Figure 1
- Figure 3 is an electrical and electronic diagram of a joint according to the invention;
- Figure 4 is a sectional view of a hinge according to the invention; and
- Figure 5 shows schematically an alternative embodiment of the invention.

 FIG. 1 shows two consecutive robot arms 1 and 2 which are mounted in relative rotation one on the other at their ends around a vertical axis 3 by means of an articulation designated under the general reference 4. The robot has several successive shafts articulated in the same way, which makes it possible to obtain any movement of the end of the last arm.

 As can be seen in FIG. 1, each articulation comprises two connectors, an upstream connector 5 and a downstream connector 6. Each connector receives a connection cable 7 which is advantageously placed in the arm 1 or 2; this connecting cable makes a connection between two neighboring joints; it includes supply conductors and a data transmission line.

 According to one embodiment, this cable comprises three supply conductors and two optical fibers made of silica constituting a data transmission line. This composite cable has a polyurethane sheath. Its speed can be 20 megabits per second.

 Figure 3 is an electrical and electronic diagram of the joint 4. This figure shows the upstream 5 and downstream 6 connectors which constitute interfaces; these connectors have three terminals connected to alternating current supply conductors two active conductors 11 and 12 and a ground conductor 13. This is for example a supply whose voltage is from 100 to 250 V and the frequency from 50 to 400 Hz.

 The upstream connector 5 comprises a device for connecting two optical fibers 14 and 15 which are connected to an optical fiber interface 16.

 The downstream connector 6 has a second optical fiber interface 17 which is connected to two optical fibers 18 and 19, which are connected to the downstream connecting cable.

 Protection against faults can be provided, such as a fuse 10, for example on the output supply conductors of the downstream connector.

 The active supply conductors 11 and 12 are connected between the two connectors 5 and 6; moreover they supply a supply device 21 intended in particular to supply the supply of the electric motor.

Each articulation comprises a brushless direct current motor 22 whose rotation is controlled and controlled by an electronic control device which essentially comprises a processor 23 of the type marketed under the name "transputer" by the company
INMOS and which essentially comprises a microcoded processor comprising a kernel architecture with few instructions, for example 32, which is used for the implementation of simple sequential programs. This processor internally includes a task scheduler with priorities, microcoded, to distribute the time of the central unit between different processes. Finally, this processor has several asynchronous quick links, for example four. The internal structure of this processor therefore comprises a main processor, a fast memory and four communication systems per link.

 This processor 23 receives the signals supplied by the optical interface 16 and by the interface 17 and it constitutes, for the upstream and downstream data transmission lines, a signal retransmission device which performs error management and performs signal regeneration. which are retransmitted. It therefore constitutes a relay for the data which must be transmitted from the articulation situated upstream to that situated downstream and vice versa.

 The motor 22 is a brushless direct current motor of known type which comprises for example a three-phase winding and a permanent magnet rotor. As indicated above, this motor is supplied by a supply circuit 21 which supplies a control circuit 24 which sends a pulse current to each of the windings.

 In accordance with the invention, the pulses supplied by the circuit 24 are controlled by the processor 23 which directly controls the power switches of the circuit 24.

 To this end, the processor 23 receives via a bus 25 information concerning the position of the geared motor and the torque supplied by the geared motor.

 The position of the gearmotor is coded by an absolute encoder 26 of the optical type, the data of which are managed by an encoder interface 27 connected to the bus 25.

 The device also includes a torque sensor 28 which is connected to a torque controller 29 which is itself connected to the bus 25.

 The encoder 26 and the sensor 28 supply digital data, for example coded on twelve bits.

Advantageously, the bus 25 is a 32-bit bus.

 Figure 4 is a sectional view of a joint according to the invention. It essentially consists of two cylindrical half-shells which are mounted in rotation one on the other around their axis of revolution.

 The upstream part, which is located on the right of the figure, comprises a half-shell 31 and the downstream part comprises a half-shell 32 which is rotatably mounted on the half-shell 31 by means of a bearing 33 which is associated with a dynamic seal 34. The two half-shells 31 and 32 each have a cover 35 respectively 36 which is fixed in a sealed manner.

 The assembly of the two shells therefore forms a sealed enclosure in which the active elements of the joint are arranged, the empty spaces being filled with a transparent dielectric liquid such as a silicone oil.

 The essential element of the articulation is constituted by a geared motor assembly comprising a brushless direct current electric motor, the stator 37 of which is integral with the upstream half-shell 31. The rotor 38 of this motor drives, on the one hand, the primary part of a reduction gear 41 and, on the other hand, a hollow shaft 39 secured to a fine encoder 45. The secondary reduction shaft 42 is secured to the downstream half-shell 32 and drives a slow shaft 43 which is disposed inside the rapid hollow shaft 39 and opens into the upstream half-shell 31.

 On the slow shaft 43 is arranged a coarse encoder 14 of absolute optical type. The two encoders placed side by side are arranged in the upstream half-shell.

 All the electronic circuits are arranged on printed circuit boards which are in the form of washers and arranged around the hollow shaft 39 in a space 46 disposed between the encoders 44 and 45 and the electric motor itself, this makes it possible to limit the size of the joint.

 Each half-shell has a connector 47 respectively 48. As can be seen in FIG. 1, the arms 1 and 2 are mounted on the connectors 47 and 48 with the interposition of a seal 49.

 The brushless electric motor is a direct current motor of the sealed type and comprising radiators. The use of such an engine makes it possible to very clearly improve the reliability and the maintenance of such a joint.

 The entire enclosure is maintained in a bath of dielectric liquid which is under pressure with the external pressure so as to obtain correct operation of the dynamic seal. This arrangement makes it possible to obtain good cooling of the joint and good sealing; as indicated above, this liquid is transparent so as to allow the use of optical motor position encoders.

 As indicated above, the motor position coding device comprises a fine encoder 45 secured to the shaft 39 connected to the engine and a coarse encoder 44 secured to the slow shaft 43. Both are absolute optical encoders and the combination of their signals makes it possible to obtain a coding equivalent to that obtained with a fifteen-bit coder which would be mounted on the reduction shaft.

 The use of a processor of the “transputer” type makes it possible to obtain an “intelligent” articulation; in fact, each of the buses arranged between two arms transmit information coming from a central control unit as well as from each of the articulations.

Each processor can therefore control the geared motor as a function of the information received both from the central control unit and from the other articulations.

 For this purpose, the processor does not only constitute a relay between the various buses of the robot but it develops messages concerning its articulation which are sent to the whole system.

 The use of a processor of the “transputer” type also makes it possible to directly control the brushless electric motor and therefore to eliminate the control variator of the latter.

 The invention therefore makes it possible to produce modular joints which can be assembled one behind the other between robot arms. The last arm may include an effector or a positioning tracking device such as a video camera. In this case, the last arm has at its end a processor which controls the effector or the locating device and provides messages on the bus arranged in this last arm.

 The embodiment which has just been described relates to a joint in which the two consecutive arms rotate relative to each other in two parallel planes. FIG. 5 schematically represents an embodiment in which the two arms are aligned and rotate around the same axis, namely the axis of revolution of the two half-shells.

 In the first embodiment, the two connectors are arranged on the side walls of two half-shells. In the embodiment of Figure 5, the two connectors are arranged on the covers of the two half-shells.

 It can be seen that the invention makes it possible to produce robots or manipulators comprising several arms in which the expenditure on connection cables and on connectors is reduced.

 The use of optical fiber data transmission lines makes it possible to avoid signal interference and, in the particular case of silica fibers, this allows use in radioactive media. The use of a "transputer" type processor simplifies the gearmotor control circuit and provides intelligent articulation.

 The use of a closed enclosure filled with a dielectric liquid makes it possible to improve the cooling of the joint.

Claims (14)

 1. Robot articulation intended to achieve a relative rotation of two consecutive robot arms (1,2), characterized in that it comprises a sealed enclosure constituted by two half-shells (31,32) each secured to the end of an arm and mounted in rotation one on the other with the interposition of a dynamic seal (34), in that one of the two half-shells (31) contains a geared motor (37-39,41-43 ) electric brushless direct current and the other half-shell (32) is driven by said gearmotor, in that said enclosure is filled with an electrically insulating liquid, in that each half-shell (31,32) comprises a connector (5,6 :: 47,48) fixed on one of its external faces and intended to receive a connection cable (7) comprising supply conductors (11-13) and a data transmission line (14 , 15) and connected to the neighboring joint, and in that said enclosure contains a device for controlling the motoredu ctor which comprises a processor (23) and which operates autonomously as a function of the data received from the other joints and of a centralized control via the data transmission lines.  2. Robot joint according to claim 1, characterized in that the data transmission lines (14,15) are fiber optic lines.  3. Robot joint according to claim 2, characterized in that the data transmission lines comprise optical fibers (14,15) made of silica.  4. Robot articulation according to claim 1, characterized in that the data transmission lines (14,15) connect two neighboring articulations and in that the enclosure contains a data retransmission circuit (16,17,23) connected between the two connectors (5,6).  5. Robot articulation according to claim 4, characterized in that said retransmission device performs signal regeneration and error management.  6. Robot joint according to claim 1, characterized in that the enclosure comprises an optical coding device (26; 44,45) of the movement of the gearmotor and in that the insulating liquid is transparent.  7. Robot articulation according to claim 6, characterized in that the optical encoder comprises two absolute encoders, a fine encoder (44) fixed on the motor shaft and a coarse encoder (45) fixed on the reduction gear shaft ( 41-43).  8. Robot articulation according to claim 1, characterized in that the processor (23) is a microcoded processor comprising a task scheduler with priorities, a fast memory and four asynchronous communication systems per link, of the "transputer" type.  9. Robot joint according to claim 1, characterized in that the connector (5,6; 47,48) is arranged on the side of the half-shell perpendicular to the axis of rotation of the gearmotor and in that the cable link (7) is housed in the arm.  10. Robot joint according to claim 1, characterized in that the gearmotor control device comprises printed circuits in the form of washers arranged around a central axis (39) of the gearmotor.  11. Robot characterized in that it comprises a centralized control unit and a succession of arms connected together by a hinge according to one of the preceding claims.  12. Robot according to claim 11, characterized in that the last arm comprises at its end a tool.  13. Robot according to claim 11, characterized in that the last arm comprises at its end a video camera.  14. Robot according to claim 11, characterized in that one carries out a download of the processor of each joint.