Abstract:
The robot comprises: —a controller (C), including power modules ( 22 ) for supplying the motors ( 10 ) of the arm (A) of the robot (R), a CPU unit ( 26 ), for calculation and processing and connection means ( 52 , B), between the arm (A), the power modules ( 22 ) and the CPU unit ( 26 ). The connection means ( 52 , B) comprise a single functional bus (B) which connects a control unit ( 30 ), associated with the CPU unit ( 26 ), firstly to the power modules ( 22 ) and, also, to the digital interfaces ( 14 ) with the sensors ( 12 ) of the arms (A). Said interfaces ( 14 ) are either integrated with the arm (A) or located in the immediate vicinity thereof.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a multi-axis robot provided with a control system. 
   2. Brief Description of the Related Art 
   It is known that multi-axis robots can be controlled by supplying their electric motors with control signals generated from a calculation and processing unit in which the path of the robot is determined. For the path computation to be effective, to have the abovementioned unit work in closed loop mode, by using feedback signals originating from position sensors carried by the arm of the robot, is known, for example from U.S. Pat. No. 4,786,847. In the known robots, a large number of cables must be installed between the arm and its control unit, which leads to long connection and wiring times and not inconsiderable risks of error resulting in complex and costly debugging operations. 
   The use of an optical fiber bus to connect a digital controller to amplifiers each linked to an encoder by a conventional line is known from EP-A-0 777 167. These links between the amplifiers and the coders make the job of installing these devices lengthy and complicated. 
   Moreover, JP-A-10 178 437 provides for encoders to be linked by a bus to an external computer, independently of the power part of the installation. 
   It is these drawbacks that the invention seeks in particular to remedy by proposing a novel architecture for a robot provided with a control system which simplifies the production of the controller, on the one hand, and of the arm, on the other hand, and the installation of this robot in its place of use. The invention also seeks to improve the quality and speed of transfer of the control and feedback signals. 
   SUMMARY OF THE INVENTION 
   In this spirit, the invention relates to a multi-axis robot comprising an arm for moving a tool in space and actuated by electric motors, and a control system comprising:
         a controller which includes at least one power module for supplying the motors and at least one calculation and processing unit used in particular to compute the path of the arm and generate control signals for the abovementioned module or modules;   link means between the arm, the power module or modules and the abovementioned unit, these link means being used at least to supply the motors from the power module or modules and control this or these modules by the calculation and processing unit, and to, transmit feedback signals from the arm to this unit and/or this or these modules.       

   This system is characterized in that the abovementioned link means comprise a single functional bus linking a control unit associated with the calculation and processing unit, on the one hand, to the power module or modules and, on the other hand, to at least one digital interface with at least one position sensor on the arm, this interface being, incorporated in the arm or located in its immediate vicinity. 
   With the invention, the feedback information relating to the position and the speed of the moving elements of the robot, as well as to the current consumed by the various motors, is available for the calculation and processing unit at the bus frequency. Furthermore, the digital signals traveling on the bus in digital form are relatively undisturbed by the ambient noise, unlike analog signals. Optimization of the path control is obtained by the centralized processing of the closed loops. The use of the interface or interfaces allows for serializing the information originating from digital sensors or for digitizing and serializing the information from analog sensors, then for conveying the information to the serial bus. The invention retains the advantages of a system functionally centralizing path generation and closed-loop controls. The interface or interfaces are also used to compute, as near as possible to the sensors or encoders, the speeds and/or accelerations of the moving parts, at a frequency that is a multiple of that of the bus, which reduces the delay between the position, speed and/or acceleration information, in order to provide better closed-loop control. The fact of using a functional bus minimizes the number of conductor cables in the installation, particularly inside the arm, hence a better layout of the connecting cable or cables, relaxed dimensional constraints for the elements of the arm, better accessibility to the elements included in this arm and ease of obtaining mobility of this arm because the minimum bending radius of the bus can be relatively low. The robot according to the invention is more economical to design and build and can benefit from algorithms that make it faster and more accurate than those of the prior art. 
   According to a particularly advantageous aspect of the invention, the single functional bus is divided into at least two structural buses linking, for the first, the control unit to the power module or modules and, for the second or second and subsequent modules, the control unit to the interface or interfaces. The fact of having at least two separate structural buses means that each of these buses can be adapted to the place in which it is installed: the first bus can be metallic, particularly made of copper, whereas another bus can, for example, be made of optical fibers, this type of bus being particularly immune to ambient electromagnetic noise and able to be longer while maintaining high speed. The fact of using several structural buses circumvents the problem caused by the limitations of their bandwidth for adding, as necessary, more elements or more information processed for each element. 
   Advantageously, the control unit is linked to the calculation and processing unit by a PCI (Peripheral Component Interconnect) type bus. As a variant, the control unit is incorporated in the calculation and processing unit. 
   An identification and calibration card can be included on the arm or located in its immediate vicinity, this card being incorporated in the bus. This makes it easy to download the parameters specific to the robot to the calculation and processing unit. A connection can then said to be “plug and play”. 
   The or each structural bus can be designed to be extended by additional connection means to at least one external unit, such as a seventh axis, in particular a conveyor axis, or any unit processing information, such as a safety device. 
   The link means can, furthermore, comprise a power conductor linking the abovementioned module or modules to the robot, independently of the functional bus. 
   The first structural bus is advantageously connected directly or indirectly to power modules, each dedicated to a motor of the robot. It is also possible to provide for the abovementioned interface to be an interface card for computing the speed and/or the acceleration of the movement measured by the or each associated sensor, serializing its output signal and, where appropriate, first digitizing the output signals of the sensor or sensors when they are analog. As a variant, the interface concerned is incorporated in the associated sensor, with the same functions as above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and other advantages of the latter will become more clearly apparent in light of the description that follows of an embodiment of a multi-axis robot and its control system according to the invention, given purely by way of example and with reference to the appended drawing in which the single FIGURE is a theoretical diagrammatic representation of an associated control system and multi-axis robot. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The arm A of the robot R represented in the FIGURE is disposed along a conveyance path indicated by a direction X-X′. This arm is provided with six motors, each for moving a moving part of the arm about one of its six axes to move a tool O in space. These motors are represented by a motorization set  10  in the FIGURE. In practice, they are distributed inside the arm A. Six analog position sensors or encoders  12  are distributed in the robot R and used to measure the movements of the arm about each of its six axes. 
   Three interface cards  14  are mounted on the arm A and are each associated with two sensors  12 . Each card  14  is used to digitize and serialize the analog signal output from a sensor or encoder  12 . Each card  14  is also used to compute the first drift and/or the second drift of the duly generated signal, which is used to determine the speed and/or corresponding acceleration for the moving part concerned of the robot R. Since the cards  14  are located near the sensors or encoders  12 , the drift computations can be performed with a high frequency, of around 20 kHz, whereas the information frames are transmitted at 10 kHz. 
   In practice, the cards  14  can, according to the construction choices, be incorporated in the sensors  12 , common to two sensors and distributed in the arm A, as represented, or disposed at the foot of the arm A. A single card can take the place of the various abovementioned cards  14 . 
   The robot R also includes a controller C controlling the arm A, this controller comprising an enclosure  20  housing six power modules  22  receiving power supply via a cable  24 . Each module  22  is dedicated to one of the motors of the arm A, these six modules  22  being linked to the arm A by a first link cable  52 , with eighteen conductors. In practice, the motors of the subassembly  10  are three-phase motors and each module  22  is linked to the corresponding motor by three conductors. 
   A calculation and processing unit  26 , commonly called a “CPU”, is also disposed inside the enclosure  20  and is linked by PCI bus  28  to a control card  30  provided with an interface  32 . 
   As a variant, the card  30  can be incorporated in the card  26 . 
   An external portable computer  60  can be linked by an Ethernet link  62  to the unit  26  for its programming and/or to display its operating parameters. 
   The unit  26  is used to compute the path of the robot R and generate control signals for each of the modules  22  which in turn each control a motor of the subassembly  10 . To control these modules  22  by taking into account the actual behavior of the arm A, the assembly formed by the elements  26  to  30  is linked by a single functional bus B, on the one hand, to three cards  34  each controlling two modules  22  and, on the other hand, to the three interface cards  14 . 
   The bus B is divided into two structural buses B 1  and B 2 . 
   The bus B 1 , made of copper and contained in the enclosure  20 , is used to convey to the cards  34  the control signals from the modules  22  and, in this way, control the motors of the subassembly  10 . Information also circulates from the cards  34  to the card  30  via the bus B 1 . 
   The second structural bus B 2  is formed by optical fibers and comprises a link cable  54  between the interface  32  and an identification and calibration card  16  mounted near the foot of the arm A, this card  16  being linked, in series, by the second bus B 2  to each of the cards  14 . 
   The fact that the bus B 2  is made of optical fibers provides immunity from the electromagnetic disturbances that can result from the operation of the motors of the subassembly  10  or of the encoders  12 . 
   For the unit  26 , the two structural buses B 1  and B 2  form a single functional bus B with which it interacts, via the card  30 , to send or receive control signals. 
   Given the use of the structural buses B 1  and B 2 , the transmission of information to the control card  30  is particularly fast, in practice completed with a repeat interval of less than 100 microseconds. The information also travels rapidly between the elements  26  and  30 , via the PCI bus  28 . 
   As represented by a broken line in the FIGURE, the structural bus B 2  can be open to incorporate additional connection means B′ 2  to control an external axis, such as a conveyor axis, with a power module  22 ′, two sensors  12 ′ and an interface card  14 ′. 
   Similarly, connection means B′ 1  can be used to link the bus B 1  to an interface card  14 ″ associated with a sensor  12 ″, for example within a safety device. 
   Thus, the invention makes the control system highly flexible and able to be adapted to its working environment. In particular, there is no need to add cables to the link between the controller C and the arm A when the control of an external axis needs to be added. 
   Installation of the robot R and its control system is particularly easy because the information stored on the card  16  makes it possible to consider having the robot R recognized by the controller C on connecting the bus B 2  between the interface  32  and this card  16 . 
   The invention significantly reduces the design, production and wiring costs of the control system of a robot, while the information collected, in particular regarding positions, speeds and accelerations of the moving parts of the robot, is available as fast as and with greater accuracy than in the most powerful devices with structurally centralized system with parallel bus. 
   The invention is represented with a functional bus formed by two structural buses B 1  and B 2 . However, a single bus or, conversely, more than two structural buses can be provided. 
   The invention is not limited to robots provided with analog position sensors. It can also be implemented with digital sensors, in which case the interface provided by the cards  14  of the example described can be incorporated in each sensor. 
   The identification and calibration card  16  can be provided in the controller C and not on the arm A, in which case the elements A and C are paired because it is the card  16  which enables the unit  26  to “recognize” the arm A.