BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to machines used for forming the shed in weaving looms, and more particularly to weaving mechanisms of the Jacquard type. The invention also relates to a weaving loom equipped with such a mechanism. 
     2. Brief Discussion of the Related Art 
     In their conventional construction, Jacquard mechanisms comprise a head actuation device, placed above the loom, and a harness connecting this head to the warp yarns stretched on the loom. This harness comprises a series of harness cords directly and individually controlled by the head in a vertical movement of displacement. Each of the harness cords is assembled by a collar on one or more heddles, each heddle bearing a mail traversed by a warp yarn. 
     The known devices most often comprise griffe frames bearing griffes or knives intended to raise, or not, hooks kinematically linked to the harness cords. The fact of driving these griffe frames with a vertical reciprocating movement requires the use of an elaborate mechanical transmission, from the central shaft of the loom, while the precision of the shed obtained depends on the mechanical clearances of this kinematic assembly. The known mechanical devices are complex and not readily accessible, which is detrimental to assembly and maintenance thereof. 
     It is an object of the present invention to overcome the limitations set forth above by proposing a weaving mechanism and a weaving loom which are compact, economical and easily accessible, thus facilitating use thereof. 
     SUMMARY OF THE INVENTION 
     To that end, the invention relates to a weaving mechanism of the Jacquard type for forming the shed in a weaving loom, this mechanism being associated with a harness comprising harness cords, secured to heddles associated with the warp yarns of the loom, characterized in that the harness cords are controlled by electric actuators arranged in rows and/or in columns forming two panels disposed above the loom, and in that a unit for supplying and monitoring these actuators is housed in a compartment defined between these panels. 
     Thanks to the invention, it is possible for the panels formed by these actuators and the unit for supplying and monitoring these actuators, to cohabit in a compact and economical assembly which is easy to access for the operations of assembly and maintenance of the weaving loom. The compartment thus formed efficiently protects the supply and monitoring unit from its environment, particularly from mechanical shocks and dust or surrounding fluff. 
     According to advantageous but optional aspects of the invention, the mechanism incorporates one or more of the following features: 
     Two plates arranged at the ends of the panels border the compartment, one of these plates supporting means monitoring the temperature of this compartment and/or of the actuators. In that case, the temperature monitoring means advantageously comprise a ventilation unit adapted to direct a stream of cooling air towards the supply and/or monitoring unit and/or towards the actuators. Thanks to this aspect of the invention, the monitoring unit and the actuators may be cooled with the same device, which is advantageous from the standpoint of reliability and cost price of the mechanism of the invention. It may also be provided that panels form or bear channels for the circulation of air for ventilating the actuators, these panels extending substantially between the plates from the ventilation unit. 
     The mechanism comprises a chamber for placing the cooling air from the ventilation unit under excess pressure, this chamber being in communication with the compartment and/or the channels formed or borne by the panels, through orifices made in the plate. In that case, the opposite plate is advantageously provided with orifices for the evacuation of the cooling air coming from the compartment or the channels. 
     The panels are inclined with respect to one another, their spaced apart relationship increasing upwardly, an opening for access to the compartment being provided at the upper edges of these panels. In that case, a removable cover for closing this opening is advantageously provided. A walkway accessing this opening may also be integrated in the structure of the loom. 
     The panels are formed by boxes receiving the actuators, these boxes being assembled on one another in rows and/or columns. 
     The invention also relates to a weaving loom equipped with a weaving mechanism as described hereinbefore. This weaving loom is simpler to use and to maintain than the looms of the prior art. Its output is substantially improved with respect to the known art and it allows the control yarn-by-yarn or by groups of several yarns of a Jacquard harness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more readily understood on reading the following description of an embodiment of a weaving mechanism and a weaving loom in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic vertical section through a weaving loom according to the invention. 
     FIG. 2 is a partial section on a larger scale along line II—II in FIG. 1; I—I therein indicates the plane of section of FIG.  1 . 
     FIG. 3 is a partial section on a larger scale along line III—III in FIG. 1, and 
     FIG. 4 is a view in detail of a box visible in FIG.  1 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the drawings, the mechanism schematically shown in FIGS. 1 to  4  is formed by the mutual assembly of a multitude of boxes  1  of which each contains a plurality of rotary actuators  2  whose driven shaft bears a pulley  3  for winding a harness cord  4  connected to a heddle  5  intended to control the warp yarns  6  of the weaving loom. Each heddle is connected to the frame of the loom by an elastic return system  7 . 
     The different boxes  1  are assembled in rows perpendicular to the plane of FIG.  1  and in columns parallel to this plane, with the result that they form two panels A and B disposed above the weaving area, i.e. above the loom itself. Panels A and B form an upwardly open V structure and support plates  8  for guiding the harness cords  4  so as to avoid interferences between these harness cords, while a harness board  9  is provided above the heddles  5 . 
     A framework  10  supports the panels A and B above the loom in the configuration mentioned above. This framework comprises a walkway  11  accessible by a staircase  12 . 
     Between panels A and B there is defined a space whose cross-section in the plane of FIG. 1 is substantially triangular and inside which is housed a unit  20  for electrical supply to and for monitoring the actuators  2 . 
     The unit  20  comprises, inter alia, a transformer, a rectifier-regulator unit for supplying power and for supplying one or more electronic cards controlling the actuators  2 . The unit  20  also comprises a battery and a stand-by battery, as well as a system of switching between the different possible sources of voltage. Unit  20  is connected by webs of conducting wires or conducting rods to the actuators  2  of each of the panels A and B. In practice, the conducting webs or rods are connected to electronic control cards  2 ′ associated with the motors  2  in each of the boxes  1 , such a card being shown only in FIG.  4 . 
     A cover  21  covers the unit  20  and the panels A and B. 
     In this way, the above-mentioned space forms a compartment  22  for receiving and protecting the unit  20 . 
     The cover  21  is advantageously mounted tightly on the panels A and B, in order to obturate the upper opening  22   a  of the compartment  22 , which enables it to protect the unit  20  efficiently from the fluff of the ambient atmosphere. 
     Two plates  23  and  24  are provided at the ends of the compartment  22  and extend in planes substantially perpendicular to panels A and B. 
     The unit  20  is supported in the compartment  22  thanks to two brackets  25  respectively fixed on the plates  23  and  24 . 
     Thanks to a bracket  26 , the plate  23  also supports a ventilation unit  27  disposed inside a chamber  28  formed by a cover  29  mounted on the plate  23  and provided with an air inlet orifice  29   a  equipped with a filter  30 . The unit  27  makes it possible to create an excess pressure in the chamber  28 , this excess pressure being distributed towards the interior of the compartment  22  in the form of a flow of air represented by arrows F in FIGS. 2 and 3. This flow of air has the effect of cooling the unit  20  which tends to heat up due to the consumption of current. To that end, a plurality of orifices  23   a  are provided in the plate  23  for the passage of the cooling air, while corresponding orifices  24   a  are provided on the plate  24  for the cooling air to evacuate. 
     Channels  21  for cooling the actuators or motors  2  are also provided in the panels A and B to the rear of the actuators  2 , these channels  31  being in communication with the chamber  28  thanks to specific orifices  23   b  aligned with the evacuation orifices  24   b  provided in the plate  24 . 
     Due to the flow F of the air coming from chamber  28 , an excess pressure is created in the compartment  22  and in the channels  31 , which avoids the accumulation of fluff in these volumes. In order to improve heat transfer, the channels  31  may be provided with internal fins for cooling the boxes  1 . 
     Access to unit  20  is possible by removing the cover  21  from the opening  22   a  which it obturates at the upper edges of the panels A and B. An operator who is standing on the walkway  11  may then easily proceed with operations of assembly, monitoring or maintenance of the elements constituting the unit  20 , working in a satisfactory position from the ergonomic standpoint and with excellent accessibility to these elements. The walkway  11  also allows access to the actuators  2  and/or to the harness cords  4  for assembly and maintenance thereof. 
     The invention therefore makes it possible to increase the reliability of the interventions of an operator and to save time during assembly and maintenance of a weaving loom in accordance with its principle. In effect, most of the wirings and electrical connections may be made in the workshop and tested before being sent to the site where the loom is used, while the assembly obtained is compact, robust and economical.
A loom and a weaving mechanism of the Jacquard type for forming the shed in the loom wherein the weaving mechanism is associated with a harness including harness cords secured to heddles. The harness cords are controlled by electric actuators mounted to two panels extending above the heddles and between which a compartment is formed in which a control unit for supplying and monitoring the operation of the actuators is housed.