each other so that they are free to rotate independently of each other one of the two load bars is equipped with a master control circuit 32 a the other one with a slave control circuit 32 b both control circuits are equipped with means for wireless communication between them the master control circuit further includes an interface for communication with a remote wired or wireless remote control not shown and an interface for communication with a slave control circuit of the other control unit when an order for deployment or retraction of the screen 14 is given for example by a user acting on a tactile interface of the remote control the master control circuit 32 a controls the master gear motor 28 a in the desired direction and imposes that the slave control circuit 32 b follows this movement so that the angles of rotation of both gear motors 28 a 28 b coincide if necessary provision may be made for equipping the accelerometer arms 34 a 34 b communicating with the master control circuit 32 a and or with the slave control circuit 32 b for example in order to correct the control of the slave gear motor according to an angular difference between both arms and to the angle of rotation of both driving shafts with respect to the drum it is also possible to detect the horizontality of the axis of rotation of the gear motors or that of.