A screening and/or feeder vibrator machine which includes: a vibratory system comprising shaft lines (1, 2), each shaft line (1, 2) having an unbalance module (12, 21), said vibratory system also having a drive device configured to drive the shaft lines (1, 2) in rotation in synchronous manner and in the same direction, said vibratory system comprising an angle modifier device configured to modify the angular position of the unbalance module of one shaft line relative to the angular position of the unbalance module of the other shaft line or of one of the other shaft lines; wherein the vibratory system also comprises a control unit configured to control the drive device and the angle modifier device, the angle modifier device enabling the unbalance modules (21, 12) to take up an angular position relative to one or each of the others, according to which the unbalance modules are in phase, and another angular position relative to one or each of the others, according to which the unbalance modules are in phase opposition; characterized in that the control unit includes a processor and computer instructions which, when executed by the processor, causes the processor to: - prior to driving the shaft lines (1, 2) in rotation by means of the drive device, bring the unbalance modules (21, 12) into phase opposition; - drive the shaft lines (1, 2) in rotation by means of the drive device, - until the unbalance modules have reached a given operating speed, keep the unbalance modules of the shaft lines in phase opposition; - after said given speed of rotation has been reached for the shaft lines (1, 2), bring the unbalance modules (21,12) in phase; - prior stopping rotary drive of the shaft lines (1, 2), bring the unbalance modules (21, 12) into phase opposition, and stop the rotary drive of the shaft lines (1, 2) when said unbalance modules (21, 12) have been brought into phase opposition, and - when rotation of the shaft lines (1, 2) is stopped, bring the unbalance modules (21, 12) in phase and into a low position. a vibratory system comprising shaft lines (1, 2), each shaft line (1, 2) having an unbalance module (12, 21), said vibratory system also having a drive device configured to drive the shaft lines (1, 2) in rotation in synchronous manner and in the same direction, said vibratory system comprising an angle modifier device configured to modify the angular position of the unbalance module of one shaft line relative to the angular position of the unbalance module of the other shaft line or of one of the other shaft lines; wherein the vibratory system also comprises a control unit configured to control the drive device and the angle modifier device, the angle modifier device enabling the unbalance modules (21, 12) to take up an angular position relative to one or each of the others, according to which the unbalance modules are in phase, and another angular position relative to one or each of the others, according to which the unbalance modules are in phase opposition; characterized in that the control unit includes a processor and computer instructions which, when executed by the processor, causes the processor to: - prior to driving the shaft lines (1, 2) in rotation by means of the drive device, bring the unbalance modules (21, 12) into phase opposition; - drive the shaft lines (1, 2) in rotation by means of the drive device, - until the unbalance modules have reached a given operating speed, keep the unbalance modules of the shaft lines in phase opposition; - after said given speed of rotation has been reached for the shaft lines (1, 2), bring the unbalance modules (21,12) in phase; - prior stopping rotary drive of the shaft lines (1, 2), bring the unbalance modules (21, 12) into phase opposition, and stop the rotary drive of the shaft lines (1, 2) when said unbalance modules (21, 12) have been brought into phase opposition, and - when rotation of the shaft lines (1, 2) is stopped, bring the unbalance modules (21, 12) in phase and into a low position. - prior to driving the shaft lines (1, 2) in rotation by means of the drive device, bring the unbalance modules (21, 12) into phase opposition; - drive the shaft lines (1, 2) in rotation by means of the drive device, - until the unbalance modules have reached a given operating speed, keep the unbalance modules of the shaft lines in phase opposition; - after said given speed of rotation has been reached for the shaft lines (1, 2), bring the unbalance modules (21,12) in phase; - prior stopping rotary drive of the shaft lines (1, 2), bring the unbalance modules (21, 12) into phase opposition, and stop the rotary drive of the shaft lines (1, 2) when said unbalance modules (21, 12) have been brought into phase opposition, and - when rotation of the shaft lines (1, 2) is stopped, bring the unbalance modules (21, 12) in phase and into a low position.