Abstract: The device according to the invention comprises a vibrating frame (10) to which a vibrating housing (11) is attached, supporting a vibrating screen (12). Below this screen are attached a certain number of fixed bars (14), as well as a certain number of movable bars (15), each held at the extremity of two arms (16) attached by a flexible connection (17). The vibrating housing 11 is driven by a first electric motor (20) used during the normal screening process and a second electric motor (23) which rotates at a lower speed than that of the other motor (20) for unblocking the device by maintaining the movable bars in resonance so that they strike the lower surface of the vibrating screen (12). This device is particularly advantageous because it is adaptable to all vibrating machines.