Abstract: A continuous stream ink jet print head has a droplet generator with an elongate cavity for containing the ink, and nozzle orifices in a wall of the cavity for passing ink from the cavity to form jets. The nozzle orifices are disposed at spaced positions along the length of the cavity. An actuator for vibrating the ink in the cavity is provided such that each jet breaks up into ink droplets at the same predetermined distance from the wall of the cavity. The actuator is disposed on the opposite side of the cavity to the wall, includes a vibrator which is divided up along the length of the cavity at least partially into at least two parts, and includes a backing member disposed further from the cavity than the vibrator and secured to and bridging the parts into which the vibrator is at least partially divided. The vibrator is interposed in line between the backing member and the cavity.

Abstract: A laser marker employs a laser beam, an optical scanner that scans the laser beam along an optical path, and an optical element having a variable image distance. The optical element is located after the scanner and is tilted with respect to the optical axis of the scanner by an amount sufficient to create a desired variable image distance as the laser is scanned across the optical element. The scanning of the scanner is synchronized to the motion of the substrate by determining a first component of motion of a substrate to be marked by using an encoder and storing data representing a second component of motion of the substrate in a memory. In a preferred embodiment, the optical element is a spherical lens.

Abstract: A droplet generator for a continuous stream ink jet print head has a cavity for containing ink, and nozzle orifices passing ink from the cavity to form jets. An actuator means vibrates the ink in the cavity such that each jet breaks up into ink droplets. The actuator means is disposed on the opposite side of the cavity to the nozzle orifices, and a surrounding wall of the cavity extends between the actuator means and nozzle orifices for containing the ink therebetween. The surrounding wall has inner and outer constituent wall. The resistive component of the wave impedance of the outer wall passively damps vibration of the inner wall by dissipating its vibration; the reactive component of the wave impedance of the outer wall actively restrains vibration of the inner wall, ensuring that each jet breaks up into ink droplets at the same predetermined distance from its respective nozzle orifice.

Abstract: An ink jet printing system comprising a droplet generator (5), a supply tank (3), supply transfer means for driving the ink from said tank to said generator and means for measuring the flow rate of the stream of ink droplets by monitoring the change of ink level in said tank, said system including a bleed connection (19) from the generator to the tank in closed circuit with said tank. An ink jet printing system comprising means for using measurements of the rate of change of liquid level in an ink supply tank to provide an indication that there has been a fault in the system. An ink jet printing system comprising a holding tank (101) for receiving liquid issued from the ink jet generator during preparation of the system.