Write head control device and method

A write head 10 for an ink jet printer is disclosed. The head includes one or more chambers 12 having a lower portion containing a quantity of liquid metal 20 and an upper ink reservoir 15, an ink channel 14 connecting the ink reservoir to an ink cartridge and a nozzle 13 for ejecting ink droplets from the ink reservoir. A magnetic field is established across the liquid metal by opposite magnetic bodies 18, 19 and opposing electrodes 16, 17 are provided to pass an electric current through the liquid metal 20 perpendicular to the magnetic field to cause the liquid metal 20 to move and expel an ink droplet from the ink reservoir through the nozzle 13. A temperature sensor 21 senses the temperature at a predetermined position on the write head 10 and a heating element 22 heats the liquid metal 20 when the temperature sensed drops below a preset value. This maintains the temperature of the liquid metal 20 above its melting point.