Printheads and systems using printheads

1. A printing apparatus comprising:

a jetting assembly including a plurality of nozzles for ejecting droplets on a substrate moving relative to the jetting assembly;

a mounting rack to support the jetting assembly;

a mechanism comprising a servo-controlled lead screw assembly for changing the displacement of the mounting rack relative to the substrate; and

a first alignment element associated with the mounting rack and a second alignment element associated with the substrate support, the second alignment element positionally corresponding with the first alignment element and being stationary relative to the substrate support,

wherein the first alignment element being detachable from the second alignment element.

2. The apparatus of claim 1 , wherein the mechanism further comprises a lift actuator.

3. The apparatus of claim 1 further comprising a conveyor for supporting the substrate.

4. The apparatus of claim 3 , wherein the mechanism changes the displacement of the mounting rack with a speed based on the speed of the conveyor.

5. The apparatus of claim 1 , further comprising a sensor configured to activate the mechanism for changing the displacement of the mounting rack relative to the substrate upon detecting a predetermined dimension of the substrate surface relative to the mounting rack.

6. The apparatus of claim 5 , wherein the sensor comprises a receiver configured to receive signals from a transmitter and on the basis of those signals, activate the mechanism.

7. The apparatus of claim 6 , further comprising the transmitter and a conveyer having a first side and a second, opposite side, the transmitter being mounted on the first side of the conveyer, and the receiver being mounted on the second, opposite side of the conveyor.

8. The apparatus of claim 1 , wherein the first alignment element comprises V-blocks.

9. The apparatus of claim 1 , wherein the second alignment element comprises locator pins configured to be received by the first alignment element.

10. The apparatus of claim 9 , wherein the locator pins are in the form of spherical pins.

11. The apparatus of claim 1 , wherein the mechanism changes the displacement of the mounting rack relative to the substrate with a speed based on the displacement of the mounting rack relative to the substrate.

12. A printing apparatus comprising:

a jetting assembly including a plurality of nozzles for ejecting droplets on a substrate moving relative to the jetting assembly;

a mounting rack to support the jetting assembly;

a mechanism for changing the displacement of the mounting rack relative to the substrate; and

a first alignment element comprising V-blocks associated with the mounting rack and a second alignment element associated with the substrate support, the second alignment element positionally corresponding with the first alignment element and being stationary relative to the substrate support,

wherein the first alignment element being detachable from the second alignment element.

13. The apparatus of claim 12 , wherein the second alignment element comprises locator pins configured to be received by the first alignment element.

14. The apparatus of claim 13 , wherein the locator pins are in the form of spherical pins.

15. The apparatus of claim 12 , wherein the mechanism changes the displacement of the mounting rack relative to the substrate with a speed based on the displacement of the mounting rack relative to the substrate.

16. The apparatus of claim 12 , further comprising a sensor configured to activate the mechanism for changing the displacement of the mounting rack relative to the substrate upon detecting a predetermined dimension of the substrate surface relative to the mounting rack.

17. The apparatus of claim 16 , wherein the sensor comprises a receiver configured to receive signals from a transmitter and on the basis of those signals, activate the mechanism.