Using light-scattering drop detector to determine turn-on-energy for fluid-ejection nozzle

1. A method for determining a turn-on energy (TOE) for a fluid-ejection nozzle of a fluid-ejection device using a plurality of energy values corresponding to different amounts of energy that can be applied to the fluid-ejection nozzle to cause the fluid-ejection nozzle to eject a fluid drop, comprising:

for each energy value,

applying the energy value to cause the fluid-ejection nozzle to eject the fluid drop;

after applying the energy value, determining a velocity of the fluid drop using a light-scattering drop detector; and,

determining the TOE for the fluid-ejection nozzle based on at least the velocities of the fluid drops determined after applying the energy values.

2. The method of claim 1 , wherein determining the velocity of the fluid drop using the light-scattering drop detector comprises:

measuring an elapsed time between applying the energy value and the light-scattering drop detector detecting the fluid drop; and,

dividing a distance between the fluid-ejection nozzle and a light beam emitted by the light-scattering drop detector by the elapsed time measured.

3. The method of claim 1 , wherein determining the velocity of the fluid drop using the light-scattering drop detector comprises:

measuring an elapsed time between the fluid drop entering a light beam of the light-scattering drop detector and the fluid drop exiting the light beam of the light-scattering drop detector; and,

dividing a width of the light beam by the elapsed time measured.

4. The method of claim 1 , wherein determining the TOE for the fluid-ejection nozzle based on at least the velocities of the fluid drops determined after applying the energy values comprises:

determining a TOE curve indicating the velocity of the fluid drop as a function of the energy value applied; and,

locating the energy value on the TOE curve at which the velocity of the fluid drop enters a horizontal asymptote of the TOE curve.

5. The method of claim 1 , further comprising, for each energy value of the plurality of energy values, after applying the energy value,

detecting fluid aerosol associated with the fluid drop, using the light-scattering drop detector,

wherein determining the TOE for the fluid-ejection nozzle is further based on the fluid aerosol detected after applying the energy values.

6. The method of claim 5 , wherein detecting the fluid aerosol associated with the fluid drop, using the light-scattering drop detector, comprises:

performing a spectral analysis technique on a signal output by the light-scattering drop detector; and,

after performing the spectral analysis technique on the signal, inspecting the signal to locate increased spectral power at low frequencies,

wherein the fluid aerosol causes the increased spectral power at the low frequencies.

7. The method of claim 5 , wherein detecting the fluid aerosol associated with the fluid drop, using the light-scattering drop detector, comprises:

measuring a fall time of a signal output by the light-scattering drop detector, the fall time corresponding to a length of time between when the light-scattering drop detector reaches a peak amplitude caused by light reflected by the fluid drop and/or the fluid aerosol ejected by the fluid-ejection nozzle and when the light-scattering drop detector no longer detects any fluid ejected by the fluid-ejection nozzle; and,

associating an increase in the fall time of the signal with a presence of the fluid aerosol.

8. The method of claim 5 , wherein determining the TOE for the fluid-ejection nozzle comprises:

determining a lower threshold of the TOE based on the velocities of the fluid drops determined after applying the energy values; and,

determining an upper threshold of the TOE based on the fluid aerosol detected after applying the energy values.

9. The method of claim 8 , wherein determining the upper threshold of the TOE comprises locating a lowest energy value at which the fluid aerosol is detected,

and wherein determining the lower threshold of the TOE comprises:

determining a TOE curve indicating the velocity of the fluid drop as a function of the energy value applied; and,

locating the energy value on the TOE curve at which the velocity of the fluid drop enters a horizontal asymptote of the TOE curve.

10. The method of claim 1 , further comprising determining the TOE for the fluid-ejection nozzle at different residual thermal energy levels of the fluid-ejection nozzle.

11. A fluid-ejection device comprising:

a fluid-ejection nozzle to eject fluid, where a plurality of energy values correspond to different amounts of energy that can be applied to the fluid-ejection nozzle to cause the fluid-ejection nozzle to eject a fluid drop;

a light-scattering drop detector to assist determination of a velocity of the fluid drop ejected by the fluid-ejection nozzle for each energy value applied; and,

a controller implemented at least in hardware to determine a turn-on energy (TOE) for the fluid-ejection nozzle based on at least the velocities of the fluid drops.

12. The fluid-ejection device of claim 11 , wherein the light-scattering drop detector is further to detect fluid aerosol associated with the fluid drop ejected by the fluid-ejection nozzle for each energy value applied,

wherein the controller is to determine the TOE for the fluid-ejection nozzle further based on the fluid aerosol detected.

13. The fluid-ejection device of claim 11 , wherein the fluid-ejection device further comprises a plurality of other fluid-ejection nozzles,

and wherein the controller is to individually determine a TOE for each other fluid-ejection nozzle based on velocities of fluid drops ejected by the other fluid-ejection nozzle for the plurality of energy values applied to the other fluid-ejection nozzle.

14. A non-transitory computer-readable data storage medium to store a computer program executable by a fluid-ejection device having a fluid-ejection nozzle and a light-scattering drop detector to cause performance of a method for determining a turn-on energy (TOE) for the fluid-ejection nozzle using a plurality of energy values corresponding to different amounts of energy that can be applied to the fluid-ejection nozzle to cause the fluid-ejection nozzle to eject a fluid drop, comprising:

for each energy value,

applying the energy value to cause the fluid-ejection nozzle to eject the fluid drop;

after applying the energy value, determining a velocity of the fluid drop using the light-scattering drop detector; and,

determining the TOE for the fluid-ejection nozzle based on at least the velocities of the fluid drops determined after applying the energy values.

15. The non-transitory computer-readable data storage medium of claim 14 , wherein the method further comprises, for each energy value of the plurality of energy values, after applying the energy value,

detecting fluid aerosol associated with the fluid drop, using the light-scattering drop detector,

wherein determining the TOE for the fluid-ejection nozzle is further based on the fluid aerosol detected after applying the energy values.