Fluid ejection dies including strain gauge sensors

1. A fluid ejection die comprising:

a plurality of actuation devices to eject fluid drops;

at least one strain gauge sensor to sense strain; and

a comparator to provide a fault signal in response to the sensed strain exceeding an impact threshold.

2. The fluid ejection die of claim 1 , further comprising:

a circuit between the at least one strain gauge sensor and the comparator, the circuit to scale and offset the sensed strain and provide the scaled and offset sensed strain to the comparator.

3. The fluid ejection die of claim 2 , wherein the circuit comprises:

a direct current (DC) blocking capacitor between the at least one strain gauge sensor and the comparator;

a bleeder resistor or blanking switch to prevent parasitic charge from accumulating on a node between the DC blocking capacitor and the comparator; and

at least one of a low pass filter between the at least one strain gauge sensor and the DC blocking capacitor and a scaling buffer between the DC blocking capacitor and the comparator.

4. The fluid ejection die of claim 1 , further comprising:

a biasing circuit to bias the at least one strain gauge sensor.

5. The fluid ejection die of claim 1 , further comprising:

a circuit to provide an analog impact threshold value,

wherein the comparator compares the analog impact threshold value to the sensed strain.

6. The fluid ejection die of claim 1 , further comprising:

a latch set in response to the fault signal to maintain the fault signal until the latch is reset.

7. The fluid ejection die of claim 6 , further comprising:

a fluid ejection termination circuit to prevent the ejection of fluid drops from the actuation devices while the fault signal is maintained.

8. The fluid ejection die of claim 1 , wherein the at least one strain gauge sensor comprises a piezoelectric sensor element.

9. The fluid ejection die of claim 1 , wherein the at least one strain gauge sensor comprises four piezoelectric sensor elements configured in a Wheatstone bridge configuration.

10. A fluid ejection die comprising:

a plurality of actuation devices to eject fluid drops;

at least one strain gauge sensor to sense strain; and

a digital magnitude detector to detect the magnitude of the sensed strain.

11. The fluid ejection die of claim 10 , further comprising:

a circuit between the at least one strain gauge sensor and the digital magnitude detector, the circuit to scale and offset the sensed strain and provide the scaled and offset sensed strain to the digital magnitude detector.

12. The fluid ejection die of claim 10 , further comprising:

a direct current (DC) blocking capacitor between the at least one strain gauge sensor and the digital magnitude detector;

a bleeder resistor or blanking switch to prevent parasitic charge from accumulating on a node between the DC blocking capacitor and the digital magnitude detector;

at least one of a low pass filter between the at least one strain gauge sensor and the DC blocking capacitor and a scaling buffer between the DC blocking capacitor and the digital magnitude detector; and

a biasing circuit to bias the at least one strain gauge sensor.

13. The fluid ejection die of claim 10 , wherein the digital magnitude detector comprises:

a peaking diode to receive the sensed strain from the at least one strain gauge sensor;

a peaking capacitor charged in response to the output of the peaking diode;

a bleeder resistor or blanking switch to discharge the peaking capacitor between strain events; and

an analog to digital converter to convert the peak analog signal from the peaking capacitor to a digital impact magnitude.

14. The fluid ejection die of claim 10 , wherein the at least one strain gauge sensor comprises a piezoelectric sensor element.

15. The fluid ejection die of claim 10 , wherein the at least one strain gauge sensor comprises four piezoelectric sensor elements configured in a Wheatstone bridge configuration.

16. A method for maintaining a fluid ejection system, the method comprising:

monitoring at least one strain gauge sensor integrated within a fluid ejection die; and

continuously analyzing the sensed strain from the at least one strain gauge sensor to determine whether the fluid ejection die has impacted an object,

wherein continuously analyzing the sensed strain comprises comparing a peak sensed strain to an impact threshold and providing a fault signal in response to the peak sensed strain exceeding the impact threshold.

17. The method of claim 16 , wherein the at least one strain gauge sensor comprises a piezoelectric sensor element.

18. The method of claim 16 , wherein the at least one strain gauge sensor comprises four piezoelectric sensor elements configured in a Wheatstone bridge configuration.

19. A method for maintaining a fluid ejection system, the method comprising:

monitoring at least one strain gauge sensor integrated within a fluid ejection die;

continuously analyzing the sensed strain from the at least one strain gauge sensor to determine whether the fluid ejection die has impacted an object;

detecting a peak magnitude of the sensed strain; and

converting the peak magnitude to a digital value.

20. A method for maintaining a fluid ejection system, the method comprising:

monitoring at least one strain gauge sensor integrated within a fluid ejection die;

continuously analyzing the sensed strain from the at least one strain gauge sensor to determine whether the fluid ejection die has impacted an object; and

stopping or modifying operation of the fluid ejection system in response to determining the fluid ejection die has impacted an object.