WO2013154586A1

WO2013154586A1 - Printhead with dual switched piezoelectric actuators

Info

Publication number: WO2013154586A1
Application number: PCT/US2012/033638
Authority: WO
Inventors: Andrew L. Van Brocklin; Peter James Fricke
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2012-04-13
Filing date: 2012-04-13
Publication date: 2013-10-17

Abstract

A printhead with dual switched piezoelectric actuators (206) includes an operation switch (204) connected between a piezoelectric actuator (206) for a printhead nozzle (100) and driving circuitry (202) to drive the piezoelectric actuator (206), and a testing switch (208) connected between the piezoelectric actuator (206) and a bus line (210), the bus line (210) connected to multiple piezoelectric actuators (206) through testing switches (208).

Description

PRINTHEAD WITH DUAL SWITCHED PIEZOELECTRIC ACTUATORS

BACKGROUND

[0001] Printing systems utilize a variety of technologies to eject ink onto a print medium. One type of technology used in printing systems is piezoelectric technology. A piezoelectric material is one that expands and contracts under applied electrical conditions such as a voltage. Such material can be used as an actuator for inkjet nozzles within a printhead. Specifically, application of a voltage to a specific nozzle's piezoelectric actuator is done to eject ink from that nozzle as the printhead holding that nozzle moves in relation to the print medium.

[0002] Throughout the manufacturing process and life of a printhead that utilizes piezoelectric actuators, it is often desirable to perform tests on the piezoelectric actuators or the circuitry that drives those actuators. While many electronic products can be tested through use of a probe card connected to the semiconductor wafer on which the circuitry is formed, use of a probe card can be difficult in the case of printheads. Moreover, a probe card cannot be used to perform diagnostics once the printhead is finalized within a printing system product. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The accompanying drawings illustrate various examples of the principles described herein and are a part of the specification. The drawings are merely examples and do not limit the scope of the claims.

[0004] Fig. 1 is a diagram showing a piezoelectric printhead nozzle, according to one example of principles described herein.

[0005] Fig. 2 is a diagram showing illustrative dual switch actuators, according to one example of principles described herein.

[0006] Fig. 3A is a diagram showing an illustrative standard operation of the dual switch actuator, according to one example of principles described herein.

[0007] Fig. 3B is a diagram showing an illustrative testing operation of the dual switch actuator, according to one example of principles described herein.

[0008] Fig. 4 is a diagram showing an illustrative multiplexing of bus lines for the dual switch actuators within a printhead, according to one example of principles described herein.

[0009] Fig. 5 is a flowchart showing an illustrative method for operating a dual switch piezoelectric nozzle actuator, according to one example of principles described herein.

[0010] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.

DETAILED DESCRIPTION

[0011] As mentioned above, it is beneficial to perform various diagnostic tests on piezoelectric actuators and the circuitry that drives those actuators. Such tests may be, for example, to test the capacitance voltage curve of the piezoelectric actuator or the resonant frequency of the piezoelectric actuator. However, such testing can be complicated and expensive. [0012] In light of this and other issues, the present specification discloses methods and system for a dual switched piezoelectric actuator that allows for efficient testing and diagnostics. According to certain illustrative examples, a first switch, which will be referred to as the operation switch, is used to connect the piezoelectric actuator to the driving circuitry that provides a voltage pulse to the actuator. A second switch, which will be referred to as the testing switch, is used to connect the actuator to a testing bus line. The testing bus line is connected to multiple piezoelectric actuators through similar testing switches associated with each of those piezoelectric actuators. During normal operation, the testing switch remains open while the operation switch remains closed, allowing voltage pulses to drive the actuator at the appropriate times.

[0013] During testing operation, the second switch is closed to allow connection of the piezoelectric actuator to testing circuitry on the other end of the bus line. The operation switch may be open or closed depending on the type of testing. If the operation switch is closed, the testing circuitry can test the driving circuitry. Alternatively, if the operation switch is open, then the testing circuitry can run tests on the piezoelectric actuator itself.

[0014] Through use of methods and systems embodying principles described herein, efficient diagnostic of piezoelectric actuators and the circuitry that drives them can be performed at relatively low cost. Moreover, the circuitry and nozzle actuators for each of the many nozzles within a printhead can be testing for specific nozzle actuators. This allows for monitoring the reliability of the nozzle actuators and driving circuitry over the life of the printhead.

[0015] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough

understanding of the present systems and methods. It will be apparent, however, to one skilled in the art that the present apparatus, systems and methods may be practiced without these specific details. Reference in the specification to "an example" or similar language means that a particular feature, structure, or characteristic described in connection with that example is included as described, but may not be included in other examples. [0016] Referring now to the figures, Fig. 1 is a diagram showing a piezoelectric printhead nozzle. According to certain illustrative examples, a nozzle includes a small chamber (108) which is filled with ink. A piezoelectric actuator (104) is placed within the small chamber (108). When a voltage is applied to the actuator (104), the actuator (104) expands. This expansion creates a pressure wave within the chamber (108) which forces the ink out of the nozzle opening (1 10). The ejected ink droplet (106) is then propelled onto a print medium. When the voltage is no longer applied to the actuator (104), the actuator (104) contracts. This contraction creates a void in the chamber. This void will draw in more ink through a feed line (102).

[0017] Fig. 2 is a diagram showing illustrative dual switch actuators (200). According to certain illustrative examples, a number of nozzle actuators (206) share a single bus line (210) for testing purposes. As mentioned above, each nozzle actuator (206) is connected to driving circuitry (202) through an operation switch (204). Additionally, each actuator (206) is connected to the bus line (210) through a testing switch (208). Based on the configuration of the switches (204, 206) the actuators may operate as normal or have diagnostic tests performed thereon.

[0018] The driving circuitry (202) is used to cause the actuator (208) to expand at the appropriate time, expelling an ink droplet from the associated ink nozzle. The driving circuitry typically includes a Digital-to-Analog Converter (DAC) that receives a digital input signal. The DAC then outputs an analog voltage pulse. This analog voltage pulse is then amplified by an amplifier circuit. The amplifier circuit ensures that the voltage pulse is of a large enough value so as to expand the actuator (206) appropriately.

[0019] Both the operation switch (204) and the testing switch (208) may be made out of made of standard electronic switching devices. For example, the switches (204, 206) may be standard Field Effect Transistor (FET) devices or Bipolar Junction Transistor (BJT) devices. The switches (204, 206) may be connected to controlling circuitry to cause them to open and close at the appropriate times, either for standard operations or testing operations. [0020] Fig. 3A is a diagram showing an illustrative standard operation (300) of the dual switched actuator. As mentioned above, during standard operation, the operation switch (302) is closed and the testing switch (304) is open. In this state, the driving circuitry provides voltage pulses which passes through the closed operation switch (302) and to the nozzle actuator (206). To print the appropriate image, the driving circuitry (202) sends the pulse at a particular time for each nozzle to eject ink onto a specific spot on the print medium as it passes in relation to that nozzle.

[0021] Fig. 3B is a diagram showing an illustrative testing operation (310) of the dual switch actuator. As mentioned above, to perform various tests, the testing switch (314) is closed. The operation switch (312) may be opened or closed depending on the type of testing being done. While several actuators (206) are connected to the same bus line (210), each through a testing switch (314), only the actuator (206) or accompanying driving circuitry (202) being tested will have its testing switch (314) closed. This allows for testing of specific nozzle actuators (206) or driving circuitry (202).

[0022] To testing the driving circuitry (202), the operation switch (312) is closed. Thus, the voltage pulse sent to the actuator can also be measured by testing circuitry (316) on the other side of the bus line (210). This sensing circuitry can make sure that an appropriate voltage level is being supplied to the piezoelectric actuator (206).

[0023] To test the piezoelectric actuator itself, the operation switch (312) is opened. The testing circuitry (316) can then apply various signals along the bus line (210) to the actuator (206) with its associated testing switch (314) closed. Based on the nature of these signals and how they are affected by the actuator (206), the testing circuitry can take various measurements of that actuator. For example, the testing circuitry can determine a

capacitance/voltage curve for the actuator. The testing circuitry (316) may also measure the resonant frequency of the piezoelectric actuator (206).

[0024] These examples of tests which may be performed are not an exhaustive list of possible tests which may be performed on the actuator (206) or associated driving circuitry (202). Various other tests that are helpful in measuring the reliability and robustness of the actuators and driving circuitry may be performed through use of the dual switched actuator described herein.

[0025] Fig. 4 is a diagram showing an illustrative multiplexing (400) of bus lines for the dual switch actuators within a printhead. A printhead may include hundreds or thousands of nozzles. If each of those nozzles were connected to testing circuitry (408) though a single bus line, then the capacitive loading on that testing circuitry (408) may interfere with the testing operations.

[0026] In light of this issue, a multiplexing scheme may be used to connect each nozzle to the testing circuitry. According to certain illustrative examples, multiple bus lines may be multiplexed using at least one multiplexer. In some cases, the multiplexing scheme may be hierarchical. This reduces the number of nozzle actuators connected to a single bus line and thus the capacitive loading on the testing circuitry (408).

[0027] Fig. 4 illustrates a two layer multiplexing scheme. A first multiplexing layer includes a first multiplexer (404) and a second multiplexer (406). Both the first multiplexer (404) and the second multiplexer (406) switch four different bus lines (402) to a single output. The outputs of the first multiplexer (404) and the second multiplexer (406) are input into a third multiplexer (410). The third multiplexer switches between the two different multiplexer inputs to the testing circuitry (408). In this example, there are eight total bus lines (402). If, for example, each bus line connects to 50 different nozzle actuators, then the multiplexing scheme can select any of the 400 nozzles within the printhead while being limited to having 50 nozzles connected to a single bus line (403)

[0028] Fig. 5 is a flowchart showing an illustrative method for operating a dual switch piezoelectric nozzle actuator. According to certain illustrative examples, the method includes closing (block 502) an operation switch connected between a piezoelectric actuator for a printhead nozzle and driving circuitry used to drive the actuator. The method further includes opening (block 504) a testing switch connected between the piezoelectric actuator and a bus line for normal operation of the printhead nozzle. [0029] In conclusion, through use of methods and systems

embodying principles described herein, efficient diagnostic of piezoelectric actuators and the circuitry that drives them can be performed at relatively low cost. Moreover, the circuitry and nozzle actuators for each of the many nozzles within a printhead can be testing for specific nozzle actuators. This allows for monitoring the reliability of the nozzle actuators and driving circuitry over the life of the printhead.

[0030] The preceding description has been presented only to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.

Claims

CLAIMS WHAT IS CLAIMED IS:

1 . A printhead with dual switched piezoelectric actuators (206) comprising: an operation switch (204) connected between a piezoelectric actuator

(206) for a printhead nozzle (100) and driving circuitry (202) to drive said piezoelectric actuator (206);

a testing switch (208) connected between said piezoelectric actuator (206) and a bus line (210), said bus line (210) connected to multiple

piezoelectric actuators (206) through testing switches (208).

2. The printhead of claim 1 , wherein said bus line (210) is multiplexed between a number of actuators (210) for nozzles of said printhead.

3. The printhead of claim 2, wherein said multiplexing (400) is hierarchical.

4. The printhead of claim 1 , further comprising, testing circuitry (316) to test a voltage signal from said driving circuitry (202) while both said operation switch (204) and said testing switch (208) are closed.

5. The printhead of claim 1 , further comprising, testing circuitry (316) to test said piezoelectric actuator (206) with said operation switch (204) open and said testing switch (208) closed.

6. The printhead of claim 5, wherein said testing circuitry (316) is to apply a signal to said bus line (210), said signal being used to test characteristics of said piezoelectric actuator (206).

7. The printhead of claim 6, wherein said characteristics comprise at least one of: a capacitance/voltage curve and a resonant frequency.

8. A method for operating a dual switched piezoelectric actuator (206), the method comprising:

closing an operation switch (204) connected between a piezoelectric actuator (206) for a printhead nozzle (100) and driving circuitry (202) used to drive said actuator (206); and

opening a testing switch (208) connected between said piezoelectric actuator (206) and a bus line (210) for normal operation of said printhead nozzle (100).

9. The method of claim 8, further comprising, closing said testing switch (208) to test a voltage signal from said voltage pulse signal input.

10. The method of claim 8, further comprising:

closing said testing switch (208);

opening said operation switch (204); and

applying testing signals to said bus line (210) to test said actuator (206).

1 1 . The method of claim 10, wherein said signals are to test at least one of: a capacitance voltage curve of said actuator (206) and a resonant frequency of said actuator (206).

12. The method of claim 8, wherein said bus line (210) is one of several bus lines connected to multiple dual switched actuators (210), each of said bus lines being multiplexed to said testing signals.

13. The method of claim 12, wherein said multiplexing (400) is hierarchical.

14. A printhead comprising:

a number of piezoelectric nozzles (100), wherein a piezoelectric actuator (206) for each of said nozzles comprises:

an operation switch (204) connecting said actuator to a voltage pulse signal input; and a testing switch (208) connecting said actuator (206) to a bus line (210), said bus line (210) common to each of said nozzles (100);

wherein said testing switch (208) is open during normal operation of said printhead and closed during testing operation of said printhead.

15. The printhead of claim 14, further comprising a number of multiplexers (404, 406, 410) to connect multiple bus lines (210) to testing circuitry (310), each of said bus lines (210) connected to multiple piezoelectric actuators (206) through testing switches (208).