Liquid dispensing device

Abstract

To provide a liquid dispensing device that can be driven at high frequency by increasing the weight of the dispensed liquid droplets. [Solution] A liquid dispensing device comprising: a pressure chamber substrate provided with a pressure chamber communicating with a nozzle for dispensing liquid; a diaphragm provided on the pressure chamber substrate; a piezoelectric element provided on the diaphragm, with a piezoelectric layer sandwiched between two electrodes; and a control unit for controlling the driving of the piezoelectric element, wherein the control unit drives the piezoelectric element to apply pressure to the liquid in the pressure chamber and discharge the liquid from the nozzle, wherein at the minimum voltage Vb and maximum voltage Vh applied to the piezoelectric element by the control unit, the compliance value ΔC1 of the piezoelectric element at the minimum voltage Vb is smaller than the compliance value ΔC2 of the piezoelectric element at the maximum voltage Vh.

Description

Technical Field

[0001] The present invention relates to a liquid ejection device including a piezoelectric element, and particularly to an inkjet recording device that ejects ink as a liquid.

Background Art

[0002] A liquid ejection device that ejects a liquid onto an ejection medium includes an inkjet recording device that ejects ink as a liquid to perform printing on an ejection medium (recording medium) such as paper or a recording sheet.

[0003] An inkjet recording head mounted on an inkjet recording device includes a diaphragm that defines a pressure chamber on one surface side of a pressure chamber substrate in which a pressure chamber communicating with a nozzle is formed, and a piezoelectric element provided on the diaphragm. By driving the piezoelectric element with a drive signal, a pressure change is imparted to the ink in the pressure chamber to eject the ink from the nozzle.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventional piezoelectric elements are considered to have a smaller compliance of the piezoelectric element that depends on the natural vibration period of the pressure chamber and the natural vibration period as the applied drive voltage is higher. In recent years, there has been a demand for a piezoelectric element that can perform high-frequency driving from the viewpoint of improving productivity. Since the relationship between the applied drive voltage and each parameter related to high-frequency driving is different for a piezoelectric element that performs high-frequency driving, it is necessary to review the relationship between the applied drive voltage and each parameter.

Means for Solving the Problems

[0006] An aspect of the present invention that solves the above problems is a liquid dispensing device comprising: a pressure chamber substrate provided with a pressure chamber communicating with a nozzle for dispensing liquid; a diaphragm provided on the pressure chamber substrate; a piezoelectric element provided on the diaphragm and having a piezoelectric layer sandwiched between two electrodes; and a control unit that controls the driving of the piezoelectric element, wherein the control unit drives the piezoelectric element to apply pressure to the liquid in the pressure chamber and discharge the liquid from the nozzle, characterized in that, at the minimum voltage and maximum voltage applied to the piezoelectric element by the control unit, the compliance value of the piezoelectric element at the minimum voltage is smaller than the compliance value of the piezoelectric element at the maximum voltage.

[0007] Another aspect of the present invention is a liquid dispensing device comprising: a pressure chamber substrate provided with a pressure chamber communicating with a nozzle for dispensing liquid; a diaphragm provided on the pressure chamber substrate; a piezoelectric element provided on the diaphragm and having a piezoelectric layer sandwiched between two electrodes; and a control unit for controlling the driving of the piezoelectric element, wherein the control unit drives the piezoelectric element to apply pressure to the liquid in the pressure chamber and discharge the liquid from the nozzle, characterized in that, at the minimum voltage and the maximum voltage applied to the piezoelectric element, the natural oscillation period of the pressure chamber at the minimum voltage is smaller than the natural oscillation period of the pressure chamber at the maximum voltage.

[0008] Another aspect of the present invention is a liquid dispensing device comprising: a pressure chamber substrate provided with a pressure chamber communicating with a nozzle for dispensing liquid; a diaphragm provided on the pressure chamber substrate; a piezoelectric element provided on the diaphragm and having a piezoelectric layer sandwiched between two electrodes; and a control unit for controlling the driving of the piezoelectric element, wherein the control unit drives the piezoelectric element to apply pressure to the liquid in the pressure chamber and discharge the liquid from the nozzle, characterized in that, at the minimum voltage and the maximum voltage applied to the piezoelectric element, the resonant frequency of the piezoelectric element at the minimum voltage is greater than the resonant frequency of the piezoelectric element at the maximum voltage. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the schematic configuration of the liquid dispensing device according to Embodiment 1. [Figure 2] This is an exploded perspective view of the liquid dispensing head according to Embodiment 1. [Figure 3] This is a plan view of the liquid discharge head according to Embodiment 1. [Figure 4] This is a cross-sectional view of the liquid dispensing head according to Embodiment 1. [Figure 5] This is a cross-sectional view of the liquid dispensing head according to Embodiment 1. [Figure 6] This is a schematic diagram showing the driving state of the liquid discharge head according to Embodiment 1. [Figure 7] This is a block diagram showing the electrical configuration of a liquid dispensing device according to Embodiment 1. [Figure 8] This is a waveform diagram showing the drive signal according to Embodiment 1. [Figure 9] This graph shows the compliance (natural oscillation period)-voltage curve. [Figure 10] This graph shows the compliance (natural oscillation period)-voltage curve. [Figure 11] This is a graph showing the resonant frequency-voltage curve. [Figure 12] This is a graph showing the resonant frequency-voltage curve. [Figure 13] This table shows the results for the examples and comparative examples. [Modes for carrying out the invention]

[0010] The present invention will be described in detail based on embodiments. However, the following description shows one aspect of the present invention and can be arbitrarily changed within the scope of the present invention. In each figure, the same reference numerals are used to indicate the same members, and the description is appropriately omitted. Also, in each figure, X, Y, and Z represent three mutually orthogonal spatial axes. In this specification, the directions along these axes are referred to as the X direction, Y direction, and Z direction. The direction in which the arrow in each figure points is defined as the positive (+) direction, and the opposite direction of the arrow is defined as the negative (-) direction for explanation. Also, the Z direction indicates the vertical direction, the +Z direction indicates vertically downward, and the -Z direction indicates vertically upward. Furthermore, for the directions of the three spatial axes without limiting the positive and negative directions, they are described as the X-axis direction, Y-axis direction, and Z-axis direction.

[0011] (Embodiment 1) FIG. 1 is a diagram showing a schematic configuration of a liquid ejection device according to Embodiment 1 of the present invention.

[0012] As shown in FIG. 1, the liquid ejection device 1 includes a liquid ejection head H, conveys a medium S in the X-axis direction, and reciprocates the liquid ejection head H in the Y-axis direction while ejecting liquid in the +Z direction from the liquid ejection head H toward the medium S to perform printing, which is a so-called serial printer. As the medium S, in addition to cloth, any material such as recording paper or resin film can be used. Also, the direction in which the liquid ejection head H reciprocates is not limited to the Y-axis direction and may be a direction inclined with respect to both the X-axis direction and the Y-axis direction. Also, in the present embodiment, the +Z direction is an example of the "ejection direction".

[0013] Such a liquid ejection device 1 includes a liquid ejection head H, a liquid storage section 3, a control section 4, a conveyance mechanism 5 for feeding out the medium S, and a moving mechanism 6.

[0014] The liquid ejection head H ejects the liquid supplied from the liquid storage section 3 that stores the liquid as droplets in the +Z direction.

[0015] The liquid storage section 3 stores a plurality of types of liquids having different colors and components discharged from the liquid ejection head H individually. Examples of the liquid storage section 3 include, for example, a cartridge detachable from the liquid ejection device 1, a bag-shaped ink pack formed of a flexible film, an ink tank capable of replenishing ink, and the like. In FIG. 1, one liquid storage section 3 is illustrated. Incidentally, the liquid storage section 3 may be a liquid storage section 3 having divided rooms for storing a plurality of types of liquids individually, or may be a plurality of liquid storage sections 3 provided individually according to a plurality of types of liquids. Further, the liquid storage section 3 may be divided into a main tank and a sub-tank. A configuration may be adopted in which the sub-tank is connected to the liquid ejection head H and the liquid consumed by ejecting droplets from the liquid ejection head H is replenished from the main tank to the sub-tank.

[0016] The control section 4 comprehensively controls each element of the liquid ejection device 1, that is, the liquid ejection head H, the conveyance mechanism 5, the moving mechanism 6, and the like.

[0017] The conveyance mechanism 5 conveys the medium S in the X-axis direction and has conveyance rollers 5a. The conveyance mechanism 5 conveys the medium S in the X-axis direction by rotating the conveyance rollers 5a. The conveyance rollers 5a are rotated by driving a conveyance motor (not shown). The control section 4 controls the conveyance of the medium S by controlling the driving of the conveyance motor. Note that the conveyance mechanism 5 for conveying the medium S is not limited to one including the conveyance rollers 5a, and for example, one that conveys the medium S by a belt or a drum may be used.

[0018] The moving mechanism 6 is a mechanism for reciprocating the liquid discharge head H in the Y-axis direction and comprises a holder 6a and a conveyor belt 6b. The holder 6a is a so-called carriage that holds the liquid discharge head H and is fixed to the conveyor belt 6b. The conveyor belt 6b is an endless belt installed along the Y-axis direction. The conveyor belt 6b is rotated by the drive of a conveyor motor (not shown). The control unit 4 controls the drive of the conveyor motor to rotate the conveyor belt 6b, causing the liquid discharge head H to reciprocate in the Y-axis direction together with the holder 6a. The holder 6a may also be configured to mount the liquid storage unit 3 together with the liquid discharge head H.

[0019] The liquid discharge head H, under the control of the control unit 4, performs a discharge operation in which it discharges liquid supplied from the liquid storage unit 3 as droplets in the +Z direction from each of the multiple nozzles 21. This discharge operation by the liquid discharge head H is performed in parallel with the transport of the medium S by the transport mechanism 5 and the reciprocating movement of the liquid discharge head H by the moving mechanism 6, thereby coating the medium S with liquid, or printing, is performed.

[0020] Figure 2 is an exploded perspective view of the liquid discharge head H according to Embodiment 1 of the present invention. Figure 3 is a plan view of the pressure chamber substrate 10 of the liquid discharge head H as seen in the +Z direction. Figure 4 is a cross-sectional view of the liquid discharge head H according to line AA' in Figure 3. Figure 5 is a cross-sectional view of the liquid discharge head H according to line BB' in Figure 3. The directions of the liquid discharge head H will be described based on the directions when mounted on the liquid discharge device 1, i.e., the X-axis direction, Y-axis direction, and Z-axis direction.

[0021] As shown in the figure, the liquid discharge head H of this embodiment comprises a pressure chamber substrate 10, a communication plate 15, a nozzle plate 20 on which a plurality of nozzles 21 are formed, a protective substrate 30, a case member 40, a piezoelectric actuator 300, and a wiring member 110.

[0022] The pressure chamber substrate 10 is made of, for example, a silicon substrate, a glass substrate, an SOI substrate, or various ceramic substrates. Multiple pressure chambers 12 are arranged in a line along the X-axis on the pressure chamber substrate 10. The multiple pressure chambers 12 are arranged on a straight line along the X-axis so that they are in the same position with respect to the Y-axis. Two pressure chambers 12 adjacent to each other in the X-axis direction are separated by a partition wall 11. In this embodiment, two rows of pressure chambers 12 arranged in a line along the X-axis direction are provided in the Y-axis direction. Of course, the arrangement of the pressure chambers 12 is not particularly limited to this, and for example, multiple pressure chambers 12 may be arranged in a staggered pattern along the X-axis direction. Here, staggered arrangement of pressure chambers 12 along the X-axis direction means that the pressure chambers 12 arranged in a line along the X-axis direction are alternately offset in the Y-axis direction. In other words, two rows of pressure chambers, each consisting of pressure chambers 12 arranged in parallel along the X-axis, are provided in the Y-axis direction, and the two rows of pressure chambers are positioned with a half-pitch offset from each other in the X-axis direction, which is known as a half-pitch offset.

[0023] On the surface of the pressure chamber substrate 10 facing the +Z direction, the communication plate 15 and the nozzle plate 20 are sequentially stacked in the +Z direction. On the surface of the pressure chamber substrate 10 facing the -Z direction, the diaphragm 50 and the piezoelectric actuator 300 are sequentially stacked in the -Z direction.

[0024] The communication plate 15 consists of a plate-shaped member joined to the surface of the pressure chamber substrate 10 facing the +Z direction. The communication plate 15 is provided with a nozzle communication passage 16 that connects the pressure chamber 12 and the nozzle 21. The communication plate 15 is also provided with a first manifold section 17 and a second manifold section 18 that constitute part of a manifold 100, which is a common liquid chamber through which multiple pressure chambers 12 communicate. The first manifold section 17 is provided penetrating the communication plate 15 in the Z-axis direction. The second manifold section 18 is provided opening to the surface facing the +Z direction without penetrating the communication plate 15 in the Z-axis direction. Furthermore, the communication plate 15 is independently provided with a supply communication passage 19 that communicates with one end of the pressure chamber 12 in the Y-axis direction. The supply passage 19 connects the second manifold section 18 and the pressure chamber 12, supplying ink from the manifold 100 to the pressure chamber 12. In other words, the liquid discharge head H of this embodiment includes the supply passage 19, the pressure chamber 12, and the nozzle passage 16 as individual flow paths communicating with the nozzle 21. A silicon substrate or an SOI substrate is preferably used as such a communication plate 15. However, the material of the communication plate 15 is not limited to these, and a glass substrate, various ceramic substrates, a metal substrate such as a stainless steel substrate, etc. may also be used.

[0025] The nozzle plate 20 is a plate-shaped member joined to the surface of the communication plate 15 opposite to the pressure chamber substrate 10, i.e., the surface facing the +Z direction. Multiple nozzles 21 are formed on the nozzle plate 20, communicating with each pressure chamber 12 via nozzle communication passages 16. In this embodiment, the multiple nozzles 21 are arranged in a line along the X-axis direction. In this embodiment, two rows of nozzles 21, arranged side by side along the X-axis direction, are provided separated in the Y-axis direction. Such a nozzle plate 20 is preferably made of a silicon substrate or an SOI substrate. However, the material of the nozzle plate 20 is not limited to these, and glass substrates, various ceramic substrates, metal substrates such as stainless steel substrates, or organic materials such as polyimide resin may also be used. The diaphragm 50 is composed solely of an elastic film 51 made of silicon oxide, for example, provided on the pressure chamber substrate 10 side. By constructing the diaphragm 50 solely of an elastic film 51 made of silicon oxide in this way, the internal stress is a compressive stress.

[0026] The piezoelectric actuator 300 comprises a first electrode 60, a piezoelectric layer 70, and a second electrode 80 sequentially stacked on a diaphragm 50 in the -Z direction. Such a piezoelectric actuator 300 is also called a piezoelectric element, and refers to the portion including the first electrode 60, the piezoelectric layer 70, and the second electrode 80. Furthermore, the portion in the piezoelectric layer 70 where piezoelectric strain occurs when a voltage is applied between the first electrode 60 and the second electrode 80 is called the active portion 310. In contrast, the portion in the piezoelectric layer 70 where no piezoelectric strain occurs is called the inactive portion. That is, the active portion 310 refers to the portion of the piezoelectric layer 70 sandwiched between the first electrode 60 and the second electrode 80. In this embodiment, an active portion 310 is formed for each pressure chamber 12. In other words, multiple active portions 310 are arranged in parallel in the X-axis direction of the piezoelectric actuator 300. These multiple active portions 310 act as driving elements that cause pressure changes in the ink within the pressure chamber 12. Generally, one electrode of the active part 310 is configured as an individual electrode independent of each active part 310, and the other electrode is configured as a common electrode common to multiple active parts 310. In this embodiment, the first electrode 60 constitutes an individual electrode, and the second electrode 80 constitutes a common electrode. Of course, the first electrode 60 may constitute a common electrode, and the second electrode 80 may constitute an individual electrode. Furthermore, of the piezoelectric actuator 300, the part facing the pressure chamber 12 in the Z-axis direction becomes a flexible part, and the outer part that does not face the pressure chamber 12 in the Z-axis direction becomes a non-flexible part.

[0027] The first electrode 60 is divided into individual electrodes for each pressure chamber 12, forming independent electrodes for each active section 310.

[0028] The piezoelectric layer 70 is provided with a predetermined width in the Y-axis direction and continuously extending in the X-axis direction. The width of the piezoelectric layer 70 is longer than the length of the pressure chamber 12 in the Y-axis direction. Therefore, on both the +Y and -Y directions of the pressure chamber 12, the piezoelectric layer 70 extends to the outside of the region facing the pressure chamber 12. In addition, recesses 71 corresponding to each partition wall 11 are formed in the piezoelectric layer 70. The width of the recess 71 in the X-axis direction is the same as or wider than the width of the partition wall 11. In this embodiment, the width of the recess 71 in the X-axis direction is wider than the width of the partition wall 11. As a result, the rigidity of the portion of the diaphragm 50 facing both ends of the pressure chamber 12 in the X-axis direction, the so-called arm portion of the diaphragm 50, is suppressed, so that the piezoelectric actuator 300 can be displaced more with a smaller voltage, thus improving displacement efficiency. The recess 71 may be provided extending through the piezoelectric layer 70 in the Z-axis direction, which is the thickness direction, or it may be provided only partway through the piezoelectric layer 70 in the thickness direction without penetrating it in the Z-axis direction. In other words, the piezoelectric layer 70 may be completely removed at the bottom surface of the recess 71 in the +Z direction, or a portion of the piezoelectric layer 70 may remain.

[0029] Such a piezoelectric layer 70 is constructed using a piezoelectric material consisting of a composite oxide with a perovskite structure represented by the general formula ABO3. In this embodiment, lead zirconate titanate (PZT; Pb(Zr,Ti)O3) is used as the piezoelectric material. By using PZT as the piezoelectric material, a piezoelectric layer 70 with a relatively large piezoelectric constant d31 can be obtained. The piezoelectric material used for the piezoelectric layer 70 may be a material with a reduced Pb content, a so-called low-lead material, or a material that does not use Pb, a so-called lead-free material. Examples of lead-free materials include bismuth ironate (BFO; BiFeO3), barium titanate (BT; BaTiO3), and potassium sodium niobate (KNN; (K,Na)(NbO3)).

[0030] The second electrode 80 is provided on the side of the piezoelectric layer 70 facing the -Z direction and constitutes a common electrode common to multiple active parts 310. The second electrode 80 is provided on a surface along the XY plane defined by the X axis and Y axis of the surface of the piezoelectric layer 70 facing the -Z direction, on the side surface of the piezoelectric layer 70, that is, on the surface intersecting the aforementioned XY plane, and on the diaphragm 50 that is not covered by the piezoelectric layer 70. In addition, the second electrode 80 in this embodiment is also provided on the side surface of the recess 71 of the piezoelectric layer 70 and on the diaphragm 50 which is the bottom surface of the recess 71. Of course, the second electrode 80 may be provided only on a part of the inner surface of the recess 71, or not on the entire inner surface of the recess 71.

[0031] Furthermore, the first electrode 60 and the second electrode 80 of the piezoelectric actuator 300 are connected to individual lead electrodes 91 and a common lead electrode 92, which are the lead wires of this embodiment.

[0032] A wiring member 110 made of a flexible substrate is connected to the ends of the individual lead electrodes 91 and the common lead electrode 92 opposite to the ends connected to the piezoelectric actuator 300. The wiring member 110 is equipped with a drive circuit 111 having multiple switching elements that select whether or not to supply drive signals to each active part 310 to drive each of the active parts 310. In other words, the wiring member 110 in this embodiment is a COF (Chip On Film). Note that the wiring member 110 does not necessarily have to be provided with a drive circuit 111. In other words, the wiring member 110 may be an FFC (Flexible Flat Cable), an FPC (Flexible Printed Circuits), etc.

[0033] A protective substrate 30, having approximately the same size as the pressure chamber substrate 10, is bonded to the surface of the pressure chamber substrate 10 facing the -Z direction. The protective substrate 30 has a housing portion 31, which is a space for protecting the piezoelectric actuator 300. The housing portion 31 is provided independently for each row of active portions 310 arranged in the X-axis direction, and two of them are arranged side by side in the Y-axis direction. The protective substrate 30 also has a through hole 32 that penetrates in the Z-axis direction between the two housing portions 31 arranged side by side in the Y-axis direction. The ends of the individual lead electrodes 91 and common lead electrodes 92 drawn from each electrode of the piezoelectric actuator 300 are extended so as to be exposed in this through hole 32, and the individual lead electrodes 91 and common lead electrodes 92 and the wiring member 110 are electrically connected in the through hole 32. A silicon substrate or an SOI substrate is preferably used for such a protective substrate 30. However, the material of the protective substrate 30 is not limited to these, and glass substrates, various ceramic substrates, metal substrates such as stainless steel substrates may also be used.

[0034] Furthermore, a case member 40 is fixed to the surface of the protective substrate 30 facing the -Z direction, defining a portion of the manifold 100 that communicates with a plurality of pressure chambers 12. The case member 40 has substantially the same shape as the communication plate 15 when viewed in the Z-axis direction, and is joined to the protective substrate 30 as well as to the aforementioned communication plate 15. Such a case member 40 has a recess 41 that opens on the surface facing the +Z direction and has a depth to accommodate the pressure chamber substrate 10 and the protective substrate 30. The case member 40 also has a third manifold portion 42 that communicates with the first manifold portion 17 of the communication plate 15. The manifold 100 in this embodiment is composed of the first manifold portion 17 and the second manifold portion 18 provided on the communication plate 15, and the third manifold portion 42 provided on the case member 40. The manifold 100 is provided for each nozzle row. In other words, different types of ink can be sprayed for each nozzle row. Furthermore, the case member 40 is provided with an inlet 44 that communicates with the manifold 100 and supplies ink to each manifold 100. The case member 40 is also provided with a connection port 43 that communicates with the through hole 32 of the protective substrate 30 and through which the wiring member 110 is inserted, and the wiring member 110 is led out through the connection port 43 to the side of the liquid discharge head H facing the -Z direction. For example, the case member 40 can be made of a metal material, a resin material, or the like.

[0035] Furthermore, a compliance substrate 45 is provided on the surface of the communication plate 15 facing the +Z direction, where the first manifold portion 17 and the second manifold portion 18 are open. This compliance substrate 45 seals the openings on the +Z direction side of the first manifold portion 17 and the second manifold portion 18. In this embodiment, the compliance substrate 45 comprises a sealing film 46 made of a flexible thin film and a fixed substrate 47 made of a hard material such as metal. The region of the fixed substrate 47 facing the manifold 100 is a compliance opening 48 that is completely removed in the thickness direction, and one side of the manifold 100 is a compliance portion 49 sealed only by the flexible sealing film 46.

[0036] In this type of liquid discharge head H, liquid is drawn in through the inlet 44 and the flow path is filled with ink from the manifold 100 to the nozzle 21. Then, according to the signal from the drive circuit 111, voltage is applied to each active part 310 corresponding to the pressure chamber 12, causing the diaphragm 50 to bend and deform together with the piezoelectric actuator 300 so that the pressure chamber 12 side becomes convex, as shown in Figure 6. As a result, the pressure of the liquid in the pressure chamber 12 increases and droplets are ejected from the predetermined nozzle 21.

[0037] Here, when a voltage is applied to the active part 310 of the piezoelectric actuator 300 to drive it, the diaphragm 50 and the piezoelectric actuator 300 deform so as to become convex toward the pressure chamber 12, as shown in Figure 6. Figure 6 is a schematic diagram along the BB' line showing the deformation state of the piezoelectric actuator 300 and the diaphragm 50.

[0038] Furthermore, the diaphragm 50 in this embodiment is provided in a region facing the pressure chamber 12, and on both sides in the X-axis direction of the piezoelectric layer 70 in the region facing the pressure chamber 12, there are portions called arms 55, which are provided with the diaphragm 50 without the piezoelectric layer 70. In this embodiment, the arms 55 are provided with the diaphragm 50 and the second electrode 80. The arms 55 deform so that the center of curvature is mainly on the pressure chamber 12 side of the diaphragm 50, and the active portion 310 on the inside of the arms 55 deforms so that the center of curvature is mainly on the side opposite to the pressure chamber 12 of the diaphragm 50.

[0039] Such a diaphragm 50 may be a single layer or a laminated structure of multiple layers. Alternatively, only the arm portion 55 of the diaphragm 50 may be made of a single layer, while the other areas may be made of laminated multiple layers. Furthermore, the laminated structure may differ between the arm portion 55 and the areas other than the arm portion 55, i.e., the active portion 310 and the non-flexible portion, or the thickness of each layer may differ.

[0040] In such a diaphragm 50, the internal stress of at least the uppermost layer of the arm portion 55, i.e., the layer located furthest in the -Z direction, is compressive stress. Furthermore, the sum of the internal stresses of the arm portion 55 of the diaphragm 50 is compressive stress. However, if the sum of the internal stresses of the layers above the center of the thickness of the diaphragm 50 is compressive stress, the internal stress of the uppermost layer, i.e., the layer located furthest in the -Z direction, may be tensile stress. Moreover, it is preferable that the internal stresses of the arm portion 55 and other regions of the diaphragm 50 are compressive stress.

[0041] Such a diaphragm 50 is constructed by laminating one or more layers. When the diaphragm 50 is composed of a single layer, the internal stress of the diaphragm 50 is composed of a compressive stress film. Therefore, both the internal stress of the uppermost layer of the arm portion 55 and the sum of the internal stresses are compressive stresses.

[0042] Furthermore, in the first case where the diaphragm 50 is composed of multiple layers, including the arms 55 and other regions, it is also possible to have a configuration in which the top layer and other layers have a tensile stress film, provided that the sum of the internal stresses in the layers above the center of the thickness of the diaphragm 50 is compressive stress. However, at least the sum of the internal stresses in the arms 55 is compressive stress. It is more preferable that the internal stress of the top layer is compressive stress. It is even more preferable that the diaphragm 50 has a configuration in which the internal stress of the top layer is compressive stress, and the sum of the internal stresses in the layers above the center of the thickness of the diaphragm 50 is compressive stress. It is even more preferable that all layers of the diaphragm 50 are under compressive stress.

[0043] Compressive stress refers to the internal stress generated in the first layer when it is compressed by the second layer in a configuration that includes a first layer and a second layer in contact with the first layer. In this case, the first layer has a force that repels the compressive force it receives from the second layer. On the other hand, tensile stress refers to the internal stress generated in the first layer when it is pulled by the second layer. In this case, the first layer has a force that repels the tensile force it receives from the second layer.

[0044] The material for such a diaphragm 50 is not limited to silicon oxide, but includes elements, compounds, oxides, or nitrides containing one or more of the following: silicon, zirconium, titanium, hafnium, lead, barium, potassium, sodium, niobium, aluminum, bismuth, or iron.

[0045] In this embodiment, the diaphragm 50 is constructed from a single layer of elastic film 51 made of silicon oxide, which has an internal stress of compressive stress. In other words, a silicon substrate is used as the pressure chamber substrate 10, and the elastic film 51 of silicon oxide formed by thermal oxidation of the surface of the silicon substrate has an internal stress of compressive stress.

[0046] Furthermore, the internal stress also changes depending on the manufacturing method of the film constituting the diaphragm 50. For example, when a silicon substrate is used as the pressure chamber substrate 10 and an elastic film 51 is formed by thermal oxidation of the silicon substrate, the internal stress changes depending on the heating temperature. By thermal oxidation of the silicon substrate, a silicon oxide layer can be formed in which the internal stress is compressive stress. In addition, the magnitude of the compressive stress can be adjusted by the heating temperature.

[0047] Furthermore, if the diaphragm 50 has a layer made of zirconium oxide, the internal stress of that layer can be converted to compressive stress by adjusting the temperature at which it is thermally oxidized. Similarly, if the diaphragm 50 has a layer made of titanium oxide, the internal stress of that layer can be converted to compressive stress by adjusting the temperature at which it is thermally oxidized. With other materials, the internal stress can also be converted to compressive stress depending on the manufacturing method.

[0048] By making the sum of the internal stresses in the arm portion 55 a compressive stress, when the active portion 310 is driven, the direction of the force is the same for the external stress that needs to be stretched and the internal compressive stress, allowing the diaphragm 50 to be deformed efficiently. In particular, the arm portion 55 deforms so that its center of curvature faces the pressure chamber 12, which greatly affects the amount of displacement of the diaphragm 50. Conversely, for example, if the sum of the internal stresses in the arm portion 55 is a tensile stress, the direction of the force is opposite for the external stress that needs to be stretched and the internal tensile stress when the active portion 310 is driven, and efficient deformation is not possible. Therefore, if the driving voltage is increased, the greater the external force that needs to be stretched, the more the diaphragm 50 is forcibly stretched even though it wants to contract, and the more the diaphragm 50 is deformed, the stiffer it becomes. As a result, the amount of displacement of the diaphragm 50 when ejecting ink is suppressed, and it becomes more difficult for ink to be ejected.

[0049] Figure 7 is a block diagram showing the electrical configuration of the liquid dispensing device 1 according to Embodiment 1 of the present invention.

[0050] The control unit 4 is the element that controls the entire liquid discharge device 1. The control unit 4 comprises an external interface 211 (hereinafter referred to as external I / F211), a RAM 212 for temporarily storing various data, a ROM 213 for storing control programs, etc., a control processing unit 214 which includes a CPU, etc., an oscillation circuit 215 for generating a clock signal (CK), a drive signal generation unit 216 for generating a drive signal to supply to the liquid discharge head H, and an internal interface 217 (hereinafter referred to as internal I / F217).

[0051] External I / F 211 is an interface for sending and receiving data with a host computer (not shown). Examples of data received by the control unit 4 from the host computer via External I / F 211 include print data, which consists of character codes, graphic functions, and image data. Examples of data transmitted by the control unit 4 via External I / F 211 include busy signals (BUSY) and acknowledgment signals (ACK). RAM 212 functions as a receive buffer 212A, an intermediate buffer 212B, an output buffer 212C, and a work memory (not shown). The receive buffer 212A temporarily stores the print data received by External I / F 211, the intermediate buffer 212B stores the intermediate code data converted by the control processing unit 214, and the output buffer 212C stores dot pattern data. This dot pattern data is composed of recorded data (SI) obtained by decoding (translating) grayscale data.

[0052] The drive signal generation unit 216 generates a drive signal COM. The drive signal COM will be described in more detail later, but it is a signal that has a discharge pulse DP within one unit period T that drives the active unit 310 to discharge droplets from the nozzle 21, and is repeatedly generated at each unit period T. This unit period T is the repeating unit of the drive signal COM, and is the discharge period T, also called the recording period T, and corresponds to one pixel of the image to be printed on the medium S.

[0053] ROM 213 stores control programs (control routines) for instructing the control processing unit 214 to perform various data processing tasks, as well as font data, graphic functions, and the like. The control processing unit 214 reads the print data from the receive buffer 212A and stores the intermediate code data obtained by converting this print data in the intermediate buffer 212B. It also analyzes the intermediate code data read from the intermediate buffer 212B and, referring to the font data and graphic functions stored in ROM 213, expands the intermediate code data into recording data. After applying the necessary formatting, the control processing unit 214 stores this expanded recording data in the output buffer 212C. The control program may be read from a recording medium such as a floppy disk, CD-ROM, DVD-ROM, or USB memory directly connected via the external I / F 211, or connected via a host computer. Alternatively, the control program may be provided as a printer driver on the host computer.

[0054] During printing, if the control processing unit 214 obtains recording data equivalent to one line of data for the liquid ejection head H, it outputs this one line of recording data to the liquid ejection head H via the internal I / F 217. Also, when one line of recording data is output from the output buffer 212C, the expanded intermediate code data is erased from the intermediate buffer 212B, and the expansion process for the next intermediate code data is performed.

[0055] The liquid discharge head H is equipped with a drive circuit 111 as described above. The drive circuit 111 is a circuit that supplies a drive signal COM to the active unit 310 based on recorded data (SI) sent from the control unit 4 via the internal I / F 217.

[0056] The recorded data consists of multiple pixel data to be ejected for each of the multiple dots that make up a single row. For example, suppose the pixel data is binary, where "1" represents the formation of a dot and "0" represents the non-formation of a dot. If the pixel data is "1", the drive circuit 111 supplies an ejection pulse DP to the active unit 310 which ejects a droplet from the nozzle 21 corresponding to that pixel data. If the pixel data is "0", the drive circuit 111 does not supply an ejection pulse DP to the active unit 310.

[0057] In this manner, the liquid ejection head H ejects droplets from each nozzle 21 at timings defined by recorded data, etc., under the control of the control unit 4. The control unit 4 then, via the internal I / F 217, carries the transport of the medium S by the transport mechanism 5 and moves the liquid ejection head H back and forth by the moving mechanism 6, in parallel with the ejection operation of the liquid ejection head H. Printing is performed on the medium S under the control of the control unit 4 in this way.

[0058] Figure 8 shows an example of a drive waveform of the drive signal COM in this embodiment. As shown in Figure 8, the drive signal COM is repeatedly generated by the drive signal generation unit 216 at unit periods T defined by the clock signal emitted from the oscillation circuit 215. The unit period T corresponds to one pixel of an image to be printed on the medium S. In this embodiment, the ejection pulse DP is generated at unit period T.

[0059] In this embodiment, the drive signal COM is supplied to the first electrode 60, which is an individual electrode, with the second electrode 80, which is a common electrode of the active unit 310, as the reference potential. That is, the voltage applied to the second electrode 80 by the drive signal COM is expressed as a potential with the reference potential as the reference potential.

[0060] The discharge pulse DP of the drive signal COM has, in this order and in sequence, an expansion element P1, an expansion maintenance element P2, a contraction element P3, a contraction maintenance element P4, and an expansion return element P5.

[0061] The expansion element P1 changes the potential from the intermediate potential V0 to the first potential V1, thereby expanding the volume of the pressure chamber 12 from its reference volume. This expansion element P1 draws the liquid level in the nozzle 21 towards the pressure chamber 12, while simultaneously supplying liquid to the pressure chamber 12 from the manifold 100.

[0062] The expansion maintenance element P2 maintains the first potential V1 for a certain period of time. While the expansion maintenance element P2 is supplied, pressure oscillations with a natural oscillation period Tc occur in the liquid in the pressure chamber 12.

[0063] The contraction element P3 changes the voltage from a first potential V1 to a second potential V2, thereby contracting the volume of the pressure chamber 12 and ejecting droplets from the nozzle 21. The potential difference from the first potential V1 to the second potential V2 is the maximum voltage Vh of the ejection pulse DP. In contrast, the potential difference from the intermediate potential V0 of the expansion element P1 to the first potential V1 is called the minimum voltage Vb.

[0064] The contraction maintenance element P4 maintains the second potential V2 for a certain period of time. While the contraction maintenance element P4 is supplied to the active part 310, pressure oscillations with a natural oscillation period Tc occur in the liquid in the pressure chamber 12.

[0065] The expansion-recovery element P5 changes the potential from the second potential V2 to the intermediate potential V0, thereby expanding the volume of the pressure chamber 12. This expansion-recovery element P5 weakens the pressure oscillations of the liquid in the pressure chamber 12. In other words, the contraction-maintaining element P4 and the expansion-recovery element P5 function as vibration damping elements, weakening the vibrations of the ink in the nozzle 21 after the ink has been ejected.

[0066] Here, the compliance ΔC of the piezoelectric actuator 300 will be explained. The compliance ΔC of the piezoelectric actuator 300 is a physical quantity of the piezoelectric actuator 300 and the diaphragm 50 when viewed in the short direction, that is, in the cross-sectional view along line BB' shown in Figure 5, and indicates the softness and hardness of the piezoelectric actuator 300 and the diaphragm 50.

[0067] In this embodiment, compliance ΔC refers to one component of acoustic compliance. Acoustic compliance is expressed as the sum of compliance due to the compressibility of the acoustic medium and compliance due to the deformation of the structure surrounding the acoustic medium. In this embodiment, the acoustic medium corresponds to the ink or gas entering the pressure chamber 12, and the structure surrounding the acoustic medium corresponds to the diaphragm 50 and partition walls 11 that form the pressure chamber 12. Furthermore, the compliance due to the deformation of the structure surrounding the acoustic medium is mainly caused by the deformation of the diaphragm 50 by the piezoelectric actuator 300.

[0068] In this embodiment, the compliance resulting from the deformation of the structure surrounding the latter acoustic medium, that is, the compliance resulting from the deformation of the piezoelectric actuator 300 and the diaphragm 50, is used as compliance ΔC. Hereafter, the compliance ΔC of the piezoelectric actuator 300 will simply be referred to as compliance ΔC.

[0069] Compliance ΔC is correlated with the natural vibration period Tc of the pressure chamber 12 and the resonant frequencies fa of the piezoelectric actuator 300 and diaphragm 50, as shown in equation (1) below. Therefore, compliance ΔC can be derived from the natural vibration period Tc and the resonant frequency fa. Compliance ΔC can also be measured by applying pressure such as pneumatic pressure.

[0070]

number

[0071] Here, the compliance-voltage curves are shown in Figures 9 and 10. In Figures 9 and 10, the compliance ΔC of the piezoelectric actuator 300 and diaphragm 50 of this embodiment, i.e., the diaphragm 50 being composed of a single layer of elastic film 51 made of silicon oxide, is shown by a solid line. As a comparative example, the compliance ΔC of the diaphragm 50 being composed of a single layer of zirconium oxide with internal stress being tensile stress is shown by a dotted line. Incidentally, even when the diaphragm 50 is composed of multiple layers and the uppermost layer is a compression stress film, the curve is approximately the same as the solid line shown in Figures 9 and 10, and even when the diaphragm 50 is composed of multiple layers and the uppermost layer is a tensile stress film, the curve is approximately the same as the dotted line shown in Figures 9 and 10.

[0072] As shown in Figures 9 and 10, the compliance ΔC-voltage curve of this embodiment shows that compliance ΔC increases as the voltage increases, and then decreases as the voltage increases beyond a certain voltage. The voltage at which this compliance ΔC is maximum is referred to as the peak voltage Vp.

[0073] Therefore, as shown in Figure 9, the control unit 4 controls the compliance value ΔC1 at the minimum voltage Vb of the drive signal COM to be smaller than the compliance value ΔC2 at the maximum voltage Vh. Also, as shown in Figure 10, the control unit 4 controls the compliance value ΔC5 at the minimum voltage Vb to be smaller than the compliance value ΔC6 at the maximum voltage Vh. Note that in Figure 9, the minimum voltage Vb and the maximum voltage Vh are set so that the peak voltage Vp is not between them. In other words, the minimum voltage Vb and the maximum voltage Vh are determined within a range that does not exceed the peak voltage Vp. Also, in Figure 10, the minimum voltage Vb and the maximum voltage Vh are set so that the peak voltage Vp is between them.

[0074] In contrast, as shown in Figures 9 and 10, the compliance ΔC-voltage curve of the comparative example is roughly downward sloping, meaning that compliance ΔC tends to decrease as the voltage increases. Therefore, as shown in Figure 9, when driven with the same minimum voltage Vb and maximum voltage Vh as in this embodiment, the compliance value ΔC3 at the minimum voltage Vb is greater than the compliance value ΔC4 at the maximum voltage Vh for the piezoelectric actuator and diaphragm of the comparative example. Also, as shown in Figure 10, when driven with the same minimum voltage Vb and maximum voltage Vh as in this embodiment, the compliance value ΔC7 at the minimum voltage Vb is greater than the compliance value ΔC8 at the maximum voltage Vh.

[0075] As in this embodiment, when the compression element P3 compresses the pressure chamber 12, if the compliance values ​​ΔC2 and ΔC6 at the maximum voltage Vh are relatively large, the piezoelectric actuator 300 and diaphragm 50 become softer when driven at the maximum voltage Vh. Conversely, as in the comparative example, if the compliance values ​​ΔC4 and ΔC8 at the maximum voltage Vh are relatively small, the piezoelectric actuator 300 and diaphragm 50 become stiffer when driven at the maximum voltage Vh. Note that "relatively large" or "relatively small" refers to the compliance value being relatively large or relatively small when comparing the range from the minimum voltage Vb to the maximum voltage Vh in each compliance ΔC-voltage curve.

[0076] Therefore, in this embodiment, even when driven with the same maximum voltage Vh as the comparative example, the deformation amount of the piezoelectric actuator 300 and the diaphragm 50 can be made larger than in the comparative example, and the weight of ink ejected from the nozzle 21 can be increased. In particular, in the case of the comparative example, since the compliance values ​​ΔC4 and ΔC8 of the maximum voltage Vh are relatively small, the piezoelectric actuator 300 and the diaphragm 50 driven by the contraction element P3 become stiffer, the amount of displacement decreases, and the weight of the ejected ink decreases. Also, in this embodiment, in order to eject ink droplets with the same ink weight as the comparative example, the maximum voltage Vh can be made smaller. This also allows the ejection period of the ejection pulse DP to be shortened. In particular, as shown in Figure 10, by setting the minimum voltage Vb and the maximum voltage Vh to straddle the peak voltage Vp, a region in which the diaphragm 50 deforms more significantly is included, so a larger amount of displacement can be obtained even with the same maximum voltage Vh as the comparative example.

[0077] Furthermore, in this embodiment, if the compliance values ​​ΔC1 and ΔC5 at the minimum voltage Vb when the expansion element P1 expands the pressure chamber 12 are relatively small, the piezoelectric actuator 300 and the diaphragm 50 become stiffer when driven at the minimum voltage Vb. As a result, the vibration of the meniscus of the nozzle 21 after the expansion element P1 fills the pressure chamber 12 with ink is dampened more quickly, and the time of the expansion maintenance element P2 after the expansion element P1 can be shortened. Therefore, by shortening the time of the expansion maintenance element P2, the ejection period T of the ejection pulse DP can be shortened, and high-frequency drive can be performed.

[0078] Furthermore, as shown in Figure 9, the compliance ΔC at the intermediate potential V0 is greater than the compliance value ΔC1 at the minimum voltage Vb and less than the compliance value ΔC2 at the maximum voltage Vh. Therefore, the expansion-recovery element P5 makes the piezoelectric actuator 300 and the diaphragm 50 stiffer when the intermediate potential V0 is applied than when they are driven by the contraction element P3 at the maximum voltage Vh. Consequently, the time for maintaining the intermediate potential V0 after the expansion-recovery element P5 is supplied, i.e., the time for damping vibrations in the pressure chamber 12, can be shortened. This also shortens the time between supplying the discharge pulse DP and supplying the next discharge pulse DP, thereby shortening the discharge period T of the discharge pulse DP and enabling high-frequency drive.

[0079] Furthermore, as shown in Figure 10, the compliance ΔC at the intermediate potential V0 is greater than the compliance value ΔC5 at the minimum voltage Vb and the compliance value ΔC6 at the maximum voltage Vh. Near the peak of compliance ΔC, i.e., near the peak voltage Vp, the internal stress approaches zero, resulting in a state where no stress is applied to the diaphragm 50. Therefore, by making the compliance ΔC at the intermediate potential V0 greater than the compliance values ​​ΔC5 and ΔC6, the intermediate potential V0 can be brought closer to the peak voltage Vp, making it less likely for cracks or other damage to occur in the diaphragm 50 while the intermediate potential V0 is being supplied.

[0080] Furthermore, as shown in Figure 10, by setting the minimum voltage Vb and maximum voltage Vh to straddle the peak voltage Vp, the change in compliance ΔC at the minimum voltage Vb and the compliance ΔC at the maximum voltage Vh can be reduced, simplifying waveform design and stabilizing ink ejection. In other words, since compliance ΔC is proportional to the natural oscillation period Tc, the change in the natural oscillation period Tc between the minimum voltage Vb and the maximum voltage Vh can be reduced, thus simplifying waveform design and stabilizing ink ejection. Incidentally, if the change in the natural oscillation period between the minimum voltage Vb and the natural oscillation period of the maximum voltage is large, waveform design becomes difficult, and waveform design of voltage, time, slope, etc. becomes difficult, and ink ejection will not be stable if not set correctly.

[0081] The natural vibration period Tc of the pressure chamber 12 in this embodiment will now be described. The natural vibration period Tc is the period of pressure vibration of the liquid when the pressure chamber 12 is filled with ink. Hereafter, the natural vibration period Tc of the pressure chamber 12 will be simply referred to as the natural vibration period Tc.

[0082] Such a natural vibration period Tc can be obtained, for example, by detecting a residual vibration signal that indicates fluctuations in the electromotive force generated in the active part 310 due to the vibration of the active part 310 caused by pressure vibrations remaining in the liquid in the pressure chamber 12 after the active part 310 is driven, and by analyzing that residual vibration signal. The method for obtaining the natural vibration period Tc is not particularly limited, and for example, the natural vibration period Tc may be obtained by calculation or experiment.

[0083] Here, as described above, the natural vibration period Tc is proportional to the compliance ΔC of the piezoelectric actuator 300 and the diaphragm 50. Therefore, the natural vibration period Tc-voltage curve is the same as the compliance ΔC-voltage curve shown in Figures 9 and 10. For this reason, Figures 9 and 10 show both the compliance ΔC-voltage curve and the natural vibration period Tc-voltage curve. Incidentally, similar to the compliance ΔC described above, in Figures 9 and 10, the natural vibration period Tc of the piezoelectric actuator 300 and diaphragm 50 of this embodiment, that is, when the diaphragm 50 is composed of a single layer of elastic film 51 made of silicon oxide, is shown by a solid line. Also, as a comparative example, the natural vibration period Tc of the diaphragm 50 composed of a single layer of zirconium oxide with internal stress being tensile stress is shown by a dotted line.

[0084] As shown in Figures 9 and 10, the natural oscillation period Tc-voltage curve of the pressure chamber 12 in this embodiment shows that the natural oscillation period Tc increases as the voltage increases, and beyond a certain voltage, the natural oscillation period Tc tends to decrease as the voltage increases. The voltage at which this natural oscillation period Tc is maximum is called the peak voltage Vp.

[0085] Therefore, as shown in Figure 9, the control unit 4 controls the natural period value Tc1 at the minimum voltage Vb of the drive signal COM to be smaller than the natural period value Tc2 at the maximum voltage Vh. Also, as shown in Figure 10, the control unit controls the natural period value Tc5 at the minimum voltage Vb to be smaller than the natural period value Tc6 at the maximum voltage Vh. Note that in Figure 9, the minimum voltage Vb and the maximum voltage Vh are set so that the peak voltage Vp is not between them. In other words, the minimum voltage Vb and the maximum voltage Vh are determined within a range that does not exceed the peak voltage Vp. Also, in Figure 10, the minimum voltage Vb and the maximum voltage Vh are set so that the peak voltage Vp is between them.

[0086] In contrast, as shown in Figures 9 and 10, the natural period Tc-voltage curve of the pressure chamber 12 of the comparative example is roughly downward sloping, meaning that as the voltage increases, the natural period Tc tends to decrease. Therefore, as shown in Figure 9, when driven with the same minimum voltage Vb and maximum voltage Vh as in this embodiment, the natural period value Tc3 at the minimum voltage Vb is greater than the natural period value Tc4 at the maximum voltage Vh for the piezoelectric actuator and diaphragm of the comparative example. Also, as shown in Figure 10, when driven with the same minimum voltage Vb and maximum voltage Vh as in this embodiment, the natural period value Tc7 at the minimum voltage Vb is greater than the natural period value Tc8 at the maximum voltage Vh.

[0087] In this embodiment, when the natural vibration period values ​​Tc2 and Tc6 at the maximum voltage Vh are relatively large when the contraction element P3 contracts the pressure chamber 12, it indicates that the compliance ΔC is also large, and the piezoelectric actuator 300 and diaphragm 50 become softer when driven at the maximum voltage Vh. In contrast, as in the comparative example, when the natural vibration period values ​​Tc4 and Tc8 at the maximum voltage Vh are relatively small, it indicates that the compliance ΔC is small, and the piezoelectric actuator 300 and diaphragm 50 become stiffer when driven at the maximum voltage Vh. Therefore, in this embodiment, even when driven at the same maximum voltage Vh as the comparative example, the amount of deformation of the piezoelectric actuator 300 and diaphragm 50 can be increased compared to the comparative example, and the weight of ink ejected from the nozzle 21 can be increased. In particular, in the case of the comparative example, the natural vibration period values ​​Tc4 and Tc8 at the maximum voltage Vh are relatively small, and the compliance ΔC is also relatively low, so when driven by the contraction element P3, the piezoelectric actuator 300 and diaphragm 50 become stiffer, the amount of displacement decreases, and the weight of ink ejected decreases. Furthermore, in this embodiment, the maximum voltage Vh can be reduced in order to eject ink droplets with the same ink weight as the comparative example. This also shortens the ejection period of the ejection pulse DP. In particular, as shown in Figure 10, by setting the minimum voltage Vb and the maximum voltage Vh to surround the peak voltage Vp, a region in which the diaphragm 50 deforms more significantly is included, so a larger displacement can be obtained even with the same maximum voltage Vh as the comparative example.

[0088] Furthermore, as in this embodiment, the natural vibration period values ​​Tc1 and Tc5 at the minimum voltage Vb when the pressure chamber 12 is expanded by the expansion element P1 are relatively small. As a result, the vibration of the meniscus of the nozzle 21 dampens quickly after the ink is filled into the pressure chamber 12 by the expansion element P1. Therefore, the time of the expansion maintenance element P2 after the expansion element P1 can be shortened, and the ejection period T of the ejection pulse DP can be shortened, enabling high-frequency drive.

[0089] Furthermore, as shown in Figure 9, the natural oscillation period Tc at the intermediate potential V0 is greater than the natural oscillation period Tc1 at the minimum voltage Vb and smaller than the natural oscillation period Tc2 at the maximum voltage Vh. Therefore, the time during which the intermediate potential V0 is maintained after the expansion recovery element P5 is supplied, i.e., the time during which vibrations in the pressure chamber 12 are damped, can be shortened. This also shortens the time between supplying one discharge pulse DP and supplying the next discharge pulse DP, thereby shortening the discharge period T of the discharge pulse DP and enabling high-frequency drive.

[0090] Furthermore, as shown in Figure 10, the natural vibration period Tc at the intermediate potential V0 is greater than the natural vibration period value Tc5 at the minimum voltage Vb and the natural vibration period value Tc6 at the maximum voltage Vh. The vicinity of the peak of the natural vibration period Tc, i.e., the vicinity of the peak voltage Vp, is near the peak of compliance ΔC, and since the internal stress of the diaphragm 50 approaches zero, the diaphragm 50 is in a state where no stress is applied. Therefore, by making the natural vibration period Tc at the intermediate potential V0 greater than the natural vibration period values ​​Tc5 and Tc6, the intermediate potential V0 can be brought closer to the peak voltage Vp, making it less likely for cracks or other damage to occur in the diaphragm 50 while the intermediate potential V0 is being supplied.

[0091] Furthermore, as shown in Figure 10, by setting the minimum voltage Vb and maximum voltage Vh to straddle the peak voltage Vp, the change in the natural oscillation period value Tc5 at the minimum voltage Vb and the natural oscillation period value Tc6 at the maximum voltage Vh can be reduced, simplifying the waveform design and stabilizing ink ejection. Incidentally, if the change in the natural oscillation period between the minimum voltage Vb and the natural oscillation period of the maximum voltage is large, waveform design becomes difficult, and waveform design of voltage, time, slope, etc. becomes difficult, and ink ejection will not be stable if not set correctly.

[0092] The resonant frequency fa of the piezoelectric actuator 300 in this embodiment will now be described. The resonant frequency fa is the resonant frequency of the piezoelectric actuator 300 and the diaphragm 50 when the pressure chamber 12 is not filled with ink. Hereafter, the resonant frequency fa of the piezoelectric actuator 300 will be simply referred to as the resonant frequency fa.

[0093] This resonant frequency fa can be measured by electrically resonating the piezoelectric actuator 300 and the diaphragm 50. In other words, since the impedance changes at the timing of resonance, the resonant frequency can be measured from the movement of the electrical signal.

[0094] Here, the resonance frequency-electrode curves are shown in Figures 11 and 12. In Figures 11 and 12, the resonance frequency fa of the piezoelectric actuator 300 and diaphragm 50 of this embodiment, i.e., the diaphragm 50 being composed of a single layer of elastic film 51 made of silicon oxide, is shown by a solid line. As a comparative example, the resonance frequency fa of the diaphragm 50 being composed of a single layer of zirconium oxide with internal stress being tensile stress is shown by a dotted line. Incidentally, even when the diaphragm 50 is composed of multiple layers and the uppermost layer is a compression stress film, the curve is approximately the same as the solid line shown in Figures 11 and 12, and even when the diaphragm 50 is composed of multiple layers and the uppermost layer is a tensile stress film, the curve is approximately the same as the dotted line shown in Figures 11 and 12.

[0095] As shown in Figures 11 and 12, the resonant frequency fa-voltage curve of this embodiment shows a tendency for the resonant frequency fa to decrease as the voltage increases, and then to increase as the voltage rises beyond a certain voltage. The voltage at which this resonant frequency fa is minimized is called the peak voltage Vp.

[0096] Therefore, as shown in Figure 11, the control unit 4 controls the resonant frequency value fa1 at the minimum voltage Vb of the drive signal COM to be greater than the resonant frequency value fa2 at the maximum voltage Vh. Also, as shown in Figure 12, the control unit 4 controls the resonant frequency value fa5 at the minimum voltage Vb to be greater than the resonant frequency value fa6 at the maximum voltage Vh. Note that in Figure 11, the minimum voltage Vb and the maximum voltage Vh are set so that the peak voltage Vp is not between them. In other words, the minimum voltage Vb and the maximum voltage Vh are determined within a range that does not exceed the peak voltage Vp. Also, in Figure 12, the minimum voltage Vb and the maximum voltage Vh are set so that the peak voltage Vp is between them.

[0097] In contrast, as shown in Figures 11 and 12, the resonance frequency fa-voltage curve of the comparative example is roughly upward sloping, meaning that the resonance frequency fa tends to increase as the voltage increases. Therefore, as shown in Figure 11, when driven with the same minimum voltage Vb and maximum voltage Vh as in this embodiment, the resonance frequency value fa3 at the minimum voltage Vb of the comparative piezoelectric actuator and diaphragm is smaller than the resonance frequency value fa4 at the maximum voltage Vh. Also, as shown in Figure 12, when driven with the same minimum voltage Vb and maximum voltage Vh as in this embodiment, the resonance frequency value fa7 at the minimum voltage Vb of the comparative piezoelectric actuator and diaphragm is smaller than the resonance frequency value fa8 at the maximum voltage Vh.

[0098] In this embodiment, when the resonant frequency values ​​fa2 and fa6 at the maximum voltage Vh when the pressure chamber 12 is contracted by the contraction element P3 are relatively small, it indicates that the inversely proportional compliance ΔC is large, and the piezoelectric actuator 300 and diaphragm 50 become soft when driven at the maximum voltage Vh. In contrast, as in the comparative example, when the resonant frequency values ​​fa4 and fa8 at the maximum voltage Vh are relatively large, it indicates that the inversely proportional compliance ΔC is small, and the piezoelectric actuator 300 and diaphragm 50 become stiff when driven at the maximum voltage Vh. Therefore, in this embodiment, even when driven at the same maximum voltage Vh as the comparative example, the amount of deformation of the piezoelectric actuator 300 and diaphragm 50 can be increased compared to the comparative example, and the weight of ink ejected from the nozzle 21 can be increased. In particular, in the case of the comparative example, the resonant frequency values ​​fa4 and fa8 at the maximum voltage Vh are small and the compliance ΔC is large, so when driven by the contraction element P3, the piezoelectric actuator 300 and diaphragm 50 become stiff, the amount of displacement decreases, and the weight of ink ejected decreases. Furthermore, in this embodiment, the maximum voltage Vh can be reduced in order to eject ink droplets with the same ink weight as the comparative example. This also shortens the ejection period of the ejection pulse DP. In particular, as shown in Figure 12, by setting the minimum voltage Vb and the maximum voltage Vh to surround the peak voltage Vp, a region in which the diaphragm 50 deforms more significantly is included, so a larger displacement can be obtained even with the same maximum voltage Vh as the comparative example.

[0099] Furthermore, as in this embodiment, the resonance frequency values ​​fa1 and fa5 at the minimum voltage Vb when the pressure chamber 12 is expanded by the expansion element P1 are relatively large. As a result, the inversely proportional natural vibration period Tc becomes smaller, and the vibration of the meniscus of the nozzle 21 after ink has been filled into the pressure chamber 12 by the expansion element P1 is dampened more quickly. Therefore, the time of the expansion maintenance element P2 after the expansion element P1 can be shortened, and the ejection period T of the ejection pulse DP can be shortened, enabling high-frequency drive.

[0100] Furthermore, as shown in Figure 11, the resonant frequency fa at the intermediate potential V0 is smaller than the resonant frequency value fa1 at the minimum voltage Vb and larger than the resonant frequency value fa2 at the maximum voltage Vh. Therefore, the time during which the intermediate potential V0 is maintained after the expansion recovery element P5 is supplied, i.e., the time during which vibrations in the pressure chamber 12 are damped, can be shortened. This also shortens the time between supplying one discharge pulse DP and supplying the next discharge pulse DP, thereby shortening the discharge period T of the discharge pulse DP and enabling high-frequency drive.

[0101] Furthermore, as shown in Figure 12, the resonant frequency fa at the intermediate potential V0 is smaller than the resonant frequency value fa5 at the minimum voltage Vb and the resonant frequency value fa6 at the maximum voltage Vh. The vicinity of the peak of the resonant frequency fa, i.e., the vicinity of the peak voltage Vp, is near the peak of compliance ΔC, and since the internal stress of the diaphragm 50 approaches zero, the diaphragm 50 is in a state where no stress is applied. Therefore, by making the resonant frequency fa at the intermediate potential V0 smaller than the resonant frequencies fa5 and fa6, the intermediate potential V0 can be brought closer to the peak voltage Vp, making it less likely for cracks or other damage to occur in the diaphragm 50 while the intermediate potential V0 is being supplied.

[0102] Furthermore, as shown in Figure 12, by setting the minimum voltage Vb and maximum voltage Vh to straddle the peak voltage Vp, the change in the resonant frequency value fa5 at the minimum voltage Vb and the resonant frequency value fa8 at the maximum voltage Vh can be reduced, simplifying the waveform design and stabilizing ink ejection. Incidentally, if the change in the resonant frequency between the minimum voltage Vb and the maximum voltage is large, the change in the natural oscillation period Tc will also be large, making it difficult to design the waveform of each element of the ejection pulse DP, such as voltage, time, and slope, and if not set correctly, ink ejection will not be stable.

[0103] (Example 1) The configuration of Embodiment 1 described above, namely the diaphragm 50, is made of a single layer of a silicon oxide compressive stress film in which the internal stress is compressive stress.

[0104] (Example 2) The diaphragm 50 is constructed of a two-layer laminate consisting of a zirconium oxide tensile stress film in which the internal stress is tensile stress, and a silicon oxide compressive stress film in which the internal stress is compressive stress, with the uppermost layer being the compressive stress film, and the internal stress of the arm portion 55 of the diaphragm 50 being compressive stress. Except for this, the configuration is the same as in Embodiment 1 described above.

[0105] (Comparative Example 1) The diaphragm was constructed of a single layer of zirconium oxide tensile stress film, the internal stress being tensile stress, except that the configuration was the same as in Embodiment 1 described above.

[0106] (Comparative Example 2) The diaphragm is constructed from a two-layer laminate consisting of a silicon oxide compression stress film where the internal stress is compressive stress, and a zirconium oxide tensile stress film where the internal stress on the opposite side is tensile stress, with the uppermost layer being the tensile stress film, and the internal stress in the arm portion of the diaphragm being tensile stress. The configuration is the same as in Embodiment 1 described above.

[0107] Table Ta1 in Figure 13 shows the combinations of minimum voltage Vb and maximum voltage Vh, compliance ΔC, natural oscillation period Tc, and resonant frequency fa, as well as the resulting effects and evaluations for Examples 1 and 2 and Comparative Examples 1 and 2. Note that Table Ta1 distinguishes between cases using the minimum voltage Vb and maximum voltage Vh shown in Figures 9 and 11, and cases using the minimum voltage Vb and maximum voltage Vh shown in Figures 10 and 12. Furthermore, in Table Ta1, the waveform length of the resulting effect refers to the waveform length of the ejection pulse DP when ejecting the same ink weight. The weight of the resulting effect refers to the weight of ink ejected by the same ejection pulse DP.

[0108] As shown in Table Ta1, numbers 1 to 6 are those in which the minimum voltage Vb and maximum voltage Vh are within a range that does not exceed the peak voltage Vp, as shown in Figures 9 and 11 above. Numbers 7 to 12 are those in which the minimum voltage Vb and maximum voltage Vh are used with the peak voltage Vp in between, as shown in Figures 10 and 12 above.

[0109] Since the compressive stress of the diaphragm 50 in Example 1 is greater than that of the diaphragm 50 in Example 2, the waveform length can be made as short as possible in numbers 1, 3, 5, 7, 9, and 11.

[0110] In Example 2, the diaphragm 50 was constructed from a zirconium oxide tensile stress film and a silicon oxide compressive stress film. However, the invention is not limited to this configuration. Even if a tensile stress film made of titanium oxide with an internal tensile stress is further placed between the zirconium oxide tensile stress film and the silicon oxide compressive stress film, the same results as in Example 2 of Table Ta1 can be obtained.

[0111] Furthermore, after forming a tensile stress film on the pressure chamber substrate 10, the tensile stress film corresponding to the arm portion 55 can be removed by ion milling or the like, and then a compressive stress film can be formed to create a single layer of compressive stress film only on the arm portion 55. Even with this configuration, the same results as in Example 1 in Table Ta1 can be obtained.

[0112] Furthermore, in Comparative Example 2, the diaphragm 50 was constructed from a silicon oxide compression stress film and a zirconium oxide tensile stress film. However, the invention is not limited to this, and even if a tensile stress film made of titanium oxide with internal stress as tensile stress is further placed between the silicon oxide compression stress film and the zirconium oxide tensile stress film, the same results as in Comparative Example 2 in Table Ta1 can be obtained.

[0113] (Other embodiments) Although one embodiment of the present invention has been described above, the basic configuration of the present invention is not limited to that described above.

[0114] In the above-described embodiment 1, a configuration having expansion elements P1 to expansion recovery elements P5 as the ejection pulse DP of the drive signal COM was illustrated, but the invention is not limited to this, and the ejection pulse DP may be a trapezoidal wave. That is, it may be a signal having an expansion element, an expansion maintenance element, and a contraction element in that order. In the case of such a trapezoidal wave, the minimum voltage Vb is the disclosure voltage of the expansion element, and the maximum voltage Vh is the voltage of the expansion maintenance element. Even with such a trapezoidal wave, as in the above-described embodiment 1, the control unit 4 can increase the amount of ink ejected by setting the minimum voltage Vb and the maximum voltage Vh, and can also shorten the waveform length to perform high-frequency driving.

[0115] Furthermore, in the above-described embodiment 1, the liquid ejection device 1 is exemplified as having a liquid ejection head H mounted on a holder 6a that moves in the main scanning direction. However, the present invention is not limited to this, and can also be applied to so-called line-type printers in which the liquid ejection head H is fixed and printing is performed simply by moving the medium S in the sub-scanning direction.

[0116] Furthermore, the present invention broadly applies to liquid spraying devices in general that are equipped with liquid spraying heads. Examples of liquid spraying heads include recording heads such as various inkjet recording heads used in image recording devices such as printers, and colorant spraying heads used in the manufacture of color filters for liquid crystal displays. Other examples of liquid spraying heads include electrode material spraying heads used in electrode formation for organic EL displays and FEDs (field emission displays), and bio-organic material spraying heads used in biochip manufacturing, and the invention can also be applied to liquid spraying devices equipped with these liquid spraying heads.

[0117] (Note) From the forms exemplified above, the following configuration can be understood, for example.

[0118] A liquid dispensing device according to Embodiment 1, which is a preferred embodiment, comprises a pressure chamber substrate provided with a pressure chamber communicating with a nozzle for dispensing liquid, a diaphragm provided on the pressure chamber substrate, a piezoelectric element provided on the diaphragm with a piezoelectric layer sandwiched between two electrodes, and a control unit for controlling the driving of the piezoelectric element, wherein the control unit drives the piezoelectric element to apply pressure to the liquid in the pressure chamber and discharge the liquid from the nozzle, wherein the compliance value of the piezoelectric element at the minimum voltage is smaller than the compliance value of the piezoelectric element at the maximum voltage, at the minimum and maximum voltages applied to the piezoelectric element by the control unit. As a result, the piezoelectric element and diaphragm become softer when driven at the maximum voltage, so the amount of deformation of the piezoelectric element and diaphragm when driven at the maximum voltage can be increased, and the weight of the discharged liquid droplet can be increased. Also, since the piezoelectric element and diaphragm become harder when driven at the minimum voltage, the damping of the meniscus vibration of the nozzle after the liquid droplet is discharged is accelerated. Therefore, the damping time can be shortened, and high-frequency driving can be performed by shortening the waveform length.

[0119] In Embodiment 2, which is a specific example of Embodiment 1, the minimum voltage and the maximum voltage are set so as to surround the peak voltage at which the compliance-voltage curve of the piezoelectric element reaches its maximum value. This makes it possible to reduce the amount of change between the compliance at the minimum voltage and the compliance at the maximum voltage, simplify the waveform design of voltage, time, slope, etc., and stabilize the discharge of liquid.

[0120] In Embodiment 3, which is a specific example of Embodiment 2, the compliance value of the piezoelectric element at the intermediate potential applied to the piezoelectric element is greater than the compliance value of the piezoelectric element at the minimum voltage and the compliance value of the piezoelectric element at the maximum voltage. This allows the compliance at the intermediate potential to be near the maximum compliance, reducing the stress on the diaphragm and making it less likely for cracks or other damage to occur in the diaphragm.

[0121] A liquid dispensing device according to Embodiment 4, which is a preferred embodiment, comprises a pressure chamber substrate provided with a pressure chamber communicating with a nozzle for dispensing liquid, a diaphragm provided on the pressure chamber substrate, a piezoelectric element provided on the diaphragm with a piezoelectric layer sandwiched between two electrodes, and a control unit that controls the driving of the piezoelectric element, wherein the control unit drives the piezoelectric element to apply pressure to the liquid in the pressure chamber and discharge the liquid from the nozzle, wherein the control unit controls the natural vibration period of the pressure chamber at the minimum voltage and the maximum voltage applied to the piezoelectric element, and the natural vibration period of the pressure chamber at the minimum voltage is smaller than the natural vibration period of the pressure chamber at the maximum voltage. According to this, since the natural vibration period is proportional to compliance, a large natural vibration period when driven at the maximum voltage means that the piezoelectric element and the diaphragm are softer, so the amount of deformation of the piezoelectric element and the diaphragm when driven at the maximum voltage can be increased, and the weight of the discharged liquid droplets can be increased. Furthermore, a small natural vibration period when driven at the minimum voltage means that the piezoelectric element and diaphragm are rigid, resulting in faster damping of the nozzle meniscus vibration after droplet ejection. Consequently, the damping time can be shortened, allowing for shorter waveform lengths and high-frequency drive.

[0122] In Embodiment 5, which is a specific example of Embodiment 4, the minimum voltage and the maximum voltage are set so as to surround the peak voltage at which the value in the natural period-voltage curve is maximum. This makes it possible to reduce the amount of change between the natural period at the minimum voltage and the natural period at the maximum voltage, simplify the waveform design of voltage, time, slope, etc., and stabilize the discharge of liquid.

[0123] In embodiment 6, which is a specific example of embodiment 5, the natural vibration period of the pressure chamber at the intermediate potential applied to the piezoelectric element is greater than the natural vibration period of the pressure chamber at the minimum voltage and the natural vibration period of the pressure chamber at the maximum voltage. This makes it possible to set the natural vibration period at the intermediate potential near the maximum natural vibration period, reducing the stress on the diaphragm and making it less likely for cracks or other damage to occur in the diaphragm.

[0124] A liquid dispensing device according to Embodiment 7, which is a preferred embodiment, comprises a pressure chamber substrate provided with a pressure chamber communicating with a nozzle for dispensing liquid, a diaphragm provided on the pressure chamber substrate, a piezoelectric element provided on the diaphragm with a piezoelectric layer sandwiched between two electrodes, and a control unit for controlling the driving of the piezoelectric element, wherein the control unit drives the piezoelectric element to apply pressure to the liquid in the pressure chamber and discharge the liquid from the nozzle, wherein at the minimum voltage and maximum voltage applied to the piezoelectric element, the resonant frequency of the piezoelectric element at the minimum voltage is greater than the resonant frequency of the piezoelectric element at the maximum voltage. According to this, since the resonant frequency is inversely proportional to compliance, a small resonant frequency when driven at the maximum voltage means that the piezoelectric element and diaphragm are softer, so the amount of deformation of the piezoelectric element and diaphragm when driven at the maximum voltage can be increased, and the weight of the discharged liquid droplets can be increased. Furthermore, a high resonant frequency when driven at the minimum voltage means that the piezoelectric element and diaphragm are rigid, resulting in faster damping of the nozzle meniscus vibration after droplet ejection. Consequently, the damping time can be shortened, allowing for shorter waveform lengths and high-frequency drive.

[0125] In embodiment 8, which is a specific example of embodiment 7, the minimum voltage and the maximum voltage are set so as to surround the peak voltage at which the value on the resonant frequency-voltage curve of the piezoelectric element is minimized. This makes it possible to reduce the amount of change between the resonant frequency at the minimum voltage and the resonant frequency at the maximum voltage, simplify the waveform design such as voltage, time, and slope, and stabilize the discharge of liquid.

[0126] In embodiment 9, which is a specific example of embodiment 8, the resonant frequency of the piezoelectric element at the intermediate potential applied to the piezoelectric element is smaller than the resonant frequency of the piezoelectric element at the minimum voltage and the resonant frequency of the piezoelectric element at the maximum voltage. This makes it possible to set the resonant frequency at the intermediate potential near the minimum resonant frequency, reducing the stress on the diaphragm and making it less likely for cracks or other damage to occur in the diaphragm. [Explanation of symbols]

[0127] DP...Discharge pulse, fa, fa1~fa8...Resonant frequency, H...Liquid discharge head, S...Media, T...Unit period, Tc, Tc1~Tc8...Natural vibration period, V0...Intermediate potential, Vb...Minimum voltage, Vh...Maximum voltage, Vp...Peak voltage, 1...Liquid discharge device, 3...Liquid storage section, 4...Control unit, 5...Transport mechanism, 6...Moving mechanism, 10...Pressure chamber substrate, 11...Partition wall, 12...Pressure chamber, 15...Communication plate, 16...Nozzle communication passage, 17...First manifold section, 18...Second manifold section, 19...Supply communication passage, 20...Nozzle plate, 21...Nozzle, 30...Protective substrate, 31...Housing section, 32...Through hole, 40...Case Components, 41...recess, 42...third manifold section, 43...connection port, 44...inlet, 45...compliance substrate, 49...compliance section, 50...diaphragm, 51...elastic membrane, 55...arm section, 60...first electrode, 70...piezoelectric layer, 71...recess, 80...second electrode, 90...lead electrode, 91...individual lead electrode, 92...common lead electrode, 100...manifold, 110...wiring component, 111...drive circuit, 211...external interface, 214...control processing section, 215...oscillation circuit, 216...drive signal generation section, 217...internal interface, 300...piezoelectric actuator, 310...active section.

Claims

1. A pressure chamber substrate is provided with a pressure chamber that communicates with a nozzle for discharging liquid, A diaphragm provided on the pressure chamber substrate, A piezoelectric element is provided on the diaphragm, with a piezoelectric layer sandwiched between two electrodes, The system comprises a control unit for controlling the driving of the piezoelectric element, A liquid dispensing device that applies pressure to the liquid in the pressure chamber by driving the piezoelectric element with the control unit, thereby dispensing the liquid from the nozzle, At the minimum and maximum voltages applied to the piezoelectric element by the control unit, the compliance value of the piezoelectric element at the minimum voltage is smaller than the compliance value of the piezoelectric element at the maximum voltage. A liquid dispensing device characterized by the following features.

2. The minimum voltage and the maximum voltage are set to straddle the peak voltage at which the value on the compliance-voltage curve of the piezoelectric element is the maximum value. The liquid dispensing device according to feature 1.

3. The compliance value of the piezoelectric element at the intermediate potential applied to the piezoelectric element is greater than the compliance value of the piezoelectric element at the minimum voltage and the compliance value of the piezoelectric element at the maximum voltage. The liquid dispensing device according to feature 2.

4. A pressure chamber substrate is provided with a pressure chamber that communicates with a nozzle for discharging liquid, A diaphragm provided on the pressure chamber substrate, A piezoelectric element is provided on the diaphragm, with a piezoelectric layer sandwiched between two electrodes, The system comprises a control unit for controlling the driving of the piezoelectric element, A liquid dispensing device that applies pressure to the liquid in the pressure chamber by driving the piezoelectric element with the control unit, thereby dispensing the liquid from the nozzle, The control unit ensures that, at the minimum and maximum voltages applied to the piezoelectric element, the natural oscillation period of the pressure chamber at the minimum voltage is smaller than the natural oscillation period of the pressure chamber at the maximum voltage. A liquid dispensing device characterized by the following features.

5. The minimum voltage and the maximum voltage are set to straddle the peak voltage that has the maximum value in the natural oscillation period-voltage curve. The liquid dispensing device according to feature 4.

6. The natural oscillation period of the pressure chamber at the intermediate potential applied to the piezoelectric element is greater than the natural oscillation period of the pressure chamber at the minimum voltage and the natural oscillation period of the pressure chamber at the maximum voltage. The liquid dispensing device according to feature 5.

7. A pressure chamber substrate is provided with a pressure chamber that communicates with a nozzle for discharging liquid, A diaphragm provided on the pressure chamber substrate, A piezoelectric element is provided on the diaphragm, with a piezoelectric layer sandwiched between two electrodes, The system comprises a control unit for controlling the driving of the piezoelectric element, A liquid dispensing device that applies pressure to the liquid in the pressure chamber by driving the piezoelectric element with the control unit, thereby dispensing the liquid from the nozzle, At the minimum and maximum voltages applied to the piezoelectric element, the resonant frequency of the piezoelectric element at the minimum voltage is greater than the resonant frequency of the piezoelectric element at the maximum voltage. A liquid dispensing device characterized by the following features.

8. The minimum voltage and the maximum voltage are set to surround the peak voltage at which the value on the resonant frequency-voltage curve of the piezoelectric element is minimized. The liquid dispensing device according to feature 7.

9. The resonant frequency of the piezoelectric element at the intermediate potential applied to the piezoelectric element is smaller than the resonant frequency of the piezoelectric element at the minimum voltage and the resonant frequency of the piezoelectric element at the maximum voltage. The liquid dispensing device according to feature 8.

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