Patent Application
20230150260
The present invention relates to a liquid ejection apparatus that ejects a liquid from an ejection port and a control method of the same.
Recent years, along with development in micromachine technology (MEMS technology), there has been proposed a liquid transportation device that transports liquid on the order of μms.
Japanese Patent Laid-Open No. 2003-286940 discloses a micropump that takes advantage of a flow channel resistance that is changed non-linearly with respect to a flow velocity and uses the action of fluid as a valve mechanism without using a mechanical valve structure. According to the micropump disclosed in Japanese Patent Laid-Open No. 2003-286940, it is possible to transport a liquid on the order of μms with a simple and small configuration including a few parts. Japanese Patent Laid-Open No. 2003-286940 discloses a driving method that allows the piezoelectric element to function as a pump by using a piezoelectric element in the form of membrane as a driving source and changing a voltage applied to the piezoelectric element asymmetrically against time.
In the liquid transportation device disclosed in Japanese Patent Laid-Open No. 2003-286940, the liquid is quantitatively transported by displacing the piezoelectric element and repeating an operation to rapidly expand (contract) the inner volume of a liquid transportation chamber and an operation to moderately contract (expand) the inner volume of the liquid transportation chamber. In a case where the liquid transportation device is used for a liquid transportation operation in a flow channel of a liquid ejection apparatus, a pressure variation that occurs due to the rapid change in the inner volume of the liquid transportation chamber may affect an ejection operation of a liquid droplet, and degradation in the ejection characteristics may be caused.
The present invention is made in view of the above-described problems, and an object thereof is to provide a liquid ejection apparatus that is capable of suppressing an effect on an ejection operation of a liquid even in a case where the ejection operation of the liquid from an ejection port and a liquid transportation operation to a flow channel communicating with the ejection port are performed in parallel.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of a liquid ejection apparatus according to the present invention are described below in detail with reference to the drawings. In the embodiments described below, as a liquid ejection apparatus ejecting a liquid, an ink jet printing apparatus in which a printing head ejecting ink is mounted is described as an example. The embodiments below are not intended to limit the present invention according to the scope of claims, and not all the combinations of the characteristics described in the present embodiments are necessarily required for the means for solving the problems of the present invention.
The printing head 10 is a full line type printing head extending in a Y direction crossing (in the present example, orthogonal to) the conveyance direction of the printing medium S (X direction). In the printing head 10, the multiple ejection ports capable of ejecting the ink are arrayed along the Y direction. The ejection ports may also be referred to as nozzles. A later-described circulation flow channel is formed inside the printing head 10. The ink is supplied to the circulation flow channel from an ink supply unit 105 (see
Next, the control system of the printing apparatus 1 is described with reference to
In the printing head 10, a liquid transportation mechanism 208 that generates a pressure to flow the ink in the circulation flow channel is provided. The liquid transportation mechanism 208 is driven by a voltage applied from a liquid transportation driving circuit 208d, and an operation of the liquid transportation driving circuit 208d is controlled by the CPU 21. Details of the liquid transportation mechanism 208 and driving control thereof are described later.
Each of the element substrates 114 is connected to the same electric wiring substrate 102 through a flexible wiring substrate 101. On the electric wiring substrate 102, a power supply terminal 103 that accepts power and a signal input terminal 104 that receives an ejection signal are arranged. The power supplied to the power supply terminal 103 and the signal received by the signal input terminal 104 are supplied from the ejection driving circuit 201d and the liquid transportation driving circuit 208d.
On the other hand, in the ink supply unit 105, there is formed a flow channel to supply the individual element substrate 114 with the ink supplied from a not-illustrated ink tank and collect the ink that is not consumed for printing.
As illustrated in
The combination of the ejection ports 202, the pressure chambers 203, the supply flow channels 205, and the collection flow channels 206 provided in each flow channel block is not limited to the example illustrated in
As illustrated in
The ink stored in each pressure chamber 203 forms a meniscus in the ejection port 202 in a stable state. Once a voltage pulse is applied to the ejection element 201 in accordance with the ejection signal, film boiling occurs in the ink that is put in contact with the ejection element 201, and the ink is ejected as a droplet from the ejection port 202 in the +Z direction with the growth energy of the generated bubble.
The ink in the pressure chamber 203 consumed by the ejection operation is newly supplied by the capillary force of the pressure chamber 203 and the ejection port 202, and a meniscus is formed again in the ejection port 202.
As illustrated in
The pressure chamber 203 is provided for each ejection element 201. The supply flow channel 205 and the collection flow channel 206 are provided for every four ejection elements 201 in the flow channel block 200. The supply flow channel 205 supplies the four pressure chambers 203 with the ink commonly, and the collection flow channel 206 collects the ink from the four pressure chambers 203 commonly.
One liquid transportation chamber 222 and one connection flow channel 207 are provided for every four ejection elements. Accordingly, two liquid transportation chambers 222 and two connection flow channels 207 are provided in each flow channel block 200. Each liquid transportation chamber 222 is arranged in a position overlapped with the four ejection elements 201 in an XY plane. In each liquid transportation chamber 222, the liquid transportation mechanism 208 capable of changing the inner volume of each liquid transportation chamber 222 is arranged, and the liquid transportation mechanism 208 circulates the ink for the four pressure chambers 203 commonly. The connection flow channel 207 is arranged in the substantially center in the Y direction of a range in which the four pressure chambers 203 are formed and connects the liquid transportation chamber 222 with the supply flow channel 205. The position of the supply flow channel connected with the connection flow channel 207 is a position upstream of a diverging point into the two supply flow channels 205.
In the above configuration, with the liquid transportation mechanism 208 driven by applying a later-described voltage thereto, the circulation can be made in the circulation flow channel formed in each flow channel block 200 through a supply port 219 from the common liquid chamber 218. That is, the ink can be flowed in the order of the supply flow channel 205, the pressure chamber 203, the collection flow channel 206, the liquid transportation chamber 222, and the connection flow channel 207 of each flow channel block 200. This circulation of the ink (liquid) is referred to as a first circulation, and the flow of the circulated ink is referred to as a first circulation flow. On the other hand, the circulation in which the ink flows in the order of the supply flow channel 205, the connection flow channel 207, the liquid transportation chamber 222, the collection flow channel 206, the pressure chamber 203, and the supply flow channel 205 is referred to as a second circulation, and the flow of the circulated ink is referred to as a second circulation flow.
The flowing direction of the ink can be switched by changing a voltage waveform applied to the liquid transportation mechanism 208. The voltage waveform is described later. The circulation of the ink is stably performed regardless of whether there is the ejection operation or the frequency of the ejection operation, and it is possible to supply fresh ink constantly to the vicinity of the ejection port 202. Although it is not illustrated, it is favorable to provide a filter for preventing entering of foreign matters or air bubbles in the middle of the supply flow channel 205 upstream of the pressure chamber 203. As a filter, a columnar structure or the like can be employed.
The element substrate 114 can be manufactured as follows, for example. First, a structure is formed in advance in each of the first substrate 212 and the second substrate 213. Thereafter, the first substrate 212 and the second substrate 213 are pasted together with the middle layer 214 arranged therebetween, the middle layer 214 including a groove that is formed in a position in which the connection flow channel 207 is formed later. With this, the element substrate 114 can be manufactured.
Here is described a specific dimension example of each ejection unit formed in the element substrate 114. In the present embodiment, the individual ejection elements 201, ejection ports 202, and pressure chambers 203 are arrayed in the Y direction at a density of 600 npi (nozzles per inch). The size of the ejection element 201 is 20 μm×20 μm, the diameter of the ejection port 202 is 18 μm, and the thickness of the ejection port 202, that is, the thickness of the ejection port formation member 211 is 5 μm. The size of the pressure chamber 203 is the length in the X direction (length) of 100 μm×the length in the Y direction (width) of 37 μm×the length in the Z direction (height) of 5 μm. The viscosity of the ink to be used is 2 cP, and the ink ejection amount from the individual ejection port is 2 pL.
In the present embodiment, the driving frequency of the individual ejection element 201 is 10 KHz. Such a driving frequency is set based on the time required to apply a voltage to the individual ejection element, the ink is actually ejected, new ink is refilled additionally, and the next ejection operation is available in the individual ejection element 201.
On the other hand, in the element substrate 114 of the present embodiment, the size of the liquid transportation chamber 222 is designed appropriately in accordance with an area occupied by the flow channel block. For example, in a case of the flow channel block including the eight pressure chambers 203 (600 npi), the size of the liquid transportation chamber 222 is 250 μm in the X direction×290 μm in the Y direction×250 μm in the Z direction. In a case of the flow channel block including the four pressure chambers 203 (600 npi), the size of the liquid transportation chamber 222 is 250 m in the X direction×120 μm in the Y direction×250 μm in the Z direction. The size of the connection flow channel 207 is based on 25 μm in the X direction×25 μm in the Y direction×25 μm in the Z direction. Additionally, the flow channel width (cross-section area) is optimized such that the liquid transportation efficiency is maximized in view of a flow channel load ratio (the connection flow channel 207, the supply flow channel 205, the pressure chamber 203, and the collection flow channel 206) with respect to the liquid transportation chamber 222.
In the present embodiment, with the dimension relationship as described above, the flow channel resistance and the inertance of the connection flow channel 207 are lower than the flow channel resistance and the inertance of a flow channel as a combination of the supply flow channel 205, the collection flow channel 206, and the pressure chamber 203. Here, “the flow channel resistance and the inertance of a flow channel as a combination of the supply flow channel 205, the collection flow channel 206, and the pressure chamber 203” indicates a total of a sum of the parallel flow channel resistances of the respective supply flow channel 205, multiple pressure chamber 203, and collection flow channel 206 and a sum of the series flow channel resistances thereof. The dimension values of the portions described above are merely an example and may be changed as needed in accordance with required specifications.
The diaphragm 221 mainly includes a laminate including an inorganic material with a thickness of about few m and a piezoelectric element with a thickness of about 1 to 3 μm. With a voltage applied to the piezoelectric element 224 through the two electrodes 223, the diaphragm 221 is bent with respect to the piezoelectric element 224, and the inner volume of the liquid transportation chamber 222 is changed. That is, with a change in the voltage applied to the two electrodes, the diaphragm 221 can be displaced in the ±Z directions, and the inner volume of the liquid transportation chamber 222 can be changed.
It is possible to form the liquid transportation device (pump) including such a liquid transportation mechanism 208 by using general-purpose Micro Electro Mechanical Systems (MEMS) technology. For example, the liquid transportation device including the liquid transportation mechanism 208 can be formed by vacuum plasma etching, anisotropic etching using an alkaline solution, or a combination thereof performed on an Si substrate (silicon substrate). The liquid transportation device may be formed by forming a flow channel including the liquid transportation chamber 222 and the liquid transportation mechanism 208 separately on multiple Si substrates and thereafter bonding or adhering the flow channel and the liquid transportation mechanism 208 to paste them together.
A unimorph piezoelectric actuator is used for the liquid transportation mechanism 208. The unimorph piezoelectric actuator is formed by forming the piezoelectric element 224 on one surface side of the second substrate (also called a vibration plate) 213. A material of the vibration plate 213 is not particularly limited as long as the conditions such as required mechanical characteristics and endurance reliability are satisfied. For example, silicon nitride film, silicon, metal, heat-resistant glass, and the like can be used properly.
The piezoelectric element 224 can be film-formed by using a method such as vacuum sputtering film formation, sol-gel film formation, and CVD film formation and is fired after the film formation in many cases. The firing method is not particularly limited; however, for example, a lamp annealing heating method in which firing at about 650° C. at the maximum is performed under oxygen atmosphere can be employed. In view of consistency with a process flow, the piezoelectric element 224 may be directly film-formed on the vibration plate 213 and fired integrally or may be film-formed on a substrate different from the vibration plate 213 to be fired and then peeled and transferred onto the vibration plate 213. Alternatively, the piezoelectric element 224 may be film-formed on a substrate different from the vibration plate 213 and then fired integrally after being peeled and transferred onto the vibration plate 213.
For the electrodes 223, it is preferable to select a Pt or Ir system if the firing process is included; however, if the firing process can be separated, an AL system is selectable. In the present embodiment, a piezoelectric material of PZT system is used for the piezoelectric element 224, and for the electrodes 223, a material that allows the piezoelectric element 224 to be displaced with a state of high linearity, that is, being highly responsive to the applied voltage is used. As the outermost layer exposed to the atmosphere, a protection film of SiN system is used, and the entire liquid transportation mechanism 208 may be sealed with the protection film.
Then, a relay board for transmitting a signal wiring to the liquid transportation device and the liquid transportation device are adhered to a not-illustrated holding frame body, and the liquid transportation device and the relay board are electrically implemented by wire bonding. Additionally, a manifold to be an inlet port and an outlet port of the ink is fixed with an adhesive agent so as to be connected to the supply flow channel (first flow channel) 205 and the collection flow channel (second flow channel) 206.
In the present specification, an absolute value of a voltage change amount per unit time (voltage change rate) is referred to as a rate. Additionally, the rate in the step-up waveform 302 is referred to as a step-up rate, and the rate in the step-down waveform 303 is referred to as a step-down rate; the rates are defined as follows:
step-up rate=|(reached voltage−initial voltage)|/step-up period;
step-down rate=|(reached voltage−initial voltage)|/step-down period.
It is preferable to use an asymmetric triangle wave in order to maximize a difference between a rapid change and a moderate change in a deformation speed of the diaphragm 221; however, a trapezoidal waveform including a component of an asymmetric triangle wave that generates a rapid change and a moderate change may also be used. In the present specification, descriptions are given by using an asymmetric triangle wave.
In the triangle wave 301 exemplified in
In a case where such a triangle wave 301 is applied to the piezoelectric element 224, in the step-up period t1, the piezoelectric element 224 is displaced in a direction in which the liquid transportation chamber 222 is expanded rapidly by the step-up waveform 302 with the great rate. On the other hand, the step-down waveform 303 is a waveform in which the voltage drops moderately in the step-down period t2. With the step-down waveform 303 applied to the piezoelectric element 224, the piezoelectric element 224 is displaced in a direction in which the liquid transportation chamber 222 is contracted moderately. As a result, in the liquid transportation chamber 222, a flow in a direction illustrated in
As the driving voltage of the piezoelectric element 224, it is also possible to use a triangle wave in which the step-down period t2 is set to be a period shorter than the step-up period t1. In the triangle wave, the voltage drops rapidly in the step-down waveform 303, and the voltage rises moderately in the step-up waveform 302. In this case, with the step-up waveform 302 applied, the piezoelectric element 224 is displaced in a direction in which the liquid transportation chamber 222 is expanded moderately. With the step-down waveform 303 applied, the piezoelectric element 224 is displaced in a direction in which the liquid transportation chamber 222 is contracted rapidly. As a result, in the flow channel block 200, a flow in an opposite direction of the first direction S1 (second direction S2) is generated.
As described above, the driving voltage of the piezoelectric element used in the present embodiment includes the step-up period and the step-down period, and those two voltage change periods are periods different from each other. That is, one is a period shorter than the other, and the piezoelectric element 224 is changed more rapidly by the voltage waveform that is changed in the short period (first period), and a more rapid flow of the ink is generated.
Here is simply described a mechanism of generating a constant flow by making a rapid inner volume change and a moderate inner volume change in the liquid transportation chamber 222. In a case where the liquid transportation chamber 222 is expanded rapidly, a vortex is generated under a high flow velocity on a side of the connection flow channel 207 with a small area of flow channel cross-section, and the flow channel resistance is increased greatly. As a result, flow of the ink from the connection flow channel 207 into the liquid transportation chamber 222 is obstructed. In contrast, on a side of the connection flow channel 207 with a wide area of flow channel cross-section, a variation in the flow channel resistance due to a flow velocity is less, and the ink flows smoothly from the collection flow channel 206 into the liquid transportation chamber 222. Thereafter, once the liquid transportation chamber 222 is contracted moderately, the ink in the liquid transportation chamber 222 flows to the connection flow channel 207 side at a low speed; thus, no vortex is generated and an increase in the flow channel resistance is suppressed, and therefore the ink in the liquid transportation chamber 222 flows moderately to the supply flow channel side through the connection flow channel 207. Thus, with the rapid expansion and the moderate contraction of the liquid transportation chamber 222, the flow in the first direction S1 from the collection flow channel 206 to the supply flow channel 205 through the liquid transportation chamber 222 and the connection flow channel 207 is generated, and the first circulation is performed.
In a case where the liquid transportation chamber 222 is contracted rapidly, a vortex is generated under a high flow velocity on the side of the connection flow channel 207 with a small area of flow channel cross-section, and the flow channel resistance is increased greatly. As a result, flowing out of the ink from the liquid transportation chamber 222 to the connection flow channel 207 is obstructed. In contrast, on the side of the connection flow channel 207 with a wide area of flow channel cross-section, the ink smoothly flows out from the liquid transportation chamber 222 to the collection flow channel. Thereafter, once the liquid transportation chamber 222 is expanded moderately, the ink flows from the connection flow channel 207 into the liquid transportation chamber 222 at a low speed. Accordingly, with the rapid contraction and the moderate expansion of the liquid transportation chamber 222, the flow of the ink in the second direction S2 from the connection flow channel 207 to the collection flow channel 206 through the liquid transportation chamber 222 is generated, and the second circulation is performed.
In the printing head 10 used in the ink jet printing apparatus, the ink (liquid) may be deteriorated because of evaporation of volatile components in the ejection port in which the ejection operation is not performed for a while. If the degree of the evaporation is varied between multiple ejection ports depending on the ejection frequency, the ejection amount and the ejection direction are also varied, and unevenness in the density and a streak may be found in an image. For this reason, in the ink jet printing head 10, it is necessary to flow the ink in the flow channel block 200 in order to constantly supply fresh ink to the vicinity of the ejection port. However, in a case where a great pressure variation during the flow of the ink is propagated to the ejection port, the ejection of the liquid droplet from the ejection port may be affected. Therefore, it is required to achieve both the appropriate ejection of the liquid droplet and liquid transportation operation.
Next, liquid transportation control in the printing head 10 of the present embodiment is described in more details.
On the other hand,
Thus, in the present embodiment, liquid transportation of a constant amount of the ink in the S1 direction or the S2 direction can be performed with cycles of the rapid inner volume change and the moderate inner volume change in the liquid transportation chamber 222 by using the fluid characteristics that the flow channel resistance is non-linearly changed in accordance with a pressure. This liquid transportation operation may be continuously repeated by continuously applying the driving voltage as illustrated in
Thus, in the present embodiment, a function as the liquid transportation device (also called a pump) is achieved by the flow channel that includes the liquid transportation chamber 222 and the liquid transportation mechanism 208 as a driving source, in which the flow channel resistance is non-linearly changed by a flow velocity of the ink flowed by the liquid transportation mechanism 208. A merit of the configuration of this pump may include improvement in the reliability obtained by not using a mechanical part to implement a valve function. However, a valve using the non-linearity of the flow channel resistance like the present embodiment has a lower performance as a check valve than a valve using a mechanical part, and thus the liquid transportation efficiency is low. For this reason, it is favorable to perform the circulation of the ink in the vicinity of the ejection port 202 in the ejection unit of the liquid droplet, and to this end, the liquid transportation chamber 222 needs to be arranged in a flow channel in the vicinity of the nozzle. In this case, once the rapid inner volume change occurs in the liquid transportation chamber 222, a great pressure applied to the ink due to the rapid inner volume change is likely to be propagated to the ejection port 202, and this may affect the ejection of the liquid droplet. If a rapid pressure variation occurs in the liquid transportation chamber 222 during the ejection operation of the liquid droplet, the ejection characteristics such as the ejection amount and the ejection direction of the liquid droplet are likely to be varied due to the effect of the pressure variation.
The liquid transportation chamber 222 communicates with the common liquid chamber 218, and in a case where there are the multiple liquid transportation chambers 222, the liquid transportation chambers 222 communicate with each other through the common liquid chamber 218. Once the rapid inner volume variation occurs in the liquid transportation chamber 222, a great pressure is propagated also to a common liquid chamber 218 side. Once the multiple liquid transportation mechanisms 208 are operated concurrently, pulsation close to the ejection cycle occurs in the common liquid chamber 218, and a variation in the meniscus positions in the ejection ports 202 is caused. As a result, the ejection characteristics is likely to be varied. The preconditions for stable liquid transportation is that the pressure in the common liquid chamber 218 with respect to the liquid transportation chamber 222 is a constant open pressure. Accordingly, an increase and decrease in the pressure in the common liquid chamber 218 from the open pressure is unfavorable because the liquid transportation operation itself is affected.
Here, the voltage waveform that causes the rapid inner volume change in the liquid transportation chamber 222 is the step-up waveform 302 prompting the expansion operation of the liquid transportation chamber 222 in
In a case where the piezoelectric element 224 is used as the driving source of the liquid transportation mechanism 208, a time corresponding to the rapid inner volume change in the liquid transportation chamber 222 (t1 in
The voltage waveform that causes the moderate inner volume change in the liquid transportation chamber 222 is the step-down waveform 303 prompting the contraction operation of the liquid transportation chamber 222 in
In the above configuration, in order to achieve both the appropriate ejection operation of the liquid droplet and liquid transportation operation by the liquid transportation mechanism 208, satisfying the following conditions for the ejection operation of the liquid droplet and the liquid transportation operation is effective.
(1) The ejection operation timing of the liquid droplet and the rapid inner volume variation timing in the liquid transportation chamber 222 do not coincide with each other.
(2) The number of the liquid transportation mechanisms 208 driven concurrently is small.
(3) The liquid transportation operations in opposite phases are performed in the liquid transportation mechanisms 208 arranged adjacent to each other or in the vicinity to compensate the pressure generated in the common liquid chamber 218.
In order to satisfy the above-described conditions, in the present embodiment, driving control of the ejection elements 201 that generate the ejection energy of the liquid droplet and the liquid transportation mechanisms 208 is performed according to the sequence below.
First, driving timings of the multiple ejection elements 201 provided in the printing head 10 are described. As described above, in the printing head 10, an ejection port row including the multiple ejection ports 202 is formed, and the multiple ejection elements 201 are arranged corresponding to the multiple ejection ports 202. Hereinafter, a row including the multiple ejection elements 201 is referred to as an ejection element row. The ejection element row is divided into multiple groups for every predetermined number of the ejection elements in accordance with physical array positions. The inside of each group is divided into driving blocks driven for corresponding ejection elements in different timings, and block numbers are provided to the driving blocks, respectively.
Here is more specifically described the group and the driving block in the printing head 10 with reference to
The ejection elements of each group are divided into eight blocks driven in different timings, and each ejection element belongs to any one of a zeroth block to a seventh block. That is, first, ninth, seventeenth, and not-illustrated twenty-fifth, thirty-third, forty-first . . . belong to the zeroth block, and second, tenth, eighteenth, and twenty-sixth, thirty fourth, four second . . . belong to the first block. The same applies to the second to seventh blocks, and those eight blocks are driven with time-division.
In the printing head 10 formed as above, all the ejection elements are driven in accordance with pulses (ejection timing signals) 501 to 508 illustrated in
Since it is possible to suppress the power consumption in the printing operation by dividing the number of the ejection elements driven concurrently, the time-division method is an effective method for downsizing an electric power source for driving the printing head and a member for the electric power source such as a connector and a cable. In a case of the printing head using a heater as the ejection element, reduction of a voltage variation and fine adjustment of a voltage value are required in order to perform stable ejection taking into consideration the characteristics of the heater, the ink, and the like. Thus, with the time-division driving, it is possible to reduce the capacity of the electric power source, and it is possible to satisfy the requirements relating to the electric power source.
As described above, in a case where the time-division driving is performed in eight different timings, for example, if the cycle T is 10 KHz (100 μsec), a timing difference between adjacent ejection signals is 12.5 μsec. Since the ejection signal is about 1 to 2 μsec, the following remaining period that is about 10 μsec is a blanking period. In the blanking period, no ejection signal is applied to each ejection element. As with the number of time-division, there are eight periods as the blanking period in which no ejection signal is applied in the cycle T. That is, in the cycle T illustrated in
Next, a driving timing of the pump that is the liquid transportation device performing the liquid transportation operation in the circulation flow channel is described. In the example illustrated in
In
In the example illustrated in
A waveform conformable to the triangle wave illustrated in
The above-described driving voltage was inputted to the liquid transportation mechanism of the pump, and a flow of the ink in the pressure chamber 203 was evaluated. As the evaluation method, commonly known Particle Tracking Velocimetry (PTV) was employed. With measurement of a flow velocity, it was confirmed that the ink is circulated at a favorable speed in the supply flow channel 205, the pressure chamber 203, the collection flow channel 206, the liquid transportation chamber 222, and the connection flow channel 207, and fresh ink can be supplied stably to the vicinity of the ejection port 202. In a state where the ink is circulated, the ejection operation of the liquid droplet (ink droplet) was started, and the situation of the ejection of the ink droplet was observed by a high-speed camera. The ejection situation of the liquid droplet was observed while changing the relationship between the driving timing of the ejection element to eject the liquid droplet and the timing of the rapid operation of the actuator.
With the driving timing 509 of the pump in which the inner volume of the liquid transportation chamber 222 is changed rapidly set to the blanking period including no ejection signal of the ejection element 201 as illustrated in
In the above-described embodiment, the flow channel block 200 of the mode illustrated in
In
In the above-described embodiment, a mode in which the electrothermal conversion element is used as the ejection element 201 and the ink is ejected by the growth energy of the bubble generated by making film boiling on the electrothermal conversion element is applied; however, it is not limited to such an ejection method. For example, various types of elements such as a piezoelectric actuator, a static actuator, a mechanical/impact driving type actuator, a voice coil actuator, and a magnetostriction driving type actuator can be employed as the ejection element.
In the above descriptions, a configuration to perform the liquid transportation operation in the long full line type printing head 10 in which the ejection elements and the ejection ports are arrayed in a range corresponding to the width of the printing medium is described as an example; however, it is not limited thereto. A configuration to perform the liquid transportation operation in the printing head 10 indicated in the above-described embodiment is also applicable to and effective for a relatively short serial type printing head in which the ejection ports and the ejection elements are arrayed along a conveyance direction of the printing medium. Note that, since the ink is likely to be evaporated and deteriorated in the long full line type printing head 10, it is possible to enjoy more apparent effect by applying the configuration to perform the above-described liquid transportation operation to the full line type printing head.
Next, a second embodiment of the present invention is described. The configuration of
The liquid transportation performance of the pump is substantially proportional to the number of operations per unit time. For this reason, in the present embodiment, the ejection cycle T of the ejection elements 201 is 100 μsec, the driving cycle of the liquid transportation mechanism 208 is 50 μsec, and two cycles of the driving voltages are inputted to each pump during the cycle T of the ejection elements. With this, in the second embodiment, the driving voltages are inputted continuously, and accordingly, the liquid transportation operations are also performed continuously. On the other hand, in the above-described first embodiment, one cycle of the driving voltage is inputted during the ejection cycle T, and thus the pump is driven intermittently.
As with the first embodiment, the flow of the ink in the pressure chamber 203 was evaluated by the PTV in the present embodiment as well. As a result, it was confirmed that the flow velocity of the ink in the pressure chamber 203 is improved about twofold. Additionally, with the ejection of the ink and the liquid transportation operation performed concurrently based on the present sequence, it was confirmed that the ejection operation of the liquid droplet is performed stably.
Next, a third embodiment of the present invention is described.
The liquid transportation direction of the ink can be switched by switching the voltage waveform of the driving voltage applied to the piezoelectric element 224 of the liquid transportation mechanism 208. For example, a flow in the forward direction is generated in the pressure chamber 203 by applying the driving voltage illustrated in
That is, if a flow in a certain direction continues, a vortex is generated in the flow of the ink in a curved portion and the like in the flow channel, and the ink stagnates. Aggregates, air bubbles, and the like in the ink are likely to be accumulated in a portion with the stagnation, and if this state continues, the aggregates and air bubbles are increased, and the suppling capacity of the ink and the ejection performance of the liquid droplet may be reduced. To deal with this, in the present embodiment, control to switch the direction of the flow of the ink at a predetermined timing is performed. With this, even if there temporarily occur a vortex and stagnation in a curved portion and the like in the flow channel, the vortex and stagnation are moved and disappear by switching the flow of the ink. As a result, the aggregates and air bubbles do not stay in a fixed position and are discharged in accordance with the flow of the ink. Thus, it is possible to maintain the ejection performance in the printing head 10 for a longer period of time.
Next, a fourth embodiment of the present invention is described. In the present embodiment, driving of the pump is controlled such that flows of the ink generated by adjacent pumps have opposite phases to compensate the pulsation of the pressure generated in the common liquid chamber 218. With this, it is possible to reduce a pressure variation in the pressure chamber 203 due to a pressure variation in the common liquid chamber 218, and unevenness of the ejection performance in a macro perspective can be suppressed.
In
303 illustrated in
The spatial distance between the adjacent pumps is close; thus, the adjacent pumps are driven concurrently by the step-up waveform 302 and the step-down waveform 306 prompting the rapid change in the liquid transportation chamber 222, respectively. In this case, the local pressures generated in the common liquid chamber 218 by the pumps have opposite directions, and thus, in a macro perspective, a pressure distribution in the common liquid chamber 218 can be compensated. As a result, the pulsation generated in the common liquid chamber 218 can be suppressed more than a case of driving the adjacent pumps only by the voltage waveforms of the same phases. As a result, the pressure variation provided to the ink near the ejection port 202 from the common liquid chamber 218 is reduced, and it is possible to stabilize the ejection characteristics.
One of the two pumps is driven by the driving voltage of the waveform illustrated in
Accordingly, the pumps adjacent to each other in the same group (same flow channel block) perform the rapid liquid transportation operations that generate the rapid inner volume change in the respective liquid transportation chambers 222 in the same driving timing in opposing directions. That is, the pump A and the pump B perform the rapid liquid transportation operation in each of the blanking periods 511 and 515 concurrently in opposing directions, and the pump C and the pump D perform the rapid liquid transportation operation in each of the blanking periods 513 and 517 concurrently in opposing directions. Additionally, the pump E and the pump F perform the rapid liquid transportation operation in each of the blanking period 511 and 515 concurrently in opposing directions.
In the present embodiment, the driving timings of the two pumps in the first group are synchronized but do not coincide with the driving timings of the pumps of the adjacent second group. However, the driving timings of the pumps in the third group in a position away from the first group are synchronized with the driving timings of the pumps in the first group.
With the pumps driven as described above and the ejection characteristics in each ejection unit measured, it was confirmed that a periodic swell, variation, and the like of the ejection characteristics are suppressed. In the present embodiment, the mode in which the two pumps are provided in each group is exemplified; however, the number of the pumps provided in each group is not limited thereto. Note that, in order to make the compensation by performing the rapid liquid transportation operations in the adjacent pumps in the same driving timing in opposing directions as described above, the number of the pumps provided in each group is preferably an even number.
Next, a fifth embodiment of the present invention is described.
Note that, in the present embodiment, driving of the pump A is performed after driving of the first to fourth ejection elements ends and before the fifth to eighth ejection elements are driven. Driving of the pump B is performed after driving of the first to fourth ejection elements and before driving of the fifth to eighth ejection elements starts. Thus, in the present embodiment, the rapid liquid transportation operation by the pump is temporally away from the ejection operation of the liquid droplet, and therefore an effect on the ejection performance can be reduced. Additionally, since driving of the pumps is controlled such that the flows of the ink generated by the two pumps in the same group have opposite phases, pressures generated in the pressure chamber 203 can be compensated. With a reduction in the liquid transportation amount by the pump, an effect on the ejection operation due to driving of the pump can be suppressed.
Next, a sixth embodiment of the present invention is described. In the above-described embodiments, an example of performing the opposite phase operation to flow the ink in opposite directions in the two pumps corresponding to the same nozzle group is described. In contrast, in the present embodiment, the opposite phase operation to flow the ink in opposite directions is performed between the pumps in nozzle groups adjacent to each other.
In the example illustrated in
In the present example, the opposite phase operation is performed between the pumps not adjacent to each other; however, it is possible to obtain an effect to suppress the pulsation in the common liquid chamber 218 in this case as well. Regarding routing of a driving wiring and the flow channel structure, it may be difficult to perform the opposite phase operation of pumps adjacent to each other, and the present example is effective in such a case.
Next, a seventh embodiment of the present invention is described.
The opposite phase operation between the adjacent pumps is performed in the present embodiment as well. That is, the opposite phase operation is performed between the pump A corresponding to all the ejection elements in the first group and the pump B corresponding to all the ejection elements in the second group. Additionally, the opposite phase operation is performed between the pump C corresponding to all the ejection elements in the third group and the pump D corresponding to all the ejection elements in the fourth group.
In the present embodiment, a case where the density of the ejection elements is 1200 npi is assumed. In a case where the ejection elements 201 have a high density of about 1200 npi, an area occupied by each flow channel block is small, and an area of about eight nozzles is required to form one pump. In such a case, it is possible to achieve both the ejection operation and the liquid transportation operation of the ink by employing the driving sequence as illustrated in
In the above embodiments, drying in the ejection unit is likely to progress near an end portion of the ejection port row; thus, the liquid transportation amount by the liquid transportation mechanism 208 may be increased to be relatively greater than that in a portion other than the end portion of the ejection port row (for example, central portion). This increase can be made by increasing an absolute value (rate) of the change amount in the voltage applied to the piezoelectric element of the liquid transportation mechanism 208.
In a case of executing the printing operation, it is possible to grasp in advance the number of times of ejection of the liquid droplet, that is, the number of times of driving of the ejection element 201, based on the printing data; for this reason, it is also possible to relatively increase the liquid transportation amount to the vicinity of the ejection unit in which the number of times of ejection is less.
Additionally, in a case where the ejection unit is positioned outside the printing medium in a serial type printing apparatus that performs printing by relatively moving the printing head 10 with respect to the printing medium, the liquid transportation amount may be increased more than a case where the ejection unit is positioned inside the printing medium. With this, thickening, drying, and the like of the ink caused by the ejection unit positioned outside the printing medium can be suppressed more effectively.
Preliminary ejection to perform ejection that does not contribute printing may be a situation where the ejection unit is positioned outside the printing medium. In the preliminary ejection, in general, more ink is ejected from the ejection port than that in the printing operation period. For this reason, in a preliminary ejection period, more ink needs to be supplied to the ejection port. Thus, in a case where the preliminary ejection is performed, the liquid transportation amount of the ink by the pump is favorably increased to be greater than that in the printing operation period. The liquid transportation amount is increased by increasing the driving amount of the pump. That is, the liquid transportation amount is increased by increasing the number of times of applying the driving voltage to the liquid transportation mechanism 208. In the preliminary ejection, it is unnecessary to take into consideration a landing accuracy of the liquid droplet; for this reason, there is no problem even if a little variation occurs in the pressure near the ejection port due to the increase in the liquid transportation amount of the pump.
As described above, according to the printing apparatus of the embodiments, flowing and circulation of the ink in the printing head 10 can be performed while suppressing an effect on the ejection performance of the ink, and it is possible to maintain the ejection performance in the printing head 10 for a long period of time. The driving sequences of the liquid transportation devices described in the embodiments may be combined with each other.
In the above-described embodiments, the liquid transportation unit that changes the inner volume of the liquid transportation chamber 222 is formed of the liquid transportation mechanism 208 using the piezoelectric element (piezo) that responses substantially linearly to the voltage waveform of the applied driving voltage; however, it is not limited thereto. For example, it is also possible to arrange an energy generation unit such as an electrothermal conversion element (heater) in the liquid transportation chamber to use as the driving source of the liquid transportation. In a case where the electrothermal conversion element is used as the energy generation unit, an electrothermal converter is driven based on the driving signal inputted by the control unit, and heat energy is generated. With this heat energy, film boiling occurs in the liquid (ink), and the liquid in the liquid transportation chamber flows with the bubble generation energy in the film boiling. In this case, the relatively rapid pressure change during bubble generation and the relatively moderate pressure change during bubble disappearance are used to change the inner volume ratio occupied by the air bubbles in the liquid transportation chamber, and thus the liquid transportation operation based on the operations illustrated in
Accordingly, in a case where the electrothermal conversion element is used, the input timing of the driving signal to control driving of the electrothermal conversion element is controlled by the control unit. That is, the input timing of the driving signal is controlled such that the timing of the bubble generation by the electrothermal conversion element does not coincide with the ejection timing of the liquid. As an example, the input timing of the driving signal may be controlled such that the ejection timing coincides with a bubble disappearance period. Since the pressure of the liquid is changed moderately during the bubble disappearance, if the bubble disappearance period coincides with the ejection timing, it is possible to suppress the reduction in the ejection performance. However, the input timing of the driving signal is not limited thereto. The input timing of the driving signal may be controlled arbitrarily as long as the ejection timing of the liquid and the bubble generation timing do not coincide with each other. As the driving voltage of the electrothermal conversion element, not the driving voltage of an analog waveform like the piezoelectric element but the driving voltage of a pulse waveform is used. Therefore, the driving timing of the electrothermal conversion element can be controlled by controlling the pulse width of the pulse waveform, a combination of multiple pulses, or the like.
According to the present invention, even in a case where an ejection operation of a liquid from an ejection port and a liquid transportation operation to a flow channel communicating with the ejection port are performed in parallel, it is possible to suppress an effect on the ejection operation of the liquid.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2021-186526 filed Nov. 16, 2021, which is hereby incorporated by reference wherein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-186526 | Nov 2021 | JP | national |
