阅读说明：本技术 流体贮存器 (Fluid reservoir ) 是由 达赖尔·E·安德森 史蒂文·T·卡斯特 安德鲁·克利 于 2017-12-11 设计创作，主要内容包括：流体贮存器可以包括用于容纳流体的流体腔室,以及暴露于流体腔室内的流体的阻抗传感器。阻抗传感器感测阻抗传感器处的阻抗；基于所感测到的阻抗,确定流体腔室内的流体的颗粒载体分离水平；以及基于所感测到的阻抗,将启动信号发送到流体贮存器被耦合到的可移动托架,以搅拌流体贮存器内的流体。(The fluid reservoir may include a fluid chamber for containing a fluid, and an impedance sensor exposed to the fluid within the fluid chamber. An impedance sensor senses an impedance at the impedance sensor; determining a level of particulate carrier separation of the fluid within the fluid chamber based on the sensed impedance; and based on the sensed impedance, sending an activation signal to a movable carriage to which the fluid reservoir is coupled to agitate fluid within the fluid reservoir.)

1. A fluid reservoir, comprising:

a fluid chamber for containing a fluid; and

an impedance sensor exposed to fluid within the fluid chamber for:

sensing an impedance at the impedance sensor;

determining a level of particle carrier separation of the fluid within the fluid chamber based on the sensed impedance; and

based on the sensed impedance, sending an activation signal to a movable carriage to which the fluid reservoir is coupled to agitate the fluid within the fluid reservoir.

2. The fluid reservoir of claim 1, wherein:

the activation signal is transmitted in response to a determination that the sensed impedance indicates that particle carrier separation exceeds a threshold; and

the activation signal is not transmitted in response to a determination that the sensed impedance indicates that particle carrier separation is below the threshold.

3. The fluid reservoir of claim 1, wherein the level of particulate carrier separation of the fluid is defined by an impedance value based on the sensed impedance, and wherein:

a relatively lower impedance corresponds to a higher concentration of particles within the fluid; and

a relatively higher impedance corresponds to a lower concentration of particles within the fluid.

4. The fluid reservoir of claim 1, comprising:

a sensing die extending through a level of fluid in the reservoir; and

first and second impedance sensors coupled to the sensing die at different portions of the sensing die to sense a degree of separation of pigment in the fluid at different levels of the fluid.

5. The fluid reservoir of claim 4, comprising a controller to:

determining a sensed impedance at the first impedance sensor;

determining a sensed impedance at the second impedance sensor;

determining a particle carrier separation level of a fluid within the fluid chamber based on the sensed impedance at the first impedance sensor and the sensed impedance at the second impedance sensor; and

sending the activation signal to the movable carriage to agitate the fluid within the fluid chamber based on the level of particle carrier separation of the fluid.

6. The fluid reservoir of claim 5, comprising: a third impedance sensor intermittently placed between the first impedance sensor and the second impedance sensor, wherein a maximum impedance is sensed and ignored when any of the first impedance sensor, the second impedance sensor, and the third impedance sensor is not in contact with the fluid.

7. The fluid reservoir of claim 1, comprising: a fluid level sensor for providing a sensed level of fluid within the fluid reservoir.

8. A fluid dispensing system comprising:

a movable carriage for transporting a fluid reservoir; and

a controller to activate the movable carriage to move the fluid reservoir in a coordinate direction based on an impedance sensing particle carrier separation level of fluid within the fluid reservoir.

9. The fluid dispensing system of claim 8, comprising:

a sensing die extending through a level of fluid in the reservoir; and

first and second electrodes coupled to the sensing die at different portions of the sensing die to sense the level of particle carrier separation in the fluid at different levels of the fluid;

wherein the controller:

determining a sensed impedance at the first electrode;

determining a sensed impedance at the second electrode;

determining the level of particle carrier separation of the fluid within the fluid reservoir based on the sensed impedance at the first electrode and the sensed impedance at the second electrode; and

sending an activation signal to the movable carriage to agitate the fluid within the fluid reservoir based on the level of particle carrier separation of the fluid.

10. The fluid dispensing system of claim 8,

wherein the impedance sensed at the first and second electrodes corresponds to a dispersion level of a solid within a fluid carrier of the fluid,

wherein the controller activates the carriage in response to a determination that the sensed impedance indicates that particle carrier separation exceeds a threshold, and

wherein the level of particle carrier separation of the fluid is defined by an impedance value based on the sensed impedance, and wherein:

a relatively lower impedance corresponds to a higher concentration of particles within the fluid; and

a relatively higher impedance corresponds to a lower concentration of particles within the fluid.

11. The fluid dispensing system of claim 10, comprising: a third electrode intermittently positioned between the first electrode and the second electrode, wherein a maximum impedance is sensed and ignored when any of the first electrode, the second electrode, and the third electrode is not in contact with the fluid.

12. The fluid dispensing system of claim 9, wherein the first electrode, the second electrode, or a combination thereof measures a level of the fluid within the fluid reservoir.

13. A method of correcting for particulate carrier separation within a fluid, comprising:

receiving a first sensed impedance value of the fluid from a first impedance sensor located at a first fluid level within a fluid reservoir;

receiving a second sensed impedance value of the fluid from a second impedance sensor located at a second level within the fluid reservoir;

determining a level of particulate carrier separation of the fluid based on the first sensed impedance at the first impedance sensor and the sensed impedance at the second impedance sensor; and

based on the level of particle carrier separation of the fluid, sending an activation signal to a movable carriage to which the fluid reservoir is coupled to move the fluid reservoir in a coordinate direction to agitate the fluid within the fluid reservoir.

14. The method of claim 13, comprising:

receiving a third sensed impedance value of the fluid from a third impedance sensor; and

determining a particle carrier separation level of the fluid based on the first sensed impedance at the first impedance sensor, the sensed impedance at the second impedance sensor, and the third sensed impedance at the third impedance sensor.

15. The method of claim 14, wherein the gradient of particle carrier separation within the fluid is compared to gradient values maintained in a lookup table to determine the pigment separation between any of the first, second and third impedance sensors.

Background

The fluid dispensing system comprises any device capable of ejecting fluid onto a substrate. Example fluid dispensing systems may include print cartridges, lab-on-a-chip devices, fluid dispensing cartridges, page wide arrays, and the like, implemented in a printing device. Each of these examples may include a fluid reservoir that is fluidly coupled to, for example, a fluid die, where the fluid die ejects and/or moves fluid within the fluid die. The fluid die may be used to move fluid within the fluid die, eject fluid onto a substrate, such as a print medium, or a combination thereof. The fluid within the fluid die may include any fluid that may be moved within or ejected from the fluid die. For example, the fluid may include inks, dyes, chemicals, biological fluids, gases, and other fluids. For example, fluids may be used to print images on media or to effect chemical reactions between different fluids. Further, in additive manufacturing processes such as those using three-dimensional (3D) printing devices, the fluid die may eject build material, adhesives, and other fluids that may be used to build the 3D object.

Drawings

The accompanying drawings illustrate various examples of the principles described herein and are a part of the specification. The illustrated examples are for illustration only and do not limit the scope of the claims.

Fig. 1 is a block diagram of an example fluid reservoir according to principles described herein.

Fig. 2 is a block diagram of an example fluid dispensing system according to principles described herein.

Fig. 3 is a block diagram of another example fluid dispensing system according to principles described herein.

Fig. 4 is a block diagram of a fluid dispensing system according to yet another example of principles described herein.

Fig. 5 is a flow chart depicting a method of correcting particle carrier segregation within a fluid, according to an example of principles described herein.

Fig. 6 is a flow chart depicting a method of correcting particle carrier segregation within a fluid, according to an example of principles described herein.

Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale and the dimensions of some portions may be exaggerated to more clearly illustrate the example shown. Moreover, the figures provide examples and/or embodiments consistent with the description; however, the description is not limited to the examples and/or implementations provided in the figures.

Detailed Description

Some fluids being moved within and/or ejected from the fluid die may include a fluid carrier and particles, where the fluid carrier is used to carry or suspend the particles within the fluid carrier. These types of fluids may include, for example, printing fluids that include color pigments suspended in an ink vehicle. A printing system, such as an inkjet printer, includes a printhead, and the printhead includes a firing chamber including a nozzle region having printing fluid therein and a fluid ejector to eject the printing fluid in the nozzle region onto a medium. Over time, the color pigments in the ink vehicle located in the nozzle area may diffuse and leave the homogeneous fluid, causing the pigment ink vehicle to separate. The separation of pigment particles from the ink vehicle may be referred to herein as pigment ink vehicle separation or pigment vehicle separation (PIVS), or may be referred to herein generally as Particle Vehicle Separation (PVS).

PVS can occur when a fluid containing particles stays in a portion of a fluidic die or a reservoir coupled thereto for a period of time, e.g., a few seconds or minutes, without being refreshed, circulated, or mixed. Due to evaporation, sedimentation, and other effects associated with the fluid formulation, particles within the fluid may migrate out of the first portion of the fluid reservoir over time and collect in other portions of the fluid reservoir, such as at the bottom of the fluid reservoir. This leaves a certain amount of fluid in the fluid reservoir without its particulate component when PVS occurs. In the case of pigmented inks, the fluid may contain more particles than the fluid carrier if the pigmented ink is subsequently sent to a fluid die to be ejected from a nozzle or to be moved within the fluid die under such PVS conditions. This, in turn, can result in the PVS fluid not working as intended, for example, plugging channels, chambers, and fluid nozzles of the fluid die. The first volume of fluid flowing out of the fluid reservoir will not have the correct amount or concentration of pigment particles or colorant and, if fluid is ejected from the fluid die, may affect the function of the fluid die and the print quality of a portion of the printed image.

In addition, sometimes pigment ink vehicle separation can result in curing of the printing fluid in the nozzle area. Particle interactions in a PVS scenario may elicit a series of responses based on the properties of the particles and the environment in which the fluid is present (including properties such as the geometry of the particles and the design of the cavity within the fluid mold). In this case, the respective nozzle regions may prevent ejection of printing fluid and reduce the life of the corresponding fluid ejectors.

Although pigment inks are used as examples herein to describe fluid carriers and particles, where a fluid carrier is used to carry or suspend particles within a fluid carrier, similar fluids including particles and fluid carriers may be equally suitable. For example, some biological fluids, such as blood, may include particles suspended in a fluid carrier. In the case of blood, blood includes blood cells suspended in plasma. In this example, the blood cells may be separated or dispersed, with a higher concentration of blood cells being present in a first portion of the plasma relative to another portion of the plasma where a relatively lower concentration of blood cells may be present.

Thus, PVS may occur in a plurality of fluids being moved within and/or ejected from the fluid die. Detection of separation of a particle from its fluid carrier may allow remedial action to be taken to correct for any particle concentration differences within the fluid. One such remedial action may be to measure the PVS level in the fluid reservoir and agitate the fluid in the fluid reservoir to change the fluid from the PVS state to a homogeneous state.

Examples described herein provide a fluid reservoir. The fluid reservoir may include a fluid chamber for containing a fluid, and at least one impedance sensor exposed to the fluid within the fluid chamber. The impedance sensor senses an impedance at the impedance sensor, determines a level of particle carrier separation of the fluid within the fluid chamber based on the sensed impedance, and sends an activation signal to a movable carrier to which the fluid reservoir is coupled to agitate the fluid within the fluid reservoir based on the sensed impedance.

The activation signal may be sent in response to a determination that the sensed impedance indicates that the particle carrier separation exceeds a threshold. The activation signal is not transmitted in response to a determination that the sensed impedance indicates that the particle carrier separation is below the threshold. The level of particle carrier separation of the fluid may be defined by an impedance value based on the sensed impedance. A relatively lower impedance may correspond to a higher concentration of particles within the fluid, while a relatively higher impedance corresponds to a lower concentration of particles within the fluid.

The fluid reservoir may include a sensing die extending through a level of fluid in the reservoir, and first and second impedance sensors coupled to the sensing die at different portions of the sensing die to sense a degree of separation of pigment in the fluid at different levels of the fluid. Further, the fluid reservoir may include a controller to determine a sensed impedance at the first impedance sensor, determine a sensed impedance at the second impedance sensor, determine a particle carrier separation level of the fluid within the fluid chamber based on the sensed impedance at the first impedance sensor and the sensed impedance at the second impedance sensor, and send an activation signal to the movable carriage to agitate the fluid within the fluid reservoir based on the particle carrier separation level of the fluid.

The fluid reservoir may further include a third impedance sensor intermittently positioned between the first impedance sensor and the second impedance sensor. When any one of the first impedance sensor, the second impedance sensor, and the third impedance sensor is not in contact with the fluid, the maximum impedance is sensed and ignored. A fluid level sensor may be included in the fluid reservoir to provide a sensed level of fluid within the fluid reservoir.

Examples described herein also provide a fluid dispensing system. The fluid dispensing system may include: a movable carriage for transporting a fluid reservoir; and a controller for actuating the movable carriage to move the fluid reservoir in a coordinate direction based on an impedance sensing particle carrier separation level of fluid within the fluid reservoir. The fluid dispensing system may include a sensing die extending through a level of fluid in the reservoir, and first and second electrodes coupled to the sensing die at different portions of the sensing die to sense levels of particulate carrier separation in the fluid at different levels of the fluid. The controller determines a sensed impedance at the first electrode, determines a sensed impedance at the second electrode, determines a particle carrier separation level of the fluid within the fluid reservoir based on the sensed impedance at the first electrode and the sensed impedance at the second electrode, and sends an activation signal to the movable carrier to agitate the fluid within the fluid reservoir based on the particle carrier separation level of the fluid.

The impedance sensed at the first and second electrodes corresponds to or is proportional to a level of dispersion of the solids within the fluid carrier of the fluid. The controller activates the carriage in response to a determination that the sensed impedance indicates that the particle carrier separation exceeds a threshold. The level of particle carrier separation of the fluid is defined by an impedance value based on the sensed impedance. A relatively lower impedance corresponds to a higher concentration of particles within the fluid, while a relatively higher impedance corresponds to a lower concentration of particles within the fluid.

The fluid dispensing system may include a third electrode intermittently positioned between the first electrode and the second electrode. When any of the first, second, and third electrodes is not in contact with the fluid, the maximum impedance is sensed and ignored. The first electrode, the second electrode, or a combination thereof measures a level of fluid within the fluid reservoir.

Examples described herein also provide a method of correcting particulate carrier separation within a fluid. The method may include receiving a first sensed impedance value of the fluid from a first impedance sensor located at a first level within the fluid reservoir, and receiving a second sensed impedance value of the fluid from a second impedance sensor located at a second level within the fluid reservoir. The method may further comprise: determining a particle carrier separation level of the fluid based on the first sensed impedance at the first impedance sensor and the sensed impedance at the second impedance sensor; and sending an activation signal to a movable carriage to which the fluid reservoir is coupled based on the particle carrier separation level of the fluid to move the fluid reservoir in a coordinate direction to agitate the fluid within the fluid reservoir.

The method can comprise the following steps: receiving a third sensed impedance value of the fluid from a third impedance sensor; and determining a particle carrier separation level of the fluid based on the first sensed impedance at the first impedance sensor, the sensed impedance at the second impedance sensor, and the third sensed impedance at the third impedance sensor. The gradient of particle carrier separation within the fluid is compared to gradient values maintained in a look-up table to determine pigment separation between any of the first impedance sensor, the second impedance sensor, and the third impedance sensor.

Turning now to the drawings, fig. 1 is a block diagram of an exemplary fluid reservoir (100) according to principles described herein. The fluid reservoir (100) may comprise a fluid chamber (101) for containing a fluid (120). The fluid reservoir (100) may be a stand-alone fluid containing device or may be fluidly and/or mechanically coupled to another device or system. For example, the fluid reservoir (100) may be fluidly and mechanically coupled to a fluid dispensing device, such as a printhead or a fluid ejection die, to serve as a source of fluid dispensed by the printhead or the fluid ejection die. The fluid (120) within the fluid reservoir (100) may be any fluid containing particles suspended within a fluid carrier.

The fluid reservoir (100) may include at least one impedance sensor (105) exposed to a fluid (120) within a fluid chamber (101) of the fluid reservoir (100). At least one impedance sensor (105) senses an impedance of the fluid (120) at a location of the impedance sensor (105), and determines a particulate carrier separation (PVS) level of the fluid within the fluid chamber (101) of the fluid reservoir (100) based on the sensed impedance. The impedance sensor (105) may also send an activation signal to a movable bracket (130) to which the fluid reservoir (100) is coupled based on the sensed impedance to agitate the fluid (120) within the fluid reservoir (100).

The at least one impedance sensor (105) may be any device capable of sensing an impedance value of the fluid (120). In one example, the impedance sensor (105) may be an electrode electrically coupled to a voltage or current source. The electrode may be a thin film electrode formed on an inner surface of a fluid chamber (101) within the fluid reservoir (100). In one example, when the fluid particle concentration is to be detected, a current may be applied to the electrodes and a voltage may be measured. In another example, when the fluid particle concentration is to be detected, a voltage may be applied to the electrodes and a current may be measured.

In examples where a fixed current is applied to the fluid (120) surrounding the at least one impedance sensor (105), the resulting voltage may be sensed. The sensed voltage may be used to determine an impedance of the fluid (120) surrounding the at least one impedance sensor (105) at a region within the fluid reservoir (100) in which the at least one impedance sensor (105) is located. Electrical impedance is a measure of the resistance presented to a current by the circuit formed by the at least one impedance sensor (105) and the fluid (120) when a voltage is applied to the impedance sensor (105) and may be expressed as follows:

where Z is the impedance in ohms (Ω), V is the voltage applied to the impedance sensor (105), and I is the current applied to the fluid (120) surrounding the impedance sensor (105). In another example, the impedance may be complex in nature, such that the impedance may have a capacitive element where the fluid (120) may act in part like a capacitor. For complex impedances, the current applied to the impedance sensor (105) may be applied for a specific time and the resulting voltage may be measured at the end of that time. The capacitance measured in this example may vary with the properties of the fluid (120): one such property of the fluid (120) is particle concentration.

The detected impedance (Z) is proportional to or corresponds to the concentration of particles in the fluid (120). In other words, the impedance (Z) is proportional to or corresponds to a level of dispersion of the particles within the fluid carrier of the fluid (120). In one example, if the impedance is relatively lower, this may indicate that there is a higher concentration of particles within the fluid (120) in the region where the concentration of particles is detected. Conversely, if the impedance is relatively higher, this indicates that there is a lower concentration of particles within the fluid in the region where the concentration of particles is detected. A lower concentration of particles within a portion of the fluid (120) may indicate that PVS has occurred, and remedial action may be taken to ensure that the concentration of particles is homogenized in all of the fluid within the fluid reservoir (100). Homogeneity may include homogeneity based on empirical homogeneity data, homogeneity based on original or manufactured homogeneity of the fluid (120), a threshold level of homogeneity, or a combination thereof.

In one example, when the impedance value reaches a maximum value or is within a threshold of the maximum value, this may indicate that the at least one impedance sensor (105) is not actually in contact with the fluid (120). In this case, the impedance value detected by the at least one impedance sensor (105) may be ignored when determining whether a remedial process, such as agitation of the fluid reservoir (100) by activation of the carriage (130), should be performed to cause the fluid (120) to be homogeneous again. Further, by receiving an input from the impedance sensors (315-1, 315-2) that none of the impedance sensors (315-1, 315-2) are exposed to the fluid (120) based on the detected maximum, those impedance values may be ignored in determining the PVS value of the fluid (120).

The output impedance values from the at least one impedance sensor (105) may be evaluated by a processing device, e.g., communicatively coupled to the at least one impedance sensor (105). the processing device may execute an evaluation module that evaluates detected impedance values for the raw or manufactured homogeneity values.

In one example including a plurality of impedance sensors (105), each impedance value detected by each of the impedance sensors (105) may be evaluated against those of L UT, and the remediation process may be initiated based on whether the detected PVS value of the fluid (120) is within a threshold concentration of particles indicated by a value of L UT.

In another example, acceptable homogeneity of a fluid (120) with respect to particle concentration may be based on empirical homogeneity data in this example, empirical homogeneity data may be obtained by testing the PVS values of the fluid (120) over a period of time, since time-varying impedance values are detected and recorded in L UT, the empirical homogeneity data may be stored in L UT L UT may be referenced in order to compare the current PVS values detected by the impedance sensor (105) to the empirical homogeneity data.

The remedial process for correcting the PVS condition of the fluid (102) and homogenizing the fluid (120) may include any process and use of any means of re-homogenizing the fluid (120) in terms of its concentration of particles. In one example, the remediation process can include agitating the fluid (120) within the fluid chamber (101). In one example, a fluid reservoir (100) may be movably coupled to a bracket (130). In this example, the carriage (130) may be a device that moves a fluid reservoir (100) from one location to another location in a printing system, where the fluid reservoir is fluidly coupled to fluid ejection dies, such as those found in a printhead. In this example, the fluid reservoir (100) may be a scanning cartridge in a printing apparatus. However, in another example, the fluid reservoir (100) may be movably coupled to the bracket (130) without being mechanically or fluidly coupled to another device. The carriage (130) may move the fluid reservoir (100), for example, in the direction indicated by arrow a. By moving the fluid reservoir (100) in the direction indicated by arrow a, the fluid (120) within the fluid chamber (101) may be agitated as the fluid moves within the fluid chamber (101) due to the movement of the fluid reservoir (100) relative to the carriage (130).

In one example, the cradle (130) may vigorously shake the fluid reservoir (100) sufficient to generate movement of the fluid (120) within the fluid chamber (101). In this example, shaking of the fluid reservoir (100) may occur at any intensity, duration, and number of shaking iterations.for example, an initial PVS value may be detected using the impedance sensor (105). The cradle (130) may vigorously shake the fluid reservoir (100) for a few seconds, and the impedance sensor (105) may perform subsequent PVS value detections using the impedance sensor (105). The subsequent PVS values may be compared to empirical homogeneity data in L UT, to raw or manufactured homogeneity data stored in L UT, to detected initial PVS values, or to a combination thereof.

If the detected PVS values after the initial or subsequent PVS detection instances are not homogeneous based on empirical homogeneity data, raw or manufactured homogeneity of the fluid (120), or a combination thereof, or are not within a threshold of these homogeneity bases, the cradle (130) may again vigorously shake the fluid reservoir (100) in order to again stir the fluid (120) and bring the fluid (120) closer to homogeneity. Thus, the process of detecting the PVS value of the fluid (120) and shaking the fluid reservoir (100) may be performed any number of times until the fluid (120) enters a homogeneous state.

In one example, in each iteration of the remediation process, the carriage (130) moves the fluid reservoir (100) multiple times (such as, for example, 20 round trips) in the direction indicated by arrow a until the difference between the measured PVS level and the expected or actual PVS value is within a certain increment or the same as the expected or actual PVS value.

Fig. 2 is a block diagram of an example fluid dispensing system (200) according to principles described herein. The fluid dispensing system may include: a movable carriage (130) for transporting the fluid reservoir (100); and a controller (201) for activating the movable carriage (130) to move the fluid reservoir (100) in at least one coordinate direction based on an impedance sensing particle carrier separation level of the fluid within the fluid reservoir (100). In this example, the fluid reservoir (100) may include the elements described herein in connection with fig. 1. The impedance sensor (105) of fig. 1 may be included within the fluid reservoir (100) of fig. 2, and may provide the PVS value to the controller (201). The controller (201) may then instruct the carriage (130) to move the fluid reservoir (100) in the direction indicated by arrow a in order to agitate the fluid (120) within the fluid reservoir (100), as described herein in connection with fig. 1.

Fig. 3 is a block diagram of another example fluid dispensing system (300) according to principles described herein. The fluid dispensing device (300) of fig. 3 includes similar elements as described herein in connection with fig. 1 and 2. The example of fig. 3 may include a sensing die (310) included within a fluid chamber (101) of a fluid reservoir (100). The sensing die (310) may be any substrate on which a functional element, such as at least one impedance sensor (105), may be formed. In one example, the sensing die (310) may be made of any number of silicon layers, and as described herein, may facilitate electrical coupling of, for example, the first impedance sensor (315-1) and the second impedance sensor (315-2) to other electrical components associated with the fluid reservoir (100).

The first impedance sensor (315-1) and the second impedance sensor (315-2) may be any device capable of sensing an impedance value of the fluid (120) and may function the same as the impedance sensor (105) of fig. 1. In one example, the first impedance sensor (315-1) and the second impedance sensor (315-2) may be electrodes electrically coupled to a voltage source or a current source. The electrodes may be thin film electrodes formed on an inner surface of a fluid chamber (101) of the fluid reservoir (100) and may be formed on the sensing die (310).

The sensing die (310) may extend along a height of the fluid chamber (101) such that the first impedance sensor (315-1) and the second impedance sensor (315-2) may be located at different levels of the sensing die (310) and at respective levels of the fluid (120) within the fluid chamber (101). In the example of fig. 3, the first impedance sensor (315-1) is not in contact with the fluid (120). In this example, the fluid (120) may have been depleted sufficiently to expose the first impedance sensor (315-1) to air within the fluid chamber (101) rather than the fluid (120) itself.

In contrast, the second impedance sensor (315-2) in the example of fig. 3 is located at the bottom of the sensing die (310) and is exposed to the fluid (120). In this case, the first impedance sensor (315-1) may detect the maximum impedance value because the first impedance sensor (315-1) is not exposed to any fluid (120). In contrast, the second impedance sensor (315-2) as depicted in fig. 3 is fully exposed to the fluid (120) and may detect the PVS value of the fluid (120) at that level of the fluid (120) within the fluid chamber (101).

In one example, the fluid reservoir (100) may include a fluid level sensor to detect a level of fluid (120) within the fluid reservoir (100). The fluid level sensor may be used in conjunction with the impedance values sensed by the first impedance sensor (315-1) and the second impedance sensor (315-2) to determine which impedance values should be considered and which impedance values should not be considered. For example, after an amount of fluid (120) is delivered to a fluidly coupled fluid ejection die (325), the first impedance sensor (315-1) may no longer be in physical contact with the fluid (120) in the fluid reservoir (100). As described herein, the first impedance sensor (315-1) may detect the maximum impedance value because the first impedance sensor (315-1) is not in contact with the fluid (120). Such impedance sensed by the first impedance sensor (110) should not be used to determine the particle concentration of the fluid (120). By receiving an input from the fluid level sensor that none of the impedance sensors (315-1, 315-2, collectively referred to herein as 315) are exposed to the fluid (120), those impedance values may be ignored. In one example, the impedance sensor (315) itself functions as a fluid level sensor. However, in another example, the fluid level sensor may be a separate element electrically coupled to the sensing die (310) in addition to being an impedance sensor (315) that detects a level of the fluid (120) within the fluid chamber (101).

In one example, each of the impedance values sensed by the impedance sensors (315) may be compared to determine which, if any, of the impedance sensors (315) is defective. In this example, a sanity check may be initiated to determine whether any sensed impedance values are unreasonable based on other sensed impedance values. For example, if five different impedance sensors (315) are included on the sensing die (310), wherein the vertical depth of four of the five impedance sensors (315) along the fluid (120) indicates a monotonic trend of moving down the sensing die (310), this may indicate that PVS has occurred. If a fifth impedance sensor (315) placed between the four other impedance sensors (315) indicates a relatively higher or lower concentration of particles that exceeds a threshold, this may indicate an abnormal or defective impedance sensor (315), and the sensed impedance from the fifth impedance sensor (315) may be ignored regardless of the level of fluid (120) within the fluid chamber (101). Alternatively, in another example, instead of ignoring the sensed impedance value of the fifth impedance sensor (315), the fifth impedance sensor (315) may reinitiate the impedance measurement to verify that the anomalous measurement is valid and repeatable. After repeating multiple iterations of the anomaly measurements, the sensed impedance from the fifth impedance sensor (315) may be ignored.

Fig. 4 is a block diagram of a fluid dispensing system (400) according to yet another example of principles described herein. The fluid dispensing system (400) of fig. 4 includes similar elements as described herein in connection with fig. 1-3. The example of fig. 4 may include a third impedance sensor (315-3) between the first and second impedance sensors (315-1, 315-2). The example of fig. 4 is included to demonstrate that any number of impedance sensors (315) may be included on the sensing die (310), and that these impedance sensors (315) may be used to detect PVS values at different levels of fluid (120) within the fluid chamber (101), and may be used to detect the level of fluid (120) within the fluid chamber (101) with a granularity and accuracy defined by the number of impedance sensors (315) included on the sensing die (310).

Fig. 5 is a flow chart depicting a method (500) of correcting particle carrier separation within a fluid (120), according to an example of principles described herein. The method may include receiving (block 501) a first sensed impedance value of a fluid (120) from a first impedance sensor (315-1) located at a first fluid level within a fluid reservoir (100). A first impedance sensor (315-1) may be coupled to sense a first level of a mold (310). The method may also include receiving (block 502) a second sensed impedance value of the fluid from a second impedance sensor (315-2) located at a second fluid level within the fluid reservoir (100). A second impedance sensor (315-2) may be coupled to sense a second level of the mold (310).

A particle carrier separation (PVS) level of the fluid (120) may be determined based on a first sensed impedance at the first impedance sensor (315-1) and a sensed impedance at the second impedance sensor (315-2) (block 503). When the fluid (120) is located in the fluid reservoir (100), sedimentation of pigment within the fluid carrier of the fluid (120) may occur, and PVS occurs. Because the pigment within the fluid (120) settles to the bottom and the second impedance sensor (315-2) is located at a lower level of the fluid (120) than the first impedance sensor (315-1), the PVS value detected by the first impedance sensor (315-1) may be higher than the PVS value detected by the second impedance sensor (315-2). In another example, the PVS values detected by the first and second impedance sensors (315-1, 315-2) may be compared to empirical homogeneity data, homogeneity based on raw or manufactured homogeneity of the fluid (120), a threshold level of homogeneity, or a combination thereof.

Although the first and second impedance sensors (315-1, 315-2) are described in connection with blocks 501-503, any number of impedance sensors (315) and their detected PVS values may be used to determine (block 503) the PVS level of the fluid (120). Further, the method may include sending (block 504) an activation signal to a movable carriage (130) to which the fluid reservoir (100) is coupled to move the fluid reservoir (100) in a coordinate direction based on the particle carrier separation level of the fluid (120) to agitate the fluid (120) within the fluid reservoir (100).

With respect to fig. 5, the method may further comprise: receiving a third sensed impedance value of the fluid (120) from a third impedance sensor (315-3); and determining a particle carrier separation level of the fluid based on the first sensed impedance at the first impedance sensor, the sensed impedance at the second impedance sensor, and the third sensed impedance at the third impedance sensor. Further, in one example, the gradient of particle carrier separation within the fluid (120) may be compared to gradient values maintained in a lookup table to determine PVS levels between any of the first, second, and third impedance sensors.

Fig. 6 is a flow chart depicting a method (600) of correcting particulate carrier separation within a fluid (120), according to an example of principles described herein. The method (600) may include measuring (block 601) a plurality of PVS delta values in a plurality of impedance sensors (315) coupled to a sensing die (310) along a length of the sensing die (310). The impedance sensors (315) may each measure different PVS values because the pigment separates from the fluid carrier of the fluid (120) as the pigment settles in the fluid chamber (101) of the fluid reservoir (100).

The incremental value measured in the impedance sensor (315) may be above or below a threshold value. Accordingly, the method (600) may include determining (block 602) whether an incremental value measured in the impedance sensor (315) is above a threshold, wherein an incremental value above the threshold indicates that PVS has occurred within the fluid (120) to an extent that may be corrected. Accordingly, in response to a determination (block 602, yes determination) that the increment value is above the threshold, the carriage (130) may be activated (block 604) so as to cause agitation of the fluid (120) within the fluid chamber (101). The method may then loop back to block 601 to allow another measurement of the PIVS value, and a determination of the PVS delta may be made to determine whether another iteration of agitation of the fluid at block 604 may be performed. Conversely, in response to a determination that the delta value is not above the threshold (block 602, no determination), a different operation may be performed, such as, for example, a multiple printing operation or other operation in which fluid in a non-PVS state may be used because the pigment of the fluid (120) is not separated from its fluid carrier. The method may loop back to block 601 to allow another measurement of the PIVS value, and a determination of PVS delta may be made to determine whether the pigment within the fluid (120) has not settled and may be used for other operations.

The specification and drawings describe a fluid reservoir. The fluid reservoir may include a fluid chamber for containing a fluid, and an impedance sensor exposed to the fluid within the fluid chamber. The impedance sensor senses an impedance at the impedance sensor, determines a level of particle carrier separation of the fluid within the fluid chamber based on the sensed impedance, and sends an activation signal to a movable carrier to which the fluid reservoir is coupled to agitate the fluid within the fluid reservoir based on the sensed impedance.

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