WO2021150211A1

WO2021150211A1 - Capacitive fluid level sensing

Info

Publication number: WO2021150211A1
Application number: PCT/US2020/014423
Authority: WO
Inventors: Jody L Clayburn; Russell Sterling SAUER; Robert Yraceburu
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-01-21
Filing date: 2020-01-21
Publication date: 2021-07-29

Abstract

An example fluid dispenser includes: a reservoir for holding a fluid; a capacitive level sensor disposed in the reservoir and extending between a lower fluid level and an upper fluid level of the reservoir; a first conductive pin extending into the reservoir to terminate at the lower fluid level, to detect that a current level of the fluid is at the lower fluid level; and a second conductive pin extending into the reservoir to terminate at the upper fluid level, to detect that the current level of the fluid is at the upper fluid level.

Description

CAPACITIVE FLUID LEVEL SENSING

BACKGROUND

[0001] Fluid dispensing devices, such as ink cartridges for printers, may include reservoirs holding fluid (e.g. ink) to be dispensed. The devices may also include mechanisms to determine a volume of fluid contained in the reservoir. Such mechanisms may be subject to constraints on available space, manufacturing cost, or the like.

BRIEF DESCRIPTIONS OF THE DRAWINGS [0002] FIG. 1 is a diagram of a fluid dispenser.

[0003] FIG. 2 is a diagram of the fluid dispenser with fluid at an upper fluid level.

[0004] FIG. 3 is a diagram of the fluid dispenser with fluid at a lower fluid level.

[0005] FIG. 4 is a diagram of the fluid dispenser with fluid at an intermediate fluid level.

[0006] FIG. 5 is a flowchart of a method of self-calibration and fluid level detection.

DETAILED DESCRIPTION

[0007] To provide continuous sensing of fluid level in a reservoir of a fluid dispensing device, a primary capacitive sensor may be provided within the reservoir. For example, the reservoir may hold printing fluid for application by a printing system. The primary capacitive sensor may extend at least a portion of a length of the cartridge, e.g. between a low level and a full level. A current level of fluid (e.g. ink or other printing fluid) within the reservoir may be determined from an output signal of the primary capacitive sensor, indicating a proportion of the primary capacitive sensor that is in contact with the fluid.

[0008] To generate a fluid level, e.g. expressed as a fraction of the total capacity of the reservoir, from the output signal of the primary capacitive sensor, the fluid dispensing device may include additional calibration sensors. The calibration sensors can include a capacitive sensor disposed within the reservoir at a full position, and a capacitive sensor disposed within the reservoir at a low position. The calibration sensors thus serve to detect when the current fluid level in the reservoir has reached a low level or a full level. The output signal of the primary capacitive sensor when a low or full level is detected via a calibration sensor can be stored as a boundary value. With upper and lower boundary values, intermediate fluid levels can be determined from output signals of the primary capacitive sensor, e.g. via linear interpolation.

[0009] The use of capacitive calibration sensors as mentioned above may increase the manufacturing cost of the fluid dispensing device, however. In addition, capacitive calibration sensors may be difficult to accommodate physically within the reservoir. Further, the capacitive calibration sensors may provide ambiguous level detections for the above-mentioned low and full levels, increasing the complexity of the calibration procedure.

[0010] To provide continuous fluid level sensing for fluid dispensing devices, while reducing manufacturing costs and the physical footprint of the sensing mechanism and increasing calibration accuracy, a hybrid fluid level sensing system includes a capacitive sensor and conductive pin calibration sensors.

[0011] FIG. 1 shows a cross sectional view of a fluid dispenser 100. The fluid dispenser 100 includes a housing 104 that defines a fluid reservoir 108 therein. The fluid reservoir 108 is to contain a fluid, such as printer ink, liquid printer toner, or the like. The fluid dispenser 100, in other words, can be a printer cartridge that stores ink or toner and dispenses ink or toner to a print head for application to print media. The fluid dispenser 100 may also be used by a 3D printer to apply fluid to a bed of material. The fluid dispenser 100 therefore also includes at least one outlet 112, to dispense fluid e.g. towards the print head, and at least one inlet 116 to receive fluid to replenish the reservoir 108. In some examples, multiple outlets 112 may be provided. In some examples, multiple inlets 116 may also be provided.

[0012] The fluid dispenser 100 also includes a sensing system to provide continuous sensing of a level of fluid within the reservoir 108. The sensing system includes a capacitive level sensor 120, which may be disposed within the reservoir 108 as illustrated, or placed outside the housing 104, e.g. against an outer wall of the housing 104. The capacitive level sensor 120 can include a gap 124 between plates thereof. Depending on a current level of fluid within the reservoir 108, the portion of the capacitive level sensor 120 in contact with the fluid changes, and an output signal of the capacitive level sensor 120 therefore also changes. The fluid dispenser 100 also includes a controller 128 connected with the capacitive level sensor 120. The controller 128 can be implemented as at least one microcontroller, sensing circuit, field-programmable gate array (FPGA), or the like.

[0013] The controller 128 receives a sequence of output signals, e.g. at a predetermined frequency, from the capacitive level sensor 120. For each output signal, the controller 128 determines an indication of a current fluid level within the reservoir 108. The current fluid level as determined by the controller 128 can be expressed as a fraction (e.g. a percentage, a score between predetermined extremes, or the like) of a “full” volume of the reservoir 108. The determination of the current fluid level by the controller 128 can be performed via interpolation, such as linear interpolation, between boundary values that may also be referred to as calibration values.

[0014] The boundary values mentioned above indicate output signals from the capacitive level sensor 120 that correspond, respectively, to an upper fluid level 132 and a lower fluid level 136 (also referred to as upper and lower boundary levels). In other words, an upper boundary value is the output of the capacitive level sensor 120 when the fluid within the reservoir 108 is at the upper fluid level 132. The lower boundary value is the output of the capacitive level sensor when the fluid within the reservoir as at the lower fluid level 136. The capacitive level sensor 120 therefore extends at least between the upper fluid level 132 and the lower fluid level 136. In the illustrated example, the capacitive level sensor 120 extends beyond both the upper fluid level 132 and the lower fluid level 136. Intermediate fluid levels, that is fluid levels between the upper fluid level 132 and the lower fluid level 136, can be interpolated based on the boundary values and the current output signal of the capacitive level sensor 120.

[0015] The upper fluid level 132, which may also be referred to as a full level, represents a level beyond which filling the reservoir 108 may result in damage to the fluid dispenser 100, spillage, leakage or the like. The lower fluid level 136, which may also be referred to as a low level, represents a level below which the reservoir 108 contains too little fluid to reliably dispense fluid via the outlet 112. [0016] The fluid dispenser 100 also includes components to detect when the fluid level within the reservoir 108 reaches the upper fluid level 132 or the lower fluid level 136. Further, the fluid dispenser 100 includes components enabling the updating of the above- mentioned boundary or calibration values. That is, the fluid dispenser enables self calibration of the capacitive level sensor 120.

[0017] In particular, the fluid dispenser 100 includes a first conductive pin 140 extending into the reservoir 108 to terminate at the lower fluid level 136, and a second conductive pin 144 extending into the reservoir 108 to terminate at the upper fluid level 132. The first and second conductive pins 140 and 144 can extend into the reservoir 108 from a sensor mount 148, which can also support the capacitive level sensor 120. In the illustrated example, the sensor mount 148 is coupled to an upper portion of the housing 104.

[0018] The fluid dispenser 100 also includes a drive pin 152 extending (e.g. from the sensor mount 148) into the reservoir 108 to term inate at or below the lower fluid level 136. The controller 128 applies a drive signal to the fluid in the reservoir 108 via the drive pin 152. The drive signal is detected by either or both of the first and second conductive pins 140 and 144, depending on the level of the fluid within the reservoir 108. Specifically, if a given one of the conductive pins 140 and 144 is in contact with the fluid, that conductive pin 140 or 144 detects the drive signal. The conductive pins 140 and 144 are connected to the controller 128, and the controller 128 determines, based on signal detections from the conductive pins 140 and 144, whether the fluid level within the reservoir 108 has reached the upper fluid level 132 or the lower fluid level 136.

[0019] Turning to FIG. 2, the fluid dispenser 100 is shown with a fluid level 200 that is at the predetermined upper fluid level 132. As shown in FIG. 2, for the fluid level 200 and any fluid levels above the fluid level 200, both the first conductive pin 140 and the second conductive pin 144 are in contact with the fluid. The conductive pins 140 and 144 therefore detect drive signals applied to the reservoir 108 via the drive pin 152. When both conductive pins 140 and 144 detect the drive signals, the controller 128 can determine that the fluid level has reached the upper fluid level 132. In response to such a determination, the controller 128 can update an upper boundary value. That is, a current upper boundary value can be replaced with an output signal from the capacitive level sensor 120 that is contemporaneous with the detection that the fluid level 200 has reached the upper fluid level 132.

[0020] Turning to FIG. 3, the fluid dispenser 100 is shown with a fluid level 300 that has fallen below the predetermined lower fluid level 136. For the fluid level 300 and any fluid levels below the fluid level 300, neither of the conductive pins 140 and 144 is in contact with fluid in the reservoir 108. Therefore, neither of the conductive pins 140 and 144 detects drive signals applied via the drive pin 152. The controller 128 can, in response to determining that neither conductive pin 140 and 144 is in contact with the fluid, update the lower boundary value. Specifically, a current lower boundary value can be replaced with an output signal from the capacitive level sensor 120 that is contemporaneous with the detection that the fluid level 300 has fallen below the lower fluid level 132. As seen in FIGS. 1-4, the capacitive level sensor 120 extends below the lower fluid level 136, and therefore still produces an output signal indicative of fluid level in the scenario shown in FIG. 3.

[0021] Turning to FIG. 4, the fluid dispenser 100 is shown with a fluid level 400 that is intermediate, i.e. falling between the predetermined upper fluid level 132 and lower fluid level 136. The controller 128 can generate an indication of the current fluid level based on an output signal from the capacitive level sensor 120, and on the boundary values mentioned above. For example, the controller 128 can interpolate (e.g. via linear interpolation) the indicator based on the boundary values which represent, for example, indicators of 0% (empty) and 100% (full).

[0022] Turning to FIG. 5, and as will also be apparent from the discussion above, the controller 128 can implement a method for monitoring fluid levels via the hybrid sensing system of FIGS. 1-4.

[0023] FIG. 5 illustrates a flowchart of a method 500. The method 500 can be performed, for example, by the controller 128. At block 505, the controller 128 receives an output signal from the capacitive level sensor 120. At block 510, the controller 128 determines whether the current fluid level in the reservoir 108 has reached a boundary level. That is, at block 510 the controller 128 determines whether the fluid level has reached the upper fluid level 132, as shown in FIG. 2, or has fallen below the lower fluid level 136, as shown in FIG. 3.

[0024] The determination at block 510 is based on which of the conductive pins 140 and 144 are in contact with fluid in the reservoir. When neither conductive pin 140 and 144 is in contact with fluid, the determination at block 510 is that the lower boundary level has been reached, and the controller 128 proceeds to block 515. When both conductive pins 140 and 144 are in contact with fluid, the determination at block 510 is that the upper boundary level has been reached, and the controller 128 proceeds to block 520. When the conductive pin 140 is in contact with the fluid, but the conductive pin 144 is not in contact with the fluid, the determination at block 510 is that neither boundary level has been reached, and the controller 128 proceeds to block 525.

[0025] At block 515, the controller 128 updates the lower boundary value as discussed above, by selecting an output signal from a sequence of output signals produced by the capacitive level sensor 120 that corresponds to the detection of the fluid having reaching the lower fluid level 136. The selected output signal is stored as the new lower boundary value, e.g. replacing a previous lower boundary value. The controller 128 can also generate an alert, for example indicating that the reservoir 108 is empty or approaching empty, for communication to a central printer controller or other computing hardware and display or other subsequent processing.

[0026] At block 520, the controller 128 updates the upper boundary value as discussed above, by selecting an output signal from a sequence of output signals produced by the capacitive level sensor 120 that corresponds to the detection of the fluid having reaching the upper fluid level 132. The selected output signal is stored as the new upper boundary value, e.g. replacing a previous upper boundary value. The controller 128 can also generate an alert, for example indicating that the reservoir 108 is full, for communication to a central printer controller or other computing hardware and display or other subsequent processing.

[0027] At block 525, the controller 128 retrieves the current boundary values (e.g. as updated via blocks 515 and 520), and generates an indication of a current fluid level within the reservoir 108 based on the boundary values and a current output signal from the capacitive level sensor 120. At block 530 the controller 128 can provide the indication of the current fluid level to another component, such as a printer controller coupled to the controller 128, for display and/or other processing.

[0028] It should be recognized that features and aspects of the various examples provided above can be combined into further examples that also fall within the scope of the present disclosure. In addition, the figures are not to scale and may have size and shape exaggerated for illustrative purposes.

Claims

1. A fluid dispenser, comprising: a reservoir for holding a fluid; a capacitive level sensor; a first conductive pin extending into the reservoir to terminate at a lower fluid level of the reservoir, to detect that a current level of the fluid is at the lower fluid level; and a second conductive pin extending into the reservoir to terminate at an upper fluid level of the reservoir, to detect that the current level of the fluid is at the upper fluid level.

2. The fluid dispenser of claim 1 , further comprising a controller to: generate an indication of the current level of the fluid based on output of the capacitive level sensor and upper and lower boundary values corresponding to the capacitive level sensor.

3. The fluid dispenser of claim 2, wherein the controller is to, responsive to a level detection by at least one of the first conductive pin and the second conductive pin, update at least one of the upper and lower boundary values.

4. The fluid dispenser of claim 1 , further comprising: a sensor mount adjacent to the upper fluid level of the reservoir, wherein the first and second conductive pins extend from the sensor mount towards the lower fluid level.

5. The fluid dispenser of claim 1 , further comprising: a drive pin extending into the reservoir to terminate at or below the lower fluid level and to apply a signal to the fluid for detection by at least one of the first and second conductive pins.

6. The fluid dispenser of claim 1 , wherein the capacitive level sensor extends from the lower fluid level to the upper fluid level.

7. The fluid dispenser of claim 1 , further comprising an inlet for receiving fluid into the reservoir, and an outlet for dispensing fluid from the reservoir.

8. The fluid dispenser of claim 7, wherein the fluid is an ink.

9. A sensing system, comprising: a capacitive level sensor to extend between an upper fluid level and a lower fluid levels of a reservoir, the capacitive level sensor to generate an output signal indicating a portion of the capacitive level sensor in contact with a fluid; a first conductive pin to terminate at the lower fluid level; a second conductive pin to terminate at the upper fluid level; and a controller coupled to each of the capacitive level sensor, the first conductive pin and the second conductive pin, the controller to: determine lower and upper boundary values for the capacitive level sensor based on output of the first conductive pin and output of the second conductive pin; and determine a current fluid level based on the upper and lower boundary values and the output signal of the capacitive level sensor.

10. The sensing system of claim 9, further comprising a sensor mount supporting each of the capacitive level sensor, the first conductive pin and the second conductive pin, the sensor mount to engage with a housing defining the reservoir.

11. The sensing system of claim 9, further comprising a drive pin to terminate at the lower fluid level and to apply a signal to the reservoir.

12. A method, comprising receiving a sequence of outputs from a capacitive level sensor in a fluid reservoir; responsive to detecting at least one of a lower boundary level of the fluid and an upper boundary level of the fluid via respective first and second conductive pin sensors in the fluid reservoir, updating at least one of an upper boundary value and a lower boundary value; retrieving current upper and lower boundary values; and based on current upper and lower boundary values and a current output from the sequence of outputs, determining a fluid level in the fluid reservoir.

13. The method of claim 12, wherein updating at least one of an upper boundary value and a lower boundary value includes: selecting one of the outputs from the sequence of outputs of the capacitive level sensor that corresponds to the detection of the at least one of the lower boundary level and the upper boundary level; and updating the at least one of the upper boundary value and the lower boundary value with the selected output.

14. The method of claim 12, further comprising: responsive to detecting the at least one of the lower boundary level and the upper boundary level, generate an alert.

15. The method of claim 12, further comprising providing the fluid level to a printer controller.