Patent Application
20130050313
This invention relates to fluid level sensing and more particularly to ink tank level sensing.
Ink level detection in a printhead is required in printing systems where the main volume of liquid ink is stored in a reservoir away from the printhead. In order to perform full color printing, four kinds of inks, i.e., cyan ink, magenta ink, yellow ink and black ink, must be used. Accordingly, color printers may include four different fluid reservoirs, one reservoir for each type of ink. As the printhead consumes ink, the reservoirs periodically need to be refilled. Sensors are used to detect whether or not the printhead has adequate ink.
There are numerous methods by which liquid ink detection has previously been performed. Most of these methods rely on the electrical conductivity of the ink and use the ink to complete a “sensing” circuit. In these systems the reservoir containing the ink is frequently made of a conductive material and forms part of the circuit. A probe made of conductive material, either a metal protrusion insulated from the reservoir or a conductive pad on an insulated circuit board, is used as the sensor and the ink bridges the space between the probe and the reservoir to complete the circuit.
These sensing systems suffer from various shortcomings. For example, the systems typically have limited sensitivity leading to inaccuracies and some systems are unable to detect various inks, particularly those with low levels of conductivity.
Thus, printers having sensing systems with good sensitivity or that sense an ink level without relying on the conductive properties of the reservoir containing the fluid would be beneficial.
An ink level sensing system that exhibits good sensitivity is described herein. The system includes a first probe having a first active surface, a second probe having a second active surface facing the first active surface, a memory in which data indicative of a conductivity curve and command instructions are stored, and a processor configured to execute the command instructions to associate a level of fluid in a reservoir with a first signal indicative of the electrical coupling between the first active surface and the second active surface with reference to the data indicative of a conductivity curve.
In accordance with another embodiment, a method of sensing the level of at least one fluid in a device includes applying a voltage to a first probe in a first reservoir to generate a first calibration current, receiving the first calibration current with a first surface of a second probe, obtaining a plurality of first data indicative of the received first calibration current, associating each of the plurality of first data with a different one of a plurality of surface areas of the first surface contacting a first fluid in the first reservoir, storing the associated plurality of first data in a memory, applying the voltage to the first probe to generate a first operational current, receiving the first operational current with the first surface of the second probe, obtaining a first signal indicative of the received first operational current, and associating the first signal with one of the plurality of first data.
Pursuant to yet another embodiment, a printer device includes at least one reservoir for storing ink used by the device, a first driver probe positioned within the at least one reservoir, a sense probe positioned within the at least one reservoir and spaced apart from the first driver probe, a boot supporting the first driver probe and the sense probe, the boot configured to electrically isolate the first driver probe and the sense probe from each other and from the at least one reservoir, a memory in which data indicative of a conductivity curve associated with ink stored in the at least one reservoir and command instructions are stored, and a processor configured to execute the command instructions to associate a level of the ink in the at least one reservoir with a signal indicative of the electrical coupling between the first driver probe and the sense probe using the data indicative of a conductivity curve.
With initial reference to
The probe assemblies 102, 104, 106, and 108 are identically formed in this embodiment and are further described with reference to the probe assembly 102 depicted in
The sense probe 130 includes a shank portion 140 and a plate portion 142. The sense probe 130 and the prong 136 are integrally formed as a sense member 144. In this embodiment, the sense member 144 is formed from a single sheet of conductive material, such as stainless steel, which can be easily stamped and formed into the desired shape.
Similarly, the driver probes 132 and 134 and the prong 138 are integrally formed as a drive member 150 which can be formed from a single sheet of conductive material such as stainless steel which can be easily stamped and formed into the desired shape. The drive member 150 includes a crossbar 152 which joins the driver probes 132 and 134. The driver probes 132 and 134 include shank portions 154 and 156 and plate portions 158 and 160, respectively. A curved section 162 joins the shank portion 154 and the plate portion 158 while a curved section 164 joins the shank portion 156 and the plate portion 160.
The sense member 144 and the drive member 150 are supported by a boot 170. The boot 170 includes a platform 172, a seal portion 174 and a barb portion 176. A sleeve 178 extends downwardly from the lower surface of the barb portion 176. The boot 170 in this embodiment is made of silicone rubber, but other elastomeric materials could also be used.
The probe assembly 102 may be manufactured by inserting the sense member 144 and the drive member 150 into a compression mold, and then over-molding the silicone rubber material of the boot 170 around them. Alternatively, multiple materials may be overlaid in multiple steps or by other processes. Additionally, while the sense probe 130 the driver probes 132 and 134 may be constructed from the same metal and in the particular shapes shown herein, a probe, which is an electrically conductive member, may be made from any conductive material in sheet or other form. Additionally, the shapes of the probes may be modified for different applications.
The sensor assembly 100 may be used with the tank 180 of
Other ports (not shown) may be provided for each of the reservoirs 182, 184, 186, and 188 for other purposes such as for filling and draining. The ports 190, 192, 194, and 196, however, are configured to allow for sensing of a fluid level within the respective reservoir. Accordingly, each of the ports 190, 192, 194, and 196 is sized to receive a probe assembly such as probe assembly 102. Referring to
Insertion of the probe assembly 102 in the direction of the arrow 200 continues until the barb portion 176 is adjacent the port 190. As shown in
The seal portion 174 also has a diameter larger than the diameter of the port 190, although smaller than the diameter of the barb portion 176. Accordingly, continued pressure in the direction of the arrow 200 causes the seal portion 174 to deform and enter into the port 190. The distance between the top of the barb portion 176 and the bottom of the platform 172 is selected to be just slightly less than the wall thickness of the tank 180 about the port 190. Accordingly, as the platform 172 contacts the tank 180, continued pressure in the direction of the arrow 200 causes deformation of the platform 172 sufficient to force the barb portion 176 through the port 190 and into the reservoir 182 and the barb portion 176 flexes back to its un-deformed shape. The diameter of the platform 172 is larger than the diameter of the port 190, however, and the shape of the platform 172 is selected to inhibit movement of the platform 172 fully into the port 190. Accordingly, the platform 172 does not deform to the extent necessary to fit within the port 190.
At this point, the probe assembly 102 is in the condition shown in
Similarly, the probe assemblies 104, 106 and 108 may be inserted into the ports 192, 194, and 196 and electrically connected to form the sensor assembly 100 as depicted in
The memory 214 is programmed with command instructions which, when executed by the processor 212, provide performance of various control functions. In one embodiment, the processor 212 executes command instructions which associate a signal received from the sensor assembly 100 with a fluid level within the tank 180 in accordance with the procedure 220 of
The description of process 220 continues herein with reference to the probe assembly 102, but the process applies as well to the operation of the probe assemblies 104, 106, and 108. The applied voltage is connected through supply lead 112 to the prong 138 of the probe assembly 102 (see
The received current is measured (block 228). The processor 212 then associates the measured current with a fluid level for the reservoir 182 (block 230) and the process 220 ends (block 232). Data obtained or derived during execution of the process 220 may be stored for use by other processes.
Association of the received signal with a fluid level is possible by insertion of the sensor assembly 100 into a tank wherein the fluid being measured has a conductivity that is significantly different from the fluid, such as air, which replaces the measured fluid. In such a system, the resistance experienced by current passing between the probe surfaces can be shown as:
wherein:
The resistance to passing a current is thus a function of the fluid located between the probes. When the sensor assembly 100 is used in an ink printing device, the fluid between the probes is ink, air, or a combination of ink and air. The liquid ink has a significantly higher conductivity than the air. Accordingly, as the ink forms a current path between the driver probes 132 and 134 and the sense probe 130, the total resistance to passing the signal decreases. Thus, the magnitude of the transmitted current received by the sense probe 130 increases.
The transmissivity factor is a function of other variables which affect the magnitude of the transmitted current received by the sense probe 130 such as the distance between the probes and the surface area of the probes through which current flows from the driver probes 132 and 134 to the sense probe 130. This relationship can be shown as:
wherein:
Thus, for a given applied current with a constant distance between probes, an increase in the surface transmission/reception area results in a smaller transmissivity constant. Accordingly, the resistance to passage of a current between the probes decreases. As the resistance to passage of a current decreases, the received current increases. Additionally, as the distance between the probes decreases, the transmissivity constant decreases and the resistance to passage of a current between the probes decreases.
In general, as the magnitude of the received current increases, the sensitivity of the system to changes in resistance to the passing of current increases. Thus, optimal sensitivity is achieved by minimizing the distance between probes and maximizing the surface area of the probes. The minimization of distance between probes and the surface area of the probes, however, are constrained by the particular application.
With reference to the distance between the probes, a fluid begins to “wick” or draw up between the probes as the distance between the probes is reduced. The sensed level of fluid in a system wherein wicking is occurring in the sensor is higher than the actual level in the system. The error is exacerbated as the fluid level decreases because the surface tension of the fluid acts to keep the fluid in contact with areas of the probe that have previously been wetted, even if the actual fluid level has been lowered. In extreme cases, wicking can result in “bridging” between probes, wherein the surface tension of the fluid maintains the wicked fluid between the probes even when the fluid in the remainder of the system is no longer in contact with the probes. For particular ink systems, maintaining a minimum of about 2 millimeters distance between adjacent surfaces reduces the effects of wicking to an acceptable level.
The area of the probes that can be used in a particular system is also constrained. In the tank 180 of
The surface area through which current is passed for a driver probe/sense probe combination can be increased by shaping the probes differently. By way of example, a driver probe 240 and a sense probe 242 are shown in
Thus, the driver probe 240 and the sense probe 242 are much more sensitive than the driver probe 230 and the sense probe 232. The manufacturing costs, however, of the driver probe 240 and the sense probe 242 are greater than the manufacturing costs for the driver probe 230 and the sense probe 232 because of the more complicated shape.
An alternative approach to increasing sensitivity without the same increase in manufacturing costs incurred with the driver probe 240 and the sense probe 242 is to utilize two surfaces of a sense probe to pass current. For example, the system 250 shown in
In order to maintain a spacing of 2 millimeters between each of the probes, the cross-sectional length of the probes in the system 250 must be reduced as compared to the cross-sectional length of the driver probe 230 and the sense probe 232. In this embodiment, the driver probes 252 and 254 and the sense probe 256 have a length of just over 7 millimeters. Both active surfaces 262 and 264 of the sense probe 256, however, receive current from a driver probe 252 and 254, respectively as indicated by the arrows 266. Accordingly, each millimeter change in liquid level along the height of the system 250 results in an area change which is greater than 14 square millimeters. Accordingly the sensitivity of the system 250 is greatly increased as compared to the driver probe 230 and the sense probe 232 without making the manufacture of the system substantially more complicated.
The probe assembly 102 of
The plate portions 142, 158 and 160 in this embodiment are spaced 2 millimeters apart to reduce the potential for wicking while maintaining good sensitivity. As shown in
Specifically, when ink reaches the bottom of the barb portion 176 of the probe assembly 102, the boot 170 provides an additional surface to which the ink or other fluid can adhere. Accordingly, a permanent surface tension bridge can be created which spans a distance larger than the distance at which wicking for the particular fluid occurs. A permanent fluid bridge between two active surfaces would produce a constant current path, resulting in an artificially high received current. Providing the non-conductive sleeve 178 about the shank portion 140 of the sense probe 130 prevents any fluid bridging on the bottom of the barb portion 176 from joining two active surfaces.
Comparing the cross-sections of the shank portions 154 and 156 of
The conductivity curve 280 shown in
The conductivity curve portion 282 exhibits three distinct characteristics. As the ink level in the tank first reaches the bottom of the sense probe 130, the received current suddenly increases at segment 286 because the conductivity of the ink is greater than the conductivity of air. The value to which the received current rises is normalized to 100% in the
If desired, the sudden increase characteristic may be used as a level indicator to indicate whether or not the measured fluid is at a particular level in the tank. In such embodiments, a processor may be controlled to detect the sudden increase using data from a probe assembly, such as one or more of the probe assemblies 102, 104, 106, and 108, compared to single threshold value. The threshold value may be established at a value less than the value to which the received current is expected to rise to provide a robust system. Such values may be between about 25% and 50% of the value to which the received current is expected to rise. According to this embodiment, the entire conductivity curve 280 need not be stored for use by the processor.
Continuing with the conductivity curve 280, a substantially linear segment 288 extends from 0 to about 4 millimeters, corresponding to increased current received by the probe 130 as the level of fluid increases from the bottom of the plate portion 142 to the bottom of the non-conductive sleeve 178. The conductivity curve portion 282 then exhibits a curved segment 290 indicating decreased sensitivity to change in fluid level as the level of fluid continues to increase along the active shank portions 154 and 156 of the driver probes 132 and 134, respectively, to the bottom of the boot 170 at 8 millimeters. If desired, the driver probes 132 and 134 and/or the sense probe 130 could be of a non uniform shape in one or more axes to compensate for the non-linearity or to alter the conduction slope relative to volume.
As the ink level is lowered, the value of the received calibration current (conductivity curve portion 284) is consistently greater than the value of the calibration current received as the ink level was raised (conductivity curve portion 282) for a given level below about 7 millimeters. This difference is the result of the resistance to movement of fluid between the sense probe 130 and the driver probes 132 and 134 produced by surface tension of the ink. Thus, a portion of the probes located above the nominal level of the fluid remains in contact with the fluid as the fluid level is lowered.
The shape of the conductivity curve portion 284 above the 0 millimeter mark is similar to the conductivity curve portion 282 with a curved segment 292 extending from about 7 millimeters to about 4 millimeters followed by a substantially linear segment 294 down to 0 millimeters. Below 0 millimeters, the conductivity curve portion 284 exhibits a second curved segment 296 which is explained with reference to
As shown in
Accordingly, the conductivity curves 282 and 284 may be obtained for a particular fluid exhibiting a particular conductivity through a calibration procedure and thereafter used to associate the received current with the level of fluids in the tank 180 during operation of the device using the fluid. In the event the fluids in the reservoirs 182, 184, 186, and 188 vary from each other, different conductivity curves may be generated for each fluid. Data reflective of the conductivity curve or curves may then be stored within the memory 214 (
Depending upon the accuracy desired, data indicative of both conductivity curve portion 282 and conductivity curve portion 284 may be stored in the memory 214. The storage of this data allows the data indicative of conductivity curve portion 282 to be used for recalibration of the curve 280, as discussed below, and level determination as the reservoir 182 is filled while the data indicative of conductivity curve portion 284 is used for associating received operational signals with a fluid level as the fluid level decreases.
In addition to being used to identify the absence or presence of a fluid, the sudden rise characteristic of the conductivity curve 282 at the segment 286 of
For embodiments wherein the initial increase in conductivity is used to calibrate the system, the sense probe may be shortened to reduce the introduction of errors in the event the tank is not level or in the event the surface of the fluid is not level, such as when ripples on the surface of the fluid are generated during fill operations.
By way of example,
As the level of the fluid 320 increases to the level 322, the fluid 320 first contacts the driver probe 316 and then the sense probe 314. Thus, when the fluid 320 rises to the level 322, a current path exists between both the driver probe 316 and the sense probe 314 and the driver probe 318 and the sense probe 314.
In contrast,
In a further embodiment, a probe assembly is provided with a removable tank. Referring to
A probe assembly 338 is mounted on the cartridge 336. The probe assembly 338 is substantially the same as the probe assemblies 102, 104, 106, and 108. Rather than a connector such as the connector 110, however, the probe assembly 338 is controlled through a printed circuit board. Thus, supply lead 340 and a return lead 342 extend between the probe assembly 338 and a printed circuit board (not shown) within the housing of the cartridge 336. Although the printer 330 includes a single removable cartridge, in other embodiments multiple removable cartridges are provided in a printer, each of the cartridges including a probe assembly.
Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. Moreover, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.
This document claims priority to co-pending U.S. patent application Ser. No. 12/164,714, which was filed on Jun. 30, 2009 and is entitled “Fluid Level Sensing System And Method.” The co-pending application issued as U.S. Pat. No. ______ on mm/dd/year.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12164714 | Jun 2008 | US |
| Child | 13664538 | US |
