Measurement of fluid continuity in a fluid carrying member

#This invention relates to the measurement of fluid continuity in the fluid inside of a fluid carrying member.

#In a certain class of imaging devices, known as off axis inkjet printers, liquid colorant is delivered from a reservoir to an imaging head through a fluid carrying member, such as a tube. The reservoir and the imaging head are separated to reduce the mass of the imaging head and allow lower cost replenishment of the ink in the inkjet printer. Through a variety of ways, voids can form in the liquid colorant. These voids can interfere with the proper working of the imaging head. Another possible problem is that replacement of an ink reservoir is done improperly so that liquid colorant cannot flow from the reservoir to the imaging head. A need exists for a method and apparatus to detect voids within a fluid carrying member.

#Accordingly, in an imaging device an apparatus for measuring a parameter related to a flow of power through a fluid within a member includes a power source arranged to supply the power to the fluid within the member. In addition, the apparatus includes a measurement device configured to measure the parameter and generate a corresponding signal.

#A more thorough understanding of embodiments of the fluid continuity measurement apparatus may be had from the consideration of the following detailed description taken in conjunction with the accompanying drawings in which:

#Shown in FIG. 1 is a simplified diagram of an embodiment of the fluid continuity measurement apparatus.

#Shown in FIGS. 2A-2I are alternative embodiments of the fluid continuity measurement apparatus.

#Although an embodiment of the fluid continuity measurement apparatus will be discussed in the context of detecting an absence of continuity between an ink reservoir and a print head or a decrease in the ability of ink to easily move in a tube between an ink reservoir and a print head in an inkjet printer, it should be recognized that the disclosed principles are broadly applicable. For example, an embodiment of the fluid continuity measurement apparatus could be used in an application in which it is important to deliver a fluid at a substantially constant rate through a fluid carrying member. The embodiment of the fluid continuity measurement apparatus would detect the presence of voids in the fluid inside of the fluid carrying member and signal a controller. In response to receiving the signal, the controller would either stop dispensing fluid through the fluid carrying member or generate a warning that the fluid dispensing is not being performed correctly.

#Shown in FIG. 1 is a simplified diagram of an embodiment of the fluid continuity measurement apparatus. A power source, such as electric power source 10, provides electric energy to fluid carrying member 12. In FIG. 1, electric power source 10 is shown as delivering electric power to fluid carrying member 12 in a general fashion. That is, the coupling of electric power source 10 to fluid carrying member 12 shown in FIG. 1 could be implemented in a wide variety of specific ways depending upon the type of electric power source used and the circuit configuration in which it is used. The electric energy supplied could be substantially constant with respect to time or it could be time varying. Fluid carrying member 12 is adapted to carry a fluid. The fluid inside of fluid carrying member 12 is at least somewhat conductive. A measuring device, such as measuring device 14, measures a parameter related to the flow of electrical energy through the fluid included within fluid carrying member 12. The measuring device 14 generates a signal corresponding to the parameter measured by measuring device 14. In FIG. 1, measuring device 14 is shown as measuring the parameter related to the flow of electrical energy in a general fashion. That is, the coupling of measuring device 14 to fluid carrying member 12 shown in FIG. 1 could be implemented in a wide variety of specific ways depending upon the type of measuring device used and the circuit configuration in which it is used. If the continuity of fluid present in fluid carrying member 12 is obstructed, the flow of electric energy through the fluid will change. The magnitude of the change in the flow of electric energy is dependent upon the degree of obstruction. Consider the case in which electric power source 10 includes a voltage source, the current flowing through the fluid will be inversely proportional to the effective resistance of the fluid over the length of fluid carrying member 12. When voids are present within the fluid in fluid carrying member 12, the effective electrical resistance between the ends of fluid carrying member 12 is above the value present when fluid substantially fills the interior volume of fluid carrying member 12. As the fluid flow is progressively obstructed in fluid carrying member 12, the effective resistance increases, thereby reducing the flow of current. Corresponding to the decrease in the flow of current, the signal generated by measuring device 14 changes as the flow of electric energy through the fluid changes. Therefore, the signal generated by measuring device 14 provides an indication of the continuity of fluid within fluid carrying member 12. The relationship between the effective resistance and the fraction of the volume inside fluid carrying member 12 filled by voids can be empirically derived or analytically estimated. Using this relationship, the degree to which fluid carrying member 12 is filled by voids can be estimated from the measured values of the parameter.

#A variety of different measuring devices could be used for measuring device 14. For example, measuring device 14 could be a voltage measuring device, a current measuring device, or an electric power measuring device. In addition, the different types of measuring devices may be used in a variety of circuit configurations to measure continuity of fluid. Shown in FIG. 2A is a first configuration of an embodiment of the fluid continuity measurement apparatus using a voltage measuring device, such as voltage measurement circuit 100. Voltage measurement circuit 100 generates a signal related to the voltage between the ends of fluid carrying member 12 (with voltage measurement circuit 100 coupled between the ends of fluid carrying member 12). A resistance, such as resistive element 102, is coupled in series with electric power source 104 and fluid carrying member 12. In this embodiment of the fluid continuity measurement apparatus, electric power source 104 could be either a voltage source or a current source. The signal from the output of voltage measurement circuit 100 changes substantially proportionally to the voltage appearing across fluid carrying member 12.