Patent Description:
The present invention relates generally to fluid pumps and, more specifically, to peristaltic pumps for conveying a fluid pumping medium through a compressible hose, particularly for use in an aquarium, terrarium, or vivarium, and methods of operating the pump.

Peristaltic metering pumps are a well-developed technology in the science and medical fields, with very high accuracy and repeatability standard. A peristaltic metering pump is a type of positive displacement pump, wherein fluid is metered through a flexible tube (or tubing) in a peristaltic motion (i.e., supplied or pumped in a measured or regulated amount).

A peristaltic roller pump typically comprises a flexible tube of fixed length within a housing of the pump, which tube is deformable and displaces liquid via peristalsis as one or more rollers pass along the length of the deformable tube. The rollers are attached to a rotor that is controlled by an electric motor. As the rotor turns, the rollers pinch the tube to force the fluid through towards an outlet. When the tube is not compressed, the fluid is drawn into the tube through an inlet. The amount of displaced liquid is a constant volume per unit of revolution of the rollers. For technological reasons, the amount of liquid peristaltically displaced through the tube can vary.

Peristaltic roller pumps are generally used whenever the pump environment requires that the pump mechanism not contact the fluid to be pumped. Such pumps are widely used in the areas of research and medicine, for example for pumping blood and other fluids wherein it is desired to maintain the blood or fluid in a sterile environment without the possibility of contamination from the pump mechanism. Peristaltic metering pumps also excel at pumping dirty fluids that contain particulate matter into lower pressure systems because they have no check valves to clog. The gentle forces created during the peristaltic pumping action do not damage delicate liquids within the tube.

In the aquarium field, peristaltic metering pumps have been used for years as well, but due to cost and design constraints, there have been many tradeoffs in accuracy and features to compete in this cost sensitive market.

<CIT> discloses a peristaltic pump in which a parking position is provided for the rollers by a depression in a wall structure against which the tube is occluded.

While the art of designing and building peristaltic roller pumps has been relatively well developed over the years, problems associated with pump surge, undue complexity, and entanglement or kinking of the flexible tubing still persist. Thus, while known peristaltic metering pumps have proven to be acceptable for various applications, such pumps are nevertheless susceptible to improvements that may enhance their performance and cost-effectiveness.

Therefore, there exists a need to develop improved peristaltic metering pumps, particularly for use in an aquarium, terrarium, or vivarium.

An object of the invention is to provide fluid pumps, more specifically to peristaltic pumps, for conveying a fluid pumping medium through a compressible tube. The pumps are useful in metering liquids, particularly for use in an aquarium, terrarium, or vivarium. To minimize inaccuracy of the pump due to permanent deformation of the compressible tube, the pump is configured to stop at a fixed position. When stopped outside of that fixed position, the pump reverses its cycle to return the pump it the fixed position.

Another object of the invention provides an aquarium, terrarium or vivarium containing the peristaltic pump for metering liquids in the aquarium, terrarium, or vivarium. Methods for making and using the different aspects of the present invention are also provided. A method of operating a pump comprises the steps of providing a peristaltic pump having the rollers located at fixed positions. Pumping a liquid by activating the motor. Stopping the motor, and thereafter causing the controller to reverse the pump until the rollers are in the fixed positions and memorize number of micro-steps the motor ran in reverse.

Other aspects of the invention, including apparatus, devices, kits, processes, and the like which constitute part of the invention, will become more apparent upon reading the following detailed description of the exemplary embodiments.

The accompanying drawings are incorporated in and constitute a part of the specification. The drawings, together with the general description given above and the detailed description of the exemplary embodiments and methods given below, serve to explain the principles of the invention. The objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, in which like elements are given the same or analogous reference numerals and wherein:.

Reference will now be made in detail to exemplary embodiments and methods of the invention as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the drawings. It should be noted, however, that the invention in its broader aspects is not limited to the specific details, representative devices and methods, and illustrative examples shown and described in connection with the exemplary embodiments and methods.

This description of exemplary embodiment(s) is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as "horizontal," "vertical," "up," "down," "upper", "lower", "right", "left", "top" and "bottom", "front" and "rear", "inwardly" and "outwardly" as well as derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms concerning attachments, coupling and the like, such as "connected" and "interconnected," refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term "operatively connected" is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. The term "integral" (or "unitary") relates to a part made as a single part, or a part made of separate components fixedly (i.e., non-moveably) connected together. The words "smaller" and "larger" refer to relative size of elements of the apparatus of the present invention and designated portions thereof. Additionally, the word "a" and "an" as used in the claims means "at least one" and the word "two" as used in the claims means "at least two".

<FIG> and <FIG> depict a peristaltic metering pump <NUM> according to an exemplary embodiment of the present invention. The peristaltic metering pump <NUM> is particularly useful for non-medical environments, and especially for aquarium, vivarium, and terrarium applications. More specifically, the peristaltic metering pump <NUM> meters any liquid that would be relevant for an aquarium, terrarium, vivarium, or hydroponic system. Preferably, an aquarium includes a container and the metering pump connected to the container for metering liquids into and out of the container for being supplied to the aquarium. The liquid may be water, salt solutions, or any other liquid necessary for the aquarium, terrarium, vivarium, or hydroponic system. Moreover specifically, the peristaltic metering pump <NUM> is provided to meter at least one of the following liquids:.

The peristaltic metering pump <NUM> is also adapted to remove "old" seawater from the aquarium and using a second pump or an arrangement of valves to add "new" water for a water change, which is a common method to remove excessive nutrients from the water column.

The peristaltic metering pump <NUM> comprises a casing <NUM> fixed (i.e., non-movably secured) to a base member <NUM> by threaded fasteners <NUM> (best shown in <FIG> and <FIG>), and a cover (or hood, best shown in <FIG>) <NUM>. Preferably, the cover <NUM> is slidable relative to the casing <NUM> to allow for access the interior of the casing by sliding the cover <NUM> away from the casing <NUM>. When the cover <NUM> is mounted on the casing <NUM>, the two components form the outer housing of the pump <NUM>. The peristaltic metering pump <NUM> further comprises a pump stator <NUM> fixed to a support member <NUM>, and a pump rotor <NUM> mounted within the stator <NUM> and rotatable about an axis. The pump stator <NUM> is fixed to the support member <NUM> by threaded fasteners <NUM>. In turn, the support member <NUM> is fixed to the base member <NUM> by threaded fasteners <NUM>, such as screws (best shown in <FIG> and <FIG>). The pump stator <NUM> has an internal surface <NUM> including a circular portion 19c (preferably, at least half of a circle) and two straight portions 19t leading to the circular portion 19c.

The pump rotor <NUM> is rotatably driven by an electric rotary stepper motor <NUM>, which is mounted on the support member <NUM>, as best shown in <FIG>. Thus, the pump rotor <NUM> is configured to be rotatable relative to the pump stator <NUM>. The peristaltic metering pump <NUM> further comprises a motor controller <NUM> for controlling operation of the electric rotary stepper motor <NUM>. The pump rotor <NUM> includes a roller carrier <NUM> carrying two or more, preferably three, cylindrical rollers <NUM> rotatably mounted to the roller carrier <NUM>. The roller carrier <NUM> is preferably a flat plate whose center is fixed on the motor shaft of the stepper motor <NUM> and is rotatably driven by the stepper motor <NUM>. The rollers <NUM> are cylindrical in shape and equiangularly mounted on the periphery of the roller carrier <NUM>. The center axis of each of the rollers <NUM> is preferably perpendicular to the plane of the roller carrier <NUM> and/or parallel to the motor shaft. Each of the rollers <NUM> is rotatable about its axis, and the axes of the rollers <NUM> extend in parallel. Thus, the cylindrical rollers <NUM> are rotatable relative to the stator <NUM> and the roller carrier <NUM>. The rollers <NUM> have a length substantially equal to the height of the stator <NUM>. Moreover, the rollers <NUM> travel in a circular path about a rotational axis of the pump rotor <NUM>, when the stepper motor <NUM> is activated. The cover <NUM>, pivotally mounted to the pump stator <NUM> or the casing <NUM>, covers the pump rotor <NUM> and the circular portion 19c of the internal surface <NUM> of the pump stator <NUM>.

The stepper motor <NUM> is preferably a brushless DC electric motor characterized by a discrete number of steps during a rotation. Specifically, the stepper motor <NUM> divides a full rotation into a number of equal steps. The position of the rotor of the stepper motor <NUM> can be commanded to move and hold at any one of these steps without any position sensor for feedback (an open-loop controller), as long as the motor <NUM> is sized to the application in respect to torque and speed. In other words, the stepper motor <NUM> may be held at any certain step without the need for any feedback, resulting in a precisely controlled pump.

The peristaltic metering pump <NUM> further comprises a flexible tube (or tubing) <NUM> having an inlet end <NUM> and an outlet end <NUM>. The flexible tube <NUM> is disposed within the stator <NUM> between the internal surface <NUM> of the pump stator <NUM> and the pump rotor <NUM>, as best shown in <FIG>, so that at least one of the cylindrical rollers <NUM> of the pump rotor <NUM> is in contact with and thereby compresses the flexible tube <NUM> between one of the cylindrical rollers <NUM> and the internal surface <NUM>. Thus, the flexible tube <NUM> is disposed within the pump stator <NUM> around the pump rotor <NUM> and is squeezed flat between at least one of the rollers <NUM> and the internal surface <NUM> of the pump stator at all times. The tubing <NUM> may be made of a soft resilient material, such as polyvinyl chloride, silicone rubber, fluoropolymer, thermoplastic, fluoroelastomer, or combinations thereof. As the cylindrical rollers <NUM> rotate with the pump rotor <NUM>, they move the liquid contained in the flexible tubing <NUM> in the direction of rotation. The circular portion 19c of the internal surface <NUM> of the pump stator <NUM> defines the circular path of travel of the rollers <NUM> when in an operating position shown in <FIG>.

Moreover, the peristaltic metering pump <NUM> comprises an inlet fitting (or port) <NUM> and an outlet fitting (or port) <NUM>. As best illustrated in <FIG>, the inlet end <NUM> of the flexible tube <NUM> is attached to the inlet fitting <NUM>, while the outlet end <NUM> of the flexible tube <NUM> is attached to the outlet fitting <NUM>. Preferably, the inlet and outlet fittings <NUM> and <NUM>, respectively, are integrally connected to one another by a connecting plate <NUM>. As best illustrated in <FIG>, the inlet and outlet fittings <NUM> and <NUM> are mounted on the casing <NUM> and are retained between the casing <NUM> and the cover <NUM>. Preferably, clips <NUM> and <NUM> secure the inlet and outlet ends <NUM> and <NUM> of the flexible tube <NUM> to the inlet and outlet fittings <NUM> and <NUM>, respectively.

In operation, when the electric stepper motor <NUM> is activated and rotates the rotor <NUM>, the cylindrical rollers <NUM> of the rotor <NUM> rotate about the axis of the rotor <NUM> and about their own axes, and compress the tube <NUM> inside the pump stator <NUM> of the peristaltic metering pump <NUM> (the tube <NUM> is compressed between least one of the rollers <NUM> and the internal surface <NUM>). The compression of the flexible tube <NUM> forces the non-compressible liquid therein to move through the flexible tube <NUM> as the rollers <NUM> rotate inside the pump stator <NUM>. Therefore, the flexible tube <NUM> inside the pump stator <NUM> undergoes repeated compression and expansion while pumping the liquid. For example, in <FIG>, the pump rotor <NUM> rotates in a clockwise direction to move the liquid from the inlet fitting <NUM> to the outlet fitting <NUM>.

During repeated compression and expansion cycles of the tube <NUM>, the flexible tube <NUM> deforms uniformly along its entire length. When the peristaltic metering pump <NUM> stops rotating though, the point(s) at which the rollers <NUM> stop on the flexible tube <NUM> are held in a compressed state, causing longer lasting, permanent deformation to the flexible tube <NUM>. Deformation of the flexible tube <NUM> causes an internal volume change of the flexible tube <NUM>, which alters the volume of liquid that is metered (or dosed) out of the pump <NUM> in subsequent actions.

To aggravate this situation, depending on the volume of liquid being metered in each repeated compression/expansion cycle, the pump rotor <NUM> has random stop positions on the flexible tube <NUM> for every metering (or dosing) action. Repeated start/stop events cause deformation of the flexible tube <NUM> along the entire length of the circular portion 19c of the internal surface <NUM> of the pump stator <NUM> with various different magnitudes of deformation of the flexible tube <NUM>, depending on time stopped in a position, time since stoppage, and other factors, such as whether the stoppage point is in close proximity to a previous deformation. This is not typically a problem in the medical or science fields since tubing in the peristaltic medical pump is replaced often in order to eliminate cross contamination. However, in aquarium, vivarium and terrarium applications, the flexible tube <NUM> is not expected to be replaced (at least not frequently). Not accounting for this deformation can cause inaccuracy and repeatability problems, particularly where precise control over the liquid is necessary.

There exist flexible tube material formulations that deform less during extended operation of peristaltic pumps and thus exhibit less memory of deformation. Those formulations require more force to compress the tube, necessitating a larger operating force and therefore a larger motor at increased cost. A flexible tube is generally more resistant to change and tends to have a lower lifetime of operation before the tube tears or splits due to repeated deformation. A softer tubing would have a longer lifetime before tearing, but the softer tubing stretches and deforms more readily. As noted, permanent deformation equates to a volumetric change and distorts the predictable volume during peristalsis.

In order to resolve the above-mentioned problem, the peristaltic metering pump <NUM> implements a fixed (or constant, invariable, same) parking position (or a single stop point) of the rollers <NUM> of the pump rotor <NUM>. As such, the rollers <NUM>, in their parked positions, always contact the same portion of the tubing <NUM>, which as a consequence becomes deformed. For example, in an embodiment with three rollers <NUM>, the rollers <NUM> are separated by <NUM> degrees, so that there are three possible parked positions. When stopped, it is desirable that a roller <NUM> occupy the same position every time, and it does not matter which roller <NUM> is in contact with the deformed portion of the tubing <NUM>, just as long as one roller <NUM> is in that position. As such any one of the three possible positions is appropriate. Preferably, the position that requires the least amount of motor reversing is effected by the controller of the motor of pump <NUM>. Deformation of the flexible tube <NUM> can be accounted for, such as through calculations and calibration, so long as the deformation of the flexible tube <NUM> is limited to a known position or multiple known positions on the flexible tube <NUM> and is not random. It is not possible to ensure a single stop point after dosing since the liquid dosing (or metering) action can be for any specific volume given. After the dosing action is complete, the peristaltic metering pump <NUM> therefore reverses direction to rotate backwards to the fixed parking position(s) in increments of <NUM>° divided by the number of rollers <NUM>. For example, for three rollers <NUM> according to the exemplary embodiment of the present invention, the increment is <NUM>°. Rotor <NUM> rotates to a position so that each of the rollers <NUM> is always parked in the same position of <NUM>°, <NUM>°, <NUM>° degrees. The goal of parking the rollers at fixed points on the tubing <NUM> eliminates random tubing deformation to allow more accurate and precise volumetric dosing. Therefore, the actual position of the rollers <NUM> relative to the stator <NUM> does not matter as long as the same portion of the tubing <NUM> is deformed when the pump <NUM> and the rotor <NUM> are in the park position. In preferred embodiment, two rollers <NUM> are parked on the tubing <NUM>, thus creating two fixed deformation points in the tubing <NUM>. Having two rollers <NUM> compressing the tubing <NUM> allows for higher backflow pressure holding, but does not have an impact on the goal of parking the rollers <NUM> to improve accuracy. If there were more or fewer rollers than three, then there might be more or fewer rollers parked in fixed tubing positions, but the intention is to always park them in the same position(s) on the tubing to create a consistent deformation rather than random deformation.

Because the peristaltic metering pump <NUM> uses the stepper motor <NUM> for rotating the pump rotor <NUM>, the location of each of the rollers <NUM> can easily be determined based upon the number of steps rotated during dosing. Thus, the number of steps to be moved in reverse can be determined and saved, because those steps will not dose liquid during the next dosing action. This feature may not be beneficial in the medical or scientific fields, since reverse operation can lead to creating a vacuum and/or reverse pull of dosed liquids. However, in the aquarium, vivarium and terrarium applications for which the pump <NUM> is particularly useful, this reverse action is acceptable and is even beneficial. One benefit of reverse operation of rotor <NUM> at the end of the dosing action is improved dosing accuracy. Moreover, this reverse action creates a vacuum that pulls liquid back into the outlet end <NUM> of the flexible tube <NUM>, thus reducing evaporation at the outlet end <NUM> of the flexible tube <NUM>, which can cause blockages when the chemical dissolved in the additive solution forms a precipitate after evaporation. Typically, the outlet of the tubing <NUM> is not submerged in water, and is suspended over or in the aquarium, vivarium or terrarium and allowed to drip or flow into the aquarium, vivarium or terrarium. In that situation, when the pump <NUM> is stopped, liquid is present throughout the tubing <NUM> to the outlet port <NUM>. As noted above, the liquid at the outlet port <NUM> can evaporate, which in the case of a solution or suspension liquid, can leave dissolved or suspended solids at the outlet port <NUM> leading to clogging of the tubing <NUM> or decreased flow area. Clogging or decreased flow area can lead to inaccuracies in the dosing calculation of the pump. By drawing the liquid back from the outlet port <NUM> during the parking operation, evaporation is minimized due to less liquid contact with air and/or air convection.

The volume of liquid dosed during one rotation of the pump rotor <NUM> of the peristaltic pump <NUM> is not linear. The flexible tube <NUM> has the following regions: an initial region when each of the rollers <NUM> is first making contact and starts to compress the flexible tube <NUM>, a constant flow rate (or dosing) region, and an end (or non-dosing) region when each of the rollers <NUM> moves off the flexible tube <NUM>. In the initial region, the output flow rate of the peristaltic pump <NUM> is slow but increasing. In the constant flow rate region, the output flow rate of the peristaltic pump <NUM> is constant. In the end region, there is no output flow through the peristaltic pump <NUM> with a slight pressure drop.

In order to dispense or dose a specific volume of liquid, there will be random start and stop positions which can begin or end in either dosing or non-dosing regions during rotation of the pump rotor <NUM>. Many existing inexpensive metering pumps use time-based calculations to determine how long to run the metering pump to dispense specified volumes of liquid based upon the assumed flowrate in volume per second, and others use the number of rotations from a known fixed start or stop position. These existing methods do not factor in the regions of rotation that do not dispense liquid, which leads to less accurate and less repeatable dosing actions.

The peristaltic metering pump <NUM>, by using a stepper motor <NUM>, rotates in discrete micro-steps, or fractions of a revolution. Micro-stepping is a method of controlling stepper motors, typically used to achieve high resolution or smoother motion at low speeds. Specifically, micro-stepping is a way of moving the stator flux of a stepper motor more smoothly than in full- or half-step drive modes. Micro-stepping control divides each full step into equal sized smaller steps to help smooth out rotation of the stepper motor, especially at slow speeds. This results in less vibration, and makes noiseless stepping possible down to <NUM>. It also makes smaller step angles and better positioning possible. While a stepper motor is limited by the known number of discrete steps per revolution, a micro-stepping enabled motor controller allows the motor to move in fractions of a step. A micro-step is generally defined as splitting a single step into multiple smaller steps. This is accomplished by controlling the current in each stepper motor phase, which can effectively produce multiple partial steps within a single step, for thereby increasing the dispenser resolution.

Consequently, to increase accuracy and repeatability, the peristaltic metering pump <NUM> preferably uses a gearing system so that the each complete roller rotation includes <NUM>,<NUM> micro-steps per rotation of the stepper motor <NUM> for positional accuracy throughout the rotation of the pump rotor <NUM>, including those regions with no flow rate. Although <NUM>,<NUM> micro-steps are preferred for high accuracy at a reasonable cost, other numbers of micro-steps are also appropriate for the invention. The motor controller <NUM>, which has software and/or firmware for assuring operation, includes a first flow rate lookup table storing a plurality of preset values of amount (such as volume) of liquid dispensed per micro-step for each starting angular position of the stepper motor <NUM> throughout one <NUM>° rotation of the pump rotor <NUM>. The first lookup table correlates angular position and volume per unit time to the number of steps of the motor <NUM>, and is determined by measuring the flow rate at the various rotational angles of the rollers <NUM> on the stator. It was found that flow rate varies and even stops at different rotational angles and the first lookup table compensates for this variance. This first lookup table provides the number of steps required to provide a given volume at a given angular position of the stepper motor <NUM>, and is fixed for the pump <NUM>. The first lookup table is stored in the controller <NUM>, and is used by the controller <NUM> to calculate the number of micro-steps required from the last random stop position for every dosing action.

A calibration factor may also be calibrated by a user (the manufacturer initially provides a default calibration factor) to compensate for external plumbing and pressure requirements for the user aquarium, vivarium, or terrarium installation. The calibration factor is used to offset manufacturing variance in the volume of the tubing <NUM> in the peristaltic pump <NUM>. For this process, the user specifies a volume of liquid (such as in mL) to dispense and a dispensing rate (such as in mL/sec) to use while the outlet of the tubing <NUM> is placed into a graduated cylinder or other volumetric measuring device. The input end of the pump <NUM> is placed into a supply of liquid and the pump <NUM> then dispenses the specified volume at the given rate. The user observes the actual volume dispensed by the pump <NUM> using the graduated cylinder and inputs that actual volume into the controller <NUM>. The controller <NUM> uses this actual volume to calculate and save a calibration factor for the tubing <NUM>. This calibration factor is calculated using the following steps: first the controller <NUM> saves the parameters including a default calibration factor provided by the manufacturer or previous user determined calibration factor, the values from the first and second tables (see below), and the full number of rotations that are used to dispense the specified volume. The user then measures the volume dispensed by the pump <NUM> when the specified volume is entered, and enters that measured volume into the controller <NUM>. Next, the actual volume dispensed, the saved values from the first and second tables, and the saved number of full rotations are used by the controller <NUM> in the calculation process described below to back calculate the calibration factor. In the back calculation, the measured volume is used as Vt; and since the values from the first and second tables and the number of full rotations are known, the calibration factor can be calculated using the process described below. This calibration factor is then saved in the controller <NUM> to be used for performing further dispensing actions as discussed below. This calibration process is recommended when the tubing <NUM> is changed or when altering other tubing connected to the input or outlet of the peristaltic pump <NUM>. The pump <NUM> is initially provided with a default calibration factor by the manufacturer; however, it is recommended that the calibration process be initiated before the first dosing action.

The controller <NUM> takes into account any parking position advancement needed on account of tube deformation parking, throughout each rotation based on the first lookup table to complete the dispensing/dosing of a specified volume of liquid. Thus, when the motor <NUM> is stopped after dispensing fluid (random stop), the motor <NUM> is reversed to place the rollers <NUM> in the fixed parked position(s). The number of micro-steps required to reach that parked position are memorized by controller <NUM>. At the beginning of the next dosing event, the same number of micro-steps are advanced before the next dosing begins. In this way, the pump <NUM> advances the rollers <NUM> from the parked position to the terminus of the previous dosing event, so that thereafter the next dosing event can commence and an accurate volume of liquid dispensed.

Current aquarium metering pumps operate at a small number of finite flow rates in order to maintain acceptable accuracy levels without the above-mentioned complexities. Contrary to typical aquarium metering pumps, the motor controller <NUM> of the peristaltic metering pump <NUM> performs the above-mentioned calculations and includes a second flow rate lookup table. This second table contains multiplication factors for different motor speeds. It was observed during testing that the volume dispensed varied from expectations based on the flow rate or speed at which the motor <NUM> was rotating. It was determined that further measurements were needed to be taken to quantify this variation. The end result, from a number of automated dispensing actions and volume measurements form those dispensing actions, provided a table of multiplication factors referenced to a wide range of motor speeds that are used in calculating a dosing action by the controller <NUM>. To generate the second table, volume measurements at different motor speeds are obtained over a specified number of rotations. Preferably, at least about <NUM> different motor speeds and volume measurements are effected to provide the second table. These volume measurements are then compared to the expected volume. The expected volume is obtained by multiplying the calibration factor by the specified number of rotations. Each of the multiplication factors provided in the second table is the ratio between the volume measured and the corresponding expected volume. Each of the multiplication factors is correlated to a flow rate (F) associated with the motor speed (F = motor speed (revolution/time) * calibration factor (volume/time)). This second table is unique to the pump <NUM>, provided by the manufacturer, stored in the controller <NUM>, and used for every dosing action.

A dosing action, as specified by the user, is a volume (Vt) to dose over a certain amount of time. From this specification, the flow rate (F, volume per time) can be determined. The flow rate (F) is used to determine a multiplication factor (fm) from the second table. Multiplying the multiplication factor from the second table and the calibration factor (fc which is in volume per rotation) discussed previously results in the volume dispensed by the pump <NUM> per rotation of the motor <NUM>. The product (volume per rotation) is used to determine the number of rotations (R) needed to dispense the bulk of the dosing volume specified by dividing the volume (Vt) by the product, R = Vt/(fm * fc) (Equation <NUM>). The integer of R is the number of full rotations the motor must operate to dispense the liquid. The volume obtained by the full rotations is referred to herein as Vf= INT(R) * (fm * fc), where INT(R) is the integer of R. Since it would be very unlikely that the specified volume results in a whole number of full rotations (R), the partial rotation needed is calculated using the previously discussed first table to determine the number of steps necessary to provide the volume needed in the partial rotation. To do that, the volume associated with the partial rotation (Vp) is obtained by subtracting the volume obtained by the full rotations (Vf) from the volume entered by the user (Vt) (Vp = Vt - Vf). Vp and the initial angle of the motor <NUM> are then used to look up, in the first table, the number of steps required to dispense Vp. Thus, to achieve the volume entered by the user (Vt), the motor <NUM> must rotate the number of full rotations plus the number of micro-steps obtained from the first table. The controller <NUM> is programmed to perform the calculations necessary to operate the motor <NUM> to provide the desired dosing action. Before this motion is started and after it is completed, the controller <NUM> also calculates any initial steps that do not dispense and any steps to the parking position after the motion.

Thus, the peristaltic metering pump <NUM> can operate at an extremely wide range of flow rate volumes with high accuracy. The peristaltic metering pump <NUM> is able to use a single point calibration value in addition to the internal flow rate lookup tables to calculate parameters to deliver (or pump) a specified amount of liquid in an exactly specified amount of time without having to round to the nearest fixed flow rate like typical metering pumps do. This allows the peristaltic metering pump <NUM> to add an additional feature: continuous dosing. Typical metering pumps dispense the liquid at a fixed rate until a volume target is reached and then pumping is stopped. For some additives or liquids, it is beneficial to be dispensed at a constant rate continuously, because the concentrated additive is not dispensed too quickly to increase concentration levels in an aquarium too quickly, for example. With continuous operation, the additive may be added as slowly as possible in order to maintain a relatively constant concentration of the additive. Existing pumps operate at discrete, fixed flow rates, sometimes one fixed flow rate, sometimes multiple fixed flow rates. These flow rates rarely provide the desired volume over <NUM> hours. For instance, if a user wants <NUM> of volume over <NUM> hours, that would equate to ~<NUM>/minute flow rate. It would be unlikely that the existing pump would have that flow rate as a pre-programmed fixed flow rate available to use since they are implemented in a fixed method at design time. If that pump had <NUM> per minute as an available flow rate, the pump would dispense <NUM> in a <NUM> hour span, not the <NUM> that was desired. Conversely, the more likely outcome is that the pump would dispense the <NUM>, but only operate for <NUM> hours over the course of the day, not continuously. The previously mentioned volume multiplication factor versus flow rate table of measured values and its implementation allows the present pump to provide any possible flow rate as necessary to accurately dispense a desired volume over a full <NUM> hours.

Typical aquarium metering pumps use either synchronous or asynchronous DC motors (brushed or brushless) or DC stepper motors. Asynchronous DC motors are the least precise motors to use due to lack of fine feedback on position. Stepper motors are very loud due to their trapezoidal torque profile throughout their rotation, but stepper motors are very precise. The stepper motor <NUM> of the peristaltic metering pump <NUM> is not only very accurate, but also generates low audible noise to create a quiet stepper motor driven peristaltic pump. By using a <NUM>,<NUM> micro-step drive method for the motor controller <NUM>, the trapezoidal torque profile is smoothed to a near sinusoidal drive current, thus reducing mechanical noise in the stepper motor <NUM>.

The motor controller <NUM> controls the operation of the stepper motor <NUM> by selectively applying pulse width modulated (PWM) pulses to the stepper motor <NUM> to control the speed and/or torque of the stepper motor <NUM>. The stepper motor <NUM> is driven with the PWM pulses to provide a micro-step drive current that is stepped for predetermined time intervals to provide an approximation of a sinusoid. The stepper motor <NUM> is energized by the PWM pulses to drive the pump rotor <NUM> in both forward (clockwise as illustrated in the figures) and reverse (counterclockwise as illustrated in the figures) directions.

A voltage mode PWM current regulator in the stepper motor <NUM> further reduces electrical noise in a motor stator, which is the most common audible noise in a stepper motor during operation. The standard constant current regulation method applies a constantly changing switching signal to the motor stator which causes the audible switching noise in a stepper motor. In voltage control PWM regulation, a fixed PWM signal is configured into the motor stator <NUM> to drive the appropriate current through the motor <NUM> without additional switching harmonics that create audible noise.

The following illustrates an example of a dosing operation of a pump <NUM> operable at <NUM> steps/rotation with a calibration factor of <NUM>/rotation. Assume the user enters a volume (Vt) of <NUM> and a time (t) of <NUM> hour (<NUM>). The controller first divides the volume by the time to obtain a flow rate (F) of <NUM>µL/s. The flow rate is then used to look up in the second table the multiplication factor to obtain a value of <NUM>. Multiplying the multiplication factor and the calibration factor obtains a value of <NUM>/rotation. Dividing Vt by that value (<NUM> / <NUM>/rotation) results in <NUM> rotations. The integer value, <NUM>, indicates the number of full rotations required to dispense Vf which is <NUM> (<NUM> rotations x <NUM>/rotations). The remaining volume Vp is <NUM> (<NUM> - <NUM>) which must be accounted for by looking up the first table to determine the number of steps needed to provide Vp at the particular starting angle of the motor <NUM>. The first table gives <NUM> steps to provide Vp. Therefore, to dispense Vt, the motor <NUM> must operate <NUM> full rotations and an additional <NUM> steps, or <NUM>,<NUM> steps (<NUM> rotations x <NUM> steps/rotation + <NUM> steps). Once the <NUM>,<NUM> steps are completed, the angular position of motor <NUM> (before reversing) is memorized by the controller <NUM> for the next dosing action. Additionally, the motor <NUM> reverses to place the rollers in the parking position. The number of steps the motor operates in reverse is also memorized by the controller <NUM> for the next dosing action. In the case of a pump <NUM> containing three rollers <NUM> placed <NUM>° apart, the motor <NUM> would reverses <NUM> steps (<NUM> steps-<NUM> steps (the <NUM> step is the closest parking position for the rollers in the <NUM>-rollers configuration)). The next dosing action would add <NUM> steps to account for the steps that were reversed in the immediate prior dosing action. All of the calculations required for the dosing operation, including the parking of the roller positions and the forwarding of the rollers prior to dosing are performed by the controller <NUM> using its software and firmware.

Claim 1:
A peristaltic metering pump (<NUM>) for aquariums, vivariums and terrariums, comprising
a. an inlet port (<NUM>);
b. an outlet port (<NUM>);
c. a stator (<NUM>) having an internal surface (<NUM>);
d. a tubing (<NUM>) having an inlet end (<NUM>) connected to the inlet port (<NUM>), and an outlet end (<NUM>) connected to the outlet port (<NUM>);
e. a rotor (<NUM>) comprising a roller carrier (<NUM>) and two or more rollers (<NUM>) rotatably mounted to the roller carrier (<NUM>), a portion of the tubing (<NUM>) is compressed between at least one roller (<NUM>) and the internal surface (<NUM>);
f. a stepper motor (<NUM>) configured to rotate the pump rotor (<NUM>); and
g. a controller (<NUM>) operably connected to the motor (<NUM>);
characterized in that the controller (<NUM>) is configured to advance the rotor (<NUM>) during each of a plurality of dosing events in order to dispense a specified volume and to reverse the motor (<NUM>) to return the rollers (<NUM>) to a park position after each of the dosing events is completed.