Miniature pumps have been made for applications in microfluidics for fields such as chemical analysis and other “lab-on-a-chip” applications. Many of these miniature pumps are diaphragm pumps driven by an electromagnetic mechanism. The interaction between a permanent magnet and an electromagnetic coil (capable of having its polarity reversed) causes the diaphragm to reciprocate and drive the pump. The diaphragm is typically fixed to either the coil or to the permanent magnet and other element of the electromagnetic pairing is held fixed with respect to the diaphragm.
Such arrangements can operate efficiently when pumping fluid or in conditions where there is not a large pressure differential. However, if there is a large pressure differential across the diaphragm of such a pump, more power is needed to drive the pump. In the context of miniature pumps, it can be difficult to send more power to the electromagnetic mechanism without creating undesirable problem such as heat build-up.
Larger scale pumps deal with large pressure differentials across a diaphragm by using mechanical energy to help propel the diaphragm during the pump stroke. For example, while electromagnetic forces alone may drive the diaphragm during the exhaust stroke, a mechanical spring can help drive the diaphragm during the pump stroke. That is, during the exhaust stroke a mechanical spring is compressed and when the electromagnetic field is reversed the mechanical spring unloads its loaded energy to return the diaphragm. However, such an arrangement has its highest energy at the beginning of the pump stroke and loses energy at the same time the diaphragm is encountering high resistance. Further, such mechanical loading is not practical in a miniature pump.
These challenges and others can be addressed by the embodiments disclosed herein.
Certain embodiments of the present invention are related to devices and methods for improving the efficiency of miniature diaphragm pumps and in particular miniature diaphragm pumps driven by electromagnetic actuators.
In some embodiments, the miniature diaphragm pump is loaded with energy during the exhaust stroke and the loaded energy is released during the pump stroke, which improves the efficiency of the miniature pump.
In some embodiments, a supplemental permanent magnet is fixed to a diaphragm of a miniature electromagnetically driven diaphragm pump. The supplemental permanent magnet is separated from a fixed pole magnet during the exhaust stroke of the pump and is magnetically attracted to the fixed pole magnet during the pump stroke. Separating the permanent magnet from the pole magnet loads energy during the exhaust stroke.
Certain embodiments of the present invention include a control system for operating a miniature diaphragm pump. The control system can include control, storage, sensing, and I/O components.
Certain embodiments of the present invention include a processor for dynamically controlling the position and/or performance of the diaphragm in the miniature diaphragm pump. In some embodiments, the offset and/or the gain is dynamically controlled in response to measured operational parameters in order to achieve desired operational characteristics.
Before the present devices and methods are described, it is to be understood that this invention is not limited to particular embodiments described. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.
Short summaries of certain terms are presented in the description of the invention. Each term is further explained and exemplified throughout the description, figures, and examples. Any interpretation of the terms in this description should take into account the full description, figures, and examples presented herein.
The singular terms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an object can include multiple objects unless the context clearly dictates otherwise. Similarly, references to multiple objects can include a single object unless the context clearly dictates otherwise.
The terms “substantially,” “substantial,” and the like refer to a considerable degree or extent. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation, such as accounting for typical tolerance levels or variability of the embodiments described herein.
The term “about” refers to a value, amount, or degree that is approximate or near the reference value. The extent of variation from the reference value encompassed by the term “about” is that which is typical for the tolerance levels or measurement conditions.
All recited connections may be direct connections and/or indirect operative connections through intermediary structure.
A set of elements includes one or more elements.
Unless otherwise stated, performing a comparison between two elements encompasses performing a direct comparison to determine whether one element is larger (or larger than equal to) the other, as well as an indirect comparison, for example by comparing a ratio or a difference of the two elements to a threshold
Generally speaking, the operation of the inlet valve 20a and the outlet valve 20b is similar to a positive displacement diaphragm pumps. That is, when the diaphragm is withdrawn away from the inlet port 12, the inlet valve 20a is also drawn away by negative pressure from upper inlet chamber port 202a and engages against inlet port offset 201a. This movement creates a flowpath down through the inlet port 12, through the upper inlet chamber port 203a (see
When the diaphragm 55 begins its return stroke towards the inlet port 12, positive pressure forces the inlet valve 20a away from the inlet port offset 201a and into sealing engagement with the upper inlet chamber port 203a. The positive pressure also forces the outlet valve 20b away from the lower outlet chamber port 202b and into engagement with the outlet port offset 201b. This movement creates a flowpath from the diaphragm chamber, through the lower outlet chamber port 202b, across outlet valve 20b, through upper outlet chamber port 203b (see
The valves are sized and configured to be movable by the range of pressure expected from the use environment of the miniature pump 10. For example, the valves should have a weight to surface area ratio such that they are movable by the flow of liquid or gas when the miniature pump is in use. Further, the valves are made of a material that enables the valves to sealingly engage against their respective ports when moved into such as sealing position by liquid or gas flow. Rubber is one example of a suitable material for making valves in such a miniature pump.
When known diaphragm displacement pumps are connected to a closed chamber in order to pull vacuum on such a chamber, each pump stroke requires successively more energy than the last stroke as the pressure difference across the diaphragm increases. That is, the greater the vacuum in the closed chamber, the more difficult it is for the diaphragm to travel a full stroke. Generally, pumps are driven with more power in order to generate longer pump strokes under higher vacuum conditions.
In contrast, pumps according to certain embodiments do not require as much of an increase in power to generate longer pump strokes under higher vacuum conditions because these miniature pumps are loaded on the exhaust stroke. In contrast to previously known positive displacement diaphragm pumps, the miniature pump 10 includes the magnet 57, which functions to load the pump stroke of the miniature displacement pump during the exhaust stroke. The actuator membrane 5 can be driven using a sinusoidal signal such that the actuator membrane 5 reciprocates between an upper position and a lower position. Since the actuator membrane 5 is attached to the diaphragm 55, the reciprocation of the actuator membrane 5 causes a similar reciprocation of the diaphragm 55. When the actuator membrane 5 and diaphragm 55 reciprocate away from the pump body 11, the diaphragm motion is expanding the size of the diaphragm chamber and drawing gas or liquid within the chamber in a pump stroke. When the actuator membrane 5 and diaphragm 55 reciprocate toward the pump body 11, the diaphragm motion is contracting the size of the diaphragm chamber 54 in an exhaust stroke. The inlet valve 20a and the outlet valve 20b are, of course, moving in concert with such pump strokes and exhaust strokes to allow gas or liquid to flow one way through the miniature pump from the inlet to the outlet.
The actuator 15 can be an electromagnetic voice coil, which includes an electromagnetic drive element coupled to the actuator membrane 5. Such a voice coil actuator performs essentially like a loudspeaker, such that waveform signals sent to the electromagnetic drive element drive the actuator membrane in a pattern generated by the waveform.
During the pump stroke, electric current is applied to the actuator coil 3 to create an electromagnetic field that attracts the actuator coil 3 to the actuator pole magnet 7. The actuator coil 3 is fixed to the actuator membrane 5, which is connected to the diaphragm 55. Thus, the diaphragm 55 is pulled away from the diaphragm chamber 54, thereby increasing the volume of the chamber and drawing air or liquid through the inlet valve and into the diaphragm chamber in a pump stroke.
Referring still to
Advantageously, the magnet 57 is moved away from the actuator pole magnet 7 during the exhaust stroke. This is an advantage because the diaphragm 55 encounters comparatively low resistance during the exhaust stroke as gas or liquid is displaced from the diaphragm chamber 54. Thus, the exhaust stroke separates the magnet 57 from the actuator pole magnet 7 with relatively low additional power requirement than if the magnet 57 was not on the diaphragm 55. Then, during the pump stroke, the separation between the magnet 57 from the actuator pole magnet 7 provides additional magnetic force as described above. As a result, the miniature pump is able to operate more efficiently at low power than a conventional electromagnetic diaphragm pump.
The relative strength of the magnetic forces among the actuator components (i.e., the electromagnetic coil and the pole magnet) and the diaphragm magnet can be used to tune the efficiency of the miniature pump. For example, a stronger diaphragm magnet will provide more loaded energy to the pump stroke of the diaphragm when separated from the pole magnet, but will also require more power to be separated during the exhaust stroke.
In some embodiments, the diaphragm magnet is fitted with an adjustment mechanism that allows the separation between the diaphragm magnet and the pole magnet to be varied. For example, the diaphragm magnet could be housed within a recess fixed to the upper surface of the actuator membrane. The diaphragm magnet could rest atop a tapered adjustment screw such that when the screw is turned one direction the magnet moves closer to the actuator membrane and when the screw is turned the opposite direction the magnet moves farther from the actuator membrane.
Advantageously, magnetic fields are sensitive to distance. The strength of the magnetic field between the two permanent magnets (the actuator pole magnet and the diaphragm magnet) can decay following the inverse cube of the distance from the source. That is, if D is the distance between the magnets and F is the strength of the forces, then F=1/D3. This is advantageous for embodiments of the invention because the force is much higher when the permanent magnets are closer, such as at the maximum displacement of the diaphragm during the pump stroke. And, the force is much lower at the minimum displacement of the diaphragm during the exhaust stroke. The loaded miniature pump designs of embodiments of the invention can operate with significantly more efficiency than unloaded pump designs because of this inverse relationship between force and distance.
In accordance with some embodiments, the miniature pump preferably is about 12 to 20 mm long, about 10 to 15 mm wide and about 3 to 9 mm high, more preferably about 18 mm long, about 12 mm wide and about 7 mm high. The mass is preferably about 1 to 5 grams, more preferably about 3 grams. The miniature pump preferably operates with a voltage between about 3.5 to 5 volts, peak current when running of about 100 to 200 mA, and standby current of about 20 to 40 mA. The miniature pump is self-priming and preferably is less than about 90 dB two inches away, more preferably, less than about 70 dB two inches away. The miniature pump preferably has a peak suction of about −6 in Hg, more preferably about −8 in Hg. The suction rate is preferably about 0 to −6 in Hg in less than about 10 seconds with 10 mL volume of air, more preferably about 0 to −8 in Hg in less than about 10 seconds with 10 mL volume of air.
The blow-off valve 60, the sensor 80, and the control board 70 work together in a closed loop control system for monitoring and adjusting the performance of the miniature pump. In one example, the closed loop control systems can be programmed to maintain a level of negative pressure within the diaphragm chamber. That is, the sensor continuously monitors the pressure level in the diaphragm chamber and provides that data to the control board. The firmware (or software) on the control board can compare the data to the programmed pressure level and then send power to the actuator to drive the miniature pump to increase the pressure or send a signal to the blow-off valve to release negative pressure. In another example, a pre-programmed or user-selected suction profile can be generated using the closed loop control system. That is, rather than seeking a set level of negative pressure, the closed loop control system seeks a time-dependent pattern of pressure levels by continuously comparing the negative pressure level in the diaphragm chamber with the time-dependent level specified in the profile. The blow-off valve or the pump can then be activated as needed.
In another example, the closed loop control system can help optimize the efficiency of operation and reduce noise levels. In this example, the firmware uses a look-up table to find optimal operating conditions for the miniature pump at a given level of negative pressure. At a given pressure the miniature pump may operate most efficiently at a certain power signal profile. That is, a particular shape of the signal waveform (e.g., the amplitude and frequency of a sinusoidal signal) may allow the miniature pump to operate more quietly than another similar shape at a given pressure. Generally, noise in the miniature pump is generated by the diaphragm hitting the walls of the diaphragm chamber and by the valves hitting the walls of their valve recesses and offsets. By calibrating the position of the diaphragm and valves at given power levels and pressure levels and cross-referencing those positions against power and pressure levels in a look-up table accessible to the firmware, the miniature pump can be operated in a way that reduces or eliminated valve and/or diaphragm noise. Further, reducing or minimizing diaphragm and valve noise increases the efficiency of the miniature pump since less energy is lost to the pump body through collisions between the valves and/or diaphragm and the pump body.
Another advantage of the closed loop control system is that the blow-off valve can be activated under certain conditions. For example, if the negative pressure exceeds a certain level, the firmware can activate the blow-off valve to allow air into the diaphragm chamber. As another example, if the valve temperature rises above a certain level (as detected by a temperature sensor integrated into the miniature pump and in communication with the control board), the firmware can activate the blow-off valve.
Generally, the control and sensing components of the miniature pump can reside within the pump housing or can be remote from the pump. That is, a processor and sensor can be located away from the actual pump body and still be able to provide the sensing and control features described herein. Also, the blow-off valve maybe located remotely from the pump body provided it has the fluid connection necessary to provide the pressure relief performance. Thus, the closed loop feedback system can exist in a system of physically separate components that are functionally interconnected.
In some embodiments, the processor 224 comprises a microcontroller integrated circuit or other microprocessor configured to execute computational and/or logical operations with a set of signals and/or data. Such logical operations are specified for the processor 224 in the form of a sequence of processor instructions (e.g. machine code or other type of software). A memory unit 226 may comprise random access memory (RAM, e.g. DRAM) storing data/signals read and/or generated by processor 224 in the course of carrying out instructions. The processor 224 may also include additional on-die RAM and/or other storage.
Storage devices 228 include computer-readable media enabling the non-volatile storage, reading, and writing of software instructions and/or data, such as EEPROM/flash memory devices. Communications interface controller(s) 230 allow the subsystem 220 to connect to digital devices/computer systems outside the control board 70 through wired and/or wireless connections. For example, wired connections may be used for connections to components such as user I/O devices 232, while wireless connections such as Wi-Fi or Bluetooth connections may be used to connect to external components such as a smartphone, tablet, PC or other external controller. Buses 250 represent the plurality of system, peripheral, and/or other buses, and/or all other circuitry enabling communication between the processor 224 and devices 226, 228, 230, 234, and 236. Depending on hardware manufacturer, some or all of these components may be incorporated into a single integrated circuit, and/or may be integrated with the processor 224.
User I/O devices 232 include user input devices providing one or more user interfaces allowing a user to introduce data and/or instructions to control the operation of subsystem 220, and user output devices providing sensory (e.g. visual, auditory, and/or haptic) output to a user. User input devices may include buttons, touch-screen interfaces, and microphones, among others. User output devices may include one or more display devices, speakers, and vibration devices, among others. Input and output devices may share a common piece of hardware, as in the case of touch-screen devices.
In some embodiments, the processor 224 controls the positioning of the diaphragm 55 by using analog circuitry 240 to dynamically control a direct current (DC) offset and a gain of a diaphragm drive signal. The offset level controls the resting position of diaphragm 55, while the gain controls the amplitude of a sinusoidal or other periodic signal waveform which determines the amplitude of the excursion of the diaphragm 55 from its resting position. The offset and gain may be controlled dynamically in response to measured operational parameters in order to achieve desired operational characteristics, as described below. In particular, the offset and/or gain may be changed in response to variations in pressure measured using the sensor 80.
As the pump operates over time in a given evacuation sequence, the pressure differential across the diaphragm 55 generally increases. Without changes in offset and gain, the increasing pressure differential would lead to a gradual change in the resting position of the diaphragm 55. The increase in pressure difference leads to changes in the optimal offset and gain values for achieving particular pump characteristics such as maximum rate of increase in pressure difference (pumping speed), minimum current consumption (or maximum energy efficiency), or minimal noise. In some embodiments, the offset is decreased (or increased) over time to compensate for the effect of the increased pressure differential across diaphragm 55 on the resting position of diaphragm 55. The offset and gain values may be varied according to a pressure lookup table, and/or according to dynamically measured changes in one or more parameters of interest, such as a pressure difference (delta) observed over one pump cycle.
In a step 306, it is determined whether the offset is to be updated for the next pump cycle. In some embodiments, the determination whether to update the offset may be performed independently of the pressure delta comparison described above. For example, offset updates may be performed during certain blocks of cycles while gain updates are performed during other blocks of cycles, in order to attempt to separate the measured effects on pressure delta of offset and gain changes. In another example, offset and gain updates may be performed on alternating pump cycles. In some embodiments, both offset and gain updates may be performed during at least some pump cycles. In some embodiments, a determination whether to update the offset may be performed according to the pressure delta comparison described above, if it is determined that an offset change is likely to improve pump performance.
In a step 308, the offset is updated according to the pressure delta comparison performed in step 304. In some embodiments, updating the offset comprises incrementing or decrementing the offset by a fixed step (e.g. ±1) if it is determined that such incrementing/decrementing is likely to lead to improve pump performance on the next pump cycle.
In a step 310, is it determined whether the gain is to be updated for the next pump cycle. Step 310 may be performed in a manner similar to that described above for step 306. Subsequently, in a step 312, the gain is updated according to the pressure delta comparison performed in step 304. In some embodiments, updating the gain comprises incrementing or decrementing the gain by a fixed step (e.g. ±1) if it is determined that such incrementing/decrementing is likely to lead to improve pump performance on the next pump cycle.
As illustrated in
In some embodiments, a pump and associated control system as described above may be used to generate pressure patterns other than a monotonically-increasing one such as the one illustrated in
In some embodiments, step 512 may include turning on and off the pump so as to maintain a certain level of negative pressure. Step 512 may include monitoring parameters such as the fraction of time that the pump is on or the pump pressure slow to determine whether to increase or decrease the pump's activity. The pump then self-regulates to maintain a certain level of negative pressure.
Still referring to
Again still referring to
The flow paths in the upper body 1011a provide several connections, such as: (1) a connection between the blow-off valve and the inlet port of the miniature pump; (2) a connection between the blow-off valve and the outlet port of the miniature pump; and (3) a connection between the pressure sensor and the suction chamber.
The blow-off valve diaphragm 1065 can be formed from materials such as silicone rubber or its equivalents. The blow-off valve attractor plate 1068 and the blow-off valve yoke 1067 can be formed from alloys with comparatively high magnetic permeability, such as a nickel-iron alloy. The blow-off valve coil 1069 can be formed from winding copper or other conductive wire. The blow-off valve case 1061 can be formed from a polymer-based material, such as a glass-filled polycarbonate.
The blow-off valve functions by having a minimum preload that presses the diaphragm against the valve port to ensure that the valve is closed prior to initiating suction. The preload can be chosen by using a diaphragm material with sufficient elastic modulus such that the diaphragm remains engaged against valve port in the assembled state. In some embodiments, the blow-off valve can further include a non-magnetic compression spring within the electromagnet assembly that always pushes up on the attractor plate. In this scenario, the diaphragm would be designed to be as flexible as possible and preload could vary in accordance with the tolerances associated with the spring constant and the free length.
Because this electromagnetic blow-off valve operates within a miniature pump that itself is driven by electromagnetic forces, it is necessary to take into account the overall magnetic fields experience by the attractor plate. The valve diaphragm should be stiff enough to not be affected by such peripheral magnetic forces. That is, the diaphragm should resist unwanted displacement via interaction between the attractor plate coupled to the diaphragm and the peripheral magnetic fields. Yet, a stiffer diaphragm requires a stronger local magnetic field to displace it and the attractor plate. One method to achieve a desirable local magnetic field is to optimize the number of coil turns in the blow-off valve coil. A greater number of coil turns can be achieved by growing the overall electromagnet in height or diameter. While it is more space efficient to grow in height (resistance increases more slowly given lower total wire length which can prevent having to jump to a lower gauge wire), increases in the outer diameter can also provide space for more coils, which may utilize the available enclosure space more effectively.
In some embodiments, the maximum current available to the electromagnet is assumed to be 300 mA. This is based on limitations of the battery (1 C max). If higher currents could be sourced, the resistance of the component (current 10-12 ohms) would also have to be reduced given the assumed minimum battery voltage of 3.0 V for a miniature pump. In general, the current draw of the blow-off valve should be monitored according to the application of the miniature pump.
The term “blow-off” valve as used herein refers generally to a type of valve used to control or limit the pressure in a system or vessel. Such valves may also be known as relief valves, safety valves, and the like, and certain embodiments herein encompass such valves regardless of how they are named.
While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
Filing Document | Filing Date | Country | Kind |
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PCT/US14/52430 | 8/24/2014 | WO | 00 |
Number | Date | Country | |
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61993041 | May 2014 | US | |
61871832 | Aug 2013 | US |