BACKGROUND
FIELD OF INVENTION
The current invention describes a low flow rate measurement sensor and syringe pump for pumping low flow rate liquid.
DISCUSSION OF THE PRIOR ART
US 4767406 titled "syringe pumps" describes a pump with a casing, within which a motor is fitted. The motor is used to rotate a drive rod, which at one end is connected to the motor. The other end of the drive rod rotates in a journal bearing. Further, the invention describes a carriage which is fixed in such a way that it can slide back and forth. The carriage acts against the plunger to expel the fluid from the syringe. The exit end of the syringe is provided with a sensor to gauge the carriage position and a microprocessor for detenrdning the fluid delivery rate and pressure.
EP2440762 titled "Dual power input fluid pump" describes a fluid pumping device consisting of housing, a motor, a gear set for a vehicle with an internal combustion engine. Further, the invention also describes a controller that controls the electric motor. The planetary gear set's one member is controlled by the IC engine; one member is controlled by the electric motor and the third member drives the pump for delivering the fluid. The described invention, unlike the current invention does not disclose a method for determining the characteristics of the fluid being pumped.
US20130098005 titled "Delivery pump for a fluid, metering device having the delivery pump and motor vehicle having the metering device" describes a delivery pump that is suitable for delivering fluids at a controlled pressure. The device consists of inlet, outlet and a delivery piston designed to move in the delivery direction. It further consists of an axial bearing for supporting the delivery piston. The control unit receives the signal from at least one pressure sensor to control the pressure of the fluid at the outlet. The control unit further controls the delivery pump.
SUMMARY OF THE INVENTION
The current invention describes a syringe pump and method to pump a fluid inside a micro reactor at a very small flow rate. Further, it describes a low flow rate sensor that has been designed for measuring the flow rate of the syringe pump. This is attached to an exit section of the syringe. In the present construction, irrespective of the size of the syringe, the pump can control the flow rate accurately. The sensor is initially used to calibrate any syringe and then the voltage corresponding to the desired flow rate is fed to a 12V DC motor. The small flow rate measurement can be estimated accurately, especially when the flow rate is in micro litre range. The syringe pump is capable of pumping the fluid at smaller flow rate ranging from 100 micro liters to 1000 micro liters inside a capillary reactor.
The flow from a small capillary section breaks into drop. The flow rate from the capillary tube can be estimated by measuring the frequency of the drop formation and the size of the drop. Size of the drop at very small flow rate is dependent on the diameter of the capillary section and the flow rate of the fluid inside the capillary tube. The size of the drop and the frequency of the drop formation can be used to estimate the flow rate and hence can be used for measuring the flow rate from the syringe.
BRIEF DESCRIPTION OF THE DRAWINGS ACCOMPANYING THE PROVISIONAL SPECIFICATION
Figure la and Figure lb shows the schematic diagram of a syringe.
Figure 2 shows the locking system of the syringe
Figure 3 shows the syringe when the fluid has been expelled out.
Figure 4 describes the flow rate sensor attached to the exit section of the syringe.
Figure 5 describes the block diagram of the flow control of the signals.
DETAILED DESCRIPTION OF THE ACCOMPANYING EMBODIMENTS
Figure la and Figure lb describes a schematic diagram of a syringe, along with a base block, a slider, a lead screw and a 12 v DC motor. The 12 v DC motor 4 is attached to the base block 5. The lead screw 2 is rigidly attached to the DC motor 4, such that it only rotates, and does not translate (slide/move along the axis of rotation). The slider 3 is internally threaded and attached to the lead screw 2 similar to a nut and bolt assembly. A groove 8 is formed on the base block 5 to arrest the rotary motion of the slider 3. This is because; a leg of the slider 9 is placed deep inside the groove 8 which restricts the rotary motion. The slider 3 then translates or slides over the groove 8; the lead screw 2 is rotated and pushes a piston 11 of a syringe 1. The rotary speed of the lead screw 2 can be controlled by a voltage regulator by controlling the DC motor 4 speed. The translation speed of the slider 3 depends on the rotary speed of the lead screw 2 and the pitch of the lead screw 2. The slider 3 is controlled by controlling the voltage very precisely. The whole set up is mounted on a base plate 7, to provide rigidity to the system. The DC motor 4 spindle and the lead screw rod 2 are attached to a ratchet 12. After one complete pushing the slider 3 has to move backwards. This is done by reverse rotating the DC motor 4, as the speed of the motor 4 is low, the motor 4 takes time to bring the slider 3 back in position. The syringe pump 1 described in the current invention is provided with a locking mechanism, which can be unlocked after one complete cycle. The locking mechanism 10 described has an internal threading and the rest of the part of the slider 3 does not have internal threading, and is loosely fitted with the screw rod, such that after one complete push the lock 10 is loosened and the slider 3 is brought back to position.
Figure 2 describes enlarged view of the locking system of the syringe. The locking mechanism can be unlocked after one complete cycle. The slider 3 has no internal threading; hence even lead screw 2 rotates, the slider 3 cannot slide over a groove 8.
The Slider 3 is connected to the lead screw 2 by locking mechanism 10. Locking mechanism 10 has internal threading which matches with threading of the lead screw 2. When locking mechanism 10 engages with lead screw 2, slider 3 is able to slide over the groove 8.
Figure 3 describes the syringe when the fluid is being expelled out. Locking mechanism 10 is disengaged from the lead screw 2. As mentioned earlier, once fluid is expelled out of the syringe 1, the slider 3 has to move backward to its initial position before starting the next cycle. By disengaging the locking mechanism 10 from the lead screw 2; the slider 3 can be reset back to its initial position without need to operate the DC motor 4 in reverse direction. This saves the time and the energy required to reset the complete setup before next pumping cycle.
Figure 4 describes the flow rate sensor 6 attached to the exit section of the syringe 1. The principle behind measuring the flow rate of an order of micro liter per minute is different from the other measuring principle. Most of the transducer for measuring the flow rate uses a hot anemometer. Here, the flow rate is very small. Therefore the fluid after exiting from the barrel of the syringe 1, break into drops. The volume of the drops depends on many factors such as diameter of the exit section, viscosity of the fluid, and the volumetric flow rate. The drop exiting from the barrel of the syringe 1 is collected into the sensor 6. The high frequency sinusoidal potential difference is applied across the two terminals. After each drop, the magnitude of the peak current rises because of the increase in the capacitance. Since the level of fluid is increasing, the output current is measured and the difference between the two different consecutive peak values is measured which signifies the volume of the drop.
Flow sensor 6 is a capacitance based flow sensing device. Let 'H' be the height flow sensor;'D' be the distance between the two terminals and 'X' be the height of water level in the fluid sensor 6. (All dimensions in metres) V sin(wt) is applied with a high frequency sinusoidal potential; in volt; across the terminals and I is the current; in
ampere; flowing through circuit of the flow sensor 6. Initially when there is no water flowing out of the syringe pump, only air is present between the terminals of the sensor 6 so output current I corresponds to capacitance of air. As water drops enters into the flow sensor 6, water level X increases with time. Since the capacitance of water is more than air, the magnitude of output current (I) also increases with time. The fluid flow is measured till the flow sensor 6 gets completely filled with water till height H.
The frequency of the drop formation can be estimated by noting the time difference between the two consecutive different output current peaks. The ratio of the difference between the two different consecutive peak value of the current and the time difference between two consecutive peaks gives the measure of the flow rate.
Figure 5 describes the flow control of the signals. The current from the sensors is first converted into voltage and then is sent to a data acquisition card 18. The data acquisition card 18 is programmed to record the difference between the two consecutive peak values of the current as well as the time difference between the two consecutive peaks. The ratio of these values measure the flow rate of the fluid. From the data acquisition card 18, the voltage signal at a constant high frequency 19 is calculated . The voltage is then regulated using a voltage regulator 20 and processed in a processor block 21. The signal from the sensor 22 is filtered using a low pass filter 23 and then it is amplified using an amplifier 24. Further, data acquisition and filtering 26 is performed.
Before using the pump, calibration 27 is done with the help of the voltage signal fed to the 12 V DC motor from the data card 18. The different voltage signals from the data card at fixed time interval was amplified 25 and then fed to the dc motor 4. At each signal the voltage flow rate was recorded and the calibration 27 was done. The same procedure can be used to calibrate any syringe irrespective of its size. After
calibration 27, the voltage corresponding to the desired flow rate (measured from the calibration) can be supplied to the dc motor 4.
WE CLAIM
1. A syringe pump 1 for pumping low flow rate liquid comprising (a) a syringe 111, (b) a lead screw 2, (c) a slider 3, (d) a 12 v DC motor 4, (e) a base block 5, (f) a flow rate sensor 6, (g) a base plate 7, (h) a groove 8, (i) a leg of the slider 9, (j) a locking system (mechanism) 10, (k) a piston 11 of the syringe 111 and (1) a ratchet 12 wherein:
a. The syringe pump 1 comprises of the piston 11 which is pushed in and
out for exerting out the liquid;
b. The lead screw 2 is rigidly attached to the DC motor 4, such that it
only rotates, and does not move along the axis of rotation;
c. The slider 3 is internally threaded and attached to the lead screw 2
similar to a nut and bolt assembly;
d. The 12V DC motor 4 is attached to the base block 5;
e. The low flow rate measurement sensor 6 is capacitance based flow
sensing device attached to the exit section of the syringe pump 1 such
that irrespective of the size of the syringe pump 1, the flow rate can be
controlled accurately;
f. The base plate 7 has the whole set up mounted on it to provide rigidity
to the system;
g. The leg of the slider 9 is placed deep inside the groove 8 formed on
the base block 5 to restrict the rotary motion of the slider 3;
h. Locking system 10 is loosely fitted with the screw rod and comprises of internal threading which matches with threading of lead screw 2; and
i. The motor 4 spindle and the lead screw rod 2 are attached to the ratchet 12.
The syringe pump as in 1 wherein the voltage regulator controls the rotary speed of the lead screw 2 by controlling the motor 4 speed wherein the slider 3 is controlled by controlling the voltage and the sliding speed of the slider 3 depends on the rotary speed of the lead screw 2 and the pitch of the lead screw 2.
The syringe pump as in 1 wherein the locking system 10 has internal threading and the rest of the part of the slider 3 does not have internal threading such that:

When the locking mechanism is unlocked after one complete cycle the lead screw 2 rotates and pushes the piston 11 of the syringe 111 and the slider 3 cannot slide over groove 8; and
When the locking mechanism is locked it engages with lead screw 2 and the slider 3 is able to slide over groove 8.

The syringe pump as in 1 wherein once fluid is expelled out of syringe 111, the slider 3 moves backward to its initial position before starting next cycle, disengages locking mechanism 10 from lead screw 2 and is reset back to its initial position without need to operate motor 4 in reverse direction to save time and energy required to reset the complete setup before next pumping cycle.
The syringe pump as in 1 wherein after one complete pushing the slider 3 is made to move backwards by reverse rotating the motor 4 at low speed.
The syringe pump as in 1 wherein the sensor 6 collects the fluid which after exiting from the barrel of the syringe 111 breaks into drop such that:
a) The volume of the drop depends on factors of diameter of the exit section, viscosity of the fluid and the volumetric flow rate;
The high frequency sinusoidal potential difference is applied across the two terminals of the sensor 6;
After each drop, the magnitude of the peak current rises because of the increase in the capacitance; and
The output current is measured and the difference between the two different consecutive peak values is measured as the level of fluid increases to signify the volume of the drop.
7. The syringe pump as in 1 wherein the output current flow I is measured till
flow sensor 6 gets completely filled with water till height H as:
The capacitance of air when there is no water flowing out of syringe pump 1 and air is present between the terminals of sensor;
Increased output current, I with increase of water level X in the flow sensor 6, which in-turn increases with time
8. The syringe pump as in 1 wherein the flow rate from the syringe 111 is
estimated by measuring:
The frequency of the drop formation and the size of the drop;
The ratio of the difference between the two different consecutive peak value of the current; and
The time difference between two consecutive peaks.
9. The syringe pump as in 1 is capable of pumping the fluid at smaller flow rate
ranging from 100 micro litres to 1000 micro litres inside the capillary reactor,
wherein the sensor 6 initially calibrates any syringe 111 so that a voltage
corresponding to the desired flow rate is fed to the 12 V DC motor and the
size of the drop at very small flow rate is dependent on the diameter of the
syringe pump 1 and the flow rate of the fluid..
10. A method for flow control of the signals in the syringe pump 1 for pumping low flow rate liquid comprising (a) the syringe 111 (b) a lead screw 2, (c) a slider 3, (d) a 12 v DC motor 4, (e) a base block 5, (f) a flow rate sensor 6, (g) a base plate 7, (h) a groove 8, (i) a leg of the slider 9, (j) a locking system 10, (k) a piston of the syringe 11 and (1) a ratchet 12 having the steps of:
Converting the current from the sensors into voltage and sending it to a data acquisition card 18;
Recording the difference between the two consecutive peak values of the current as well as the time difference between the two consecutive peaks and measuring the flow rate by the data acquisition card;
Calculating the voltage signal at a constant high frequency from the data acquisition card 19;
Regulating 20 and processing 21 the voltage;
Filtering the signal from the sensor 22 using low pass filter 23;
Amplifying the signal from the sensor 24;
Amplifying the different voltage signals from the data card at fixed time interval and feeding to the motor 25;
h) Performing data acquisition and filtering 26;
i) Calibrating the pump by using the voltage signal fed to the 12 V DC
motor from the data card 27; and j) Recording and calculating the voltage flow rate at each signal.