PUMP CONTROL FOR LOW FLOW VOLUMES

Abstract

A method for controlling a gas flow of a pump for high flow rates at a low average flow rate by changing the gas pressure inside a cavity in said pump. The method includes decreasing the gas pressure in said cavity during a first predetermined time period, increasing the gas pressure in said cavity during a second predetermined time period, and stopping the active change of gas pressure during at least a third predetermined time period. Additionally, a pump assembly for high flow rates operated at a low average flow rate is disclosed that includes a number of pumps, a pump motor with a number of stator windings adapted to drive said pumps, and a control unit adapted to control said pump motor. In one embodiment the number of pumps is equal to said number of stator windings. The motor can momentarily increase its force on the pumps.

Claims

1. A method for controlling a gas flow of a pump for high flow rates at a low average flow rate by changing the gas pressure inside a cavity in said pump, said method comprising the steps of: decreasing the gas pressure in said cavity, during a first predetermined time period; increasing the gas pressure in said cavity during a second predetermined time period; stopping the active change of gas pressure during at least a third predetermined time period; and wherein the decreased gas pressure and the increased gas pressure are predefined to overcome an opening resistance of an inlet valve and an outlet valve, respectively.

2. The method of claim 1, wherein said first predetermined time period is substantially equal to said second predetermined time period.

3. The method of claim 1, wherein said first predetermined time period and said second predetermined time period correspond to a part of a pump cycle of said pump.

4. The method of claim 1, wherein said pump is connected to a control unit, said method including controlling with said control unit said gas pressure decrease and said gas pressure increase; and said first predetermined time period and said second predetermined time period.

5. The method of claim 1, wherein said pump is a membrane pump.

6. The method of claim 4, wherein said control unit controls two or more membrane pumps, said pumps having individual pump cycles that are maximally phase shifted in relation to each other.

7. The method of claim 5, further comprising the step of: controlling the main gas flow of the pump by repeatedly introducing a short interrupt of flow between one or several pump cycles of said membrane pump for reducing the average gas flow over time.

8. The method of claim 1, wherein said gas is air.

9. The method of claim 1, wherein said pump is adapted to be used in connection with a sampling device for measuring air quality.

10. The method of claim 4, wherein said pump includes a pump motor, said pump motor is an electrical motors and said method includes controlling the increase of gas pressure and said decrease of gas pressure by said control unit based on a voltage provided to a pump motor of said pump or pumps.

11. The method of claim 10, further including momentarily increasing said voltage provided to said pump motor of said pump or pumps to a voltage substantially higher than a specified input voltage for said pump motor.

12. The method of claim 10, wherein said pump motor includes a rotor, the method further comprising the steps of: detecting an angle of the rotor in said pump motor; comparing said angle with the positions of said pump or pumps; and providing a higher voltage to the electrical motor to increase angular velocity in order to increase or decrease said gas pressure inside the pump chamber sufficiently fast to let said inlet valve and outlet valve operate.

13. The method of claim 12, further comprising the step of monitoring output gas flow during one revolution or a part of a revolution of the pump motor for detecting possible pump failure of any one of said pump or pumps.

14. A pump assembly for high flow rates operated at a low average flow rate comprising: a plurality of pumps; a pump motor with a number of stator windings adapted to drive a rotor, said rotor driving the crank shafts of said plurality pumps; a control unit adapted to control said pump motor; wherein said number of pumps is equal to said number of windings.

15. The pump assembly according to claim 14, wherein said stator windings are positioned relative to said pumps with such an angle that the maximum torque by said rotor and windings is exerted at an angle of said rotor where most force is required to operate said pumps.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

[0021] FIG. 1 is a schematic view of a membrane pump with one membrane.

[0022] FIG. 2 is a schematic view of a membrane pump having four pump heads, i.e. four membranes.

[0023] FIG. 3a illustrates the function of the valves for a membrane pump membrane when the pressure in the pump chamber is decreased during inlet of gas.

[0024] FIG. 3b illustrates the function of the valves for a membrane pump membrane when the pressure in the pump chamber is increased during outlet of gas.

[0025] FIG. 4 illustrates malfunction identification of a four membrane pump according to the present invention.

[0026] FIG 5a is a schematic view of a the pump motor windings of a membrane pump.

[0027] FIG 5b is a schematic view of a the pump motor windings of a membrane pump in relation to the three pump heads of the membrane pump.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0028] FIG. 1 is a schematic view of a membrane pump with one membrane, showing only the drive shaft 1, the crank shaft 2 and the membrane 11. The pump chamber and the inlet and outlet valves are not shown. FIG. 2 is a schematic view of a membrane pump of a similar type as in FIG. 1 but having four pump heads, i.e. four membranes 11, 12, 13, 14. The use of four pump heads will reducing the maximum torque required by the pump motor and it will achieve a smother flow since the pump cycles of the four individual pump cycles are phase shifted 90 degrees to each other.

[0029] FIG. 3a illustrates the function of the valves 3, 4 for a membrane pump membrane when the pressure in the pump chamber 5 is decreased during inlet of gas. As can be seen the inlet valve 3 is forced to open while the outlet valve 4 is forced to close due to the decrease in pressure in the pump chamber 5 and a flow of gas indicated by the arrow 17 enter through the inlet valve 3 into the pump chamber 5. FIG. 3b illustrates the function of the valves 3, 4 for a membrane pump membrane when the pressure in the pump chamber 5 is increased during outlet of gas. As can be seen the inlet valve 3 is forced to close while the outlet valve 4 is forced to open due to the increase in pressure in the pump chamber 5 and a flow of gas indicated by the arrow 18 exit through the outlet valve 4 exiting the pump chamber 5. When running membrane pump heads with passive valves, a certain speed is required to induce enough backpressure dΔP/dt change for opening valves. Due to the torque required to compress the membrane at each pump head, it is hard for a small electrical motor to drive the pump heads slowly with a fixed angular velocity. By pulsing one revolution at a time, these problems are overcome. A high enough backpressure is induced and the electrical motor can be precisely controlled. High accuracy, high speed and instant (simple) data processing of non-averaged values are required in order to measure flow correctly when induced with such a pump. This is achieved by a revolution sensor, preferably a hall sensor (not shown), keeping track of the pump revolution speed. The flow is measured by a mass flow meter.

[0030] Data processing of flow curve and characterization of flow pulses induced by membrane strokes gives a diagnostic indication of pump condition as shown in FIG. 4. FIG. 4 illustrates malfunction identification in a four membrane pump according to the present invention.

[0031] For starting the pump according to the present invention when pulsing one revolution at a time, a power boost (e.g. higher voltage on driver bridges) may assist a pump motor otherwise too weak. By measuring how the pump motor manages to keep speed up (depending on load) the signal to the driver bridges can be reduced while maintaining the same pace. Accurate control of the pump motor may thus be achieved.

[0032] FIG. 5a shows a schematic image of the motor 20 for the pump assembly according to the invention. The motor has three windings 21, 22, 23 and a dipole magnet 24, 25 having a north pole 24 and a south pole 25, said dipole magnet having the drive shaft 1 of the pump assembly arranged in the center of the magnet. The rotation of the magnet and the drive shaft is indicated by the arrow 26. In FIG. 5a the motor is positioned for an easy start by having the winding 21 pull the north pole 24 towards it, while the winding 22 is operated in counter phase so that it will push the north pole 24. In that way the rotation is initiated. The rotation is then continued in a normal manner for driving an electrical motor, well known for a person skilled in the art.

[0033] FIG. 5b shows the schematic image of the motor 20 as in FIG. 5a, having three pump heads 31, 32, 33 superposed on the engine 20 attached to the drive shaft 1 of the pump assembly. The pump head outlets are connected to a common outlet flow channel (not shown) and the pump head inlets are connected to a common inlet channel (not shown).

[0034] It is understood that other variations in the present invention are contemplated and in some instances, some features of the invention can be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly in a manner consistent with the scope of the invention.