Noise explanation and how to control micro pump

Noise pollution is one of the environmental pollution. It is the most important environmental problem in the world with water pollution, air pollution and solid pollution. In physics, noise is the sound produced by an irregular vibration, which is transmitted through the air or other elastic medium to the human ear. Physiologically, noise that interferes with normal rest, learning and work, and the noise that people listen to is noise. The frequency that the human ear can hear is 20Hz to 20000Hz. Noise can cause people to be agitated, reduce work efficiency, endanger people’s physical and mental health, and all countries pay more and more attention to noise control. Micro pump is a common component of instruments and meters, and is widely used in scientific research and medical treatment. Scientific research and medical units have strict requirements for noise control. For example, China’s hospital management standards require operation room noise is not higher than 38dB. The medical instruments are the main noise sources in operation room, and some ventilators and suction devices have noise as high as more than 70 dB. Reducing noise pollution in operation room is the necessity of modern medical development. Micro pumps are also common equipment in almost all laboratories. As customers pay more and more attention to the noise of pumps, reducing the noise of micropump has become an important direction for manufacturers.
Diaphragm pump is a kind of micro pump, it is the use of motor driven film reciprocating movement to create a vacuum, so as to suction and extrusion fluid. The high efficiency of the micro pump; movement mechanism and the transmission medium is completely isolated, no pollution to the medium; non dynamic seal, no leakage; reliability; small volume and light weight; not idling; no lubrication and maintenance; its low noise. When the vacuum pump is used for pumping, the pump does not need to be pumped, and the water can be pumped and drained immediately after starting. The utility model can pump air and pump water, and when the water is not dry, the utility model is also not afraid of dry turning. Many advantages of micro pump make it widely used in instrument and meter industry.
From the source point of view, the noise of micro pumps can be divided into three parts: fluid dynamic noise, mechanical noise of mechanical parts and motor noise.
The fluid dynamic noise is a pulse that continuously generates fluid pressure when the micropump works, thus causing the noise radiated by the pump, the valve and the pipe and so on to radiate to the outside. The ajk company researchers measured fluid dynamic noise is the main noise of micro pump. The hydrodynamic noise of micropump belongs to medium and low frequency noise. Micro vacuum pump suction when the intake valve opens, outlet valve closed, air is sucked into the pump chamber and inlet valve cavity pressure fluctuation, the pressure fluctuation of gas in the form of waves radiated from the air inlet, the air inlet noise form. The inlet noise is a wide-band continuous spectrum, and its fundamental frequency can be calculated using the formula f=2n/60 (N per minute rpm). Besides the first harmonic and high frequency, high frequency harmonic frequency than the sound level but lower level. The higher the speed, the greater the degree of vacuum, the greater the flow rate, the greater the noise intake. When the air is exhausted, the intake valve is closed, the air outlet valve is opened, the air expands, and the air flow flows rapidly through the outlet to generate sound waves to form an exhaust outlet noise. Exhaust noise is also a broadband continuous spectrum. The higher the speed, the greater the pressure, the greater the flow rate, the greater the noise exhaust. When the long plastic pipe is connected, the noise of the exhaust port and exhaust port will decrease. The cause of noise in miniature vacuum pump is complicated. Because of the periodic fluctuation of the pressure in the pump chamber, the unsteady flow of water causes a great deal of eddy current. The pressure of the water on the film, the pump cavity and the valve is changing rapidly, and the friction between the water flow and the pump body is produced. Especially when the water temperature is high, the vacuum pump is low, may be saturated steam at the temperature below the water pressure in the suction stroke pump chamber pressure, water will be vaporized, produce a lot of bubbles, the formation of two phase flow complex flow. The pump in the compression stroke, the higher pressure under the action of the bubble quickly burst, and the bubbles around the water at great speed toward the center of the bubble, resulting in high frequency, high impact of water hammer, constantly blow pump parts. There is vibration and noise in the pump. This phenomenon is called cavitation. Cavitation occurs on the solid boundary, which is the result of the constant impact of the impact force on the solid boundary caused by the rapid collapse of the cavitation in the high pressure region. Cavitation damage is more serious, it will damage parts, reduce efficiency, and produce vibration and noise. The noise produced by micro vacuum pump belongs to low frequency noise. The hydrodynamic noise is determined by the principle of the vacuum pump. The improvement of the pump body design can play a role in noise reduction, but the effect of this active noise reduction is still a little away from people’s expectation.
Mechanical noise is not the main source of noise in micro pump. It is caused by the vibration of the film inside the pump, the friction of the bearing, the eccentric motion of the crankshaft and the connecting rod, the impact of the one-way valve, etc.. This kind of noise is random and exhibits broadband characteristics. In the field of active noise reduction, it is necessary to improve the material selection, design, machining accuracy and balance of components.
The motor is also the main noise source of micro pump. There are three kinds of motor noise. One is electromagnetic noise, two is mechanical noise, three is aerodynamic noise. Electromagnetic noise is mainly caused by periodic radial electromagnetic force or unbalanced magnetic pull in the motor, which results in magnetostriction and vibration of the core. The electromagnetic noise is also related to the vibration characteristics of the stator and rotor itself. When the exciting force and the natural frequency resonate, even if the electromagnetic force is very small, it will produce a lot of noise. In order to reduce the electromagnetic noise, sine wave winding should be adopted to reduce the harmonic component. The proper air gap magnetic density should be chosen; the proper slot combination should be adopted; and the rotor slot shall be adopted