Stirrers are widely used in chemical experiments, especially in the chemical, pharmaceutical and food fields. Traditional manual mixing is not only time-consuming and labor-intensive, but also prone to uneven mixing of the solution. The magnetic stirrer solves this problem because it is not only easy to operate, but also adjusts the speed and direction of stirring, especially for stirring highly viscous or toxic solutions. However, the traditional magnetic stirrer is large due to the use of electric motors, which makes it difficult to meet the needs of portable equipment for miniaturization. To this end, an ultra-thin magnetic stirrer is designed in this paper, which directly converts electrical energy into magnetic energy, simplifying the structure and reducing the thickness of the equipment.
Design Principles
According to the principle of electromagnetic conversion, a magnetic field with periodic changes is directly generated by multiple spiral coils with pulse currents of different phases to drive the stir bar to rotate. Compared with the traditional way of driving the external magnet to rotate by the electric motor, the design of this paper omits the middle part of the machine, significantly reduces the volume and thickness of the device, and reduces the thickness to 1 cm, which is more suitable for portable inspection systems.
Spiral coil design
Using the right-hand spiral rule, when the current passes through the spiral coil, an N-pole magnetic field is generated above and an S-pole magnetic field below, and the magnetic field polarity can be switched by changing the direction of the current. In order to ensure the smooth rotation of the stir bar, the design uses 4 diagonally placed spiral coils, the two sets of coils are energized alternately, and the direction of the magnetic field is controlled by timing to control the rotation of the stir bar clockwise or counterclockwise.
Stirrer motion timing
To achieve the clockwise rotation of the stir bar, a circle is divided into 8 directions (northwest, true north, northeast, etc.), each corresponding to a specific magnetic field configuration of the spiral coil. By precisely controlling the current timing of each coil, the direction of the resultant magnetic field changes and the stir bar rotates continuously.
Hardware design
The hardware part consists of a microcontroller, a driving circuit, a spiral coil and a power supply.
MCU - AT89S51 is selected as the control core, which is responsible for reading the keys and generating current timing signals.
The driver IC is L6219DS with an output current range of 300~500 mA, which supports the control of the windings of the two-pole stepper motor and can generate accurate current timing.
Spiral coil - made of copper wire, designed with parameters such as stir bead mass, solution viscosity and beaker radius in mind.
Power Supply - Provide stable power supply for the entire system.
Software design
The program is written in C language, which is divided into the main program and the timed interrupt module.
Main program——Initialize the microcontroller and timer, complete the key detection and adjust the working state according to the user's input, such as forward rotation, reversal, acceleration, deceleration, etc.
Timed interruptions——Responsible for generating accurate current timing signals, adjusting the direction and size of coil current in real time according to the stirring state, and ensuring the smooth operation of the stir bar.
Performance & Applications
The ultra-thin magnetic stirrer is adjustable in the range of 150~1500 r/min, and has the advantages of simple structure, stable operation and flexible operation. Compared to conventional agitators, the thickness is significantly reduced to 1 cm, making it more suitable for use in portable devices, especially in electrochemical portable detection systems. The direct conversion of electrical energy into magnetic energy not only simplifies the structure, but also improves the mixing efficiency and stability.
conclusion
The ultra-thin magnetic stirrer designed in this paper realizes the efficient stirring function, and its small size, light weight and easy to carry provide a new solution for portable experimental equipment. In the future, its magnetic field control accuracy and power consumption performance can be further optimized to adapt to a wider range of application scenarios.
