Application Cases

Experiment Name: Electrostatic Levitation Position Control System

Experimental Principle:
Charged objects experience electrostatic force in an electric field. If this force is sufficient to overcome gravity, the charged object will levitate. When a small sphere of radius *r* is placed between two vertically aligned electrode plates, and a negative voltage U is applied between the upper and lower plates, an electrostatic field of intensity E is generated, directed from bottom to top. The upper plate carries a negative charge, while the lower plate carries a positive charge. The sphere becomes positively charged by induction in this electrostatic field and experiences an upward Coulomb force F. The condition for levitation is that the electrostatic force on the sphere must counteract its gravitational force. This experiment is primarily applied in materials science for material preparation and solidification theory research under deep supercooling conditions.

Testing Equipment:
Host computer, ATA-7020 high-voltage amplifier, electrode plates, position-sensitive detector (PSD), laser.

Experimental Procedure:
The fundamental control method of the electrostatic levitation position control system is as follows:

1. Detect the actual position of the levitated sample.

2. If the sample deviates downward from the center position between the two plates, the control system increases the plate voltage to enhance the upward levitation force.

3. If the sample deviates upward from the center position, the control system decreases the plate voltage to reduce the upward levitation force.

Figure 1 shows the electrostatic levitation experimental system diagram. The system uses a PSD as the position measurement sensor and parallel laser light as the illumination source for the PSD. The control unit processes the two-dimensional (X, Z) position signals measured by the PSD using a control algorithm and outputs control signals to the ATA-7020 high-voltage amplifier. The ATA-7020 amplifier amplifies the voltage control signals, which are then applied to the upper/lower electrodes and horizontal electrodes. By adjusting the intensity of the electrostatic field, the electrostatic force on the charged sample is modified, enabling position control of the levitated sample in the Z and X directions.

Figure 1: Experimental Block Diagram

The levitated object is a graphite-coated ceramic sphere with a diameter of approximately 3 mm. When the system is powered on, the sphere immediately levitates and gradually stabilizes at the center position between the upper and lower plates. The levitation state is shown in Figure 2.

Figure 2: Levitation State Diagram

Figure 3 shows the levitation initiation process plotted by MATLAB based on calibrated Z-direction position data measured by the PSD and received by the host computer. Upon zooming in, it is observed that the levitation accuracy is within ±0.05 mm, as shown in Figure 4, which depicts the levitation state over 0.7 seconds. Figure 5 displays the Z-direction position signal and control voltage signal output by the PSD during levitation initiation, as observed on an oscilloscope. Here, CH1 represents the position signal, and CH2 represents the control voltage signal (with an actual-to-observed ratio of 2000:1). It is evident that the control voltage required during levitation initiation is approximately 7000 V, while the control voltage needed to maintain levitation at the center position between the plates is only about 4000 V.

Figure 3: Levitation Initiation Process

Figure 4: Levitation Accuracy Measurement Diagram

Figure 5: Oscilloscope Observation of Levitation Initiation Process

Experimental Results:
When different target levitation positions are set online for the microcontroller via the host computer’s serial port, the sphere successfully moves up or down to the specified position, as shown in Figure 6. This demonstrates that the designed electrostatic levitation position control system effectively achieves stable levitation and position control.

Figure 6: Position Adjustment Process Diagram

The position control accuracy of the vertical direction system using a 650 nm light source is ±0.05 mm, meeting the design requirement of 0.25 mm for this electrostatic levitation position control system. In the future, using a higher-performance 808 nm laser for position measurement will further enhance the vertical direction control accuracy. Additionally, since horizontal position control does not need to counteract gravity and the center position is the equilibrium point for the horizontal electrostatic force, the horizontal position control primarily serves to resist external disturbances. Thus, even higher precision can be achieved in horizontal position control.

Figure: ATA-7020 High-Voltage Amplifier Specifications

The experimental materials in this article were compiled and released by Xi’an Aigtek Electronics. For more experimental solutions, please continue to follow the Aigtek official website.