This project was developed as part of my studies, with the aim of creating a gripper specifically designed for handling thin lithium foil (less than 20 micrometers). Lithium is a highly reactive and sensitive material, making traditional handling methods challenging. For instance, pneumatic grippers, such as large-area suction pads commonly used for film handling, pose significant issues. These methods would require the use of inert gas as the process medium, which complicates the handling of lithium foil. Additionally, pneumatic systems carry the risk of contaminating the foil with particles from the environment. Consequently, electrostatic grippers present a viable solution.
The contactless gripper is an advanced version of the electrostatic gripper previously presented in electrostatic_gripper. It features an innovative design with four zones, each consisting of a concentric pair of electrodes. In the center of each electrode pair, there is a distance sensor that measures the gap between the gripper and the film being handled.
The voltage for each individual zone (up to a maximum of 1000V) is now regulated based on the measured distance, ensuring that the attractive electrostatic forces and gravitational forces remain balanced.
The foundation of the system is a STM32F103 (Bluepill) microcontroller, which processes the distance measurements and calculates the corresponding voltages for each zone using a PID controller. The required voltage range of 0 to 1000V is generated by a specially designed circuit based on the half-bridge driver "FAN73912mx". For distance sensing, we have selected inductive sensors "DWAD 509 M8 390," which have a measuring range of 0 to 4 mm and provide an analog output. The analog-to-digital conversion is performed by four ADS1115 chips, which are connected to the microcontroller via I2C. Since the distance sensors do not produce a linear voltage signal, the microcontroller must linearize the output using calibration data, which is obtained by measuring voltage over distance with a PI linear axis, achieving an accuracy of 0.1 µm as a reference.
The user interface is a Python-Gui, that runs on a computer, allowing users to visualize measurement and control signals, as well as configure parameters. Communication with the microcontroller occurs via a serial interface.
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| Halfbridges | Microcontroller and AD converter |
In practice, this appears as follows: on the left, you can see the gripper with the suspended film, and on the right, the corresponding measurement and control values are displayed.
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| Levitating Foil | Python Interface |