The SPM System Based On Digital PID Control

Scanning Probe Microscopy (SPM) is a general designation of ScanningTunneling microscope (STM) and other new type Probe Microscopes (such as AtomicForce Microscope, Lateral Force Microscope, Magnetic Force Microscope and so on).It is a kind of surface analyzing instrument which is developing recently in the world.And, a high-tech product integrates many advanced technologies such as photoelectricity, laser, low-level signal detection, mechanical design, automatic controltheory, digital signal processing and so on.Since its birth of 1980s, SPM has applied widely in many fields such as nanotechnology, material sciences, physics, chemistry, and life sciences with thedevelopment and innovation of SPM. However, nowadays, analog PID controltechnology has been still adopted in the majority SPM's control system. This kind ofanalog PID control technology uses normal circuit to design PID controller. Itsshortcoming is that we have to redesign the hardware if we want to improve theanalog system's performance. That means time will be wasted.In this paper, we develop a new control system for SPM. The system based onthe hardware of SPM with the core of DSP TMS320C6713, which is designed by ourlab. Based the hardware, we realize function of digital PID control throughprogramming the DSP. So the new workflow of SPM bases on the control of digitalclosed loop. Consequently, it avoids the shortcomings of the previous SPM withanalog PID controller such as difficulty in upgrading,difficulty in maintenance and soon.Firstly, the key of our work is, to write the testing program for DSP to testhardware and bring the function of system to perfection or completion. Secondly ourwork is to write PID program for DSP to realize the design of digital PID controller.DSP of SPM control system communicated with PC by Universal Serial Bus 2.0 interface.CY7C68013 was used as USB interface chip. When the system is working, DSP adjusts the errorsignal according to the PID arithmetic. At the same time, it transmits the control signal to PC byUSB interface.We use Visual Basic 6.0 and Visual C++ 6.0 as program tools to design the PCapplication based on Universal Serial Bus 2.0 communication interface. At the end ofthis article, the scanning waveform and images of sample's surface based on DigitalPID control system will be achieved and discussed.This work was also supported by the National Natural Science Foundation ofChina (No.10427401).