Description:

Computer controlled submicron positioning will enable us to investigate methods of non-contact cell membrane detection for use as a position regulator. To this end we intend to explore the use of piezo tube positioners in addition to our linear stepper motor approach. To drive a piezo tube in 3 axes, 5 bipolar voltage sources are needed. The pulse width modulators from a PIC16f73 are used to construct a pair of boost converters capable of producing up to ±500 Volts. The PIC monitors the voltage through an on-chip analog to digital converter and adjusts the duty cycle on its pulse width monitor to achieve the voltage requested by the host computer. For ultra fine control, analog inputs may be used to set the voltage through a pair of transistors. In this mode the PIC will set the boost converters potential 2 volts above the requested value to reduce heating. A fine position property has been added to allow the positioner to work smoothly with the existing BRC micro-manipulator.

Progress:

Piezo Tube:
There has been no progress on this piezo component of the project, however, this will benefit from the development of the dielectrophorises oscillator as part of another project. This will be reported on next year. The PIEZO will then be a Field Programmable Gate Array (FPGA) based system. A CPU has been synthesized in the FPGA. It interfaces to a host computer and 24 bit DACs. High voltage amplifiers provide the necessary voltage gain. Transformers driven by Pulse With Modulators in the FPGA will generate the required voltages.

Joystick Interface:
We have written a stand-alone program to interface a joystick to our micromanipulators. Inexpensive game control joysticks can now be used for very precise positioning of electrodes. The speed is proportional to the distance the joystick is moved. This application uses Windows API functions to determine the joysticks state and then calculates the proper step and direction signals to send to the motor drivers.

Microelectrode positional control and automatic data acquisition:
We have produced a multifunction microcontroller circuit board (Omni board) that interfaces to our motion systems. It has been programmed for three-dimensional scanning and Z-axis height regulation of a sensing electrode. It records voltage from two analog inputs and sends position and voltage data to the host computer. One of the analog channels feeds back to the Z-axis motor to keep its position constant. The program on the computer sends the Z value to track the scan parameters. During the scan the program plots the voltages and the Z-topology graphically in a XY grid, the value being represented by the color of a point. The data is then saved as images and as a spreadsheet. The parameters are:
· Number of X points
· Distance between X points
· Number of Y pints
· Distance between Y points
· Time spent averaging at each point
· Speed to move
· Z tracking value
This system will be replaced by the FPGA system we are working on. The programming will not have to be modified. The Z-track data is magnitude derived from a lock in amplifier. We intend to perform the lock-in amplifier function in the FPGA. This will eliminate the lock-in amplifier hardware, simplifying the system and greatly reducing its cost.