Manipulation of Microparts Using Force Controlled Pushing

Motivation

Manipulation of microparts requires different strategies than in the macroworld. The human operator or the electronic controller has to be provided with reliable information from the microworld. Video microcopy widely used requires visibility thus severely restricting the flexibility of handling maneu- vers. A different strategy is to use local process information, such as contact forces, to control precise and flexible operations. Different micro- physical effects, such as adhesion, additionally aggravate manipula- tion at the microscale. Methods to avoid or control sticking have to be found in order to perform precise positioning and assembly of microparts.

Approach

In this project, we explore the force controlled active pushing of microparts. Manipulation by pushing is programmable, does not require carrying or lifting of objects and works by accessing the workpiece W from one side only. As a pushing tool, we chose an AFM (atomic force microscope) cantilever with an integrated piezoresistive force sensor to measure the contact force. W's local position is inferred from contact events derived from the force signal (Fig. right) and the manipulator's joint sensors.

Results

We have built a 3-degree-of-freedom robot with a resolution of 0.5 mm. Statistical analysis of the pushing signal was used to extract contact events from the pushing force, such as touch, loss of contact, and hitting of obstacles. Built into a finite state machine controller, this allowed us to push 500 micron sized parts on a straight path, orient them, and align them with a (moveable) reference with a final accuracy of 3 mum / 0.1°. A graphical representation of such a push-alignment with the reference, as well as a top view of the initial and final configurations are shown below.


Alignment sequence	Initial position	Aligned Position

Download a MPEG-video showing the alignment process (6.7 MB!).

References

Zesch W., Fearing R.S., Alignment of microparts using force controlled pushing, presented at SPIE Conf. on Microrobotics and Micromanipulation, Nov. 2-5 1998, Boston, MA, USA.
Mason M.T., Mechanics and planning of manipulator pushing operations, Int'l J. of Rob. Res., vol 5(3):53-71, 1986.
Son J.S., Monteverde E.A., Howe R.D., A tactile sensor for localizing events in manipulations, IEEE Int'l Conf. on Rob. & Autom. ICRA 94, vol.1(1:471-476, May 1994, San Diego, CA, USA.

Contacts:

Wolfgang Zesch,

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Intelligent Machines and
Robotics Lab

Zesch Wolfgang, last updated June 11, 2000