Ortho-tweezers is a micromanipulation apparatus with two probes mounted orthogonally to each other which make "chop stick"-like tweezers. As shown in the picture above, this arrangement allows the tweezers not only to grasp a part but to rotate it. This work is developed in Prof. Ron Fearing's group.

This page is an overview of Ortho-tweezers. For details and source code, please see the Ortho-tweezers User Manual.

The ortho-tweezers apparatus was originally developed by Eiji Shimada. Mr. Shimada's ortho-tweezers web page includes a detailed description and many movies showing the basic grasping and rotation operations. The system is also described in the following paper:

Ortho-tweezers Software

We have developed a Java application which provides an interface to the orthotweezers system as shown in this screen shot. It provides direct manual control and readouts of the stage and probe positions and tip forces, as well as automated primitives for grasping and orienting parts. It also allows a Python script to call the Java primitives. In this way, the convenience of Python can be used to automate an entire assembly sequence as shown below. Details are in the Ortho-tweezers User Manual.

Movie: assemble clock script

Here is a movie of the assemble clock script. (The movie is shown at 10x speed.) There are 12 blocks on a pre-arranged pallet. The script locates each block, grasps it, and places it around the circle of a "clock face." Note that it rotates each block according to its position on on the clock face. Note also that before grasping the block for a position, it first tests the position to determine the exact Z level of the surface.

Movie: grasp block algorithm

Here is a movie of the grasp block algorithm. The algorithm first sweeps each probe to find the lower and left corner of a square block. (The block is at a tilted angle.) This is done with feedback from the tip strain gauges. Once the two corners are know, the algorithm can compute the grip points and lift the block. Once lifted, it is possible to rotate the block.

back to Jeff Thompson's homepage