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.
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:
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.
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