The MSRAL is interested in applying flexible manufacturing techniques to micro, meso, and nano-scale manipulation tasks utilizing simple or minimalistic actuation and sensing schemes. Therefore, we have designed, prototyped, and customized a flexible automation system for meso-,micro-, and nano-scale manipulation tasks. This test-bed has an inverted optical microscope with a CCD camera attached to one of the ports. As a result, whatever is observed in the field of view (FOV) of the microscope can be routed to a control PC for image processing. There are multiple micromanipulators in the system configuration which are capable of being computer controlled with minimum incremental motions on the order of 60 nm along each degree of freedom. There is a computer controlled motorized XY stage on the microscope platform for automating planar movements of a sample residing on the stage. For example, during meso-scale manipulations, a 4X objective is placed on the microscope yielding a FOV of approximately 3.3 mm x 2.5 mm. The images from the camera are 640 x 480 pixels in size, thus each pixel in the image corresponds to approximately 5 µm. Typically, each manipulator is outfitted with one or two 5 µm or 25 µm tip diameter tungsten probes, which can also be attached in-line with a 10g capacity load cell to sense forces at the mN level. Custom image processing and control software used to interface the hardware components of the platform with a quasi-static dynamics simulator and path planning algorithms to simulate and execute various tasks.
For manipulation and assembly tasks at the meso-scale,
surface forces, such as stiction, friction, and electrostatic forces,
dominate. Most parts are planar so access to the parts from the top is
possible. Grasping the part with a suction gripper can be performed, however
it can only be used to approximately position the parts due to the
difficulties in part release resulting from aforementioned dominant surface
forces. Therefore, manipulation and assembly with a gripper is not a
preferred technique and manipulations with point probes are required. To
study this problem, the canonical peg-in-the-hole problem at the meso-scale
had been investigated. The peg-in-the-hole problem involves assembling a
planar, rectangular part into a planar, rectangular slot with uncertainties.
The parts are about 40um thick and manufactured out of beryllium copper using a photochemical machining process. The hole or fixture is attached to a glass microscope slide which is coated with a thin layer of mineral oil. This system has uncertainties from three different sources. There are uncertainties in estimating (or sensing) the state of system (peg); errors in the control/actuation of the probe position relative to the part; and uncertainties in the geometric (from manufacturing) and physical parameters (from modeling) of the system. Two types of support surface friction models have been considered for the system: a three-point support surface and a viscous damping layer along the surface. Open-loop plans from a sampling-based motion planner have been implemented experimentally to successfully manipulate the peg into the hole. These manipulations involved a single 5um tip probe on the active (computer-controlled) manipulator.
Subsequent work on closing-the-loop has been performed and also resulted in successful manipulations of the peg into the hole. In this work, both manipulators are used. This time the passive (manual) probe is outfitted with the single tip probe (STP) while the active manipulator has a dual tip probe (DTP). Three types of interactions with system are allowed: (a) one-point contact with the DTP, (b) two-point contact with the DTP, and (c) one-point contact with the DTP along with one-point contact with the STP. These types of interactions are combined in different ways to generate robust motion primitives to predictably manipulate the position and orientation of peg and move it from the starting position to the goal location.
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