Force Reflecting Micro-Teleoperation with Haptic Feedback

 

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Introduce a new approach to micro-force-guided assembly with preliminary results.

Motivation

Micro-machines are machines that straddle the size range between microelectromechanical system (MEMS) and conventional machines. Micro-machines are not MEMS devices per se even though they may include MEMS components, or may be fabricated in part using similar techniques (such as deep x-ray lighography (LIGA), stereolithography, ion milling).  Thus, micro-machines can take advantage of the best of MEMS and conventional fabrication techniques. While there is a wide array of micro-machining technologies that can produce sub-millimeter to micron sized parts, there is presently no technology that provides automated or assisted 3-D assembly of machines based upon small parts. Figure 1 shows the basic technologies available for mechanical assembly.

Figure 1.  Production rate related to scale.

Teleoperator Control

One of the challenges associated with micro-teleoperation is the scaling between the human hand and micro parts. Assembly of micro- and millimeter-sized parts requires fine position resolution, below the micron range. In addition, parts may be spread over a relatively large surface area, such as a 20 cm diameter wafer. As with macro assembly, force reflection is essential.

Figure 2 shows the master workspace for our micro-teleoperation system. There are two video monitors: one showing an overview of the remote workspace and a second showing a closeup of the task. The master robot is a Phantom haptic interface. The slave micromanipulator is shown in Figure 3. There are two components to this system. The first is a 3-axis table with a 50 cm x 50 cm x 10 cm workspace with 0.1 micron position resolution. In addition, we have added a voice coil to the vertical axis to achieve higher bandwidth and nanometer vertical positioning resolution. Motion scaling from the human to the micro-teleoperator is presently 1000:1. Thus, 10 cm of motion by the human results in 10 microns of motion on the slave.  Likewise, force amplification from the micro-environment permits normally undetectable forces to be experienced by the operator. Part pick-up and release is achieved through controlling a vacuum across a micro-tube attached to the end of the micromanipulator. The end of this tube is visible in Figure 4.  Finally, a video microscope system provides 330x vision amplification to the operator.

Figure 2.  Master workspace.

Figure 3.  Slave micro-manipulator.

Figure 4.  Mico-gears.

Fine motion control in teleoperation is generally achieved through position control with de-amplification from the master to the slave. However, the higher the resolution of the position control, the smaller the remote workspace. Clearly, there is a trade-off here between fine position control and range of motion. Our objective is to establish a teleoperation methodology that enables a seamless transition between position control for fine motion control with velocity control to expand the reachable workspace. The approach, shown in Figure 5, consists of constraining the master manipulator with a compliant box.

Figure 5.  Teleoperation methodology.

Micro-Assembly Forces

Figure 6 shows the resulting comparison of forces as a function of scale. It is clear that all of the forces decay with decreasing size, some more rapidly than others. Clearly, gravity is the most sensitive with a cubic relationship, followed by both compliance and electrostatic forces which decay with the square of scale, with surface adhesion and van der Waals being the least sensitive decaying with a linear relationship to scale. Above the millimeter range, gravity and compliance are the dominant forces. However, below the millimeter range, van der Waals and electrostatic interactions experience forces in the same order of magnitude as gravitational loads and rapidly dominate at scales below the 10s of microns to nanometers.

Figure 7 shows preliminary experiments on the assembly of millimeter sized gears. The experiment, inserting the gears onto their complimentary posts, is a micro-version of the peg-in-the-hole problem. The hole diameter is 500 microns with one micron of clearance. The gears, shown in Figure 4, experience assembly forces in the 10’s of grams which is approximately in the same order of magnitude as the compliance forces shown in Figure 6.

Figure 6.  Comparison of scale dependent forces.

Figure 7.  Measured assembly force.

 

For publications related to micro-assembly, see the following link: http://www.ornl.gov/sci/engineering_science_technology/ROBOTICSGROUP/robotics/publicationslist.htm#meso2 .

For further information, contact Dr. Lonnie J. Love.

 

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Last updated:  December 15, 2003