Force Reflecting Micro - Teleoperation with Haptic Feedback 1

Traditional force reflecting teleoperation focuses on master and slave systems that have approximately the same workspace volume. This paper addresses force reflecting teleoperation in which the workspace of the master is many orders of magnitude greater than the workspace of the slave. In addition, the forces experienced in the remote environment are one to two order of magnitude below human tactile perception. The two primary contributions are a new approach to force reflecting teleoperation which seamlessly transitions between position and velocity control and experimentally measured assembly forces of micro gears. In addition, we introduce a new approach to micro-force-guided assembly with preliminary results. I. BACKGROUND 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) [1]. Thus, micro-machines can take advantage of the best of MEMS and conventional fabrication techniques. While there is a wide array of micromachining 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 1 This work was supported, in part, by the Office of Naval Research under Interagency Agreement No. 1866-Q356-A1 with the Oak Ridge National laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, and in part by the Office of Naval Research under Interagency Agreement No. 1866-Q356-A1 Submitted to IEEE’s Transaction on Robotics and Automation -2based upon small parts [2]. Figure 1 shows the basic technologies available for mechanical assembly. Manual labor is the preferred method of assembly when production rates are low and part sizes are large. As demand increases, assembly migrates towards automation. This general trend does not hold as parts sizes begin to fall below the millimeter threshold. In this regime, assembly is based on manual labor limiting the production rate as well as increasing cost. As part sizes reduce further into the micron scale, manual assembly is not possible without the assistance of microscopes and tweezers. Furthermore, no method of assembly exists as parts fall between the micron and nanometer scale. Studies have shown that in a wide variety of industries, assembly costs account for approximately 40 to 50 percent of the total production cost [3]. This figure is expected to be dramatically higher for micro-machines where parts are, in general, extremely inexpensive and labor and assembly time is high. Figure 1: Production rate related to scale It can be formally shown that, as the parts scale down in size, the conventional physics associated with mechanics and assembly break down [4]. Gravitational forces become insignificant in comparison to surface and adhesion forces, making trivial tasks, Submitted to IEEE’s Transaction on Robotics and Automation -3such as picking up and releasing a part, impossible with traditional methods [5,6]. New concepts and innovative approaches to micro-assembly are needed to provide rapid, cost effective assembly of complex micro-machines. Self-assembly is clearly one of the more impressive approaches to the construction of micro components but, so far, requires formations of systems fabricated using the same technology [7]. The focus of this paper is on the development of systems that are flexible in terms of the part selection and technologically feasible today. We begin by focusing on human-assisted microassembly. First, we describe a new approach to force reflecting micro-teleoperation. Next, we describe the impact scale has on assembly forces. As an example, we provide experimental results on the assembly of gears with sub-micron clearances. We conclude with a description of a new approach to force guided micro-assembly with preliminary results. II. TELEOPERATOR CONTROL One of the challenges associated with micro-teleoperation is the scaling between the human hand and micro parts. Assembly of microand 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. In this section, we describe an approach to microteleoperation that we have developed to overcome this disparity between relatively large workspace volume and fine motion resolution with force reflection. Submitted to IEEE’s Transaction on Robotics and Automation -4Figure 2: Master workspace Figure 3: Slave micro-manipulator 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 micro-manipulator. The end of this tube is visible in Figure 4. Finally, a video microscope system provides 330x vision amplification to the operator. One of the desired attributes of this system is that all of the components are commercially available. Submitted to IEEE’s Transaction on Robotics and Automation -5In micro-assembly, there are conflicting requirements. Fine motion control with force reflection is required to assemble parts. In our case, the clearance between gears and posts, shown in Figure 4, is less than 1 micron. This is far below positioning resolution of the hand so some form of motion de-amplification and force amplification is required from human to machine. However, parts may be spread over a much larger area. For example, parts from one wafer may need to be combined with parts from a second wafer. 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 4: Micro-Gears Submitted to IEEE’s Transaction on Robotics and Automation -6Virtual Box in Slave Environment