Annjoe Wong-Foy

Diamagnetically levitated robots: An approach to massively parallel robotic systems with unusual motion properties

Using large numbers of micro robots to build unique macrostructures has long been a vision in both popular and scientific media. This paper describes a new class of machines, DiaMagnetic Micro Manipulator (DM3) systems, for controlling many small robots. The robots are diamagnetically levitated with zero wear and zero hysteresis and are driven using conventional circuits. System test results have reported unusual motion properties, including exceptional open loop repeatability of motion (200 nm rms) and relative speeds (37.5 cm/s or 217 body lengths/s) [1]. A system using 130 micro robots as small as 1.7 mm with densities up to 12.5 robots/cm2 has been demonstrated. This paper reports initial data on robot trajectories, and shows that open loop trajectory repeatabilities on the order of 0.8 μm rms or better are feasible in a levitated state compared with 15 μm rms repeatability in a non-levitated state with surface contact. These results suggest an encouraging path to complex micro-robotic systems with broad capabilities.

Force requirements for artificial muscle to create an eyelid blink with eyelid sling.

OBJECTIVE To determine the force requirements, optimal vector, and appropriate materials of a novel eyelid sling device that will be used to rehabilitate eyelid closure (blink) in congenital or acquired permanent facial paralysis with an artificial muscle. METHODS The force required to close the eyelids in human cadavers (n = 6) were measured using a load cell system. The eyelid sling using either expanded polytetrafluoroethylene (ePTFE) or temporalis muscle fascia was implanted. The ideal vector of force and placement within the eyelid for a natural eyelid closure were compared. RESULTS The eyelid sling concept was successful at creating eyelid closure in a cadaver model using an upper eyelid sling attached to the distal tarsal plate. Less force was necessary to create eyelid closure using a temporalis muscle fascia sling (627 +/- 128 mN) than for the ePTFE eyelid sling (1347 +/- 318 mN). CONCLUSIONS The force and stroke required to close an eyelid with the eyelid sling are well within the attainable range of the electroactive polymer artificial muscle (EPAM). This may allow the creation of a realistic and functional eyelid blink that is symmetric and synchronous with the contralateral, normally functioning blink. Future aims include consideration of different sling materials and development of both the EPAM device and an articulation between the EPAM and sling. The biocompatibility and durability studies of EPAM in a gerbil model are under way. The successful application of artificial muscle technology to create an eyelid blink would be the first of many potential applications.

Artificial Muscle for Reanimation of the Paralyzed Face Durability and Biocompatibility in a Gerbil Model

BACKGROUND Current management of permanent facial paralysis centers on nerve grafting and muscle transfer; however, limitations of those procedures call for other options. OBJECTIVES To determine the durability and biocompatibility of implanted artificial muscle in a gerbil model and the degree of inflammation and fibrosis at the host tissue-artificial muscle interface. METHODS Electroactive polymer artificial muscle (EPAM) devices engineered in medical-grade silicone were implanted subcutaneously in 13 gerbils. The implanted units were stimulated with 1 kV at 1 Hz, 24 h/d via a function generator. Electrical signal input/output was recorded up to 40 days after implantation. The animals were euthanized between 23 and 65 days after implantation, and the host tissue-implant interface was evaluated histologically. RESULTS The animals tolerated implantation of the EPAM devices well, with no perioperative deaths. The muscle devices created motion for a mean of 30.3 days (range, 19-40 days), with a mean of 2.6 × 106 cycles (range, 1.6 × 106 to 3.5 × 106 cycles). Histologic examination of the explanted devices revealed the development of a minimal fibrous capsule surrounding the implants, with no evidence of bacterial infection or inflammatory infiltrate. No evidence of device compromise, corrosion, or silicone breakdown was noted. CONCLUSIONS Artificial muscle implanted in this short-term animal model was safe and functional in this preliminary study. We believe that EPAM devices will be a safe and viable option for restoration of facial motions in patients with irreversible facial paralysis.

Application of micro-robots for building carbon fiber trusses

Using diamagnetic micro-manipulation, micro-robots (~10 mm in size) with specialized end-effectors are able to grasp and manipulate small light weight (~mg) carbon fiber elements to construct macroscopic cubic carbon fiber trusses (~1000 parts and 300 mm long) that can achieve mechanical crush performances surpassing those of commercially available aluminum honey combs. Employing low cost micro-robots and end-effectors allows the implementation of both parallelization and new functionality without the need for expensive fixed tooling. We demonstrate this concept by modifying the micro-robot end effectors to build carbon fiber octet trusses and carbon fiber trusses with integrated electronics.

Optimal control of diamagnetically levitated milli robots using automated search patterns

This paper reports early results of optimal control using diamagnetically levitated robot (DLR) systems. Levitated robots, typically 1-4 mm in size, are driven locally by printed circuit boards (PCBs) with zero friction and near-zero hysteresis. As previously reported [1, 2], these properties give the levitated system excellent repeatability at the micron and submicron levels for both positioning and trajectories. Highly repeatable systems are generally good candidates for optimal control because variability in identifying and exploiting optimized control parameters are minimized. In the data reported here, levitated milli robots are characterized, and we present experiments showing a 5× reduction in oscillations using a debouncing routine that is manually optimized in time. Manual optimization is effective in some cases, but due to the multi-degree-of-freedom (DOF) aspects of levitated robots, a more robust self-tuning method is desirable. Toward this goal, we describe experiments using automatic optimization of robot motion using a computerized search-and-test routine that varies PCB trace currents and selects optimal currents based on automatic measurement of motion error. The automatic optimization using this method has shown settling times to micron and submicron levels that are 20-40 times faster than simple bang-bang control of equilibrium currents. In one test reported here, 150-μm moves were demonstrated at 90-nm rms error with 15-ms move times.

Stretching the Capabilities of Energy Harvesting: Electroactive Polymers Based on Dielectric Elastomers

Dielectric elastomer actuators are “stretchable capacitors” that can offer muscle-like strain and force response to an applied voltage. As generators, dielectric elastomers offer the promise of energy harvesting with few moving parts. Power can be produced simply by stretching and contracting a relatively low-cost rubbery material. This simplicity, combined with demonstrated high energy density and high efficiency, suggests that dielectric elastomers are promising for a wide range of energy-harvesting applications. Indeed, dielectric elastomers have been demonstrated to harvest energy from human walking, ocean waves, flowing water, blowing wind, pushing buttons, and heat engines. While the technology is promising and advances are being made, there are challenges that must be addressed if dielectric elastomers are to be a successful and economically viable energy-harvesting technology. These challenges include developing materials and packaging that sustain a long lifetime over a range of environmental conditions, designing the devices that stretch the elastomer material uniformly, and system issues such as practical and efficient energy-harvesting circuits.

Automated 2D micro-assembly using diamagnetically levitated milli-robots

In this article, we demonstrate the application of diamagnetically levitated milli-robots for the 2D micro-assembly of 10-μm polymer microspheres and other silicon microfabricated parts. By using an optical microscope for feedback (imaged at 27 Hz), we are able to demonstrate long-term open-loop stability (up to 78 hr) and sub-micron stability of the levitated micro-robots. Furthermore, due to the low hysteresis and high compliance in the magnetic drive of the milli-robots, we are able to directly use the milli-robots in conjunction with machine vision as a force sensor. Soft polymer-based end effectors are used for the micromanipulation of parts and show modest reliability of pick (>70%) and high reliability of place (>99%) that is insensitive to the pick surface material. Finally, we implement autonomous micro-assembly from randomly deposited microspheres into ordered arrays.

Incremental Inspection for Microrobotic Quality Assurance

This paper addresses inspection techniques that can be performed by microrobots used for fabricating three dimensional structures. In contrast to most commercial rapid prototyping processes, the parallelism afforded by microrobot teams allows incremental inspection of structures during assembly. In the present case, this approach is applied to parts fabricated from carbon fiber struts bonded with UV-cured epoxy. Preliminary tests involving thermal and vibrational inspection methods are described and compared with the results of FEA models of the joints. Vibrational inspection performed by microrobots and recorded using a directional microphone, characterizes bond joint natural frequency with good resolution (an average measurement standard deviation of 5Hz over a range of 650–1215 Hz). These effective stiffness measurements are correlated with ultimate bond strength as well. The measurements are sufficient to distinguish between joints that do or do not have desired amounts of adhesive.Copyright

Multi-agent systems using diamagnetic micro manipulation — From floating swarms to mobile sensors

Multi-agent robotic systems on small scales typically use, or envision using, small mobile robots. This paper takes a broad-brush look at a relatively recent development in milli and micro robots, Diamagnetic Micro Manipulation (DM3) systems, in a multi-agent context. We report various multi-agent operations, such as multi-agent part manipulation, robots-acting-on-other-robots for enhanced functionality, and robot-supplied local feed, to assess the state of the art of this new type of system. In addition, we explore and analyze the multi-agent implications of known DM3 properties and earlier single-agent results to motivate future research in this area. As reported here, some of these multi-agent implications include mobile high-precision sensor transducers, near-field communications channels using robots as both transmitters and receivers, and novel swarm architectures.

Self-assembly of milli-scale robotic manipulators: A path to highly adaptive, robust automation systems

Today, trends in manufacturing automation favor high levels of adaptability and flexibility for rapid product change, customization, and new process integration. This paper looks at a new technology, diamagnetic micro manipulation (DM3), for taking adaptability of automation to a higher level. Experiments reported here show a path to automation systems that can self-assemble their own robotic manipulators, fabricate tools-on-demand to execute new processes, optimize existing processes, and/or replace or repair tools. These printed circuit board (PCB) systems can control very large numbers of milli-scale robots. Hence, as described in this paper and in contrast to conventional robotic systems, only a small percentage of DM3 system resources, approximately 5-10% of system area and robot numbers, are needed to achieve on-board self-assembly and tool-on-demand functions. This paper describes the key step of self-assembly of self-levitating magnet arrays using 1 mm × 1 mm × 0.4 mm magnets, with self-assembly times of less than 10 s. We also report experiments showing how milli-robots can build simple end effector tools (a straight probe tip, a forked tip, and a hook tip) on other milli-robots for on-board, tool-on-demand functions.