Erik Steltz

Towards a 3g crawling robot through the integration of microrobot technologies

This paper discusses the biomimetic design and assembly of a 3g self-contained crawling robot fabricated through the integrated use of various microrobot technologies. The hexapod structure is designed to move in an alternating tripod gait driven by two piezoelectric actuators connected by sliding plates to two sets of three legs. We present results of both the kinematic and static analyses of the driving mechanism that essentially consists of three slider cranks in series. This analysis confirmed the force differential needed to propel the device. We then review various other microrobot technologies that have been developed including actuator design and fabrication, power and control electronics design, programming via a finite state machine, and the development of bioinspired fiber arrays. These technologies were then successfully integrated into the device. The robot is now functioning and we have already fabricated three iterations of the proposed device. We hope with further design iterations to produce a fully operational model in the near future

Universal robotic gripper based on the jamming of granular material

Gripping and holding of objects are key tasks for robotic manipulators. The development of universal grippers able to pick up unfamiliar objects of widely varying shape and surface properties remains, however, challenging. Most current designs are based on the multifingered hand, but this approach introduces hardware and software complexities. These include large numbers of controllable joints, the need for force sensing if objects are to be handled securely without crushing them, and the computational overhead to decide how much stress each finger should apply and where. Here we demonstrate a completely different approach to a universal gripper. Individual fingers are replaced by a single mass of granular material that, when pressed onto a target object, flows around it and conforms to its shape. Upon application of a vacuum the granular material contracts and hardens quickly to pinch and hold the object without requiring sensory feedback. We find that volume changes of less than 0.5% suffice to grip objects reliably and hold them with forces exceeding many times their weight. We show that the operating principle is the ability of granular materials to transition between an unjammed, deformable state and a jammed state with solid-like rigidity. We delineate three separate mechanisms, friction, suction, and interlocking, that contribute to the gripping force. Using a simple model we relate each of them to the mechanical strength of the jammed state. This advance opens up new possibilities for the design of simple, yet highly adaptive systems that excel at fast gripping of complex objects.

JSEL: Jamming Skin Enabled Locomotion

A soft, mobile, morphing robot is a desirable platform for traversing rough terrain and navigating into small holes. In this work, a new paradigm in soft robots is presented that utilizes jamming of a granular medium. The concept of activators (as opposed to actuators) is presented to jam and unjam cells that then modulate the direction and amount of work done by a single central actuator. A prototype jamming soft robot utilizing JSEL (Jamming Skin Enabled Locomotion) with external power and control is discussed and both morphing results and mobility (rolling) results are presented. Future directions for the design of a soft, hole traversing robot are discussed, as is the role and promises of jamming as an enabling technology for soft robotics.

RoACH: An autonomous 2.4g crawling hexapod robot

This work presents the design, fabrication, and testing of a novel hexapedal walking millirobot using only two actuators. Fabricated from S2-glass reinforced composites and flexible polymer hinges using the smart composite microstructures (SCM) process, the robot is capable of speeds up to 1 body length/sec or approximately 3 cm/s. All power and control electronics are onboard and remote commands are enabled by an IrDA link. Actuation is provided by shape memory alloy wire. At 2.4 g including control electronics and battery, RoACH is the smallest and lightest autonomous legged robot produced to date.

Power Electronics Design Choice for Piezoelectric Microrobots

Piezoelectric actuators are advantageous for microrobots due to their light weight, high bandwidth, high force production, low power consumption, and simplicity of integration. However, the main disadvantage of either stack or cantilever piezoelectric actuators are the high drive voltages required for adequate force and displacement. This especially limits the ability for such actuators to be used in autonomous microrobots because of the weight and complexity of necessary power electronics. This paper approaches the design of all the component parts of an autonomous piezoelectric robot as a linear constraint on the weight and efficiency of those components. It then focuses on the choice and optimization of the power electronics section of the robot, specifically exploring three different high voltage generation methods. Finally, one of these power electronics designs is implemented and its behavior is experimentally explored

Lift force improvements for the micromechanical flying insect

This paper presents some recent improvements in the fabrication and control of the micromechanical flying insect (MFI), a centimeter sized aerial vehicle currently being developed at the University of California, Berkeley. We report a lift of 506 /spl mu/N from a single wing, which is sufficient for a 100 mg machine to lift itself off the ground. This lift matches very well with predictions based on quasi steady state models. We present some recent improvements in thorax fabrication leading to the development of a light weight platform (/spl sim/ 100 mg), which generates 400 /spl mu/N of lift with a single wing. We also present a new sensor mechanism, which makes it possible to sense the motion of the actuators without having to add anything to the structure itself.

Nonlinear Performance Limits for High Energy Density Piezoelectric Bending Actuators

To keep pace with recent advances in micro robotic structures demands actuator technologies which can deliver high power and precise motion. For electroactive material based actuators, high power typically implies either high field or high current drives which may lead to greater nonlinearities such as saturation, softening, and increased loss. Physical modeling of actuators is normally taken to be linear since the range of displacements, applied loads, and applied fields is typically small. If extrapolated to high drive conditions, these linear models significantly over predict the power which can be delivered. For actuators driving dynamic systems, a complete nonlinear model of the system will improve controllability and give more accurate estimations of power delivery capabilities. Here static nonlinearities and dynamic linear and nonlinear parameters are derived for high performance piezoelectric bending actuators.

Design, fabrication and initial results of a 2g autonomous glider

Utilizing the core technologies of emerging microrobotic structures, the rapid design and prototyping of a passive micro air vehicle with the final goal of locating an audio source while avoiding hazardous obstacles is presented. The airfoil and control surfaces are optimized empirically to maximize lift and maneuverability while minimizing drag. Bimorph piezoelectric bending cantilevers actuate the control surfaces. Since such actuators require high voltages, an efficient boost circuit is presented along with appropriate high voltage electronics. To locate audio sources, a pair of acoustic sensors is designed and prototyped using a phase detection algorithm while a custom optic flow sensor is developed to avoid obstacles and give estimates of object distances and velocities. Finally, each subsystem is demonstrated and the complete glider is integrated to demonstrate initial open loop control performance.

High lift force with 275 Hz wing beat in MFI

The Micromechanical Flying Insect (MFI) project aims to create a 25 mm (wingtip to wingtip) flapping wing micro air vehicle inspired by the aerodynamics of insect flight. A key challenge is generating appropriate wing trajectories. Previous work showed a lift of 506 muN at 160 Hz using feedforward control. In this paper, refinements to the MFI design including those in [2] increased wing beat frequency to 275 Hz and lift to 1400 muN using pure sinusoidal drive for a fixed benchtop experiment. We show through simplified aerodynamic models that not only do sinusoidal actuator drives produce close to maximal lift, but significantly improved wing trajectories due to non-sinusoidal actuator drives are practically unobtainable due to actuator limitations.

An Autonomous Palm-Sized Gliding Micro Air Vehicle

This article has concentrated on the development of a set of core technologies key to the realization of an autonomous 2-g glider. One aspect which was not discussed in detail was the ease of construction and low cost of an individual MicroGlider. Integration is simplified through a number of rapid prototyping techniques and the low costs of most components allow rigorous testing to be done without worry of substantial damage.