Kaushik Jayaram

Cockroaches traverse crevices, crawl rapidly in confined spaces, and inspire a soft, legged robot

Significance Cockroaches intrude everywhere by exploiting their soft-bodied, shape-changing ability. We discovered that cockroaches traversed horizontal crevices smaller than a quarter of their height in less than a second by compressing their bodies’ compliant exoskeletons in half. Once inside vertically confined spaces, cockroaches still locomoted rapidly at 20 body lengths per second using an unexplored mode of locomotion—body-friction legged crawling. Using materials tests, we found that the compressive forces cockroaches experience when traversing the smallest crevices were 300 times body weight. Cockroaches withstood forces nearly 900 times body weight without injury, explaining their robustness to compression. Cockroach exoskeletons provided inspiration for a soft, legged search-and-rescue robot that may penetrate rubble generated by tornados, earthquakes, or explosions. Jointed exoskeletons permit rapid appendage-driven locomotion but retain the soft-bodied, shape-changing ability to explore confined environments. We challenged cockroaches with horizontal crevices smaller than a quarter of their standing body height. Cockroaches rapidly traversed crevices in 300–800 ms by compressing their body 40–60%. High-speed videography revealed crevice negotiation to be a complex, discontinuous maneuver. After traversing horizontal crevices to enter a vertically confined space, cockroaches crawled at velocities approaching 60 cm⋅s−1, despite body compression and postural changes. Running velocity, stride length, and stride period only decreased at the smallest crevice height (4 mm), whereas slipping and the probability of zigzag paths increased. To explain confined-space running performance limits, we altered ceiling and ground friction. Increased ceiling friction decreased velocity by decreasing stride length and increasing slipping. Increased ground friction resulted in velocity and stride length attaining a maximum at intermediate friction levels. These data support a model of an unexplored mode of locomotion—“body-friction legged crawling” with body drag, friction-dominated leg thrust, but no media flow as in air, water, or sand. To define the limits of body compression in confined spaces, we conducted dynamic compressive cycle tests on living animals. Exoskeletal strength allowed cockroaches to withstand forces 300 times body weight when traversing the smallest crevices and up to nearly 900 times body weight without injury. Cockroach exoskeletons provided biological inspiration for the manufacture of an origami-style, soft, legged robot that can locomote rapidly in both open and confined spaces.

Development of a flexure-based, force-sensing microgripper for micro-object manipulation

This paper presents the design and development of a flexure-based microgripper, accompanied with a real-time, vision-based force sensing system to handle objects of various sizes ranging from 100 ?m to 1 mm. A simulation-based design methodology is adopted to develop an initial microgripper design, which is then optimized using theoretical modeling. The final prototype developed generated a large stroke length of over 500 ?m with high-deflection magnification (ratio of the end deflection (output) to the input deflection) of 3.52. A spring system has been incorporated into the microgripper for easy measurement and control of the gripping forces. The web-camera-based visual system enables real-time force measurement with a resolution of 2.37 mN and can be operated in both manual and automatic modes to control the applied forces. The system has successfully demonstrated gripping of a variety of micro-objects including a 100 ?m human hair and a 1 mm steel rod with forces as small as 43 mN and 159 mN, respectively.

Mechanical processing via passive dynamic properties of the cockroach antenna can facilitate control during rapid running

The integration of information from dynamic sensory structures operating on a moving body is a challenge for locomoting animals and engineers seeking to design agile robots. As a tactile sensor is a physical linkage mediating mechanical interactions between body and environment, mechanical tuning of the sensor is critical for effective control. We determined the open-loop dynamics of a tactile sensor, specifically the antenna of the American cockroach, Periplaneta americana, an animal that escapes predators by using its antennae during rapid closed-loop tactilely mediated course control. Geometrical measurements and static bending experiments revealed an exponentially decreasing flexural stiffness (EI) from base to tip. Quasi-static experiments with a physical model support the hypothesis that a proximodistally decreasing EI can simplify control by increasing preview distance and allowing effective mapping to a putative control variable – body-to-wall distance – compared with an antenna with constant EI. We measured the free response at the tip of the antenna following step deflections and determined that the antenna rapidly damps large deflections: over 90% of the perturbation is rejected within the first cycle, corresponding to almost one stride period during high-speed running (~50 ms). An impulse-like perturbation near the tip revealed dynamics that were characteristic of an inelastic collision, keeping the antenna in contact with an object after impact. We contend that proximodistally decreasing stiffness, high damping and inelasticity simplify control during high-speed tactile tasks by increasing preview distance, providing a one-dimensional map between antennal bending and body-to-wall distance, and increasing the reliability of tactile information.

Phase control for a legged microrobot operating at resonance

We present an off-board phase estimator and controller for leg position near the resonance of the Harvard Ambulatory MicroRobots (HAMR) two degree-of-freedom transmission. This control system is a first step towards leveraging the significant increase in stride length at transmission resonance for faster and more efficient locomotion. We experimentally characterize HAMRs transmission and determine that actuator phase is a sufficient proxy for leg phase across the range of useful operating frequencies (1–120Hz). An estimator is developed to determine actuator phase using off-board position sensors and it converges within a cycle on average. We also fit a nonlinear dynamic model of the transmission to the experimental data, and utilize the model to determine a suitable open-loop resonant leg trajectory and define feed forward control inputs. This resonant (100Hz) trajectory is theoretically 50% more efficient than pre-resonant high speed running trajectories. The controller converges to this trajectory in 0.05 ± 0.02 seconds (5.3 ± 2.4 cycles) in air, and in 0.05 ± 0.01 seconds (4.7 ± 0.6 cycles) under perturbations that approximate ground contact.

Design and development of a vision-based micro-assembly system

Cost- and time-effective automated assembly of micro-sized objects within small tolerances is still a challenge to the present-day manufacturing industry. In this article, the details of the development of a low-cost, two-dimensional system capable of rapid micro-assembly are presented. The use of a basic webcamera without any external optics makes the system light and compact. In addition, an innovative thresholding technique for binarization and a novel algorithm for fast autofocusing with defocused images have also been discussed. Peg-in-hole insertion tasks using micro-objects of 100 μm have been successfully demonstrated using the system. The system has an accuracy of about 20 μm along the X- and Y-axes and a repeatability of less than 4 μm in performing peg-in-hole tasks.

Transition by head-on collision: mechanically mediated manoeuvres in cockroaches and small robots

Exceptional performance is often considered to be elegant and free of ‘errors’ or missteps. During the most extreme escape behaviours, neural control can approach or exceed its operating limits in response time and bandwidth. Here we show that small, rapid running cockroaches with robust exoskeletons select head-on collisions with obstacles to maintain the fastest escape speeds possible to transition up a vertical wall. Instead of avoidance, animals use their passive body shape and compliance to negotiate challenging environments. Cockroaches running at over 1 m or 50 body lengths per second transition from the floor to a vertical wall within 75 ms by using their head like an automobile bumper, mechanically mediating the manoeuvre. Inspired by the animals behaviour, we demonstrate a passive, high-speed, mechanically mediated vertical transitions with a small, palm-sized legged robot. By creating a collision model for animal and human materials, we suggest a size dependence favouring mechanical mediation below 1 kg that we term the ‘Haldane limit’. Relying on the mechanical control offered by soft exoskeletons represents a paradigm shift for understanding the control of small animals and the next generation of running, climbing and flying robots where the use of the body can off-load the demand for rapid sensing and actuation.