Jorge G. Cham

Fast and Robust

Robots to date lack the robustness and performance of even the simplest animals when operating in unstructured environments. This observation has prompted an interest in biomimetic robots that take design inspiration from biology. However, even biomimetic designs are compromised by the complexity and fragility that result from using traditional engineering materials and manufacturing methods. We argue that biomimetic design must be combined with structures that mimic the way biological structures are composed, with embedded actuators and sensors and spatially-varied materials. This proposition is made possible by a layered-manufacturing technology called shape deposition manufacturing (SDM). We present a family of hexapedal robots whose functional biomimetic design is made possible by SDMs unique capabilities and whose fast (over four body-lengths per second) and robust (traversal over hip-height obstacles) performance begins to compare to that seen in nature. We describe the design and fabrication of the robots and we present the results of experiments that focus on their performance and locomotion dynamics.

Cognitive Neural Prosthetics

Research on neural prosthetics has focused largely on using activity related to hand trajectories recorded from motor cortical areas. An interesting question revolves around what other signals might be read out from the brain and used for neural prosthetic applications. Recent studies indicate that goals and expected value are among the high-level cognitive signals that can be used and will potentially enhance the ability of paralyzed patients to communicate with the outside world. Other new findings show that local field potentials provide an excellent source of information about the cognitive state of the subject and are much easier to record and maintain than spike activity. Finally, new movable probe technologies will enable recording electrodes to seek out automatically the best signals for decoding cognitive variables.

Stride Period Adaptation for a Biomimetic Running Hexapod

We demonstrate an adaptation strategy for adjusting the stride period in a hexapedal running robot. The robot is inspired by discoveries about the self-stabilizing properties of insects and uses a sprawled posture, a bouncing alternating-tripod gait, and passive compliance and damping in the limbs to achieve fast, stable locomotion. The robot is controlled by an open-loop clock cycle that activates the legs at fixed intervals. For maximum speed and efficiency, this imposed stride period should be adjusted to match changes in terrain or loading conditions. An ideal adaptation strategy will complement the design philosophy behind the robot and take advantage of the self-stabilizing role of the mechanical system. In this paper we describe an adaptation scheme based on measurements of ground contact timing obtained from binary sensors on the robot’s feet. We discuss the motivation for the approach, putting it in the context of previous research on the dynamic properties of running machines and bouncing multi-legged animals, and show results of experiments.

An Analysis of Sketching Skill and Its Role in Early Stage Engineering Design

Previous studies have demonstrated the importance of sketching in design cognition, particularly in the early stages of engineering design. The goal of this preliminary study is to consider the role of a designers sketching ability and to examine the potential link between sketching skill and measures of engineering design performance. Sketching ability was evaluated on three distinct aspects relevant to engineering design: visual recall, rendering, and novel visualization. These evaluations were correlated with each other and with measures for sketch fluency, reviewer ranking, and design project outcome. The results of this study suggest that sketching skill is not comprehensive nor is it solely task based. Rather, a designers sketching ability lies between these two poles. Positive correlations were found between the quantity of sketches produced and two of the sketching skills that emphasize drawing facility, but a negative correlation was found between sketch quantity and a skill related to mechanism visualization. No conclusive correlations were found between the sketching skills and design outcome and reviewer ranking. This studys findings suggest an important interplay between a designers ability to sketch and their ability to visualize in their heads or through prototypes. Results also suggest that designers who are given sketch instruction tended to draw more overall.

Biomimetic Robotic Mechanisms via Shape Deposition Manufacturing

At small scales, the fabrication of robots from off-the-shelf structural materials, sensors and actuators becomes increasingly difficult. New manufacturing methods such as Shape Deposition Manufacturing offer an alternative approach in which sensors and actuators are embedded directly into three-dimensional structures without fasteners or connectors. In addition, structures can be fabricated with spatially varying material properties such as specific stiffness and damping. These capabilities allow us to consider biomimetic designs that draw their inspiration from crustaceans and insects. Recent research on insect physiology has revealed the importance of passive compliance and damping in achieving robustness and simplifying control. We describe the design and fabrication of small robot limbs with locally varying stiffness and embedded sensors and actuators. We discuss the process planning issues associated with creating such structures and present results obtained via Shape Deposition Manufacturing.

A New Multi-Site Probe Array with Monolithically Integrated Parylene Flexible Cable for Neural Prostheses

This work presents a new multi-site probe array applied with parylene technology, used for neural prostheses to record high-level cognitive neural signals. Instead of inorganic materials (e.g. silicon dioxide, silicon nitride), the electrodes and conduction traces on probes are insulated by parylene, which is a polymer material with high electrical resistivity, mechanical flexibility, biocompatibility and easy deposition process. As a result, the probes exhibit better electrical and mechanical properties. The all dry process is demonstrated to fabricate these probe arrays with monolithically integrated parylene flexible cables using double-side-polished (DSP) wafers. With the parylene flexible cables, the probes can be easily assembled to a high density 3-D array for chronic implantation

Recording advances for neural prosthetics

An important challenge for neural prosthetics research is to record from populations of neurons over long periods of time, ideally for the lifetime of the patient. Two new advances toward this goal are described, the use of local field potentials (LFPs) and autonomously positioned recording electrodes. LFPs are the composite extracellular potential field from several hundreds of neurons around the electrode tip. LFP recordings can be maintained for longer periods of time than single cell recordings. We find that similar information can be decoded from LFP and spike recordings, with better performance for state decodes with LFPs and, depending on the area, equivalent or slightly less than equivalent performance for signaling the direction of planned movements. Movable electrodes in microdrives can be adjusted in the tissue to optimize recordings, but their movements must be automated to be a practical benefit to patients. We have developed automation algorithms and a meso-scale autonomous electrode testbed, and demonstrated that this system can autonomously isolate and maintain the recorded signal quality of single cells in the cortex of awake, behaving monkeys. These two advances show promise for developing very long term recording for neural prosthetic applications.

Comparing the Locomotion Dynamics of the Cockroach and a Shape Deposition Manufactured Biomimetic Hexapod

We describe the locomotion dynamics of a biomimetic robot and compare them with those of its exemplar: the cockroach. The robot is a small (0.275kg) hexapod created using a layered manufacturing technique that allows us to tailor the compliance and damping of the limbs to achieve passive stabilization similar to that observed in insects. The robot runs at over 3 body-lengths per second (55 cm/s) and easily traverses hip-height obstacles. However, high-speed video and force data reveal differences between the robot’s locomotion dynamics and the inverted spring-pendulum model that characterizes most running animals, including cockroaches. Closer examination of the individual leg forces shows that these differences stem from the behavior of the middle and rear legs and points to suggestions for future designs and further experimentation.

Dynamic Stability of Open-Loop Hopping

Simulations and physical robots have shown that hopping and running are possible without sensory feedback. However, stable behavior is often limited to a certain range of the parameters of the open-loop system. Even the simplest of hopping systems can exhibit unstable behavior that results in unpredictable nonperiodic motion as system parameters are adjusted. This paper analyzes the stability of a simplified vertical hopping model driven by an open-loop, feedforward motor pattern. Periodic orbits of the resulting hybrid system are analyzed through a generalized formula for the systems Poincare Map and Jacobian. The observed behavior is validated experimentally in a physical pneumatically actuated hopping machine. This approach leads to observations on the stability of this and similar systems, revealing inherent limitations of open-loop hopping and providing insights that can inform the design and control of dynamic legged robots capable of rapid and robust locomotion.

A Robotic Neural Interface for Autonomous Positioning of Extracellular Recording Electrodes

In this paper we describe a set of algorithms and a novel miniature device that together can autonomously position electrodes in neural tissue to obtain high-quality extracellular recordings. This robotic system moves each electrode to detect the signals of individual neurons, optimize the signal quality of a target neuron, and then maintain this signal over time. Such neuronal signals provide the key inputs for emerging neuroprosthetic medical devices and serve as the foundation of basic neuroscientific and medical research. Experimental results from extensive use of the robotic electrodes in macaque parietal cortex are presented to validate the method and to quantify its effectiveness.