James Andrew Smith

Modeling and Experiments of Untethered Quadrupedal Running with a Bounding Gait: The Scout II Robot

In this paper we compare models and experiments involving Scout II, an untethered four-legged running robot with only one actuator per compliant leg. Scout II achieves dynamically stable running of up to 1.3 m s -1 on flat ground via a bounding gait. Energetics analysis reveals a highly efficient system with a specific resistance of only 1.4. The running controller requires no task-level or body-state feedback, and relies on the passive dynamics of the mechanical system. These results contribute to the increasing evidence that apparently complex dynamically dexterous tasks may be controlled via simple control laws. We discuss general modeling issues for dynamically stable legged robots. Two simulation models are compared with experimental data to test the validity of common simplifying assumptions. The need for including motor saturation and non-rigid torque transmission characteristics in simulation models is demonstrated. Similar issues are likely to be important in other dynamically stable legged robots as well. An extensive suite of experimental results documents the robot’s performance and the validity of the proposed models.

PAW: a hybrid wheeled-leg robot

This paper discusses current wheeled mobility work on a hybrid wheeled-leg robot called PAW. In addition to providing design details, controllers are proposed for inclined turning and sprawled braking which take advantage of the hybrid nature of the platform and improve stability. Power consumption values for a number of its basic behaviours are given, as is the range of the robot

On the Dynamics of Bounding and Extensions: Towards the Half-Bound and Gallop Gaits

This paper examines how simple control laws stabilize complex running behaviors such as bounding. First, we discuss the unexpectedly different local and global forward speed versus touchdown angle relationships in the self-stabilized Spring Loaded Inverted Pendulum. Then we show that, even for a more complex energy conserving unactuated quadrupedal model, many bounding motions exist, which can be locally open loop stable! The success of simple bounding controllers motivated the use of similar control laws for asymmetric gaits resulting in the first experimental implementations of the half-bound and the rotary gallop on Scout II.

Rotary gallop in the untethered quadrupedal robot scout II

This paper discusses recent galloping results obtained using the Scout II quadrupedal robot, an underactuated robot with minimal sensing. The rotary variation of the gallop has been implemented, resulting in a motion which demonstrates both emergent stability and a circular trajectory, as predicted in earlier simulation studies by other researchers. It also demonstrates phase relationships in the leg touchdown pattern which resemble results from biology.

Experimentally validated bounding models for the Scout II quadrupedal robot

In this paper the authors discuss control and modeling issues significant for constructing simple running controllers and building experimentally validated simulation models for dynamically stable robots. A bounding controller resulting in dynamically stable running up to 1.3 m/s for the Scout II quadruped is presented. Simulation models are built and compared with experimental data to test the viability of various simplifying assumptions common in the literature for running robots. The authors demonstrate the need for including motor saturation and nor rigid torque transmission characteristics into simulation models. Similar issues are likely to be important in other legged robots as well. An extensive suite of experimental results documents the robots performance and validates simulation models.

Bounding with Active Wheels and Liftoff Angle Velocity Adjustment

The bounding gait for the Platform for Ambulating Wheels (PAW), a new and unique hybrid wheeled—leg system is presented. Two hypotheses are tested and discussed: first, that the robot’s forward speed can be increased by increasing the leg liftoff angles and, second, that the addition of distally mounted actuated wheels can be used in running gaits such as the bound. Both hypotheses were tested experimentally and found to be valid.

Enlarging regions of stable running with segmented legs

In human and animal running spring-like leg behavior is found, and similar concepts have been demonstrated by various robotic systems in the past. In general, a spring-mass model provides self-stabilizing characteristics against external perturbations originated in leg-ground interactions and motor control. Although most of these systems made use of linear spring-like legs. The question addressed in this paper is the influence of leg segmentation (i.e. the use of rotational joint and two limb-segments) to the self-stability of running, as it appears to be a common design principle in nature. This paper shows that, with the leg segmentation, the system is able to perform self-stable running behavior in significantly broader ranges of running speed and control parameters (e.g. control of angle of attack at touchdown, and adjustment of spring stiffness) by exploiting a nonlinear relationship between leg force and leg compression. The concept is investigated by using a two- segment leg model and a robotic platform, which demonstrate the plausibility in the real world.

Bounding Gait in a Hybrid Wheeled-Leg Robot

This paper discusses the first implementation of a dynamically stable bounding gait on a hybrid wheeled-leg robot. Design of the robot is reviewed and the controllers which allow this mode of mobility to occur are discussed. Experimental results demonstrating the key dynamic characteristics of the gait, including footfall patterns, are given. The hypothesis that varying leg takeoff angles can lead to regulation of forward speed of the bounding gait is presented and verified. In addition, comparisons are made between the bounding gait which uses active wheel control and bounding which uses passive mechanical blocking of the wheels

30 Years of Neurosurgical Robots: Review and Trends for Manipulators and Associated Navigational Systems.

This review provides an examination of contemporary neurosurgical robots and the developments that led to them. Improvements in localization, microsurgery and minimally invasive surgery have made robotic neurosurgery viable, as seen by the success of platforms such as the CyberKnife and neuromate. Neurosurgical robots can now perform specific surgical tasks such as skull-base drilling and craniotomies, as well as pedicle screw and cochlear electrode insertions. Growth trends in neurosurgical robotics are likely to continue but may be tempered by concerns over recent surgical robot recalls, commercially-driven surgeon training, and studies that show operational costs for surgical robotic procedures are often higher than traditional surgical methods. We point out that addressing performance issues related to navigation-related registration is an active area of research and will aid in improving overall robot neurosurgery performance and associated costs.

Development of an integrated optical coherence tomography-gas nozzle system for surgical laser ablation applications: preliminary findings of in situ spinal cord deformation due to gas flow effects

Gas assisted laser machining of materials is a common practice in the manufacturing industry. Advantages in using gas assistance include reducing the likelihood of flare-ups in flammable materials and clearing away ablated material in the cutting path. Current surgical procedures and research do not take advantage of this and in the case for resecting osseous tissue, gas assisted ablation can help minimize charring and clear away debris from the surgical site. In the context of neurosurgery, the objective is to cut through osseous tissue without damaging the underlying neural structures. Different inert gas flow rates used in laser machining could cause deformations in compliant materials. Complications may arise during surgical procedures if the dura and spinal cord are damaged by these deformations. We present preliminary spinal deformation findings for various gas flow rates by using optical coherence tomography to measure the depression depth at the site of gas delivery.