In this article, we characterize the passivity of a class of haptic systems modeled as a simple sampled-data system. We guarantee passivity by ensuring that there is sufficient damping in the haptic interface. Previous work established a necessary and sufficient bound on damping, but the corresponding mathematical expressions were complicated, and the derivation was not completely rigorous. After providing a rigorous proof, we derive a more tractable expression. Using this improved expression, we establish passivity conditions for several classes of transfer functions representing virtual environments, including some special cases with time delay. The original results assumed that the operator can be modeled by a passive but otherwise arbitrary transfer function. This assumption is weakened to allow the operator model to have a shortage of passivity. This requires only a slight modification of the passivity bound.

In this paper we introduce a novel optimal trajectory planning method for robots in static and dynamic environments while accounting for the robot’s kinematic and dynamic constraints. The proposed method is called Danger Field Sampling Based Model Predictive optimization (DF-SBMPO). This new method includes the advantages of SBMPO such as dealing with non-linear constraints and non-invertible models and planning in the input space while improving its computational efficiency in local minima situations. By introducing a new cost function and combining the Danger Field method in the collision checking process, our method can efficiently find a near time-optimal and smooth trajectory to the goal. We verify the method in simulation using a car-like robot model in an environment containing both static and moving obstacles. By comparing it systematically to other sampling-based path planning algorithms and the Time-Scaling time-optimal trajectory planning method, the results show that our method generally produces collision-free, smoother, near time-optimal trajectories that satisfy constraints with less computation time and fewer samples.

To meet the demand for high additive manufacturing efficiency, we are working on an FDM (Fused Deposition Modeling) printer called DEXTER which has dual Selective Compliance Articulated Robot Arms (SCARA). We develop a path planner to produce time-optimal motion paths for each of DEXTER's arms while guaranteeing that the arms do not collide with one another. We present a collision-free path planner for DEXTER's arms using an improved Sampling-Based Model Predictive Optimization (SBMPO) based on A* type optimization by adding efficient collision determination and a new type of cost function. The simulation results show that the improved SBMPO can be used to efficiently generate smooth collision-free paths and trajectories with bounded velocity and acceleration.

The wave variable method allows for stable bilateral teleoperation in the presence of time delay. However, the appearance of transient oscillations, known as wave reflections, affect teleoperation performance when using the wave variable method. The frequency characteristics of these wave reflections have been previously considered to be primarily related to the time delay across the communication channel. In this paper we show that the frequency characteristics of wave reflections are also affected by changes to the mass of the teleoperated system. We propose a wave-variable-based controller that diminishes the effects of wave reflections as the slave dynamics changes during teleoperation. Simulation results using our proposed method is compared to the traditional wave variable method.

Parallel manipulators are widely used in industrial applications due to their rigid structures and ability to perform automated tasks at high speeds. However, because the links on a parallel manipulator are mechanically coupled, solving its kinematics and dynamics equations can be more difficult than for its serial counterpart. Nevertheless, the inverse kinematics and inverse dynamics models are a critical component of a manipulator's controller. Specifically, a more computationally simple formulation of the inverse kinematics and dynamics is necessary to achieve efficient and fast manipulator control. In this paper, both the inverse kinematics and dynamics equations for the Omega-3, a three degree-of-freedom (3-DOF) parallel manipulator, are developed. For the inverse kinematics problem, the concept of loop closure equations is used to simplify the analysis. The virtual work principle is used to create a numerically simple inverse dynamics model. Using the inverse kinematics and dynamics model, a trajectory tracking controller is implemented on the manipulator and the resulting experiments reveal good tracking behavior.

A haptics investigation is conducted when human subjects have to deal with a bilateral teleoperation system with two levels of time delay (400 and 1,000 ms) and four types of scaling matrices that provide a passivity form of stabilization. The wave variable method was implemented to produce a controllable human-machine response. What is of interest is the resulting performance that occurs from such systems which remain passive but impacts the overall human tracking performance that can be achieved. The question addressed is how these imposed stability restrictions (via architecture constraints) may degrade human tracking performance?

We present a novel way of modeling wheeled vehicles on outdoor terrains. Adapting concepts from dextrous manipulation, we precisely model the way that three dimensional wheels roll over uneven ground. The techniques used are easily adaptable to other vehicle designs of arbitrary complexity. Our modeling method is used to validate a new concept for design of off-road vehicle wheel suspensions, called passive variable camber (PVC). Simulation results of a three-wheeled vehicle with PVC demonstrate that the vehicle can negotiate an extreme terrain without kinematic slip, thus improving vehicle efficiency and performance.

Unmanned ground vehicles (UGV's) commonly used in military applications must possess the capability to traverse various terrains that may largely affect the performance and controllability of the vehicle. A UGV that can autonomously perceive its terrain using navigational sensors can make necessary changes to its control strategy. The research presented uses the output of the induced vehicle's vibration measured by navigational sensors to classify the underlying terrain at multiple speeds. The classification algorithm incorporates Principal Component Analysis (PCA) for feature extraction and dimension reduction. The PCA transformation coefficients are then used to develop a manifold curve that uses these known coefficients to interpolate unknown coefficients of the terrains as the robot's speed changes. Experimental data is collected using two distinctly different unmanned ground vehicle platforms. Results demonstrate the performance of the method for classifying multi-differentiated terrains broadly classified as grass, asphalt, mud, and gravel.

Aerial missions that require unmanned aerial vehicles (UAVs) to fly autonomously in unknown and hostile environments are inevitable. These UAVs must be equipped with a fully autonomous navigation system. Many methods that have been proposed for navigation of autonomous systems either lack the necessary intelligence or are not responsive enough to cope with the flying speeds of UAVs. This paper presents a new method for autonomous navigation of UAVs using reactive fuzzy behaviors. It extends a 2D fuzzy behavior navigation system used in unmanned ground vehicles to a 3D navigation system suitable for UAVs. The research is based on a range finding sensor system by judicious use of a 2D range finder. A novel defuzzification method for 3D navigation systems is developed to generate the most desired flying orientation. Simulation results carried out using MATLAB's Virtual Reality Toolbox show that the proposed system works very well to avoid static obstacles.

Cobots are devices for human/robot interaction, in which axes of motion are coupled to one another by computer-controlled continuously variable transmissions rather than individually driven by servomotors. We have recently built a cobot with a three-dimensional workspace and a 3-revolute parallelogram-type mechanism. Here we present the control methods for the display of virtual surfaces and for free mode in which the cobot endpoint moves as if it were unconstrained. We provide experimental results on the performance of the free, virtual path, and virtual surface controllers.

Cobots are devices for human/robot interaction, in which axes of motion are coupled to one another by computer-controlled continuously variable transmissions rather than individually driven by servomotors. We have recently built a 3R parallelogram cobot. Here we present a control method for the display of virtual surfaces and for free-mode in which the cobot endpoint moves as if it were unconstrained. We show experimental results on the performance of the cobot in these modes.

We describe a new robot architecture: the collaborative robot, or cobot. Cobots are intended for direct physical interaction with a human operator. The cobot can create smooth, strong virtual surfaces and other haptic effects within a shared human/cobot workspace. The kinematic properties of cobots differ markedly from those of robots. Most significantly, cobots have only one mechanical degree of freedom, regardless of their taskspace dimensionality. The instantaneous direction of motion associated with this single degree of freedom is actively servo-controlled, or steered, within the higher dimensional taskspace. This paper explains the kinematics of cobots and the continuously variable transmissions (CVT) that are essential to them. Powered cobots are introduced, made possible by a parallel interconnection of the CVT. We discuss the relation of cobots to conventionally actuated robots and to nonholonomic robots. Several cobots in design, prototype, or industrial testbed settings illustrate the concepts discussed.

Cobots are capable of producing virtual surfaces of high quality, using mechanical transmission elements as their basic element in place of conventional motors. Most cobots built to date have used steerable wheels as their transmission elements. We describe how continuously variable transmissions (CVTs) can be used in this capacity for a cobot with revolute joints. The design of an "arm-like" cobot with a three-dimensional workspace is described . This cobot can implement virtual surfaces and other effects in a spherical workspace approximately 1.5 meters in diameter. Novel elements of this cobot include the use of a power disk that couples three CVTs directly.

Describes a new architecture for passive robots and haptic displays, which the authors call a programmable constraint machine (PCM). An n-DOF PCM can, under computer control, exhibit constraints (smooth, impenetrable virtual surfaces of dimensionality