Oscar Chuy

Analysis and Experimental Verification for Dynamic Modeling of A Skid-Steered Wheeled Vehicle

Skid-steered vehicles are often used as outdoor mobile robots due to their robust mechanical structure and high maneuverability. Sliding, along with rolling, is inherent to general curvilinear motion, which makes both kinematic and dynamic modeling difficult. For the purpose of motion planning, this paper develops and experimentally verifies dynamic models of a skid-steered wheeled vehicle for general planar (2-D) motion and for linear 3-D motion. These models are characterized by the coefficient of rolling resistance, the coefficient of friction, and the shear deformation modulus, which have terrain-dependent values. The dynamic models also include motor saturation and motor power limitations, which enable correct prediction of vehicle velocities when traversing on hills. It is shown that the closed-loop system that results from inclusion of the dynamics of the [proportional--integral--derivative (PID)] speed controllers for each set of wheels does a much better job than the open-loop model of predicting the vehicle linear and angular velocities. For a vehicle turning with small linear and angular accelerations, the model provides accurate predictions of velocities and reasonable predictions of torques. Hence, the closed-loop model is recommended for motion planning.

A Control Approach Based on Passive Behavior to Enhance User Interaction

This paper proposes a new control approach for an active (motorized) robotic walking support system based on passive behavior concept. The control approach aims to enhance the interaction between the support system and the user. The passive behavior of a support system allows the user to safely interact with the system since it removes the systems capability to move when there is no users intention. This passive behavior is realized using imposed apparent dynamics, which uses the users intention represented by the applied force/torque to derive the systems desired motion. The control approach is extended into a user-oriented motion control algorithm to adapt users controlling characteristics. This is implemented by varying the point of application of the apparent dynamics. The control approach is further extended to use environment information and realize environment feedback concept. This is implemented by varying the parameters of the apparent dynamics based on environment data. Experimental results are presented to show the validity of the proposed control approach.

A New Control Approach for a Robotic Walking Support System in Adapting User Characteristics

This paper proposes a new control approach for a robotic walking support system to adapt a users controlling characteristic. The control approach will be implemented by changing the kinematic structure of the robotic walking support system based on a variable center of rotation. This new control approach aims to help users who have difficulties in controlling their walking support system. In this study, we have a training stage to evaluate and adapt users controlling characteristics. This will be implemented by allowing the user to follow some training paths. In the event a large path error occurs, a learning algorithm will vary the center of rotation of the support system until the user can successfully follow the training path. The relationship between the user intent in the form of applied force/torque and the new center of rotation will be taken by considering several training paths. This relationship will be used in actual control of the robotic walking support system. Experimentation and evaluation are presented to show the validity of the proposed control algorithm

Approach in Assisting a Sit-to-Stand Movement Using Robotic Walking Support System

This paper presents an approach in assisting a sit-to-stand movement using a robotic walking support system. In general, robotic walking support system is used to provide walking stability. We will extend its function to assist a user in executing a sit-to-stand movement. The first approach would be called passive support. In this approach, the support system would be stationary as the user execute the sit-to-stand movement. The knee torque would be determined and this would be compared to a sit-to-stand movement without support. The second approach would be called active support and the knee torque would be supported. A motion control algorithm would be proposed such that the support system will move based on the supporting torque. The actual experimentation on both approaches in assisting a sit-to-stand movement will be presented. The experimental result on active support shows the validity of the proposed motion control algorithm

Power modeling of a skid steered wheeled robotic ground vehicle

Analysis of the power consumption of a robotic ground vehicle (RGV) is important for planning since it enables motion plans that do not violate the power limitations of the motors, energy efficient path planning, prediction of the ability to complete a task based upon the vehicles current energy supply, and estimation of when the vehicle will need to refuel or recharge. Power modeling is particularly difficult for skid steered vehicles because of the complexities of properly taking into account the skidding that is used for vehicle turning. This paper begins with a 2-dimensional, second order differential equation of a skid steered, wheeled RGV and shows that the power model is terrain dependent and is a function of both the turning radius and linear velocity of the vehicle. This model was verified experimentally, and a comprehensive set of experiments was performed to describe the power consumption of a skid steered RGV on asphalt.

Dynamic modeling of a skid-steered wheeled vehicle with experimental verification

Skid-steered vehicles are often used as outdoor mobile robots due to their robust mechanical structure and high maneuverability. Sliding along with rolling is inherent to general curvilinear motion, which makes both kinematic and dynamic modeling difficult. For the purpose of motion planning this paper develops and experimentally verifies dynamic models of a skid-steered wheeled vehicle for general planar (2D) motion and for linear 3D motion. These models are characterized by the coefficient of rolling resistance, the coefficient of friction, and the shear deformation modulus, which have terrain-dependent values. The dynamic models also include motor saturation and motor power limitations, which enable correct prediction of vehicle velocities when traversing hills. It is shown that the closed-loop system that results from inclusion of the dynamics of the (PID) speed controllers for each set of wheels does a much better job than the open loop model of predicting the vehicle linear and angular velocities. Hence, the closed-loop model is recommended for motion planning.

Motion control algorithms for a new intelligent robotic walker in emulating ambulatory device function

This paper propose a new motion control algorithms for an intelligent robotic walker that emulate ambulatory device function such as cane, wheeled walker, and standard walker. Usually, the objective in designing robotic walker is to replaced conventional wheeled walker and introduce new high level functions such as guidance, health monitoring, and others. We extend the objective of a robotic walker in different direction and propose a new motion control algorithms in replacing other ambulatory device such as cane and standard walker. In this study, we consider the motion control algorithm for wheeled walker, cane, and standard walker based on imposed apparent dynamics to the robotic walker. In cane function emulation, one hand control is considered. This method of controlling a robotic walker leads to some unintentional applied force/torque and makes the system uncontrollable. With that, we propose to change the kinematic structure of the robotic walker to make the system controllable. In standard walker function emulation, supported weight will be monitored and used to make the system in halt mode during weight transfer. The motion control algorithms were experimentally implemented and the results show its validity.

Active type robotic mobility aid control based on passive behavior

This paper proposes a motion control algorithm for an active type of robotic mobility aid based on passive behavior concept. Passive behavior is an important characteristic of a system that provides mobility to elderly or person with walking disability. It allows the user to control the system based on intention. Passive behavior is implemented using imposed desired dynamics, which represents the actual behavior of passive system. This approach uses user intention represented by applied force/torque to derive the mobility aid desired motion. In addition, a guideline in parameter selection of the desired dynamics is also presented. This guideline is used to ensure the stability of the active robotic mobility aid with passive behavior. Experimental results are presented to show the validity of the proposed control method.

Sampling-Based Direct Trajectory Generation Using the Minimum Time Cost Function

This paper presents a methodology for computationally efficient, direct trajectory generation using sampling with the minimum time cost function, where only the initial and final positions and velocities of the trajectory are specified. The approach is based on a randomized A* algorithm called Sampling-Based Model Predictive Optimization (SBMPO) that exclusively samples in the input space and integrates a dynamic model of the system. The paper introduces an extended kinematic model, consisting of the standard kinematic model preceded by two integrators. This model is mathematically a dynamic model and enables SBMPO to sample the acceleration and provide the acceleration, velocity, and position as functions of time that are needed by a typical trajectory tracking controller. A primary contribution of this paper is the development of an appropriate “optimistic A* heuristic” (i.e, a rigorous lower bound on the chosen cost) based on the solution of a minimum time control problem for the system q = u; this heuristic is a key enabler to fast computation of trajectories that end in zero velocity. Another contribution of this paper is the use of the extended kinematic model to develop a trajectory generation methodology that takes into account torque constraints associated with the regular dynamic model without having to integrate this more complex model as has been done previously. This development uses the known form of the trajectory following control law. The results are initially illustrated experimentally using a 1 degree of freedom (DOF) manipulator lifting heavy loads, which necessitates the development of trajectories with appropriate momentum characteristics. Further simulation results are for a 2 DOF manipulator.

Augmented variable center of rotation in controlling a robotic walker to adapt user characteristics

This paper propose a new control algorithm for a robotic walker based on augmented variable center of rotation (COR) to adapt to users controlling characteristics. The new CORs are taken from environment-based training. This is done by allowing the user to use the robotic walker from a start point to a goal point in a training environment and path following algorithm is employed. The users intention represented by applied force/torque is logged during training. The logged data is segmented to correspond to the straight and curve segments in the training environment. This data is used to regenerate the path of the robotic walker. The error between the regenerated and the desired path is taken and in case a large path error exists, an optimization program is used to change the COR until the sum of the square of the path error is minimized. This approach refers to an offline COR determination. A variable COR controller as a function of applied torque is designed based on the new CORs. This is augmented and used in the actual control of the robotic walker. The proposed control algorithm was experimentally implemented and results show its validity.