Youngwoo Kim

Robust control of CPG-based 3D neuromusculoskeletal walking model

This paper proposes a method for enhancing the robustness of the central pattern generator (CPG)-based three-dimensional (3D) neuromusculoskeletal walking controller. The CPG has been successfully applied to walking controllers and controllers for walking robots. However, the robustness of walking motion with the CPG-based controller is not sufficient, especially when subjected to external forces or environmental variations. To achieve a realistic and stable walking motion of the controller, we propose the use of an attracting controller in parallel with the CPG-based controller. The robustness of the proposed controller is confirmed through simulation results.

Traffic Network Control Based on Hybrid Dynamical System Modeling and Mixed Integer Nonlinear Programming With Convexity Analysis

This paper presents a new framework for traffic flow control based on an integrated model description by means of a hybrid dynamical system. The geometrical information on the traffic network is characterized by a hybrid Petri net (HPN). Then, the algebraic behavior of the traffic flow is transformed into a mixed logical dynamical system (MLDS) form to introduce an optimization technique. These expressions involve both a continuous evolution of the traffic flow and an event-driven behavior of the traffic light. The HPN allows us to easily formulate the problem for a complicated and large-scale traffic network due to its graphical understanding. The MLDS enables us to optimize the control policy for a traffic light by means of its algebraic manipulability and use of the model predictive control framework. Since the behavior represented by the HPN can be directly transformed into the corresponding MLDS form, the seamless incorporation of two different modeling schemes provides a systematic design scenario for traffic flow control.

Robust Slippage Degree Estimation Based on Reference Update of Vision-Based Tactile Sensor

In this paper, we propose a new slippage degree estimation method of a vision-based tactile sensor. The advantage of the vision-based tactile sensor is simultaneous acquisition of the slippage degree, a multidimensional force and a moment. A CCD camera captures the sensor surface which has regularly arrayed dots. The slippage degree on the sensor surface is determined by the stick ratio obtained from the displacements of dots in the captured images. In our previous work , the stick ratio was successfully applied to avoid slippage or the shape deformation of grasped objects. Based on the adaptive selection of the reference image and the compensation of the dot displacement, the proposed method in this study extends use of the previously developed algorithm, to dynamically complex but general situations as follows. First, the contact surface deforms after the macroscopic slippage or the slippage direction is changed. Second, the contact surface rotates with an applied moment. Third, the captured image is locally zoomed with a significant change of a grip force. A heuristic weighted average method is also proposed to decrease each dots variation in the captured image. Usefulness of the proposed method is confirmed through experimental results.

Vision-Based Tactile Sensing and Shape Estimation Using a Fluid-Type Touchpad

In this paper, we propose a new method to estimate the shape and irregularity of objects by a vision-based tactile sensor, which consists of a CCD camera, LED lights, transparent acrylic plate, and a touchpad which consists of an elastic membrane filled with translucent red water. Intensities of red, green and blue bands of the traveling light in the touchpad are analyzed in this study to estimate the shape/irregularity of the object. The LED light traveling in the touchpad is scattered and absorbed by the red pigment in the fluid. The depth of the touchpad is estimated by using the intensity of the light obtained from the red-green-blue (RGB) values of the image, in consideration of the scattering and reflection effects. The reflection coefficient that depends on the shape of the membrane, was decoupled in the proposed formulation. The intensity of the traveling light is represented with the geometrical parameters of the touchpad surface. In order to reduce the approximation error caused by unmodeled factors, we compensate the error by using a function of the deformation of the membrane. The validation of the proposed method is confirmed through experimental results.

Contact State Estimation by Vision-based Tactile Sensors for Dexterous Manipulation with Robot Hands Based on Shape-Sensing

We propose a new method for estimating the contact state of objects with varying shapes on a vision-based fluid-type tactile sensor, which touch pad is an elastic transparent membrane of silicon rubber with dotted pattern printed on its inner side. The membrane is filled with translucent red colored water. The proposed method leads to better understanding of the objects shape and movement, and can be applied for accomplishing reliable and dexterous handling tasks by robot hands.

Slippage degree estimation for dexterous handling of vision-based tactile sensor

In this paper, we propose a new slippage degree estimation method, where the vision-based tactile sensor was used to measure multi-dimensional force and moment in contact with an object. We proposed a new method using a reference image to obtain the stick ratio. The reference image is defined as previous image from which the grasped object moves a certain distance while updating the images. We show that the proposed method can be successfully applied to the following situations, after the macroscopic slippage occurs, the moving direction of the grasped object changes, or a moment is applied.

Operability of joystick-type steering device considering human arm impedance characteristics

In this paper, we present some results from the study on the impedance characteristics of a human arm during the execution of vehicle steering control tasks by using a joystick-type steering device. We propose a new model of human-machine interaction where the damping coefficient of the interface device can be tuned to match the impedance characteristics of the human arm. To verify the proposed model, we developed a special experimental setup. We used a robot and force/torque sensors to simulate the joystick operation. We explored human-machine interactions when the operator uses only one hand to control the vehicle. The reaction forces of the joystick were simulated by a virtual impedance field tuned to match human arm impedance. In the tests, we simulate situations when the movement of the joystick in the forward-backward direction sets the speed of the vehicle while the lateral rotation of the same control stick changes the turning radius of the vehicle. The robot allowed us to simulate various impedance characteristics. With the tests, we investigated the operability of the simulated vehicle by tuning the viscosity coefficient of the joystick in order to match it with the stationary human arm impedance and time-varying human arm impedance. The test results allowed us to propose a new method to improve the operability of a joystick-type steering device, based on the online adaptive matching of the impedance characteristics of the human arm. The usefulness of the proposed method is confirmed through experiments.

Trajectory planning of a robot for lower limb rehabilitation

We introduce a method for lower-limb physical rehabilitation by means of a robot that applies preliminary defined forces to a patients foot while moving it on a preliminary defined trajectory. We developed a special musculoskeletal model that takes into consideration the generated muscle forces of 27 musculotendon actuators and joint stiffness of the leg and allows the calculation of the motion trajectory of the robot and the forces that the robot needs to apply to the foot in each moment of the therapeutic exercise. Robotic treatment programs are customized for the individual patient by using a genetic algorithm (GA) that refers to the musculoskeletal model and calculates the parameters of the spline curves of the motion trajectory of the robot and forces acting on the foot.

FMS scheduling based on timed Petri net model and RTA* algorithm

Presents a scheduling method for a manufacturing system based on a timed Petri net model and a reactive fast search algorithm. The following two typical problems are addressed in the paper. (1) Minimize the maximum completion time. (2) Minimize the total deadline over-time. As for problem (1), a search algorithm which combines RTA* and a rule-based supervisor is proposed. Since both RTA* and the rule-based supervisor can be executed in a reactive manner, machines and AGVs allocations can be scheduled reactively, and simultaneously. As for problem (2), the original Petri net model is converted to its reverse model and the algorithm developed in problem (1) is applied with regard to the due time as a starting time in the reverse model.

Slippage Degree Estimation by Using Vision-Based Tactile Sensor for Dexterous Handling

Abstract In this paper, we present a new slippage degree estimation method, where the vision-based tactile sensor is used to measure multi-dimensional force and moment in contact with an object. We proposed a new method to obtain the stick ratio based on a quantization process of the maximum displacement in the stick region. The stick ratio is useful when we detect macroscopic slippage in advance. We show that the proposed method can be applied to wider situations and obtain more accurate estimation of stick ratio than the previous method. We can use the proposed method for the following situations. First, the applied normal force seriously changes or a certain amount of moment applies to the contact surface. Second, a macroscopic slippage occurs and the sensor surface re-establishs the contact. Third, a complex history of contact makes each local behavior of the surface difficult. The image processing method has been proposed to decrease the data variation of the captured CCD camera image and to cope with the wider situations of contact conditions. The usefulness of the proposed method is confirmed through the experimental results.