Jahng Hyon Park

Auto-tuning of sliding mode control parameters using fuzzy logic

Sliding mode control guarantees robustness in the presence of modeling uncertainties and external disturbances. However, this can be obtained at the cost of high control activity that may lead to chattering. As one way to alleviate this problem, a boundary layer around sliding surface is typically used. In this case, the selection of control bandwidth and boundary layer thickness is a crucial problem for a trade-off between tracking error and chattering. The parameter tuning is usually done by a trial-and-error method in practice, causing significant effort and time. An auto-tuning method based on fuzzy rules is proposed. In this method, tracking error and chattering are monitored by performance indices and a controller tunes the design parameters intelligently in order to compromise both indices. To demonstrate the efficiency of the proposed method, a mass-spring translation system and a robotic control system are simulated and tested. It is shown that the proposed algorithm is effective in facilitating parameter tuning for sliding mode controllers.

Fuzzy logic based tuning of sliding mode controller for robot trajectory control

Sliding control guarantees system performance in the presence of modeling uncertainties and parameter inaccuracies. However this is obtained at the price of high control activity that may exacerbate chattering. As one way to alleviate this problem a continuation method using a boundary layer around switching is usually used. In this case selecting the control bandwidth and boundary layer thickness is a crucial problem for the trade-off between sliding performance and chattering. The parameter tuning is usually done by trial-and-errors in practice causing significant effort and time. An auto-tuning method based on fuzzy rules is suggested. To this end, the tracking error index and chattering index are defined first and then the fuzzy rules are designed to compromise the error and chattering indices. To demonstrate the efficiency of the proposed method a robotic control system is simulated and tested. It is shown that the proposed algorithm is effective to facilitate the parameter tuning for sliding mode controllers.

Design and fabrication of a bio-material property measurement system

Recently, diseases in gastro-intestinal tract have drastically increased. As a result, endoscopic technologies are being developed to diagnose and treat these diseases. Biomaterial property is essential information to develop endoscopic devices especially capsule type endoscope. For the past decades, experiments to obtain material property of gastro-intestinal tract are performed on in-vitro state. Therefore, material properties of digestive organs are not in-vivo test result but in-vitro result. In this research, we design, develop, and fabricate a bio-material property measurement (BMPM) system. The measuring system consists of a probing device, tendon device and suction part. The probe measures the force transmitted from the biomaterial as the sensing module protrudes based on the tendon controls, while the suction device seizes the organ. By using the system, we can measure the local deformation force and the piercing force. The measured deformation and piercing force data can be used for the locomotive and clamping mechanism design of the capsule type endoscope. In order to evaluate the validity of the BMPM, we perform the operation in an esophagus, stomach and colon of a pig. In conclusion, we could measure each organs material properties under in-vitro state without dissection of digestive organs. Some in-vivo test results are expected to design endoscopic devices using the proposed BMPM system.

Real time bilateral control for Internet based telerobotic system

There is a growing tendency to use the Internet as the transmission medium of the telerobotic system since the Internet is inexpensive and available all over the world. However, the bilateral real-time teleoperation can be unstable due to the random time delays of the Internet. The event-based teleoperation is one of the fine approaches to overcome the ransom time delays. Since the event based control uses a non-time action reference, the stability and response performance of the system are affected by the time, which an event is held for. This study introduces the variable holding time to secure stability and response performance at once. The proper holding time for each event is obtained depending on the characteristics of the task through the fuzzy logic. The proposed control scheme was implemented on a robot arm over the Internet to show its effectiveness.

Multi-objective genetic algorithm for high-density robotic workcell

This paper presents a scheduling problem for a high-density robotic workcell using multi-objective genetic algorithm. Multi-robots motions are coordinated to perform with efficiency under various working conditions in the limited area while avoiding collisions between the robots. We make the best use of genetic algorithm by adding multi-object for scheduling of the multi robot system. We simulate motion of six robots with the optimized schedule and show effectiveness of the proposed multi-objective genetic algorithm.

Path Planning of Swarm Mobile Robots Using Firefly Algorithm

Abstract: A swarm robot system consists of with multiple mobile robots, each of which is called an agent. Each agent interacts with others and cooperates for a given task and a given environment. For the swarm robotic system, the loss of the entire work capability by malfunction or damage to a single robot is relatively small and replacement and repair of the robot is less costly. So, it is suitable to perform more complex tasks. The essential component for a swarm robotic system is an inter-robot collaboration strategy for teamwork. Recently, the swarm intelligence theory is applied to robotic system domain as a new framework of collective robotic system design. In this paper, FA (Firefly Algorithm) which is based on firefly’s reaction to the lights of other fireflies and their social behavior is employed to optimize the group behavior of multiple robots. The main application of the firefly algorithm is performed on path planning of swarm mobile robots and its effectiveness is verified by simulations under various conditions.

A Novel z-axis Accelerometer Fabricated on a Single Silicon Substrate Using the Extended SBM Process

This paper presents a novel z-axis accelerometer with perfectly aligned vertical combs fabricated using the extended sacrificial bulk micromachining (extended SBM) process. The z-axis accelerometer is fabricated using only one (111) SOI wafer and two photo masks without wafer bonding or CMP processes as used by other research efforts that involve vertical combs. In our process, there is no misalignment in lateral gap between the upper and lower comb electrodes, because all critical dimensions including lateral gaps are defined using only one mask. The fabricated accelerometer has the structure thickness of , the vertical offset of , and lateral gap between electrodes of . Torsional springs and asymmetric proof mass produce a vertical displacement when an external z-axis acceleration is applied, and capacitance change due to the vertical displacement of the comb is detected by charge-to-voltage converter. The signal-to-noise ratio of the modulated and demodulated output signal is 80 dB and 76.5 dB, respectively. The noise equivalent input acceleration resolution of the modulated and demodulated output signal is calculated to be and . The scale factor and linearity of the accelerometer are measured to be 1.1 mV/g and 1.18% FSO, respectively.

Two-stage sliding mode controller for bending mode suppression of a flexible pointing system

The performance of a flexible pointing system mounted on the top of a vehicle is greatly affected by the bending vibrations as the vehicle runs on a bumpy course. In order to improve the pointing accuracy, the pointing structures vibrations should be suppressed. In this paper, a nonlinear controller is designed to control the tip position of the pointing system while actively suppressing the vibrations. To cope with high order dynamics and nonlinearity of the plant and the hydraulic actuating system, a two-stage sliding mode controller is devised. The desired actuating pressure is obtained in the first stage and then the input current to the hydraulic servo system is computed to generate the pressure. The simulation results show the effectiveness of this scheme and improvements in pointing accuracy.

Inverse Kinematics of a Redundant Manipulator based on Conformal Geometry using Geometric Approach

This paper describes a geometrical approach for analysing the inverse kinematics of a 7 Degrees of Freedom (DOF) redundant manipulator. The geometric approach is desirable since it provides complete and simple solutions to the problem and determines the relationship between the joints and the end-effector without iterative process. This paper introduces the approach to solve kinematic solution of 7 DOF in an intuitive way using conformal geometric approach step by step. We finally present the comparison with pseudo inverse solution which is the most well-known method in redundant manipulator kinematic problem at the same simulation environment.

Kinematics Optimization of a 3-SPS Parallel Redundant Motion Mechanism Using Conformal Geometric Algebra

In this paper, an actuation mechanism for high-speed aiming of a target is proposed. The mechanism is a 3DOF-SPS (spherical-prismatic-spherical) parallel manipulator and can be used for a missile defense system with a fast reaction time. This type of parallel mechanism has high rigidity against external disturbances and accordingly high stiffness and precision. The target aiming requires 2 degrees of freedom and this 3 DOF mechanism has one redundancy. For fast manipulation of the proposed mechanism, the redundancy can be exploited and an optimal solution can be found out of the infinite number of inverse kinematic solutions. For finding a near time-optimal solution, a cost function is formulated considering displacement of each parallel link and an optimization technique is used for solution of the inverse kinematic problem.