Soo Jeon

Kinematic Kalman Filter (KKF) for Robot End-Effector Sensing

In control of industrial manipulators, the position from the motor encoder has been the only sensor measurement for axis control. In this case, it is not easy to estimate the end-effector motion accurately because of the kinematic errors of links, joint flexibility of gear mechanisms, and so on. Direct measurement of the end-effector using the vision sensor is considered as a solution but its performance is often limited by the slow sampling rate and the latency. To overcome these limitations, this paper extends the basic idea of the kinematic Kalman filter (KKF) to general rigid body motion leading to the formulation of the multidimensional kinematic kalman filter (MD-KKF). By combining the measurements from the vision sensor, the accelerometers and the gyroscopes, the MD-KKF can recover the intersample values and compensate for the measurement delay of the vision sensor providing the state information of the end-effector fast and accurately. The performance of the MD-KKF is verified experimentally using a planar two-link robot. The MD-KKF will be useful for widespread applications such as the high speed visual servo and the high-performance trajectory learning for robot manipulators, as well as the control strategies which require accurate velocity information.

Error Analysis of the Cylindrical Capacitive Sensor for Active Magnetic Bearing Spindles

This paper discusses the effects of mechanical errors of the cylindrical capcitive sensor (CCS) for active magnetic bearing (AMB) spindles, including the roundness error of a rotor and the mounting error of a sensor. The CCS has earned much interest as an AMB sensor due to its advantages of high resolution and spatial-averaging effect. An analytical model of the CCS is given and its spatial-averaging effect is shown quantitatively. The analytical model of the measuring process with the variation of sensor geometry shows that the CCS is more robust to roundness errors than the generally used probe sensor. This is verified through simulations and experiments on measuring orbits of rotors with harmonic roundness errors. In addition, the effects of mounting errors of the sensor are modeled and investigated.

State estimation based on kinematic models considering characteristics of sensors

The major benefit of the state estimation based on kinematic model such as the kinematic Kalman filter (KKF) is that it is immune to parameter variations and unknown disturbances and thus can provide an accurate and robust state estimation regardless of the operating condition. Since it suggests to use a combination of low cost sensors rather than a single costly sensor, the specific characteristics of each sensor may have a major effect on the performance of the state estimator. As an illustrative example, this paper considers the simplest form of the KKF, i.e., the velocity estimation combining the encoder with the accelerometer and addresses two major issues that arise in its implementation: the limited bandwidth of the accelerometer and the deterministic feature (non-whiteness) of the quantization noise of the encoder at slow speeds. It has been shown that each of these characteristics can degrade the performance of the state estimation at different regimes of the operation range. A simple method to use the variable Kalman filter gain has been suggested to alleviate these problems using the simplified parameterization of the Kalman filter gain matrix. Experimental results are presented to illustrate the main issues and also to validate the effectiveness of the proposed scheme.

A Control Systems Concept Inventory Test Design and Assessment

Any meaningful initiative to improve the teaching and learning in introductory control systems courses needs a clear test of student conceptual understanding to determine the effectiveness of proposed methods and activities. The authors propose a control systems concept inventory. Development of the inventory was collaborative and iterative. The diagnostic test was administered to students before (pre) and after (post) student learning activities. Test responses were analyzed to provide instructors with feedback on their teaching. Using classical test theory and item response theory, aggregated results were analyzed to assess internal consistency and measurement error, respectively. Students demonstrated an improvement from pre- to post-test scores, showing gains of 23%-34% in understanding of new concepts learned. The internal consistency of the test has ranged from 0.61 to 0.68. It can be shown that the precision of the test is highest in the score range of 33%-66%, which is where most post-test scores occurred.

On the Damping-Induced Self-Recovery Phenomenon in Mechanical Systems with Several Unactuated Cyclic Variables

The damping-induced self-recovery phenomenon refers to the fundamental property of underactuated mechanical systems: if an unactuated cyclic variable is under a viscous damping-like force and the system starts from rest, then the cyclic variable will always move back to its initial condition as the actuated variables come to a stop. The regular momentum conservation phenomenon can be viewed as the limit of the damping-induced self-recovery phenomenon in the sense that the self-recovery phenomenon disappears as the damping goes to zero. This paper generalizes the past result on damping-induced self-recovery for the case of a single unactuated cyclic variable to the case of multiple unactuated cyclic variables. We characterize a class of external forces that induce new conserved quantities, which we call the damping-induced momenta. The damping-induced momenta yield first-order asymptotically stable dynamics for the unactuated cyclic variables under some conditions, thereby inducing the self-recovery phenomenon. It is also shown that the viscous damping-like forces impose bounds on the range of trajectories of the unactuated cyclic variables. Two examples are presented to demonstrate the analytical discoveries: the planar pendulum with gimbal actuators and the three-link planar manipulator on a horizontal plane.

Braking Availability Tester for Realistic Assessment of Aircraft Landing Distance on Winter Runways

AbstractThis paper is concerned with the development of a new measurement device for the realistic assessment of braking capability of landing airplanes for winter runways. The conventional and current practice of runway condition monitoring has been focused on identifying the maximum tire-pavement frictional drag (μ value) and often neglected the characteristics of actual aircraft braking systems as well as the comprehensive effects coming from various factors such as deformable contaminants on the winter runway. The braking availability tester (BAT) proposed in this paper is designed to take a different approach for the realistic assessment of braking availability of landing airplanes. The main idea of the BAT is to mimic the braking operation of actual aircrafts as closely as possible by incorporating the same brake mechanism and antiskid braking system (ABS) used in existing aircrafts. In doing so, the BAT also incorporates a suite of sensors for monitoring the status of braking operation in real time...

Stability of Controlled Mechanical Systems With Ideal Coulomb Friction

When a mechanical system with Coulomb friction is under feedback control, the closed-loop system may asymptotically converge to a point in the equilibrium set or generate nonlinear oscillations such as limit cycles depending on the control algorithm. Thus, it is important to know how to guarantee the stability in the presence of Coulomb friction. This paper presents the stability analysis of controlled mechanical systems with multiple ideal Coulomb friction sources. Common properties of controlled mechanical systems with multiple ideal Coulomb friction sources have been explored and generalized into the state space formulation leading to a class of ideal relay feedback systems. Various stability criteria are considered and a new sufficient condition for the pointwise global stability is suggested. Simulation results for a single mass system and experimental results for a single link flexible joint mechanism are presented to confirm the analysis and to illustrate various aspects of stability conditions for controlled mechanical systems with ideal Coulomb friction. The results given in this paper can be useful for the design of mechanical systems free from the limit cycle.

Rollover stabilities of three-wheeled vehicles including road configuration effects

This study investigates the rollover stabilities of three-wheeled vehicles including the effects of road configurations. Tripped and untripped rollovers on flat and sloped roads are studied, and a new rollover index is introduced. To explore the unique dynamic behaviours of three-wheeled vehicles, the rollover stability is investigated on the basis of the lateral load transfer ratio, and the proposed rollover index is expressed in terms of measurable vehicle parameters and state variables. In addition to the effects of the lateral acceleration and the roll angle, the proposed rollover index takes the effects of the longitudinal acceleration and the pitch angle into account as well as the effects of banked roads and graded roads. Lateral and vertical road inputs are also considered since they can represent the effects of kerbs, soft soil and road bumps as the main causes of tripped rollovers. Sensitivity analysis is also provided in order to evaluate and compare the effects of different vehicle parameters and different state variables on the rollover stabilities of three-wheeled vehicles. To evaluate the proposed rollover index, simulations are also conducted using a high-fidelity CarSim model for a three-wheeled vehicle.

On the Self-Recovery Phenomenon for a Cylindrical Rigid Body Rotating in an Incompressible Viscous Fluid

The damping-induced self-recovery phenomenon is well understood for finite-dimensional mechanical systems. In this paper, we discover a self-recovery phenomenon in a composite system that consists of a cylindrical vessel and a surrounding fluid, where the vessel is equipped with an internal rotor and the fluid is incompressible and viscous. In the system dynamics, interactions between the vessel and the ambient fluid are fully taken into account. A combination of the Lyapunov method and the final-value theorem is applied for analysis of the dynamics. It is mathematically shown that after the spin of the rotor comes to a complete stop in finite time or exponentially as time tends to infinity, the vessel, which has deviated from its initial position due to the reaction to rotor spinning, converges back to its initial position as time tends to infinity, and so does every fluid particle. An experimental test is conducted to verify the occurrence of this phenomenon. The simultaneous self-recovery of the vessel and the fluid to the initial configuration is induced by the fluid viscosity as if the viscosity has a memory of the initial configuration. We envision that our discovery may be useful in designing and operating mechatronic systems interacting with fluids such as underwater vehicles.

Cooperative road condition estimation for an adaptive model predictive collision avoidance control strategy

This paper proposes a model predictive collision avoidance scheme for use in autonomous driving, based on cooperative on-line estimation of unknown and time varying road conditions. The autonomous vehicle is linearly modelled with constraints dependent on the road condition parameter. The proposed model predictive controller (MPC) is designed to be adaptive to this parameter. To accommodate this adaptive design, a particular method is developed for estimating the road friction coefficient cooperatively, by disseminating individual estimates in a vehicular network and using a consensus algorithm to converge these estimates to the maximum likelihood value. Presented simulation results demonstrate that the cooperative consensus scheme improves estimation significantly, and accordingly, the adaptive MPC incorporates road condition properly in collision avoidance planning.