Sungsoo Rhim

Adaptive time-delay command shaping filter for flexible manipulator control

We introduce a new formulation of the time-delay command shaping filter using a commuted shaping order approach, which leads to the development of a simple and effective adaptive command shaping technique for both single- and multi-mode cases. The authors derived the conditions that the time-delay command shaping filter should satisfy to suppress the residual vibration. From the conditions, they calculated the minimum number of command shaping filter terms required to completely cancel the residual vibrations as a function of the number of elastic modes to be canceled. Using this new formula they also prove that the time-delay value is not a function of the system parameters and can be chosen freely even for multiple elastic modes. Making use of this freedom in choosing the time delay, the authors propose a direct adaptation of the time-delay command shaper for both single and multi-mode systems. Finally, the simulation and experimental results of the adaptation are included to show the effectiveness of the direct adaptive command shaping approach.

Noise effect on adaptive command shaping methods for flexible manipulator control

Since its introduction, the command shaping method has been applied to the control of many types of flexible manipulators and the effectiveness in the vibration suppression has been verified. However, designing an effective command shaper requires a priori knowledge about the system parameters. Recently, some efforts have been made to make the command shaper adapt to the changes in the system parameters. In this paper, the indirect and the direct adaptive command shaping methods in the time domain are compared, especially in terms of the noise effect on the performance. Analysis shows that the direct approach is less sensitive to the noise and this analytic result is verified by the proper simulation. Finally, experimental results using the direct approach are included.

Performance Evaluation Criteria for Autonomous Cleaning Robots

This paper is a report on the initial trial for its kind in the development of the performance index of the autonomous mobile cleaning robot. The unique characteristic features of the cleaning robot have been identified as autonomous mobility, dust collection, and operation noise. Along with the identification of the performance indices the standardized performance-evaluation methods including the corresponding performance evaluation platform for each indices have been developed as well. The validity of the proposed performance evaluation methods has been demonstrated by applying the proposed evaluation methods on two commercial cleaning robots available in market. The proposed performance evaluation methods can be applied to general-purpose autonomous service robots which will be introduced in the consumer market in near future.

Combining a Multirate Repetitive Learning Controller With Command Shaping for Improved Flexible Manipulator Control

Sungsoo Rhim School of Mechanical Engineering Georgia Institute of Technology Atlanta, Georgia 30332 Email: gt5543a@prism.gatech.edu NaderSadegh School of Mechanical Engineering Georgia Institute of Technology Atlanta, Georgia 30332 Email: nader.sadegh@me.gatech.edu Command shaping, a feedforward approach used to control flexible manipulators, performs most effectively when applied to a linear system. In practice, various nonlinearities are present in a given system that will deteriorate the performance of command shaping. In this work, a multirate repetitive learning controller (MRLC) is used in conjunction with a command shaping method known as the optimal arbitrary time-delay filter (OATF) for discrete-time joint control of a single flexible link manipulator containing nonlinearities. With very little a priori knowledge of the given system, a MRLC is able to cancel the nonlinearities at select frequencies and achieve near-perfect tracking of a periodic desired trajectory. By doing this, a MRLC controls the joint to follow a given shaped command more closely, thus allowing the OATF to more effectively attenuate residual tip vibrations. It is shown both analytically and experimentally that this controller is more effective than a conventional PID and OATF controller at attenuating residual tip vibrations. INTRODUCTION Having flexibility in a mechanical manipulator will degrade trajectory tracking control and manipulator tip positioning. In practice, however, constraints imposed by manufacturing and operating costs, as well as by various operating environments, will render the presence of such flexibility unavoidable. Ai-Ping Hu School of Mechanical Engineering Georgia Institute of Technology Atlanta, Georgia 30332 Email: gt0162c@prism.gatech.edu Wayne J. Book School of Mechanical Engineering Georgia Institute of Technology Atlanta, Georgia 30332 Email: wayne.book@me.gatech.edu Numerous researchers have proposed control schemes to attenuate tip vibration due to flexure during mechanical manipulator motion. These methods may be divided into two categories: feedback and feedforward. Feedback algorithms utilize measurement signals, whereas feedforward algorithms will only utilize desired reference signals. In this work, we will consider a particular feedforward method known as command shaping. Command shaping seeks to reduce tip vibrations by reshaping the desired trajectory to be tracked in order to produce a new trajectory that will not excite the resonances of the flexible manipulator. Command shaping is advantageous because it is able to accomplish this task without regard to the particular form of the desired trajectory. Since its introduction (Singer and Seering, 1990), the command shaping method has been applied successfully in several different applications ((Magee and Book, 1994), (Rhim and Book, 1997)). In our work, we have used a particular command shaping method known as the optimal arbitrary time-delay filter (OATF) (Magee, 1996). The effectiveness of command shaping relies on the linearity of the flexible manipulator system the (reshaped) desired trajectory is commanding. If this system is not linear, we will still observe excitation of the manipulator tip even when using a properly reshaped desired trajectory. The particular flexible mechanical manipulator we have used in our experiments is a gantry-type robot with a prismatic joint and a single flexible link. This is a configuration which is widely used in industry. It is often modFigure 1. CONCEPTUAL BLOCK DIAGRAM WITH COMMAND SHAP-

Simulation and Experimental Methods for Media Transport System: Part II, Effect of Normal Force on Slippage of Paper

Many daily appliances for examples copiers, printers and ATMs contain the media transport system (MTS) and the slippage between the medium in the MTS deteriorates the performance quality of the whole system The slippage of the medium in the MTS is affected by many parameters including the friction coefficient between the feeding rollers and the medium, the velocity of the feeding rollers, and the normal force exerted on the medium by feeding rollers This paper focuses on the effect of the normal force on the slippage while the medium is being fed For this purpose, we developed a two-dimensional simulation model for a paper feeding system. Using the simulation model, we calculated the slippage of the paper for different normal forces We have also constructed a testbed of the paper feeding system to verify the simulation results Experimental results are compared with the simulation resultsKey Words: Media Transport System, Slippage, Normal Force, Friction Coefficients, Paper Modeling

Development of Paper Feeding Speed Control System Using Co-Simulation Tool

Recently, the demand of a high speed and high accuracy increases in the media transport (or feeding) system (MTS) which is one of the most essential parts in copiers, digital printers, ATM’s and so forth. This paper illustrates the development of a high-speed, high-accuracy paper feeding system including a feedback feeding speed control system with a learning controller. The controller is designed to reduce the slippage between the feeding rollers and paper in the presence of the periodic disturbance in the nip force of the driven roller which is mainly caused by the eccentricity of the driven roller. The lack of an accurate model of the plant often makes control system designers to face difficulties at an early stage in designing a robust controller for highly non-linear multi-body dynamics system such as the MTS with flexible media. To mitigate the problem, a so-called co-simulation approach, the combination of a controller development tool and a model developed in MBD, is often adopted and it would allow the controller designer to expedite the design and evaluation of control systems. In the paper, using a co-simulation approah a MTS with a paper is modeled and a repetitive learning controller is develped and evaluated.Copyright

Internet-Based Visual Snow-Cover Monitoring and Measuring System

In this paper, an Internet-based snow-cover monitoring system is developed which analyzes visual image of drifted snow and measures the amount of snowing. The system is composed with a reference ruler, a CCD camera, and a PC with an image processing unit. The snow-depth is estimated based on the position of the lowest uncovered marker on the ruler which is extracted from the captured image. An image processing algorithm is devised to obtain proper resolution and good accuracy of the uncovered marker position in spite of the week intensity of ambient light and disturbances from the light rays of outdoors. The system also acts as monitoring server, which transfers the raw images in real-time to a remotely located client using TCP/IP. With bi-direction communication through Internet, users can adjust the orientation of the camera view. Experimental results show that this system improves reliability and accuracy of measurement of drifted snow

Summary of recent standardization activities in the field of robotics

This paper summarizes the recent standardization activities in the field of robotics by ISO International Organization for Standardization, IEC International Electrotechnical Commission, OMG Object Management Group, and other organizations. While the standards in industrial robots have been mainly developed by ISO, the standards on the emerging service robots are initiated by many organizations. One of the goals of this paper is to coordinate the efforts among these groups so that more effective standardization activity can be executed. Standardization in the emerging service robots will eventually promote the proliferation of service robot markets in the near future.

Extraction of Optimal Time-Delay in Adaptive Command Shaping Filter for Flexible Manipulator Control

The performance of the direct adaptive time-delay command shaping filter depends on the select time-delay. In the previously introduced direct adaptive command shaping filter, however, the time-delay value is fixed and only the magnitudes of the impulses are learned. In this paper, the authors introduce a new scheme to adapt the time-delay which is to be used in conjunction with the direct adaptive command shaping for the improved vibration suppression in flexible motion system. In order to formulate the time-delay adaptation scheme, the authors have analyzed the effect of the time-delay value on the performance of the direct adaptive command shaping filter. By modifying the direct adaptation formula based on the analysis result the authors have established a set of equations to adapt the time-delay toward the optimal value. Simulation results show the effectiveness of the proposed time-delay adaptation approach for the improved vibration suppression.

A simple model for constant storage modulus of poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes nanocomposites at low frequencies assuming the properties of interphase regions and networks

The networks of nanoparticles in nanocomposites cause solid-like behavior demonstrating a constant storage modulus at low frequencies. This study examines the storage modulus of poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes (CNT) nanocomposites. The experimental data of the storage modulus in the plateau regions are obtained by a frequency sweep test. In addition, a simple model is developed to predict the constant storage modulus assuming the properties of the interphase regions and the CNT networks. The model calculations are compared with the experimental results, and the parametric analyses are applied to validate the predictability of the developed model. The calculations properly agree with the experimental data at all polymer and CNT concentrations. Moreover, all parameters acceptably modulate the constant storage modulus. The percentage of the networked CNT, the modulus of networks, and the thickness and modulus of the interphase regions directly govern the storage modulus of nanocomposites. The outputs reveal the important roles of the interphase properties in the storage modulus.