Residual Vibration Reduction Research Articles

5自由度制御型能動空気軸受(第1報)

The aim of this research is to develop the air rotary bearing which has the following capability: (1) compensation of motion errors of the axis (high accuracy), (2) reduction of motion errors and residual vibrations which external disturbances cause (high stiffness and high vibration damping), (3) control of five degrees of freedom axis motion of the rotating axis (new function). To realize these, the authors propose an "Active Air Rotary Bearing" #(AARB). The AARB comprises an axis, two active air journal bearings which consist of four non-contact actuators and two non-contact sensors and an active air thrust bearing which consists of a non-contact actuator and a non-contact sensor. The AARB can support and drive the axis using the non-contact actuators. This paper describes the principle of the AARB and the identification of dynamic parameters. The models used for the identification are simple and the frequency responses of dynamic models agree well with those of an experimental mechanism.

5自由度制御型能動空気軸受(第2報)

The aim of this research is to develop the air rotary bearing which has the following capability: (1) compensation of motion errors of the axis (high accuracy), (2) reduction of motion errors and residual vibrations which external disturbances cause (high stiffness and high vibration damping), (3) control of five degrees-of-freedom axis motion of the rotating axis (new function). To realize these, the authors have proposed an "Active Air Rotary Bearing" (AARB). In this report, a control system with PID-PD controllers is designed to control the five degrees-of-freedom axis motion. By using the control system, the AARB achieves; (1) 10nm positioning resolutions (x, y, z directions), 0.02arcsec positioning resolutions (φΨ directions), (2) almost infinite static stiffness and increased damping capability, (3) compensation of motion errors of the rotating axis.

The Design, Experimentation, and Simulation of a Novel Coulomb Friction Device for Automotive Valve Spring Damping

This investigation contains experimental and computer modeling results of an alternative method for damping automotive valve springs, in which a nondestructive elastomeric sleeve that slides over the spring with an interference fit is used to provide coulomb damping on the outside of the valve spring coils. The damper and valve spring dynamics are modeled using the wave equation with a damping term composed of both viscous and coulomb components. Although the damper is very simple and inexpensive, the reduction in residual spring vibrations are shown to be significant without loss of valve spring performance. Experimental data taken from a 1983 Pontiac family-II, 1.8 liter, four cylinder, single overhead cam engine equipped both with and without the new elastomeric dampers is used to verify the results of the computer simulation and demonstrate the effectiveness of the damper.

Fourier-based optimal design of a flexible manipulator path to reduce residual vibration of the endpoint

SUMMARYA method is presented for generating the path which significantly reduces residual vibration. The desired path is optimally designed so that the system completes the required move with minimum residual vibration. The dynamic model and optimal path are effectively formulated and computed by using special moving coordinates, called virtual rigid link coordinates, to represent the link flexibilities. Also joint compliances are included in the model. Characteristics of residual vibration are identified from the linearized equations of motion. From these results, the performance index is selected to reduce residual vibration effectively. The path to be designed is developed by a combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems. The concept of correlation coefficients is used to select the minimum number of design variables, i.e. Fourier coefficients, the only ones which have a considerable effect on the reduction of residual vibration. A two-link manipulator is used to evaluate this method. Results show that residual vibration can be drastically reduced by selecting an appropriate manipulator path.

Adaptive Nonlinear Compensation for a Scara Robot with Flexible Joints

Abstract Nonlinear dynamic compensation, which is derived from inverse dynamics, is very useful for controlling robot manipulators. An accurate modeling of the robot system and a precise estimation of the physical parameters, however, are necessary in order to get enough control performance with that method. In this paper, on the mathematical model of robot manipulator with PD controller, the stiffness of the transmission system between motor and robot arm is taken into consideration. Furthermore, the controller parameters are adjusted only by using actual motor angles and reference robot arm angles. The effectiveness of this method is examined by an experiment using an industrial SCARA robot. The result proves that this method provides satisfactory performance for a reduction of both residual vibration and tracking errors.

Adaptive Nonlinear Compensation for a SCARA Robot with Flexible Joints.

Nonlinear dynamic compensation, which is derived from inverse dynamics, is very useful for controlling robot manipulators. An accurate modeling of the robot system and a precise estimation of the physical parameters, however, are necessary in order to get enough control performance with that method. In this paper, on the mathematical model of robot manipulator with PD controller, the stiffness of the transmission system between motor and robot arm is taken into consideration. Furthermore, the controller parameters are adjusted only by using actual motor angles and reference robot arm angles. The effectiveness of this method is examined by an experiment using an industrial SCARA robot. The result proves that this method provides satisfactory performance for a reduction of both residual vibration and tracking errors.

Experimental Evaluation of Shaped Inputs to Reduce Vibration for a Cartesian Robot

Since all robots have some inherent flexibility, fast motions tend to excite system vibrations. This paper develops shaped inputs that generate fast motions with minimum residual vibration. Shaped force inputs are constructed from a versine series, with coefficients of the harmonic terms chosen to maximize kinetic energy and minimize excitation energy at the system natural frequencies. These force inputs are doubly integrated to obtain position waveforms that serve as reference profiles for a closed-loop controller. A Cartesian robot is used as an experimental system to test these shaped reference inputs and to compare their responses to simple step responses. Results indicate considerable reduction in residual vibration with the shaped inputs. This is especially useful when modal coupling exists, since vibration in other axes can be prevented by driving the moving axis with shaped inputs having no excitation energy at the coupled mode frequencies.

Preshaping Command Inputs to Reduce System Vibration

A method is presented for generating shaped command inputs which significantly reduce or eliminate endpoint vibration. Desired system inputs are altered so that the system completes the requested move without residual vibration. A short move time penalty is incurred (on the order of one period of the first mode of vibration). The preshaping technique is robust under system parameter uncertainty and may be applied to both open and closed loop systems. The Draper Laboratory’s Space Shuttle Remote Manipulator System simulator (DRS) is used to evaluate the method. Results show a factor of 25 reduction in endpoint residual vibration for typical moves of the DRS.

Reduction of Residual Vibrations in Positioning Control Mechanism

This paper clarifies numerically and experimentally the characteristics of residual vibrations caused by the natural frequency variation for a positioning mechanism, such that a load modeled as a one-degree-of-freedom vibratory system is driven by a servomotor. Moreover, a multi-design-point method is proposed, which can reduce residual vibrations over a comparatively wide range of parameter variations. It is also shown that this method enables high-speed and accurate positioning for a serial printer carriage.