Task-Space Control Design and Performance Evaluation for a 6DOF Stewart Nanoscale Platform

2008 ◽  
Author(s):  
Chun-Chung Li ◽  
Yung Ting ◽  
Yi-Hung Liu ◽  
Yi-Da Lee ◽  
Chun-Wei Chiu
Keyword(s):  
Feedback Control ◽  
Hybrid Control ◽  
Feedforward Control ◽  
Feedback Controller ◽  
Test Method ◽  
Computation Method ◽  
Task Space ◽  
Force Output ◽  
End Effector ◽  
Control Scheme

A 6DOF Stewart platform using piezoelectric actuators for nanoscale positioning objective is designed. A measurement method that can directly measure the pose (position and orientation) of the end-effector is developed so that task-space on-line control is practicable. The design of a sensor holder for sensor employment, a cuboid with referenced measure points, and the computation method for obtaining the end-effector parameters is introduced. A control scheme combining feedforward and feedback is proposed. The inverse model of a hysteresis model derived by using a dynamic Preisach method is used for the feedforward control. Hybrid control to maintain both the positioning and force output for nano-cutting and nano-assembly applications is designed for the feedback controller. The optimal gain of the feedback controller is searched by using relay feedback test method and genetic algorithm. In experiment, conditions with/without external load employed with feedforward, feedback, and feedforward with feedback control schemes respectively are carried out. Performance of each control scheme verifies the capability of achieving nanoscale precision. The combined feedforward and feedback control scheme is superior to the others for gaining better precision.

Finite-time output feedback control for a pneumatic servo system

2016 ◽  
Vol 38 (12) ◽  
pp. 1520-1534 ◽  
Author(s):  
Xiangyu Wang ◽  
Guipu Li ◽  
Shihua Li ◽  
Aiguo Song
Keyword(s):  
Feedback Control ◽  
Output Feedback ◽  
Finite Time ◽  
Tracking Error ◽  
Output Feedback Control ◽  
Feedback Controller ◽  
Nonlinear Observer ◽  
Position Tracking ◽  
Piston Velocity ◽  
Control Scheme

In this paper, the position tracking control problem of pneumatic servo systems is investigated. These systems usually have high nonlinearities and unmeasurable piston velocities. Firstly, by using adding a power integrator technique, a global finite-time state feedback controller is proposed. Secondly, based on homogeneous theory, a nonlinear observer is developed to estimate the piston velocity. Finally, the corresponding output feedback controller is derived, which local finite-time stabilizes the position tracking error system. Compared with the conventional backstepping output feedback control scheme, the developed nonsmooth output feedback control scheme offers a faster convergence rate and a better disturbance rejection property. Numerical simulations illustrate the effectiveness of the proposed control scheme.

scholarly journals Control Performance Evaluation of Serial Urology Manipulator by Virtual Prototyping

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Hu Shi ◽  
Jiajie Li ◽  
Lianjie Guo ◽  
Xuesong Mei
Keyword(s):  
Fixed Point ◽  
Feedback Control ◽  
Feedforward Control ◽  
Tracking Error ◽  
Dynamics Simulation ◽  
Average Error ◽  
Bottom Surface ◽  
End Effector ◽  
Manipulator Design ◽  
Control Implementation

AbstractProstatic hyperplasia and tumor are common diseases, and the minimally invasive surgery inserting the instruments through the urethra into the prostate is commonly conducted. Taking the robotic manipulator for such surgery into consideration, this paper analyses the workspace of the end effector, and proposes the distribution error of the fixed point and the tracking error of manipulator end effector on the cone bottom surface of the workspace as the basis for control implementation of the manipulator. The D-H coordinate system of the manipulator is established and the trajectory planning of the end effector in the Cartesian space is carried out. The digital model was established, and dynamics simulation was performed in Solidworks and Matlab/Simulink environment to guide the manipulator design. Trajectory mapping and synchronization control between virtual model and the actual manipulator are realized based on digital twin technique. The virtual manipulator can reflect the real-time state of the manipulator with data interaction by comparing the dynamics simulation results with the motor current values obtained by experiment. Experiment was carried out with PD feedback control and Newton–Euler dynamics based feedforward control to get the trajectory tracking characteristic of each motor, errors of the fixed point and tracking performance of the end effector of the manipulator. The results show that compared with PD feedback control, feed forward control implementation can achieve a reduction of 30.0% in the average error of the fixed point of the manipulator and a reduction of 33.3% in the maximum error.

Design of force/position control laws for constrained robots, including effects of joint flexibility and actuator dynamics

Robotica ◽  
1999 ◽  
Vol 17 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Hariharan Krishnan
Keyword(s):  
Feedback Control ◽  
Position Control ◽  
Mathematical Representation ◽  
Control Law ◽  
Differential Algebraic Equation ◽  
Force Output ◽  
End Effector ◽  
Joint Flexibility ◽  
Actuator Dynamics ◽  
Constrained Robot

In this paper, a mathematical representation of constrained robot systems in the form of a differential-algebraic equation model is first considered. This model in modified further to include the joint flexibility between the linkages of the robot, and the actuator dynamics. The objective is to design a feedback control law for the system so that the position output variables (typically the end-effector position) and the force output variables (typically the contact force between the robot's end-effector and the contact surface) of the robot follows the desired position and the desired force trajectories, respectively, despite the presence of joint flexibility and actuator dynamics. A systematic procedure is developed for designing a feedback control law which ensures that the position variables track the desired position trajectories exponentially, and the force variables track the desired force trajectories exponentially. Since the development of the control law is based on the model of a constrained robot system which includes the effects of actuator dynamics and joint flexibility, it is possible to achieve better tracking performance using the force/position control law developed in this paper in cases where such effects are significant.

scholarly journals An Adaptive Hybrid Force/Motion Control Design for Robot Manipulators Interacting in Constrained Motion With Unknown Non-Rigid Environments

2012 ◽  
Author(s):  
Aghil Jafari ◽  
Mehdi Rezaei ◽  
Ali Talebi ◽  
Saeed Shiry Ghidary ◽  
Reza Monfaredi
Keyword(s):  
Motion Control ◽  
Lyapunov Method ◽  
Hybrid Control ◽  
Control Law ◽  
Environment Interaction ◽  
Task Space ◽  
Constrained Motion ◽  
End Effector ◽  
Control Approach ◽  
Rigid Environment

In the present paper, the objective of hybrid control is specified and an adaptive hybrid force/motion control approach is proposed. Based on the concept of hybrid control, the task space is decomposed into position and force controlled subspaces. An adaptive scheme is presented which makes the controller robust when the robot is in interaction with an unknown non-rigid environment. By using the classical Lyapunov method, it is demonstrated that the proposed control law ensures the tracking of the unconstrained components of the desired end-effector trajectories, with regulation of the desired contact force along the constrained direction. Simulation results verify the effectiveness of our prosperous adaptive hybrid control in robot-environment interaction.

Adaptive path-constrained control of a robotic manipulator in a task space

Robotica ◽  
2006 ◽  
Vol 25 (1) ◽  
pp. 103-112 ◽  
Author(s):  
Mirosław Galicki
Keyword(s):  
Degrees Of Freedom ◽  
Path Following ◽  
Lyapunov Stability Theory ◽  
Robotic Manipulator ◽  
Task Space ◽  
End Effector ◽  
State Dependent ◽  
Control Scheme ◽  
Robot Task ◽  
Three Degrees Of Freedom

This study addresses the problem of adaptive controlling of both a nonredundant and a redundant robotic manipulator with state-dependent constraints. The task of the robot is to follow a prescribed geometric path given in the task space, by the end-effector. The aforementioned robot task has been solved on the basis of the Lyapunov stability theory, which is used to derive the control scheme. A new adaptive Jacobian controller is proposed in the paper for the path following of the robot, with both uncertain kinematics and dynamics. The numerical simulation results carried out for a planar redundant three-DOF (three degrees of freedom) manipulator whose end-effector follows a prescribed geometric path given in a two-dimensional (2D) task space, illustrate the trajectory performance of the proposed control scheme.

Nonlinear Feedforward-Feedback Control of an Electric Clutch Actuator

2014 ◽  
Vol 1014 ◽  
pp. 339-343 ◽  
Author(s):  
Xin Li ◽  
Hui Zhou ◽  
Hao Li ◽  
Xue Song Li
Keyword(s):  
Feedback Control ◽  
Feedforward Control ◽  
Experimental Tests ◽  
Linear Feedback ◽  
Original Form ◽  
Model Errors ◽  
Nonlinear Characteristics ◽  
Control Scheme ◽  
Control Requirement ◽  
Feedforward Controller

For a novel electric clutch actuator, a nonlinear feedforward-feedback control scheme is proposed to improve the performance of the position tracking control. The feedforward control is designed based on flatness in consideration of the system nonlinearities, and the linear feedback control is given to accommodate the model errors and the disturbances. Lookup tables, which are used to represent nonlinear characteristics of the actuator systems, such as friction force, appear in their original form in the designed feedforward controller. The designed controller is evaluated through simulations and experimental tests, which show that the proposed controller satisfied the control requirement. Comparison with PID control is given as well.

scholarly journals Fuzzy PID Feedback Control of Piezoelectric Actuator with Feedforward Compensation

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Ziqiang Chi ◽  
Minping Jia ◽  
Qingsong Xu
Keyword(s):  
Feedback Control ◽  
Piezoelectric Actuator ◽  
Pid Control ◽  
Feedforward Control ◽  
Comparative Investigation ◽  
Preisach Model ◽  
Fuzzy Pid ◽  
Fuzzy Pid Control ◽  
Control Scheme ◽  
Feedforward Controller

Piezoelectric actuator is widely used in the field of micro/nanopositioning. However, piezoelectric hysteresis introduces nonlinearity to the system, which is the major obstacle to achieve a precise positioning. In this paper, the Preisach model is employed to describe the hysteresis characteristic of piezoelectric actuator and an inverse Preisach model is developed to construct a feedforward controller. Considering that the analytical expression of inverse Preisach model is difficult to derive and not suitable for practical application, a digital inverse model is established based on the input and output data of a piezoelectric actuator. Moreover, to mitigate the compensation error of the feedforward control, a feedback control scheme is implemented using different types of control algorithms in terms of PID control, fuzzy control, and fuzzy PID control. Extensive simulation studies are carried out using the three kinds of control systems. Comparative investigation reveals that the fuzzy PID control system with feedforward compensation is capable of providing quicker response and better control accuracy than the other two ones. It provides a promising way of precision control for piezoelectric actuator.

Use of vent stack temperature as a feedforward variable for dissolver total titratable alkali (TTA) control

TAPPI Journal ◽  
2018 ◽  
Vol 17 (05) ◽  
pp. 261-269
Author(s):  
Wei Ren ◽  
Brennan Dubord ◽  
Jason Johnson ◽  
Bruce Allison
Keyword(s):  
Feedback Control ◽  
Current Practice ◽  
Feedforward Control ◽  
Control Variable ◽  
Indirect Measurement ◽  
Tight Control ◽  
Transfer Lines ◽  
Green Liquor ◽  
Process Dynamics ◽  
Downstream Processes

Tight control of raw green liquor total titratable alkali (TTA) may be considered an important first step towards improving the overall economic performance of the causticizing process. Dissolving tank control is made difficult by the fact that the unknown smelt flow is highly variable and subject to runoff. High TTA variability negatively impacts operational costs through increased scaling in the dissolver and transfer lines, increased deadload in the liquor cycle, under- and over-liming, increased energy consumption, and increased maintenance. Current practice is to use feedback control to regulate the TTA to a target value through manipulation of weak wash flow while simultaneously keeping dissolver density within acceptable limits. Unfortunately, the amount of variability reduction that can be achieved by feedback control alone is fundamentally limited by the process dynamics. One way to improve upon the situation would be to measure the smelt flow and use it as a feedforward control variable. Direct measurement of smelt flow is not yet possible. The use of an indirect measurement, the dissolver vent stack temperature, is investigated in this paper as a surrogate feedforward variable for dissolving tank TTA control. Mill trials indicate that significant variability reduction in the raw green liquor TTA is possible and that the control improvements carry through to the downstream processes.

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