Robot Finger Stiffness Control in the Presence of Mechanical Nonlinearities

1988 ◽  
Vol 110 (3) ◽  
pp. 236-245 ◽  
Author(s):  
R. Vossoughi ◽  
M. Donath
Keyword(s):  
Controller Design ◽  
Contact Stiffness ◽  
Nonlinear Effects ◽  
Nonlinear Damping ◽  
Pole Placement ◽  
Robot Hand ◽  
Nonlinear Friction ◽  
Linear Subsystem ◽  
Stiffness Control ◽  
Unconstrained Motion

Stiffness control provides a mechanism for controlling finger position or force, and facilitates stable behavior during the transition between unconstrained motion and sudden contact with the environment. The method proposed here provides uniformity of response upon finger contact for any contact stiffness, as long as no separation occurs. The stiffness control system of a finger joint in a robot hand was partitioned into linear and nonlinear subsystems. The controller design used pole placement techniques based on the linear subsystem while the mechanical nonlinearities (i.e., load and velocity dependent nonlinear friction and nonlinear damping) in the drive were modeled separately. The parameters of the nonlinear model were experimentally identified off-line. These identified parameters were then used in a real-time estimator for compensation of the nonlinear effects while the system was under stiffness control. The technique was implemented successfully at 40 HZ on the actual finger under investigation. The results are a significant improvement on traditional techniques for nonlinear systems which result in large offsets or unstable behavior.

scholarly journals Anℋ∞Optimal Robust Pole Placement with Fixed Transparent Controller Structure on the Basis of Nonnegativity of Even Spectral Polynomials

2012 ◽  
Vol 2012 ◽  
pp. 1-25 ◽  
Author(s):  
Andrej Sarjaš ◽  
Rajko Svečko ◽  
Amor Chowdhury
Keyword(s):  
Controller Design ◽  
Polynomial Equation ◽  
Pole Placement ◽  
Robust Controller ◽  
Reference Tracking ◽  
Common Criteria ◽  
Sensitivity Problem ◽  
The Common ◽  
Partial Fraction Decomposition ◽  
Iterative Evolution

This paper presents the synthesis of an optimal robust controller with the use of pole placement technique. The presented method includes solving a polynomial equation on the basis of the chosen fixed characteristic polynomial and introduced parametric solutions with a known parametric structure of the controller. Robustness criteria in an unstructured uncertainty description with metrics of normℋ∞are for a more reliable and effective formulation of objective functions for optimization presented in the form of a spectral polynomial with positivity conditions. The method enables robust low-order controller design by using plant simplification with partial-fraction decomposition, where the simplification remainder is added to the performance weight. The controller structure is assembled of well-known parts such as disturbance rejection, and reference tracking. The approach also allows the possibility of multiobjective optimization of robust criteria, application of mixed sensitivity problem, and other closed-loop limitation criteria, where the common criteria function can be composed from different unrelated criteria. Optimization and controller design are performed with iterative evolution algorithm.

Model Based Control of Laminar Wake Using Fluidic Actuation

2010 ◽  
Vol 5 (4) ◽  
Author(s):  
Imran Akhtar ◽  
Ali H. Nayfeh
Keyword(s):  
Dynamical System ◽  
Stokes Equations ◽  
Control Function ◽  
Practical Importance ◽  
Nonlinear Damping ◽  
Open Loop ◽  
Pole Placement ◽  
Cylinder Surface ◽  
Control Input ◽  
Laminar Wake

Control of fluid-structure interaction is of practical importance from the perspective of wake modification and reduction of vortex-induced vibrations (VIVs). The aim of this study is to design a control to suppress vortex shedding. We perform a two-dimensional simulation of the flow past a circular cylinder using a parallel Computational Fluid Dynamics (CFD) solver. We record the velocity and pressure fields over a shedding cycle and compute the proper orthogonal decomposition (POD) modes of the divergence-free velocity and pressure, respectively. The Navier–Stokes equations are projected onto these POD modes to reduce the dynamical system to a set of ordinary-differential equations (ODEs). This dynamical system exhibits a limit cycle with negative linear damping and positive nonlinear damping. The reduced-order model is then modified by placing a pair of suction actuators and applying a control strategy using a control function method. We use the pressure POD mode distribution on the cylinder surface to optimally locate the actuators. We design a controller based on the linearized system and make it positively damped using pole-placement technique. The control-input settles to a constant value, suggesting constant suction through the actuators. We validate the results using CFD simulations in an open-loop setting and observe suppression of the hydrodynamic forces acting on the cylinder.

Efficient Damping Prediction of Bolted Structures Using Harmonic Balance Method

2012 ◽  
Author(s):  
Pascal Reuss ◽  
Jens Becker ◽  
Lothar Gaul
Keyword(s):  
Harmonic Balance ◽  
Normal Force ◽  
Contact Stiffness ◽  
Harmonic Balance Method ◽  
Computation Time ◽  
Nonlinear Effects ◽  
Element Model ◽  
Balance Method ◽  
Friction Damper ◽  
Step Size

In this paper damping induced by extensive friction occurring in the interface between bolted structures is considered by simulations and experiments. A friction damper is attached to a beam-like flexible structure by screws such that the normal force in the interface can be varied by the clamping force of the screws. Contact and friction force parameters are identified by the comparison of simulated and experimentally determined FRFs for a particular normal force. Afterward a prediction of damping for different configurations is established. For simulations a finite element model is used where suitable contact and friction models are implemented. A time simulation of the system is expensive due to the large number of DoFs of the discretized substructures and the required small step size due to the high contact stiffness. Therefore model reduction methods are used. A further reduction of the computation time can be achieved by using the Harmonic Balance Method (HBM) for a direct frequency domain computation of FRFs. This enables an efficient procedure to approximate the reachable damping as well as to search the optimal damper position and the optimal normal force. The dependency of the friction to the vibration amplitude is therefore taken into account. A more detailed investigation of the nonlinear effects, e.g. higher harmonic response, is then accomplished by transient simulations for the optimal configured system in the time domain and the results are compared to experimental results.

scholarly journals Optimal robust stabilizer design based on UPFC for interconnected power systems considering time delay

2017 ◽  
Vol 66 (3) ◽  
pp. 459-474
Author(s):  
Hamid Reza Koofigar ◽  
Ghader Isazadeh
Keyword(s):  
Time Delay ◽  
Power Systems ◽  
Power Flow ◽  
Controller Design ◽  
Design Procedure ◽  
Pole Placement ◽  
Wide Area ◽  
Linear Matrix ◽  
Unified Power Flow Controller ◽  
Input Signals

AbstractA robust auxiliary wide area damping controller is proposed for a unified power flow controller (UPFC). The mixedH2/H∞problem with regional pole placement, resolved by linear matrix inequality (LMI), is applied for controller design. Based on modal analysis, the optimal wide area input signals for the controller are selected. The time delay of input signals, due to electrical distance from the UPFC location is taken into account in the design procedure. The proposed controller is applied to a multi-machine interconnected power system from the IRAN power grid. It is shown that the both transient and dynamic stability are significantly improved despite different disturbances and loading conditions.

scholarly journals A Review on Eigenstructure Assignment Methods and Orthogonal Eigenstructure Control of Structural Vibrations

2009 ◽  
Vol 16 (6) ◽  
pp. 555-564 ◽  
Author(s):  
Mohammad Rastgaar ◽  
Mehdi Ahmadian ◽  
Steve Southward
Keyword(s):  
Vibration Suppression ◽  
Controller Design ◽  
Pole Placement ◽  
Structural Vibration ◽  
Eigenstructure Assignment ◽  
Large Space ◽  
Mode Localization ◽  
The Past ◽  
Recent Developments ◽  
Design Freedom

This paper provides a state-of-the-art review of eigenstructure assignment methods for vibration cancellation. Eigenstructure assignment techniques have been widely used during the past three decades for vibration suppression in structures, especially in large space structures. These methods work similar to mode localization in which global vibrations are managed such that they remain localized within the structure. Such localization would help reducing vibrations more effectively than other methods of vibration cancellation, by virtue of confining the vibrations close to the source of disturbance. The common objective of different methods of eigenstructure assignment is to provide controller design freedom beyond pole placement, and define appropriate shapes for the eigenvectors of the systems. These methods; however, offer a large and complex design space of options that can often overwhelm the control designer. Recent developments in orthogonal eigenstructure control offers a significant simplification of the design task while allowing some experience-based design freedom. The majority of the papers from the past three decades in structural vibration cancellation using eigenstructure assignment methods are reviewed, along with recent studies that introduce new developments in eigenstructure assignment techniques.

Controller Design for a Force-Reflecting Teleoperator System With Kinematically Dissimilar Master and Slave

1992 ◽  
Vol 114 (4) ◽  
pp. 641-649 ◽  
Author(s):  
J. F. Jansen ◽  
R. L. Kress ◽  
S. M. Babcock
Keyword(s):  
Controller Design ◽  
Mathematical Problem ◽  
Degree Of Freedom ◽  
Euler Angles ◽  
Euler Parameters ◽  
Liapunov Stability ◽  
Basic Properties ◽  
Control Scheme ◽  
Stiffness Control ◽  
Six Degree Of Freedom

The purpose of this paper is to develop a controller for a force-reflecting teleoperator system having kinematically dissimilar master and slave. The controller is a stiffness controller for both the master and the slave. A mathematical problem associated with representing orientations using Euler angles is described, and Euler parameters are proposed as a solution. The basic properties of Euler parameters are presented, specifically those pertaining to stiffness control. The stiffness controller for both the master and the slave is formulated using Euler parameters to represent orientation and a Liapunov stability proof is presented for the controller. The master portion of the control scheme is implemented on a six-degree-of-freedom master.

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