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On robust impedance force control of robot manipulators

Authors:
Seul Jung at Chungnam National University
Seul Jung
T.C. Hsia
T.C. Hsia
T.C. Hsia
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R.G. Bonitz
R.G. Bonitz
R.G. Bonitz
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Abstract

An impedance function is proposed to achieve accurate force tracking under the presence of uncertainties in robot dynamics and environment models. The new impedance function is formulated on the basis of PID control of the force tracking error which compensates for the unknown environment stiffness and position. The robot dynamics uncertainties are compensated by a simple time-delayed robust control algorithm. Stability and convergence of the control scheme are analyzed. Simulation studies with a three link rotary robot manipulator are shown. Furthermore, experimental results on a PUMA 560 arm are carried out to confirm the proposed impedance controller's performance
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... The first state occurs when carrying the brick from a conveyor belt to the placement position, the second state occurs when the brick starts to touch the existing mortar layer, and the third state occurs while placing the brick onto the mortar layer. Generally, three basic force-and-motion dependent control structures are discussed in the literature: position control, force or compliance control, and impedance control (Hogan 1985;Paul 1987;Goldenburg 1988). Position control is based on the assumption that resistance to the robot movement is negligible (e.g. ...
... Impedance control, which also uses the relationship between position and force, provides a mechanism for dealing with these situations. "The objectives of this control can be loosely defined as: 1) exerting a desired force on the environment by the robot, and 2) generating a desired (target) relationship between the force and the relative location of the point of interaction (contact) with respect to the commanded robot location" (Goldenburg 1988). ...
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... Impedance control is used to govern the relationship between velocity and force [28]. This control strategy is commonly used in many haptics researches [29], [30], [31]. Raibert and Craig [32] proposed a hybrid position-force control scheme in which a position control law is designed along force constrained directions and vice versa. ...
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... In [16] a neural network-based computed torque robot control in cartesian scheme is presented to yield stable behavior. In [17], a neural network impedance force control of robot the neural network is used to achieve tracking in free motion and stable behavior in constrained motion. Passivity-based neural network schemes are presented in [12,14,25,26,29], however, they use a great number of neurons in each layer and sometimes additional terms in the control law are necessary to provide robustness in the presence of approximation error [3,20,23]. ...
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  • May 2009
The joint robot control requires to map desired cartesian tasks into desired joint trajectories, by using the ill-posed inverse kinematics mapping. In order to avoid inverse kinematics, the control problem is formulated directly in task space to gives rise to cartesian robot control. In addition, when the robot is constrained due to its kinematic mappings yields a stiff system and an additional complexity arises to implement cartesian control for constrained robots. In this paper, an alternative approach is proposed to guarantee global convergence of force and position cartesian tracking errors under the assumption that the jacobian is not exactly known. A neuro-sliding mode controller is presented, where a small size adaptive neural network compensates approximately for the inverse dynamics and an inner control loop induces second order sliding modes to guarantee tracking. The sliding mode variable tunes the online adaptation of the weights. A passivity analysis yields the energy Lyapunov function to prove boundedness of all closed-loop signals and variable structure control theory is used to finally conclude convergence of position and force tracking errors. Experimental results are provided to visualize the expected performance.
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Tactile Sensing of Shapes of Unknown Surfaces with Sliding Motion
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Accuracy/Robustness Dilemma in Impedance Control
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  • Sep 2003
Impedance control facilitates the execution of tasks that involve contact with the environment. However, task performance depends on the accuracy at which the desired impedance is attained. This paper focuses on feedback methods for implementing impedance control and reveals the underlying conflict between impedance accuracy and robustness to uncertainties. Furthermore, we propose a novel yet practical method that facilitates robustness while maintaining accurate impedance tracking. Eigenvalue analysis and simulation results are presented to demonstrate the accuracy/robustness dilemma and the relative met-its of the different methods.
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Static characteristics of an in-parallel actuated manipulator for clamping and bracing applications
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  • Jun 1989
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Variable structure adaptive motion and force control of robot manipulators
Article
Full-text available
  • Sep 1994
  • AUTOMATICA
A variable structure adaptive method is developed for robust motion and force tracking control of robot manipulators in the presence of uncertainties in parameters of robot dynamics, contact surface, and external disturbances. The method takes advantages of both variable structure control (VSC) and adaptive control which results in a two-loop controller structure. VSC utilized in the inner-loop drives the system to reach and be maintained on a dynamic sliding mode which is provided by the outer-loop design. Adaptive control is used in the outer-loop to estimate contact surface parameters for ensuring the system with force tracking property. Overall stability of the two-loop system is established and simulation results are presented.
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Reinterpretation of Force Integral Control considering the control ability of system input
Conference Paper
  • Oct 2010
  • Rep U S
In the paper, the new force control, which is called the D'Alambertian force Error based Force Integral Control (DEFIC), is proposed based on the force integral control by considering the ability of the system input. From the system input point of view, the external force and system acceleration cannot be distinguished from each other. Thus, the best solution is to handle those quantities together. DEFIC is motivated from this observation. The external disturbance robustness and the plant/model mismatch compensation of DEFIC are explained based on the passivity-based control and Disturbance OBserver(DOB). Furthermore, it is illustrated how DEFIC can be extended to n-DOF manipulator control. The performance of DEFIC is verified with simulations, and the conclusion is followed directly.
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Exploration based on neural networks with applications in manipulator control
Article
Motivated by the notion of natural human-machine communication and cooperation, the thesis introduces a novel controller architecture for a special robotic hand using force control based on mixed feedback from several sensors. A finite state machine approach to reflex and behaviour simulation allows the seamless integration of higher level operations like path planning and obstacle avoidance. A a means of state space representation, a new type of vector quantization network, the Instantaneous Topological Map, or ITM, is introduced, which allows efficient adaptation even with serially correlated data as produced by control systems where stimuli follow trajectories in state space. These new approaches blend to produce a robust, fast learning robotics control system which performs active exploration to learn about its action space and dynamics. Additionally, the ITM is analyzed in detail to exhibit its suitability for other tasks, especially robust and fast dimensionality and structure analysis of large data sets. Ausgehend von der Vision von natürlicher und intuitiver Mensch-Maschine-Kommunikation und -Kooperation stellt die Arbeit eine neuartige Regelungsarchitektur für eine besondere Roboterhand vor, die eine Mischung mehrerer Sensor-Feedbacks für die Kraftregelung verwendet. Ein Zustandsautomat simuliert einfache Reflexe und Verhaltensmuster und ermöglicht die nahtlose Integration komplizierterer Vorgänge, wie Pfadplanung und Hindernisvermeidung. Für die innere Darstellung des Zustandsraums wird ein neuer Typ Vektorquantisierungsnetzwerk eingeführt, das ITM (Instantaneous Topological Map), der die effiziente Adaptation sogar mit stark seriell korrellierten Daten erlaubt, wie sie von Regelungssystemen produziert werden; dort entstehen Reizmuster in der Gestalt von Trajektorien. Die neuen Ansätze verschmelzen zu einem robusten, schnell lernenden Roboterregelsystem, das aktiv die eigenen Bewegungsfreiheitsgrade und die eigene Dynamik exploriert. Zusätzlich wird in der Arbeit das ITM im Detail analysiert, um seine Eignung für andere Aufgaben darzustellen, insbesondere die robuste und schnelle Analyse der Dimensionalität und Struktur von großen Datensätzen.
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Neural network techniques for robust force control of robot manipulators
Conference Paper
Full-text available
  • Sep 1995
In this paper a neural network force/position control scheme is proposed to compensate uncertainties in both robot dynamics and unknown environments. The proposed impedance control allows us to regulate force directly by specifying a desired force. Training signals are proposed for a feedforward neural network controller. The robustness analysis of the uncertainties in environment position is presented. Simulation results are presented to show that both the position and force tracking are excellent in the presence of uncertainties in robot dynamics and unknown environments
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On Force Tracking Impedance Control with Unknown Environment Stiffness
Article
Full-text available
  • Apr 1996
In impedance control for contact force tracking, it is well known that the reference trajectory of the robot is calculated from known environment stiffness [1]. Here we present a simple technique for determining the reference trajectory under the condition that the environment stiffness is unknown. The technique is developed based on the replacement of the unknown stiffness with a function of the measured contact force. The design technique is shown to be robust in the presence of sensor noise. Computer simulation studies have demonstrated that force tracking using the proposed technique is excellent for unknown environment stiffness. The practicality of the technique is also verified experimentally using a PUMA 560 manipulator. Key Words Impedance Control, Force Tracking, Trajectory Modification Scheme I Introduction The impedance control technique proposed by Hogan has been one of the fundamental approaches for force tracking control of robot manipulators with constrained motion....
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Impedance control: An approach to manipulation. Part I, II, III
Conference Paper
  • Jul 1984
Manipulation fundamentally requires a manipulator to be mechanically coupled to the object being manipulated. A consideration of the physical constraints imposed by dynamic interaction shows that control of a vector quantity such as position or force is inadequate and that control of the manipulator impedance is also necessary. Techniques for control of manipulator behaviour are presented which result in a unified approach to kinematically constrained motion, dynamic interaction, target acquisition and obstacle avoidance.
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Force Tracking in Impedance Control
Conference Paper
  • Jun 1993
Two simple and computationally efficient schemes for force tracking using impedance control are presented. The schemes generate the reference position trajectory required to produce a desired contact force despite lack of knowledge of the environmental stiffness and location. The first scheme uses direct adaptive control to generate the reference position on-line as a function of the force tracking-error. The second scheme utilizes an indirect adaptive strategy in which the environmental parameters are estimated on-line, and the required reference position is computed based on these estimates. Simulation studies are presented for a 7-degrees-of-freedom (DOF) robotics research arm using full arm dynamics. It is shown that the adaptive schemes are able to compensate for uncertainties in both the environmental stiffness and location, so that the end-effector applies the desired contact force while exhibiting the specified impedance dynamics
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Intelligent control of manipulators interacting with an uncertain environment based on generalized impedance
Conference Paper
  • Sep 1991
When a manipulator executes a partially constrained task under dynamic interaction with an uncertain environment or arbitrary stiffness, it is required to monitor and control both position and force simultaneously to bring them into acceptable ranges. Generalized impedance control (GIC) is presented as a method of intelligent position and force control of manipulators dynamically interacting with an uncertain environment. The GIC is achieved by representing the desirable behavior of a manipulator end-effector as a general dynamic relationship between a motion error and a contact force error, referred to as generalized impedance. The approach differs from previous manipulator control approaches in that it neither assumes the orthogonality between force and position control nor requires the switching of control for the transition between free and constrained motions. Furthermore, it is robust to the environmental stiffness ranging from zero stiffness (free space) to high stiffness (rigid contact)
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On force-tracking impedance control of robot manipulators
Conference Paper
  • May 1991
A reference force-tracking impedance control system is proposed, consisting of a conventional impedance controller in the inner-loop and a trajectory modifying controller in the outer-loop for force-tracking. The design of the outer-loop is presented and the stability of the two-loop control system is analyzed. A computationally efficient control algorithm for the inner-loop is suggested. Simulation results are presented. The controller is able to achieve excellent position and force-tracking with unknown environment stiffness and the presence of a burr on the tracking surface
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Robust Internal Force-tracking Impedance Control for Coordinated Multi-arm Manipulation - Theory and Experiments
Article
  • Sep 1997
Robust internal-force impedance control has been shown to be an effective control strategy for coordinated multiple-arm manipulation. It enforces a relationship between the the velocity of each manipulator and the internal force on the manipulated object and does not require knowledge of the object dynamic model. Each manipulator's nonlinear dynamics is compensated by a robust auxiliary controller which is insensitive to robot-model uncertainty and payload variation. For accurate force tracking, exact knowledge of the kinematic models of the manipulators and the object and the transformations between the manipulator base frames is required. Errors in the kinematic models can cause steady-state internal force errors which are proportional to the kinematic error and the desired manipulator stiffness. In this paper, we introduce an internal force-tracking impedance controller which compensates for kinematic uncertainty and regulates the desired internal force error to zero. Conditions for...
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\Simple robust schemes for cartesian space control of robot manipulators
  • Jan 1994
  • INT J ROBOT AUTOM
  • 167-174
  • T C Hsia
T.C. Hsia, \Simple robust schemes for cartesian space control of robot manipulators", International Journal of Robotics and Automation, pp. 167{174, 1994.
An approach to manipulator, part i, ii, iii
  • Jan 1985
  • 1-24
  • N Hogan
N. Hogan, \Impedance control : An approach to manipulator, part i, ii, iii", ASME Journal of Dynamic Systems, Measurement, and Control, vol. 3, pp. 1{24, 1985.