Volpi, R. and Khosla, P., "A Theoretical and Experimental Investigation of Explicit Force Control Stategies for Manipulators", IEEE Trans. Automatic Control, Vol. 38, No. 11, November 1993.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....They found that the fundamental limit on the force control bandwidth is the link stiffness. Like Cannon [8] they found that non colocated dynamics can lead to unstable systems. They also considered the effects of simple force control laws on a model of an actuator and the environment. Volpi [36] has undertaken work to assess the performance of torque control schemes under a variety of simple controllers, using an experimentally determined transfer function. One problem with all these schemes is that they exhibit instability while contacting stiff environments. This can result as the ....

....the environment is reduced, for example bycovering the endpoint of the manipulator with a compliantcovering (Roberts [26] and Whitney [39] or alternatively by increasing the damping on the system. Other methods for dealing with the contact instabilityhave been through simple control laws (Volpi [36], Yousef Toumi [44] or the use of nonlinear control (Xu et al. 42] to alter the characteristics of the control system so that low gains are used when the force is moving towards the setpoint, and high when it is moving away. Wu and Paul used joint torque control (Wu and Paul [41] and argued ....

Volpi, R. and Khosla, P., "A Theoretical and Experimental Investigation of Explicit Force Control Stategies for Manipulators", IEEE Trans. Automatic Control, Vol. 38, No. 11, November 1993.

....joint friction, and friction arising at the contact point between the tool tip and the surface. Note that the control problem of rigidly constrained rigid arms addressed herein differs significantly from the problem of control of arms in contact with a compliant environment, e.g. in [7] and [23]. This paper addresses the problem of single point contact between the tool and a rigid environment. In [15] the authors report experiments using a different manipulator for the more complex case in which the tool maintains multiple point contacts between the tool and a rigid environment. In ....

....experimental data on the comparative performance of the IDCF (13) IDCFA (15) and PDF (11) force control algorithms. 1) The Effect of Model Based Rigid Body Feedforward: Given the diversity of experimental results for model based control of unconstrained robot motion, e.g. 1] 8] 14] [23], 25] 27] in the present context of force control it seems essential to investigate the comparative performance of model based versus nonmodel based force controllers. The purpose of this section is to compare the performance of the nonmodel based PDF controller (11) with the fully adaptive ....

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R. Volpe and P. Khosla, "A theoretical and experimental investigation of explicit force control strategies for manipulators," IEEE Trans. Automat. Contr, vol. 38, pp. 1634--40, Nov. 1993.

....1 shows a schematic of the three approaches for the one dimensional case. Note that in one dimension, the hybrid control problem reduces to a pure force control problem. Other force control approaches which incorporate either fourth or sixth order dynamics in the contact model have been reported [28], 6] 1] but are not reviewed here. The explicit hybrid control method was first proposed in [18] with the aim of implementing force control on torque controlled robot arms (typically direct drive arms) The controller guaranteed asymptotically exact force set point regulation. A variety of ....

R. Volpe and P. Khosla. A theoretical and experimental investigation of explicit force control strategies for manipulators. IEEE Transactions on Automatic Control, 38(11):1634-1650, Novem- ber 1993.

....robot. Fig. 1 shows a schematic of the three approaches for the 1 D case. Note that, in one dimension, the hybrid control problem reduces to a pure force control problem. Other force control approaches which incorporate either fourth or sixth order dynamics in the contact model have been reported [13] [15] but are not reviewed here. The explicit hybrid control method was first proposed in [5] with the aim of implementing force control on torque controlled robot arms (typically direct drive arms) The controller guaranteed asymptotically exact force set point regulation. A variety of explicit ....

R. Volpe and P. Khosla, "A theoretical and experimental investigation of explicit force control strategies for manipulators," IEEE Trans. Automat. Contr., vol. 38, pp. 1634--1650, Nov. 1993.

....joint friction, and friction arising at the contact point between the tool tip and the surface. Note that the control problem of rigidly constrained rigid arms addressed in herein, e.g. 20] di#ers significantly from the problem of control of arms in contact with a compliant environment, e.g. [32, 8]. This paper addresses the problem of single point contact between the tool and a rigid environment. In [18] the authors report an experiments using a di#erent manipulator for the more complex case in which the tool maintains multiple point contacts between the tool and a rigid environment. In ....

....presents actual experimental data on the comparative performance of the IDCF (13) IDCFA (14) and PDF (11) force control algorithms. 4.2. 1 The E#ect of Model Based Rigid body Feedforward Given the diversity of experimental results for model based control of unconstrained robot motion, e.g. [1, 9, 14, 17, 35, 36, 32], in the present context of force control it seems essential to investigate the comparative performance of model based versus non model based force controllers. The purpose of this section is to compare the performance of the non model based PDF controller (11) with the fully adaptive model based ....

R. Volpe and P. Khosla. A theoretical and experimental investigation of explicit force control strategies for manipulators. IEEE Transactions on Automatic Control, 38(11):1634--40, November 1993.

....detail the first part of this solution: experimental extraction of physical system model parameters. Elsewhere, we have used the parameters in the model to analyze the wide variety of force control strategies, and confirmed the analysis and model with experimental implementation of the strategies [11, 12]. Currently at The Jet Propulsion Laboratory (MS 198 219) California Institute of Technology, Pasadena, California 91109. Email: volpe telerobotics.jpl.nasa.gov) This work was completed while the author was a member of the Department of Physics, The Robotics Institute, Carnegie Mellon ....

....m, k, and c are the mass, stiffness, and damping parameters. This is similar to the model presented in [4] However, the following analysis will result in different parameter values for the system, and leads to different predicted behavior for the force controllers having this system as a plant [11]. This paper is organized as follows: Section 2 outlines a vibration analysis of the model for the undamped and underdamped, low frequency oscillation cases. Also presented is an approximate relation between the measured force and the position and velocity of the first oscillatory mass. Section 3 ....

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R. Volpe and P. Khosla. A Theoretical and Experimental Investigation of Explicit Force Control Strategies for Manipulators. IEEE Transactions on Automatic Control, 38(11), November 1993.

....active control. It is the goal of impedance control to mask the intrinsic properties of the arm and replace them with the target impedance. The impedance relation can have any functional form. It has been shown that general impedances are useful for obstacle avoidance [Hogan (1985) Khatib (1986) Volpe and Khosla (1990)] However, it will be made clear in this section that sensor based, feedback controlled interaction with the environment is best achieved if the impedance is linear and of second order at most. This is for two reasons. First, the dynamics of a second order system are well understood and familiar. ....

....employed, as will be shown. 4. 2 Manipulator Model Based Control Manipulator model based control involves the use of a dynamic model of the manipulator to determine the actuation torques, Bejczy (1974) Model based impedance control may be summarized by the following equations [Hogan (1985) Volpe (1990)] D( m )u h( m ; m ) g( m ) J T ( m )f m (12) u = J Gamma1 ( m ) h x u Gamma J( m ) m i (13) x u = M Gamma1 [C Delta x K Deltax Gamma f m ] 14) Deltax = x c Gamma F( m ) 15) Delta x = x c Gamma J( m ) m : 16) Equation (12) compensates for ....

Volpe, R. and Khosla, P. 1993a (November). A Theoretical and Experimental Investigation of Explicit Force Control Strategies for Manipulators. IEEE Transactions on Automatic Control, 38(11).

....knowledge of the position of the environment. And fourth, it limits the forces that may be applied beyond a certain range of operation the compliant material is not linear and is prone to physical failure. Integral Explicit Force Control Integral force control acts as a low pass filter [76, 64, 55]. Thus, for impact transients, the high frequency components are filtered effectively. For impacts with low energy or with an inelastic environment this may be sufficient [76] Otherwise, bouncing and possible instability will occur [65] This is because of the nonlinear loss of contact with the ....

....0 0:2. These are the best values for impact control. It is important to point out that this locus also indicates that positive gain proportional force control, as well as impedance control, will become unstable for this system. The instability of these schemes has been confirmed experimentally [56, 61, 63, 64]. The points on the locus in the right half plane correspond to values of H 1 or H 0 2, and have been shown to be unstable. While the root locus suggests that very high gains would again be stable, experimentation has indicated that the system model breaks down for these large parameter ....

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R. Volpe and P. Khosla. A Theoretical and Experimental Investigation of Explicit Force Control Strategies for Manipulators. IEEE Transactions on Automatic Control, 38(11), November 1993.

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R. Volpe and P. Khosla, "A Theoretical and Experimental Investigation of Explicit Force Control Strategies for Manipulators", IEEE Trans. of Automatic Control, vol. 38, no. 11, Nov. 1993, pp. 1634-50.

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