R. Volpe and P. Khosla. Computational considerations in the implementation of force control strategies. In Journal of Intelligent and Robotic Systems 9, pages 121--148, 1994.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....of multifingered grippers. Since the joints of the Salisbury Hand are tendon driven, there is the problem of elasticity [21] which is introduced in Section 3. Looking at the position force control of a multifingered robot it is useful to modelise the dynamic environment. Since linear models [24] are not able to model the impact behaviour, a nonlinear approach of [14] will be used in Section 4. Section 5 deals with the implementation of the control system. 2 Friction Disturbances like friction play an important role in controlling [2] 19] e.g. to move a still standing joint out of the ....

R. Volpe and P. Khosla. Computational considerations in the implementation of force control strategies. In Journal of Intelligent and Robotic Systems 9, pages 121--148, 1994.

....the Karlsruhe Dexterous Hand discussed in Section 2, there are still problems left and new solutions have to be worked out for the control of multifingered grippers. Looking at the position force control of a multifingered robot it is useful to modelise the dynamic environment. Since linear models [23] are not able to model the impact behaviour, a nonlinear approach of [14] will be used in Section 3. Section 4 deals with the implementation of the control system. 2 Friction Disturbances like friction play an important role in controlling [2] 19] e.g. to move a still standing joint out of the ....

R. Volpe and P. Khosla. Computational considerations in the implementation of force control strategies. In Journal of Intelligent and Robotic Systems 9, pages 121--148, 1994.

....damping present in the oscillating fourth order system. contact, the stiffness of the environment makes this gain too small for critical damping. However, it could not be increased for several reasons directly effecting system stability: sampling rate, sensor noise, and plant model consistencies [14]. To measure the system response, the environmental surface was struck softly so as to excite only low frequency oscillations. The measured force, position and velocity of one of these tests is shown as a function of time in Figure 8. While damping is present, the system is obviously underdamped, ....

R. Volpe and P. Khosla. Computational Considerations in the Implementation of Force Control Strategies. In Journal of Intelligent and Robotic Systems: Theory and Applications. Special Issue on Computational Aspects of Robot Kinematics, Dynamics, and Control, (accepted for publication in 1994).

....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. 1994b. Computational Considerations in the Implementation of Force Control Strategies. Journal of Intelligent and Robotic Systems: Theory and Applications, 9:121--148.

....well as the reference force and filtered force (long dash curve) for K fp = 0:5, K fd = 0:01, and a = 10. The results are not much better than for proportional gain alone. As will be reviewed below, improvements in the performance of this controller can not be made by varying the gains given here [27]. First, increasing the derivative gain does not improve the response of the system because the amplified low frequency noise can still drive the system unstable. While Figure 19 seems to show a fairly smooth filtered force signal, Figure 20 shows a closer view of a section of the curve. ....

R. Volpe and P. Khosla. Computational Considerations in the Implementation of Force Control Strategies. In Journal of Intelligent and Robotic Systems: Theory and Applications. Special Issue on Computational Aspects of Robot Kinematics, Dynamics, and Control, (accepted for publication in 1993).

....causes this active damping value to be insufficient for critically damped motion in the force controlled degrees of freedom. Increasing the damping is not possible with our system due to velocity signal lag, inaccuracies, and noise as discussed in Section 2. 1 and elsewhere [Volpe (1990) Volpe and Khosla (1993)] The control sampling rate for these experiments was 300 Hz. The Lord force sensor is designed to provide raw strain gauge information at 400 Hz. Therefore, sampling of the force data was asynchronous, as every fourth set of data was missed. However, since the sampling rate was an order of ....

Volpe, R. and Khosla, P. (accepted for publication in 1993). Computational Considerations in the Implementation of Force Control Strategies. In Journal of Intelligent and Robotic Systems: Theory and Applications. Special Issue on Computational Aspects of Robot Kinematics, Dynamics, and Control.

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