Control in Robotics and Automation

88 CHAPTER 2 / OBSERVER-BASED VISUAL SERVOING

100

50

0

-50

-100 t

i t

0 10 20

t t l

(a) 30 40 50

Time [sec]

100

50

-50

-100

i ,

60 70

i L i i i | ,. i

(b) 0 10 20 30 40 50 60 70

Time

[s~]

FIGURE 2.27

Control input. (a) Feedforward part -

LWO~

(b) feedback part - K~.

a feedforward control scheme is effective. The results given in this chapter emphasize the

usefulness of object velocity feedforward in the application of vision-based control.

We have introduced a visual feedback controller with a velocity observer. The observer

compensates the delay by estimating the object velocity. Also, the observer provides

intersample information to the joint servo by updating the visual information with the

sampling rate of the joint servo. Thus the problems of slow sampling time and delay of the

vision sensor are resolved. The tracking performance is improved by feedforwarding the

object velocity. Stability of the observer-based control system is presented in a nonlinear

form. Simulations and experiments with a two-link direct drive robot have exhibited the

effectiveness of the observer-based control scheme. A linearized version suitable for industrial

robot control is also presented. Experimental results with PUMP 560 have shown stable and

accurate performance of the observer-based visual servo controller.

REFERENCES

[1] P. K. Allen, A. Timcenko, B. Yoshimi, and P. Michelman. Automated tracking and grasping of a moving object

with a robotic hand-eye system.

IEEE Trans. Robotics and Automation,

9(2):152-165, 1993.

[-2] F. Chaumette and A. Santos. Tracking a moving object by visual servoing. In

12th IFA C World Congress, Vol.

9, pages 409-414, Sydney, Australia, 1993.

[3] P. I. Corke. Video-rate robot visual servoing. In

Visual Servoing,

K. Hashimoto ed., World Scientific, pages

257-283, Singapore, 1993.

[4] P. I. Corke. Visual control of robot manipulators--a review. In

Visual Servoing,

K. Hashimoto ed., World

Scientific, pages 1-32, Singapore, 1993.