Tham khảo tài liệu 'control problems in robotics and automation - b. siciliano and . valavanis (eds) part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 186 . Corke and . Hager most laboratory systems should easily achieve this level of performance even through ad hoc tuning. In order to try and achieve performance closer to what is achievable classic techniques can be used such as increasing the loop gain and or adding some series compensator which may also raise the system s Type . These approaches have been investigated 6 and while able to dramatically improve performance are very sensitive to plant parameter variation and a high-performance specification can lead to the synthesis of unstable compensators which are unusable in practice. Predictive control in particular the Smith Predictor is often cited 3 33 6 but it too is very sensitive to plant parameter variation. Corke 6 has shown that estimated velocity feedforward can provide a greater level of performance and increased robustness than is possible using feedback control alone. Similar conclusions have been reached by others for visual 8 and force 7 control. Utilizing feedforward changes the problem from one of control system design to one of estimator design. The duality between controllers and estimators is well known and the advantage of changing the problem into one of estimator design is that the dynamic process being estimated the target generally has simpler linear dynamics than the robot and vision system. While a predictor can be used to cover an arbitrarily large latency predicting over a long interval leads to poor tracking of high-frequency unmodeled target dynamics. The problem of delay in vision-based control has also been solved by nature. The eye is capable of high-performance stable tracking despite total open-loop delay of 130 ms due to perceptual processes neural computation and communications. Considerable neurophysiological literature 11 30 is concerned with establishing models of the underlying control process which is believed to be both non-linear and variable structure. 4. Control and Estimation in Vision The discussion above
