Incorporating the piezoelectric effect into classical laminate plate theory, distributed sensors and actuators capable of sensing and controlling the modal vibration of a one-dimensional cantilever plate are derived theoretically and verified experimentally. It is shown that critical damping of a particular mode can be achieved using such a modal sensor/actuator combination as long as the vibrational amplitude of the controlled structure does not saturate the modal actuator. Since the sensor signal is proportional to the modal coordinate time derivative, velocity feedback control can be employed without using any element tuned to the resonant frequency in the feedback controller. Therefore, the sensitivity of the closed-loop performance and stability to resonant frequency variations is minimized. By eliminating electromagnetic interference and ground loop noise, critical damping is experimentally demonstrated for the first mode of a one-dimensional cantilever plate using PVF2 as the sensor/actuator material.
A series of piezoelectric sensors which measure the strain rate of a structyre directly arc dcvclopcd hy recognizing the fact that'due to the high output irnpedancc nature oS piczoclectric scnsors the measured signal i.; strongly influenced by the impctlancc matching circuit. tlxperimentnl data which verifies thc performance of a local strain ratc sensor is presented. A uniaxial strain ratc sensor which cornplctely eliminates the cross-axis sensitivity is developed, as well as a pure shcar strain rate scnsor which measurcs the in-planc shcar rate. T o achieve rnorc clTcctivc distributed control, a singlc-input singlc-output multi-modc scnsor/actuator dcsign approach is prcscntcd for controlling
This paper presents the very high performance achieved experimentally with a wrist carried on a very flexible arm and designed for extremely quick, precise pick-and-place tasks. There are substantial potential advantages to using robot manipulators that are very lightweight and flexible- advantages in power, quickness, and performance, as well as in weight. Control using end-point sensing is of course essen tial in such a system. However, the closed-loop control band width of a robot manipulator is still physically limited ulti mately by its structural flexibility, as the end effector and the actuator are separated. Basically, there is a wave propaga tion time delay. A minimanipulator can be added to the end of such a main robot arm to perform special tasks with high accuracy and bandwidth and thus to enhance significantly and funda mentally the robot's performance. However, dynamic interac tion between the minimanipulator and the structural flexibil ity of the main robot arm may tend to destabilize the system, making the control design very difficult and sensitive to parameter variations. In the research described in this article, analyses were performed to'study the dynamic interaction between the mo tion of a minimanipulator and the structural flexibility of the main robot arm that carries it. A general geometric relation between end effector/sensor location and the center ofpercus sion was found, which assures that a simple controller design can be obtained that is insensitive to modeling uncertainty while achieving good stability and high performance. A plane-motion mechanical mini-macro manipulator system was designed and built, and with it fast, precise ma neuvers of several demanding kinds were demonstrated ex perimentally. The end-effector position control bandwidth achieved was more than eight times the frequency of the beam's first mode, and accuracy was excellent. 1. Only the case of a one-degree-of-freedom wrist is analyzed here. The corresponding characteristic in a multidimensional case will be more complicated because of the nonlinear coupling effect.
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