This paper discusses the problem of robust allocation of unmanned vehicles (T.N) to targets with uncertainties. In particular, the team consists of heterogeneous vehicles with different exploration and exploitation abilities. A general framework is presented to model uncertainties in the planning problems, which goes beyond traditional Gaussian noise. Traditionally, exploration and exploitation are decoupled into two assignment problems are planned with un-correlated goals. The coupled planning method considered here assign exploration vehicles based on its potential influence of the exploitation. Furthermore, a fully decentralized algorithm, Consensus-Based Bundle Algorithm (CBBA), is used to implement the decoupled and coupled methods. CBBA can handle system dynamic constraints such as target distance, vehicle velocities, and has computation complexity polynomial to the number of vehicles and targets. The coupled method is shown to have improved planning performance in a simulated scenario with uncertainties about target classification.
LIGO is dedicated to the detection of gravitational waves. To achieve the design sensitivity of the proposed Advanced LIGO detectors, the seismic isolation system is required to isolate the interferometer mirrors from ground motion above 0.1 Hz. The dominant source of motion above 0.1 Hz is the microseismic peaks near 0.15 Hz. The system needs to isolate the payload from this motion by at least a factor of five in all three translational degrees of freedom.
Tilt-horizontal coupling is the most challenging problem for
seismic isolation below 1 Hz. Tilt-horizontal coupling results from the principle of equivalence: inertial horizontal sensors cannot distinguish horizontal acceleration from tilt motion. Tilt-horizontal coupling rises dramatically at low frequencies, which makes low frequency isolation difficult.
Several techniques are used to address the tilt-horizontal
coupling problem. The isolation platform is designed to separate
horizontal motions from tilt motions. Feedback control to
displacement sensors is used to command the platform in all
degrees of freedom. These sensors are "corrected" by ground
seismometers, using an optimal FIR filtering technique to separate
tilt noise from horizontal acceleration. With these techniques, we
obtained isolation factors of 10 to 20 simultaneously in all three
degrees of freedom at 0.15 Hz.
This paper discusses a new testbed developed at the Stanford Aerospace Robotics Laboratory (ARL) to address some of the key issues associated with semi-autonomous construction in a hazardous environment like space. The new testbed consists of a large two-link manipulator carrying two smaller two-link arms. This macro/mini combination was developed to be representative of actual space manipulators, such as the SSRMS/SPDM planned for the Space Station. This new testbed will allow us to investigate several key issues associated with space construction, including teleoperation versus supervised autonomy, dexterous control of a robot with flexibility, and construction with multiple robots. A supervised autonomy approach has several advantages over the traditional teleoperation mode, including operation with time delay, smart control of a redundant manipulator, and improved contact control. To mimic the dynamics found in space manipulators, the main arm was designed to include joint flexibility. The arm operates in 2-D, with the end-point floating on air-bearing. This setup allows cooperation with existing free-flying robots in the ARL. This paper reports the first experiments with the arm which explore the advantages of moving from teleoperation or human-in-the-loop control to the human supervisory or task-level control. A simple task, such as capturing a satellite-like object floating on the table, is attempted first with the human directly driving the end-point and second with the human directing the robot at a task-level. Initial experimental results of these two control approaches are presented and compared.
KEYWORDS: Sensors, Digital signal processing, Signal processing, Feedback control, Ferroelectric polymers, Electronics, Actuators, Spatial filters, Amplifiers, Digital electronics
A reconfigurable actuator-sensor array is demonstrated for the active control of sound and vibration. The concept is motivated by applications in which shaped polyvinylidene fluoride films are used as error sensors for feedforward and feedback noise control. The advantage of the present concept, as compared to a fixed-shape sensor, is that the reconfigurable array can be adapted on line to account for uncertain structural dynamics, making it a more effective error sensor for applications in which the structural dynamics are not accurately known a priori. The array developed for this work consists of twenty-two polyvinylidene fluoride film sensors and four multilayer piezoceramic actuators connected to a set of reprogrammable electronics. The reprogrammable electronics consist of two 16 by 1 digitally programmable gain boards and a digital signal processor with two analog inputs and outputs. The gains on the sensor array are set via the digital I/O of the digital signal processor. An off-line, frequency domain technique is used to design modal filters with the array of film sensors. Feedback and feedforward control algorithms are then implemented to demonstrate the use of the actuator-sensor array for noise and vibration suppression. The results indicate that the reconfigurable array technique has merit for noise and vibration control, although a fully adaptive, on-line algorithm has yet to be implemented.
The goal is to develop and demonstrate the potential benefits of applying the controlled structures technology (CST) approach to active and adaptive optics. The potential advantages were outlined in a previous paper. Two testbeds are envisioned for the experimental work. CST techniques are demonstrated experimentally on the first, a simple deformable mirror testbed (DMT) incorporating piezoelectric sensors and actuators and a single optical displacement sensor. Implementation of passive damping augmentation, local control and global high authority control is demonstrated. Some of the key issues in the approach to the control of larger interferometers or lightweight Cassegrain telescopes are discussed. Finally, some of the open areas for future research are summarized.
The progress to date and essential features of approaches to optics and controlled structures technology (CST) are reviewed. The CST framework is suggested as a means of gaining new insight on deformable optical surface control. Within the CST approach, control bandwidths may extend into the frequency range of structural vibration modes, enabling possible reduction in area density and improvements in performance.
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