Nonlinear Extended State Observer based Active Disturbance Rejection Control of a Laser Seeker System

In this paper, the laser seeker control problem is solved in the framework of active disturbance rejection control (ADRC). The considered problem, which consists of laser seeker stabilisation and target tracking, is expressed here as a regulation problem. A nonlinear extended state observer (NESO) with varying gains is used to improve the performance of linear ESO (LESO), and thus enable better control performance in both transient period and steady-state, with lower control effort. Based on a detailed analysis of system disturbances, a special ADRC tuning method is proposed. The stability of the overall control structure is analysed with a description function method. Through comparative simulations LESO-based and the introduced NESO-based ADRC for the laser seeker system, the advantages of the proposed scheme are shown

Development of a miniaturized multisensory positioning device for laser dicing technology

AbstractIn this study we propose a multisensory laser tracker system for measuring and tracking the TCP (Tool Center Point) of e.g. high precision motion systems. An experimental platform composed of four tracker modules is developed in order to track the TCP of a linear positioning system based upon the length measurement (multi-lateration). Concepts and first devices for miniaturization of the tracker system are presented

A Photogrammetry-Based Hybrid System for Dynamic Tracking and Measurement

Noncontact measurements of lightweight flexible aerospace structures present several challenges. Objects are usually mounted on a test stand because current noncontact measurement techniques require that the net motion of the object be zero. However, it is often desirable to take measurements of the object under operational conditions, and in the case of miniature aerial vehicles (MAVs) and deploying space structures, the test article will undergo significant translational motion. This thesis describes a hybrid noncontact measurement system which will enable measurement of structural kinematics of an object freely moving about a volume. By using a real-time videogrammetry system, a set of pan-tilt-zoom (PTZ) cameras is coordinated to track large-scale net motion and produce high-speed, high-quality images for photogrammetric surface reconstruction. The design of the system is presented in detail. A method of generating the calibration parameters for the PTZ cameras is presented and evaluated and is shown to produce good results. The results of camera synchronization tests and tracking accuracy evaluation are presented as well. Finally, a demonstration of the hybrid system is presented in which all four PTZ cameras track an MAV in flight

Performance interface document for users of Tracking and Data Relay Satellite System (TDRSS) electromechanically steered antenna systems (EMSAS)

Satellites that use the NASA Tracking and Data Relay Satellite System (TDRSS) require antennas that are crucial for performing and achieving reliable TDRSS link performance at the desired data rate. Technical guidelines are presented to assist the prospective TDRSS medium-and high-data rate user in selecting and procuring a viable, steerable high-gain antenna system. Topics addressed include the antenna gain/transmitter power/data rate relationship; Earth power flux-density limitations; electromechanical requirements dictated by the small beam widths, desired angular coverage, and minimal torque disturbance to the spacecraft; weight and moment considerations; mechanical, electrical and thermal interfaces; design lifetime failure modes; and handling and storage. Proven designs are cited and space-qualified assemblies and components are identified

Efficient Embedded Hardware Architecture for Stabilised Tracking Sighting System of Armoured Fighting Vehicles

A line-of-sight stabilised sighting system, capable of target tracking and video stabilisation is a prime requirement of any armoured fighting tank vehicle for military surveillance and weapon firing. Typically, such sighting systems have three prime electro-optical sensors i.e. day camera for viewing in day conditions, thermal camera for night viewing and eye-safe laser range finder for obtaining the target range. For laser guided missile firing, additional laser target designator may be a part of sighting system. This sighting system provides necessary parameters for the fire control computer to compute ballistic offsets to fire conventional ammunition or fire missile. System demands simultaneous interactions with electro-optical sensors, servo sensors, actuators, multi-function display for man-machine interface, fire control computer, logic controller and other sub-systems of tank. Therefore, a complex embedded electronics hardware is needed to respond in real time for such system. An efficient electronics embedded hardware architecture is presented here for the development of this type of sighting system. This hardware has been developed around SHARC 21369 processor and FPGA. A performance evaluation scheme is also presented for this sighting system based on the developed hardware

High Precision Dual-Stage Pointing Mechanism for Miniature Satellite Laser Communication Terminals

This paper presents an innovative mechatronic design of a high-accuracy pointing mechanism for orbital laser communication terminals. The system is based on a dual-stage architecture and is miniaturized to fit nanosatellite-class spacecraft, aiming to enable optical communication on small-size space platforms. The focus is on control design aspects and on the performance assessment of an experimental prototype under emulated external environmental disturbances

Systems Development of a Two-Axis Stabilised Platform to Facilitate Astronomical Observations

Inertially Stabilised Platforms (ISPs) aim to control the line-of-sight between a sensor and a target. They perform two distinct operations; keeping track of the target as the sensor host and the target move in inertial space and attenuating rotational disturbances incurred to the sensor by host vehicle motion. This project aimed to develop a two-axis ISP for use in astronomical applications. It represents the initial development of all systems of a low-cost ISP designed for a 3.5” compound telescope. To achieve this, relevant literature describing the various components of an ISP were reviewed to inform the design, implementation and testing cycle which comprised most of the project. A set of system specifications was developed to guide design decisions. The performance of the implemented system was compared against these specifications once the project was complete. During the project, the electro-mechanical structure of the ISP was designed and implemented, including a mechanical assembly designed to mount a camera and inertially and geometrically model the specified telescope. This allowed the ISP to be tested at a lower cost than with the telescope itself. The associated electrical systems were specified and configured. An image processing script capable of detecting and locating the centre of the Moon in the camera field of view was written in Python and implemented on a Raspberry Pi Computer. A complete simulation model for the system was written in the simulation language, Simul_C_EM, and used to design various controllers for the ISP control system and help verify certain estimated system parameters such as gimbal friction. For each gimbal, PI controllers were designed to allow manual orientation control of the telescope, compensated P controllers were designed to achieve target tracking, and compensated PI controllers were designed to reject rotational disturbances. These were implemented in C on an STM32F0 microcontroller tasked with managing the various control and communications tasks required by the system. Finally, a user interface was written in LabVIEW to facilitate intuitive user control of the system and perform datalogging of the system runtime data. Testing of the system showed good correlation between the hardware and the simulated results indicating an accurate simulation model that can be used to test future design developments

Spacecraft system study: A study to define the impact of laser communication systems on their host spacecraft

The mutual influence of a laser communication system and its host spacecraft and the degree to which the mutual influence limited acquisition, tracking and pointing processes were investigated. A laser klink between a low earth orbiting (LEO) satellite and a geosynchronous earth orbiting (GEO) satellite was used as a baseline. The laser link between satellites was a generic channel transferring 500 Mbps data from the LEO to GEO using the GaAlAs laser as the laser light source. Major aspects of pointing and tracking with a satelliteborne optical system were evaluated including: (1) orbital aspects such as spacecraft relative motions, point ahead, and Sun snd Moon optical noise; (2) burst errors introduced by the electronic and optical noise levels; (3) servo system design and configurations, and the noise sources such as, sensor noise, base motion disturbances, gimbal friction torque noise; (4) an evaluation of the tracking and beacon link and the type of sensors used; (5) the function of the acquisition procedure and an evaluation of the sensors employed; and (6) an estimate of the size, weight and power needed for the satellite system