Attitude Control Approach Research Articles

位置決め性能向上を目指した高精度外乱モデルの構築

This paper presents a modeling methodology for unknown disturbances in mechatronics systems, based on disturbance estimation using an iterative learning process. In disturbance modeling, nonlinear frictions are specially handled as disturbances in the mechanisms, which mainly degrade trajectory control performance. Friction can be mathematically modeled by using learned estimation data as a function of the displacement, velocity. acceleration, and jerk of the actuator. This model has the distinctive feature that friction compensation can be achieved with a generalization capability for different conditions. The proposed positioning control approach with disturbance modeling and compensation has been verified by experiments using a table drive system on a machine stand. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(2): 31–39, 2010; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/eej.20928

New attitude control approach for satellites in elliptic orbits using solar radiation pressure

The paper proposes the use of solar radiation pressure for satellite attitude control in elliptic orbits. The system comprises of a satellite with two-oppositely placed solar panels. A simple approximate analytical approach has been adopted to develop control law for suitably rotating the solar panels so as to neutralize the adverse effect of eccentricity normally responsible for a considerable deterioration in the attitude control performance of the conventional passive or semi-passive methods. The detailed numerical simulation of the governing nonlinear equation of motion of the system establishes the feasibility of the proposed control strategy. The proposed controller is found to improve the satellite attitude performance significantly by simply rotating the solar panel by fraction of a degree only. Thus, the semi-passive nature of the proposed control strategy makes it attractive for future space applications requiring modest attitude accuracies.

非線形摩擦のモデル化と摩擦補償による位置決め制御系の高精度化

This paper presents a performance improvement approach for the fast and precise positioning using a 2-degrees-of-freedom (2DOF) controller. In the controller design, effects of nonlinear friction on the positioning performance are especially paid attention, where a precise nonlinear friction characteristic with rolling friction behaviors is mathematically modeled and considered. A disturbance observer with an initial value compensation, therefore, is adopted in order to improve the disturbance suppression characteristic in positioning. The proposed positioning control approach with the friction modeling and compensation has been verified by experiments using a prototype for industrial positioning devices.

Position Control of Direct-Drive Robot Manipulators with PMAC Motors Using Enhanced Fuzzy PD Control

A position control approach for direct-drive robot manipulators with permanent magnet AC (PMAC) motors is proposed. The conventional vector control architecture has been simplified by specifying the motor stator phase so that the rotating d-axis current is zero. The position control is designed to be an enhanced fuzzy PD controller, by incorporating two nonlinear tracking differentiators into a conventional fuzzy PD controller. The proposed control methodology is easy to implement, and exhibits better control performance than conventional control methods. Experiments conducted on a single-link manipulator directly driven by a PMAC motor demonstrate the validity of the proposed approach.

An LMI-based nonlinear attitude control approach

This paper presents a nonlinear control law for large-angle attitude control of spacecraft. For the ROCSAT-3 spacecraft, a highly accurate and robust attitude control is desired during the orbit-raising phase. The three-axis attitude control is achieved using four body-fixed canted thrusters. In the paper, the nonlinear dynamic equations of the satellite are derived and the control requirements are stated. A novel nonlinear attitude control structure is then proposed for spacecraft control problems. The nonlinear controller contains linear feedback terms for stabilization and nonlinear terms for performance enhancement. One salient feature of the proposed approach is that the nonlinear controller parameters are designed using a linear matrix inequality (LMI) method. It turns out the controller design of stabilization and H/sub /spl infin//-type performance problems for spacecraft dynamics become rather transparent when the proposed controller structure and LMI method are employed. The design is shown to generalize many existing results. Simulation results based on the ROCSAT-3 system are then presented to demonstrate the proposed design method.

Improved proximate time-optimal sliding-mode control of hard disk drives

An improved proximate time-optimal (PTO) positioning control approach with discrete-time sliding-mode control theory for a Hard Disk Drive (HDD) servo is presented. A third order velocity reference profile is introduced to improve the second order ones in the conventional proximate time-optimal servomechanism (PTOS). The proposed approach eliminates the mode-switching mechanism and dramatically reduces the seek time by 5–50%. Moreover, it is robust to unmodelled dynamics and parameter variations. Its effectiveness is verified in a simulation.

Visual Servoing of Robotic Manipulator in a Virtual Learned Articular Space

A position control approach for Robotic Manipulator based on visual feedback is presented. This feedback, originated from a pair stereo fixed camera, is converted into a Virtual Articular Space, so-called because it is an approximation of real articular space of robot. A multilayered neural network trained to build the correspondence from the visual information of the robot hand and the articular position of the arm generates this approximation. By using this mapping we avoid the complexity of the analytic approach which requires the both robot inverse kinematics and the inverse camera-space mappings, including calibration. This approach is tested experimentally in real time on a 5 degrees-offreedom laboratory manipulator, including the required cameras and image processing boards.

The position control of induction motors using a binary disturbance observer

A control approach for the robust position control of an induction motor based on the binary disturbance observer is described. The binary controller with the binary disturbance observer is implemented for the position control of the induction machine subjected to load disturbances and realizes continuous control. The binary disturbance observer is used to eliminate the chattering problem of a sliding mode disturbance observer. In order to eliminate the steady-state error, the binary disturbance observer with an integral augmented switching hyperplane is proposed. The robustness is achieved, and continuous control is realized by employing the proposed observer without the chattering problem and the steady-state error. The effectiveness of the proposed observer is confirmed by the comparative experimental results.

Line-of-sight pointing stability for "drifting" satellites

Explored here is the feasibility of a new attitude control approach for satellites in high altitude elliptic orbits, in order to compensate for the effect of longitudinal periodic drift relative to the ground station. A simple attitude control technique using tethers has been proposed for achieving the fixed apparent satellite orientation with respect to the ground segment of the space mission. Combining the proposed feedback tether length control law with the analytically developed open-loop control policy results in a significant improvement of the controller performance. To illustrate implementation of the proposed concept, the particular case of 24 h elliptic orbits has been considered. A high degree of satellite pointing along the drifting line-of-sight made possible even with modest tether lengths makes the concept particularly attractive.

A co-operating neural approach for spacecrafts attitude control

A locally recurrent neural network is described as a key component of a control system able to rule an artificial satellite whose attitude must be kept close to zero-angle with respect to an inertial reference system earth centred. The main idea is to join a simple linear adaptive controller with a neural network trained to compensate the inadequacy of the former. The control signal is the sum of the signal computed by the two devices; the feedback for training the neural network comes from the attitude error w.r.t. a reference trajectory and is computed by means of a linear inversion of the satellite dynamics. Thanks to such co-operation, the resulting system is easily trainable and performs efficiently. In fact, the whole system acts as a MRAC controller whose accuracy has been tested on numerical simulations of an Olympus class spacecraft. Considerations on stability, reactions to unexpected solicitations, extension to non-geocentric missions and power consumption are included as well.

Satellite attitude stabilization through tether

Effective utilization of gravity gradient moments for attitude control demands rather slender satellite shapes. This imposes a major system design constraint and, further, provides only limited attitude accuracies, especially in the presence of disturbances and/or excitation. A new attitude control approach is presented here that overcomes most of these limitations. The proposed system configuration assumes a downward deployment of a ‘pendulum-like’ small mass from the satellite through a pair of identical tethers attached to its two distinct but symmetrically off-set points around the mass center. The well-known Lagrangian approach is utilized to obtain the governing equations of motion for the system in a circular orbit. A detailed stability analysis of motion-in-the-small is undertaken that establishes the feasibility of the concept. Furthermore, it leads to useful design criteria in the form of inequality constraints on the control parameters.

A Position Control Autotuner for Handling Systems

This paper describes an autotuning approach for position control in handling systems. The main features of the autotuning system are simplicity of use and high degree of performances. The involved simplicity is provided by an appropriate pretuning procedure using a relay experiment. The high performances are achieved by a partial state reference model controller. An experimental evaluation using a realistic pilot is reported to emphasize the applicability of the proposed approach.

Torque from solar radiation pressure gradient during eclipse

A general formulation is developed for calculating penumbra solar-pressure-gradient torque. A literal expression for the dependence of light intensity on position is given and the three-dimensional gradient about any point of interest in the spacecraft is computed. Solar-gradient torques are studied, via numerical simulation, for both Earth-pointing and sun-pointing planar spacecraft in geostationary orbit. Both specularly reflecting and totally absorbing surfaces are considered. Eclipse conditions are identified for the following critical cases: 1) maximum solar-gradient pitch torque; 2) maximum solar-gradient roll torque; and 3) longest duration within penumbra. The maximum instantaneous torque and angular impulse from solar-gradient torque are compared with those arising from gravity-gradient torque and are shown to be significant for some spacecraft orientations. A comparison of equivalent center-of-mass-center-of-pressure offsets for solar-gradient and conventional solar torque indicates that solar-gradient torque may potentially become dominant for very large spacecraft. It is also argued that the symmetry present within an eclipse season permits an attitude control approach based on angular momentum storage.

An attitude control approach for compensation of satellite drift in elliptic synchronous orbits

This paper explores the possibility of developing a new attitude control method for satellites in elliptic, 24-hour orbits, in order to compensate for the effect of longitudinal periodic drift relative to the ground station. A simple solar attitude control technique has been proposed for achieving the fixed apparent satellite orientation with respect to the ground segment of the space mission. The proposed control approach appears to be quite attractive for various satellite applications as it can substantially overcome the problems created by the continual periodic angular drift as well as undesirable pitching excitation in the elliptic orbits. Generalizing the analytically developed open-loop control policy results in a significant improvement of the controller performance.

New Solar Attitude Control Approach for Satellites in Elliptic Orbits

The investigation explores the feasibility of developing a simple solar attitude controller. The case of gravityoriented satellites carrying two sets of solar surfaces in elliptic orbits has been considered. An approximate analytical approach has been used to evolve the suitable control criteria for regulating the movement of solar surfaces so as to counter the adverse effect of eccentricity normally responsible for a considerable deterioration in the attitude control characteristics of the conventional passive or semipassive methods. The solar controller thus developed is found to be quite effective in limiting the librational amplitude of motion. It is felt that the simplicity of the proposed controller configuration and ease of its operation make it particularly attractive for several satellite applications requiring modest attitude accuracies.