Real-time Servo Research Articles

A Novel Approach for Trajectory Tracking Control of an Under-Actuated Quad-Rotor UAV

A novel Udwadia-Kalaba approach for the trajectory tracking control of an under-actuated quad-rotor unmanned aerial vehicle (UAV) is presented. Compared to standard control approaches, the desired trajectories are treated as constraints called trajectory tracking constraints in this approach. Neither making any approximations or linearization of the nonlinear system nor imposing any a priori structure on the nature of the nonlinear controller, this methodology provides closedform nonlinear control. The control inputs satisfying the desired trajectory requirements can be obtained explicitly in compact closed form by solving Udwadia-Kalaba equation. Nonlinear dynamics modeling of a quad-rotor UAV is processed and a desired trajectory is given in this paper to illustrate this approach. The theoretical analysis and MATLAB simulation results verify the validity and efficiency of this approach. The real-time servo constraint forces are obtained conveniently and the quad-rotor UAV's movement meets the designed trajectory precisely.

Micro ECDM scanning process with feedback control of flexible contact force

Quartz glass has been widely used in frontier fields of MEMS (micro electro-mechanical systems) and sensors due to its excellent chemical and mechanical properties. Although ECDM (electrochemical discharge machining) is a non-traditional material removal process suitable for machining electrically non-conductive materials of high temperature resistance and hard brittleness, the adopted feeding strategy of tool electrode directly affects the machining results, especially in a micro ECDM scanning process. The existing feed methods still cannot maintain a suitable machining gap with a minimum given contact force during the micro ECDM scanning process, causing inconsistent gap state and the damage to machining stability and geometric accuracy of micro structures. In this research, a novel spindle combining a flexure hinge and a high-resolution micro-force sensor is designed, achieving the function of real-time servo control of a given micro contact force. Using the micro tool electrodes (<Φ200 μm) fabricated by the combined process of reverse-copying micro EDM and TF-WEDG (tangential feed-wire electrode discharge grinding), the circular structures are successfully machined on quartz glass with the optimized parameters of open-circuit voltage, scanning speed, and number of scanning. To guarantee the consistent depth along a scanning layer, a feed strategy of quantified depth with servo control of flexible micro force (SCFMF-QDFS) is proposed, and micro 3D structures of S-shape and square are machined with controllable accuracy of ±2 μm and ±4 μm in depth and width.

Improving Tracking of Trajectories through Tracking Rate Regulation: Application to UAVs

The tracking problem (that is, how to follow a previously memorized path) is one of the most important problems in mobile robots. Several methods can be formulated depending on the way the robot state is related to the path. "Trajectory tracking" is the most common method, with the controller aiming to move the robot toward a moving target point, like in a real-time servosystem. In the case of complex systems or systems under perturbations or unmodeled effects, such as UAVs (Unmanned Aerial Vehicles), other tracking methods can offer additional benefits. In this paper, methods that consider the dynamics of the path's descriptor parameter (which can be called "error adaptive tracking") are contrasted with trajectory tracking. A formal description of tracking methods is first presented, showing that two types of error adaptive tracking can be used with the same controller in any system. Then, it is shown that the selection of an appropriate tracking rate improves error convergence and robustness for a UAV system, which is illustrated by simulation experiments. It is concluded that error adaptive tracking methods outperform trajectory tracking ones, producing a faster and more robust convergence tracking, while preserving, if required, the same tracking rate when convergence is achieved.

Adaptive robust control for tank stability: A constraint-following approach

This article addresses a control problem for tank stability based on constraint following. The objective is to design a control to drive the tank stability control system to follow a pre-specified stability constraint approximately: with the consideration of (possibly) time-varying uncertainty (including system modeling error and road excitation), if the barrel deviates from the target angle, drive it to be arbitrarily close to the target angle; and if the barrel points to the target angle, drive it to stay there. This is formulated as a problem of approximate constraint-following control. First, as the model-based control design object, the dynamic equation of the tank stability control system with the system modeling error and the road excitation is obtained. Second, as the control objective, the stability constraint is formulated. Third, as the control strategy, an adaptive robust control is proposed for approximate constraint following. Fourth, as the control object, a virtual prototype model of tank driving on bumpy road is established with multi-body dynamics software RecurDyn. Finally, real-time servo control and target observation of the tank stability system are performed by co-simulation. It shows that the constraint-following error converges quickly to [Formula: see text] in 1.5 s. By this, the tank stability control system can be always stable even if the tank is driving and disturbed with frequent road excitation.

Lyapunov approach based design of a gain adaptive interval type-2 fuzzy controller for servo systems

This paper focuses on the development of a stable Mamdani type-2 fuzzy logic based controller for automatic control of servo systems. The stability analysis of the fuzzy controller has been done by employing the concept of Lyapunov. The Lyapunov approach results in the derivation of an original stability analysis that can be used for designing the rule base of our proposed online gain adaptive Interval Type-2 Fuzzy Proportional Derivative controller (IT2-GFPD) for servo systems with assured stability. In this approach a quadratic positive definite Lyapunov function is used and sufficient stability conditions are satisfied by the adaptive type-2 fuzzy logic control system. Illustrative simulation studies with linear and nonlinear models as well as experimental results on a real-time servo system validate the stability and robustness of the developed intelligent IT2-GFPD. A comparative performance study of IT2-GFPD with other controllers in presence of noise and disturbance also proves the superiority of the proposed controller.

Sliding Mode Control for Position Tracking of Servo System with a Variable Loaded DC Motor

In this paper, the real-time position control of servo system is carried out using sliding mode control (SMC) method based on variable structure control (VSC). As DC Motors are commonly used in many industrial applications and robotics, studies in this paper have are tested on a DC servo system, which is designed and produced by Quanser Inc. Three different types of sliding mode controllers are designed for position control of servo system and, later, performance comparison of DC Motor on Servo system is made. According to results obtained from real-time servo system, it is shown that SMC method is robust against to disturbing effects, variabilities, and uncertainties on the systems. Outstanding part of this paper is that designed controllers are implemented to servo system in real-time with a variable loaded DC Motor. Moreover, this study shows that this control structure can be performed as high performance in the real-time motor control applications.

Real Time Modeling and Control of Three Tank Hybrid System

AbstractThis study discusses the modeling and linear quadratic regulator (LQR) controller based closed loop control of a three tank hybrid (TTH) process. A pseudo random binary signal (PRBS) based excitation data obtained from a real time TTH setup is utilized in validating its first principle model (FPM). Based on top and bottom interactions, various modes prevalent are considered based on steady state physical reachability analysis of the TTH for a given input range for controller design. The FPM is linearized using nominal values of process parameters using Jacobians from each existing mode. LQR controllers are designed for each mode. A supervisory structure is designed for selecting estimation model and controller for each appropriate mode. Results from real time servo tracking and disturbance rejection experiments are discussed.

Research and Development of Economical CNC Software for 2D Lean Friction Stir Welding Machine

This project is developing a two-dimensional friction stir machine, relatively low cost to achieve four axis friction stir welding equipment with real-time servo control, where the corresponding trajectory planning function in cam is relatively independent by making a full use of Galil motion controller has a strong multi axis linkage control capability and fast real-time communication capabilities and the Galil motion controllet G code analysis software module is developped. This paper is studying the trajectory planning software system design and development of friction stir for different trajectories in the plan and is aiming to solve the motion trajectory control problem with complex welding path. A deep study of three polynomial spline function trajectory planner is done, and the complex motion trajectory of the multi axis welding machine controlled by acceleration and speed is realized. The micro arc transition approximation method is applied to optimize the inflection point with abrupt change of track path and achieve smooth inflection motion.

High-Resolution Real-Time Visual Inspection System for Micro Assembly

For precise assembly of miniature parts, the precise inspection for parts’ posture and real-time servo control for assembly greatly depend on the performance of visual inspection system. This paper proposed a high-resolution real-time visual inspection system of micro assembly. The CMOS image sensor and high-speed digital signal processing chip were chosen to design the image acquisition module, image processing module and image display module. High-accuracy display on the common display device was implemented with the video encoding chip and FPGA. The test results showed that the processing speed with preprocessing could reach 3.5 frames per second with 5 mega-pixel resolution, and the display accuracy after threshold processing had little loss. Micro parts assembly experiment and high accuracy Peg-in-Hole assembly experiment are done to test the performance of the proposed visual inspection system. This visual inspection system can be used for high-resolution real-time micro assembly and other real-time visual servo control.

Variable-structure-systems based approach for online learning of spiking neural networks and its experimental evaluation

Raising the level of biological realism by utilizing the timing of individual spikes, spiking neural networks (SNNs) are considered to be the third generation of artificial neural networks. In this work, a novel variable-structure-systems based approach for online learning of SNN is developed and tested on the identification and speed control of a real-time servo system. In this approach, neurocontroller parameters are used to define a time-varying sliding surface to lead the control error signal to zero. To prove the convergence property of the developed algorithm, the Lyapunov stability method is utilized. The results of the real-time experiments on the laboratory servo system for a number of different load conditions including nonlinear and time-varying ones indicate that the control structure exhibits a highly robust behavior against disturbances and sudden changes in the command signal.

Comparative Study of Motion Control Card Based on NI PXIe and cRIO Platform for Three-Axis Turntable

In this paper, the Brushless DC motor (BLDCM) and reducer are used to drive each axis of three-axis turntable. In real-time servo control systems, the position loop parameters are designated by the software CME2, and the frequency band of the middle frame with the specified amplitude can be measured. Then, the drive model is alternated to the velocity loop, and two frequency bands will be got by using the controller of NI PXI-7344 and NI 9514 separately. The reason why the three frequency bands are different can be given by analyzing the data of the three sweep tests. In addition, both advantages and disadvantages of two NI motion controllers are illustrated. Finally, the paper points out the new motion control solutions to improve the performance of the servo system by autonomous intelligent control algorithm.

A servo system control with time-varying and nonlinear load conditions using type-2 TSK fuzzy neural system

Abstract A type-2 Takagi-Sugeno-Kang fuzzy neural system is proposed and its parameter update rules are derived using fuzzy clustering and gradient learning algorithms. The proposed type-2 fuzzy neural system is used for the control and the identification of a real-time servo system. Fuzzy c-means clustering algorithm is used to determine the initial places of the membership functions to ensure that the gradient descent algorithm used afterwards converges in a shorter time. A number of different load conditions including nonlinear and time-varying ones are used to investigate the performance of the proposed control algorithm. The control structure has the ability to regulate the servo system with reduced oscillations when compared with the results of its type-1 counterpart around the set point signal in the presence of load disturbances.

Analysis and Modeling of Servo Motor Controls in Military Vehicle Control Systems Update

Abstract : This paper covers the analysis of various concepts that are used to implement Servo Motor Control in military vehicular control systems. A survey of existing hard real-time servo controls and applicable design patterns is presented. These design patterns along with their critical parameters are identified and described. Potential solutions are created from combinations of design patterns and parameter choices. The solutions are modeled with plausible parameters to identify parameter sensitivities. As the modeling progresses, the solutions' frequency responses, sensitivities and functional performance are also evaluated. This paper concludes with a summary of architectural guidelines.

움직이는 원통형 물체를 잡는 매니퓰레이터를 위한 레이저 거리계 기반의 서보시스템

We implemented a real-time servo system for a manipulator based on Laser Range Finder (LRF). and established algorithms for grasping a moving cylinder. We devised a manipulator mechanism and driving hardware based on a system board equipped with Xscale Processor with real-time operating system RTAI on Linux. The manipulator motor driver is connected to the system board via CAN communication link, and LRF is connected via RS-232C. We implemented real-time software including CAN device driver, RS-232C device driver, manipulator trajectory generator, and LRF control software. A typical application experiment for grasping a cylinder with circle motion demonstrated our system`s real-time performance.

Real time servo control of the holographic data storage system with an additional servo beam

Holographic data storage is a next generation data storage device, which has high storage density, high data transfer rate and short access time. The device is very sensitive to disturbances due to its enormous storage density. In the disk type holographic data storage device deviation occurs successionally on the position of the data as the disk rotates. Therefore the spot where the probe beam is illuminated should directly be corrected in order to exactly retrieve the desired data. In this paper we suggest a method using an additional beam containing a servo pattern in order to detect the deviation of the media. We also propose a real time servo control method to compensate the affect of the unpredicted disturbance.

Adaptive-backstepping-based design of a nonlinear position controller for an IPMSM servo drive

This paper presents the design of a novel nonlinear position controller for an interior permanent-magnet synchronous motor (IPMSM) servo drive. The motor model equations provide the basis for the proposed controller, which is designed with the adaptive backstepping technique. Various system uncertainties, particularly mechanical-parameter uncertainties, are incorporated in the design of the controller. Using Lyapunov's stability theory, it is verified that the control variables are asymptotically stable. The complete drive system is then simulated with MATLAB/Simulink software. Performance of the proposed adaptive-backstepping-based nonlinear position controller (ABNPC) is investigated under different dynamic operating conditions such as step changes in command positions, step changes in load, and parameter variations. The results indicate that the proposed ABNPC-based IPMSM drive could be a candidate for real-time industrial servo motor drive applications.

The mass transfer process and the growth rate of protein crystals

In this paper, protein crystal growth is studied by a Mach-Zehnder interferometer and an image process system. The interference fringe images are recorded during the crystallization of tetragonal hen egg white lysozyme crystal. Concentration distributions of the protein solution are given from the interference fringe images recorded by the Mach-Zehnder interferometer with a real time servo system of a four-step phase shift. The mass transfer flux and the crystal growth rates are obtained from the concentration distribution. The results show that the observed rates are in accordance with those demonstrated by measurements of the experimental images; therefore the method for determining growth rate by the diffusion process is reasonable.

Vibration-compensated interferometer for surface metrology

An advanced interferometer was built for surface metrology in environments with severe vibration. This instrument uses active control to compensate for effects of vibration to allow surface measurement with high-resolution phase-shifting interferometry. A digital signal processor and high-speed phase control from an electro-optic modulator allows phase measurements at 4000 Hz. These measurements are fed back into a real-time servo in the digital signal processor that provides a vibration-corrected phase ramp for the surface measurements taken at video rates. Unlike fringe locking, which compensates vibration to keep the phase constant, we show a true phase servo that allows the phase to be stabilized while it is ramped, enabling surface measurements using phase-shifting interferometry that requires multiple images with controlled phase shifts.

Astronomical interferometry, from the visible to sub-mm waves

The history of astronomical interferometry dates back to the 19th century, when Fizeau, Stephane and later Michelson set out to measure the angular diameters of stars. Whereas Stephane could only obtain an upper limit of0.158 arcseconds for the stars he observed in 1874, Michelson published interferometric diameters of Jupiter's Galilean moons in 1891. These early experiments used masks with two small openings placed on the aperture of astronomical telescopes to perform double-slit experiments ala Young. Around 1920 Michelson increased the resolution by placing a periscope on the front-end of the 100inch telescope on Mt. Wilson; this arrangement enabled him and his collaborators to determine the orbit of the binary system Capella, and to measure the diameter of Betelgeuse. After these initial successes, technological difficulties slowed further progress for several decades. In the 1950's and 60's Hanbury Brown, Twiss, and collaborators invented intensity interferometry! and used it to measure the diameters of 32 stars this is still the best data set on hot stars available today. The era of modern stellar interferometry began in 1974 when Labeyrie successfully combined the light from two telescopes spaced by 12 m. This breakthrough was soon followed by the construction of similar instruments, which took advantage of modern electronic detectors and computer control to track and stabilize the interference fringes with real-time servo loops, which drive optical delay lines that compensate for the optical pathlength difference and thus maintain coherence between the two arms of the interferometer (see Figure 1). This active pathlength controlwith millisecond time resolution is a crucial aspect of ground-based astronomical interferometry, because the Earth's rotation and random atmospheric fluctuations have to be tracked continuously.

The MARTINI adaptive optics instrument

The Multi-Aperture Real Time Image Normalisation Instrument (MARTINI) is an adaptive optics system designed to operate at one of the Nasmyth focal stations of the 4.2 m William Herschel Telescope. Correction of atmospherically distorted images is achieved by the action of a six element segmented mirror in a real-time servo loop controlled by the signal from a CCD based Shack–Hartmann wavefront sensor. A unique aspect of the MARTINI instrument is that, from its conception, it was designed to be capable of image sharpening at visible wavelengths. An outline of the mechanical and electronic arrangement of MARTINI is given, together with a description of its modes of operation, facilities and performance. Also described are some of the first scientific results obtained with the instrument.