Research on vibration suppression mode of sorting arm structure in high-frequency reciprocating motion

The sorting arm structure is under the inertia impact of high frequency reciprocating motion. The vibration characteristics are related to the operation process so that the precision of the chip sorting is uncertain. Thus, the accuracy of chips and efficiency of LED sorting machine are reduced. In the paper, the relationship between the vibration of the sorting arm and the positioning error of the chip has been studied. Besides, the correlation between the sorting arm structure’s vibration and the working precision of the separator are pointed out. The operation control is optimized based on the dynamics of the sorting arm and the operation parameters are optimized based on time sequence setting, in order to shorten the vibration attenuation time of the sorting arm for suppress vibration and provide efficiency. The incentives, which are introduced by variable structure and by the operation, can be effectively controlled. The array accuracy of chips and working efficiency of chip sorting machine are improved

Force control of lightweight series elastic systems using enhanced disturbance observers

This paper analyzes the control challenges associated to lightweight series elastic systems in force control applications, showing that a low end-point inertia can lead to high sensitivity to environment uncertainties. Where mainstream force control methods fail, this paper proposes a control methodology to enhance the performance robustness of existing disturbance observers (DOBs). The approach is validated experimentally and successfully compared to basic control solutions and state of the art DOB approaches

Virtual Sensor for Kinematic Estimation of Flexible Links in Parallel Robots

The control of flexible link parallel manipulators is still an open area of research, endpoint trajectory tracking being one of the main challenges in this type of robot. The flexibility and deformations of the limbs make the estimation of the Tool Centre Point (TCP) position a challenging one. Authors have proposed different approaches to estimate this deformation and deduce the location of the TCP. However, most of these approaches require expensive measurement systems or the use of high computational cost integration methods. This work presents a novel approach based on a virtual sensor which can not only precisely estimate the deformation of the flexible links in control applications (less than 2% error), but also its derivatives (less than 6% error in velocity and 13% error in acceleration) according to simulation results. The validity of the proposed Virtual Sensor is tested in a Delta Robot, where the position of the TCP is estimated based on the Virtual Sensor measurements with less than a 0.03% of error in comparison with the flexible approach developed in ADAMS Multibody Software.This work was supported in part by the Spanish Ministry of Economy and Competitiveness under grant BES-2013-066142, UPV/EHU's PPG17/56 projects, Spanish Ministry of Economy and Competitiveness' MINECO & FEDER inside DPI-2012-32882 project and the Basque Country Government's (GV/EJ) under PRE-2014-1-152 and BFI-2012-223 grants and under recognized research group IT914-16

The development of embedded positive input shaping for vibration control of a flexible manipulate using PIC

This thesis presents investigation into the applications and performance of positive input shaping in command shaping techniques for the vibration control of a flexible robot manipulator. A constrained planar single-link flexible manipulator is considered and the dynamic model of the system is derived using the assume mode method and is explained. An unshaped bang-bang torque input is used to determine the characteristic parameters of the system for design and evaluation of the input shaping control techniques. The positive shaping technique is designed based on the properties of the system. Simulation result of the response of the manipulator to the shaped inputs form matlab simulation tools are presented in the time ·and frequency domains. Performances of the shapers are examined in terms of level of vibration reduction, time response specifications. The effects of derivations orders of the input shaper on the performance of the system are investigated. Next, the positive input shaping algorithm is embedded into PIC. Comparative of the PIC and simulation in matlab is presented. Finally, an analysis assessment of the impact amplitude polarities of the input shapers on the system performance is presented and discussed

Control of flexible robots with prismatic joints and hydraulic drives

The design and control of long-reach, flexible manipulators has been an active research topic for over 20 years. Most of the research to date has focused on single link, fixed length, single plane of vibration test beds. In addition, actuation has been predominantly based upon electromagnetic motors. Ironically, these elements are rarely found in the existing industrial long-reach systems. One example is the Modified Light Duty Utility Arm (MLDUA) designed and built by Spar Aerospace for Oak Ridge National Laboratory (ORNL). This arm operates in larger, underground waste storage tanks located at ORNL. The size and nature of the tanks require that the robot have a reach of approximately 15 ft and a payload capacity of 250 lb. In order to achieve these criteria, each joint is hydraulically actuated. Furthermore, the robot has a prismatic degree-of-freedom to ease deployment. When fully extended, the robot`s first natural frequency is 1.76 Hz. Many of the projected tasks, coupled with the robot`s flexibility, present an interesting problem. How will many of the existing flexure control algorithms perform on a hydraulic, long-reach manipulator with prismatic links? To minimize cost and risk of testing these algorithms on the MLDUA, the authors have designed a new test bed that contains many of the same elements. This manuscript described a new hydraulically actuated, long-reach manipulator with a flexible prismatic link at ORNL. Focus is directed toward both modeling and control of hydraulic actuators as well as flexible links that have variable natural frequencies

Inverse and variable structure trajectory control of a flexible robotic manipulator

This thesis introduces two schemes that control the end effector trajectory and stabilize a two-link flexible robotic arm. They are (i) The Inverse Trajectory Control scheme and (ii) The Variable Structure System (VSS) scheme; The Inverse Trajectory Control scheme develops a control law based on the inversion of an input-output map. The stable maneuver of the arm depends on the stability of the zero dynamics of the system. A linear stabilizer is designed for the final capture of the terminal state and stabilization of the elastic modes; The second scheme incorporates a Variable Structure Control law which includes robustness in its design. A discontinuous output control law is derived which accomplishes the desired trajectory tracking of the output. This control scheme involves two phases, the \u27reaching phase\u27 and the \u27sliding phase\u27; Simulation results are presented to show that large maneuvers can be performed in the presence of payload uncertainty. (Abstract shortened with permission of author.)

Variable structure and singular perturbation control of elastic dynamical systems

This thesis treats the question of control of flexible dynamical systems for space applications. Two elastic dynamical systems are considered; The multibody system developed in Phillips Laboratory, Edwards Air Force Base, CA consists of two elastic links actuated by electric motors at the joints and rotate on a smooth horizontal granite table. An air bearing is used, which allows the whole system to float on the air so that the frictional forces do not exist between the support plate and the granite table. The controlled output is judiciously chosen such that the zero dynamics are stable or almost stable. For the control of the end point, two kinds of parameterizations of end effector position are considered. A variable structure control (VSC) law is derived for the end point trajectory control of each chosen output. Stability of zero dynamics associated with end point control is examined. Although, the VSC law accomplishes precise end point tracking, elastic modes are excited during the maneuver of the arm. A linear stabilizer is designed for the final capture of the terminal state; The second flexible system considered in this thesis is the elastic space vehicle. For the attitude control and vibration stabilization of the elastic space craft (spacecraft-beam-tip body configuration), singular perturbation technique is used. Based on nonlinear inversion, a control law is derived to decouple the attitude angle and the dominant flexible modes from the remaining elastic modes. The inverse control law decomposes the spacecraft dynamics into a slow and a fast subsystem. Based on singular perturbation theory, controllers are designed for each lower-order subsystem. Then a composite state feedback control is obtained by combining the slow and the fast control laws. (Abstract shortened by UMI.)

Dynamic modeling, property investigation, and adaptive controller design of serial robotic manipulators modeled with structural compliance

Research results on general serial robotic manipulators modeled with structural compliances are presented. Two compliant manipulator modeling approaches, distributed and lumped parameter models, are used in this study. System dynamic equations for both compliant models are derived by using the first and second order influence coefficients. Also, the properties of compliant manipulator system dynamics are investigated. One of the properties, which is defined as inaccessibility of vibratory modes, is shown to display a distinct character associated with compliant manipulators. This property indicates the impact of robot geometry on the control of structural oscillations. Example studies are provided to illustrate the physical interpretation of inaccessibility of vibratory modes. Two types of controllers are designed for compliant manipulators modeled by either lumped or distributed parameter techniques. In order to maintain the generality of the results, neither linearization is introduced. Example simulations are given to demonstrate the controller performance. The second type controller is also built for general serial robot arms and is adaptive in nature which can estimate uncertain payload parameters on-line and simultaneously maintain trajectory tracking properties. The relation between manipulator motion tracking capability and convergence of parameter estimation properties is discussed through example case studies. The effect of control input update delays on adaptive controller performance is also studied