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Suppressing the vibration of cable-driven parallel mechanisms (CDPMs) is of great significance for improving their performance such as positioning accuracy. In this paper, a hybrid vibration suppression strategy based on stiffness enhancement and input shaping is proposed to reduce the vibration of a CDPM in the process of moving. Firstly, the stiffness model and vibration model of the CDPM are established. Then, based on the stiffness model and the vector set λ that meets the requirements of the cable tensions, a stiffness enhancement algorithm is proposed to improve the stiffness of the mechanism by adjusting cable tensions. In order to reduce the vibration of the mechanism to the maximum extent, a hybrid vibration suppression strategy is proposed by combining the stiffness enhancement algorithm with the multi-modal input shaping technique. Finally, the effect of stiffness enhancement algorithm and hybrid vibration suppression strategy on reducing mechanism vibration is verified by experiments. The hybrid vibration suppression strategy proposed in this paper does not require additional components and therefore does not increase the cost of vibration suppression, and it has good performance. [ABSTRACT FROM AUTHOR]

A crane system with distributed mass payload (DMP) is highly nonlinear and it is a multi-mode system with different oscillation frequencies. The crane dynamics are also largely affected when operating under different cable and payload lengths. This paper investigates robust multi-mode input shapers for effective oscillation control of an overhead crane carrying DMP. Three robust shapers which are Zero Vibration Derivative (ZVD), Extra-Insensitive (EI) and Equal Shaping-Time and Magnitude (ETM) are considered and modified to be multi-mode shapers. These are obtained by convolving two input shapers that are designed separately based on the hook and payload oscillation frequencies. To assess the effectiveness of the shapers, Matlab simulations are performed by using the nonlinear dynamic model of the crane and applied under three distinct cases involving different cable and payload lengths. Simulation results show that the multi-mode EI shaper (MM-EI) has the highest performance in reduction of the hook and payload oscillations, with the lowest maximum transient sway and mean average error. In addition, with 40% errors in the oscillation frequencies, the MM-EI provides the highest robustness by achieving 50% reductions in the payload oscillations as compared to the case with an unshaped input.

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An overhead crane system is a complex time-varying system if it includes simultaneous hoisting and moving operations. To address the problem that time-varying systems usually have no exact analytical solution, an anti-swing method based on linear approximation of the phase plane trajectory is proposed. Specifically, the phase plane trajectory of the swing angle is first analyzed and it is found that the double-step acceleration method with unequal acceleration amplitude and acceleration time has a combination of limit loops in the phase plane trajectory of the swing angle when the rope length varies, so the average rope length of each section is used to approximate the natural oscillation frequency. Next, the input shaping technique is used to shape the input signal into the desired output signal so that the load swing angle can follow the planned trajectory. The desired acceleration amplitude and switching time are then derived based on the geometric relationship between the swing angle in the phase plane and the specific physical constraints. Finally, the feasibility of the proposed method is verified by numerical simulations. [ABSTRACT FROM AUTHOR]

In order to improve transport efficiency and enhance the safety of the crane system, it is required that the trolley can reach the desired position fast enough, while the load swing needs to be within the bounded limits. To achieve these goals, a novel double-step acceleration strategy with equal acceleration amplitude and acceleration time, and unequal acceleration amplitude and acceleration time is proposed for input shaping anti-sway control based on phase plane trajectory planning. Specifically, the desired double-step acceleration signal is designed using an input shaper, and then the phase plane trajectory of the load swing angle is planned using the phase plane method. The geometric constraints of the phase plane trajectory and the physical constraints of the crane allow the amplitude and switching time of the double-step acceleration to be solved. The final simulation results show that the proposed control method achieves an effective anti-sway effect on the container crane. [ABSTRACT FROM AUTHOR]

Precise control of overhead crane systems, especially when there are disturbances, is crucial for ensuring safety and efficiency in operations. This paper addresses tracking control for overhead cranes that have variable cable lengths. It employs the Takagi-Sugeno (T-S) descriptor fuzzy method combined with Input Shaping (IS) techniques to significantly reduce payload oscillation. By representing the nonlinear system as local linear sub-models over different operating regions, the T-S descriptor fuzzy method effectively controls the crane system’s high nonlinearity. The Parallel Distributed Compensation (PDC) Integral controller is integrated into the design framework to enhance tracking control performance. Using Lyapunov theory, linear matrix inequalities (LMIs) are constructed, and the controller parameters are determined by solving these inequalities. By incorporating H-infinity or L-infinity performance criterion into the fuzzy model, robust controllers are developed to effectively reject disturbances and ensure tracking performance. Finally, simulations are conducted to evaluate the performance and effectiveness of the proposed controllers.

Input shaping is a finite-impulse response (FIR) filter whose coefficients are designed to produce a shaped input that avoids exciting lightly-damped modes. As a result, flexible systems can be commanded to move quickly from point to point with minimum residual vibration. However, traditional input shaping techniques assume zero initial conditions, limiting their usability for systems with non-zero initial conditions, such as, emergency stops of cranes. Besides, in practice, movement of flexible systems is often initiated when the systems are not completely stationary. In these situations, the performance of the input shaping technique deteriorates. In this paper, a modification of shaper's impulse sequence at the beginning of the move is proposed to bring the moving flexible system to a stop before commencing movement. The modification utilizes the work and energy method to determine the distance and time as functions of the initial states for base excitation of flexible systems, rendering its application to nonlinear systems. By concatenating this modification with the existing input shapers, a novel shaper called the non-zero initial conditions zero-vibration-derivative (NI-ZVDk) input shaper is introduced. The NI-ZVDk input shaper effectively prevents the movement of flexible systems from their initial states. To demonstrate the effectiveness of the approach, a 2-mass system is utilized as a benchmark for general flexible systems with 2 degrees of freedom. Various types of motion, including pure translation, pure rotation, and combined translation-rotation, are considered. Extensive simulation results showed that, using the proposed NI-ZVDk input shaper, the flexible systems can move from non-zero initial conditions to their desired destinations with less time and less residual vibration. [ABSTRACT FROM AUTHOR]

Featured Application: The work described in the paper offers an innovative solution for mitigating unwanted oscillations in rotating systems, such as carousel systems and cranes. This technology has the potential for practical applications in various industries that rely on precise and stable rotational movements. Specific applications could include manufacturing and material handling, but but we can also find use in the warehousing and logistics, amusement park rides, robotics and automation, etc. This paper describes an innovative design based on the spectral approach of a novel shaper that eliminates frequency components that induce unwanted residual oscillations in various flexible mechanical systems, such as tower cranes or chain carousels, which are vital to many manufacturing and material-handling processes. However, their physical structure leads to flexible effects that limit their usefulness. Apart from the circular motion problem, control is provided by a single actuator, which makes it a so-called underactuated system. The input signal needs to be modified so that the spectral components from several interconnected degrees of freedom are considered together during shaper design, which increases the complexity of this task since one of its components induces nonlinear behavior. This means that traditional shaping techniques, based on linear theory, fail to provide good performance over the whole input range. The underdamped dynamics of the model and the effect of nonlinearities on the spectrum of the final signal are examined; the proposed method for application as a command shaping control technique is applied; and its effectiveness is analyzed by simulation and real-time implementation. The theoretical results verified on an experimental crane system confirm the expected oscillation phenomenon and show that the designed nonlinear shaper can reduce the payload swing significantly. [ABSTRACT FROM AUTHOR]

Featured Application: The proposed control scheme provides a direct reference for the swing control of overhead cranes. A novel swing control scheme combining optimization and input-shaping techniques is proposed for overhead cranes subjected to parameter variations and modeling errors. An input shaper was first designed using the analytical method based on the linear swing dynamic model. Then, the particle swarm optimization algorithm was used to optimize the pulse amplitudes and time of the shaper to reduce the influence of modeling errors on the residual vibration. Furthermore, an adaptive optimization method was also used to optimize the parameters of the shaper to suppress the influence of the change in the payload mass and the rope length on the residual vibration. The proposed control scheme can suppress the influence of uncertainties on residual vibration and improve the anti-disturbance ability of a closed-loop system via offline and online dual optimization. Finally, the simulation results verify the effectiveness of the scheme. [ABSTRACT FROM AUTHOR]

Piezoelectric objective driver positioners are increasingly used in the field of microscopy. They have the advantages of high dynamic and fast response. This paper presents a fast autofocus algorithm for highly interactive microscope system. First, the Tenengrad gradient of the down‐sampled image is used to calculate the image sharpness, and Brent search method is adopted to quickly converge to the correct focal length. At the same time, the input shaping method is used to eliminate the displacement vibration of the piezoelectric objective lens driver and further accelerate the image acquisition speed. Experimental results show that the proposed scheme can improve the speed of the automatic focusing task of the piezoelectric objective driver and improve the real‐time focus of the automatic microscopic system. Highlights: A high real‐time autofocus strategy.A vibration control method suitable for a piezoelectric objective driver. [ABSTRACT FROM AUTHOR]

This article proposes a hybrid control strategy that integrates the merits of both zero-vibration double derivative input shaping control and neuro-adaptive sliding mode control. The approximation ability of the radial basis function neural network is utilized to estimate the unknown dynamics of the gantry crane system. The input shaping control is used to shape the trolley position, velocity, and acceleration references. These reference trajectories are generated as the state trajectories of a closed-loop system obtained by controlling a nominal system model with a sliding mode control constructed based on the nominal model. The shaped trajectories are sent to the proposed neuro-adaptive sliding mode control as references to be tracked. In comparison with the conventional sliding mode control, the proposed control has higher tracking accuracy and robustness to external disturbances, and effectively reduces the sway angle without suffering from the chattering phenomenon. Moreover, the proposed control has a very high insensitivity to parameter uncertainties. The adaptation mechanisms of the radial basis function neural networks are established based on the Lyapunov stability theory. The effectiveness of the proposed controller is verified through some numerical simulations. [ABSTRACT FROM AUTHOR]

Laser machining is widely used in micro/nanomachining owing to its noncontact nature, environmental friendliness, high level of automation, and short process time. Notably, for micro/nanomachining, the precisions of both the laser and optical systems and motion control systems are crucial. Typically, residual vibrations generated during the motion of machine parts reduce precision at the micro/nanoscales. The input-shaping method is simple and effective for reducing such residual vibrations. Hence, traditional input-shaping methods are primarily used in flexible systems, such as cranes, robots, and motion systems. This is because a flexible system has a low rigidity, damping ratio, and natural frequency; thus, its residual vibration is higher than that of a high-rigidity motion system. In this study, residual vibrations were reduced by applying the input-shaping method to a high-rigidity motion system for precision laser machining. A modified zero-vibration (ZV) shaper was used to apply input shaping to the high natural frequency of a high-rigidity motion system. The modified ZV shaper was evaluated, and its residual vibration suppression performance was confirmed based on its application to a flexible system. Furthermore, errors caused by accelerations in corner machining were quantified, and residual vibrations were suppressed via the application of the modified ZV shaper. [ABSTRACT FROM AUTHOR]

The Delta robot is a high-speed and high-precision parallel robot. When it is in function, the end effector generates residual vibration, which reduces the repeat positioning accuracy and positioning efficiency. The input shaping method has previously been shown to suppress the residual vibration of the robot, but the vibration suppression effect of the single-modal input shaper is not good for the delta robot, which has multiple dominant modes for the residual vibration. To solve this problem, this paper proposes an effective method for residual vibration suppression of Delta robots based on dual-modal input shaping technology. Firstly, the modal analysis of the Delta robot is performed using finite element software, and the dominant modal of its residual vibration is determined. Secondly, six dual-modal input shapers are designed according to the obtained modal parameters. Finally, Simulink is used for simulation analysis to verify the robustness and vibration suppression performance of the designed six dual-modal input shapers and traditional single-modal input shapers. The simulation results show that the designed ZVD-EI dual-modal input shaper has good robustness, can effectively suppress the residual vibration of the Delta robot, and can effectively improve the repetitive positioning accuracy and work efficiency of the Delta robot when it is running at high speed. [ABSTRACT FROM AUTHOR]

This paper describes an innovative design based on the spectral approach of a novel shaper that eliminates frequency components that induce unwanted residual oscillations in various flexible mechanical systems, such as tower cranes or chain carousels, which are vital to many manufacturing and material-handling processes. However, their physical structure leads to flexible effects that limit their usefulness. Apart from the circular motion problem, control is provided by a single actuator, which makes it a so-called underactuated system. The input signal needs to be modified so that the spectral components from several interconnected degrees of freedom are considered together during shaper design, which increases the complexity of this task since one of its components induces nonlinear behavior. This means that traditional shaping techniques, based on linear theory, fail to provide good performance over the whole input range. The underdamped dynamics of the model and the effect of nonlinearities on the spectrum of the final signal are examined; the proposed method for application as a command shaping control technique is applied; and its effectiveness is analyzed by simulation and real-time implementation. The theoretical results verified on an experimental crane system confirm the expected oscillation phenomenon and show that the designed nonlinear shaper can reduce the payload swing significantly.

This paper introduces a novel approach to supply reference inputs to feedback systems. In this approach, modified inputs are used to ensure enhancing the capability of the system to achieve the actual desired inputs. Traditionally, the difference between the reference inputs to a system and the outputs are used to decide the suitable correcting actions. In this paper, modified reference inputs are used to cancel out the steady state error of the system. Accordingly, the control effort is evaluated based on a different set of errors. As a result, more effective control actions are implemented to the system. The results show that, the performance specifications of the systems are remarkably enhanced. The enhancement results obtained, include, much limited bounds of the control effort, smaller delay, enhanced transient response, and zero steady state error. [ABSTRACT FROM AUTHOR]

In order to optimize the acceleration performance of a large inertia hydraulic actuator, this paper proposes a main valve input shaping control strategy, which makes the valve flow supply match the load-control demand by adjusting the main valve flow growth rate. Taking a load-independent flow distribution system as the research object, and aiming at the problems of large pressure overshoot, excessive overflow and oscillation tendency during the actuator acceleration process, this paper divides the acceleration process into the pressure build-up condition, the inertia-acceleration condition and the stable-flow regulation condition according to the change characteristics of the actuator driving pressure, and divides the main valve control signal into five stages to design the valve flow growth rate, thereby smoothing the driving pressure fluctuations by adjusting the actuator inertial load and mitigating the pressure release process. Based on the key structure-hydraulic parameters and test data of a 6-ton excavator, a virtual excavator that can accurately simulate the swing action and boom lifting action is built, and the software-in-the-loop test of the input-shaping control algorithm is carried out. The test results indicate that the proposed control strategy can effectively suppress the pressure overshoot, oscillation, and flow overmatching, thereby improving the dynamic stability and energy efficiency of the system. [ABSTRACT FROM AUTHOR]

Abstract Because of their elastic links and joints, high-speed parallel robots for pick-and-place operations inevitably suffer from residual vibrations that significantly degrade their positioning accuracy. An effective approach based on the input shaping technique is presented in this paper for suppressing the residual vibration in these parallel robots. After addressing the design principle of an input shaper for a parallel robot with flexible actuated joints, a robust optimal input shaper is developed by considering the configuration-dependent flexible modes and minimizing the maximum percentage of residual vibration at the end-effector. The input shaper allows a good overall performance to be achieved throughout the entire workspace. Experimental results on a 4-DOF SCARA-type parallel robot show that the residual vibration of the end-effector is dramatically reduced and the dynamic positioning accuracy of the robot significantly improved.

A novel swing control scheme combining optimization and input-shaping techniques is proposed for overhead cranes subjected to parameter variations and modeling errors. An input shaper was first designed using the analytical method based on the linear swing dynamic model. Then, the particle swarm optimization algorithm was used to optimize the pulse amplitudes and time of the shaper to reduce the influence of modeling errors on the residual vibration. Furthermore, an adaptive optimization method was also used to optimize the parameters of the shaper to suppress the influence of the change in the payload mass and the rope length on the residual vibration. The proposed control scheme can suppress the influence of uncertainties on residual vibration and improve the anti-disturbance ability of a closed-loop system via offline and online dual optimization. Finally, the simulation results verify the effectiveness of the scheme.

Under-constrained cable-driven parallel robots (UCCDPRs) manipulate the end-effector (EE) by employing fewer number of cables than the degree of freedom of the EE, which causes unwanted swaying motions and oscillations. These unwanted vibrations can be suppressed by using the regenerated EE trajectory through the input-shaper. However, in the case of the UCCDPR systems, generating the feasible EE trajectory and deriving the natural frequency for designing the input-shaper is not straightforward since finding the stable equilibrium configuration is challenging. This paper proposes a novel methodology to find the stable equilibrium configuration of the general UCCDPRs in the assigned EE position. With the proposed method, the EE trajectory can be reproduced as a vibration suppression trajectory through an input shaper designed based on the analysis of the natural frequencies, as well as generating feasible EE trajectories based on the equilibrium configuration. Also, even if the orientation trajectory is not given and only the position trajectory is given, the cable length to follow the given position trajectory of the EE can be obtained based on the equilibrium configuration corresponding to the given position trajectory. Computer simulations and hardware experiments were conducted to verify the effectiveness and performance of the proposed method.

The attitude precision requirement for satellite with large scale antenna is increasingly higher with progress of space missions. In the space environment, the drastic changes of temperature not only excite thermal vibration of antenna but also change the mode shapes and nature frequencies significantly. Under these circumstances, in order to improve satellite attitude precision, an adaptive attitude maneuver control scheme is proposed for the attitude tracking task in this paper. Firstly, a novel robust input shaper is designed based on impulse vector diagrams for vibration suppression. Secondly, an adaptive terminal sliding mode controller with radial basis function neural network and anti-windup modular is proposed and the stability is proved by Lyapunov theorem. The effectiveness of the control scheme is validated under different space thermal environments. The antenna vibration is suppressed effectively and the attitude maneuvering can be achieved in a finite time, when the mode shapes and nature frequencies of antenna change in a wide range with temperature. [ABSTRACT FROM AUTHOR]

Most robotic systems consist of heavy machine elements that help reduce the vibrations generated by motion and that support good positional accuracy. Large-sized actuators are needed for such systems. Energy consumption significantly increases in oversized robotic systems. The proposed solution to which is to design robotic systems in lightweight and flexible forms. This makes possible smaller overall structure and actuator sizes. However, such systems suffer from residual vibrations. One well-known control solution to residual vibration problem could be input shaping techniques. In this study, a new Fuzzy Logic-based intelligent input shaping selection technique has been proposed. With this proposed approach, it is possible to set optimum settling time, positioning accuracy of robotic systems, and minimum residual vibrations by implementing the crucial open-loop control approach. Comprehensive experience is needed to overcome design issues on command shaping and system modeling. Based on these design criteria constraints and extensive knowledge requirements, the recommended solution is a Fuzzy Logic-based intelligent input shaping technique for accurate modeling and parameter estimation of the systems. The proposed approach is a Fuzzy Logic-based intelligent input shaper selection and input shaper setting determination algorithm. The applicability of the proposed method was verified on the Quanser Flexible Link experimental setup. [ABSTRACT FROM AUTHOR]

The input shaping technique is widely used as feedforward control for vibration suppression of flexible dynamic systems. The main disadvantage of the input shaping technique is the increasing system time response since the input shaper contains time delay parts. However, with the same reference input, the actuator effort in the case of using an input shaper is smaller than the one in the case without an input shaper. Thus, it is possible to decrease the system response time by designing the feedback controller to maximize the actuator effort. This paper proposes a design approach to design the Proportional-Derivative (PD) controller for position control of the actuator so that the settling time of the flexible system with input shaper is minimized. The actuator system with a PD controller is equivalent to a critically damped system, and the condition for the controller gains is established. In addition, the settling time and actuator effort with shaped step input are calculated. The controller gains can be determined by solving the settling time optimization problem with the actuator effort constraint. The effectiveness of the proposed approach is verified via experiments with an overhead crane model. [ABSTRACT FROM AUTHOR]

This paper studies the design of antisloshing trajectories for application in automatic machines for packaging liquid products, with specific reference to cylindrical containers and emphasis on prescribed motion durations. Different strategies, based on a discrete linear model of the sloshing phenomenon and applicable in real-time, are analyzed to perform antisloshing feedforward control of the container motion: finite impulse response (FIR) filters (input shapers and others), dynamic-model inversion, and infinite impulse response (IIR) filters. Unlike the previous literature, these strategies are applied to highly dynamical motion laws, with maximum accelerations from to 4 m/s² to 13 m/s². The effectiveness of the proposed antisloshing trajectories is assessed by experiments. [ABSTRACT FROM AUTHOR]

When using robots to carry out grinding and polishing processing of industrial blades, due to factors such as non-zero approach speed and discontinuous dynamic characteristics, the robot grinding and polishing processing has contact force impact and oscillation problems during the contact transition process, which seriously affects the quality of the blade surface processing, contour accuracy, and control system stability. In order to solve the problem of large impact of contact force in robot grinding and polishing, this paper proposes an optimization method for impact suppression in the transition state of robot grinding and polishing. Taking the robot abrasive belt grinding and polishing as the research object, the adaptive weighted particle swarm algorithm is used to optimize the input shaper and realize the parameter self-tuning of the input shaping technology. The experimental results show that the stabilization time is shortened by about 86.5%, and the maximum overshoot of contact force is reduced by about 88.5% during contact transition. The method proposed in this paper can realize the smooth transition of the blade grinding and polishing process, does not need system modeling, effectively shorten the system stabilization time, reduce the maximum overshoot, and accelerate the system response speed, and it has strong stability and flexibility. [ABSTRACT FROM AUTHOR]

Tower cranes are needed to move heavy objects safely around construction sites. In tower cranes, payload oscillations are a typical problem that can cause safety issues, especially if the crane is not operated by an experienced user. Depending on the system, there are different causes for oscillations, e.g., inertial forces from the crane movement or external forces, such as weather conditions. Hence, the selected control law for input tracking plays an important role to limit the oscillatory motion and to help the crane operator to prevent unwanted operations. In this paper, we study the slew control of a tower crane application from the viewpoint of reducing payload oscillations. Two different approaches are studied: open-loop control based on extrainsensitive input shaping and closed-loop swing angle control, based on the estimation of the hoist cable angle. The proposed control approaches are validated by running the developed control program against a multibody mechanics simulator containing a model of a Liebherr tower crane. The studied control laws are also evaluated using an experimental setup, which consists of a two-axis manipulator, inverters, and a programmable logic controller in which the studied control methods are implemented. The results from the multibody dynamics simulations and from the experimental setup are presented and evaluated from the viewpoint of crane operation. [ABSTRACT FROM AUTHOR]

This paper presents a system for 3D scanning of a large marine propeller blade with a 3D camera mounted on an industrial robot. An industrial 3D camera with structured light is used where the accuracy is in the order of 0.1 mm. The camera is mounted on a rod attached to the robot's end-effector to have sufficient reach for scanning the propeller. This rod introduces mechanical vibrations in the system when the robot is repositioned for a new scan. Fast and efficient scanning is achieved by using vibration cancellation in a feedforward configuration based on input shaping, where the programmed pose increments of the robot are reshaped to give a fast vibration settling time after repositioning the camera. The use of input shaping techniques ensures that the imaging device is at rest during the scanning operation when the object's surface is captured. Three different input shapers are considered: The Zero Vibration (ZV), ZV Derivative (ZVD), and Extra Insensitive (EI) shapers. By minimizing the residual vibrations, the accuracy and precision of the system are increased, and complete 3D scanning of objects can be performed in a shorter time. Moreover, the resulting scan quality is improved. The effectiveness of the proposed method is validated in simulations and experiments where the ZVD and EI shapers proved to be best suited for the scanning application. The experimental validation involved a full scanning operation for a marine propeller blade where a UR10 robot with the original industrial control system was used. It was seen that the proposed system gave sufficient accuracy for determining the surface of the propeller blade.

The Delta robot is a high-speed and high-precision parallel robot. When it is in function, the end effector generates residual vibration, which reduces the repeat positioning accuracy and positioning efficiency. The input shaping method has previously been shown to suppress the residual vibration of the robot, but the vibration suppression effect of the single-modal input shaper is not good for the delta robot, which has multiple dominant modes for the residual vibration. To solve this problem, this paper proposes an effective method for residual vibration suppression of Delta robots based on dual-modal input shaping technology. Firstly, the modal analysis of the Delta robot is performed using finite element software, and the dominant modal of its residual vibration is determined. Secondly, six dual-modal input shapers are designed according to the obtained modal parameters. Finally, Simulink is used for simulation analysis to verify the robustness and vibration suppression performance of the designed six dual-modal input shapers and traditional single-modal input shapers. The simulation results show that the designed ZVD-EI dual-modal input shaper has good robustness, can effectively suppress the residual vibration of the Delta robot, and can effectively improve the repetitive positioning accuracy and work efficiency of the Delta robot when it is running at high speed.

Copyright of SDU Journal of Engineering Sciences & Design / Mühendislik Bilimleri ve Tasarım Dergisi is the property of Journal of Engineering Sciences & Design and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Automatisierungstechnik is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Because of their elastic links and joints, high-speed parallel robots for pick-and-place operations inevitably suffer from residual vibrations that significantly degrade their positioning accuracy. An effective approach based on the input shaping technique is presented in this paper for suppressing the residual vibration in these parallel robots. After addressing the design principle of an input shaper for a parallel robot with flexible actuated joints, a robust optimal input shaper is developed by considering the configuration-dependent flexible modes and minimizing the maximum percentage of residual vibration at the end-effector. The input shaper allows a good overall performance to be achieved throughout the entire workspace. Experimental results on a 4-DOF SCARA-type parallel robot show that the residual vibration of the end-effector is dramatically reduced and the dynamic positioning accuracy of the robot significantly improved. [ABSTRACT FROM AUTHOR]

Underactuated Cable-Driven Parallel Robots (CDPR) employ a number of cables smaller than the degrees of freedom (DoFs) of the end-effector (EE) that they control. As a consequence, the EE is underconstrained and preserves some freedoms even when all actuators are locked, which may lead to undesirable oscillations. This paper proposes a methodology for the computation of the EE natural oscillation frequencies, whose knowledge has proven to be convenient for control purposes. This procedure, based on the linearization of the system internal dynamics about equilibrium configurations, can be applied to a generic robot suspended by any number of cables comprised between 2 and 5. The kinematics, dynamics, stability and stiffness of the robot free motion are investigated in detail. The validity of the proposed method is demonstrated by experiments on 6-DoF prototypes actuated by 2, 3, and 4 cables. Additionally, in order to highlight the interest in a robotic context, this modelling strategy is applied to the trajectory planning of a 6-DoF 4-cable CDPR by means of a frequency-based method (multi-mode input shaping), and the latter is experimentally compared with traditional non-frequency-based motion planners.

Most industrial serial robots use decentralized joint controllers assuming rigid body dynamics. To prevent exciting the flexible mode, gains are kept low, resulting in poor control bandwidth and disturbance rejection. In this paper, a two-stage flexible joint discrete controller is presented, in which the decentralized approach is extended with a stiffness to take into account the dominant coupling mode. In the first-stage, an input shaping feedforward shapes the rigid closed-loop dynamics into desired dynamics that does not produce link vibrations. Robotic dynamic computation based on a recursive Newton-Euler algorithm is conducted to update the feedforward link inertia parameter during robot motion. A second-stage is added to increase disturbance rejection. A generalized Smith predictor (GSP) is developed to compensate for delay and feedback sensor filtering. An effective methodology is presented to optimize the control loop gains. Numerical simulations and experiments on a six-joint robot manipulator confirm that the proposed controller improves control performances in terms of bandwidth, vibration attenuation, and disturbance rejection. [ABSTRACT FROM AUTHOR]

This paper proposes an input shaping technique for efficient payload swing control of a tower crane with cable length variations. Artificial neural network is utilized to design a zero vibration derivative shaper that can be updated according to different cable lengths as the natural frequency and damping ratio of the system changes. Unlike the conventional input shapers that are designed based on a fixed frequency, the proposed technique can predict and update the optimal shaper parameters according to the new cable length and natural frequency. Performance of the proposed technique is evaluated by conducting experiments on a laboratory tower crane with cable length variations and under simultaneous tangential and radial crane motions. The shaper is shown to be robust and provides low payload oscillation with up to 40% variations in the natural frequency. With a 40% decrease in the natural frequency, the superiority of the artificial neural network–zero vibration derivative shaper is confirmed by achieving at least a 50% reduction in the overall and residual payload oscillations when compared to the robust zero vibration derivative and extra insensitive shapers designed based on the average operating frequency. It is envisaged that the proposed shaper can be further utilized for control of tower cranes with more parameter uncertainties. [ABSTRACT FROM AUTHOR]

In recent years, cable-driven-parallel robots (CDPRs) have been studied for façade operations. There are various types of CDPRs; however, underconstrained CDPRs are capable of wider operating in façade workspaces than overconstrained CDPRs. Therefore, in this article, a dual ascender robot (DAR) was used for façade operations. Herein, two suggestions for safe façade operations are presented. First, a flexible nylon fiber rope was modeled such that the vibration direction, natural frequency, and damping ratio of the DAR could be converted through a Jacobian matrix and modal decomposition from the rope model. Second, input shaping control was applied to reduce vibrations, based on the vibration model of a DAR using the rope model. Modal decomposition was verified using a verification experiment, and the effect of input shaping was evaluated by comparing the w/input shaping and w/o input shaping experiments. w/input shaping case was shown about 48% reducing robot vibration and about 35% shortening settling time compare with w/o input shaping case. [ABSTRACT FROM AUTHOR]

In order to optimize the acceleration performance of a large inertia hydraulic actuator, this paper proposes a main valve input shaping control strategy, which makes the valve flow supply match the load-control demand by adjusting the main valve flow growth rate. Taking a load-independent flow distribution system as the research object, and aiming at the problems of large pressure overshoot, excessive overflow and oscillation tendency during the actuator acceleration process, this paper divides the acceleration process into the pressure build-up condition, the inertia-acceleration condition and the stable-flow regulation condition according to the change characteristics of the actuator driving pressure, and divides the main valve control signal into five stages to design the valve flow growth rate, thereby smoothing the driving pressure fluctuations by adjusting the actuator inertial load and mitigating the pressure release process. Based on the key structure-hydraulic parameters and test data of a 6-ton excavator, a virtual excavator that can accurately simulate the swing action and boom lifting action is built, and the software-in-the-loop test of the input-shaping control algorithm is carried out. The test results indicate that the proposed control strategy can effectively suppress the pressure overshoot, oscillation, and flow overmatching, thereby improving the dynamic stability and energy efficiency of the system.

In this study, a novel fuzzy logic–based decision support system approach to provide assistance in the selection of suitable input shaping techniques is presented. The proposed approach selects the suitable input shaping technique for point-to-point motion type of systems such as precise positioning, crane operations, flexible robotic systems and so on. The problem solution addressed is the selection of the input shaping technique and the settings for the selection of the input shaper. Some of these design issues require extensive expertise in command shaping and system modeling studies. To overcome these problems and the necessity for such an expertise in these application areas, the proposed technique is provided as a solution. The presented study also provides a review of input shaping methods as well as their advantages and disadvantages in terms of vibration elimination performance, traveling time and robustness features. In the final section of the study, the details of the simulations, as well as experimental results, are provided to validate the achieved high performance of the proposed technique. The experimental studies are conducted on a Quanser IP02 Gantry Crane experimental setup. [ABSTRACT FROM AUTHOR]

Industrial robots used in manufacturing processes such as drilling of aerospace structures undergo many rapid positioning motions during each operation. Such aggressive motions excite the structural modes of the robot and cause inertial vibrations at the end-effector, which may damage the part and violate the tolerance requirements. This article presents a vibration avoidance technique based on input shaping combined with a learning-based structural dynamic model. A theoretical dynamic model is first developed for commonly used robotic arms considering the flexibilities of the first three joints of the robot. An artificial neural network is developed and used in conjunction with the dynamic model to predict the natural frequency of the system at any pose in the workspace. Transfer learning techniques are used to extend the trained artificial neural network to account for the mass of the payload with minimal data collection. To reduce the residual vibrations of the robot in rapid motions, zero-vibration derivative shapers are designed and implemented. The effectiveness of the presented methodology has been validated experimentally on a Staubli RX90CR robot with an open-architecture control system developed fully in-house. Experimental results show more than 85% reduction in residual vibrations during aggressive motions of the robot. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive multivariable continuous terminal sliding mode (CTSM) controller with robust input shaper (RIS) is proposed for flexible spacecraft under model uncertainty and external disturbance. Firstly, for the problem of flexible vibration introduced by flexible appendage, the RIS based on disturbance observer is designed. The proposed input shaper can eliminate the flexible vibration effectively even if there are some disturbances in flight. Then, an adaptive multivariable CTSM controller is proposed for attitude tracking of flexible spacecraft, using only information about the output and its first derivative. The features of the developed methods are that it is continuous multivariable controller which attenuates the chattering effectively and the attitude tracking can be achieved in finite time. The stability and robustness properties of the system are proven using Lyapunov function. Finally, some numerical simulations are performed to validate the efficiency of the developed algorithm. [ABSTRACT FROM AUTHOR]

When the vibration amplitude and resonant frequency bandwidth of each mode are different in the multiple-modal system, the response time of a system is increased but the residual vibration is effectively reduced by the positive impulses multiple-modal input shapers. However, a negative impulses hybrid multiple-modal input shaping method can solve those problems. The basic principle of this control strategy and a 3-DOF parallel robot were introduced. Six negative impulses hybrid input shapers to reduce vibration of the first two modes were constructed based on the robot. Using simulation methods, the response time and vibration suppression abilities of various negative impulses hybrid two-modal input shapers (NHTIS) were obtained by analyzing the vibration response curves of these input shapers, and comparing with positive and negative impulses two-modal input shapers, respectively. The results show that the NHTIS can improve the response speed of the system while significantly reducing the multiple-modal residual vibration.

Tower cranes are needed to move heavy objects safely around construction sites. In tower cranes, payload oscillations are a typical problem that can cause safety issues, especially if the crane is not operated by an experienced user. Depending on the system, there are different causes for oscillations, e.g., inertial forces from the crane movement or external forces, such as weather conditions. Hence, the selected control law for input tracking plays an important role to limit the oscillatory motion and to help the crane operator to prevent unwanted operations. In this paper, we study the slew control of a tower crane application from the viewpoint of reducing payload oscillations. Two different approaches are studied: open-loop control based on extrainsensitive input shaping and closed-loop swing angle control, based on the estimation of the hoist cable angle. The proposed control approaches are validated by running the developed control program against a multibody mechanics simulator containing a model of a Liebherr tower crane. The studied control laws are also evaluated using an experimental setup, which consists of a two-axis manipulator, inverters, and a programmable logic controller in which the studied control methods are implemented. The results from the multibody dynamics simulations and from the experimental setup are presented and evaluated from the viewpoint of crane operation.

This paper presents a feedforward technique for arresting motion in nonlinear systems based on two-scale command shaping (TSCS). The advantages of the proposed technique arise from its feedforward nature and ease of implementation in linear and nonlinear systems. Using the TSCS strategy, the control input required to arrest motion is decomposed into two scales—the first arrests dynamics associated with the linear subproblem, while the second eliminates response from the nonlinearities. Using direct numerical integration, the method is assessed using a traditional Duffing system and multi-degree-of-freedom nonlinear systems. Experiments are conducted on a compound pendulum attached to a servomotor, documenting effective arrest of the system in close agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]