Noise effect on adaptive command shaping methods for flexible manipulator control

©2001 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other worksDOI: 10.1109/87.896749Since its introduction, the command shaping method to design command shapers as robust as possible based on the has been applied to the control of many types of flexible manipu- available infonnation on a given system (e.g., expected varialators and sthe effectiveness in the vibration suppression has been tion range of the natural frequency) [11]. Unfortunately, the roverified. However, designing an effective command shaper requires a priori knowledge about the system parameters. Recently, some bustness of the shaper comes at the expense of the command efforts have been made to make the command shaper adapt to the shaper length, which means more delay in the response. Morechanges in the system parameters. In this paper, the indirect and _. over, this approach still requires a fair amount of a priori knowlthe direct adaptive command shaping methods in the time domain edge about the system parameters for proper design. The second are compared, especially in terms of the noise effect on the per- approach is to make the command shaper adapt to uncertain formance. Analysis shows that the direct approach is less sensitive . to the noise and this analytic result is verified by the proper simu- or varying system parameters. The indirect adaptive command lation. Finally, experimental results using the direct approach are shaping method has focused on the system identification either included. in the frequency domain [3], [14] or in the time domain [2], [8]

Improving Closed-Loop Signal Shaping of Flexible Systems with Smith Predictor and Quantitative Feedback

Input shaping is a technique used to move flexible systems from point to point rapidly by suppressing the residual vibration at the destination. The vibration suppression is obtained from the principle of destruction of impulse responses. The input shaper, when placed before the flexible system inside the control loop, proves to deliver several benefits. However, this so-called closed-loop signal shaping has one major disadvantage that it adds time delays to the closed-loop system. Being a transcendental function, the time delays cause difficulty in analysis and design of the feedback controller. In most cases, the time delays also limit the maximum achievable bandwidth. In this paper, for the very first time, Smith predictors were applied to the closed-loop signal shaping to remove the time delay from the loop. It was shown in simulation result that the detrimental effect of the time delays was completely removed in the case of perfect plant model. The quantitative feedback control was used in the study to quantify the amount of achievable bandwidth and to suppress vibrations from the plant-input disturbance

Design and optimization of input shapers for liquid slosh suppression

The need for fast maneuvering and accurate positioning of flexible structures poses a control challenge. The flexibility inherent in these lightly damped systems creates large residual vibrations in response to fast disturbances. Several control approaches have been proposed to tackle this class of problems, of which the input shaping technique seems quite appealing. While input shaping has been widely investigated to attenuate residual vibrations in flexible structures, less attention was granted to expand its viability in further applications. It is therefore the aim of this work to develop a methodology for applying input shaping techniques to suppress sloshing effects in open moving containers to facilitate safe and fast point-to-point movements. The liquid behavior is modeled using finite element analysis. The input shaper parameters are optimized to find the commands that would result in minimum residual vibration. Other objectives, such as improved robustness and motion constraints such as deflection limiting are also included in the optimization scheme. Numerical results are verified on an experimental setup consisting of a small motor-driven water tank that is precisely guided to undergo rectilinear motion, while measuring both the tank motion and free surface displacement of the water. The results obtained suggest that input shaping is an effective method for suppressing residual liquid vibrations

A review of command shaping techniques for elimination of residual vibrations in flexible-joint manipulators

Command shaping is an important open-loop control method for improving the settling time and positioning accuracy. This technique also minimizes residual vibrations. Shaped command profiles are formed by convolving a sequence of impulses or solving special functions for the desired command signal. To determine the input shaper controller commands, estimated values of the system natural frequency and damping ratio are required to make the necessary calculations. However, real systems cannot be modelled precisely, while robustness of the shaper to modelling errors is an important design consideration. Many robust input shapers have been developed and reported in the literature. It has been observed that the robust shapers typically have longer travelling time durations that lead to slow system response. This makes a relationship between shaper rising/travelling time and robustness. This paper presents a review of command shaping methods and analyses the compromise between duration of motion and shaper robustness for positive and smoothly shaped reference commands

Position and sway control of a nonlinear tower crane system using input shaping techniques

Crane systems are the most widely used tools in the shipping yards and construction sites to transport goods from one point to another. The emergence of high riser-building, encourages the use of modern systems particularly tower crane systems to conveniently execute various tasks within the shortest possible time. However, those systems suffered greatly from undesired swinging during the process. Conversely, this significantly posed problems to the systems, resulting to inaccurate positioning of the payload, unease of operation by the human operator and in some cases even damage to the system. This paper investigates the performance of input shaping techniques for sway control of a tower crane system. Unlike the conventional optimal controllers, input shaping is simple to design and cost effective as it does not require feedback sensors. Several input shapers were implemented and their performances were compared which are useful for future sway control designs. The nonlinear model of the system was derived using the Lagrange’s energy equation. To investigate the performance and robustness of input shaping techniques, zero vibration (ZV), zero vibration derivative (ZVD), zero vibration derivative-derivative (ZVDD) and zero vibration derivative-derivative-derivative (ZVDDD) were proposed with a constant cable dimension in an open loop configuration. Simulation and experimental results have shown that ZVDDD with the slowest response has the highest level of sway reduction and robustness to modelling errors as compared to ZV, ZVD and ZVDD. Moreover, to improve the response, a negative amplitude zero vibration derivative-derivative (NAZVDD) was designed and its performance was compared with ZVDD. It is found that NAZVDD gives a faster response with small robustness penalty as compared to ZVDD

Dynamics Modeling and Control of a Quadrotor with Swing Load

Nowadays, aerial robots or Unmanned Aerial Vehicles (UAV) have many applications in civilian and military fields. For example, of these applications is aerial monitoring, picking loads and moving them by different grippers. In this research, a quadrotor with a cable-suspended load with eight degrees of freedom is considered. The purpose is to control the position and attitude of the quadrotor on a desired trajectory in order to move the considered load with constant length of cable. So, the purpose of this research is proposing and designing an antiswing control algorithm for the suspended load. To this end, control and stabilization of the quadrotor are necessary for designing the antiswing controller. Furthermore, this paper is divided into two parts. In the first part, dynamics model is developed using Newton-Euler formulation, and obtained equations are verified in comparison with Lagrange approach. Consequently, a nonlinear control strategy based on dynamic model is used in order to control the position and attitude of the quadrotor. The performance of this proposed controller is evaluated by nonlinear simulations and, finally, the results demonstrate the effectiveness of the control strategy for the quadrotor with suspended load in various maneuvers

Simulation of control drives in a tower crane

The design of a control system for a tower crane is investigated. Underlying the controller design is the theory of optimal linear control. Computer models of a crane and the control systems for the crane drives are developed. Simulation data reveals that the motion of the load can be effectively controlled so that it should follow a predetermined trajectory

Method and apparatus for creating time-optimal commands for linear systems

A system for and method of determining an input command profile for substantially any dynamic system that can be modeled as a linear system, the input command profile for transitioning an output of the dynamic system from one state to another state. The present invention involves identifying characteristics of the dynamic system, selecting a command profile which defines an input to the dynamic system based on the identified characteristics, wherein the command profile comprises one or more pulses which rise and fall at switch times, imposing a plurality of constraints on the dynamic system, at least one of the constraints being defined in terms of the switch times, and determining the switch times for the input to the dynamic system based on the command profile and the plurality of constraints. The characteristics may be related to poles and zeros of the dynamic system, and the plurality of constraints may include a dynamics cancellation constraint which specifies that the input moves the dynamic system from a first state to a second state such that the dynamic system remains substantially at the second state

Comparison of polynomial profiles and input shaping for industrial applications

Command shaping creates reference commands that reduce residual vibrations in a flexible system. This thesis examines the use of command shaping for flexible system control in three industrial applications: cam-follower systems, sloshing liquids, and cherrypickers. One common type of command shaping is command smoothing which creates a smooth transition between setpoints. A specific type of command smoothing used in cam-follower systems is the polynomial profile. An alternative technique to reduce vibration in flexible systems is input shaping. In this thesis, input-shaped commands are compared to polynomial profiles for applications requiring both vibration suppression and fast motion. Simulation and experimental results show that input shaping is faster than polynomial profiles and provides a simple approach to suppressing residual vibration. Secondly, significant experimental contributions have been made in the area of slosh control. The oscillation of liquids in a container can cause liquid spillage or can cause stability issues, especially in space vehicles. In the past, a number of control techniques have been proposed, but only a few recommend the use of input shaping. This thesis describes the use of command shaping to limit slosh. Results are supported by numerical and experimental testing. Input-shaped commands reduce residual slosh amplitude compared to unshaped commands and polynomial profiles. Input-shaped commands can also accommodate uncertainties and changes in the sloshing frequencies. Lastly, a small-scale cherrypicker was constructed to study the use of input-shaping control on these types of aerial lifts. Cherrypickers have flexible dynamic effects that can cause dangerous and life-threatening situations. To study this class of machines and to provide future students an experimental testbed, several design criteria were established before construction began. The resulting machine achieved most design objectives, including a simple-to-use graphical user interface and accurate state measurements. Robust input-shaping controllers were implemented to limit endpoint vibration. The design of the cherrypicker is discussed and experimental results are reported.M.S.Committee Chair: William Singhose; Committee Member: Al Ferri; Committee Member: Jun Ued

Minimizing structural vibrations with Input Shaping (TM)

A new method for commanding machines to move with increased dynamic performance was developed. This method is an enhanced version of input shaping, a patented vibration suppression algorithm. This technique intercepts a command input to a system command that moves the mechanical system with increased performance and reduced residual vibration. This document describes many advanced methods for generating highly optimized shaping sequences which are tuned to particular systems. The shaping sequence is important because it determines the trade off between move/settle time of the system and the insensitivity of the input shaping algorithm to variations or uncertainties in the machine which can be controlled. For example, a system with a 5 Hz resonance that takes 1 second to settle can be improved to settle instantaneously using a 0.2 shaping sequence (thus improving settle time by a factor of 5). This system could vary by plus or minus 15% in its natural frequency and still have no apparent vibration. However, the same system shaped with a 0.3 second shaping sequence could tolerate plus or minus 40% or more variation in natural frequency. This document describes how to generate sequences that maximize performance, sequences that maximize insensitivity, and sequences that trade off between the two. Several software tools are documented and included