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Flexible links combined with force and torque sensors can be used to detect obstacles in mobile robotics, as well as for surface and object recognition. These devices, called sensing antennae, perform an active sensing strategy in which a servomotor system moves the link back and forth until it hits and object. At this instant, information of the motor angles combined with force and torque measurements allow calculating the positions of the hitting points, which are valuable information about the object surface. In order to move the antenna fast and accurately, this article proposes a new open loop control for driving this flexible link based sensor. The control strategy is based on an ( IS ) Input Shaping technique, in order to reduce link vibrations. The antenna performs free azimuthal and vertical movements. However, the vertical movement is clearly non-linear due to the gravity effect, which prevents the use of standard linear IS techniques. Then a new nonlinear IS has been developed in this article which includes a linearization term of the gravity. Experiments have shown the improvements attained with this technique in the accurate and vibration free motion of our antenna.

Manual tracking tasks are more difficult when the system used for tracking has flexibility and time delays. This paper uses a set of operator experiments to quantitatively examine how system flexibility and time delays degrade manual tracking. Additionally, it investigates the effects of adding input shaping to the system. Performance is quantified by root-mean-squared tracking error and subjective rating of difficulty.

Cranes are used extensively in many industries throughout the world, in a wide array of environments, including some that are hazardous to humans. The vast majority of cranes are directly controlled by human operators. In some cases, it is necessary to remove the human operator from hazardous operating conditions, creating a crane that must be remotely operated. This, however, introduces additional challenges for the operator, who must now control the oscillatory payload while suffering from decreased perception of the environment and the potential time delays caused by remote operation. This paper presents two studies of crane operator performance with varying time delays. The results show that the type of crane control and duration of the communication time delay directly influence task completion time and difficulty. Input shaping control is shown to improve completion times and lower operator effort.

High speed operation of industrial transfer robot arm generates residual vibration, which in many cases may limit productivity of the factory. In this paper, we use input shaping approach to reduce the residual vibration. The approach needs value of natural frequency and damping ratio to be identified in advance. We present an integrated tool of parameter identification and vibration control for higher modes vibration systems, as an easy and effective tool to help industrial people to analyze and solve the vibration problem. A semiconductor wafer transfer robot arm is used as an application case. Experiments have been carried out, and the results showed significant reduction in settling time as well as total movement time of the robot arm.

Control of a space robot without actuators on the main body is an underactuated control problem. As stabilization methods, various methods such as time-varying feedback controllers, discontinuous feedback controllers, center manifold-based methods, zero-dynamics methods, and sliding mode controllers have been proposed. However, the past studies have not considered an underactuated space robot equipped with flexible appendage, such as solar panels. If the manipulators were simply controlled to achieve the main body attitude using the past controllers with out taking the flexible appendage into consideration, residual vibration would be remained even after the link motion has finished. In order to suppress the residual vibration on the flexible appendage, we apply the input-shaping technique to the link motion of the underactuated plane space robot. Numerical simulations are carried out to validate the proposed method for a planar two-link space robot with flexible appendage. The results show that the proposed method was capable of not only changing the link angles and the main body attitude, but also suppressing the residual vibration on the flexible appendage.

This paper deals with signal shaping filters in form of sum of weighted time delays. The filter can be used to solve various control problems. The first important application is a control of flexible mechanical systems with respect to minimization of excited residual vibrations. The second interesting field is feedback controller design using open loop frequency response shaping. The paper presents an algorithm for parametrization of all equidistant four-pulse shaping filters with minimum set of chosen parameters.

An input shaping algorithm based on convex optimization techniques is presented for closed-loop discrete-time linear time-invariant (LTI) systems where closed-loop signals are subject to linear constraints. As an illustrative example the seeking process in a Hard Disk Drive is investigated. The closed-loop system responses to both shaped and non-shaped inputs are compared.

The method of control signal shaping has been practically used in control systems with flexible elements since the end of 80 th years of last century. The most of applications has been focused on machine engineering, e. g. speedy elevators, cranes, etc. New techniques for design of train of impulses improving system robustness appeared in the theory (mainly in time domain). The article presents alternative approach based on discrete shaping filter design as a correction filter with impulse response identical to classical solution (for properly selected filter parameters). Referring to realization of control signal shaping system by digital devices, this approach is more convenient one. The proposed modification, increasing of sampling frequency at the input of digital shaping filter, allows fast system response to control signal changes.

This paper proposes a vibration suppression tool with visual graphical interface to solve the vibration problem based on input shaping approach. The vibratory model was identified and the preshaped input was generated using the tool. The proposed tool was then applied in real industry processes such as semiconductor wafer transfer robot and gantry loader to solve the vibration problems in high speed operation and good results were obtained that confirm the validity of the tool.

Cranes provide an excellent platform for teaching system dynamics and controls. Cranes have a simple pendulum-type oscillation that is useful for demonstrating basic ideas. Cranes also have additional dynamic effects such as motor dynamics, velocity limits, payload variations, and nonlinear slewing dynamics that make them well suited for advanced study. If the cranes are made remotely operable, then students can also study tele-operation and control of systems with time delays. System dynamics and control courses taught at the Georgia Institute of Technology utilize cranes in both the lecture and laboratory exercises. The primary goal of using the cranes is to provide hands-on experiences in system dynamics and implementation of controllers on real systems. This paper describes the cranes and the complementary curriculum.

This paper proposes a design method of a damping path for a cylindrical liquid container transferred with a wheeled mobile robot. The damping path is constructed from the acceleration using the principle of an input shaping method. Although a positional error is occurred by using the input shaping method, it is easy to correct the error with the proposed method. The proposed design method can be applied to a complex reference path including multiple turn sections. In addition, a constraint condition of maximum amplitude of sloshing in the container can be taken into consideration. The effectiveness of the proposed method is clarified through simulations and experiments.

This paper proposes an algebraic expression of noncausal stable inversion based on the two-sided Laplace transform, which is a classic mathematical tool but has not been used very much in the field of control engineering. This expression brings an advantage that computing of stable inversion is reduced to simulation of the response of the plant and the reverse of time horizon without solving the boundary value problem of state-space equations as the conventional definition of stable inversion. An illustrative example demonstrates that this approach is useful to reduce the load of the programming for a search algorithm to determine the shape of a transition trajectory under the constraint of input saturation. As another application of the proposed expression, developed is a method of iterative learning control to obtain stable inversion for infinite dimensional systems. An experiment to apply the iterative learning control to tip control of a flexible arm is reported to demonstrate the effectiveness of the method.

This paper presents investigations into the development of hybrid control schemes for input tracking and 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. To study the effectiveness of the controllers, initially a collocated PD control is developed for control of rigid body motion. This is then extended to incorporate input shaper control schemes for vibration control of the system. The positive and modified specified negative amplitude input shapers are designed based on the properties of the system. Simulation results of the response of the manipulator with the controllers are presented in time and frequency domains. The performances of the hybrid control schemes are examined in terms of level of input tracking capability, vibration reduction, time response specifications and robustness to parameters uncertainty in comparison to the PD control. Finally, a comparative assessment of the amplitude polarities of the input shapers to the system performance is presented and discussed.

A 30-ton industrial bridge crane located at an aluminum sheet manufacturer has been equipped with a crane manipulation system enabling swing-free motion, disturbance rejection, and precise positioning. Previous investigations of anti-sway, positioning, and crane control have yielded important contributions in these areas. These advancements are combined into the unified crane manipulation system described here. An overview of this system is presented, along with experimental results, and a description of how human operators use the crane.

This paper presents a slew maneuver control design of three-axis rotational flexible spacecraft. The focus of the work is to investigate the nonlinear effect of the three axis maneuver for a flexible spacecraft when a vibration suppression technique for linear systems such as input shaping is used in the control design. A simple method of slewing three-axis rotational spacecraft using input shaping is proposed and the proposed technique is implemented on an experimental three-axis spacecraft simulator.

Precise manipulation of payloads is difficult with large cranes. Oscillation can be induced into the lightly damped system by motion of the overhead support point, or from environmental disturbances. A combined feedback and input shaping controller is presented here. The controller uses feedback to detect and compensate for positioning error in the overhead support unit (e.g. the bridge or trolley), and input shaping is used to negate motion-induced oscillation in the payload. The controller is implemented on a 10-ton bridge crane at the Georgia Institute of Technology. The controller generates simple on-off commands, suitable for typical cranes that employ on-off, relay-driven motors. The controller achieves good positioning accuracy, and significant payload sway reduction.

Input shaping is a vibration control technique that operates by filtering reference commands so that the modified (or shaped) command does not excite the system's natural frequencies. Usually input shaping is limited to a filtering operation outside of any feedback loops. However, this implementation prevents input shaping from effecting some vital control applications including disturbance rejection, initial condition response, etc. Therefore, some research has suggested using input shapers within feedback loops. This paper will present some initial investigations toward the fundamental understanding of how input shapers utilized within feedback loops affect closed loop stability.

TiNi SMA is a good candidate for nanoactuation due to its low operation voltage, large range of recoverable deformations, and high recovery forces. This paper addresses the modelling and control of a TiNi SMA wire in free-standing configuration. The dynamic behaviour of the wire during the cooling-heating phase under the normal operation condition (2~3 V) and the off-normal operation condition (1.2~1.8 V or 3.2~3.4 V) are studied. A first-order model is employed to characterize the system. A hybrid input shaping, consisting of normal and off-normal operation voltage, is developed to achieve the ideal wire position control. A vision system measures the displacement of the wire, and then sends the position information to the controller to adjust the input to achieve the ideal wire position.

The use of step function reference commands is often discouraged when the system has flexible dynamics. The rule of thumb is that smooth commands, such as S-curves should be used instead. This paper attempts to dispel the myth that step functions are inappropriate for flexible systems. To accomplish this, a new approach for analyzing the response of systems driven by smooth reference commands is presented. This approach treats S-curve command profiles as input-shaped functions. Input shaping is a method of reducing residual vibration by convolving a sequence of impulses with a baseline system command. The sequence of impulses is the key to predicting the system’s vibratory response. By interpreting S-curve commands as input-shaped functions, common criteria for comparing the two types of commands can be developed. The results indicate that sequences of step functions are much more effective at reducing vibration than S-curves.

This paper presents an input shaping method for buil ding in real time a shaped velocity profile according to an integer algorithm that determines the command reference signal at each interpolation step. This integer implementation has the drawback of slightly reduce shaping robustness. However, experimental results confirm residual vibration reduction when robust shapers are used in the integer input shaping process. Copyright © 2002 IFAC.

A modified input shaping control to reduce residual vibration at the end-point and to limit the sway angle of the payload during traveling for container crane systems is investigated. When the maneuvering time is minimized, a large transient amplitude and steady state oscillations may occur inherently. Since a large swing of the payload during the transfer is dangerous, the control objective is to transfer a payload to the desired place as quickly as possible while limiting the swing angle of the payload during the transfer. The conventional shapers are enhanced by adding one more constraint to limit the intermediate sway angle of the payload. The developed method is shown to be more effective than other conventional shapers for preventing an excessive transient sway. Computer simulation results are provided.

A spherical pendulum-type model was constructed to represent liquid sloshing in a cylindrical container caused by container transfer along a curved path. The model was used to design a curved path and a transfer control system in consideration of the damping of sloshing in the container. The curvature radius of the curved path and the acceleration of the container were determined using an input shaping method. The effectiveness of the present method was clarified through experiment and simulation.

This paper presents position control of the tip of a ladle, namely, a pouring mouth in a ladle, by means of synchronous control of three-axis, and suppression-control of sloshing in a ladle during tilting motion in an automatic pouring machine. In order to precisely pour the molten metal into a sprue cup of a mold in every pouring, the position of a ladle tip is controlled by the servo-control system to be kept at the fixed coordinate in three-dimensional space during tilting motion for the pouring. In addition to its servo-control, an input shaping control approach is applied to suppress the residual vibration of sloshing inside a ladle when the ladle is tilted backward after every pouring. The effectiveness of the proposed approach is demonstrated through simulations and experiments.

Stiction can be a major detriment to the performance of machines that move at low velocities or attempt to position with high accuracy. The control of machines with stiction is further complicated if the machine has flexible dynamics that lead to vibration and transient deflection. Command generation schemes have recently been shown to eliminate many of the problems associated with flexible dynamics. This paper investigates the use of command generation techniques for reducing the effects of stiction, as well as vibration. It is shown that command generation allows the positioning feedback gains to be increased, thereby reducing the positioning error associated with stiction, without increasing vibration.

Systems that exhibit flexible dynamics are susceptible to vibration caused by changes in the reference command, as well as, from external disturbances. Feedback control is an obvious choice to deal with these vibrations, but in many cases it is insufficient. Input shaping has proven very beneficial for reducing vibration that is caused by changes in the reference command. However, input shaping does not deal with vibration induced by external disturbances. On the other hand, vibration absorbers are an open-loop method that have long been used to decrease vibration from external sources, particularly sinusoidal disturbances. In this paper, non linear vibration absorbers are designed to reduce vibration from step disturbances. Furthermore, input shaping is combined with the absorbers in order to deal with the vibration induced by the reference command. The usefulness of this combined approach for dealing with both external and reference command disturbances is demonstrated with computer simulations.

This paper presents a two-degree-of-freedom control that allows the molten-metal of tilting-type pouring machine both to attain the requested angle during the backward-tilting portion of its cycle and reduce the liquid vibration normally caused by this motion. To this end, the feedforward part is constructed using the input shaping method, and a feedback compensation is performed based on the H ∞ loop shaping method. Furthermore, two kinds of model are used, and an useful application way of two different types of models for the same problem is presented, aiming at the integration of fluid analysis and control design.

This paper presents an approach for designing multi-input shapers using an s-plane pole placement technique. Slightly more information about the system model is taken into account than has been traditionally done with input shaping designs. The input shaping sequences for all system inputs are solved for simultaneously, and the resulting designs lead to shorter impulse sequences than solving for input shaping sequences for each input independently of each other.

Input shaping is a method of reducing residual vibrations in computer controlled machines. Vibration is eliminated by convolving a sequence of impulses with a desired system command to produce a shaped input that is then used to command the system. Techniques for designing input shapers for two-mode systems are presented. The properties of the various shapers are compared as a function of the mode ratio. Experimental data demonstrate key results.

The performance of many spacecraft can be improved by using closed-loop control and command-shaping techniques. However, since little information exists about the operation of controlled structures in zerogravity, it is difficult for designers to anticipate and place confidence in the on-orbit performance of their ground based control designs. To address this issue, the Middeck Active Control Experiment (MACE) was conducted aboard the Space Shuttle Endeavor in March of 1995. This paper presents the results of the command shaping experiments implemented during the mission and proposes guidelines for using command shaping to suppress unwanted vibration in flexible space structures.

The paper compares two input shaping methods designed to prevent the excitation of oscillatory modes in resonant systems. The first method produces a control signal that is the linear combination of delayed versions of the reference input. The resulting control system is linear time-invariant but infinite-dimensional. Its transfer function has an infinite number of complex zeros, and some of them are being placed exactly at the locations of the resonant modes of the plant. In contrast, the second method is based on a pole/zero cancellation of the resonant modes using a finite-dimensional controller. Experimental results are presented for a system in which a DC motor is used to control the position of a flexible arm. The step response of the plant is poorly damped, but the transient response is much improved when either input shaping method is used. It is shown that a simple method can be incorporated in the second method for the automatic adjustment of the controller parameters, making it particularly attractive.

Input shaping reduces residual vibrations by convolving a sequence of impulses, an input shaper, with the desired system command. Using negative impulses in the shaper leads to faster maneuvers. Unfortunately, when negative input shapers are used, there is no guarantee that the shaped command will satisfy actuator limitations. A new type of negative input shaper is presented that satisfies actuator limits for a large class of unshaped commands. The performance of these input shapers is compared to the time-optimal control and other types of input shapers.