Future Desired Trajectory Research Articles

Trajectory Deformations From Physical Human–Robot Interaction

Robots are finding new applications where physical interaction with a human is necessary: manufacturing, healthcare, and social tasks. Accordingly, the field of physical human-robot interaction (pHRI) has leveraged impedance control approaches, which support compliant interactions between human and robot. However, a limitation of traditional impedance control is that---despite provisions for the human to modify the robot's current trajectory---the human cannot affect the robot's future desired trajectory through pHRI. In this paper, we present an algorithm for physically interactive trajectory deformations which, when combined with impedance control, allows the human to modulate both the actual and desired trajectories of the robot. Unlike related works, our method explicitly deforms the future desired trajectory based on forces applied during pHRI, but does not require constant human guidance. We present our approach and verify that this method is compatible with traditional impedance control. Next, we use constrained optimization to derive the deformation shape. Finally, we describe an algorithm for real time implementation, and perform simulations to test the arbitration parameters. Experimental results demonstrate reduction in the human's effort and improvement in the movement quality when compared to pHRI with impedance control alone.

Guidance system for control periods under modelling threshold

This paper presents a new guidance system for process control that can improve the control performance of model-based advanced controllers or optimised adaptive controllers, when their control periods have to be selected within a lower range of time values that may increase the sensitivity of the predictive model parameters to identification errors. The guidance system generates at each control instant a future desired trajectory for the process output variable under control, from which it computes a set point for the derivative variable of the process output variable. A predictive or adaptive predictive controller drives the derivative variable to its set point and, as a consequence, the process output converges towards said desired trajectory. The new guidance system is illustrated by its application to the level control of a MIMO nonlinear process, in the presence of noises and disturbances. The results show how the control performance of the guidance system is not affected by 'small' control periods that would deteriorate the performance of an adaptive predictive controller for the same application.

B-Spline-Decomposition-Based Approach to Multiaxis Trajectory Tracking: Nanomanipulation Example

In this brief, a B-spline-decomposition (BSD)-based approach to output tracking with preview is explored to achieve high-speed, large-range nanomanipulation in experiments. The BSD approach is developed to address challenges in preview-based output tracking of nonminimum-phase systems to achieve precision tracking with good robustness to dynamics variations and no demanding online computation. In the BSD approach, a library of output elements and their corresponding input elements is constructed a priori ; then the previewed future desired trajectory is decomposed into a finite number of output elements, and the control input is synthesized using the corresponding input elements with chosen pre- and post-actuation times. The BSD technique uses the uniform B-splines to construct the output elements, the iterative learning control techniques to obtain the input elements, and the stable-inversion theory to quantify the pre- and post-actuation times. In this brief, we demonstrate and evaluate the BSD technique for preview-based precision tracking in experiments, by implementing it to a nanomanipulation application using a scanning probe microscope. The experiments showed that the tracking speed can be substantially improved using the BSD technique over using feedback control alone.

Formula omitted]-spline-decomposition-based output tracking with preview for nonminimum-phase linear systems

This article proposes a B-spline-decomposition-based approach to output tracking with preview for nonminimum-phase (NMP) systems. It has been shown that when there exists a finite (in time) preview of future desired trajectory, precision output tracking of NMP systems can be achieved by using the preview-based stable-inversion technique. The performance of this approach, however, can be sensitive to system dynamics uncertainty, and the computation involved can be demanding. We propose to address these challenges by integrating the notion of trajectory decomposition with the iterative learning control (ILC) technique. Particularly, the B-splines are used to construct a library of output elements and the corresponding input elements a priori, and the ILC techniques are used to obtain the input elements for precision tracking of the output elements. During the tracking with preview, the previewed future desired trajectory is decomposed by using the output elements, and the input is synthesized by using the corresponding input elements with chosen pre- and post-actuation times. The required pre-/post-actuation times are quantified based on the stable-inversion theory. The use of B-splines substantially reduces the number of output elements in the library, and the decomposition-synthesis occurs only at time instants separated by the difference between the preview time and pre-actuation time. The proposed approach is illustrated through a simulation study of nanomanipulation application using a NMP piezo actuator model.

Using future path information for improving the stability of an over-actuated vehicle

In this paper, model predictive control (MPC) is applied for controlling an over-actuated vehicle. The control problem is associated with the distribution of the tyre forces to ensure vehicle stability. The use of MPC is shown to be a suitable method if the vehicle's future desired trajectory is known. Simulation studies conducted show that access to information in advance, even if such information is restricted to only a few seconds, significantly contributes to maintaining vehicle stability. Furthermore, a longer prediction horizon results in earlier actions and stabilises the vehicle even better.

Optimal preview-based stable-inversion for output tracking of nonminimum-phase linear systems

In this article, a new approach to output tracking of nonminimum-phase systems is proposed. The proposed technique extends the preview-based stable-inversion method to optimally utilize finite-preview (in time) of the future desired output trajectory to find the feedforward input (called the inverse input) for achieving precision output tracking for nonminimum-phase systems. It has been shown that having a large enough preview time is critical to ensure the precision in the preview-based output tracking. The available preview time, however, can be limited due to the physical constraints, and more generally, the associated cost and/or hardware limits. Therefore, we propose obtaining the optimal preview-based inverse input by minimizing, within the preview time window, the predicted tracking error (under the preview-based inverse input) relative to the input energy. A simulation study on a piezoelectric actuator model is used to illustrate the proposed technique.

Precision preview-based stable-inversion for nonlinear nonminimum-phase systems: The VTOL example

This article quantifies the importance of the future desired trajectory in determining the exact-output-tracking input for nonlinear, nonminimum-phase systems by using system inversion techniques. It is intuitive that the effect of the desired output's distant-future values, on the output-tracking input at the current time instant, should be small. Therefore, at a current time instant ( t c ) , preview information of the desired output in a finite-time window [ t c , t c + T p ] should be sufficient to compute the output-tracking input with an arbitrarily small prescribed error, if the preview time T p is sufficiently large. The contribution of this article is the quantification of the needed preview time T p by using the benchmark VTOL aircraft model as an example. Additionally, simulation results are presented to evaluate the efficacy of the finite-preview-based stable-inversion approach.

Cancellation of Discrete Time Unstable Zeros by Feedforward Control

This paper presents a design methodology for the cancellation of unstable zeros in linear discrete time systems with tracking control objectives. Unstable zeros are defined to be those zeros of the rational transfer function that occur outside the unit circle. Unstable zeros cannot be canceled by feedback without compromising stability. In light of this fact, a feedforward scheme is used. Future desired trajectory information is required because the feedforward scheme is noncausal. The amount of future desired trajectory information that is required depends upon the zero locations and design specifications. It is shown that for a known plant with no zeros on the unit circle one can obtain a frequency response arbitrarily close to 1. Robustness issues and simulation results are discussed.

Robust missile autopilot design using a generalized singular optimalcontrol technique

The generalized singular linear quadratic (GSLQ) control technique is developed to design an optimal time-varying trajectory tracking system. The feedforward command in this system is generally computed by integrating a reduced-order system backward in time with the Future desired trajectory and the estimated disturbance or nonlinearity as the input. The output feedback control law is designed using the GSLQ contra1 techniqqe. The feedback gain matrix is synthesized to ' minimize tracking errors with pole placement capability to satisfy the control activity requirements. The resulting tracking system is capable of determining the current optimal control strategy based on the future desired trajectory. The modeling error terms such as the uncertainty, nonlinearity, and the anticipated forcing function are included in the GSLQ control problem formulation, enabling the resulting control law to adapt to these modeling changes as long as they can be approximately estimated on-line. An application of the GSLQ technique to a bank-to-turn (BlT.) missile coordinated autopilot system design is presented. The time varying tracking autopilot is f rmulated as an optimal linear tracking system pro lem consisting of an adaptive feedforward control er and a robust output feedback controller wi if robust output feedback gains, both designed b the GSLQ control technique. The closed loop system of the resulting control law is stable for a wide range of flight conditions with little changes in the location of the closed loop eigenvalues. The control loop frequency response of six flight conditions during the terminal phase are presented to show the robustness of an output feedback controller design using the GSLQ technique. Simulations of the time responses of the tracking system with sinusoidal wave disturbances and pitch, roll, and yaw nonlinear couplings are also presented to show the GSLQ control technique for tracking autopilot with adaptive feedforward control.