Computed Torque Control Research Articles

Dynamic visual servoing with Kalman filter-based depth and velocity estimator

Camera calibration error, vision latency, nonlinear dynamics, and so on present a major challenge for designing the control scheme for a visual servoing system. Although many approaches on visual servoing have been proposed, surprisingly, only a few of them have taken into account system dynamics in the control design of a visual servoing system. In addition, the depth information of feature points is essential in the image-based visual servoing architecture. As a result, to cope with the aforementioned problems, this article proposes a Kalman filter-based depth and velocity estimator and a modified image-based dynamic visual servoing architecture that takes into consideration the system dynamics in its control design. In particular, the Kalman filter is exploited to deal with the problems caused by vision latency and image noise so as to facilitate the estimation of the joint velocity of the robot using image information only. Moreover, in the modified image-based dynamic visual servoing architecture, the computed torque control scheme is used to compensate for system dynamics and the Kalman filter is used to provide accurate depth information of the feature points. Results of visual servoing experiments conducted on a two-degree of freedom planar robot verify the effectiveness of the proposed approach.

Development of a model reference computed torque controller for a human lower extremity exoskeleton robot

Exoskeleton robot–based neurorehabilitation has received a lot of attention recently due to positive evidence supporting its ability to provide different forms of physical therapy and in helping evaluate the patient recovery rate accurately. The performance of exoskeleton robot–based physical therapy depends on the accuracy of the motion control system. While the computed torque control scheme based on inverse dynamics is ideal from a theoretical perspective, the stability and tracking performance strongly depends on the model accuracy. Expecting a deterministic payload for a rehabilitation robot is impractical, which makes the computed torque controller unrealistic for such an application. In this article, a 7-degree-of-freedom human lower extremity dynamic model is developed using the Lagrange method and a novel Model Reference Computed Torque Controller is utilized for control. The computed torque controller is used to estimate the joint torque requirements for tracking a trajectory. Calculated joint torques are applied to a similarly structured plant with different parameters. The deviation of the plant from the model is calculated. A proportional–integral–derivative controller is employed to force the plant to behave like the robot model. A realistic friction model is incorporated to simulate joint friction in the plant. The stability and tracking performance of the control system is presented for sequential as well as simultaneous joint movements. To verify the robustness of the developed controller, analysis of variance statistical technique is used.

Novel Omnidirectional Aerial Manipulator With Elastic Suspension: Dynamic Control and Experimental Performance Assessment

Aerial manipulators may replace industrial manipulators for specific tasks involving large workspaces and high dynamics. However, these robots suffer from a lack of accuracy, autonomy, payload capability and a complex regulatory environment. To overcome some of these limitations, we introduce a novel aerial manipulator suspended by a spring to a robotic carrier. A computed torque controller with exteroceptive feedback is used to control the robot, using singular perturbation theory to prove the stability. We carried out various experiments to assess the workspace, accuracy and dynamics of the manipulator.

Control and signal filtering system for a quadcopter; analysis, comparison and implementation via low-cost IMU and microcontroller

This work presents the development, analysis and comparison of dynamic models, to implement in a simple way a filtering and control system for a quadcopter through the use of a microcontroller. A non-linear dynamic model obtained from the Euler Lagrange equations is approached, also a simplified non-linear model from the first model and a linear model are obtained. Subsequently, making use of each model, controllers are designed using the computed torque controller technique, then, their performance index is obtained through numerical simulations applied to the complete non-linear model to compare their response. Afterward, with the various models and through observers and Kalman filters, signal filtering systems are synthesized for a low-cost Inertial Measurement Unit (IMU), the filtering results are also compared using a performance index, later, the model and filtering system are selected to implement the controller. Finally, the selection of the model, the controller and filtering are validated through experimentation with a quadcopter prototype developed by the authors, based on an experimental platform with four rotors, a fiberglass structure, a microcontroller and an IMU MPU 6050.

A strategy to decelerate and capture a spinning object by a dual-arm space robot

With the increasing requirement of grasping the non-cooperative objects in space by space robots, this paper introduces a new strategy operated by a dual-arm space robot. The strategy includes path planning to capture a spinning target, hybrid control of the motion and the contact force for the end-effectors, coordinated control of the base attitude, and parameter identification of the spinning target during the capture phase. Notably, a pair of proper contact forces can be applied to the two grasp points of the spinning target by the two manipulators, which can decelerate the spinning speed of the target and be utilized to identify the target's moment of inertia around its spinning axis. Considering the non-cooperative situation with the spinning target like a defunct satellite, the uncertainties of the space robot and the target, such as parameters of mass and moment of inertia, are concerned in the design of the Sliding Mode Controller (SMC) with good robustness. Moreover, due to the coupling movement of the base and arms of a dual-arm space robot, the base attitude will be simultaneously maintained by the mounted reaction wheels during the capture operation for good communications and effective solar energy collection. The post-capture process is also presented in the paper to bring the entire system of the space robot and the target into stationary status. To compare the system performance against the uncertainties by different controllers, PID-type Computed Torque Controller (CTC) and SMC are designed together for comparison. When the uncertainties of the mass and the moment of inertia are applied to the system, the simulation results show that SMC has better performance against the uncertainties by delivering higher accuracy of the tracking errors to the desired trajectories than CTC.

VIRTUAL COMMISSIONING, DIGITAL TWIN AND CONTROL STRATEGIES APPLIED IN THE INDUSTRIAL ROBOT PUMA 560

The objective of this work is the evaluation, through computational simulation, of the performance and behavior of the PUMA 560 robot under different types of motion controllers. Nominal models for control design were obtained through linearization of the robot dynamic model considering selected points of operation through Denavit-Hartenberg (DH) modeling and convention. In addition to a PID joint decentralized control law and a computed torque control law that had already been implemented in the simulator, it was implemented a predictive control law and a robust control law as well. Tuning of the parameters of these control laws were performed for the Puma 560 robot and each control system was evaluated through simulation. Results about the controller design and the control system simulation were collected and discussed. Completing this study aimed to analyzing a six degree of freedom robot manipulator motion control taking in account performance and robustness aspects, it was chosen a particular structure and introduced a force control loop; this controller design and simulator extension allowed an evaluation of some force control aspects and digital twin.

Robust trajectory tracking control of a 6-DOF robotic crusher based on dynamic compensation

A robust controller is developed for the trajectory tracking control of a 6-DOF robotic crusher in task space. Firstly, the dynamic model including the mantle assembly and actuators is derived by Lagrange method according to the virtual work principle. In order to simulate the crushing behavior of cone crusher in the crushing chamber, the trajectory model of the mantle assembly is achieved by ADAMS. Then, a robust controller which contains the dynamic compensation is designed, and the convergence stability of the 6-DOF robotic crusher is strictly proved based on Lyapunov stability theory. Finally, the co-simulation is used to verify that the proposed controller can solve the problem of model uncertainties and external disturbances well. Meanwhile, numerical simulation results of the 6-DOF robotic crusher illustrate the proposed controller is able to effectively reduce the trajectory tracking errors compared with the computed torque controller.

Modeling and adaptive torque computed control of industrial robot based on lie algebra

Computed Torque Control (CTC) is the most direct and effective way to improve the motion control performance of robot. But the computation of the joint torque is quite difficult, and because of the uncertainty of the parameters, an accurate inverse robot dynamic model for torque generation is difficult to obtain. An efficient inverse dynamic model of the industrial robot based on lie algebra is proposed and applied to the computed torque control. In order to overcome the uncertainty of parameters, the inverse robot dynamic model is linearized and an adaptive computed torque control is proposed. In order to validate the adaptive torque computed control method, a multi-domain integrated system model of 6-DOF industrial robot is established and the simulation results show that the adaptive computed torque control system has the function of parameter self-learning, the inaccurate parameters converge to the true value finally. The adaptive control shows better control performance than the traditional computed torque control.

A PD Computed Torque Control Method with Online Self-gain Tuning for a 3UPS-PS Parallel Robot

SUMMARYIn this paper, an online self-gain tuning method of a PD computed torque control (CTC) is used for a 3UPS-PS parallel robot. The CTC is applied to the 3UPS-PS parallel robot based on the robot dynamic model which is established via a virtual work principle. The control system of the robot comprises a nonlinear feed-forward loop and a PD control feedback loop. To implement real-time online self-gain tuning, an adjustment method based on the genetic algorithm (GA) is proposed. Compared with the traditional CTC, the simulation results indicate that the control algorithm proposed in this study can not only enhance the anti-interference ability of the system but also improve the trajectory tracking speed and the accuracy of the 3UPS-PS parallel robot.

Computed Torque Control Method for Two-Axis Planar Serial Robotic Arm

The heat generated in reactor core is extracted using the sodium water heat exchanger system in fast breeder reactor. In the heat exchanger system there are 8 steam generators. Steam generator uses sodium and water to generate steam. Sodium–water reaction is exothermic in nature, so SG tubes need inspection to check healthiness of the tube. Due to space constraints, in-service inspection of SG needs remote-controlled robotic arm to locate SG tubes. The tube sheet is planar, so revolute joint two-link robotic arm is adapted. The movement of two-axis robotic arm needs control on position as well as velocity. The dynamic equation of two-axis robotic arm is coupled in nature which makes the control of end effector very difficult. The un-modeled phenomena, as that of friction and errors in mass distribution, will drastically affect the tracking of the end effector in the desired path. The Coriolis Effect is also accounted in the model. To precisely control the robotic arm end effector, the computed torque control technique is proposed and used in this paper.

Position-Based Fractional-Order Impedance Control of a 2 DOF Serial Manipulator

SUMMARYImpedance control is one of the interaction and force control methods that has been widely applied in the research of robotics. In this paper, a new position-based fractional-order impedance control scheme is proposed and applied to a 2 DOF serial manipulator. An RR robot manipulator with full arm dynamics and its environment were designed using Matlab/Simulink. The position control of the manipulator was utilized based on computed torque control to cancel out the nonlinearities existing on the dynamic model of the robot. Parameters of classical impedance controller (CIC) and proposed fractional-order impedance controller (FOIC) were optimized in order to minimize impact forces for comparison of the results in three conditions. In CIC condition: three constant parameters of the impedance controller were optimized: in Frac_λμ condition: Only non-integer parameters of the FOIC were re-optimized after the parameters in CIC had been accepted, and in Frac_all condition: all parameters of the FOIC were re-optimized. In order to show the effectiveness of the proposed method, simulations were conducted for all cases and performance indices were computed for the interaction forces. Results showed that impacts were reduced with an improvement of 26.12% from CIC to Frac_ λμ and an improvement of 47.21% from CIC to Frac_all. The proposed scheme improves the impedance behavior and robustness showing better impact absorption performance, which is needed in many challenging robotic tasks and intelligent mechatronic devices.

Adaptive nonlinear robust control of an underactuated micro UAV

In this article, we investigate a robust nonlinear control strategy to solve the trajectory tracking for a micro unmanned aerial vehicle, the quadrotor. The control technique is the computed torque control (CTC), this technique is widely used in the robot manipulators control. The CTC technique needs a strong knowledge of the model. In this regard, the complete dynamic model of the quadrotor has been established by the Euler–Lagrange formalism. After that, a robust nonlinear H∞ controller has been designed to stabilize the system with robustness. The proposed controller takes into account the underactuation characteristic of the quadrotor, so the controller is designed for the actuated degrees of freedom (DOF) with their coupling with the underactuated DOF. For the position tracking, we propose the backstepping controller. In both controllers, nonlinear H∞ and backstepping, the integral action is considered to get a null steady-state error. In order to improve performance quality, the control law has been reinforced by an adaptive action. This last has been performed by the linear parameterization property and the neural networks. The results show efficiency in the parametric uncertainties.

Disturbance-Observer-Based Model Predictive Control of Underwater Vehicle Manipulator Systems

Abstract This paper presents a disturbance-observer-based Model Predictive Control (MPC) for Underwater-Vehicle Manipulators Systems (UVMSs). First, the nominal MPC is formulated considering the lumped uncertainties representation for unknown terms and external disturbances. Then, a second-order Sliding Mode Disturbance Observer (SMDO) is developed to estimate the lumped disturbances, which are used by the MPC to produce unbiased predictions. The MPC-SMDO is tested through numerical simulations, considering a 5-DoF planar UVMS composed of the classical Twin-Burger autonomous vehicle presented in Ishitsuka et al. (2005) endowed with a 2-link robotic manipulator. To obtain realistic results, sensor noises, the dynamics of thrusters, and the stochasticity of ocean current are considered in the simulations. The results show good performance for the MPC-SMDO in terms of robustness, constraints meeting, and tracking errors minimization compared to two other controllers, based on the Computed Torque Control (CTC) technique and on the Super-Twisting Algorithm (STA).

On the Dynamics and Computed Torque Control of an Asymmetric Four-Limb Parallel Schonflies Motion Generator

This paper deals with the dynamic analysis and control of a four-limb parallel Schoenflies-motion generator dedicating to fast pick-and-place operations, with an asymmetric topological architecture for saving mounting space. The concise equation of motion is built with principle of virtual work to characterize robot dynamics. Computed torque control is adopted to design the control scheme, of which the control variables are optimized by minimizing the errors of joint variables.

Feedback Control Design for Robust Comfortable Sit-to-Stand Motions of 3D Lower-Limb Exoskeletons

Lower-limb exoskeletons provide people who suffer from lower limb impairments with an opportunity to stand up and ambulate. Standing up is a crucial task for lower-limb exoskeletons as it allows the user to transfer to the exoskeleton from a wheelchair, with no assistance, and can be a precursor to walking. Achieving a safe sit-to-stand motion for the exoskeleton + user system can be challenging because of the need to balance user comfort while respecting hardware bounds and being robust to changes in the user characteristics and the user's environment. We successfully achieve safe sit-to-stand motions by using constrained optimization to generate two types of dynamic sit-to-stand motions based on two hybrid system descriptions for the exoskeleton, Atalante. Due to the highly constrained nature of the equations of motions, we introduce a method to systematically design virtual constraints for highly constrained systems. We also design two quadratic program-based computed-torque controllers to achieve the sit-to-stand motion and to safely come to a stop in a standing position. We then analyze the closed-loop behaviors of the two sit-to-stand motions under the two controllers using physically motivated robustness tests. The criteria used to determine a successful sit-to-stand motion are: tracking error, the pitch acceleration of the torso, the amount of user force needed to perform the motion, and the adherence to the Zero Moment Point (ZMP), friction, and joint constraints.

The nonlinear computed torque control of a quadrotor

<p>This paper work focused on the study of the nonlinear computed torque<br />control of a quadrotor helicopter. In order to model the dynamic of the<br />vehicles, kinematics and dynamics modeling of the X4 is presented. Euler<br />angles and parameters are used in the formulation of this model and the<br />technique of Computed Torque control is introduced. In the second part of<br />the paper, we develop a methodology of control that allows the quadrotor to<br />accomplish a prospecting mission of an environment, as the follow-up of a<br />trajectory by the simulation. Results show that Computed Torque control<br />method is suitable for X4.</p>

Dynamic analysis and decoupled control of a heavy-duty walking robot with flexible feet based on super twisting algorithm

In this paper, the dynamics and control strategies of a biped robot with 6-DOF parallel leg mechanism are studied. Firstly, the multi-body kinematic model and dynamic model of the robot are established. Secondly, the insufficient stiffness of robot’s feet and the coupling effect between the kinematic chains are considered in dynamics modeling, and the rigid-flexible coupling model is established by using ADAMS and finite element method. Finally, aiming at the position deviation and system vibration caused by the flexible foot, a strategy based on the combination of a computed torque controller (CTC) and a second-order sliding-mode super twisting algorithm (STA) is designed. At the same time, the control strategy based on CTC and PID and the control strategy based on CTC and sliding mode control (SMC) are designed to compare with CTC-STA. The results show that CTC-STA has faster regulation ability and stronger robustness than CTC-SMC and CTC-PID.

One-Step Deadbeat Control of a 5-Link Biped Using Data-Driven Nonlinear Approximation of the Step-to-Step Dynamics

For bipedal robots to walk over complex and constrained environments (e.g., narrow walkways, stepping stones), they have to meet precise control objectives of speed and foot placement at every single step. This control that achieves the objectives precisely at every step is known as one-step deadbeat control. The high dimensionality of bipedal systems and the under-actuation (number of joint exceeds the actuators) presents a formidable computational challenge to achieve real-time control. In this paper, we present a computationally efficient method for one-step deadbeat control and demonstrate it on a 5-link planar bipedal model with 1 degree of under-actuation. Our method uses computed torque control using the 4 actuated degrees of freedom to decouple and reduce the dimensionality of the stance phase dynamics to a single degree of freedom. This simplification ensures that the step-to-step dynamics are a single equation. Then using Monte Carlo sampling, we generate data for approximating the step-to-step dynamics followed by curve fitting using a control affine model and a Gaussian process error model. We use the control affine model to compute control inputs using feedback linearization and fine tune these using iterative learning control using the Gaussian process error enabling one-step deadbeat control. We demonstrate the approach in simulation in scenarios involving stabilization against perturbations, following a changing velocity reference, and precise foot placement. We conclude that computed torque control-based model reduction and sampling-based approximation of the step-to-step dynamics provides a computationally efficient approach for real-time one-step deadbeat control of complex bipedal systems.

Feedback linearization control for a tandem rotor UAV robot equipped with two 2-DOF tiltable coaxial-rotors

In this paper, computed torque control as one method of feedback linearization techniques is considered for an unmanned aerial vehicle (UAV) robot that has two tiltable coaxial rotors so as to realize multifunctional locomotion modes, where each rotor has 2-DOF tilt mechanism. First, a dynamical model of such an UAV robot is derived following the Newton–Euler law. Next, under the assumptions that the anti-torque of the tiltable coaxial rotors is zero and the gyro moment effect of the tiltable coaxial rotors can be ignored, a computed torque controller is derived, because the resultant model of the UAV robot can be simplified to a fully actuated model, which has six motion inputs and six generalized coordinate outputs. In addition, a control allocation problem of the system, in which the control inputs designed using the dynamical model are assigned to all motors for tilting the rotor as well as rotating it, is solvable by using a Moore–Penrose pseudo-inverse, where a coordinate transformation is used to simply the allocation problem. Finally, some simulations are demonstrated to verify the effectiveness of the computed torque control strategy for the robot.

A New Computed Torque Control System with an Uncertain RBF Neural Network Controller for a 7-DOF Robot

A New Computed Torque Control System with an Uncertain RBF Neural Network Controller for a 7-DOF Robot