Serial Robot Manipulators Research Articles

Sampled-data control of pan-tilt platform using discrete-time high gain observer

In this paper we have presented the design of sampled-data control algorithm for Pan-tilt platform using Discrete-time High Gain Observer (DHGO). The Pan-Tilt platform is a 2-axis serial robotic manipulator having a nonlinear dynamic model. The design of the control algorithm is carried out in 2 steps. In 1st steps, a continuous time state feedback control law based on feedback linearization is designed which is subsequently discretized. In the second stage, the states of the system are estimated using DHGO. To evaluate the performance of the suggested algorithm extensive simulations are carried out in Matlab Simulink.

Development and motion control of spatial serial robotic manipulator under varying disturbances

PurposeKey challenges in evaluating the performance of a robotic manipulator are disturbances that rise internally and externally. Effects of non-linear disturbances like varying payload and joint friction can adversely affect the tracking performance in a robotic manipulator. This paper aims to discuss motion control of a three-link spatial manipulator using a computed torque observer-based control technique.Design/methodology/approachThe overall motion control problem consists of derivation of kinematic and dynamic model of the manipulator followed by the control design to achieve desired manipulator response. In this study, the manipulator is subjected to uncertain varying load disturbances. The proposed motion controller compensates the effect of the disturbances and guarantees the convergence of tracking error to steady state value.FindingsOne major advantage of using observer-based control is positioning accuracy with robustness to parameter uncertainty and fast dynamics response. The performance of the proposed control technique is validated through real-time experiments conducted on the manipulator. The experiment results confirm the superior performance of the control system in achieving perfect tracking.Originality/valueThis paper demonstrates an observer-based control technique over a serial spatial manipulator which can be applied different robotic configurations under the effect of varying disturbances.

Kinematic Synthesis of a Serial Robotic Manipulator by Using Generalized Differential Inverse Kinematics

In this paper, we propose an optimization method to determine the design parameters comprising joint displacement parameters in a serial manipulator having small degrees of freedom realizing an approximated target trajectory. Using generalized differential kinematics, we can achieve efficient optimization without solving the inner-loop optimization required to obtain the reachable points.

Extended Order High Gain Observer Based Stabilization of 2 DOF Pan Tilt Platform for Aerial Imaging System

Aerial imaging systems are mounted on two axis serial robotic manipulators with high powered pan and tilt actuations, known as a Gimbal. The angular displacement of the gimbal is measured through very high precision sensors, typically shaft encoders with high PPR specifications. The purpose of the gimbal is to keep the orientation of the payload towards the target irrespective of the displacement of the UAV (unmanned aerial vehicle) and any other vibrations/disturbances that might be introduced into the system. Because of 2-DOF (degrees of freedom) dynamical model of the gimbal, frictional force, noise, cable restraint, disturbances from the external environment along with the motions of the vehicle’s body (as a result of manoeuvring or vibration), the spotting and tracking accuracy of the gimbal platform system may significantly degrade. The nature of these redundant disturbances is mostly of nonlinear nature and their modelling is a difficult task as they keep on changing. In order to cancel out these redundant disturbances and uncertainties, extended order high gain observer (EHGO) based feedback linearization control is used and extensive simulations are performed to show the comparison of tracking control without EHGO and after augmenting EHGO.

Voltage based sliding mode control of flexible joint robot manipulators in presence of uncertainties

In this paper, a voltage-based sliding mode control (SMC) is presented to control the position of n rigid-link flexible-joint (RLFJ) serial robot manipulator in the presence of structured and unstructured uncertainties. In addition to good performance, the proposed method has three attracting properties: First, it has been developed for a class of RLFJ robot manipulators with a n degree of freedom (DOF). Second, the design process includes all the manipulator dynamical equations, the mechanical and the electrical part of the actuator. Third, the simple structure and low volume of computing make practical implementation possible. Using the idea of the independent joint control strategy, the system dynamic equations are decomposed into n independent subsystems. For each subsystem, three sliding surfaces are defined. Then using these sliding surfaces, control input laws are designed for all subsystems simultaneously. It is proved that the proposed method can guarantee the asymptotic stability of each subsystems and the global asymptotic stability of the closed-loop system in the presence of uncertainties. The results of simulations, as well as experimental results produced using MATLAB/Simulink external mode control on a flexible-joint electrically driven robot manipulator, illustrate high efficiency of the proposed control schemes.

Design and Modeling of a Three-Degree-of-Freedom Articulating Robotic Microsurgical Forceps for Trans-Oral Laser Microsurgery

Trans-oral laser microsurgery (TLM) is a surgical procedure for removing malignancies (e.g., cysts, polyps, tumors) of the laryngeal region through laser ablation. Intraoperative microsurgical forceps (i.e., microforceps) are used for tissue manipulation. The microforceps are rigid, single degree-of-freedom (DOF) devices (open–close) with precurved jaws to access different parts of the curved cylindrical laryngeal region. These microforceps are manually handled and are subject to hand tremors, poor reachability, and nonergonomic use, resulting in poor efficacy and efficiency in the surgery. A novel 3DOF motorized microforceps device is presented here, integrated with a 6DOF serial robotic manipulator. The device, referred to as RMF-3, offers three motorized DOFs: (i) open–close forceps jaw; (ii) tool rotation; and (iii) tool-tip articulation. It is designed to be compliant with TLM spatial constraints. The manual handling is replaced by tele-operation device, the omega.7. The design of the RMF-3 is characterized through theoretical and experimental analysis. The device shows a maximum articulation of 38 deg and tool rotation of 100 deg. Its performance is further evaluated through user trials using the ring-in-loop setup. The user trials demonstrate benefits of the 3DOF workspace of the device along with its teleoperation control. RMF-3 offers an improved workspace and reachability within the laryngeal region. Surgeons, in their preliminary evaluation of the device, appreciated the ability to articulate the tip, along with rotation, for hard-to-reach parts of the surgical site. RMF-3 offers an ergonomic robotic teleoperation control interface which overcomes hand tremors and extreme wrist excursion which leads to surgeon pain and discomfort.

A meta-heuristic proposal for inverse kinematics solution of 7-DOF serial robotic manipulator: quantum behaved particle swarm algorithm

In this study, a quantum behaved particle swarm algorithm has used for inverse kinematic solution of a 7-degree-of-freedom serial manipulator and the results have been compared with other swarm techniques such as firefly algorithm (FA), particle swarm optimization (PSO) and artificial bee colony (ABC). Firstly, the DH parameters of the robot manipulator are created and transformation matrices are revealed. Afterward, the position equations are derived from these matrices. The position of the end effector of the robotic manipulator in the work space is estimated using Quantum PSO and other swarm algorithms. For this reason, a fitness function which name is Euclidian has been determined. This function calculates the difference between the actual position and the estimated position of the manipulator end effector. In this study, the algorithms have tested with two different scenarios. In the first scenario, values for a single position were obtained while values for a hundred different positions were obtained in the second scenario. In fact, the second scenario confirms the quality of the QPSO in the inverse kinematic solution by verifying the first scenario. According to the results obtained; Quantum behaved PSO has yielded results that are much more efficient than standard PSO, ABC and FA. The advantages of the improved algorithm are the short computation time, fewer iterations and the number of particles.

Passivity‐based adaptive control of a 2‐DOF serial robot manipulator with temperature dependent joint frictions

SummaryMechanical systems are always suffering from the effects of temperature dependent friction forces where the system is operated in a wide range of temperature. Temperature and its variation play an important role in friction force in mechanical systems. If it is not compensated, it will tend to unwanted consequences, including steady‐state errors, limit cycling, and hunting. Therefore, it is necessary to take the temperature effects into account. This has been a strong motivation for the researchers to work on temperature effects on joint friction. In this paper, an adaptive compensation (control) scheme is proposed and applied to a 2‐degree‐of‐freedom serial robot manipulator by taking the temperature effects into account on the joints friction. In the proposed control scheme, the temperature is not required to be sensed. In this paper, joint friction is described by LuGre dynamic model with temperature dependent parameters. These parameters are described by some functions with unknown temperature dependent terms. According to the mathematical and practical concepts, the temperature dependent friction is decomposed into a viscous term and a disturbance term. An adaptive controller is designed to compensate the friction effect and it is shown that the proposed controller relaxes the condition for a priori knowledge about the environment characteristics, including the upper and lower bounds of the environment temperature and the parameters of the functions, describing the temperature dependent joint frictions. The stability and convergence of the joint position and velocity are proved in the sense of Lyapunov and then the proposed method is confirmed by the simulations.

Investigation on the impact of nongeometric uncertainty in dynamic performance of serial and parallel robot manipulators

Uncertainty in robot manipulations is a fundamental source of inaccuracy. Most nongeometric uncertainties is caused by the mechanical components of robot manipulators such as gear transmission systems and joints. This study integrates existing uncertainty models for practical applications of both three-degrees-of-freedom serial robot and parallel robot (closed-loop 5R mechanism). We first review the literature on uncertainty and existing methods for improving the precision of robot manipulation. For existing methods for uncertainty modeling: (1) the mathematical model of a harmonic drive considering kinematic error and compliance is derived; (2) joint clearance analysis that includes models of contact force and friction force is presented; (3) Archard’s wear model is used to estimate the effect of joint wear, based on which the geometry of joints is updated. Computer simulation is then used to demonstrate the application of the proposed method for serial and parallel robot manipulators. Simulations are used to examine the behavior of robot manipulators operating under uncertainty, with performance-evaluated positional error and trajectory error. The proposed method can provide some insight into nongeometric uncertainty in robot manipulations. The proposed methodology can be further used to improve the accuracy of robot manipulation under uncertainty by identifying uncertainty parameters.

A robotic microsurgical forceps for transoral laser microsurgery.

In transoral laser microsurgery (TLM), the close curved cylindrical structure of the laryngeal region offers functional challenges to surgeons who operate on its malignancies with rigid, single degree-of-freedom (DOF) forceps. These challenges include surgeon hand tremors, poor reachability, poor tissue surface perception, and reduced ergonomy in design. The integrated robotic microsurgical forceps presented here is capable of addressing the above challenges through tele-operated tissue manipulation in TLM. The proposed device is designed in compliance with the spatial constraints in TLM. It incorporates a novel 2-DOF motorized microsurgical forceps end-effector, which is integrated with a commercial 6-DOF serial robotic manipulator. The integrated device is tele-operated through the haptic master interface, Omega.7. The device is augmented with a force sensor to measure tissue gripping force. The device is called RMF-2F, i.e. robotic microsurgical forceps with 2-DOF end-effector and force sensing. RMF-2F is evaluated through validation trials and pick-n-place experiments with subjects. Furthermore, the device is trialled with expert surgeons through preliminary tasks in a simulated surgical scenario. RMF-2F shows a motion tracking error of less than 400μm. User trials demonstrate the device's accuracy in task completion and ease of manoeuvrability using the Omega.7 through improved trajectory following and execution times. The tissue gripping force shows better regulation with haptic feedback (1.624N) than without haptic feedback (2.116N). Surgeons positively evaluated the device with appreciation for improved access in the larynx and gripping force feedback. RMF-2F offers an ergonomic and intuitive interface for intraoperative tissue manipulation in TLM. The device performance, usability, and haptic feedback capability were positively evaluated by users as well as expert surgeons. RMF-2F introduces the benefits of robotic teleoperation including, (i) overcoming hand tremors and wrist excursions, (ii) improved reachability and accuracy, and (iii) tissue gripping feedback for safe tissue manipulation.

Performance quantification of observer-based robot impact detection under modeling uncertainties

This work proposes a design and performance quantification methodology for observer-based impact detection in serial robot manipulators in presence of modelling errors and without force/torque sensor. After expressing the modelling errors between the physical robot and its inverse dynamic model as the sum of contributions due to dynamic parameters uncertainties and numerical differentiation errors for a given trajectory, an observer of the external disturbance torque is designed based on the inverse dynamic model and using a Kalman filter. The influence of each design parameter of the observer on the quality of the external torque estimation is studied first based on simulation results. Then a frequency analysis is conducted to distinguish between the influence of the exact external torque, the modelling uncertainties and the measurement noise on the estimated external torque. Finally a methodology is proposed to determine the optimal design corresponding to the shortest detection time depending on the expected sensitivity.

A synchroextracting-based method for early chatter identification of robotic drilling process

The robotic drilling process has shown its high industrial application potential for millions of holes in the aviation manufacturing. However, due to the relatively low stiffness of the serial robot manipulator, the robotic drilling system is more prone to chatter, leading to poor surface roughness, unbearable noise, and even causing severe damage to the end effector spindle. Consequently, it is of vital significance to identify and suppress this undesirable vibration. In this paper, a synchroextracting-based method is proposed for the early chatter detection of robotic drilling operations. The proposed algorithm is implemented through the following steps. First, the accurate time-frequency representation of the measured vibration signal is acquired by employing the synchroextracting transform (SET), which has high energy concentration and robustness to measurement noise. Second, the whole signal is divided into a finite number of frequency bands, and the corresponding sub-signal for each frequency band can be reconstructed by retaining the maximum coefficient of the SET. Finally, working as the chatter indicator, the statistical energy entropy is utilized to capture the inhomogeneous variation of energy distribution during the chatter transition process. Robotic drilling experiments with different cutting conditions were conducted to verify the effectiveness of the proposed chatter identification method. The results demonstrate that the presented synchroextracting-based algorithm can identify the chatter at an early stage, which is useful for the subsequent chatter suppression.

Design and development of a 5 DOFs robotic surgical instrument with a force feedback for RAMIS

In this paper we report the conceptual design, fabrication and validation of a surgical robotic instrument for robotic assisted minimally invasive surgery. Medical practitioners are involved in all the phases of the interactive design and prototyping of the instrument. The instrument design parameters are derived from the surgeon’s needs such as compactness with 5 mm thickness, 5 Degrees of Freedom (DOFs) to provide a wrist-like movement inside the surgical cavity and the force feedback to obtain the feel of touch. The instrument tip has a jaw like structure to support the tissue gripping. We achieved the opening and closing of this jaw with the help of a shape memory alloy (SMA). A force sensor placed near the SMA captures the forces as low as 570 mN from the surgical environment to provide the force feedback to the surgeon. This rigid body surgical instrument exerts an adequate force required for high force demanding applications such as suturing and needle insertion. In addition, we demonstrate a 4 DOFs serial robotic slave manipulator which carries the surgical instrument as an end effector. This report paves the way towards the development and commercialization of low-cost, compact and stable surgical robotic instrument and its manipulator for biomedical applications.

Reconfigurable Tolerant Control of Uncertain Mechanical Systems With Actuator Faults: A Sliding Mode Observer-Based Approach

This paper studies a key issue of developing reconfigurable fault-tolerant control to retain a nominal feedback controller and simultaneously handles actuator faults and system uncertainty, while the closed-loop system is stabilized with all control objectives achieved. A theoretical architecture of a reconfigurable control design is presented for a class of uncertain mechanical systems by using an observer technique. As a stepping stone, a nonlinear observer-based estimation mechanism is designed to reconstruct uncertain dynamics and actuator faults with the estimation error converging to zero within finite time. A reconfigurable control effort is then synthesized from the reconstructed knowledge. This control power operates as a compensation control part, and it is added to the nominal control part to accommodate system uncertainties and actuator faults. It is proved that the overall system resulted from the developed control framework has the same control performance of the nominal closed-loop system, including certain system dynamics and the nominal control effort. The effectiveness of the scheme is validated on a serial robotic manipulator.

Artificial Intelligent Fuzzy Logic Controller Applied on 6DOF Robot Arm Using LabVIEW and FPGA

In this work an efficient Artificial Intelligent Robotic Fuzzy Logic Controller (AIRFC) system have been constructed to control the robot arm. A serial link Robot manipulator with 6 Degree of Freedom (DOF) from DFROBOT of code ROB0036 is used as a case study. A fuzzy logic type1 controller is implemented on LabVIEW to control each joint of the robot arm for nonlinearity measurements and a fuzzy logic type2 controller is applied which is more suitable for uncertainty. The hardware design is implemented and finally downloaded using the Field Programmable Gate Array (FPGA) kit named PCI-7833R from National Instrument. By using the LabVIEW FPGA MODEL the target board can be detected for software implementation of the controllers’ systems. The work shows that in case of type2 fuzzy logic the rise time is less than that of type1 fuzzy logic for the shoulder, wrist roll and the gripper angles and it is higher for base, elbow and wrist pitch angles. The settling time is the same in elbow and wrist pitch angles and for the type2 fuzzy controller it is less for other angles.

Dynamic analysis of open-loop mechanisms with multiple spatial revolute clearance joints

Dynamic model of a typical open-loop mechanism with multiple spatial revolute clearance joints were established based on the Newton–Euler equations and the Hertzian contact deformation theory. An augmented constraint violation correction method was presented to solve the nonlinear dynamic equations of motion, which improved the global convergence and stability effectively. The nonlinear dynamic behaviors of a serial robot manipulator with two spatial revolute clearance joints were studied to demonstrate the effects of the location and coupling relationship of the clearance joints. Numerical results show that the influence of spatial revolute clearance joint on the dynamic behaviors of the open-loop mechanism is relatively stronger than that of the planar ones. The location of the spatial revolute clearance joints is an important factor to dynamic behavior of the system. The closer the spatial revolute clearance joint is to the end-effector, the stronger influence it has on the system. The spatial revolute clearance joints interact significantly with each another, which exhibits vigorous vibration with a higher frequency, larger amplitude, and deeper penetration. This work provides new insights into investigating the nonlinear dynamic behaviors of the systems with spatial revolute clearance joints.

Tolerance synthesis of 2R serial robot manipulator

tolerance synthesis of 2R serial robot manipulator

Iterative Learning of Feasible Time-optimal Trajectories for Robot Manipulators

Time-optimal trajectories describe the minimum execution time motion along a given geometric path while taking system dynamics and constraints into account. By using a model of the real plant, inputs are provided that ought to yield minimal execution time and good tracking performance. In practice however, due to an imperfect model, the computed inputs might be suboptimal, result in poor tracking or even be infeasible in that they exceed given limits. This paper therefore presents a novel two-step iterative learning approach for industrial robots to find time-optimal, yet feasible trajectories and improve the tracking performance by repeatedly updating the nonlinear robot model and solving a time-optimal path tracking problem. The proposed learning algorithm is experimentally validated on a serial robotic manipulator, which shows that the developed approach results in reduced execution time and increased accuracy.

A generic method to optimize a redundant serial robotic manipulator's structure

Abstract In this paper, an optimization method for a redundant serial robotic manipulator's structure is proposed in order to improve their performance. Optimization was considered in terms of kinematics using the proposed objective function and the non-linear Levenberg-Marquardt algorithm for multi-variate optimization. Range limits of the joints, bounds of the design parameters, and a constrained workspace are enforced in the proposed method. A desired manipulator can be optimized to cover the required task points using dimensional synthesis. This approach effectively optimizes the link lengths of the manipulator and minimizes the position and orientation errors of the tool center point. A commercial heavy-duty hydraulic, underground tunneling manipulator was used to demonstrate the capability of the proposed optimization method. The obtained results encourage the use of the proposed optimization method in automated construction applications, such as underground tunneling, where the confined environment and the required task add challenges in the design of task-based robotic manipulators.

Sliding model control of robot manipulator based on a novel switching function

A novel switching function which replaces the sign function is presented in order to reduce high frequency chattering of the sliding model control. The dynamics model of multi-DOF serial robot manipulators is studied. A sliding control law with this novel switching function is designed and the asymptotic stability of the sliding model control of robot manipulators is proved. The simulation experiments of the sliding model control of 2-DOF robot manipulators illustrate that two links have higher angular position tracking accuracy and speed tracking accuracy. Moreover, its dynamic response is faster. The sliding model control system with the novel switching function reduces high frequency chattering effectively compared with the sliding model control system with the sign function. This novel switching function can be used on other sliding model control systems, for instance, the airborne electro-optical stabilized platform and missile guidance.