Large Workspace Research Articles

Sliding-surface dynamic control of a continuum manipulator with large workspace

This paper presents the trajectory tracking control of a multi-section continuum and compliant manipulator with large workspace. Fluidic muscles are utilized as actuators in this manipulator and inertial sensors used to measure its shape in configuration space. The robot's large workspace signifies the effects of the inertial, gravitational, and applied external forces on the trajectory tracking control of the robot end-effector. In this study, a model-based sliding-surface controller is proposed by deriving a simplified Pseudo-Rigid Body (PRB) dynamic model, which utilizes modified constant curvature assumptions to describe the couplings between the robot sections and actuators. Simplification steps are proposed for a PRB dynamic model by eliminating negligible dynamic effects to achieve a computationally efficient implementation with real-time control performance. The unmodeled dynamics and the error of model simplifications are considered as system uncertainties and an integral sliding surface with a variable sliding gain is proposed to overcome these uncertain dynamics. The sliding gain considers changes in the upper bounds of uncertainties. The closed-loop system stability in trajectory tracking is mathematically proved based on the Lyapunov stability theorem. Experiments throughout the manipulator's large workspace in challenging configurations including sudden release of unknown loads at the robot tip also highlight the potential of our contributed controller.

Enhanced view totally extraperitoneal approach: A better alternative to transabdominal preperitoneal approach for irreducible inguinoscrotal and giant inguinal hernias!

The advantages of enhanced view totally extraperitoneal (eTEP) over TEP approach are well established in large inguinoscrotal, recurrent inguinal, patients with short pubis to umbilicus distance and in obese patients. Irreducible inguinoscrotal hernias (IISHs) and giant inguinal hernias (GIHs) pose a great challenge. GIHs are hernias which extend below the midpoint of the inner thigh with the patient in the standing position. Majority of these hernias are managed by open, hybrid or by transabdominal pre-peritoneal (TAPP) approach. TAPP was considered the optimal minimally invasive approach for these hernias as it provides a large working space and reduction of contents under vision. My practice of eTEP has been limited to IISH and GIH. I would like to share some technical tips to manage these cases by eTEP approach.

Design and motion planning of a 7-DOF assembly robot with heavy load in spacecraft module

Currently, there is great demand for automated assembly of equipment inside spacecraft module, which would require an assembly robot with small size, large workspace, high load capacity, and high flexibility. To meet this demand, a redundant seven-degree-of-freedom (7-DOF) assembly robot with three prismatic joints and four rotating joints is proposed in this study. First, a kinematic model of the assembly robot is established, and the positional forward kinematics are derived. Then, the positional inverse kinematic equations are derived by using the fixed joint method and the coordinate inverse transformation method for the characteristics of the robot with redundant degrees of freedom. The inverse solution optimization model of the assembly robot is designed based on genetic algorithm, and B-spline interpolation algorithm is used for joint trajectory planning. Next, NSGA-2 algorithm is used to construct the trajectory optimization model, and the time-pulsation multi-objective Pareto optimal frontier is obtained. Finally, the joint simulation model of mechatronics and the prototype experiment are established to verify the effectiveness of the optimization results. Analysis shows that the proposed assembly robot has better load-bearing capacity and dynamic characteristics than similar existing assembly robots. Furthermore, the segmented trajectory optimization strategy for the assembly robot using inverse solution optimization, interpolation algorithm, and NSGA-2 based multi-objective optimization gets each motion joint to realize the trajectory tracking function quickly and stably, and the trajectory tracking error is small enough to meet the requirements of end positioning accuracy.

Design of a class of reconfigurable hybrid mechanisms for large complex curved surface machining based on topological graph theory

A design method for hybrid mechanism configuration synthesis based on topological graph theory is proposed to address the challenge of machining large and complex curved surfaces in the aerospace domain. The method leads to the generation of a new class of reconfigurable large extension hybrid mechanisms. Firstly, the spatial mechanism topological graph (SMTG) is obtained by evolving the structure of chemical molecules, which is used to express the spatial mechanism topological relationships. Then, combining graph theory methods with the SMTG, the topological relationships between motion modules of the hybrid mechanism are expressed, and the mechanisms of each motion module are designed. Finally, mechanisms of different functional modules are topologically connected and combined using the proposed topological connection relationship for the motion modules of hybrid mechanisms, thus resulting in a class of reconfigurable hybrid mechanisms (RHMs) with large extensibility. The RHMs exhibit strong structural stability, a large working space, and a small volume of occupation. It can be installed on the ends of industrial robots or in large guideways in the future to achieve high-precision machining of large complex curved structures.

Optimized Sliding Mode Control Based on Cuckoo Search Algorithm: Application for 2DF Robot Manipulator

Robot manipulators are used in high-accuracy processes they provide flexibility, adaptability, and a large workspace. Hence, in the presence of uncertainties, disturbance, and high-performance control approaches are necessary to improve their accuracy to achieve high-tracking precision requirements and transient response under load variation. We present in this article, a novel concept of robust nonsingular fast terminal sliding mode controller (NFTSMC). In fact, the use of the NFTSMC offers a fast convergence rate, avoids singularities but still suffers from chattering. To overcome this limitation, two approaches have been developed: robust nonsingular fast terminal sliding mode controller (RNFTSMC) and robust optimized nonsingular fast terminal sliding controller (RONFTSMC). In the first one an additional term called switching signal is added to the equivalent control law. The second one is a combination of the NFTSM technique, and a cuckoo search algorithm as optimum term. Simulations show that the control strategy can overcome the chattering phenomena ensures the accuracy and stability of the joint robot position control.

A Compact Three-Dimensional Two-Layer Flexible Hinge

The paper proposes a new three-dimensional flexible hinge formed of several serially linked straight- and circular-axis segments that are disposed of in two layers. The novel hinge configuration is capable of large displacements and can be implemented in precision-compliant mechanisms that need to cover large spatial workspaces. Based on simplified geometry, an analytical compliance model is formulated that connects the loads to the displacements at one end of the hinge. Finite element simulation and experimental prototype testing of actual-geometry hinge configurations confirm the analytical model predictions. A related compliance-based analytical model evaluates the maximum loads that can be applied to the hinge and the resulting displacements. The two small-deformation analytical models are subsequently utilized to investigate the relationship between geometric parameters and the hinge performance qualifiers.

Procedures and performance of a robotic machining system with metrology-in-the-loop feedback control

In recent years, the use of industrial robots in advanced manufacturing applications has become increasingly popular. With larger workspaces and lower costs relative to more traditional machine tools, the use of robots has significant upsides in machining applications. However, due to their relatively low accuracy, the use of industrial robots in these applications is limited. One way to improve robot accuracy is to provide feedback control via external sensors such as laser trackers. This paper presents several techniques used to identify key parameters for a laser tracker controlled robotic machining system. Specifically, transformations between the coordinate frames within the system are crucial to its performance since error in these parameters are generally not observable by the feedback system. The identification methods are used to perform full-scale machining experiments. These experiments demonstrate the improved machining performance of the laser tracker controlled robotic machining system when compared to the machining performance without feedback control.

Configuration design and kinematics analysis of foldable composite space capture mechanism

To meet the requirements of high flexibility, high stiffness, and large working range of space debris cleaning technology, a foldable composite space capture mechanism is proposed based on the finite screw theory in this paper. The degree of freedom of the mechanism is analyzed by using the screw theory and its degree of freedom is obtained. The closed-loop vector method and DH method are used to analyze the kinematics of the mechanism, and the position solution of the mechanism is derived. The analytical expressions of velocity and acceleration solutions are obtained by differential calculation. According to the analysis of numerical example, the kinematic model of the mechanism is built in the simulation environment, and the simulation experiment is carried out for the motion trajectory of the mechanism. The correctness of theoretical analysis solution and method is proved by contrasting and analyzing motion trajectory, and it is verified that the space capture mechanism uses the foldable property to form large workspace to complete the capture of the target.

Voice coil motor-driven multi-DOF compliant parallel micropositioning stage based on a large range beam-based spherical hinge and fully symmetrical layout

With the recent rapid developments in the field of precision engineering, demand for the large range multi-degrees-of-freedom (DOF) micropositioning stage has increased significantly. In this paper, to solve the problems of small motion range, local stress concentration, and low motion accuracy caused by the parasitic motion of the traditional flexure hinge in the multi-DOF micropositioning stage, we first propose a type of large-range beam-based flexure spherical hinge (BFSH). Subsequently, based on the proposed BFSH, a large range 3-DOF θxθyz spatial micropositioning stage driven by the voice coil motor is designed employing parallel branch chains and a fully symmetrical layout. This arrangement realizes theoretical motion decoupling in structural design. Furthermore, we use the geometric method to derive kinematic equations of the moving platform, which are used as the decoupling matrix of the control loop. Based on the compliance matrix method and Lagrange’s method, the compliance matrix model of the BFSH, the 3-DOF micropositioning stage, and the stage dynamic model are determined respectively. Additionally, finite element analysis and experimental tests are conducted to verify the accuracy of the analytical model and assess the static and dynamic performance of the designed 3-DOF stage. Moreover, a fractional order phase advanced proportional integral controller is designed for closed-loop control to track the sinusoidal trajectory and spherical trajectory. The results reveal that the stage can achieve the desired large workspace of ± 21.5 mrad × ± 20.3 mrad × ± 3.23 mm, as well as excellent decoupling and trajectory tracking performance.

Development of a novel hybrid haptic (nHH) device with a remote center of rotation dedicated to laparoscopic surgery

AbstractThis paper focuses on developing a novel hybrid-haptic (nHH) device with a remote center of rotation with 4 DOFs (degrees of freedom) intendant to be used as a haptic device. The new architecture is composed of two chains handling each one a part of the motions. It has the advantages of a parallel robot as high stiffness and accuracy, and the large workspace of the serial robots. The optimal synthesis of the nHH was performed using real-coded genetic algorithms. The optimization criteria and constraints were established and successively formulated and solved using a mono-objective function. A validation and comparison study were performed between the spherical parallel manipulator and the nHH. The obtained results are promising since the nHH is compared to other similar task devices, such as spherical parallel manipulator, and presents a suitable kinematic performance with a task workspace free singularity inside.

Analysis of kinematic characteristics of 2-P(RPS + UPS) parallel mechanism with six degrees of freedom

At present, there is an increasing demand for the workspace required for the assembly of components, and a parallel mechanism with a large workspace is urgently needed to make up for it. Therefore, in this paper, a 2-P(RPS + UPS) parallel mechanism (where S, P, R, and U represent spherical, prismatic, revolute, and universal joints) with four branched chains and six degrees of freedom is proposed and its kinematic characteristics are analyzed. First, the speed of the 2-P(RPS + UPS) parallel mechanism is numerically derived and verified by simulation using ADAMS software. Then, the motion decoupling characteristics of the mechanism are analyzed from the expression of the speed and position relationship between the input and output of the mechanism. To minimize the force on each branch in the workspace, scale optimization of the 2-P(RPS + UPS) mechanism and the Stewart mechanism is performed. Further, analysis of the dexterity, singularity, and workspace of the 2-P(RPS + UPS) mechanism is conducted, and the performance of the mechanism is compared with that of the Stewart mechanism. The proposed parallel mechanism has fewer branches, a simple kinematic model, strong motion decoupling, a high bearing capacity, a large workspace, and a low initial position height. Moreover, it can be conveniently transported and stored. Therefore, it has good application prospects in assembly and posture adjustment scenes requiring large workspaces.

Performance enhancement of the soft robotic segment for a trunk-like arm.

Trunk-like continuum robots have wide applications in manipulation and locomotion. In particular, trunk-like soft arms exhibit high dexterity and adaptability very similar to the creatures of the natural world. However, owing to the continuum and soft bodies, their performance in payload and spatial movements is limited. In this paper, we investigate the influence of key design parameters on robotic performance. It is verified that a larger workspace, lateral stiffness, payload, and bending moment could be achieved with adjustments to soft materials' hardness, the height of module segments, and arrayed radius of actuators. Especially, a 55% increase in arrayed radius would enhance the lateral stiffness by 25% and a bending moment by 55%. An 80% increase in segment height would enlarge 112% of the elongation range and 70 % of the bending range. Around 200% and 150% increments in the segment's lateral stiffness and payload forces, respectively, could be obtained by tuning the hardness of soft materials. These relations enable the design customization of trunk-like soft arms, in which this tapering structure ensures stability via the stocky base for an impact reduction of 50% compared to that of the tip and ensures dexterity of the long tip for a relatively larger bending range of over 400% compared to that of the base. The complete methodology of the design concept, analytical models, simulation, and experiments is developed to offer comprehensive guidelines for trunk-like soft robotic design and enable high performance in robotic manipulation.

Synthesis of Compliant Parallel Mechanisms Using an Improved Beam-Based Method with the Optimization of Multiple Resonant Modes

This paper proposes an improved beam-based method to synthesize a compliant parallel mechanism (CPM) with multiple degrees of freedom (DoFs). The proposed method utilizes a structural optimization technique to synthesize a three-legged CPM with a single-beam structure constructed by two perpendicular segments in each leg to achieve the desired DoFs and fully decoupled motion. In addition, an objective function is proposed to optimize the primary resonant frequencies in actuating directions to targeted values to achieve the desired dynamic behaviors. A 4-DoF CPM, with one translation and three rotations, is synthesized using the improved beam-based method and all of the primary resonant frequencies are optimized to the targeted values. The 4-DoF CPM prototype is fabricated monolithically and evaluated experimentally in terms of its mechanical characteristics, workspace, and resonant modes. The obtained results show that the experimental stiffness and dynamic properties agree with the predictions. In particular, the prototype has good motion decoupling capability, as reflected by the high stiffness ratios of more than 500 between the non-actuating and actuating directions; the large workspaces of up to 4.0 mm and 7.2° for the translation and rotations, respectively; and the resonant frequencies being close to the targeted ones. In addition, the highest deviations between the predicted and experimental results are 9.49% and 9.13% for the stiffness and dynamic behaviors, respectively, demonstrating the correctness and effectiveness of the proposed method.

Pure Retroperitoneal Laparoscopic Peritoneum Incision Technique in Right Nephrectomy and Inferior Vena Cava Tumor Thrombectomy: A Novel Surgical Technique and Long-Term Outcomes from a Large Chinese Center.

Purpose: To explore the safety and effectiveness of the Pure Retroperitoneal Laparoscopic Peritoneum Incision Technique (PREP-IT) in laparoscopic radical nephrectomy (LRN) and inferior vena cave (IVC) tumor thrombectomy for right renal-cell carcinoma (RCC) with level Mayo I to III venous tumor thrombus (VTT). Patients and Methods: From May 2015 to September 2020, 92 patients with right RCC and Mayo I to III VTT were retrospectively reviewed, including 57 patients who underwent retroperitoneal LRN and IVC thrombectomy using PREP-IT, and 35 patients who underwent open surgery. PREP-IT refers to dissecting the retroperitoneum and temporarily placing the right kidney into the abdominal cavity to enlarge the retroperitoneal workspace for a safer and faster IVC operation. Results: Compared with the open surgery group, the PREP-IT group had a larger tumor diameter, while a larger proportion of Mayo I tumor thrombus and smaller maximum tumor thrombus width. Two patients (3.5%) in the PREP-IT group had a history of abdominal surgery. No conversion to open surgery or standard laparoscopic surgery occurred in PREP-IT group. Laparoscopic surgery with PREP-IT was characterized by shorter operative time, less surgical blood loss, shorter postoperative hospital stay, and lower postoperative complication rate. With a 33-month (ranges: 2-86) follow-up time period, the estimated mean overall survival time was 57.2 ± 5.3 and 58.1 ± 71.5 months in the PREP-IT group and open surgery group, respectively. Log-rank test indicated no significant difference between the two groups in terms of overall survival and cancer-specific survival. Conclusions: The PREP-IT is relatively safe and feasible for retroperitoneal LRN with right renal tumor and IVC tumor thrombus, allowing for a large workspace and wide exposure for IVC operations.

Modeling and Trajectory Tracking Control for a Multi-Section Continuum Manipulator

This paper presents a dynamic modeling and trajectory tracking control design for a hyper-redundant continuum manipulator (HRM), which is able to continuously bend along its length. The HRM has the advantages of high flexibility, large workspace, and low inertia, but also poses challenges of complex kinematics, and dynamic coupling. To address these challenges, the kinematics model was developed based on the piecewise constant curvature (PCC) assumption that captures the relationship between the cable lengths, joint angles, and end-effector pose. Inverse kinematics is presented geometrically by solving trigonometric equations. The dynamic model for the continuum robot (CR) is derived using the Euler–Lagrange representation, which incorporates the effects of gravity and elasticity. Accordingly, three control strategies are developed and applied to a two-section continuum robot, which are the inverse dynamic proportional integral derivative controller (PID), fuzzy logic controller (FLC), and sliding mode controller (SMC). We validate our proposed methods through simulations on various 3D trajectories, utilized MATLAB symbolic math toolbox in conjunction with Simulink simulation; demonstrate and evaluate different close-loop dynamic control responses for different scenarios. This simulation used in the creation of a unique animated simulation for a whole 3D continuum robot while tracking its desired trajectories. Finally, the simulation results demonstrate that our proposed methods can effectively control the HRM with high tracking performance, exhibiting enhanced responses in terms of settling time, rising time, and steady-state error. While the developed SMC outperforms Poth's PID and FLC in terms of robustness and settling time (51% and 10.3%), respectively.

Field Model Identification and Control of a Mobile Electromagnet for Remote Actuation of Soft Robots

The actuation of miniaturized robots through external magnetic fields has great potential for medical applications. The controllability properties of the miniaturized robots are affected by magnetic field generation modality. In this work, the magnetic field of a mobile electromagnet, notably capable to generate a desired magnetic field in large 3D workspaces, has been identified first. Then, a control model of the field generation system has been developed to produce a desired magnetic field designed to generate a locomotion gait in a legged miniaturized robot. Preliminary experiments prove the viability of the approach.

Design and Analysis of an Extended Simply Supported Beam Piezoelectric Energy Harvester

The harvesting efficiency of a cantilevered piezoelectric energy harvester is limited by its uneven strain distribution. Moreover, a cantilevered harvester requires a large workspace due to the large displacement of its free end. To address these issues, a novel piezoelectric energy harvester based on an extended simply supported beam is proposed. The proposed design features a simply supported piezoelectric main beam with an extended beam attached to its roller end and a tip mass to reduce the resonant frequency. The theoretical model of the proposed piezoelectric energy harvester is developed based on the Euler–Bernoulli beam theory. The model has been experimentally validated through the fabrication of a prototype. The extended beam and tip mass are adjusted to see their influence on the performance of the harvester. The resonant frequency can be maintained by shortening the extended beam and increasing the tip mass simultaneously. A shorter extend beam leads to a more even strain distribution in the piezoelectric layer, resulting in an enhanced output voltage. Moreover, the simulation results show that a torsional spring is installed on the roller joint which greatly influences the voltage output. The strain distribution becomes more even when proper compressive preload is applied on the main beam. Experiments have shown that the proposed design enhances the output power by 86% and reduces tip displacement by 63.2% compared to a traditional cantilevered harvester.

APPLICATION OF FUZZY LOGIC IN THE ROBOT CONTROL FOR MECHANICAL PROCESSING

Robot application in mechanical machining is growing day by day because it has many advantages over conventional machines such as high flexibility, large working space, and high repeatability. Many degrees of freedom of motion give robots the ability to perform complex technological operations, but also because of that, methods of controlling robots based on dynamic models have difficulties. Applying fuzzy logic to robot control can partially or completely exclude the calculation of the robot's dynamic model as well as overcome other uncertainties of the whole technological system. The variables and parameters of the fuzzy logic-based controller are modeled in a linguistic form, called linguistic variables, and are defined by the linguistic semantic values. Fuzzy rules are an important basis for the performance of operations defining the control quantities of the controller. Fuzzy rules are constructed by natural human inference and are based on expert intelligence. The main tasks of applying fuzzy logic control include “Fuzzification” to determine fuzzy parameters in the form of fuzzy sets of input-output data; “Fuzzy Rules and Fuzzy Inference Mechanism” to perform fuzzy operations defining control quantities, and finally “Defuzzification” to convert control quantities from linguistic values to physical values for controller operation. There have been many types of research on applying fuzzy logic to control robots in general, but the percentage of fuzzy control research work for mechanical machining robots is still limited.
 The article is based on published works on fuzzy control for robots in general and mechanical processing robots to analyze the applicability of fuzzy control for mechanical machining robots. The article provides detailed information on fuzzy controller design, on determining input and output variables, proportional mapping to determine the number of fuzzy sets and the corresponding type of membership function. The construction of fuzzy rule base system and fuzzy inference mechanism is presented, and finally defuzzification. Prospects for the use of methods to perfect and develop fuzzy control systems for mechanical machining robots are also presented. Collectively, the information in this document is intended to guide the implementation of fuzzy logic-based controller designs for application to machining robots, as well as to general robot control.

A robotic treadmill system to mimic overground walking training with body weight support.

Body weight support overground walking training (BWSOWT) is widely used in gait rehabilitation. However, existing systems require large workspace, complex structure, and substantial installation cost for the actuator, which make those systems inappropriate for the clinical environment. For wide clinical use, the proposed system is based on a self-paced treadmill, and uses an optimized body weight support with frame-based two-wire mechanism. The Interactive treadmill was used to mimic overground walking. We opted the conventional DC motors to partially unload the body weight and modified pelvic type harness to allow natural pelvic motion. The performance of the proposed system on the measurement of anterior/posterior position, force control, and pelvic motion was evaluated with 8 healthy subjects during walking training. We verified that the proposed system was the cost/space-effective and showed the more accurate anterior/posterior position than motion sensor, comparable force control performance, and natural pelvic motion. The proposed system is cost/space effective, and able to mimic overground walking training with body weight support. In future work, we will improve the force control performance and optimize the training protocol for wide clinical use.

Multimode Control of a Parallel-Mobile-Coil System for Adaptable Large-Workspace Microrobotic Actuation

Recent studies on magnetic microrobotics for biomedical applications have resulted in varieties of magnetic actuation systems. However, the simultaneous actuation and tracking of magnetic microrobots in large workspace (e.g., the human-body size) remains challenging due to the fast decay of magnetic fields and the contradiction between resolution and field of view of a feedback instrument. Our previous work reported the concept of the parallel-mobile-coil system (PMCS), which comprises three electromagnetic coils that can move in large 3-D space for microrobotic actuation. Here, to make the PMCS have adaptability to different actuation scenarios or microrobot types, we propose three different control modes by utilizing the mobility of the coils. The torque control, force-assisted torque control, and force control modes are designed for pure torque actuation with energy conservation, torque actuation with force assistance, and pure force actuation, respectively. Comparative simulations and experiments validate the effectiveness of the three control modes. Moreover, to endow the system with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-vivo</i> feedback capability, we implement Hall-effect sensors and demonstrate the 3-D large-workspace actuation based on magnetic localization.