Rigid Robot Arm Research Articles

Analytical Inverse Kinematics for 2-Segment Extensible Continuum Manipulators

Abstract Fast inverse kinematics (IK) algorithm is significant for real-time precise motion control of continuum and soft manipulator. In this paper, we studied an explicit expression of two-segment continuum manipulator based on the constant curvature assumptions and discussed the existence of the IK solutions. This model used pseudo-rigid-body method, unlike 6-axis rigid industrial robot arm, we found that the two-segment extensible continuum manipulators have limited rotation angle around the direction vector of its tip, i.e., this type manipulator has limited dexterity. Then we pre-constrained five degrees of freedom (DOFs) constrained and discussed the definition of the left DOF. The IK solving process is simplified to realize small calculation cost for most applications. This model will provide a robust and real-time way to control the two-segment extensible continuum manipulators.

Deployment dynamics and experiments of a tendon-actuated flexible manipulator

The quantity of space debris on Earth orbit has escalated tremendously in recent years, presenting a significant hazard to human space operations. It is urgent to develop effective measures to capture and remove various space debris. For this purpose, this paper presents a tendon-actuated flexible deployable manipulator. The flexible manipulator consists of several deployable units connected by Cardan joints and actuated by tendons. Compared with the present technologies for capturing space debris such as rigid robotic arm or flying net, this flexible manipulator is deployable, reusable, lightweight and applicable to the capture of large space debris. In order to investigate its deployment dynamics, an accurate dynamic model of the flexible manipulator is established based on the natural coordinate formulation (NCF) and the absolute nodal coordinate formulation (ANCF). Subsequently, numerical simulations are carried out to study the effects of system parameters and the base satellite on its deployment dynamics. Finally, ground experiments for both deployment and bending of the flexible manipulator are conducted to verify its effectiveness and feasibility.

Robotic-Assisted Single-Position Prone Lateral Lumbar Interbody Fusion: Indications, Techniques, and Outcomes.

Robotic-Assisted Single-Position Prone Lateral Lumbar Interbody Fusion: Indications, Techniques, and Outcomes.

Step-by-step guide to robotic-guided minimally invasive transforaminal lumbar interbody fusion (MI-TLIF).

Robotics in spinal surgery offers a promising potential to refine and improve the minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) technique. Suitable surgeons for this technique include those who are already familiar with robotic-guided lumbar pedicle screw placement and want to advance their skillset by incorporating posterior-based interbody fusion. We provide a step-by-step guide for robotic-guided MI-TLIF. The procedure is divided into 7 practical and detailed techniques. The steps in sequential order include: (I) planning trajectories for pedicle screws and the tubular retractor; (II) robotic-guided pedicle screw placement; (III) placement of tubular retractor; (IV) unilateral facetectomy using the surgical microscope; (V) discectomy & disc preparation; (VI) interbody implant insertion; and (VII) percutaneous rod placement. We standardize surgeon training in robotic MI-TLIF by teaching our spine surgery fellows these 7 key technical steps highlighted in this guide. Current-generation robotics offers integrated navigation capability, K-wireless placement of pedicle screws through a rigid robotic arm, compatibility with tubular retractor systems to perform facetectomy, and allows for placement of interbody devices. We have found robotic-guided MI-TLIF to be a safe procedure that allows for accurate and reliable pedicle screw placement, less collateral damage to the soft tissues of the low back, and decreased radiation exposure.

A quantitative accuracy assessment of the use of a rigid robotic arm in navigated placement of 726 pedicle screws

BackgroundTraditional minimally invasive fluoroscopy-based techniques for pedicle screw placement utilize guidance, which may require fluoroscopic shots. Computerized tomography (CT) navigation results in more accurate screw placement. Robotic surgery seeks to establish access and trajectory with greater accuracy.ObjectiveThis study evaluated the screw placement accuracy of a robotic platform.MethodsDemographic data, preoperative/postoperative CT scans, and complication rates of 127 patients who underwent lumbosacral pedicle screw placement with minimally invasive navigated robotic guidance using preoperative CT were analyzed.ResultsOn the GRS scale, 97.9% (711/726) of screws were graded A or B, 1.7% (12/726) of screws graded C, 0.4% (3/726) of screws graded D, and 0% graded E. Average offset from preoperative plan to final screw placement was 1.9 ± 1.5 mm from tip, 2.2 ± 1.4 mm from tail and 2.9 ± 2.3° of angulation.ConclusionsRobotic-assisted surgery utilizing preoperative CT workflow with intraoperative fluoroscopy-based registration improves pedicle screw placement accuracy within a patient’s pedicles.

Characterization of continuum robot arms under reinforcement learning and derived improvements.

In robotics, soft continuum robot arms are a promising prospect owing to their redundancy and passivity; however, no comprehensive study exists that examines their characteristics compared to rigid manipulators. In this study, we examined the advantages of a continuum robot arm as compared to a typical and rigid seven-degree-of-freedom (7-DoF) robot manipulator in terms of performing various tasks through reinforcement learning. We conducted simulations for tasks with different characteristics that require control over position and force. Common tasks in robot manipulators, such as reaching, crank rotation, object throwing, and peg-in-hole were considered. The initial conditions of the robot and environment were randomized, aiming for evaluations including robustness. The results indicate that the continuum robot arm excels in the crank-rotation task, which is characterized by uncertainty in environmental conditions and cumulative rewards. However, the rigid robot arm learned better motions for the peg-in-hole task than the other tasks, which requires fine motion control of the end-effector. In the throwing task, the continuum robot arm scored well owing to its good handling of anisotropy. Moreover, we developed a reinforcement-learning method based on the comprehensive experimental results. The proposed method successfully improved the motion learning of a continuum robot arm by adding a technique to regulate the initial state of the robot. To the best of our knowledge, ours is the first reinforcement-learning experiment with multiple tasks on a single continuum robot arm and is the first report of a comparison between a single continuum robot arm and rigid manipulator on a wide range of tasks. This simulation study can make a significant contribution to the design of continuum arms and specification of their applications, and development of control and reinforcement learning methods.

Optimization-based Concurrent Control of a High Dexterity Robot for Vitreoretinal Surgery.

Vitreoretinal surgery requires dexterity and force sensitivity from the clinician. A system to cooperatively control an integrated surgical robot for high dexterity manipulation within the eye's vitreous space was developed and validated in simulation. The system is composed of a 2 degrees of freedom (DoF) snake-like continuum manipulator that is attached to the end-effector of a 5-DoF rigid robot arm. It is capable of receiving position and orientation commands from a 5-DoF input device in real-time, as well as following pre-planned trajectories. The manipulator is moved to each target pose in real-time, using an optimization method to calculate the inverse kinematics solution. Constraints on the position and orientation ensure the target pose does not harm the patient within the vitreous space, enabling the robot to safely assist the clinician with vitreoretinal surgery when operating in real-time. The simulation demonstrates the system's feasibility and benefits over the existing non-dexterous system.

Dynamic analysis of flexible-link manipulator in underwater applications using Gibbs-Appell formulations

The dynamic model of a flexible robotic chain by considering its motion in a fluid medium is developed in this study. The use of flexible manipulators in fluid applications offers several advantages, but the fluid-manipulator interaction forces, as well as the elasticity of each link, complicates the modeling process. To tackle this issue, the dynamic effects of the fluid on the performance of flexible arms are identified and expressed mathematically so that the resulting interaction during the robot motion can be modeled simultaneously. In this regard, the dynamic interaction between the links and the fluid as a result of link flexibility is modeled as a distributed load along the arm length. In addition to the structural damping of the links, the effect of fluid damping along with its added mass affects the performance of the considered robotic system. Thus, compared to a flexible robotic arm in the air or a rigid robotic arm in the fluid, the flexible deformation of the robot links during motion is affected by the fluid flow. The recursive Gibbs-Apple formulation is used to derive the equations of motion of an N-link robotic chain. Not only does this formulation reduce the computational complexity compared to similar algorithms, but it also allows us to consider the effect of forces exerted on the joints and robot links in the form of the Rayleigh dissipation function. The final equations of motion are simulated using MATLAB for a two-link flexible arm. Simulations of robot links are conducted for different elasticities, different initial conditions, and different media with different viscosities. According to the obtained results, the deformation of flexible manipulators decreases from 5 mm (in the air) to 3 mm (in the fluid), while the displacement in water is 10% of that in the air under similar conditions.

Aerial Contact Manipulation With Soft End-Effector Compliance and Inverse Kinematic Compensation

Abstract This paper presents the development of a six degrees-of-freedom manipulator with soft end-effector and an inverse kinematic compensator for aerial contact manipulation. Realizing the fact that aerial manipulators can hardly achieve precise position control, a compliant manipulator with soft end-effector is first developed to moderate end-effector positioning errors. The manipulator is designed to be rigid-soft combined. The rigid robotic arm employs the lightweight but high-strength materials. The compliance requirement is achieved by the soft end-effector so that the mechanical design for the joints are largely simplified. These two features are beneficial to lighten the arm and to ensure the accuracy. In the meantime, the pneumatic soft end-effector can further moderate the probable insufficient accuracy by endowing the manipulator with compliance for impact resistance and robustness to positioning errors. With the well-designed manipulator, an inverse kinematic compensator is then proposed to eliminate lumped disturbances from the aerial platform. The compensator can ensure the stabilization of the end-effector by using state estimation from the aerial platform, which is robust and portable as the movement of the platform can be reliably obtained. Both the accuracy and compliance have been well demonstrated after being integrated into a hexarotor platform, and a representative scenario aerial task repairing the wind turbine blade-coating was completed successfully, showing the potential to accomplish complex aerial manipulation tasks.

An Origami Continuum Robot Capable of Precise Motion Through Torsionally Stiff Body and Smooth Inverse Kinematics.

Continuum robot arms, with their hyper-redundant continuously deformable bodies, show great promise in applications deemed impossible for traditional rigid robot arms with discrete links and joints, such as navigating tight corners without getting stuck. However, existing continuum robots suffer from excessive twisting when subjected to offset loading, even resulting from their own body weight, which reduces their dexterity and precision. In this work, we present a continuum manipulator that is capable of providing passive torsional stiffness through an origami-inspired modular design, remedying the non-controllable twist typically present in continuum robots. Our proposed origami continuum module is ∼73 times stronger in torsion compared with similar-size continuum modules made out of silicone rubber, while being 50% lighter, and capable of 125% change in length. Building on these physical capabilities, we present an optimization-based method to solve for the inverse kinematics of our multi-segment origami continuum manipulator that ensures smooth motion to follow desired end-effector paths, minimizing vibrations of the long and slender body. Further, taking advantage of the length-change capabilities of our origami manipulator, we devise and evaluate grow-to-shape algorithms to plan for full-body robot insertion motions that follow tortuous paths. Lastly, we showcase various applications of our proposed continuum robot for pick-and-place, inspection/exploration, and robotic art. Our study presents a highly capable continuum robot for safe manipulation and structure inspection applications, with potential for real-world deployment.

Wire-Suspended Device Control Based on Wireless Communication With Multirotor for Long Reach-Aerial Manipulation

In this study, we propose a long-reach aerial manipulation system with a wire-suspended device that allows the airframe to maintain its position at the desired distance away from the target. We implemented a feedback communication between the multirotor and wire-suspended device to maintain the position of the wire-suspended device directly below the multirotor while maintaining a constant distance from the target. The multirotor communicates its velocity and relative position to the wire-suspended device to control the ducted fans, whereas the wire-suspended device transmits the attitude and distance from the ground to the multirotor to control the winch. The designed controller for the ducted fans allows the wire-suspended device to behave like a long rigid robotic arm. The performance of the designed controller was verified by navigating the multirotor over stepped surfaces while the wire-suspended device was being lowered.

Development of a Virtual Force Sensor for a Low-Cost Collaborative Robot and Applications to Safety Control.

To protect operators and conform to safety standards for human–machine interactions, the design of collaborative robot arms often incorporates flexible mechanisms and force sensors to detect and absorb external impact forces. However, this approach increases production costs, making the introduction of such robot arms into low-cost service applications difficult. This study proposes a low-cost, sensorless rigid robot arm design that employs a virtual force sensor and stiffness control to enable the safety collision detection and low-precision force control of robot arms. In this design, when a robot arm is subjected to an external force while in motion, the contact force observer estimates the external torques on each joint according to the motor electric current and calculation errors of the system model, which are then used to estimate the external contact force exerted on the robot arm’s end-effector. Additionally, a torque saturation limiter is added to the servo drive for each axis to enable the real-time adjustment of joint torque output according to the estimated external force, regulation of system stiffness, and achievement of impedance control that can be applied in safety measures and force control. The design this study developed is a departure from the conventional multisensor flexible mechanism approach. Moreover, it is a low-cost and sensorless design that relies on model-based control for stiffness regulation, thereby improving the safety and force control in robot arm applications.

Design and Implementation of Bio-inspired Snake Bone-armed Robot for Agricultural Irrigation Application

This paper proposes a bionic electric spraying rod to perform the crop watering and spraying in the farm. The design concept of multiple vertebrae structures of snake is used to realize a reproducible snake bone arm and muscles of snake, which can be regarded as multiple sets of thin wires and be pulled and released through driver module. It results in different attitudes of the snake bone arm. A water pipe is installed in the snake arm connected to the spray nozzle for spraying. The mobile application interface (APP) is designed to provide the user to control the arm remotely. The maximum bending angle of the arm, which can reach to 115.7 degrees, and the jetting distance is up to 60 cm. Some spraying tests were performed to evaluate and verify the effectiveness of proposed bionic arm. The proposed snake bone-armed robot has high degree of freedom and low cost, which is more feasible than the rigid robotic arm. The robotic arm can be installed in the unmanned field mobile robot to perform spraying operation, reducing the burden of labor and the damage of on-site pesticide spraying to farmers.

Safe Testing of Electrical Diathermy Cutting Using a New Generation Soft Manipulator

The first demonstration of a pneumatic soft continuum robot is integrated in series with a rigid robot arm, safely performing teleoperated diathermic tissue-cutting. The rigid arm autonomously maintains a safe tool contact force, while the soft arm manually follows the desired cutting path. Ex-vivo experimentation demonstrates submillimetric deviations from target paths.

Design, Characterization, and Implementation of a Two-DOF Fabric-Based Soft Robotic Arm

Traditional rigid robotic arms have been widely used in various industries. They own the merits of high force output, precise control, and high efficiency. However, a rigid robotic arm is seldom used by people in daily life, as the cost is usually high and, most importantly, its rigidity, large weight, and noncompliance can cause safety concerns when it comes to human–robot interaction. Therefore, we want to build a robotic arm that is cheap, lightweight, and provides safe interaction with humans. This soft inflatable robotic arm, which is made from low-cost fabrics and flexible plastics, is a promising solution for a domestic robotic arm. The softness and natural compliance can guarantee safe interaction with people. In this letter, we present our soft robotic arm (SRA) made from nylon fabric. The SRA contains two joints that can bend the arm vertically and horizontally, and a gripper as an end-effector that can pick up objects of different shapes and sizes. The SRA has the advantages of low cost, good portability, and adequate force output. We characterized the bending modality and force output and demonstrated the functionality of the SRA in object manipulation. This fabric-based soft robotic arm is promising for use in assisting people's daily activities, for example, mounting on a wheelchair to enable a wheelchair bound person to reach objects from a distance.

Backstepping Design of Adaptive Neural Fault-Tolerant Control for MIMO Nonlinear Systems.

In this paper, an adaptive controller is developed for a class of multi-input and multioutput nonlinear systems with neural networks (NNs) used as a modeling tool. It is shown that all the signals in the closed-loop system with the proposed adaptive neural controller are globally uniformly bounded for any external input in . In our control design, the upper bound of the NN modeling error and the gains of external disturbance are characterized by unknown upper bounds, which is more rational to establish the stability in the adaptive NN control. Filter-based modification terms are used in the update laws of unknown parameters to improve the transient performance. Finally, fault-tolerant control is developed to accommodate actuator failure. An illustrative example applying the adaptive controller to control a rigid robot arm shows the validation of the proposed controller.In this paper, an adaptive controller is developed for a class of multi-input and multioutput nonlinear systems with neural networks (NNs) used as a modeling tool. It is shown that all the signals in the closed-loop system with the proposed adaptive neural controller are globally uniformly bounded for any external input in . In our control design, the upper bound of the NN modeling error and the gains of external disturbance are characterized by unknown upper bounds, which is more rational to establish the stability in the adaptive NN control. Filter-based modification terms are used in the update laws of unknown parameters to improve the transient performance. Finally, fault-tolerant control is developed to accommodate actuator failure. An illustrative example applying the adaptive controller to control a rigid robot arm shows the validation of the proposed controller.

Impact dynamics of a differential gears based underactuated robotic arm for moving target capturing

This paper presents impact dynamic analysis of a differential gears based underactuated robotic arm colliding with a moving target. The robotic arm employs a set of one-input-dual-output planetary gears to distribute driving torque of the underactuated joints, which takes advantage of the underactuation to cope with collision. Based on an analysis of the movement relation of three joints, the driving torque is resolved into generalized force corresponding to coordinates of two underactuated joints for establishing a dynamic model of the underactuated robotic arm. Along with the dynamic equation, impulse-momentum equations involving the restitution coefficient of the system (arm and target) are used to establish the impact dynamic model which can extrapolate the impact momentum on the drive component. With the impact dynamic model, the impact-absorbing capability of the underactuated robotic arm is illustrated that the impact momentum on the drive component is reduced by a factor of three compared with a 2-DOF fully actuated rigid robotic arm. Impact experiments were carried out to validate the inference results presented in this paper by using of a prototype of the proposed arm.

Control of a hybrid robotic system for computer-assisted interventions in dynamic environments.

Minimally invasive surgery is becoming the standard treatment of care for a variety of procedures. Surgeons need to display a high level of proficiency to overcome the challenges imposed by the minimal access. Especially when operating on a dynamic organ, it becomes very difficult to align instruments reliably and precisely. In this paper, a hybrid rigid/continuum robotic system and a dedicated robotic control approach are proposed to assist the surgeon performing complex surgical gestures in a dynamic environment. The proposed robotic system consists of a rigid robot arm on top of which a continuum robot is mounted in series. The continuum robot is locally actuated with McKibben muscles. A control scheme based on quadratic programming framework is adopted. It is shown that the framework allows enforcing a set of constraints on the pose of the tip, as well as of the instrument shaft, which is commanded to slide in and out through the entry point. Through simulation and experiments, it is shown how the robot tool tip is able to follow sinusoidal trajectories of 0.37 and 2Hz, while maintaining the instrument shaft pivoting along the entry point. The positioning and tracking accuracy of such system are shown to lie below 4.7mm in position and [Formula: see text] in angle. The results suggest a good potential for applying the proposed technology to assist the surgeon during complex robot-assisted interventions. It is also illustrated that even when using flexible hence relatively safe end-effectors, it is possible to reach acceptable tracking behaviour at relatively high frequencies.

初期設計段階における多関節ロボットアームの最適な関節数，リンク長，軌道に関する研究

Existing rigid robot arms are often designed to have two or three joints in view of costs and manufacturing points. However at an initial design stage, the number of joints and lengths of arms should be designed more freely and adequately from the points of total efficiency and costs. This study aims at developing and providing a general and convenient method to obtain optimum number of joints and lengths of a rigid robot arm at initial design stage. The design of optimum joints and lengths, of course, depends upon trajectories, obstacles in working space, tasks and other many factors. At an initial design stage it is not so easy to determine optimum number of joints and lengths under consideration such many factors but is worthwhile to study on seeking for a possible method. Hence this study proposes a general design method where a trajectory itself is taken as design variables beside number of joints and lengths of robot arms because a trajectory is considered as one of prominent factors to effect on such two measures energy and manipulability are adopted as objective functions. Then an optimum problem is formulated as multi-objective optimum design problem. This problem is difficult to solve by conventional optimization methods, thus it is solved by multiple loops based on Genetic Algorithm (GA). Based on the proposed method, numerical examples in 2- and 3-dimensional spaces are demonstrated. Model experiments are also carried out. All those results are examined, and show the validity and effectiveness.

MRAS based LFFC for a Two – Link Rigid Robot Arm

MRAS based LFFC for a Two – Link Rigid Robot Arm