Category: Publications

A novel constrained wire-driven flexible mechanism and its kinematic analysis

  By
Abstract
Snake-like flexible manipulators are widely used in minimally invasive surgery (MIS), which require adequate dexterity in confined workspace. Typically, the design mechanisms of these manipulators include tendon-driven mechanism and concentric tube mechanism. Though, the workspace and dexterity of these designs are limited due to the lack of control in either the length of the bending section or the curvature of the bending section at the distal end. In this paper, we present a novel constrained wire-driven flexible mechanism (CWFM), in which both the length and the curvature of the bending section are controllable. The idea is to employ an active constraint to control the length of the bending section and use the wires to control the curvature of the bending section. Compared to the existing designs based on wire-driven flexible mechanism (WFM), CWFM has expanded workspace and enhanced dexterity while its size is not sacrificed. Additional benefits include much reduced sweeping area and controllable stiffness. Based on the computer simulation, on average, CWFM with the same size as WFM can improve the dexterity by 4.69 times and reduce the sweeping area to 20.5%.
More Information:

Data-driven methods towards learning the highly nonlinear inverse kinematics of tendon-driven surgical manipulators: XWJ_IJMRAS_IK_KNNR_GMR_ELM

  By
Abstract
Background: Accurate motion control of flexible surgical manipulators is crucial in tissue manipulation tasks. The tendon-driven serpentine manipulator (TSM) is one of the most widely adopted flexible mechanisms in minimally invasive surgery because of its enhanced maneuverability in torturous environments. TSM, however, exhibits high nonlinearities and conventional analytical kinematics model is insufficient to achieve high accuracy. Methods: To account for the system nonlinearities, we applied a data driven approach to encode the system inverse kinematics. Three regression methods: extreme learning machine (ELM), Gaussian mixture regression (GMR) and K-nearest neighbors regression (KNNR) were implemented to learn a nonlinear mapping from the robot 3D position states to the control inputs. Results: The performance of the three algorithms was evaluated both in simulation and physical trajectory tracking experiments. KNNR performed the best in the tracking experiments, with the lowest RMSE of 2.1275 mm. Conclusions: The proposed inverse kinematics learning methods provide an alternative and efficient way to accurately model the tendon driven flexible manipulator.
More Information:

Prototyping and characterisation of a variable stiffness actuation mechanism based on low melting point polymer

  By

Abstract:

With the advent of automation and robotic systems, flexible robotic manipulators are becoming increasingly popular in various applications where safe interaction with surrounding
environments is needed. This project aims to investigate stiffness varying technology for a class of flexible manipulators with the aim of online changing manipulator stiffness. We propose and develop a stiffness varying mechanism based on low melting point Polycaprolactone (PCL), characterize it and test out together with extensive experiments. The proposed mechanism is further integrated into a tendon-driven flexible manipulator and it successfully change the overall stiffness of the manipulator. This paper mainly involves design improvement, modeling, characterization and hands-on experiments.

More Information:

Full Text

Finding the Kinematic Base Frame of a Robot by Hand-Eye Calibration Using 3D Position Data

  By

Abstract

When a robot is required to perform specific tasks defined in the world frame, there is a need for finding the coordinate transformation between the kinematic base frame of the robot and the world frame. The kinematic base frame used by the robot controller to define and evaluate the kinematics may deviate from the mechanical base frame constructed based on structural features. Besides, by using kinematic modeling rules such as the product of exponentials (POE) formula, the base frame can be arbitrarily located, and does not have to be related to any feature of the mechanical structure. As a result, the kinematic base frame cannot be measured directly. This paper proposes to find the kinematic base frame by solving a hand-eye calibration problem using 3D position measurements only, which avoids the inconvenience and inaccuracy of measuring orientations and thus significantly facilitates practical operations. A closed-form solution and an iterative solution are explicitly formulated and proved effective by simulations. Comprehensive analyses of the impact of key parameters to the accuracy of the solution are also carried out, providing four guidelines to better conduct practical operations. Finally, experiments on a 7-DOF industrial robot are performed with an optical tracking system to demonstrate the superiority of the proposed method using position data only over the method using full pose data.

More information

Full-text and more information

Prototype Development of a Hand-Held Robotic Light Pipe for Intraocular Procedures

  By

Abstract

Light pipe is a tool providing illumination for delicate operations inside the eyeball in an eye surgery. Traditional light pipes with straight shafts have to be reoriented in order to enlarge its illustration range, which implies more risk of damage to the sclera and requires greater operation space for the handle. In order to overcome these limitations, this paper has proposed a novel robotized handheld light pipe based on concentric tubular structure. Tube parameters are selected based on the anatomical dimension of eyeballs. Novel actuation designs are described to meet the requirements of the intraocular procedures. Intuitive control scheme is implemented to facilitate surgeons’ operations. Furthermore, the benefit of the precurved tube compared with that of a straight tube is evaluated through experiments. It has been demonstrated that the proposed design as a light pipe holds the promise of enhancing intraocular surgeries.

More information

Full-text and more information

Design of a Novel Flexible Endoscope – Cardioscope

  By

Abstract

In this paper, we present a novel flexible endoscope (FE) which is well suited to minimally invasive cardiac surgery (MICS). It is named the cardioscope. The cardioscope is composed of a handle, a rigid shaft, a steerable flexible section, and the imaging system. The fexible section is composed of an elastic tube, a number of spacing disks, a constraint tube, and four wires. It employs the constrained wire-driven fexible mechanism (CWFM) with a continuum backbone, which enables the control of both the angulation and the length of the flexible section. Compared to other endoscopes, e.g., rigid endoscope (RE) and fixed-length FE, the cardioscope is much more dexterous. The cardioscope can bend over 180 deg in all directions, and the bending is decoupled from the distal tip position. Ex vivo tests show that the cardioscope is well suited to MICS. It provides much wider scope of vision than REs and provides good manipulation inside confned environments. In tests, the cardioscope successfully explored the full heart through a single hole, which shows that the design is promising. Despite being designed for MICS, the cardioscope can also be applied to other minimally invasive surgeries (MISs), such as laparoscopy, neurosurgery, transnasal surgery, and transoral surgery.

full text

Kinematic Analysis and Motion Control of Wheeled Mobile Robots in Cylindrical Workspaces

  By

Abstract

Wheeled mobile robots (WMRs) are often used for maintenance of round pipes or ducts, which can typically be represented as a cylindrical workspace. Working in round pipes or ducts, kinematic models of WMRs are different from those applying on a plane and thus pose significant challenges in terms of kinematic analysis and motion control. To address these challenges, the kinematic properties of WMRs in a cylindrical workspace are analyzed in this paper. First, we discuss the kinematic properties of a single wheel in a cylindrical workspace. Then, we analyze the geometric constraints of WMRs in round pipes or ducts with analytical geometry. Based on these analyses, kinematic properties of WMRs in cylindrical workspaces are discussed with screw theory. A control law based on biaxial clinometer information is proposed, and it enables the robot to move horizontally in round pipes or ducts. Finally, the motion of a single wheel purely rolling in a cylindrical workspace is simulated. Experiments using a car-like mobile robot moving in round ducts are carried out to show the feasibility of the proposed algorithm.

full text

Condition Monitoring for Image-Based Visual Servoing Using Kalman Filter

  By

Abstract

In image-based visual servoing (IBVS), the control law is based on the error between the current and desired features on the image plane. The visual servoing system is working well only when all the designed features are correctly extracted. To monitor the quality of feature extraction, in this paper, a condition monitoring scheme is developed. First, the failure scenarios of the visual servoing system caused by incorrect feature extraction are reviewed. Second, we propose a residual generator, which can be used to detect if a failure occurs, based on the Kalman filter. Finally, simulation results are given to verify the effectiveness of the proposed method.

full text

Prototype Development of a Hand-Held Robotic Light Pipe for Intraocular Procedures

  By

Abstract

Light pipe is a tool providing illumination for delicate operations inside the eyeball in an eye surgery. Traditional light pipes with straight shafts have to be reoriented in order to enlarge its illustration range, which implies more risk of damage to the sclera and requires greater operation space for the handle. In order to overcome these limitations, this paper has proposed a novel robotized handheld light pipe based on concentric tubular structure. Tube parameters are selected based on the anatomical dimension of eyeballs. Novel actuation designs are described to meet the requirements of the intraocular procedures. An intuitive control scheme is implemented to facilitate surgeons’ operations. Furthermore, the benefit of the precurved tube compared with that of a straight tube is evaluated through experiments. It has been demonstrated that the proposed design as a light pipe holds the promise of enhancing intraocular surgeries.

full text

Motion planning of continuum tubular robots based on features extracted from statistical atlas

  By

Abstract

Continuum tubular robots, which are constructed by telescoping pre-curved elastic tubes, are capable of balancing the force application and steerability during minimally invasive surgeries. These devices are able to reach the desired surgical sites in body cavities without colliding with critical blood vessels, nerves and tissues. However, the motion planning of continuum tubular robots is quite challenging because of their complicated kinematics as well as the high dimensional configuration space. In this paper, a sampling-based motion planning method is proposed based on the Rapidly-exploring Random Tree (RRT) algorithm for continuum tubular robots in 3D environments, such as medullary cavities. The proposed motion planner enables a continuum tubular robot to maneuver roughly along the central axis of the statistical humerus atlas in an approximate follow-the-leader manner. The experiment results have demonstrated the effectiveness and superiority of the proposed motion planning algorithm.

full text