Direct torque control for cable conduit mechanisms for the robotic foot for footwear testing

© 2018 Elsevier Ltd As the shoe durability is affected directly by the dynamic force/pressure between the shoe and its working environments (i.e., the contact ground and the human foot), a footwear testing system should replicate correctly this interaction force profile during gait cycles. Thus, in developing a robotic foot for footwear testing, it is important to power multiple foot joints and to control their output torque to produce correct dynamic effects on footwear. The cable conduit mechanism (CCM) offers great advantages for designing this robotic foot. It not only eliminates the cumbersome actuators and significant inertial effects from the fast-moving robotic foot but also allows a large amount of energy/force to be transmitted/propagated to the compact robotic foot. However, CCMs cause nonlinearities and hysteresis effects to the system performance. Recent studies on CCMs and hysteresis systems mostly addressed the position control. This paper introduces a new approach for modelling the torque transmission and controlling the output torque of a pair of CCMs, which are used to actuate the robotic foot for footwear testing. The proximal torque is used as the input signal for the Bouc–Wen hysteresis model to portray the torque transmission profile while a new robust adaptive control scheme is developed to online estimate and compensate for the nonlinearities and hysteresis effects. Both theoretical proof of stability and experimental validation of the new torque controller have been carried out and reported in this paper. Control experiments of other closed-loop control algorithms have been also conducted to compare their performance with the new controller effectiveness. Qualitative and quantitative results show that the new control approach significantly enhances the torque tracking performance for the system preceded by CCMs

Design and analysis of a novel long-distance double tendon-sheath transmission device for breast intervention robots under MRI field

Cancer represents a major threat to human health. Magnetic resonance imaging (MRI) provides superior performance to other imaging-based examination methods in the detection of tumors and offers distinct advantages in biopsy and seed implantation. However, because of the MRI environment, the material requirements for actuating devices for the medical robots used in MRI are incredibly demanding. This paper describes a novel double tendon-sheath transmission device for use in MRI applications. LeBus grooves are used in the original transmission wheels, thus enabling the system to realize long-distance and large-stroke transmission with improved accuracy. The friction model of the transmission system and the transmission characteristics model of the novel tendon-sheath structure are then established. To address the problem that tension sensors cannot be installed in large-stroke transmission systems, a three-point force measurement method is used to measure and set an appropriate preload in the novel tendon-sheath transmission system. Additionally, experiments are conducted to verify the accuracy of the theoretical model and multiple groups of tests are performed to explore the transmission characteristics. Finally, the novel tendon-sheath transmission system is compensated to improve its accuracy and the experimental results acquired after compensation show that the system satisfies the design requirements

Modeling and parametric optimization of 3D tendon-sheath actuator system for upper limb soft exosuit

This paper presents an analysis of parametric characterization of a motor driven tendon-sheath actuator system for use in upper limb augmentation for applications such as rehabilitation, therapy, and industrial automation. The double tendon sheath system, which uses two sets of cables (agonist and antagonist side) guided through a sheath, is considered to produce smooth and natural-looking movements of the arm. The exoskeleton is equipped with a single motor capable of controlling both the flexion and extension motions. One of the key challenges in the implementation of a double tendon sheath system is the possibility of slack in the tendon, which can impact the overall performance of the system. To address this issue, a robust mathematical model is developed and a comprehensive parametric study is carried out to determine the most effective strategies for overcoming the problem of slack and improving the transmission. The study suggests that incorporating a series spring into the system's tendon leads to a universally applicable design, eliminating the need for individual customization. The results also show that the slack in the tendon can be effectively controlled by changing the pretension, spring constant, and size and geometry of spool mounted on the axle of motor

Position tracking control in torque mode for a robotic running foot for footwear testing

Available automatic footwear testing systems still lack flexibility and bio-fidelity to represent the human foot and reproduce the wear conditions accurately. The first part of this article introduces a new design of the robotic running foot for footwear testing using cable conduit mechanisms. This robotic running foot is integrated with an upper leg mechanism to form a complete integrated footwear testing system. The cable conduit mechanisms help remove the bulky actuators and transmissions out of the fast-moving robotic foot. Thus, this robotic running foot design not only allows high-power actuators to be installed, but also avoids a significant dynamic mass and inertia effects on the upper leg mechanism. This means that the integrated footwear testing system can have multiple powered degrees of freedom in the robotic running foot and simulate much higher human running speeds than other available systems. However, cable conduit mechanisms cause significant challenges in control approaches, especially in high-speed systems, due to their nonlinear transmission characteristics. Furthermore, the robotic running foot actuators must operate in a torque/force control mode to reproduce the foot–shoe interaction during gaits while it is critical to control the foot joints’ position in the swing phase of gaits. The latter part of this article presents a study on position tracking control in torque mode for the robotic running foot joints using adaptive and proportional–integral–derivative control designs to evaluate the system’s ability to mimic the human foot kinematics in running. Both controllers proved their effectiveness, implying that the proposed control approach can be implemented on the integrated footwear testing system to control the foot joints’ position in the swing phase of running gaits

Design, Development, and Evaluation of a Teleoperated Master-Slave Surgical System for Breast Biopsy under Continuous MRI Guidance

The goal of this project is to design and develop a teleoperated master-slave surgical system that can potentially assist the physician in performing breast biopsy with a magnetic resonance imaging (MRI) compatible robotic system. MRI provides superior soft-tissue contrast compared to other imaging modalities such as computed tomography or ultrasound and is used for both diagnostic and therapeutic procedures. The strong magnetic field and the limited space inside the MRI bore, however, restrict direct means of breast biopsy while performing real-time imaging. Therefore, current breast biopsy procedures employ a blind targeting approach based on magnetic resonance (MR) images obtained a priori. Due to possible patient involuntary motion or inaccurate insertion through the registration grid, such approach could lead to tool tip positioning errors thereby affecting diagnostic accuracy and leading to a long and painful process, if repeated procedures are required. Hence, it is desired to develop the aforementioned teleoperation system to take advantages of real-time MR imaging and avoid multiple biopsy needle insertions, improving the procedure accuracy as well as reducing the sampling errors. The design, implementation, and evaluation of the teleoperation system is presented in this dissertation. A MRI-compatible slave robot is implemented, which consists of a 1 degree of freedom (DOF) needle driver, a 3-DOF parallel mechanism, and a 2-DOF X-Y stage. This slave robot is actuated with pneumatic cylinders through long transmission lines except the 1-DOF needle driver is actuated with a piezo motor. Pneumatic actuation through long transmission lines is then investigated using proportional pressure valves and controllers based on sliding mode control are presented. A dedicated master robot is also developed, and the kinematic map between the master and the slave robot is established. The two robots are integrated into a teleoperation system and a graphical user interface is developed to provide visual feedback to the physician. MRI experiment shows that the slave robot is MRI-compatible, and the ex vivo test shows over 85%success rate in targeting with the MRI-compatible robotic system. The success in performing in vivo animal experiments further confirm the potential of further developing the proposed robotic system for clinical applications

Cable-driven parallel mechanisms for minimally invasive robotic surgery

Minimally invasive surgery (MIS) has revolutionised surgery by providing faster recovery times, less post-operative complications, improved cosmesis and reduced pain for the patient. Surgical robotics are used to further decrease the invasiveness of procedures, by using yet smaller and fewer incisions or using natural orifices as entry point. However, many robotic systems still suffer from technical challenges such as sufficient instrument dexterity and payloads, leading to limited adoption in clinical practice. Cable-driven parallel mechanisms (CDPMs) have unique properties, which can be used to overcome existing challenges in surgical robotics. These beneficial properties include high end-effector payloads, efficient force transmission and a large configurable instrument workspace. However, the use of CDPMs in MIS is largely unexplored. This research presents the first structured exploration of CDPMs for MIS and demonstrates the potential of this type of mechanism through the development of multiple prototypes: the ESD CYCLOPS, CDAQS, SIMPLE, neuroCYCLOPS and microCYCLOPS. One key challenge for MIS is the access method used to introduce CDPMs into the body. Three different access methods are presented by the prototypes. By focusing on the minimally invasive access method in which CDPMs are introduced into the body, the thesis provides a framework, which can be used by researchers, engineers and clinicians to identify future opportunities of CDPMs in MIS. Additionally, through user studies and pre-clinical studies, these prototypes demonstrate that this type of mechanism has several key advantages for surgical applications in which haptic feedback, safe automation or a high payload are required. These advantages, combined with the different access methods, demonstrate that CDPMs can have a key role in the advancement of MIS technology.Open Acces

A Wearable Control Interface for Tele-operated Robots

Department of Mehcanical EngineeringThis thesis presents a wearable control interface for the intuitive control of tele-operated robots, which aim to overcome the limitations of conventional uni-directional control interfaces. The control interface is composed of a haptic control interface and a tele-operated display system. The haptic control interface can measure user???s motion while providing force feedback. Thus, the user can control a tele-operated robot arm by moving his/her arm in desired configurations while feeling the interaction forces between the robot and the environment. Immersive visual feedback is provided to the user with the tele-operated display system and a predictive display algorithm. An exoskeleton structure was designed as a candidate of the control interface structure considering the workspace and anatomy of the human arm to ensure natural movement. The translational motion of human shoulder joint and the singularity problem of exoskeleton structures were addressed by the tilted and vertically translating shoulder joint. The proposed design was analyzed using forward and inverse kinematics methods. Because the shoulder elevation affects all of the joint angles, the angles were calculated by applying an inverse kinematics method in an iterative manner. The proposed design was tested in experiments with a kinematic prototype. Two force-controllable cable-driven actuation mechanisms were developed for the actuation of haptic control interfaces. The mechanisms were designed to have lightweight and compact structures for high haptic transparency. One mechanism is an asymmetric cable-driven mechanism that can simplify the cable routing structure by replacing a tendon to a linear spring, which act as an antagonistic force source to the other tendon. High performance force control was achieved by a rotary series elastic mechanism and a robust controller, which combine a proportional and differential (PD) controller optimized by a linear quadratic (LQ) method with a disturbance observer (DOB) and a zero phase error tracking (ZPET) feedforward filter. The other actuation mechanism is a series elastic tendon-sheath actuation mechanism. Unlike previously developed tendon-sheath actuation systems, the proposed mechanism can deliver desired force even in multi-DOF systems by modeling and feedforwardly compensating the friction. The pretension change, which can be a significant threat in the safety of tendon-sheath actuation systems, is reduced by adopting series elastic elements on the motor side. Prototypes of the haptic control interfaces were developed with the proposed actuation mechanisms, and tested in the interaction with a virtual environment or a tele-operation experiment. Also, a visual feedback system is developed adopting a head mounted display (HMD) to the control interface. Inspired by a kinematic model of a human head-neck complex, a robot neck-camera system was built to capture the field of view in a desired orientation. To reduce the sickness caused by the time-varying bidirectional communication delay and operation delay of the robot neck, a predictive display algorithm was developed based on the kinematic model of the human and robot neck-camera system, and the geometrical model of a camera. The performance of the developed system was tested by experiments with intentional delays.clos