Fengfeng Xi's research while affiliated with University of Toronto and other places

Publications (100)

Article
Full-text available
Lockable joints are widely used in robotic systems and adaptive structures for energy management and/or topology reconfiguration. However, it is still challenging to design a joint with desired properties, including high locking load, infinite locking positions, short switching time, energy-efficient control, and a compact and lightweight structure...
Article
This paper proposes a robotic fish scale that serves as a cover driven by a muscle mechanism. A combinatory design method is put forward to design the underlying mechanism and the cover enclosing it for shape morphing. The muscle mechanism is bio-inspired to mimic the motion of the skin muscle. It is designed to consist of multi-loop linkages to se...
Article
This paper proposes a 3D biomechanical model of the upper body and analyzes the interaction between the upper body and aircraft seat backrest for different sitting postures and backrest recline angles. The reclined sitting postures of the upper body are defined based on the available spine biomechanical data and the multibody inverse kinematics met...
Article
An interval discretization method (IDM) is proposed for the workspace determination of parallel mechanisms to address the fundamental problems of unreliable prediction and missing-points existing in the traditional point discretization method (PDM). The IDM involves two parts: the workspace prediction using interval analytical forward kinematics (A...
Conference Paper
Full-text available
The contact loading and pressure distribution on the back are important measures to assess the comfort of a seat's backrest. On the other hand, the backrest design also influences the pressure on the back. Limited studies show how the variation on the backrest affects the loadings to the back surface, especially for the upper trunk region of the hu...
Conference Paper
In this paper, a metamorphic method is adopted to model a planar variable geometry truss manipulator (VGTM) which is designed for topology reconfiguration while maintaining the structural stability. Through locking the lengths of some variable-length limbs, this VGTM can be changed to have three distinctive topologies: 1-, 2- and 3-DOF. If the 3-DO...
Conference Paper
Reconfigurable mechanisms have a wide range of applications in aerospace. One of the ways to achieve reconfiguration is to use the lockable joints to merge the adjacent components to change the topological structures and mobility. In actual engineering applications, this lockable device needs to be designed with a compact, lightweight structure as...
Article
A new approach is put forward to enhance the stiffness of parallel mechanisms by topological reconfiguration. First, a novel 6-DOF Stewart-type parallel mechanism is designed and analyzed. This mechanism can be reconfigured into three topological configurations, each permitting one rotational motion by means of lockable prismatic joints. Then, an o...
Article
This work presents a type of kinematically hyper-redundant manipulators, namely serial-parallel manipulators (S-PMs), for shape morphing control. The proposed S-PMs use a centralized actuation method to significantly reduce the number of actuators. The basic design concept is to use flexible limbs to actuate a serial manipulator made of passively l...
Article
In this study, a novel parallel learning particle swarm optimizer (PLPSO) is proposed. The evolutionary strategy of the algorithm is quite different from that of the existing PSO algorithms. To enhance the global search capability of the particle swarm, the original particle swarm is divided into two parallel evolving independent particle subpopula...
Article
Full-text available
In this study, we demonstrated a novel jumping robot that has the ability of accurate obstacle-crossing jumping and aerial pitch control. The novel robot can quickly leap high into the air with a powerful water jet thruster. The robot was designed to overcome multiple general obstacles via accurate jumping. Then a modified whale optimization algori...
Article
Full-text available
The smooth variable structure filter (ASVSF) has been relatively considered as a new robust predictor-corrector method for estimating the state. In order to effectively utilize it, an SVSF requires the accurate system model, and exact prior knowledge includes both the process and measurement noise statistic. Unfortunately, the system model is alway...
Article
Presented in this paper is a complete morphing system consisting of a variable geometry truss manipulator (VGTM) that is fully covered by a flexible panel skin. Two approaches are studied for morphing control. The first one is to have the VGTM act as a driving mechanism and the flexible panels as a passive system. In this case, the VGTM is composed...
Article
The smooth variable structure filter (SVSF) has been considered as the robust estimator. Like other filters, the SVSF needs an accurate system model and known noise statistics to approximate the posterior state. Unfortunately, the system cannot be accurately modeled, and the noise statistic is unknown in the real application. For these reasons, the...
Article
Full-text available
Robots driven by variable stiffness actuators (VSAs) have been an important technology as they could provide intrinsic compliance for safe human-robot interaction. The internal compliance of VSA also makes it possible for the actuator to act as a torque sensor and estimate the external force. This paper presents a physical human-robot interaction c...
Article
This paper presents a novel design of a multi-segment shape morphing mechanism that combines a passive lockable reconfigurable variable geometry truss manipulator (VGTM) with an active parallel compliant mechanism. The structure of the VGTM is in a parallel-serial structure and its hyper-redundant degree-of-freedom (DOF) can be fully controlled by...
Article
Presented in this paper is a method for modeling and simulation of a complete morphing mechanism. The said mechanism has a rigid panel morphing skin that morphs along with a driving mechanism. The said skin is made of segmented panels, inspired by fish scales. Since the gaps between these panels are undesirable, a gapless design is introduced in th...
Conference Paper
This paper presents a novel design for morphing mechanisms that combine the passive lockable reconfigurable variable geometry truss manipulator (VGTM) and the active parallel compliant mechanism. The structure of the VGTM is in a parallel-serial structure and its shape can be fully controlled just by using two active panels. This mechanism is suita...
Article
This paper presents a novel non-gyro six-axis accelerometer based on a derivative of Stewart parallel mechanism (SPM). To reduce the impact of interference noise, a set of geometric constraint equations are presented to compensate the errors of redundant outputs. A decoupling algorithm is introduced for easy modelling of this multiple-axis vibratio...
Article
The ability of changing aircraft wing shape or geometry has drawn great attention of researchers in the past decades. This paper proposes a new approach to design a lengthwise morphing structure for an airfoil morphing wing. The structure is composed of n planar mechanism units. Each unit is designed to have 3 degrees-of-freedom (DOFs) that can be...
Article
This article presents a novel robot skin that integrates both proximity and tactile sensors in a nursing robot to maximize the safety of patient transfer tasks. Two types of sensors are mounted on a honeycomb substrate made of flexible photosensitive resin. The proximity sensor consists of several distance sensor arrays, each with 16 laser sensors...
Article
Human-robot interactions (HRIs) are a key technology to combine human and robot capabilities. Though many feasible methods have been proposed in this field, the current workspace mapping methods are deficient in terms of generality. In this paper, a universal control system based on the self-adaption workspace mapping method for HRI is designed. In...
Article
Continuum mechanisms have drawn wide attention to scholars due to their salient advantages including compliance and dexterity. In this paper, a planar continuum mechanism made of soft panels is proposed. This mechanism has a reduced degree-of-freedom (DOF) compared with some existing continuum mechanisms capable of 3D motion. However, it can meet s...
Article
Presented in this paper is a method for analysis and control of an actuation-redundant parallel mechanism requiring synchronization. The said mechanism is made up of two branches that are connected to drive a common end-effector with only one degree-of-freedom of motion. The two actuators must share the load exerted on the common end-effector durin...
Article
Joint torque sensing is an important technique for high-performance control of modern robotic systems, especially in an environment that requires man-machine collaboration. However, in many cases, traditional torque sensors are not suitable for robots because of the inevitable increase of joint flexibility and joint size. To address this problem, t...
Article
Continuum robots, often taking inspiration from biomimetics, are an exciting novel research field and have great capability. New continuum robots can be inspired by biology such as seahorses, pipefish, and pipehorses which have both strong skeleton and great dexterity. The main idea contained in this paper is how to effectively employ the square co...
Article
Full-text available
This paper proposes a solution to the simulated deformation of guidewires when they come in contact with the blood vessel in an interventional surgery simulation training system. Starting from the principle of minimum energy, the guidewire is evenly dispersed into a rigid light bar articulation model. A sequential quadratic programming (SQP) algori...
Article
Nerve injury after stroke leads to the disorders of locomotion and declining balance function, which enhances the risk of falling. Restriction of pelvic motions can hinder successful rehabilitation, hence a Robotic Assisted Rehabilitation Trainer (RART) is proposed to assist patients to control the pelvic motions via force field. The mechanical des...
Article
Full-text available
In this paper, we discuss about multiple coordinated robots that can form a fixtureless manufacturing cell. It is very important to ensure that the system stiffness is sufficient for manufacturing operations when external forces are exerted on the system. For this reason, a method is developed to model and analyze the stiffness of a multiple coordi...
Article
Full-text available
In this paper, an Omni-directional mobile industrial robot drilling system for aerospace manufacture is introduced. Mecanum wheels are used for the robot's maneuverability in congested workspace. An industrial robot is applied to complete the drilling work for a rocket shell. A vision system is applied to enhance the precision of mobile drilling. A...
Article
Full-text available
This paper discusses the problem of squatting training of stroke patients. The main idea is to correct the patient’s training trajectory through an iterative learning control (ILC) method. To obtain better rehabilitation effect, a patient will typically be required to practice a reference posture for many times, while most of active training method...
Article
Robotic applications in aerospace manufacturing and aircraft assembly today are limited. This is because most of the aircraft parts are relatively crowded and have complex shapes that make tasks like robotic drilling and fastening more challenging. These challenges include tool accessibility, path and motion planning. In this paper, a process metho...
Article
Full-text available
Presented in this paper is a method for the design of modular reconfigurable machine tools (MRMTs). An MRMT is capable of using a minimal number of modules through reconfiguration to perform the required machining tasks for a family of parts. The proposed method consists of three steps: module identification, module determination, and layout synthe...
Article
The robotic riveting system requires a rivet robotic positioning process for rivet-in-hole insertions, which can be divided into two stages: rivet path-following and rivet spotpositioning. For the first stage, varying parameter-linear sliding surfaces are proposed to achieve robust rivet path-following against robot errors and external disturbances...
Article
Presented in this paper is a method for the development of variable geometry truss manipulators (VGTMs) with enhanced static characteristics. The concept of statically redundant parallel robots is introduced and used to design the VGTM module through under-actuation. Under this design, each module is over-constrained, composed of both active and pa...
Article
This paper presents a practical and effective framework for updating landing gear finite element component models such that the updated reduced-order component mode synthesis model of the entire assembled system can provide accurate structural dynamic results in any possible landing gear configuration. By constructing component mode synthesis matri...
Article
This paper presents a method for modeling and analyzing the fatigue life of robots with flexible joints, with a particular focus on applications under percussive impact forces. This development is motivated by growing interests in robotic automation for operations with percussive impact tools. The most important characteristic of percussive operati...
Article
Full-text available
This paper addresses the problem of path tracking of industrial robots. The main idea is to correct a preplanned path through an iterative learning control (ILC) method. Instead of seeking the conventional ILC strategy, an iterative learning identification method, which is called calibration-based ILC, is developed to identify the robot kinematic p...
Article
In wing morphing, it is desirable to have a system that acts both as a load-bearing structure and a morphing mechanism, without any distinction between the two. When dealing with a rather large design space, designing for this requirement would be less challenging because the constituting structural elements could be topologically placed in a fashi...
Article
The ability to vary the geometry of a wing to adapt to different flight conditions can significantly improve the performance of an aircraft. However, the realization of any morphing concept will typically be accompanied by major challenges. Specifically, the geometrical constraints that are imposed by the shape of the wing and the magnitude of the...
Patent
Full-text available
A morphing wing for an aircraft includes a top surface, a bottom surface, a leading edge, a trailing edge, a tip, and a root. A plurality of structural ribs is disposed between the root and tip so that they extend between the top surface and the bottom surface and intersect with a lateral axis thereof. At least one active member connects between tw...
Article
In this paper, we propose a novel outlier diagnosis method for robust pose estimation of rigid body motions from outlier contaminated 3D point measurements. Due to incorrect correspondences in a cluttered measuring environment, observed point data are contaminated by outliers, which are unusual gross errors that lie out of an overall error distribu...
Article
In this paper, a new method is presented for stiffening a tripod made of fixed-length legs. The idea is to add a pair of clamping plates to each leg. In doing so, the out-of-plane motion of the leg is fully constrained, thereby significantly increasing its bending stiffness. Compared to the existing designs, the advantage of this new design is that...
Article
Developed in this paper is a hybrid method for calibration of modular reconfigurable robots (MRRs). The underlying problem under study is unique to MRRs, that is, how to calibrate a set of MRR's geometric parameters that are applicable to all feasible configurations. For this reason, a hybrid search method is developed to ensure a global search ove...
Conference Paper
Presented in this paper is a method for tool path planning for automated polishing. This work is an integral part of the research program on automated polishing and deburring being carried out at Ryerson University. Whereas tool path planning for machining is treated as a geometry problem, it is shown here that tool path planning for polishing shou...
Article
This paper presents a method for the design and analysis of reconfigurable parallel robots. The inherent modularity in a parallel robot lends itself as a natural candidate for reconfiguration. By taking the branches as building blocks, many modular parallel robots can be constructed, from which a reconfigurable parallel robot can be realized. Among...
Article
In this study, a data decorrelation method is developed for processing 3D position measurements obtained by a line sensors based photogrammetric measuring system. The measured 3D data suffer from correlations due to the principle of the triangulation. This nature causes complexity when a calibration procedure is carried out. Additionally, the corre...
Article
Dynamic modeling and simulation of percussive impact riveting are presented for robotic automation. This is an impact induced process to deform rivets, which involves an impact rivet gun driven under pneumatic pressure to pound a rivet against a bucking bar. To model this process, first, a new approach is developed to determine the hammer output sp...
Article
Compared with the serial mechanism, the parallel mechanism has many advantages. Using the parallel mechanism as the basic leg mechanism of a walking robot, not only the payload-weight ratio can be improved, but also the robot walking stability and security performance can be enhanced. By combining the kinematics features of 3-UPU parallel mechanism...
Article
A primary flight control assembly of an in-production business jet aircraft was analyzed to obtain the structural responses. A series of investigations were performed to develop the proper parameters required to execute the optimization runs. Two distinct optimization problems were defined and solved. The first problem consisted of minimizing th...
Article
To enlarge the workspace and improve the motion capability of a parallel robot, the base of the robot can be guided to move along a linear or curved track. This paper aims at analyzing how the motion of the base affects the dynamics of a parallel robot. For this purpose, kinematic and dynamic equations are developed for a circular track-guided trip...
Article
Full-text available
Recursive modelling for the kinematics of the Hexapod parallel robot are established in this paper. Controlled by six forces, the parallel manipulator prototype is a space six-degrees-of-freedom mechanical system with six fixed-length legs connecting to the moving platform. Knowing the position and the general motion of the platform, we develop the...
Article
Full-text available
Recursive matrix relations in kinematics and dynamics of the Hexapod parallel robot are established in this paper. Controlled by six forces, the parallel manipulator prototype is a space six-degrees-of-freedom mechanical system with six fixed-length legs connecting to the moving platform. Knowing the position and the general motion of the platform,...
Conference Paper
Recently there has been a trend in developing morphing airborne structures to positively affect the aerodynamics, flight performance and stability of aircraft, and act as replacements for control surfaces. Most wing level morphing projects focus on variable sweep, dihedral, wing twist or span, but very few combine more than one of these morphing me...
Conference Paper
The manipulator workspace denotes the work area of a manipulator and it is an important foundation of designing a robot. The workspace of a novel symmetrical 4-DOF 3-RRUR parallel manipulator is researched here based on the inverse solution. Five essential conditions of a point within the workspace of the manipulator are presented and the cause of...
Chapter
In this chapter, the inverse dynamics of hexapods with fixed-length legs is analyzed using the natural orthogonal complement method, with considering the mass of the moving platform and those of the legs. A complete kinematics model is developed, which leads to an explicit expression for the twist-mapping matrix. Based on that, the inverse dynamics...
Book
Full-text available
With increasingly complex manufacturing systems and processes, more intelligent and unique devices and machines are needed to support manufacturing operations. Smart Devices and Machines for Advanced Manufacturing presents a focussed collection of quality chapters on the state-of-the-art of research efforts in the area of smart devices and novel ma...
Article
This paper studies the problem of the nonstationary vibration of a fully flexible parallel kinematic machine (PKM) that has flexibilities both in links and in joints. In the stationary case, the PKM was treated as a varying structure and the natural frequencies and mode shapes changed with the changes in the PKM configuration, without consideration...
Article
This paper discusses a 3-dof (degree of freedom) parallel robotic attachment and its remote manipulation. This attachment is designed as a tripod that provides two rotary motions and one linear motion. The attachment can be mounted onto a variety of machines for different applications, including CNC milling machines, industrial robots, and CMM. Jav...
Article
In this paper a re-configurable parallel robot is presented which consists of two base tripods. The first tripod is made of three prismatic joints with the fixed-leg length, called slide tripod. The second tripod is made of three revolute joints, called swing tripod. While the slide tripod is fixed to the moving platform, the branches of the swing...
Article
This paper presents a real-time method for solving the forward kinematics of a tripod with fixed-length legs. The basic idea is to model the problem at hand based on a spatial four-bar linkage through which three sliding legs can be interrelated by choosing one link as a driving variable and other two links as driven variables. As a result, the ori...
Conference Paper
In this article, a new method is proposed for cutting tool wear detection and compensation based on Lipschitz exponent In general, there are three phases in tool wear, namely, incipient, normal and dramatic phase. And there are different values of Lipschitz exponents of cutting force signal in different phases. So we can identify the different phas...
Article
This paper presents a new shape adaptive motion control system that integrates part measurement with motion control. The proposed system consists of four blocks: surface measurement; surface reconstruction; tool trajectory planning; and axis motion control. The key technology used in surface measurement and surface reconstruction is the spatial spe...
Article
In this paper, a new method for modeling and predicting the surface roughness of the workpiece in the stone polishing process is developed. This method is based on the random distribution of the stone grain protrusion heights and the force balance by contact grains. To do so, first, the topography of a polishing stone is generated based on a Gaussi...
Article
This paper describes the measurement and reconstruction of the leaflet geometry for a pericardial heart valve. Tasks involved include mapping the leaflet geometries by laser digitizing and reconstructing the 3D freeform leaflet surface based on a laser scanned profile. The challenge is to design a prosthetic valve that maximizes the benefits offere...
Article
In this paper, the static balancing of spatial parallel manipulator is addressed. Static balancing is defined as that the weight of the links does not produce any force at actuators for any configuration of the manipulator. In order to obtain the balancing condition, the position vector of the global center of the mass is expressed as a function of...