ngjing Ji

Cantilever Snap-Fit Performance Analysis for Haptic Evaluation

This paper investigates the parametric effects, which include material properties, hook shape, and shear deformation, on the force=deflection relationship governing the assembly=disassembly processes of a snap-fit for developing embedded algebraic solutions to achieve realistic force feedback through a haptic device. For this purpose, an algebraic model, which isolates individual parametric factors that contribute to the cantilever hook deflection, has been derived for examining assumptions commonly made to simplify models for design optimization and real-time control. The algebraic model has been verified by comparing computed results against those simulated using ANSYS FEA workbench and published approximate solutions. Additionally, the model has been validated by comparing the friction coefficients of three different snap-fit designs (with same materials), which closely agree within 5% of their root-mean-square value. Implemented on a commercial PHANTOM haptic device, we demonstrate the effectiveness of the model as embedded algebraic solutions for haptic rendering in design. Nine individuals participated in evaluating a set of design options with different parameter settings; 78% of whom chose the optimal theoretical solution by feeling the feedback force. These findings demonstrate that the design confidence of assembly robustness can be enhanced through a relatively accurate virtual force feedback. [DOI: 10.1115/1.4005085]

A two-mode six-DOF motion system based on a ball-joint-like spherical motor for haptic applications

A ball-joint-like spherical motor capable of offering smooth, continuous multi-DOF motion is presented as an alternative design for haptic applications. With a two-mode configuration, this device can be operated as a joystick manipulating a target in six degrees-of-freedom (DOF), and provides realistic force/torque feedback in real-time. Utilizing the magnetic field measurements, the orientation and the torque-to-current coefficients can be computed in parallel; this novel scheme greatly improves the sampling rate as well as reduces error accumulation commonly found in multi-DOF robotic devices. Of particular interest here is to explore this two-mode design in a computer-aided virtual environment. As an intuitive illustration, the disassembly process of a snap-fit (consisting of a typical cantilever hook and a wedge-shaped end) is simulated, where the two-mode permanent magnet spherical motor haptic device is incorporated as an interfacing device that receives motion commands from a virtual design environment and delivers torque feedback to the designer/user.

A Passive Gait-Based Weight-Support Lower Extremity Exoskeleton With Compliant Joints

This paper presents the design and analysis of a passive body weight (BW)-support lower extremity exoskeleton (LEE) with compliant joints to relieve compressive load in the knee. The biojoint-like mechanical knee decouples human gait into two phases, stance and swing, by a dual snap fit. The knee joint transfers the BW to the ground in the stance phases and is compliant to free the leg in the swing phases. Along with a leg dynamic model and a knee biomechanical model, the unmeasurable knee internal forces are simulated. The concept feasibility and dynamic models of the passive LEE design have been experimentally validated with measured plantar forces. The reduced knee forces confirm the effectiveness of the LEE in supporting human BW during walking and also provide a basis for computing the internal knee forces as a percentage of BW. Energy harvested from the hip spring reveals that the LEE can save human walking energy.

Discrete Deformation Models for Real-Time Computation of Compliant Mechanisms in Two- and Three-Dimensional Space

Motivated by the need to develop a real-time computation method for simultaneous real-time visualization and force/torque feedback for manipulating of compliant mechanisms, this paper presents a general formulation of a reduced-order discrete state space model and its solution as a function of path lengths for a three-dimensional (3-D) curvature-based beam model (CBM). Unlike a compliant beam model where the boundary value problem is solved using a shooting method, the state-space representation decouples the 13th order CBM into two sets of reduced-order ordinary differential equations; the first solves for the orientation and moment whereas the second describes the deformed beam shape. Thus, it enables parallel computation of the deformed shape from the solutions to the orientation and moments. As illustrative examples, the state-space formulation and real-time computation method have been applied to analyze two flexure-based mobile-sensing node (FMN) designs. The new design, which overcomes several kinematic limitations and practical implementation problems commonly encountered in FMN navigation in tight 3-D space, permits bending and twisting of the compliant beam in 3-D space. The discrete linear CBM for the two FMN designs has been validated experimentally as well as verified by comparing computed results against published data and simulations using multishooting method and finite-element analysis.

An Efficient Flexible Division Algorithm for Predicting Temperature-Fields of Mechatronic System with Manufacturing Applications

This paper presents a new thermal-field modeling method referred to here as a flexible division algorithm (FDA) for predicting the temperature fields of a mechatronic system, and its real-time applications where thermal effects have a significant influence on the performance and reliability of the final products. This algorithm, which takes advantages of the flexible division in 3-D space to deal with the spatial distribution of thermal fields, is built upon physical laws to derive the governing equations in state-space representation that facilitates the reconstruction and control of the thermal field being analyzed. Three numerical models (involving both Cartesian and cylindrical coordinates) are illustrated to highlight the effectiveness and usefulness of the FDA for real-time modeling and computing. In the context of a thin-walled component machining application, the FDA is evaluated numerically and validated experimentally. Its solutions agree well with results computed using commercial finite-element analysis (FEA) software, confirming its ability to obtain accurate results, but with significantly less computation time, and its effectiveness as a complement to FEA when real-time computing of a physical field is required.

An investigation on temperature measurements for machining of titanium alloy using ir imager with physics-based reconstruction

In general, the physical field in a domain can be uniquely determined from appropriate physical laws by its field conditions on its boundary surfaces. In machining, the ability to measure the tool surface temperature distribution is highly desirable as it provides an essential basis to reconstruct the thermal model for monitoring tool and workpiece conditions, particularly when machining hard to machine materials (such as titanium alloy that exhibits excellent mechanical properties and corrosion resistance). Because of the extremely high temperature gradient within a very small area, the need for developing an effective non-contact measurement technique has been a well-recognized problem. In the context of dry lathe-turning of titanium alloy, this paper presents a method based on non-contact infrared images to reconstruct the temperature field of the tool insert. Unlike traditional methods that base on limited thermocouple measurements or direct reading of absolute temperature from infrared images, the method presented here utilizes physical laws and heat transfer properties (temperature contours and their gradients) to identify thermal discontinuities, separate chips from the tool insert and reconstruct the obtruded tool temperature field.

A Hybrid Method Based on Macro–Micro Modeling and Infrared Imaging for Tool Temperature Reconstruction in Dry Turning

In metal cutting, the ability to model its tool temperature distribution is highly desirable, as it provides an effective means to monitor the tool and workpiece conditions, particularly when machining hard-to-machine materials that have a low heat conductivity. Because of the complex heat generation in the microscale tool–chip interface, the difficulty to infer its temperature distribution is a well-known problem. In the context of dry lathe turning, this paper presents a hybrid method that considers both the macroscale tool heat transfer and microscale machining mechanics to reconstruct the 3-D tool temperature field from nonobstructed infrared (IR) images. The microscale-mechanics model identifies the contact geometry and estimates the frictional heat input to determine the complete boundary conditions to solve the macroscale heat-transfer model for the steady-state 3-D temperature distribution that provides a basis for experimentally fitting the model by comparing the computed surface temperature with actual temperature measurements. Two sets of experimental results validating the reconstructed temperature on a customized orthogonal-cutting testbed with a high-resolution IR imager and evaluating the effectiveness of the hybrid method on a lathe-turning center are presented. The results demonstrate that with the hybrid macro–micro modeling, the 3-D steady-state temperature field of a typical commercial lathe tool insert can be accurately reconstructed from a relatively low-resolution IR image.

Physical Field-Enhanced Intelligent Space with Temperature-Based Human Motion Detection for Visually Impaired Users

This paper presents a method utilizing temperature field to improve the indoor mobility of the blind/visually-impaired-people (Blind/VIP) in a physical field-enhanced intelligent space (iSpace) that takes advantages of the rapidly developing cloud-computing and personal mobile devices (generally built with sound, image, video and vibration alert capabilities) to share way-finding information among users. A method, which uses temperature fields and their gradients to detect face-orientation and analyze leg-postures for predicting the motion states of other humans in a traveling path, is introduced. The concept feasibility of the temperature-based human motion detection has been experimentally validated in a simulated school environment for the Blind/VIP where users are generally familiar with stationary objects but less confident in daily walking in a crowd where human motion is unpredictable. The experimental findings presented in this paper establish a basis for developing temperature filed-enhanced iSpace.

Cutting tool temperature field reconstruction using hybrid macro/micro scale modeling for machining of titanium alloy

In metal cutting, the ability to model its tool temperature distribution is highly desirable as it provides an effective means to monitor the tool and workpiece conditions, particularly when machining titanium alloy that has a low heat conductivity. Because of the complex cutting heat generation, the difficulty to infer the temperature distribution at the cutting interface has been well-recognized as a worldwide problem. In the context of dry lathe-turning of titanium alloy, this paper presents a method that considers both the macro-and micro-scales in the reconstruction of the temperature field at the tool insert. In micro-scale modeling, a modified constitutive material model for TC4 is incorporated in simulating the machining process, which numerically obtains the boundary conditions including contact areas and heat flux following through the tool-chip interface for the macro-scale heat-transfer model. The temperature distribution of the cutting tool can then be solved directly from the heat transfer model, which also provides a basis for experimental validation using infrared thermal imager for temperature measurements.

Design of a Passive Gait-Based Lower-Extremity-Exoskeleton for Supporting Bodyweight

This paper presents the design of a bodyweight-supporting lower-extremity-exoskeleton LEE with compliant joints to relieve compressive load in human knees during walking. Based on experimental measurements that relate plantar forces with gait phase, the design of a gait-based LEE is divided into BW-supporting and free-swinging and realized by means of built-in compliant mechanisms in its exoskeleton-knees. Design considerations to accommodate human knee geometry and adapt walking gaits are highlighted. The snap-fit mechanisms for human gait-based operations are illustrated and analyzed numerically. The effects of several different exoskeleton-knee designs on reducing plantar force are experimentally compared validating the effectiveness and light-weight advantages of LEE in reducing plantar force in walking.