Ting Zou

Design and optimization of a drivetrain with two-speed transmission for electric delivery step van

The use of a two-speed transmission in electric delivery step vans to improve performance and efficiency is discussed in this paper. Two important tasks relating to this application are considered. The first task includes the development and optimization of a two-speed transmission, where the gear ratios are used as design variables, while vehicle performance and energy consumption are design objectives. The procedure is based on simulation and optimization. The simulation model and the optimization process are described. The second task includes the estimation of the efficiency and comparison of the performance of an electric step van with a direct drive setup versus the vehicle with the two-speed transmission.

Structural and instrumentation design of a microelectromechanical systems biaxial accelerometer

Microscale biaxial accelerometers are required to be sensitive to applied accelerations and manufacturable by means of microelectromechanical systems technology. In order to meet these requirements, a compliant realization of biaxial accelerometers, dubbed simplicial biaxial accelerometers, has been proposed, as reported in this paper. Notched joints, to realize what is termed Π-joints in the parallel-robots literature, are employed and then improved by the introduction of Lamé-shaped hinges serving as flexible joints. The sensitivity of the simplicial biaxial accelerometers in estimating accelerations is investigated and validated by means of finite element analysis. The sensing system is embedded in the simplicial biaxial accelerometers, with piezoresistive sensing technology adopted in the instrumentation design. Using the principles of piezoresistive sensing, the electronic layout is developed for the accelerometer. Through the piezoresistive analysis implemented on the finite element model of the simplicial biaxial accelerometers, the matrix that maps voltage signals into acceleration signals is derived. By virtue of both the structural and electronic designs, the accelerometer is observed to be sensitive to accelerations in its plane, but fairly insensitive to accelerations in any of the other four directions of the rigid-body motion. Finally, prototypes were fabricated with microelectromechanical systems technology to test the microfabrication feasibility of the structure and measurement system of the accelerometer. Test results are the subject of a forthcoming paper.

Isotropic Accelerometer Strapdowns and Related Algorithms for Rigid-Body Pose and Twist Estimation

A novel design of accelerometer strapdown, intended for the estimation of the rigid-body acceleration and velocity fields, is proposed here. The authors introduce the concept of isotropic-polyhedral layout of simplicial biaxial accelerometers (SBA), in which one SBA is rigidly attached at the centroid of each face of the polyhedron. By virtue of both the geometric isotropy of the layout and the structural planar isotropy of the SBA, the point tangential relative acceleration is decoupled from its centripetal counterpart, which is filtered out, along with the angular velocity. The outcome is that the rigid-body angular acceleration can be estimated independent of the angular velocity, thereby overcoming a hurdle that mars the estimation process in current accelerometer strapdowns. An estimation algorithm, based on the extended Kalman filter, is included. Simulation results show an excellent performance of the proposed strapdowns in estimating the acceleration and velocity fields of a moving object along with its pose.

Decoupling of the Cartesian Stiffness Matrix: A Case Study on Accelerometer Design

The 6 × 6 Cartesian stiffness matrix obtained through finite element analysis for structures designed with material and geometric symmetries may lead to unexpected coupling that stems from discretization error. Hence, decoupling of the Cartesian stiffness matrix becomes essential for design and analysis. This paper reports a numerical method for decoupling the Cartesian stiffness matrix, based on screw theory. With the aid of this method, the translational and rotational stiffness matrices can be analyzed independently. The mechanical properties of the decoupled stiffness submatrices are investigated via their associated eigenvalue analyses. The decoupling technique is applied to the design of two accelerometer layouts, uniaxial and biaxial, with what the authors term simplicial architectures. The decoupled stiffness matrices reveal acceptable compliance along the sensitive axes and high off-axis stiffness.Copyright

OPTIMIZATION OF TOOTH ROOT PROFILE OF SPUR GEARS FOR MAXIMUM LOAD-CARRYING CAPACITY

Increasing the strength of the gear tooth is a recurrent demand from industry. The authors report a novel approach to the design of tooth-root profile of spur gears using cubic splines, with the aim of investigating the effect of tooth-root geometry on stress concentration in order to increase the gear tooth strength by optimizing the root profile. An iterative co-simulation procedure, consisting of tooth-root profile shape synthesis via nonlinear programming and finite element analysis software tools is conducted, for the purpose of forming the tooth-root geometry design with the minimum stress concentration. The proposed design was verified to be capable of reducing the stress concentration by 21% over its conventional circular-filleted counterpart. Hence, the results showcase an innovative and sound methodology for the design of the tooth-root profile to increase gear load-carrying capacity.Copyright

Design Specifications for Biaxial Navigation-Grade MEMS Accelerometers

The focus of this paper is the design of a biaxial MEMS accelerometer for navigation applications. First, a survey is conducted to outline the commercial landscape of navigation-grade and MEMS accelerometers. The survey shows a potential market for navigation-grade accelerometers at the MEMS scale. Based on the specifications for navigation applications, the design targets are derived for the proposed biaxial MEMS accelerometers, including the common concerns of natural frequency ratios and bandwidth, as well as the important parameters for MEMS devices, such as hinge width, proof-mass size and mobility range. In light of the design targets, the ideal frequency matrix of the biaxial accelerometer system is derived based on the concept of generalized spring, in connection with the design targets. The stiffness values required are estimated herein. For further structural optimization, the parametric entries of the frequency-ratio matrix act as the objectives to be maximized for the lowest off-axis sensitivity of the proposed accelerometer. A suitable architecture for MEMS biaxial accelerometers is proposed thereafter. This architecture not only provides high compliance and structural isotropy for the in-plane translation, but also allows for direct measurement of the proof-mass motion. The proposed architecture is then optimized for the highest frequency ratio between the non-sensitive and sensitive axes, with regard to the design parameters and constraints. The optimization results of the proposed accelerometer demonstrate navigation-grade mechanical performance.Copyright

Dynamic modeling and trajectory tracking control of unmanned tracked vehicles

Abstract Tracked vehicles have inherent advantages over wheeled vehicles, as the former provide stable locomotion on loose and uneven terrain. However, compared with the latter, the slippage generated due to the complex, nonlinear track-terrain interactions during skid-steering to follow a curve, brings about difficulties preventing the accurate prediction of their motions. The key to improving the accuracy of trajectory-following is the “proper” motion control methodology that can accurately factor-in the slippage behavior. In this paper, the authors propose a novel approach to the dynamic modeling and motion control of tracked vehicles undergoing skid-steering on horizontal, hard terrain, under nonholonomic constraints. Due to the skew-symmetry property of nonholonomic mechanical systems, the control methodology is established using the backstepping method based on a modified Proportional–Integral–Derivative (PID) computed-torque control. A key element in the control strategy proposed here is the reliable estimation of the pose – position and orientation – of the vehicle platform and its twist—point velocity and angular velocity. It is assumed that the vehicle is suitably instrumented to allow for accurate-enough pose and twist estimates. Validated via a numerical example, the proposed controller is proven to be effective in controlling an unmanned tracked vehicle.

Design of Isotropic Accelerometer Strapdowns for Rigid-Body Pose-and-Twist Estimation

Coupling of tangential and centripetal acceleration components occurs in the estimation of rigid-body pose and twist with current accelerometer strapdowns. To address this shortcoming and its pernicious effects, a novel design of biaxial accelerometer strapdown is proposed. By virtue of its inherent isotropy, point tangential acceleration is decoupled from its centripetal counterpart, thereby realizing a straightforward and accurate acceleration estimation. The algorithm associated with the strapdown is validated by means of a numerical example, which shows the precision of the strapdown in estimating rigid-body pose and twist.Copyright