An Advisory Conceptual Design Tool for Mechanical Transmission Systems

This paper presents an advisory conceptual design tool for mechanical transmission systems. Space consideration was taken into account during the design process. A prototype function tree was built in the form of knowledge-based system to transfer a designer’s idea into a set of mechanical components. An advisory expert system was also developed to help a designer in decision making. As an example, a packaging machine is designed using the developed system.

A New Method and Automatic Generation for Dynamic Analysis of Complex Planar Mechanisms Based on the Ordered Single-Opened-Chains

This work presents a new method for kinetostatic analysis and dynamic analysis of complex planar mechanisms, i.e. the ordered single-opened-chains method. This method makes use of the ordered single-opened chains (in short, SOC,) along with the properties of SOC, and the network constraints relationship between SOC,. By this method, any planar complex mechanism can be automatically decomposed into a series of the ordered single-opened chains and the optimal structural decomposition route (s) can be automatically selected for dynamic analysis, the paper present the dynamic equation which can be used to solve both the kinetostatic problem and the general dynamic problem. The main advantage of the proposed approach is the possibility to reduce the number of equations to be solved simultaneously to the minimum, and its high automation as well. The other advantage is the simplification of the determination of the coefficients in the equations, and thus it maybe result in a much less time-consuming algorthem. The proposed approach is illustrated with three examples. The presented method can be easily extended to the dynamic analysis of spatial mechanisms.

Estimation of Critical Damping in Robot Joints and Identification of the Joint for Design With Most Effective Damping Enhancement

A major hindrance to dynamics and control of flexible robot manipulators is the deficiency of its inherent damping. Damping enhancement, therefore, should result in lower vibration amplitudes, shorter settling times, and improvement of system stability. Since the bulk of robot vibrations is attributed to joint compliance, it is a prudent strategy to design joints with sufficient inherent damping. In this article, a method is proposed to estimate critical damping at each joint and identify the joint that should be targeted for design with sufficient built-in damping. The target joint identification process requires that a n-joint robot system is divided into n-subsystems. Subsystem i includes the compliance of joint i and the inertia of the succeeding links, joint mechanisms, and payload. An equivalent single degree of freedom torsional model is devised and the natural frequency and critical damping is evaluated for each subsystem. The estimated critical damping at the joints are used to determine the elastodynamic response of the entire robot system from a model that includes joint compliance, shear deformation, rotary inertia, and geometric stiffness. The response revealed the following conclusion: The joint of the manipulator that would result in lower amplitudes of vibrations and shorter settling times when designed with sufficient built-in damping is the one that renders a subsystem whose natural frequency is the lowest of all subsystems comprising the robot.

Multiple-Mode Input Shaping Sequences for Reducing Residual Vibrations

A closed-form method of calculating Input Shaping sequences for two modes of vibration is presented. The new method eliminates the optimization routines previously required to find the same solutions. Input Shaping is a feed forward method of reducing residual vibrations in flexible structures by convolving an Input Shaping sequence with a command profile. The two-mode sequences are installed on a four-axis robot used in the manufacture of silicon wafers — the Cassette Management System. The new sequences are found to significantly improve the performance of the system. In standard throughput tests, speed increases of 15%–25% were obtained on each axis while vibrations were simultaneously reduced by 20%–90%.

Steady-State Rigid-Body Dynamic Response of Cam-Follower Mechanisms

The camshaft of a cam-follower mechanism experiences a position-dependent moment due to the force exerted on the cam by the follower, causing the angular speed of the camshaft to fluctuate. In this work, a method to expediently predict the camshaft speed fluctuation is developed. The governing equation of motion is derived assuming that the cam-follower system is an ideal one wherein all members are treated as rigid. An existing closed-form numerical algorithm is used to obtain the steady-state rigid-body dynamic response of a machine system. The solution considers a velocity-dependent moment; specifically, a resisting moment is modeled as a velocity-squared damping. The effects of flywheel size and resisting moment on camshaft speed fluctuation are studied. The results compare favorably with those obtained from transient response using a direct integration scheme. The analytical result also shows excellent agreement with the camshaft speed variation of an experimental cam-follower mechanism. The steady-state rigid-body dynamic response obtained herein also serves as a first approximation to the input camshaft speed variation in the dynamic analysis of flexible cam-follower mechanisms in a subsequent research.

Dynamic Model of a Spur Gear System With Backlash and Friction Consideration

A new model which accounts for both backlash and friction effects is proposed for the dynamics of a spur gear system. The model estimates average friction torque and uses it to replace the instantaneous friction torque to simplify the dynamical equations of motion. Two simulations, free oscillation and constant load operation, are performed to illustrate the effects of backlash and friction on gear dynamics. The results are compared with that of a previously established model which does not account for the friction. Finally, the effect of adding a damper on the driving shaft is also studied. This model is judged to be more realistic for real time control of electronmechanical systems to reduce gear noise and to achieve high precision.

Application of Threshold Logic to the Design and Analysis of Latching Systems in Deployers of Deployable-Retractable Structures

To erect deployable structures from a compact folded state, a supplemental mechanism called a deployer is used. Many latches are present in the deployer and these are coordinated in some logical and systematic manner to bring about the deployment. This article presents an investigation into analyzing the logic behavior of a deployer and design such latching systems in deployers in a more systematic manner; the logic functions used are based on modifications of the Mechanical Threshold Logic approach.

Computer-Aided Sketching of Epicyclic-Type Automatic Transmission Gear Trains

The enumeration of epicyclic gear mechanisms in the form of graphs gives rise to the need of a methodology for reverse transformation, that is, for constructing the mechanisms from graphs. This paper addresses the issue by discretizing an epicyclic gear mechanism into Fundamental Geared Entities. Further, these geared entities are shown to be a conglomeration of four primitives; namely, the carrier, sun, ring, and the planet gear. An algorithm is formulated to create the entities from a graph by using these primitives. The entities are then connected together to form a mechanism.

A General Theory for Complete Balancing of Shaking Force and Shaking Moment of Spatial Linkages Using Counterweights and Inertia-Counterweights

The links of a spatial linkage with v independent loops can be divided into two parts — a set of v chord-links and a tree-system. Add a suitable counterweight to each chord-link for satisfying the certain conditions, under which, the v chord-links can be completely shaking force-moment-balanced by the counterweights and inertia-counterweights attached to the tree-system of the linkage; The conditions for complete balance of shaking force and shaking moment of the tree system can be written directly without extracting them from the kinematic equation of the linkage; A formula which define the minimum number of inertia-counterweights needed for a complete shaking-moment-balance and the criteria for selecting the optimum chord-link set have been presented. Two examples (a Bennett linkage and a spherical six-bar linkage) are provided.

A Finite Element Formulation of Flexible Slider Crank Mechanism Using Local Coordinates

The need for higher productivity has lead to the design of machines operating at higher speeds. At high speed the rigid body assumption is no longer valid and the links should be considered flexible. In this work a method which is based on Modified Lagrange Equation for modeling flexible mechanism is presented. The method posses a more computational efficiency for not requiring the transformation from the local coordinate system to the global coordinate system. Also an approach using the homogeneous coordinate for element matrices generation is presented. The approach leads to a formalism where the displacement vector is expressed as a product of two matrices and a vector. The first matrix is a function of rigid body motion. The second matrix is a function of rigid body configuration. The vector is a function of elastic displacement. This formal separation helps to facilitate the generation of element matrices using symbolic manipulations.