Raymond J. Cipra

Simplified Kinematic Analysis of Bevel Epicyclic Gear Trains With Application to Power-Flow and Efficiency Analyses

A kinematic analysis technique is introduced to find the angular velocities of all links in bevel epicyclic gear trains. The method relies on previous work in graph theory. It improves on existing techniques used for analysis of planar geared mechanisms in its ability to accurately solve the kinematics of spatial geared mechanisms, particularly bevel gear trains, in a simpler manner. Usefulness of the method is demonstrated through its application to power-flow and efficiency analyses as well as its implementation in computer software. This discussion is limited to gear trains whose input and output axes are collinear, such as automotive automatic transmissions.

Structural integrity during remanufacture of a topologically interlocked material

Purpose – Topologically interlocked materials are a class of materials in which individual unit elements interact with each other through contact only. Cracks and other defects occurring due to external loading are contained in the individual unit elements. Thus, topologically interlocked materials are damage tolerant and provide high structural integrity. The purpose of this paper is to investigate the concepts of remanufacturing in the context of a material for which the intended use is structural such that the materials structural integrity is of concern. In particular, the study is concerned with the mechanical behavior of a topologically interlocked material.Design/methodology/approach – A topologically interlocked material based on tetrahedron unit elements is investigated experimentally. Manufacturing with aid of a robotically controlled end‐effector is demonstrated, and mechanical properties are determined for a plate configuration. A conceptual mechanical model for failure of topologically inter...

Optimal Contact Force Distribution for Multi-Limbed Robots

One of the inherent problems of multi-limbed mobile robotic systems is the problem of multi-contact force distribution; the contact forces and moments at the feet required to support it and those required by its tasks are indeterminate. A new strategy for choosing an optimal solution for the contact force distribution of multi-limbed robots with three feet in contact with the environment in three-dimensional space is presented. The incremental strategy of opening up the friction cones is aided by using the “force space graph” which indicates where the solution is positioned in the solution space to give insight into the quality of the chosen solution and to provide robustness against disturbances. The “margin against slip with contact point priority” approach is also presented which finds an optimal solution with different priorities given to each foot contact point. Examples are presented to illustrate certain aspects of the method and ideas for other optimization criteria are discussed.

Kinetogami: A Reconfigurable, Combinatorial, and Printable Sheet Folding

As an ancient paper craft originating from Japan, origami has been naturally embedded and contextualized in a variety of applications in the fields of mathematics, engineering, food packaging, and biological design. The computational and manufacturing capabilities today urge us to develop significantly new forms of folding as well as different materials for folding. In this paper, by allowing line cuts with crease patterns and creating folded hinges across basic structural units (BSU), typically not done in origami, we achieve a new multiprimitive folding framework such as using tetrahedral, cuboidal, prismatic, and pyramidal components, called “Kinetogami.” “Kinetogami” enables one to fold up closed-loop(s) polyhedral mechanisms (linkages) with multi-degree-of-freedom and self-deployable characteristics in a single build. This paper discusses a set of mathematical and design theories to enable design of 3D structures and mechanisms all folded from preplanned printed sheet materials. We present prototypical exploration of folding polyhedral mechanisms in a hierarchical manner as well as their transformations through reconfiguration that reorients the material and structure. The explicit 2D fabrication layout and construction rules are visually parameterized for geometric properties to ensure a continuous folding motion free of intersection. As a demonstration artifact, a multimaterial sheet is 3D printed with elastomeric flexure hinges connecting the rigid plastic facets. [DOI: 10.1115/1.4025506]

Processing–microstructure-property predictions for short fiber reinforced composite structures based on a spray deposition process

Manufacturing of composite preforms by use of a programmed and controlled reinforcement spray deposition process presents itself as an attractive approach to produce short fiber reinforced composite structures. To predict properties of the final composite structure, simulations of the reinforcement deposition process are conducted to obtain the reinforcement orientation distribution. A micromechanics analysis incorporating the Mori–Tanaka method and texture tensors is used to predict the properties of the final consolidated composite parts. This processing–microstructure-property prediction scheme is applied to the analysis of composite structures in the carbon–carbon system. The effects of variations in reinforcement length in the spray deposited preform, and boundary effects as occurring in a near-net shape composite disk are discussed.

Visualization of the Contact Force Solution Space for Multi-Limbed Robots

This paper addresses the determination, representation, and visualization of the contact force solution space of a multi-limbed mobile robotic system with three feet in contact with its environment. Since the limbs of the robot have enough joints and are actively controlled, the contact forces at the feet need to be explicitly chosen to ensure that the robot does not lose its balance and does not slip at a foot. One of the major difficulties associated with finding the force distribution solution has been the indeterminate nature of the problem. Any system with three or more contact points makes it an underspecified system involving redundancy since there are more unknowns than the number of equations. The other major difficulty associated with the problem of multi-contact force distribution has been the nonlinear nature of the three-dimensional friction cone model. Instead of finding just a single contact force solution through optimization methods as is the case for most previous work on this subject, the presented method describes all the possible solutions solution space for the contact force distribution for a statically stable body under friction constraints. The optimal contact force solution can then be chosen in this solution space which maximizes the objectives given by the chosen optimization criteria. This two-step approach allows one to have more options and freedom in choosing the final solution and to satisfy other special conditions that might be considered at that instant. This paper presents the method for finding the solution space as the first step of finding the optimal contact force distribution. The second step of choosing the optimal solution in this solution space was presented in 1‐3.

A Method for Representing the Configuration and Analyzing the Motion of Complex Cable-Pulley Systems

In this paper a systematic way of representing complex cable-pulley mechanism configurations and a method to analyze their motion is presented. This technique can also be used as an aid for synthesis. The cable-pulley system model that is being considered is planar and composed of three basic elements which are pulleys, blocks, and cables. A configuration table is used to identify the constraint equations by systematically defining the connections between the cables, pulleys, and blocks. The basic strategy is to use the constraint equations to generate the relationship between each variable and a subset of the variables identified as the inputs. A row reduction process on the system of constrainst equations identifies the number of inputs and ultimately generates the relationships of each variable to the input(s). Results with different input variables can be easily obtained by a simple column interchange process. Examples are given to illustrate the procedure.

Scaling of the Elastic Behavior of Two-Dimensional Topologically Interlocked Materials Under Transverse Loading

Topologically interlocked materials (TIMs) are a class of 2D mechanical crystals made by a structured assembly of an array of polyhedral elements. The monolayer assembly can resist transverse forces in the absence of adhesive interaction between the unit elements. The mechanical properties of the system emerge as a combination of deformation of the individual unit elements and their contact interaction. The present study presents scaling laws relating the mechanical stiffness of monolayered TIMs to the system characteristic dimensions. The concept of thrust line analysis is employed to obtain the scaling laws, and model predictions are validated using finite element simulations as virtual experiments. Scaling law powers were found to closely resemble those of classical plate theory despite the distinctly different underlying mechanics and theory of TIM deformation.

Adaptive mechanical properties of topologically interlocking material systems

Topologically interlocked material systems are two-dimensional granular crystals created as ordered and adhesion-less assemblies of unit elements of the shape of platonic solids. The assembly resists transverse forces due to the interlocking geometric arrangement of the unit elements. Topologically interlocked material systems yet require an external constraint to provide resistance under the action of external load. Past work considered fixed and passive constraints only. The objective of the present study is to consider active and adaptive external constraints with the goal to achieve variable stiffness and energy absorption characteristics of the topologically interlocked material system through an active control of the in-plane constraint conditions. Experiments and corresponding model analysis are used to demonstrate control of system stiffness over a wide range, including negative stiffness, and energy absorption characteristics. The adaptive characteristics of the topologically interlocked material system are shown to solve conflicting requirements of simultaneously providing energy absorption while keeping loads controlled. Potential applications can be envisioned in smart structure enhanced response characteristics as desired in shock absorption, protective packaging and catching mechanisms.

Gaseous Cavitation and Wear in Lubricated Fretting Contacts

Fretting phenomena operating in the presence of grease was investigated experimentally and analytically. A fretting test rig was designed, developed, and equipped with a microscope and high-speed video camera to observe the effects of the lubricant entrainment within the contact during the fretting phenomena. A mixed elastohydrodynamic lubrication model was used to analytically investigate lubricated fretting and corroborate with experimental results. An analytical approach is also presented to determine the amount of lubrication entrained within the fretting contact. The results of fretting wear operating in the presence of grease are presented for case-hardened steel in the crossed cylinder configuration and hardened steel ball-on-sapphire flat configuration. The roles of lubrication, oscillation amplitude, and cavitation in fretting are presented and discussed. Lubrication was found to mitigate the effect of fretting on a surface while the effect of oscillation amplitude on fretting was more complex. The results indicate that frequency increases the amount of material transfer between fretting surfaces. Gaseous cavitation was observed to occur in the trailing edge of the fretting contact and increased with speed. A closed form equation was derived to approximate the volume of the lubricant entering the fretting contact area during the fretting motion and explain the effect of test conditions on fretting wear.