Kassim Abdul-Sater

Two-Configuration Synthesis of Origami-Guided Planar, Spherical and Spatial Revolute–Revolute Chains

This paper presents a topological and dimensional kinematic synthesis methodology that can be used to constrain the movement of kinematic planar, spherical, and spatial revolute–revolute dyads (RR dyads). The approach is inspired by a subcategory of origami called rigid origami, which deals with highly overconstrained spatial deployable linkages. An example is the Miura-ori folding pattern used to deploy solar panels in space. In addition to this application, this linkage also provides an interesting way to constrain general RR dyads so that they perform a single DOF motion. Here, these mechanisms are called origami-guided RR chains, and computer aided design models (CAD) of the planar, spherical and spatial type are presented. The dimensional synthesis approach allows us to constrain consecutive links using R or C joints so that the links satisfy two arbitrarily predefined task positions. This leads to what we call the two-configuration synthesis of linkages, and we examine a concrete synthesis procedure for an origami-guided spatial RR chain, which is also built using rapid prototyping. The procedure actually combines the two-configuration synthesis approach with the synthesis of the spatial TS dyad, and the paper provides an outlook on further ways to apply the two-configuration synthesis and also to synthesize the origami-guided RR chains.

Wheelchair Models With Integrated Transfer Support Mechanisms and Passive Actuation

The concept presented in this paper describes two new approaches to integrate transfer support functions into wheelchairs. The goal is to relieve caregivers and nurses in their daily task of lifting patients from and to the wheelchair without the need of an additional external lift device, such as commonly used lifting cranes or lifting belts. The contributions of this paper are (i) the design of two different mechanical linkages, which realize two types of transfer motions, (ii) the selection of a passive actuator for weight compensation and simulation of the force induced by it (static design), as well as (iii) the experimental evaluation of the simulation using rapid prototyping functional models of the concepts. The results are two different design concepts, each of which can realize a particular, smooth transfer motion.

Similitude of Scaled and Full Scale Linkages

This paper studies approaches for determining an optimal scaling factor for the building of scaled linkage prototypes that take similar deformation behavior to the original linkage into account. Beam theory is used for determining scaling laws with neglecting transversal contraction. A more general approach is shown, using a three-dimensional linear-elastic case. Both approaches take weight and external loads into account. It is shown that an optimal scaling factor depends on the material properties of model and original. FEM is used for validation. According to a FEM validation the scaling factor obtained by the beam theory approach was better suited for our example.

Bio-Kinematic Design of Individualized Lift-Assist Devices

Rising from a chair is a fundamental movement in daily life and a prerequisite for independent functional ability. Yet, it remains one of the most biomechanically demanding activities as it requires high levels of neuromuscular coordination, muscle strength and postural control (Ellis et al. J Biomed Eng 6:113–120 (1984), [3]). While standing up is considered a natural ubiquitous skill it becomes increasingly difficult with age. To prolong the independence of elderly we present a novel computational design procedure for lift-assist devices that are individualized to the user while complying with the limited space within the chair. Given marker-based sit-to-stand motion data task positions are defined to carry out a finite position synthesis of a four-bar linkage that provides user-specific guidance of a seat. The four-bar linkage combined with the lower limb of a user generates a biologically inspired six-bar linkage. Thus, accomplishing a bio-kinematic design of linkages where this contribution provides an exemplary design session.

Four-Position Synthesis of Origami-Evolved, Spherically Constrained Planar RR Chains

In this paper we present a dimensional four-position synthesis procedure for an overconstrained 1-DOF spatial linkage that we call the origami-evolved, spherically constrained planar RR chain. The structure is found as a mechanism equivalent of a part of the Miura-ori folding linkage. Studying the geometry of this mechanism equivalent it turns out that it only corresponds to two spherical four-bar linkages that are coupled in a special overconstraining manner. Even though the special characteristic of the coupling is necessary to preserve 1-DOF mobility, there is particular freedom left for the design and synthesis of the linkage. On the one hand it is allowed to use a spherical or either a spatial RR chain when constructing an origami-evolved, spherically constrained RR chain. On the other hand the synthesis of spherical RR dyads becomes available for the design of the spherical wrists.

Three-Position Synthesis of Spherically Constrained Planar 3R Chains

This paper presents a dimensional finite position synthesis procedure for a 8-bar linkage, that we call the spherically constrained planar 3R chain. The procedure aims at using the well-developed constraint-based synthesis equations of spherical RR chains in order to constrain a planar serial 3R guiding chain, synthesized before for a maximum number of three task poses. This maximum number of task positions results from the specific linkage topology, which requires to select specific axes of spherical RR chains. However, three-position synthesis allows it to apply a specific version of the dyad triangle equation of planar RR chains to the problem. A particular assumption forces that this version of the dyad triangle equation becomes nothing but the synthesis equation of a planar 3R chain, which is easily solved for the three prescribed task poses. An example is provided showing a synthesized spherically constrained planar 3R chain reaching three prescribed planar poses.Copyright

Computer Aided, Task-Based Kinematic Design of Linkages: A New Lecture for Engineering Students

This paper presents the topics, methods and objectives of a new lecture on CAD-integrated kinematic design of linkages for master students. The contents enable students in mechanical engineering to analyze and synthesize structures kinematically using advanced software tools such as numerical and algebraic computation software as well as 3D solid modeler. The structures range from 1-DOF mechanisms up to multi-DOF serial and parallel linkages. Using a generalized nomenclature and vector-matrix-based formulation of the geometry and kinematics of the systems, students are enabled to design both planar and spatial structures. The major objective is to provide the techniques and foundations for task specific synthesis and analysis of linkages with a strong focus on practical applications, which is demonstrated in an example design session in this paper.

Kinematic Design of Miura-Ori-Based Folding Structures Using the Screw Axis of a Relative Displacement

This chapter provides a kinematic design approach for specific folding structures, consisting of vertices with four intersecting creases, such that they can achieve two given folding configurations. These configurations are defined in terms of up to two planar curves, which are approximated by a polyline that is a particular part of the folding structure. We call these structures Miura-ori-based structures or linkages because the design approach makes use of the particular motion characteristics of the 1-DOF mechanism equivalent of the Miura-ori folding pattern. To achieve the design goal we apply a two-configuration synthesis, also provided in a previous work, which is based on the screw axis of a specific relative displacement. A classification of the slide along the screw axis allows it to determine the creases connecting consecutive links of the folding structure as revolute joints.